Patent Application
20250226687
The invention relates to an energy storage system, and particularly to an energy storage system and a start method thereof.
Self-recovery of the system after power failure of the grid at a large area is generally referred to black start. When the system is all power failure, the entire system is shut down due to fault and is in a full “black” state. When the system needs to start, the equipment having self-start capability in the system firstly start, and then drive operation of the equipment having no self-start capability, thereby gradually expanding recovery range of the system. And finally achieve recovery of the entire system without assistance of other devices.
The energy storage system is used as an active system, and after power failure of the grid, energy storage batteries can rapidly supply power for black start equipment. As shown in
When the system black starts, the voltage of the DC bus shall be established by an input of the DC/DC converter. Since a switch circuit of the DC/DC converter has antiparallel diodes, there is a huge surge impulse current when starting. Precharge resistors are arranged when establishing the voltage of the DC bus. However, in design, the power of the precharge resistor is relatively small, which cannot precharge a mF-level capacitor on the DC bus. Moreover, some DC devices connected to the DC bus self-starts when detecting the bus voltage to reach a threshold voltage, which lowers the bus voltage. It is difficult to control an output voltage to reach a target value through the precharge resistor scheme, causing black start failure.
In conclusion, the existing energy storage system has many issues when black starting, and it is necessary to make improvement.
With respect to the deficiencies, an object of the invention is to provide an energy storage system having self-start capability, which can black start successfully, and has a simple structure and a low cost.
To achieve the object, the invention provides an energy storage system, including: an energy storage converter having an AC end electrically connected to an AC power supply or a load, and a DC end electrically connected to a DC bus; at least one battery unit, each electrically connected to the DC bus through a DC/DC converter; and a start unit electrically connected between a battery unit and the DC bus. When the energy storage system starts through the battery unit, the start unit establishes a bus voltage to a set voltage through power of the battery unit.
Alternatively, the start unit includes: a start circuit having an input end electrically connected to the battery unit; and a switching circuit having one end electrically connected to an output end of the start circuit, and the other end electrically connected to the DC bus.
Alternatively, the set voltage is a voltage of the battery unit; and the switching circuit is a diode having an anode electrically connected to a positive output end of the start circuit, and a cathode electrically connected to the DC bus.
Alternatively, when the bus voltage is less than the set voltage, the switching circuit is conducted, and the start circuit outputs power to the DC bus; and when the bus voltage is greater than the set voltage, the switching circuit is turned off, and the start circuit stops outputting electric power to the DC bus.
Alternatively, the set voltage is a voltage of the battery unit; and the switching circuit is a diode having an anode electrically connected to a positive output end of the start circuit, and a cathode electrically connected to the DC bus.
Alternatively, after the start unit establishes the bus voltage to the set voltage, the at least one DC/DC converter operates to establish the bus voltage from the set voltage to a target voltage through power of the battery unit.
Alternatively, the energy storage system further includes a battery management unit electrically connected to the start unit and the DC/DC converter. When the energy storage system starts through the battery unit, the battery management unit outputs a start command to the start unit, and the start unit operates; and when the start circuit establishes the bus voltage to the set voltage, the battery management unit outputs a control signal to the DC/DC converter, and the DC/DC converter operates.
Alternatively, the start circuit is a precharge circuit, and includes a precharge resistor, a precharge switch and a main switch.
Alternatively, the start circuit includes a buck circuit having at least one controllable switch, and PWM modulation is performed to the at least one controllable switch.
Alternatively, an output voltage of the buck circuit is gradually increased by controlling a duty ratio of the at least one controllable switch, such that the bus voltage is gradually increased from zero to the set voltage.
Alternatively, the set voltage is equal to the voltage of the battery unit, the switching circuit is a diode, and when the bus voltage is greater than the voltage of the battery unit, the diode is reversely cut off.
Alternatively, the buck circuit is a flying capacitor switch circuit, and includes an input capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, a flying capacitor, a first switching tube, a second switching tube, a third switching tube, a fourth switching tube and an output inductor; wherein the input capacitor has a first end electrically connected to the precharge circuit, and a second end electrically connected to an input negative end; the first resistor, the second resistor, the third resistor and the fourth resistor are sequentially connected in series between the first end and the second end of the input capacitor; the first switching tube, the second switching tube, the third switching tube and the fourth switching tube are sequentially connected in series between the first end and the second end of the input capacitor; a second end of the second switching tube is electrically connected to a first end of the output inductor; the flying capacitor is electrically connected in parallel with the second switching tube and the third switching tube; the first resistor and the first switching tube are connected in parallel, the second resistor and the third resistor are connected in parallel with the flying capacitor, and the fourth resistor and the fourth switching tube are connected in parallel; a second end of the output inductor is electrically connected to the switching circuit.
