Patent Application
20240339839
The present invention relates to the field of distributed photovoltaic power generation technologies, and in particular, to a shutdown device, a communication method for a shutdown device, and a rapid shutdown photovoltaic system.
Over recent years, with joint efforts of upstream and downstream photovoltaic industry chains, a price of photovoltaic power generation has gradually become lower than a power purchase price and even a power generation cost of conventional coal power. A photovoltaic installed capacity has grown rapidly year by year, and will become a main source of power generation in the near future.
Due to its advantages such as a mature technology, high conversion efficiency, a high integration level, and a low price, a string photovoltaic system has been widely used in a distributed photovoltaic system such as a household rooftop and an industrial and commercial rooftop, as well as a ground power station. However, when the photovoltaic system catches fire, a direct-current high voltage of the string photovoltaic system brings a serious risk of electric shock to fire extinguishment on a roof. Fire extinguishment is extremely difficult, and in most cases the fire can only be allowed to spread. To resolve the fire extinguishment safety problem of a rooftop photovoltaic system, a module-level rapid shutdown function is required by a 2017 version of the United States National Electrical Code NEC, which requires the voltage on any conductor in a photovoltaic array to drop below 80V within 30 seconds after the rapid shutdown function is triggered, and the voltage on any external conductor not in the photovoltaic array to drop below 30V within 30 s. Subsequently, evaluation methods for a rapid shutdown apparatus and a rapid shutdown system are also added to the UL1741 standard.
A solution for the string photovoltaic system to meet the NEC 2017 rapid shutdown requirement is to add module-level rapid shutdown device, including a shutdown device and an optimizer. The shutdown device is widely used in the string photovoltaic system due to the low cost, and most shutdown devices are compatible with the Sunspec rapid shutdown protocol, so they can be replaced by each other.
The Sunspec rapid shutdown protocol is a simple and reliable simplex power line carrier communication (PLC) protocol. A conventional shutdown device using the protocol is simple, reliable, and low-cost. However, the conventional shutdown device can only receive the PLC signal, and it cannot send information, so module-level monitoring cannot be achieved. When a shutdown device or a module is abnormal, it costs lots of time to find the abnormal one in a large photovoltaic system. Some manufacturers replace a Sunspec rapid shutdown protocol receiver in the shutdown device with a power line carrier transceiver module, achieving the duplex communication of the shutdown device, and thereby providing module-level monitoring, but it increases the cost. There are also other manufacturers that replace the Sunspec rapid shutdown protocol receiver with a wireless communication transceiver to achieve the duplex communication. However, wireless communication is not very stable in the application. A relay is needed to improve stability of communication, which increases system complexity and cost.
In view of this, an objective of the present invention is to provide a low-cost shutdown device with a two-way communication capability. By controlling a switching device of the shutdown device to work in a high-frequency switching state to generate a current ripple signal carrying communication data on a power bus, data transmitting of the shutdown device is implemented.
To achieve the foregoing objective, the present invention provides a shutdown device, including:
Further, the control module adjusts an amplitude of the power control signal according to a power bus current to control a duty cycle of the first composite control signal, to keep a peak value of a voltage ripple at the input port of the shutdown device within a predetermined ripple threshold.
Further, the duty cycle of the first composite control signal is positively correlate with the power bus current, the larger the power bus current is, the larger the duty cycle is, and conversely, the smaller the duty cycle is.
Further, the control module includes:
Further, the first communication signal contains operating data of the shutdown device, and the operating data of the shutdown device includes input and output electrical parameters and internal operating data of the shutdown device, where the input and output electrical parameters include an output voltage, an output current, and a power generation of a direct-current power supply coupled to each input port of the shutdown device, and an output voltage and the power bus current of the shutdown device, and the internal operating data includes a temperature, an operating state, and alarm information of the shutdown device.
