This application relates to the field of electric power technologies, and in particular, to a direct current bus voltage control method and apparatus, and a power system.
At present, renewable energy generating equipment has a good development prospect due to its advantages in environmental protection. However, high-proportion renewable energy generating equipment represented by photovoltaic/wind power is controlled by a power electronic device and connected to a grid. For example, the generating equipment is connected to an alternating current grid by successively using a conversion circuit, a direct current bus, and an inverter circuit. Characteristics of renewable energy generating equipment are quite different from those of synchronous generators in traditional power systems, which poses a great challenge to safe and stable operation of modern power systems. All countries in the world have adopted grid connection requirements to regulate grid connection behavior of the renewable energy generating equipment, especially when transient conditions such as fault ride through occur.
A high voltage ride through power grid fault is used as an example, and a voltage of the alternating current grid rises suddenly during high voltage ride through. In this case, an inverter circuit that is not disconnected during high voltage ride through is usually required to output the same active power as active power output before the fault, and an allowable error should not exceed 10% PN (rated power). This puts forward a power controllable requirement on the inverter circuit during a power grid fault.
During high voltage ride through, because a voltage on the alternating current grid side rapidly increases, a voltage on the direct current bus increases synchronously due to a limitation of a control loop of the inverter circuit on a pulse width modulation (PWM) modulation ratio. In this case, at an initial stage of the fault process, the conversion circuit (for example, a boost circuit) has not received information about a fault on a power grid side (for example, a voltage between the alternating current grid and the inverter circuit), and control of a power system is in a maximum power point tracking (MPPT) normal operating state. Before the conversion circuit receives information about the fault on the power grid side and completes a voltage control process of the direct current bus based on the information about the fault on the power grid side, a voltage of the direct current bus on the conversion circuit side cannot keep up with an increase of a voltage of the direct current bus on the inverter circuit side, which usually results in a case in which power on a direct current side cannot be smoothly sent out and power is uncontrollable. In particular, for a distributed inverter, an inverter circuit and a conversion circuit included therein are connected by using a long-distance (usually exceeding 1 KM) direct current bus. After a voltage of an alternating current grid is detected, it is transmitted to the conversion circuit, and there is a significant delay in implementing control on the conversion circuit. In summary, the inverter circuit cannot transmit power in this case. On one hand, the alternating current grid faces unbalanced active power during high voltage ride through. Because power output to the alternating current grid decreases, the alternating current grid needs to increase frequency to maintain the active power, which will affect frequency stability of the alternating current grid. On the other hand, due to a sudden decrease in the active power, the voltage of the alternating current grid will be raised further, which is not conducive to maintaining a grid connection by the inverter circuit. With a continuous increase of a power generation and grid connection capacity of renewable energy, its impact on stability of the alternating current grid becomes extremely important.
Embodiments of this application provide a direct current bus voltage control method and apparatus, and a power system, to quickly identify a voltage between an inverter circuit and an alternating current grid, so as to timely control a voltage of a direct current bus, to improve stability of a power grid.
To achieve the foregoing objective, the following technical solutions are used in this application.
According to a first aspect, a direct current bus voltage control method is provided. The method is applied to a power system, where the power system includes a conversion circuit, a direct current bus, and an inverter circuit, and the direct current bus is connected to the conversion circuit and the inverter circuit. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid. The direct current bus voltage control method includes: obtaining an electrical parameter between the conversion circuit and the direct current bus; generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter and a voltage prediction model; and controlling a voltage between the conversion circuit and the direct current bus based on the predicted voltage. The electrical parameter in this embodiment of this application may be one or more of electrical parameters such as a voltage, a current, power, and a harmonic parameter. The power and the harmonic parameter may be generated by sampling and processing the voltage and the current. For example, the voltage prediction model is a model generated based on an equivalent circuit of the direct current bus, or the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit.
In the foregoing solution, after obtaining the electrical parameter between the conversion circuit and the direct current bus, a direct current bus voltage control apparatus can directly generate the predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter and the voltage prediction model; then, control the voltage between the conversion circuit and the direct current bus based on the predicted voltage; and can avoid a delay caused by obtaining the voltage between the conversion circuit and the direct current bus when the inverter circuit and the conversion circuit are connected by using a long-distance direct current bus, and can quickly identify a voltage between the inverter circuit and the alternating current grid, so as to implement timely control on a voltage of the direct current bus, thereby improving stability of a power grid.
In a possible implementation, for example, the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit, depending on a difference of the voltage prediction model. The generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter and a voltage prediction model includes: inputting the electrical parameter into the voltage prediction model to generate the predicted voltage between the inverter circuit and the alternating current grid. That is, the voltage between the inverter circuit and the alternating current grid is directly predicted. A relationship between the electrical parameter between the conversion circuit and the direct current bus and the voltage between the inverter circuit and the alternating current grid is mainly related to inductive reactance of an inductor and capacitive reactance of a capacitor in the equivalent circuit. Therefore, the voltage prediction model may be obtained through training by using the voltage between the conversion circuit and the direct current bus as input to a learning network, and the voltage between the inverter circuit and the alternating current grid as output of the learning network. For example, a voltage between the conversion circuit and the direct current bus may be sampled at different moments, and a voltage between the conversion circuit and the direct current bus corresponding to the voltage between the conversion circuit and the direct current bus is sampled to form a mapping relationship, and then the mapping relationship is trained by using the learning network to generate the voltage prediction model. In this way, for the obtained voltage prediction model, when a voltage between the conversion circuit and the direct current bus is input to the voltage prediction model, a voltage between the conversion circuit and the direct current bus is output.