Alternatively, duty ratios of the first switching tube and the second switching tube are controlled to gradually increase, and duty ratios of the third switching tube and the fourth switching tube are controlled to gradually decrease, such that an output voltage of the flying capacitor switch circuit is gradually increased, and the bus voltage is gradually increased from zero to the target voltage.
The invention further provides a start method of an energy storage system, the energy storage system including: an energy storage converter having an AC end electrically connected to an AC power supply or a load, and a DC end electrically connected to a DC bus; at least one battery unit electrically connected to a low-voltage port of a DC/DC converter; and a high-voltage port of each DC/DC converter electrically connected to the DC bus. The method includes: providing a start unit electrically connected between a battery unit and the DC bus; and when the energy storage system starts through the battery unit, operating the start unit to deliver power of the battery unit to the DC bus, thereby establishing a bus voltage to a set voltage.
Alternatively, when the bus voltage is established to the set voltage, operate the DC/DC converter to deliver the power of the battery unit to the DC bus, thereby establishing the bus voltage from the set voltage to a target voltage.
Alternatively, when the DC/DC converter operates and the bus voltage is greater than the set voltage, the start unit is turned off.
Alternatively, the method further includes: judging whether to start the energy storage system through the battery unit; when a judging result is yes, outputting a start command to the start unit; and
when the bus voltage is equal to the set voltage, outputting a control signal to the DC/DC converter.
To make the object, technical solution and advantage of the invention clearer, hereinafter the invention is further explained in details with reference to the accompanying drawings and the embodiments. It shall be understood that the described specific embodiments are only to explain the invention, but not limited to the invention.
It shall be noted that reference of “one embodiment”, “embodiments” and “exemplary embodiments” in the specification refers to that the described embodiment may include specific features, structures or properties, but it is not that every embodiment must include these specific features, structures or properties. Moreover, such expression does not refer to the same embodiment. Further, when the specific features, structures or properties are described with reference to the embodiments, regardless of clear description, it has indicated that such feature, structure or property combined in other embodiments is within the knowledge range of those skilled in the art.
Moreover, the specification and subsequent claims use some phrases to refer to specific components or members, and those ordinary in the art shall understand that manufacturers may name different nouns or terms to be the same component or member. The specification and subsequent claims do not use the difference of names as the way of distinguishing the component or member, but using the difference of functions of the component or member as the distinguishing criterion. “comprise” and “include” mentioned in the whole specification and subsequent claims are open words, so they shall be understood to be “include but not limited to”. Moreover, the word “connection” includes any direct or indirect electrical connection means. Indirect electrical connection means includes connecting through other devices.
Intermittent power generation features of the clean energy brings a certain challenge to safe and stable operation of the grid. Energy storage technology is an effective measure to suppress power fluctuation of the grid, and enhance quality of electric energy, and is applied to clean energy power generation system. The energy storage system is connected to the grid, and uses the common DC bus as an energy transfer carrier. The constant control of the DC bus voltage determines operation modes of the devices in the energy storage system.
The disclosure provides an energy storage system which includes an energy storage converter, at least one battery unit, at least one DC/DC converter and a start unit. The energy storage converter has an AC end electrically connected to an AC power supply or a load, and a DC end electrically connected to a DC bus. Each battery unit is electrically connected to the DC bus through the DC/DC converter, the battery unit is electrically connected to a low-voltage port of the DC/DC converter, and the DC bus is electrically connected to a high-voltage port of each DC/DC converter. In one possible embodiment, the energy storage system includes a plurality of battery units and a plurality of DC/DC converters connected in one-to-one correspondence, and the high-voltage ports of the plurality of DC/DC converters are coupled in parallel to the DC bus. The start unit has an input end electrically connected to a battery unit, and an output end electrically connected to the DC bus. When the energy storage system starts from the battery unit, for example, the energy storage system is in a full black condition, the start unit operates to deliver the electric power of the battery unit to the DC bus, thereby establishing the bus voltage to a set voltage.