Further, the control module further includes:
Further, the shutdown device further comprises a signal decoupling module, configured to separate a power line carrier signal on the power bus from the power bus current, to extract the power line carrier signal;
Further, the comprehensive control unit is further configured to parse the second data packet, to obtain control instructions in the second data packet, and adjust an operating mode of the shutdown device according to the control instructions, where the control instructions includes a permission to operate instruction, a rapid shutdown instruction, and a data collection instruction, and the operating mode of the shutdown device includes a safe disconnection mode and a normal operating mode; and
Further, an initial mode after the shutdown device is powered on is the safe disconnection mode, and when receiving the permission to operate instruction, the comprehensive control unit switches the operating mode of the shutdown device to the normal operating mode; and when the comprehensive control unit does not receive the permission to operate instruction within a first preset time period, or receives the rapid shutdown instruction, the comprehensive control unit switches the operating mode of the shutdown device to the safe disconnection mode.
Further, if the comprehensive control unit receives the data collection instruction, the comprehensive control unit packages the operating data into the first data packet and provides the first data packet to the protocol processing unit, the protocol processing unit sets the data transmitting state signal to represent the busy state upon receiving the first data packet, the power control unit generates the power control signal according to the power bus current, and the first composite control signal controls the switching device to work in the high-frequency switching state;
Further, the shutdown device further includes a discharge module, configured to provide a discharge path and discharge the power bus to keep a voltage of the power bus below a safe value within a specified time period when the shutdown device switches from the normal operating mode to the safe disconnection mode.
Further, when the shutdown device transmits the first data packet, if the power bus current is less than a current threshold, the discharge module is turned on to increase a discharge current of the shutdown module to enhance an amplitude of the current ripple signal.
Further, the shutdown module further comprises a bypass device, configured to provide a bypass path for the power bus current; and
Further, the monitoring unit is further configured to monitor an input voltage of the shutdown device, and output an input state detection signal;
Further, when monitoring that the input voltage of the shutdown device is less than a voltage threshold, the monitoring unit determines that the input state of the input port of the shutdown device is abnormal, otherwise determines that the input state of the input port of the shutdown device is normal.
Further, when the shutdown device is in the normal operating mode, if the comprehensive control unit receives the data collection instruction, the comprehensive control unit packages the operating data into the first data packet and provides the first data packet to the protocol processing unit, and the protocol processing unit sets the data transmitting state signal to the busy state upon receiving the first data packet;
Further, when the shutdown device is in the safe disconnection mode, the first composite control signal controls the switching device to be in an off state, and the second composite control signal controls the bypass device to be in an off state.
To achieve an objective of the foregoing invention, the present invention provides a communication method for a shutdown device, including:
Further, an amplitude of the power control signal is adjusted according to a power bus current of the shutdown device to control a duty cycle of the first composite control signal, to keep a peak value of a voltage ripple at the input port of the shutdown device within a predetermined ripple threshold.
Further, the duty cycle of the first composite control signal is positively correlate with the power bus current, the larger the power bus current is, the larger the duty cycle is, and conversely, the smaller the duty cycle is.
Further, the method further includes:
To achieve the foregoing objective, the present invention provides a rapid shutdown photovoltaic system. The system includes a plurality of shutdown devices, a plurality of photovoltaic modules, a main controller, and a photovoltaic inverter, each shutdown device is connected to at least one photovoltaic module, the plurality of shutdown devices are connected in series to a power bus, the power bus is connected to a direct-current input port of the photovoltaic inverter, the shutdown device includes at least one input port, at least one shutdown module, an output port, and a control module, one shutdown module corresponds to one input port, and the shutdown module includes at least one switching device, where
Compared with the related art, the present invention provides a shutdown device, a communication method for a shutdown device, and a rapid shutdown photovoltaic system, which have the following beneficial effects: In the present invention, a first composite control signal for controlling a switching device of the shutdown device is generated by modulating the first communication signal containing the operating data of the shutdown device and the power control signal that controls the output power of the direct-current power supply coupled to the input port of the shutdown device, thereby controlling the switching device to work in the high-frequency switching state to generate a high-frequency voltage ripple signal carrying the first communication signal at the output port of the shutdown device, and generate a corresponding high-frequency current ripple signal on the power bus connected to the shutdown device, to couple the operating data of the shutdown device to the power bus. So the power line carrier signal carrying the operating data of the shutdown device is injected into the power bus, implementing a function of transmitting data to the outside by the shutdown device. The shutdown device in the present invention does not need a power line carrier transceiver module or a wireless communication module, to implement data communication. Compared with a conventional shutdown device with a power line carrier communication module or a wireless communication module, the present invention has a higher integration level and fewer components, which greatly reduces cost of a product, is conducive to large-scale application of a module-level shutdown device, and improves a safety level of the photovoltaic system.