In a possible implementation, for example, the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit, depending on a difference of the voltage prediction model. The generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model includes: generating a second voltage variation between the inverter circuit and the alternating current grid based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model, where the voltage prediction model is a model generated based on the equivalent circuits of the direct current bus and the inverter circuit; and generating the predicted voltage between the alternating current grid and the inverter circuit based on the second voltage variation. That is, a voltage variation between the alternating current grid and the inverter circuit is predicted, and then the predicted voltage between the alternating current grid and the inverter circuit is generated based on the voltage variation between the alternating current grid and the inverter circuit. The relationship between the electrical parameter between the conversion circuit and the direct current bus and the voltage between the inverter circuit and the alternating current grid is mainly related to inductive reactance of an inductor and capacitive reactance of a capacitor in the equivalent circuit. Therefore, the voltage prediction model may be obtained through training by using voltages between any two conversion circuits and the direct current bus as input to the learning network, and the second voltage variation between the inverter circuit and the alternating current grid as output of the learning network. When the second voltage variation corresponds to a voltage between the conversion circuit and the direct current bus at a first moment t1 and a voltage between the conversion circuit and the direct current bus at a second moment t2, the voltage between the inverter circuit and the alternating current grid varies. Then, the second voltage variation is added to a normal voltage between the inverter circuit and the alternating current grid to obtain the predicted voltage, where the normal voltage may be a power grid voltage in a steady state, and the normal voltage may be a default value or a pre-measured value, for example, may be a voltage between the inverter circuit and the alternating current grid detected by a detection device in a steady state, and the normal voltage may be a voltage detected at any moment before a predetermined time period [t1, t2]. In addition, the electrical parameter between the conversion circuit and the direct current bus may also be a variation value of a voltage, for example, variation values of the voltage between the conversion circuit and the direct current bus at the first moment t1 and the voltage between the conversion circuit and the direct current bus at the second moment t2. In this way, the voltage prediction model may be obtained through training by using a voltage variation value between the conversion circuit and the direct current bus as input to the learning network, and the second voltage variation between the inverter circuit and the alternating current grid as output of the learning network.
In a possible implementation, for example, the voltage prediction model is a model generated based on an equivalent circuit of the direct current bus, depending on a difference of the voltage prediction model; and the generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model includes: generating a voltage between the inverter circuit and the direct current bus based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model; and generating the predicted voltage between the alternating current grid and the inverter circuit based on the voltage between the inverter circuit and the direct current bus. Because the relationship between the electrical parameter between the conversion circuit and the direct current bus and the voltage between the direct current bus and the inverter circuit is mainly related to inductive reactance of an inductor and capacitive reactance of a capacitor in the direct current bus of the equivalent circuit, the voltage prediction model is a model generated based on the equivalent circuit of the direct current bus. For example, the voltage prediction model may be obtained through training by using the voltage between the inverter circuit and the direct current bus as input to the learning network, and the voltage between the direct current bus and the inverter circuit as output of the learning network. For example, a voltage between the inverter circuit and the direct current bus may be sampled at different moments, a corresponding voltage between the direct current bus and the inverter circuit is sampled to form a mapping relationship, and then the mapping relationship is trained by using the learning network to generate the voltage prediction model. In this case, when a sampled voltage between the conversion circuit and the direct current bus is input to the voltage prediction model, a voltage between the direct current bus and the inverter circuit may be obtained. Because an electrical characteristic of the inverter circuit is fixed, a voltage ratio on two sides of the inverter circuit is mainly related to a modulation ratio of a control signal. Therefore, a voltage between the direct current bus and the inverter circuit may be directly converted into a voltage between the inverter circuit and the alternating current grid based on a modulation ratio of the inverter circuit. Generally, the modulation ratio of the inverter circuit is defined as a peak of a phase voltage between the direct current bus and the inverter circuit/a half of the voltage between the inverter circuit and the alternating current grid. The modulation ratio is generally fixed in a control process. Even in a transient state of a voltage surge fault of the alternating current grid, control logic of the inverter circuit remains unchanged, and usually a value is around 1.14 (maximum physical limit is 1.15).
In a possible implementation, for example, the voltage prediction model is a model generated based on an equivalent circuit of the direct current bus, depending on a difference of the voltage prediction model; and the generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model includes: generating a first voltage variation between the inverter circuit and the direct current bus based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model, where the voltage prediction model is a model generated based on the equivalent circuit of the direct current bus; and generating the predicted voltage between the alternating current grid and the inverter circuit based on the first voltage variation. The relationship between the electrical parameter between the conversion circuit and the direct current bus and the first voltage variation between the inverter circuit and the direct current bus is mainly related to inductive reactance of an inductor and capacitive reactance of a capacitor in the equivalent circuit of the direct current bus. Therefore, the voltage prediction model may be obtained through training by using voltages between any two conversion circuits and the direct current bus as input to the learning network, and the first voltage variation between the inverter circuit and the direct current bus as output of the learning network. When the first voltage variation corresponds to a voltage Ub1 between the conversion circuit and the direct current bus at a first moment t1 and a voltage Ub2 between the conversion circuit and the direct current bus at a second moment t2, the voltage between the inverter circuit and the direct current bus varies. Then, the electrical characteristic of the inverter circuit is fixed, and the voltage ratio on two sides of the inverter circuit is mainly related to the modulation ratio of the control signal. Therefore, the voltage between the inverter circuit and the direct current bus may be directly converted into a voltage between the alternating current grid and the inverter circuit based on the modulation ratio of the inverter circuit. Therefore, a third voltage variation between the inverter circuit and the alternating current grid is generated based on the first voltage variation and the electrical characteristic of the inverter circuit. A predicted voltage is generated based on the third voltage variation and a pre-stored normal voltage value between the inverter circuit and the alternating current grid. For example, the first voltage variation may be converted into the third voltage variation between the inverter circuit and the alternating current grid based on the first voltage variation and the electrical characteristic of the inverter circuit. The third voltage variation is added to the normal voltage between the inverter circuit and the alternating current grid to obtain the predicted voltage, where the normal voltage may be a power grid voltage in a steady state, the normal voltage may be the voltage between the inverter circuit and the alternating current grid detected by a detection device in a steady state, and for example, the normal voltage may be a voltage detected at any moment before a predetermined time period. In addition, the electrical parameter between the conversion circuit and the direct current bus may also be a variation value of a voltage, for example, variation values of the voltage between the conversion circuit and the direct current bus at the first moment t1 and the voltage between the conversion circuit and the direct current bus at the second moment t2. In this way, the voltage prediction model may be obtained through training by using a variation value between the conversion circuit and the direct current bus as input to the learning network, and the first voltage variation between the inverter circuit and the direct current bus as output of the learning network.