The start unit BS1 has an input end electrically connected to the battery unit 2, and an output end electrically connected to the DC bus. The start unit BS1 is connected in parallel to the DC/DC converter DD2. The input end of the start unit BS1 and a low-voltage port of the DC/DC converter DD2 are coupled in parallel to the battery unit 2, and the output end of the start unit BS1 and a high-voltage port of the DC/DC converter DD2 are coupled in parallel to the DC bus. The start unit BS1 only operates when the energy storage system starts from the battery unit. When the start unit BS1 operates, the DC/DC converter DD2 is correspondingly bypassed. The start unit BS1 shares the start process of the DC/DC converter. The start unit outputs power to the DC bus, and controls the bus voltage. The bus voltage can be established from zero to the set voltage by the start unit. And then the DC/DC converters operate to output power to the DC bus, and controls the bus voltage. The bus voltage can be established from the set voltage to a target voltage by the DC/DC converters. It is unnecessary for the DC/DC converters to establish the bus voltage from zero to the target voltage, and precharge resistors inside the DC/DC converter are decoupled from a DC device connected on the bus and mF-level capacitors of the bus.
The number of start units is not limited to one. In some embodiments, the energy storage system includes a plurality of start units. For example, the energy storage system 1 may further include another start unit, and the another start unit and the DC/DC converter DD1 are coupled in parallel between the battery unit 1 and the DC bus.
When the energy storage system 1 black starts, the start unit operates to release electric energy of the battery unit 2, and supplies electric energy to the DC bus. The start unit controls the bus voltage to establish the bus voltage to the set voltage. This process is only completed by the start unit, and the DC/DC converter is bypassed. After the bus voltage is established to the set voltage, the DC/DC converters start to operate. The DC/DC converters transform electric energy of the battery units, and supply power to the DC bus. The DC/DC converters control the bus voltage to establish the bus voltage from the set voltage to the target voltage. After the DC/DC converters start, the start unit stops operation. The target voltage is a reference voltage of the DC bus. After the DC bus voltage is established to the reference voltage, the energy storage converter starts through the power of the DC bus, such that the energy storage system 1 resumes operation. After start completes, the DC/DC converter performs boost or buck conversion to regulate a battery voltage, and stabilize the bus voltage. The start unit exits operation. The start unit is awaked until the energy storage system shall start from the battery unit next time.
The start unit includes a start circuit and a switching circuit. The start circuit has an input end electrically connected to the battery unit, and an output end electrically connected to the DC bus through a switching circuit. The switching circuit includes a turn-on mode and a turn-off mode. In the turn-on mode, the start circuit inputs power to the DC bus through the conducted switching circuit, and in the turn-off mode, the switching circuit blocks a power transmission path between the start circuit and the DC bus. Specifically, when the bus voltage is less than the set voltage, the switching circuit is on, and the start circuit outputs power to the DC bus; and when the bus voltage is greater than the set voltage, the switching circuit is off, and the start circuit stops outputting power to the DC bus.
When the set voltage is a voltage of the battery unit, the switching circuit may select a diode. An anode of the diode is electrically connected to a positive output end of the start circuit, and a cathode of the diode is electrically connected to the DC bus. At this time, the switching circuit is unidirectionally conducted, and the bus voltage outputted by the start unit does not exceed the voltage of the battery unit. When the bus voltage is less than the voltage of the battery unit, the diode is positively conducted, and the start circuit delivers power of the battery unit to the DC bus. When the bus voltage is greater than or equal to the voltage of the battery unit, the diode is reversely cut off, and the start circuit cannot deliver power to the DC bus, while the DC bus cannot also reversely deliver energy to the battery unit.
When the energy storage system starts from the battery side, the start circuit establishes the bus voltage from zero to the set voltage. Then the DC/DC converter starts to boost the voltage of the battery unit and output the voltage boosted to the DC bus, and the bus voltage is established from the set voltage to the target voltage. When the DC/DC converter starts and the bus voltage is greater than the set voltage, the switching circuit is changed to the turn-off mode, and the start unit stops operation to ensure seamless switching between the start unit and the DC/DC converter.
As shown in
The process of establishing the bus voltage from zero to the target voltage includes two stages. The start unit undertakes the first stage. The bus voltage is established from zero to the set voltage during the first stage. The DC/DC converter undertakes the second stage. The bus voltage is established from the set voltage to the target voltage during the second stage. The precharge resistors of the DC/DC converter are decoupled from DC devices connected on the bus and a mF-level capacitor DC_C1 of the bus. The start unit and the DC/DC converter are both controlled by the BMS, thereby achieving seamless switching between the start unit and the DC/DC converter, and stably establishing the bus voltage.