Further, the shutdown device includes a plurality of input ports, is a multi-input topology structure, and may select a switching device of a shutdown module corresponding to any input port to work in the high-frequency switching state, to implement an objective of coupling the operating data of the shutdown device to the power bus to perform data transmitting. A plurality of shutdown modules share one control module, which may improve an integration level and power density of the shutdown device, and significantly reduce production cost of a product.
Further, when the photovoltaic module at the input port of the shutdown device is abnormal and causes its maximum output current to be less than the power bus current, and when the first switching device of the shutdown module is turned off, by controlling the bypass device of the shutdown device to work in the high-frequency switching state, data transmitting of the shutdown device under an abnormal working condition is achieved, improving environmental suitability of the shutdown device.
10-input port, 11-output port, 12-shutdown module, 13-control module, 14-signal decoupling module, 15-discharge module, 16-power bus, 121-input unit, 122-switch unit, 123-output unit, 1221-switching device, 1222-bypass device, 20-first input port, 22-first shutdown module, 221-first input unit, 222-first switch unit, 223-first output unit, 2221-first switching device, 30-second input port, 32-second shutdown module, 321-second input unit, 322-second switch unit, 323-second output unit, and 3221-second switching device.
The present invention will be described in detail below with reference to specific implementations shown in the accompanying drawings. However, these implementations do not limit the present invention, and structural, method, or functional transformations made by a person of ordinary skill in the art according to these implementations are included in a protection scope of the present invention.
As shown in
The direct-current power supply includes at least one cell, which is usually one photovoltaic module or two photovoltaic modules connected in series. An example in which a photovoltaic module is used as the direct-current power supply photovoltaic module is described in the present invention. One input port 10 corresponds to one photovoltaic module. In other embodiments, the shutdown module 12 includes, for example, a plurality of switching devices connected in series and/or parallel, and a data transmitting function is implemented by controlling any switching device to work in the high-frequency switching state.
An example in which the shutdown device includes an input port 10, an output port 11, a shutdown module 12, and a control module 13, and the shutdown module 12 includes a switching device 1221 is used for description below, but the invention is not limited to the example.
The switching device 1221 is connected between the input port 10 and the output port 11, to control the output power of the photovoltaic module coupled to the input port 10. The switching device 1221 may be located between a high electric potential terminal of the input port 10 and a high electric potential terminal of the output port 11, or may be located between a low electric potential terminal of the input port 10 and a low electric potential terminal of the output port 11. In this embodiment, an example in which the switching device 1221 is located between the low electric potential terminal of the input port 10 and the low electric potential terminal of the output port 11 is used. The control module 13 is coupled to the shutdown module 12. The first composite control signal is generated to control the switching device 1221 according to the first communication signal and the power bus current. The first composite control signal adjusts the output power of the photovoltaic module coupled to the input port 10 of the shutdown device, and controls the switching device 1221 to work in the high-frequency switching state, to couple the first communication signal to the power bus for transmission. The power bus connects output ports of a plurality of shutdown devices in series to connect to a photovoltaic inverter. The length of the power bus ranges from tens to hundreds of meters, and the parasitic inductance usually ranges from 7.8 uH to 269 uH. The power bus current is controlled by the photovoltaic inverter. The photovoltaic inverter adjusts the power bus current to maximize the output power of each photovoltaic module in the photovoltaic system.
The first communication signal includes communication data of the shutdown device, and the communication data includes operating data of the shutdown device, but the invention is not limited to the example. In other embodiments, the first communication signal may further include any other data that needs to be transmitted.