In a possible implementation, the controlling a voltage between the conversion circuit and the direct current bus based on the predicted voltage includes: when it is determined that the predicted voltage is greater than a voltage threshold, converting the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus; generating a second current reference value based on the voltage reference value and a first voltage measurement value between the conversion circuit and the direct current bus; and adjusting the voltage between the conversion circuit and the direct current bus based on the second current reference value.
In a possible implementation, the converting the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus includes: converting the predicted voltage into the voltage reference value between the conversion circuit and the direct current bus based on the direct current bus and the electrical characteristic of the inverter circuit.
In a possible implementation, the controlling a voltage between the conversion circuit and the direct current bus based on the predicted voltage includes: when it is determined that the predicted voltage is less than or equal to a voltage threshold, determining a maximum power point of the direct current source based on a current measurement value between the direct current source and the conversion circuit, and generating a first current reference value corresponding to the maximum power point; and adjusting the voltage between the conversion circuit and the direct current bus based on the first current reference value.
In a possible implementation, the controlling a voltage between the conversion circuit and the direct current bus based on the predicted voltage includes: converting the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus; generating a second current reference value based on the voltage reference value and a first voltage measurement value between the conversion circuit and the direct current bus; determining a maximum power point of the direct current source based on a current measurement value between the direct current source and the conversion circuit, and generating a first current reference value corresponding to the maximum power point; and when it is determined that the first current reference value is greater than the second current reference value, adjusting the voltage between the conversion circuit and the direct current bus based on the second current reference value; or when it is determined that the first current reference value is less than or equal to the second current reference value, adjusting the voltage between the conversion circuit and the direct current bus based on the first current reference value.
In a possible implementation, before the generating a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter and a voltage prediction model, the method further includes: generating, based on equivalent circuits of the direct current bus and the inverter circuit, the voltage prediction model through training by using an electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage between the inverter circuit and the alternating current grid as an output parameter of the learning network.
In a possible implementation, before the generating a first voltage variation between the inverter circuit and the direct current bus based on the electrical parameter and a voltage prediction model, the method further includes: based on an equivalent circuit of the direct current bus, generating the voltage prediction model through training by using an electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage variation between the inverter circuit and the direct current bus as an output parameter of the learning network.
In a possible implementation, before the generating a second voltage variation between the inverter circuit and the alternating current grid based on the electrical parameter and a voltage prediction model, the method further includes: generating, based on equivalent circuits of the direct current bus and the inverter circuit, the voltage prediction model through training by using an electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage variation between the inverter circuit and the alternating current grid as an output parameter of the learning network.
According to a second aspect, a direct current bus voltage control apparatus is provided to implement the foregoing methods. A quality factor detection apparatus based on an oscillation circuit includes corresponding modules, units, or means (means) for implementing the foregoing methods. The module, unit, or means may be implemented by using hardware or software, or may be implemented through hardware executing corresponding software. The hardware or the software includes one or more modules or units corresponding to the foregoing functions.
According to a third aspect, a direct current bus voltage control apparatus is provided, which is applied to a power system, where the power system includes a conversion circuit, a direct current bus and an inverter circuit, and the direct current bus is connected to the conversion circuit and the inverter circuit. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid. The direct current bus voltage control apparatus includes a processor and a memory. The memory is configured to store computer instructions, and when the processor executes the instructions, the direct current bus voltage control apparatus performs the method in any one of the foregoing aspects.
According to a fourth aspect, a direct current bus voltage control apparatus is provided, which is applied to a power system, where the power system includes a conversion circuit, a direct current bus, and an inverter circuit, and the direct current bus is connected to the conversion circuit and the inverter circuit. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid. The direct current bus voltage control apparatus includes a processor and a transmission interface. The processor is configured to invoke program instructions stored in a memory to perform the method in any one of the foregoing aspects.
In a possible implementation, the direct current bus voltage control apparatus further includes a memory, and the memory is configured to store necessary program instructions and data. When the direct current bus voltage control apparatus is a chip system, the direct current bus voltage control apparatus may be composed of chips, or may include a chip and another discrete device.
According to a fifth aspect, a computer-readable storage medium is provided, where the computer-readable storage medium stores program instructions. When the program instructions run on a computer or a processor, the computer or the processor may perform the method in any one of the foregoing aspects.