When determining to start the energy storage system through the battery unit, the battery management unit BMS sends the start signal and controls the first precharge switch K11 closed. The first precharge resistor R11 is connected, the battery unit charges the DC bus, and the first precharge resistor R11 is configured to limit a charging current. The bus voltage is gradually increased from zero. When the bus voltage approaches the voltage of the battery unit, the first precharge switch K11 is turned off, the first main switch K1 is closed, and the bus voltage continues to increase and is equal to the voltage of the battery unit finally. A surge current can be suppressed by selecting an appropriate first precharge resistor R11, and the self-start equipment on the DC bus can normally operate. In actual application, the line has an impedance, and the diode also has a voltage drop, so “equal to”, “stabilize”, “approach”, “substantially stabilize” and “substantially equal to” in the disclosure allow an error, for example, +/−10%, preferably, +/−5%.
Please continue to refer to
When the start unit establishes the DC bus voltage to the set voltage, the battery management unit BMS outputs a control signal to the DC/DC converter for controlling the third precharge switch K31 closed. Seamless switching between the start unit and the DC/DC converter is achieved. After the third precharge switch K31 is closed, the third precharge resistor R31 is connected, and the DC bus precharges the second capacitor C1. When a voltage of the second capacitor C1 approaches the set voltage, the third precharge switch K31 is open, the third main switch K3 is closed, and the voltage of the second capacitor is equal to the set voltage. In this embodiment, the set voltage is equal to the voltage of the battery unit.
The second precharge switch K21 is closed, the second precharge resistor R21 is connected, and the battery unit precharges the first capacitor C3. When a voltage of the first capacitor approaches the voltage of the battery unit, the second precharge switch K21 is open, the second main switch K2 is closed, and the voltage of the first capacitor is equal to the voltage of the battery unit. The second precharge resistor R21 only shall suppress a surge current when precharging the first capacitor, and is decoupled from devices on the DC bus. The resistance of the second precharge resistor is small, and the cost is low. After precharging the first capacitor, PWM control is performed to the switching tubes S1˜S4, and the DC/DC converter boosts the voltage of the battery unit, thereby controlling the bus voltage to increase from the set voltage to the target voltage. Structure of the DC/DC converter in the disclosure is not limited thereto, and may be flexibly designed according to actual requirements.
When the DC/DC converter operates, the bus voltage is greater than the set voltage such that the diode D5 is reversely cut off. And the start unit stops transmitting electric energy. When the DC/DC converter establishes the bus voltage to the target voltage, the first main switch K1 is turned off, and the start unit exits to wait for next start command.
The start unit provided in this embodiment is applicable to an energy storage system with a simple structure. When the DC equipment on the DC bus or a capacitor of the DC bus changes, the first precharge resistor R11 shall be adjusted.
In another alternative embodiment, the start circuit includes a buck circuit and a precharge circuit. The precharge circuit has a first end electrically connected to a positive electrode of the battery unit, and a second end electrically connected to the buck circuit. The buck circuit means a circuit which can reduce an output voltage relative to an input voltage. The buck circuit includes at least one input capacitor and at least one controllable switch. The at least one input capacitor has one end electrically connected to the second end of the precharge circuit, and the other end electrically connected to a negative electrode of the battery unit. The precharge circuit precharges the input capacitor. After precharging the input capacitor, PWM modulation is performed on the at least one controllable switch by a control circuit such as BMS, such as BMS. The buck circuit bucks the voltage of the battery unit. When specifically implementing, a duty ratio of the at least one controllable switch is controlled, such that the bus voltage is gradually increased from zero to the set voltage. For example, the duty ratio of the at least one controllable switch is adjusted by closed loop control. The duty ratio of the at least one controllable switch is gradually increased, such that an output voltage of the buck circuit is gradually increased. And a slope of a voltage change curve establishing the bus voltage is controlled by adjusting the duty ratio of the at least one controllable switch, such that the process of establishing the bus voltage from zero to the set voltage is flexibly controllable.