As an implementation of the present invention, the control module 13 adjusts an amplitude of the power control signal according to a power bus current to control a duty cycle of the first composite control signal, to keep a peak value of a voltage ripple at the input port of the shutdown device within a predetermined ripple threshold, thereby avoiding large fluctuations of a steady-state operating point of the photovoltaic module photovoltaic module, which reduces the output power of the photovoltaic module when the switching device 1221 switches at a high frequency. The duty cycle of the first composite control signal is positively correlate with the power bus current, the larger the power bus current is, the larger the duty cycle is, and conversely, the smaller the duty cycle is.
As an implementation of the present invention, the shutdown module 12 further includes an input unit 121 coupled to the input port 10 and an output unit 123 coupled to the output port 11. The input unit 121 includes an input capacitor Cin, used to stabilize an input voltage Vin of the shutdown device. The output unit 123 includes an output capacitor Co, used to stabilize an output voltage Vo of the shutdown device.
The principle of a shutdown device transmitting the first communication signal through the high-frequency switching of the switching device 1221 is described as follows. When the switching device 1221 works in the high-frequency switching state, during an off process of the switching device 1221, because the line parasitic inductance of the power bus is large enough, and its storage energy cannot change suddenly under the energy storage inertia effect, the power bus current almost remains unchanged, the output voltage Vo of the output port 11 decreases linearly, and a drop voltage ΔVo is shown in Formula (1):
ΔVo=(I·(1−D)·T)/Co (1),
I is the power bus current, T is the cycle of the first composite control signal, D is the duty cycle of the first composite control signal, and Co is the capacitance of the output capacitor Co.
During the off process of the switching device 1221, an output current of the photovoltaic module charges the input capacitor Cin, and the input voltage Vin across the input capacitor Cin is raised. When the photovoltaic module works at a maximum power point due to the control of the photovoltaic inverter, the input voltage Vin of the shutdown device fluctuates slightly, and a fluctuation value is less than 10% of the output voltage of the photovoltaic module, which has little impact on the output current of the photovoltaic module. The output current of the photovoltaic module may be considered to be basically unchanged, approximately equal to the power bus current, the input voltage Vin of the shutdown device rises linearly in the period, and an overcharge voltage ΔVin of the shutdown device is shown in Formula (2):
ΔVin=(I·(1·D)·T)/Cin (2), where
Cin is the capacitance of the input capacitor Cin.
When the switching device 1221 is on, energy stored in the input capacitor Cin during the off process of the switching device 1221 is quickly transferred to the output capacitor Co through the switching device 1221, thereby compensating the energy discharged by the output capacitor Co during the off period of the switching device 1221. In addition, the input voltage Vin and output voltage Vo of the shutdown device return to a steady-state voltage, and the output voltage of the photovoltaic module also returns to the steady-state voltage. The photovoltaic inverter still controls the output voltage of the photovoltaic module by adjusting the power bus current, so that the photovoltaic module works at a maximum power point. In addition, the shutdown device needs to adjust the duty cycle D according to the power bus current, for example, according to the proportional relationship in Formula (1) or Formula (2), to guarantee that when the switching device 1221 is turned off, the overcharge voltage ΔVin of the input voltage Vin of the shutdown device is less than 10% of the output voltage of the photovoltaic module, thereby preventing the working point of the photovoltaic module from deviating from the maximum power point, reducing the output power of the photovoltaic module.
When the switching device 1221 works in a high-frequency switching state, the output voltage Vo of the shutdown device includes abundant high-frequency switching harmonics. By performing fourier transformation on the output voltage Vo, a direct-current component, a fundamental component, and other harmonic components of the output voltage Vo are obtained, where the frequency of the fundamental component is the switching frequency of the switching device 1221. Under the excitation of the fundamental component of the output voltage Vo, a corresponding fundamental current ripple is generated on the power bus. According to the foregoing analysis, the fundamental component included in the output voltage of the shutdown device is modulated according to the first communication signal containing the operating data of the shutdown device, the power line carrier signal carrying the first communication signal may be injected into the power bus, and data transmitting function of the shutdown device may be implemented. In this embodiment, the power line carrier signal is a fundamental component of a current ripple signal, namely, the fundamental current ripple.