According to a sixth aspect, a computer program product including instructions is provided. When the instructions run on a computer or a processor, the computer or the processor may perform the method in any one of the foregoing aspects.
According to a seventh aspect, an inverter is provided, including an inverter circuit, a conversion circuit, and a direct current bus, where the conversion circuit is connected to the inverter circuit through the direct current bus. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid. The inverter further includes any one of the direct current bus voltage control apparatuses described above.
According to an eighth aspect, a voltage conversion device is provided, including a conversion circuit and the foregoing direct current bus voltage control apparatus, where the conversion circuit is connected to an inverter circuit by using a direct current bus. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid.
According to a ninth aspect, a combiner box is provided, including a conversion circuit and the foregoing direct current bus voltage control apparatus, where the conversion circuit is connected to an inverter circuit by using a direct current bus. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid.
According to a tenth aspect, a power system is provided, including a voltage converter, a direct current bus, an inverter circuit, and an alternating current grid, where the direct current bus is connected to a conversion circuit and the inverter circuit, and the conversion circuit is connected to a direct current source, and the inverter circuit is connected to the alternating current grid. The power system further includes the foregoing direct current bus voltage control apparatus.
According to an eleventh aspect, a power system is provided, including the inverter according to the seventh aspect. The inverter includes an inverter circuit, a conversion circuit, and a direct current bus, where the conversion circuit is connected to the inverter circuit through the direct current bus. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid.
For technical effects brought by any one of design manners in the second aspect to the eleventh aspect, refer to technical effects brought by different design manners in the first aspect. Details are not described herein again.
The following describes technical solutions in embodiments of this application with reference to accompanying drawings in embodiments of this application. It is clear that the described embodiments are merely a part rather than all of embodiments of this application.
A steady state of a power system generally refers to a normal three-phase symmetrical operating state of the power system, and an operating parameter (for example, a voltage, a current, or power) of the power system continuously changes around an average value, and may be considered as a constant because it changes little. In actual operation of the power system, an ideal steady state rarely exists. Therefore, a steady state in engineering is considered as that the operating parameter of the power system continuously changes around a specified average value, and changes little. In engineering, a steady-state fluctuation range is represented by relative deviation. Common deviation values are 5%, 2%, 1%, and the like.
A transient state of a power system generally refers to a transition process from a steady state to another steady state, and an operating parameter of the power system in the transition process may change greatly. There are two types of transient processes. One is related to a rotating element in a power system, such as an electric generator and a motor. The transient process thereof is usually referred to as an electromechanical transient state caused by an imbalance in mechanical torque or electromagnetic torque. The other is in an original part such as a voltage regulator, a transmission line, and the like, and does not involve angular displacement, angular velocity, or the like, and its transient process is referred to as an electromagnetic transient state.
A photovoltaic module is direct current power composed of solar cells through series and parallel packaging.
A photovoltaic string is direct current power composed of a plurality of photovoltaic modules that are connected in series through positive and negative electrodes.
The terms “first” and “second” mentioned below are merely intended for a purpose of description, and shall not be understood as an indication or implication of relative importance or implicit indication of a quantity of indicated technical features. Therefore, a feature limited by “first” or “second” may explicitly indicate or implicitly include one or more such features.
In addition, in this application, directional terms such as “upper” and “lower” are defined relative to directions of components that are placed as shown in the accompanying drawings. It should be understood that these directional terms are relative concepts and are used for relative description and clarification, and may correspondingly change according to changes of directions in which components are placed in the accompanying drawings.
In this application, unless otherwise expressly specified and limited, the term “connection” may be a manner of implementing an electrical connection of signal transmission, and the term “connection” may be a direct electrical connection, or may be an indirect electrical connection by using an intermediate medium.
An embodiment of this application is applied to a power system. As shown in
As shown in
As shown in
With reference to
Generally, the distributed inverter uses decentralized MPPT optimization, that is, a centralized grid-connected power generation mode. That is, for each PV device, an operating voltage of a maximum power point of the PV device is determined by using separate MPPT, and inversion and grid connection are collectively performed by using a unified inverter circuit. Therefore, MPPT control mainly enables, by controlling the boost circuit based on a power signal output by the PV device, the PV device to operate at a maximum power point. The MPPT in this application is not limited, for example, may be an open-loop or closed-loop MPPT method. The open-loop MPPT method mainly includes a voltage tracking method, a short-circuit current proportional coefficient method, an interpolation calculation method, and the like. The closed-loop MPPT method mainly includes a self-optimization MPPT algorithm such as a perturbation and observation method (P&O) and an incremental conductance (INC) method. For example, with reference to
the MPPT function can implement maximum power point tracking based on a voltage Upv of the power signal output by the PV device, for example, a voltage Ub between the boost circuit and the direct current bus in a steady state is fixed. Upv is adjusted to Upvref based on Upvref indicated by a PV device port voltage instruction. Upvref and Upv may be input to a control loop to generate a reference current Ipvref1 of the PV device. Then, performing current control on the PWM generator based on Ipvref1 and Ipv may use loop control to adjust a PV device port voltage to Upvref. For example, a PI controller may be used to implement current control, which is specifically as follows: A duty cycle of a PWM signal generated by the PWM generator is controlled to increase or decrease based on a difference between Ipvref1 and Ipv, so as to implement adjustment on the duty cycle D of the TV1, thereby implementing adjustment on Upv and Ub.