Please continue to refer to
Duty ratios of the fifth switching tube S5 to the eighth switching tube S8 are controlled such as the flying capacitor switch circuit performs buck conversion on the voltage of the battery unit. For example, the duty ratios of the fifth switching tube S5 to the eighth switching tube S8 are adjusted by closed loop control. Duty ratios of the fifth switching tube S5 and the sixth switching tube S6 are gradually increased, and duty ratios of the seventh switching tube S7 and the eighth switching tube S8 are gradually decreased, such that an output voltage of the flying capacitor switch circuit is gradually increased, and the bus voltage is slowly established to the set voltage.
The output voltage of the flying capacitor switch circuit is less than one half of the input voltage before a time ta in
Before the time ta, the output voltage of the flying capacitor switch circuit is less than one half of the input voltage, and hereinafter working conditions of the circuit in
In the working mode B of
In the working mode C of
In the working mode D of
After the time ta, the output voltage of the flying capacitor switch circuit is greater than one half of the input voltage, and hereinafter working conditions of the circuit in
In the working mode A of
In the working mode B of
In the working mode C of
With increase of the duty ratios of the fifth switching tube S5 and the sixth switching tube S6, a discharge time of the input capacitor C4 is increased, such that the output voltage of the start circuit is gradually increased.
In this embodiment, structure and working process of the DC/DC converter are the same as that in the embodiment of
In the embodiments, the set voltage is equal to the voltage of the battery unit, and the switching circuit is a diode. The diode can automatically cut a power transmission path of the start unit when the bus voltage is greater than the voltage of the battery unit, thereby preventing power flow backward. So control is simple, and cost is low. However, the invention is not limited thereto. For example, the switching circuit is a switch or a relay. In some embodiments, the start circuit uses a boost-buck circuit, and the set voltage may be less than or greater than the voltage of the battery unit. Only if the energy storage system starts through the battery unit, an independent start unit shares the process of establishing the bus voltage from zero to the set voltage, and the DC/DC converter only shall complete establishing the bus voltage from the set voltage to the target voltage, which are both within the protection scope of the disclosure.
The energy storage system of the disclosure includes the independent start unit and the DC/DC converter simultaneously, expands a controllable range of the bus voltage, such that the process of establishing the bus voltage is flexibly controllable, and a voltage control dead zone is eliminated. Meanwhile, the precharge circuits in the energy storage system are all decoupled from the DC bus, such as DC equipment on the DC bus.
The invention further provides a start method of an energy storage system, which is applied to the energy storage system in the above embodiments. The start method includes: providing a start unit electrically connected between a battery unit and the DC bus; and when the energy storage system starts through the battery unit, operating the start unit to delivering power of the battery unit to the DC bus, thereby establishing a bus voltage to a set voltage. The start unit is controlled to operate to establish the voltage of the DC bus to the set voltage through the electric power of the battery unit.
The start method further includes: when the start unit establishes the bus voltage to the set voltage, operating the DC/DC converter to deliver power of the battery unit to the DC bus, thereby establishing the bus voltage from the set voltage to a target voltage. The DC/DC converter continues to establish the bus voltage to the target voltage through the electric power of the battery unit.
The start method further includes: judging whether to start the energy storage system through the battery unit; when a judging result is yes, outputting a start command to the start unit; and when the bus voltage is equal to the set voltage, outputting a control signal to the DC/DC converter.
When the bus voltage is greater than the set voltage, cut off a power transmission path of the start unit. As for the method of controlling the energy storage system and the achieved technical effect in this embodiment, description of the corresponding parts of the energy storage system provided in the above embodiments may be referred, and the details are not described here.
The energy storage system of the invention has self-started capability, and the process of establishing the bus voltage is flexibly controllable. And the precharge resistors in the energy storage system can be decoupled from the DC bus, such as capacitor capacity of the DC bus, mounting loads on the DC bus. Hardware topology of the system can be optimized.
Of course, the invention may further have various other embodiments, and in the case of not departing from spirit and essence of the invention, those skilled in the art shall make various corresponding modifications and variations according to the invention, but these corresponding modifications and variations shall belong to the protection scope of the appended claims of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202410027508.4 | Jan 2024 | CN | national |
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on patent application Ser. No. 20/241,0027508.4 filed in P.R. China on Jan. 8, 2024, the entire contents of which are hereby incorporated by reference. Some references, if any, which may include patents, patent applications and various publications, may be cited and discussed in the description of this application. The citation and/or discussion of such references, if any, is provided merely to clarify the description of the present application and is not an admission that any such reference is “prior art” to the application described herein. All references listed, cited and/or discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.