As an implementation of the present invention, a typical value of the input capacitor Cin of the shutdown device is 1 uF, a typical value of the output capacitor Co is 1 uF, a switching frequency is 100 kHz, and an impedance of the power bus at the switching frequency is 100 ohms. When the input voltage Vin of the shutdown device is 40V, the power bus current is 2 A, and the overcharge voltage ΔVin is controlled to 2V. According to Formula (1) and Formula (2), the duty cycle D=0.9, the drop voltage ΔVo is 2V, and a waveform of the input voltage Vin and a waveform of the output voltage Vo are shown in
As an implementation of the present invention, the control module 13 includes a power control unit 131 and a modulation unit 132. The power control unit 131 generates the power control signal according to the power bus current, and outputs the power control signal to the modulation unit 132. The modulation unit 132 is configured to receive the first communication signal and the power control signal, and modulate the first communication signal and the power control signal, to generate the first composite control signal. The first composite control signal controls the switching device 1221 to perform high-frequency switching. The first composite control signal controls the switching device 1221 to operate at a high frequency, generating a corresponding fundamental component of the output voltage at the output port of the shutdown device. Under the excitation of the fundamental component of the output voltage, a corresponding fundamental current ripple is generated on the power bus, thereby coupling the first communication signal containing operating data to the power bus. A current ripple signal carrying operating data is generated on the power bus, the data transmitting function of the shutdown device is implemented. And the data transmitting function of the shutdown device may be implemented without a power line carrier transceiver module or a wireless communication module in the conventional shutdown device.
The modulation unit 132 modulates the received power control signal and the first communication signal to generate the first composite control signal. The power control signal and the first communication signal are modulated based on a plurality of mature modulation technologies, in other words, the fundamental component in the output voltage of the shutdown device is modulated, so that the fundamental current ripple on the power bus carries the first communication signal containing the operating data of the shutdown device. Mature modulation technologies that may be used include frequency shift keying (FSK), phase shift keying (PSK), and the like. The FSK modulation technology, which has good anti-noise and anti-attenuation properties, is easy to implement, and has been widely used in digital communication at a medium and low speed. For example, wireless chips such as various narrowband power line carrier communication chips, Bluetooth, ZIGBEE, and the like each use the FSK modulation technology. The FSK modulation technology has two code elements: a mark frequency Fm and a space frequency Fs. The mark frequency Fm is used for representing a number “1”, and the space frequency Fs is used for representing a number “0”.
The present invention uses the FSK modulation technology as an example for description.
As an implementation of the present invention, the control module 13 further includes a monitoring unit 133, a comprehensive control unit 134, and a protocol processing unit 135. The monitoring unit 133 collects and obtains operating data of the shutdown device, and provides the operating data to the comprehensive control unit 134. The operating data of the shutdown device includes input and output electrical parameters and internal operating data of the shutdown device, where the input and output electrical parameters include an output voltage, an output current, and a power generation of a direct-current power supply coupled to each input port of the shutdown device, and an output voltage and a power bus current of the shutdown device, and the internal operating data includes a temperature, operating states, and alarm information of the shutdown device. The comprehensive control unit 134 packages the operating data of the shutdown device into a first data packet, and provides the first data packet to the protocol processing unit 135. The protocol processing unit 135 encapsulates the first data packet into the first communication signal according to a predetermined communication protocol, and provides the first communication signal to the modulation unit 132.
As an implementation of the present invention, the control module 13 further includes a drive unit 136, which is connected to the modulation unit 132, and generates a first drive signal according to the received first composite control signal. The first drive signal controls the switching of the switching device 1221.