In a transient process of a power grid, a direct current bus voltage on the inverter circuit side rapidly changes due to active control (for example, MPPT) or a passive response (for example, a voltage rise fault occurs in the alternating current grid). Because a length of a direct current bus line is long and a distribution parameter (for example, an inductance and a capacitance) is large, a change of a direct current voltage on the inverter circuit side cannot be instantaneously transmitted to the boost circuit side. After a voltage of the alternating current grid is detected, it is transmitted to the conversion circuit, and there is a significant delay in implementing control on the boost circuit. In this way, there is a delay in coordination on control of the boost circuit and the inverter circuit, which causes the foregoing problem. In this application, a variable electrical parameter such as a local direct current voltage and current of the boost circuit is measured in a predetermined time period, and a voltage between the inverter circuit and an alternating current bus is predicted by using a voltage prediction model established in advance based on the direct current bus (or the direct current bus and the inverter circuit). The boost circuit may be controlled in real time based on the predicted voltage to control a voltage of the direct current bus, so that a voltage between the inverter circuit and the alternating current grid can be quickly identified, so as to implement timely control on the voltage of the direct current bus, to improve stability of the power system.
In another solution, the power system provided in this embodiment of this application may be a DC micro grid. As shown in
Based on the foregoing power system, an embodiment of this application provides a direct current bus voltage control method. The power system further includes a direct current bus voltage control apparatus. As shown in
An embodiment of this application provides the foregoing direct current bus voltage control method, and the method is applied to the direct current bus voltage control apparatus in
101: Obtain an electrical parameter between a conversion circuit and a direct current bus.
102: Generate a predicted voltage between an inverter circuit and an alternating current grid based on the electrical parameter and a voltage prediction model.
The voltage prediction model is a model generated based on an equivalent circuit of the direct current bus, or the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit.
In this embodiment of this application, the electrical parameter (as shown in
Based on specific forms of the direct current bus and the inverter circuit, the direct current bus and the inverter circuit each may be respectively equivalent to a circuit formed through connecting an inductor and a capacitor. For example, the direct current bus generally has a π-type topology, a T-type topology, and the like. As shown in
For the foregoing electrical parameter, in an example in which the electrical parameter is the voltage Ub or ΔUb, generation of the voltage prediction model and generation of the predicted voltage provided in this embodiment of this application are specifically described as follows:
Example 1: The electrical parameter between the conversion circuit and the direct current bus is input into the voltage prediction model to generate the predicted voltage between the inverter circuit and the alternating current grid. With reference to
Example 2: A second voltage variation between the inverter circuit and the alternating current grid is generated based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model. The predicted voltage between the alternating current grid and the inverter circuit is generated based on the second voltage variation. With reference to
Example 1 and Example 2 directly predict the voltage between the inverter circuit and the alternating current grid. Examples 3 and 4 further provide a manner of indirectly predicting a voltage between the inverter circuit and the alternating current grid.
Example 3: A voltage Ui between the inverter circuit and the direct current bus is generated based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model; and a predicted voltage E between the alternating current grid and the inverter circuit is generated based on the voltage Ui.
With reference to
Example 4: A first voltage variation ΔUi between the inverter circuit and the direct current bus is generated based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model; the voltage prediction model is a model generated based on the equivalent circuit of the direct current bus; and a predicted voltage E between the alternating current grid and the inverter circuit is generated based on the first voltage variation ΔUi.
Specifically, a third voltage variation ΔE between the inverter circuit and the alternating current grid is generated based on the first voltage variation ΔUi and the electrical characteristic of the inverter circuit. The predicted voltage E is generated based on the third voltage variation ΔE and a pre-stored normal voltage value E0 between the inverter circuit and the alternating current grid. With reference to
103: Control a voltage between the conversion circuit and the direct current bus based on the predicted voltage.
Specifically, with reference to the foregoing description, in step 103, a control signal of a voltage converter is specifically generated based on the predicted voltage, so as to implement control on the voltage between the conversion circuit and the direct current bus.
In the foregoing solution, after obtaining the electrical parameter between the conversion circuit and the direct current bus, a direct current bus voltage control apparatus can directly generate the predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter and the voltage prediction model; then, control the voltage between the conversion circuit and the direct current bus based on the predicted voltage; and can avoid a delay caused by obtaining the voltage between the conversion circuit and the direct current bus when the inverter circuit and the conversion circuit are connected by using a long-distance direct current bus, and can quickly identify a voltage between the inverter circuit and the alternating current grid, so as to implement timely control on a voltage of the direct current bus, thereby improving stability of a power grid.
A specific implementation of step 103 is described as follows:
An embodiment of this application provides a direct current bus voltage control method, and the method is applied to the direct current bus voltage control apparatus in
201: Obtain an electrical parameter between a conversion circuit and a direct current bus.
202: Generate a predicted voltage between an inverter circuit and an alternating current grid based on the electrical parameter and a voltage prediction model.
For descriptions of steps 201 and 203, refer to descriptions of step 101 and step 102 directly. Details are not described herein again.
203: When it is determined that a predicted voltage E is greater than a voltage threshold kEn, convert the predicted voltage E into a voltage reference value between the conversion circuit and the direct current bus Ubref.
The voltage threshold kEn may be set based on a rated operating voltage En of the alternating current grid. For example, the voltage threshold may be set to kEn, and a value of k is determined by different power grid operators, indicating a grid-connected high voltage ride through requirement of different standards. For example, the value of k is generally set to 110% to 130%. A larger value of k indicates a higher requirement for a high voltage ride through function of a device (inverter). The inverter needs to support a case in which in a higher power grid voltage surge fault, the inverter can still be ensured not to be disconnected from the power grid, and output active power is fast and controllable. In addition, a modulation ratio M of the inverter circuit is generally fixed. In this way, a direct current voltage Ui on the inverter circuit side may rise at a same ratio when the voltage E of the alternating current grid changes (a voltage between the inverter circuit and the direct current bus). To ensure that the inverter can output active power to the alternating current grid and keep controllable during a transient fault, a voltage reference value Ubf should also be set based on the modulation ratio M in combination with the predicted voltage E, so that it can be restored to be controllable in the shortest time. For example,
(M is usually around 1.14), which can be adjusted up or down as required Ubref, it is ensured that a dynamic characteristic of the inverter is the best during a transient process. With reference to the foregoing Examples 1 to 4, when the predicted voltage E or the voltage Ui is directly measured based on the voltage prediction model, E0 does not need to be obtained. However, when ΔUi or ΔE is predicted based on the voltage prediction model, it is also necessary to measure E0 of the alternating current grid by using a detection device on the inverter circuit side in a steady state, and transmit it to the direct current bus voltage control apparatus through slow communication or in another manner (for example, may be a pre-stored configured default value or a pre-measured value). As shown in
204: Generate a second current reference value Ipvref2 based on the voltage reference value Ubref and a first voltage measurement value Ub between the conversion circuit and the direct current bus.
205: Adjust the voltage between the conversion circuit and the direct current bus based on the second current reference value Ipvref2.
In this solution, finally an adjustment result of a voltage of the direct current bus is to adjust the first voltage measurement value Ub between the conversion circuit and the direct current bus to Ubref. Therefore, in this solution, loop control may be performed on the voltage of the direct current bus in step 204 to generate a second current reference value Ipvref2 of a direct current source, and specifically, Ipvref2 is generated based on a difference between Ubref and Ub. In step 205, after the voltage between the conversion circuit and the direct current bus is adjusted based on Ipvref2, the voltage between the conversion circuit and the direct current bus is Ubref. A manner of adjusting the voltage between the conversion circuit and the direct current bus based on Ipvref2 is to use current control, for example, current control performed on a PWM generator based on Ipvref2 and Ipv may use loop control. For example, current control may be implemented by using a PI controller, which is specifically as follows: A duty cycle of a PWM signal generated by the PWM generator increases or decreases based on Ipvref2 and Ipv, thereby implementing adjustment on a duty cycle D of TV1, and implementing adjustment on Ub.
206: When it is determined that the predicted voltage E is less than or equal to the voltage threshold kEn, determine a maximum power point of the direct current source based on a current measurement value Ipv between the direct current source and the conversion circuit, and generate a first current reference value Ipvref1 corresponding to the maximum power point.
207: Adjust the voltage between the conversion circuit and the direct current bus based on the first current reference value Ipvref1.
MPPT control on the conversion circuit may be used in step 206 and step 207. For details, refer to the foregoing description corresponding to
In the foregoing Embodiment 1, step 103 in the foregoing method example is implemented by using steps 203-207. In the foregoing Embodiment 1, when the predicted voltage E is greater than the voltage threshold kEn, high voltage ride through occurs in a power system. The direct current bus voltage control apparatus directly converts the predicted voltage E into the voltage reference value Ubref between the conversion circuit and the direct current bus, then performs loop control based on a voltage measurement value Ub between the conversion circuit and the direct current bus to generate a second current reference value Ipvref2, and generates a control signal of the conversion circuit based on the second current reference value Ipvref2 to implement control, to implement voltage adjustment between the conversion circuit and the direct current bus. Because the direct current bus voltage control apparatus can obtain the predicted voltage E in real time based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model, a time delay of adjustment on the voltage between the conversion circuit and the direct current bus can be reduced. In particular, when a transient state such as high voltage ride through occurs in the power system, the voltage of the direct current bus can be adjusted in time, thereby improving stability of the power system.
An embodiment of this application provides a direct current bus voltage control method, and the method is applied to the direct current bus voltage control apparatus in
301: Obtain an electrical parameter between a conversion circuit and a direct current bus.
302: Generate a predicted voltage between an inverter circuit and an alternating current grid based on the electrical parameter and a voltage prediction model.
For descriptions of steps 301 and 303, refer to descriptions of step 101 and step 102 directly. Details are not described herein again.
303: Convert a predicted voltage E into a voltage reference value Ubref between the conversion circuit and the direct current bus.
For conversion of the predicted voltage E in this step, refer to step 203. Details are not described herein again.
304: Generate a second current reference value Ipvref2 based on the voltage reference value Ubref and a first voltage measurement value Ub between the conversion circuit and the direct current bus.
For step 304, refer to the foregoing description of step 204. Details are not described herein again.
305: Determine a maximum power point of a direct current source based on a current measurement value Ub between the direct current source and the conversion circuit, and generate a first current reference value Ipvref1 corresponding to the maximum power point.
306: When it is determined that the first current reference value Ipvref1 is greater than the second current reference value Ipvref2, adjust a voltage between the conversion circuit and the direct current bus based on the second current reference value Ipvref2.
For a manner of adjusting the voltage between the conversion circuit and the direct current bus Ipvref2 in step 306, refer to the description in step 205. Details are not described herein again.
307: When it is determined that the first current reference value Ipvref1 is less than or equal to the second current reference value Ipvref2, adjust the voltage between the conversion circuit and the direct current bus based on the first current reference value Ipvref1.