As an implementation of the present invention, the shutdown device further includes a signal decoupling module 14. The signal decoupling module 14 is configured to separate a power line carrier signal on the power bus from the power bus current, to extract the power line carrier signal. The signal decoupling module 14 includes an RLC parallel resonant circuit. The RLC parallel resonant circuit is a band-pass filter. The frequency of the power line carrier signal is in the passband of the band-pass filter. The RLC parallel resonant circuit provides a stable impedance for a power line carrier signal, thereby extracting the power line carrier signal from a power line. The control module 13 further includes a demodulation unit 137, which receives the power line carrier signal extracted by the signal decoupling module 14, and filters and amplifies the power line carrier signal, to obtain a power line carrier signal with a better signal-to-noise ratio, and demodulates the power line carrier signal, to obtain a second communication signal, and provides the second communication signal to the protocol processing unit 135. The protocol processing unit 135 parses the received second communication signal to obtain a second data packet according to a protocol format, and provides the second data packet to the comprehensive control unit 134. The comprehensive control unit 134 parses the second data packet, to obtain control instructions in the second data packet, and adjusts operating modes of the shutdown device according to the control instructions of the shutdown device, where the control instructions of the shutdown device include a permission to operate instruction, a rapid shutdown instruction, and a data collection instruction. The operating mode of the shutdown device includes a safe disconnection mode and a normal operating mode. The protocol processing unit 135 further generates a data transmitting state signal, and provides the data transmitting state signal to the power control unit 131. The data transmitting state signal represents states of data transmitting by the shutdown device, including an idle state and a busy state. The power control unit 131 controls the switching of the switching device 1221 according to the data transmitting state signal and the operating mode of the shutdown device.
As an implementation of the present invention, an initial mode after the shutdown device is powered on is the safe disconnection mode, and when receiving the permission to operate instruction, the comprehensive control unit 134 switches the operating mode of the shutdown device to the normal operating mode. When the comprehensive control unit 134 does not receive the permission to operate instruction within a first preset time period, or receives the rapid shutdown instruction, the comprehensive control unit switches the operating mode of the shutdown device to the safe disconnection mode.
As an implementation of the present invention, when the shutdown device is in the normal operating mode, if the comprehensive control unit 134 receives the data collection instruction, the comprehensive control unit 134 packages the operating data of the shutdown device into the first data packet, and the protocol processing unit 135 encapsulates the first data packet into the first communication signal, provides the first communication signal to the modulation unit 132, and sets the data transmitting state signal to represent a busy state. The power control unit 131 adjusts the amplitude of the power control signal according to the power bus current, thereby adjusting the duty cycle of the first composite control signal. The modulation unit 132 modulates the first communication signal and the power control signal, to generate the first composite control signal. In this case, the first composite control signal controls the switching device 1221 to work in the high-frequency switching state, to generate the current ripple signal carrying the operating data of the shutdown device on the power bus. When transmitting of the first data packet is completed, the protocol processing unit 135 sets the data transmitting state signal to represent an idle state, the power control unit 131 adjusts the power control signal to a first preset value, and in this case, the first composite control signal controls the switching device 1221 to be in an always-on state. When the shutdown device is in the safe disconnection mode, the power control unit 131 adjusts the power control signal to a second preset value, and in this case, the first composite control signal controls the switching device 1221 to be in an off state.
As an implementation of the present invention, when the shutdown device is in the safe disconnection mode, the modulation unit 132 outputs a low-level first composite control signal, to control the switching device 1221 to be in an off state, and the output voltage and power of the shutdown device are in a controlled safe state. When the shutdown device is in the normal operating mode and the data transmitting state signal represents an idle state, the modulation unit 132 outputs a high-level first composite control signal, to control the switching device 1221 to be in an always-on state. When the shutdown device is in the normal operating mode and the data transmitting state signal represents a busy state, the modulation unit 132 outputs the modulated first composite control signal, and the first composite control signal controls the switching device 1221 to be in the high-frequency switching state. The power control signal adjusts the duty cycle of the first composite control signal according to the power bus current, to control the fluctuation range of an operating point of the photovoltaic module, so that a peak value of a voltage ripple at the input port of the shutdown device kept within a predetermined ripple threshold, and a drop amplitude in the output power of the photovoltaic module caused by the voltage ripple at the input port of the shutdown device in the high-frequency switching state of the switching device 1221 is reduced.
When the shutdown device is in the safe disconnection mode, the same as the conventional shutdown device, the switching device 1221 is in the off state, and the photovoltaic module accessing the input port 10 is disconnected from the power bus. The output of the photovoltaic module is in an open circuit state, the output power is close to zero, and the output voltage and power of the shutdown device are limited. When the shutdown device is in the normal operating mode and the switching device 1221 is in the always-on state, the output voltage of the shutdown device is equal to its input voltage. The output power of the shutdown device is equal to the output power of the photovoltaic module. The output power of the photovoltaic module is adjusted by the power bus current. The power bus current is controlled by the photovoltaic inverter accessing the power bus. When the shutdown device is in the normal operating mode and the switching device 1221 is in the high-frequency switching state, the operating data of the shutdown device is coupled to the power bus, and the output power of the photovoltaic module is controlled by the power bus current and the duty cycle of the first composite control signal.