For a manner of adjusting the voltage between the conversion circuit and the direct current bus based on step Ipvref1, refer to the description in a step corresponding to
In the foregoing Embodiment 2, step 103 in the foregoing method example is implemented by using steps 303-307. The direct current bus voltage control apparatus directly converts the predicted voltage E into the voltage reference value Ubref between the conversion circuit and the direct current bus, and then performs loop control based on the voltage measurement value Ub between the conversion circuit and the direct current bus, to generate the second current reference value Ipvref2; and in addition, performs MPPT control on the direct current source to generate the first current reference value Ipvref1 corresponding to the maximum power point, performs loop competition on a control loop of the conversion circuit by using Ipvref2 and Ipvref1, and uses a smaller current value of the two to participate in the loop control of the conversion circuit. As described above, generally, the voltage of the alternating current grid increases to a relatively high voltage when the power system is in a transient state, and Ubref may correspondingly rise to a higher voltage. In this case, Ipvref2 may be a relatively small current value. To enable the conversion circuit to effectively output power, the voltage between the conversion circuit and the direct current bus needs to be adjusted to Ubref. Therefore, loop competition is performed on the control loop of the conversion circuit by using Ipvref2 and Ipvref1, and the smaller current value Ipvref2 of the two is used to participate in loop control of the conversion circuit, which can ensure that the conversion circuit can effectively output power in the transient state. In addition, when the power system restores to a steady state, the voltage of the alternating current grid decreases, and Ubref may also decrease. In this case, Ipvref2 may be a relatively large current value. When Ipvref2 is large enough (for example, greater than or equal to Ipvref1), control on the conversion circuit is transferred to MPPT again by using Ipvref2 and Ipvref1 to perform loop competition on the control loop of the conversion circuit. Certainly, voltage control manners of the direct current bus based on the predicted voltage E are not limited to the foregoing two manners. For example, in this solution, MPPT control may be used in step 305 to generate a reference current Ipvref1 that is used to perform loop competition on the control loop of the conversion circuit in steps 306 and 307. Alternatively, loop competition may be performed in another manner and design on the control loop of the conversion circuit. For example, a person skilled in the art may further directly design another manner of performing loop competition on the control loop of the conversion circuit based on a relationship between Ubref indicated by a port voltage instruction of a PV device and the predicted voltage E.
In the foregoing solution, when the voltage between the conversion circuit and the direct current bus is adjusted, the predicted voltage E can be obtained in real time based on the electrical parameter between the conversion circuit and the direct current bus and the voltage prediction model. Therefore, a time delay of adjustment on the voltage between the conversion circuit and the direct current bus can be reduced, especially when a transient state such as high voltage ride through occurs in the power system, the voltage of the direct current bus can be adjusted immediately, thereby improving stability of the power system.
It may be understood that the direct current bus voltage control method provided in the foregoing embodiments may be implemented by a direct current bus voltage control apparatus. The foregoing methods and/or steps may also be implemented by a component (such as a chip or a circuit) that can be used in the direct current bus voltage control apparatus.
It may be understood that, to implement the foregoing functions, the direct current bus voltage control apparatus includes corresponding hardware structures and/or software modules for performing functions. A person skilled in the art should be easily aware that units, algorithms, and steps in the examples described with reference to embodiments disclosed in this specification can be implemented in a form of hardware or a combination of hardware and computer software in this application. Whether a function is performed by hardware or hardware driven by computer software depends on a particular application and a design constraint of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of this application.
In embodiments of this application, the direct current bus voltage control apparatus may be divided into functional modules based on the foregoing method embodiments. For example, functional modules corresponding to each function may be divided, or two or more functions may be integrated into one processing module. The integrated module may be implemented in a form of hardware, or may be implemented in a form of a software functional module. It should be noted that, in embodiments of this application, division into the modules is an example and is merely logical function division, and may be other division in an actual implementation.
an obtaining unit 151, configured to obtain an electrical parameter between the conversion circuit and the direct current bus; and
a processing unit 152, configured to generate a predicted voltage between the inverter circuit and the alternating current grid based on the electrical parameter obtained by the obtaining unit and a voltage prediction model, where the voltage prediction model is a model generated based on an equivalent circuit of the direct current bus, or the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit; and control a voltage between the conversion circuit and the direct current bus based on the predicted voltage.
Optionally, the processing unit 152 is specifically configured to: generate a first voltage variation between the inverter circuit and the direct current bus based on the electrical parameter and the voltage prediction model, where the voltage prediction model is a model generated based on an equivalent circuit of the direct current bus; and generate a predicted voltage between the alternating current grid and the inverter circuit based on the first voltage variation.
Optionally, the processing unit 152 is specifically configured to: generate a third voltage variation between the inverter circuit and the alternating current grid based on the first voltage variation and an electrical characteristic of the inverter circuit; and generate the predicted voltage based on the third voltage variation and a pre-stored normal voltage value between the inverter circuit and the alternating current grid.
Optionally, the processing unit 152 is specifically configured to: generate a second voltage variation between the inverter circuit and the alternating current grid based on the electrical parameter and the voltage prediction model, where the voltage prediction model is a model generated based on equivalent circuits of the direct current bus and the inverter circuit; and generate a predicted voltage between the alternating current grid and the inverter circuit based on the second voltage variation.
Optionally, the processing unit 152 is specifically configured to: when it is determined that the predicted voltage is greater than a voltage threshold, convert the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus; generate a second current reference value based on the voltage reference value and a first voltage measurement value between the conversion circuit and the direct current bus; and adjust a voltage between the conversion circuit and the direct current bus based on the second current reference value.
Optionally, the processing unit 152 is specifically configured to: convert the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus based on the direct current bus and the electrical characteristic of the inverter circuit.
Optionally, the processing unit 152 is specifically configured to: when it is determined that the predicted voltage is less than or equal to the voltage threshold, determine a maximum power point of the direct current source based on a current measurement value between the direct current source and the conversion circuit, and generate a first current reference value corresponding to the maximum power point; and adjust the voltage between the conversion circuit and the direct current bus based on the first current reference value.
Optionally, the processing unit 152 is specifically configured to: convert the predicted voltage into a voltage reference value between the conversion circuit and the direct current bus; generate a second current reference value based on the voltage reference value and a first voltage measurement value between the conversion circuit and the direct current bus; and determine a maximum power point of the direct current source based on a current measurement value between the direct current source and the conversion circuit, and generate a first current reference value corresponding to the maximum power point; and when it is determined that the first current reference value is greater than the second current reference value, adjust the voltage between the conversion circuit and the direct current bus based on the second current reference value; or when it is determined that the first current reference value is less than or equal to the second current reference value, adjust the voltage between the conversion circuit and the direct current bus based on the first current reference value.
Optionally, the processing unit 152 is further configured to: based on equivalent circuits of the direct current bus and the inverter circuit, generate the voltage prediction model through training by using the electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage between the inverter circuit and the alternating current grid as an output parameter of the learning network.
Optionally, the processing unit 152 is further configured to: based on an equivalent circuit of the direct current bus, generate the voltage prediction model through training by using the electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage variation between the inverter circuit and the direct current bus as an output parameter of the learning network.
Optionally, the processing unit 152 is further configured to: based on equivalent circuits of the direct current bus and the inverter circuit, generate the voltage prediction model through training by using the electrical parameter between the conversion circuit and the direct current bus as an input parameter of a learning network, and a voltage variation between the inverter circuit and the alternating current grid as an output parameter of the learning network.
All related content of the steps in the method embodiments may be cited in function descriptions of corresponding functional modules. Details are not described herein again.
In this embodiment, the direct current bus voltage control apparatus is presented in a form of dividing each functional module in an integrated manner. The “module” herein may be a specific ASIC, a circuit, a processor and a memory that execute one or more software or firmware programs, an integrated logic circuit, and/or another component that can provide the foregoing functions.
For example, a direct current bus voltage control apparatus is provided, which is applied to a power system, where the power system includes a conversion circuit, a direct current bus, and an inverter circuit, and the direct current bus is connected to the conversion circuit and the inverter circuit. The conversion circuit is connected to a direct current source, and the inverter circuit is connected to an alternating current grid. The direct current bus voltage control apparatus includes a processor and a transmission interface. The processor is configured to invoke program instructions stored in a memory to perform the foregoing method. Specifically, a function/implementation process of the processing unit 152 in
Optionally, an embodiment of this application further provides a direct current bus voltage control apparatus (for example, a quality factor detection apparatus based on an oscillation circuit may be a chip or a chip system). The direct current bus voltage control apparatus includes a processor, configured to implement the method in any one of the foregoing method embodiments. In a possible design, the direct current bus voltage control apparatus further includes a memory. The memory is configured to store necessary program instructions and data. The processor may invoke program code stored in the memory to indicate the direct current bus voltage control apparatus to perform the method in any one of the foregoing method embodiments. Certainly, the memory may not be in the direct current bus voltage control apparatus. When the direct current bus voltage control apparatus is a chip system, the direct current bus voltage control apparatus may be composed of chips, or may include a chip and another discrete device. This is not specifically limited in this embodiment of this application.
All or some of the foregoing embodiments may be implemented by using software, hardware, firmware, or any combination thereof. When a software program is used to implement the embodiments, all or some of the embodiments may be implemented in a form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the procedures or functions according to embodiments of this application are at least partially generated. The computer may be a general-purpose computer, a dedicated computer, a computer network, or another programmable apparatus. The computer instruction may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. The computer-readable storage medium may be any usable medium accessible by a computer, or a data storage device, such as a server or a data center, integrating one or more usable media. The usable medium may be a magnetic medium (for example, a floppy disk, a hard disk, or a magnetic tape), an optical medium (for example, a DVD), a semiconductor medium (for example, a solid-state disk (SSD)), or the like. In this embodiment of this application, the computer may include the foregoing apparatus.
Although this application is described with reference to embodiments, in a process of implementing this application that claims protection, a person skilled in the art may understand and implement another variation of the disclosed embodiments by viewing the accompanying drawings, disclosed content, and the appended claims. In the claims, “comprising” (comprising) does not exclude another component or another step, and “a” or “one” does not exclude a case of multiple. A single processor or another unit may implement several functions enumerated in the claims. Some measures are set forth in dependent claims that are different from each other, but this does not mean that these measures cannot be combined to produce great effect.
Although this application is described with reference to specific features and all the embodiments thereof, it is clear that various modifications and combinations may be made to them without departing from the spirit and scope of this application. Correspondingly, this specification and the accompanying drawings are merely example description of this application defined by the appended claims, and are considered as any or all of modifications, variations, combinations or equivalents that cover the scope of this application. It is clearly that a person skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. This application is intended to cover these modifications and variations of this application provided that they fall within the scope of protection defined by the following claims and their equivalent technologies.
Number | Date | Country | Kind |
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202010706718.8 | Jul 2020 | CN | national |
This application is a continuation of International Patent Application No. PCT/CN2021/083085, filed on Mar. 25, 2021, which claims priority to Chinese Patent Application No. 202010706718.8, filed on Jul. 21, 2020. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties.
Number | Date | Country | |
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Parent | PCT/CN2021/083085 | Mar 2021 | US |
Child | 18156672 | US |