As an implementation of the present invention, the shutdown device further includes a discharge module 15. When the shutdown device switches from the normal operating mode to the safe disconnection mode, the comprehensive control unit 134 turns on the discharge module 15, providing a discharge path, and quickly discharges the power bus to keep its voltage below a safe value within a specified time period. In other words, the output voltage of the power bus is decreased to below 30V within 30 seconds, to meet the requirement of North American national electrical code NEC2017. The discharge current through the discharge path generally ranges from 5 to 10 mA. When the shutdown device switches from the safe disconnection mode to the normal operating mode, the comprehensive control unit 134 turns off the discharge module 15, and break the discharge path.
When the photovoltaic inverter in the photovoltaic system is in a standby mode, the power bus current may be extremely low, such as less than 1 mA. According to Formula (2) and parameters of a specific embodiment of the present invention, when the input voltage Vin of the shutdown device is 40V, the power bus current is 1 mA, and the duty cycle D is 0.5, the drop voltage ΔVo of the output voltage Vo is 5 mV. By performing fourier transformation on the waveform of the output voltage Vo, it can be seen that the amplitude of the fundamental component is 1.9 mV, and the amplitude of the fundamental current ripple on the power bus is 19 uA. The amplitude of the power line carrier signal (namely, the current ripple signal) is too low, leading to the shutdown device communication failure. Therefore, when the power bus current is less than a specific value, there will be a signal transmitted by the shutdown device, which is the current ripple signal coupled to the power bus, with a too small amplitude, making the main controller to be unable to receive the operating data transmitted by the shutdown device. In this case, the present invention provides an implementation, when the shutdown device transmits the first data packet, if the power bus current is less than a current threshold, the discharge module 15 is turned on, and a discharge current through the output unit of the shutdown module is increased, to enhance the amplitude of the current ripple signal. For example, the discharge module 15 may be turned on, to additionally provide an output current ranging from 5 to 10 mA to the shutdown device. When the duty cycle D is still 0.5, the fundamental current ripple on the power bus increases 5 to 10 times, reaching 114 uA to 209 uA. The amplitude of the power line carrier signal (namely, the current ripple signal) is greatly improved, improving the success rate of communication. When transmitting of the first data packet is completed, the discharge module 15 is controlled to be turned off.
As an implementation of the present invention, the shutdown device further includes a bypass device, which is connected in parallel to the output unit 123, and forms a switch unit 122 with the switching device 1221. When the photovoltaic module is blocked, and the control module or the photovoltaic module fails, a bypass path is provided for the power bus current. The bypass device may be implemented by a diode.
Because the shutdown device supplies power to the control module 13 by using an auxiliary power from the photovoltaic module corresponding to the input port 10, when the shutdown device is in the normal operating mode, and the maximum output current of the photovoltaic module is less than the power bus current, for example, working conditions such as the photovoltaic module is blocked by shadows and dust, or has a great attenuation, the output voltage of the photovoltaic module is gradually pulled down to zero, causing the supply of auxiliary power to be interrupted and the control module 13 to be powered off. To prevent the control module 13 from being powered off, the switching device 1221 is usually turned off, and the power bus current flows through the bypass device of the switch unit 122. Under the working condition, the operating data of the shutdown device cannot be coupled to the power bus through the high-frequency switching of the switching device 1221. To implement the data transmitting function of the shutdown device, the present invention performs improvement based on the first embodiment, and proposes a shutdown device of the second embodiment. Compared with the shutdown device of the first embodiment of the present invention, the bypass device of the shutdown module 12 is implemented by a switching device, for example, IGBT, MOSFET, and the like. When the photovoltaic module is blocked by shadows and dust, or has a great attenuation, causing the maximum output current of the photovoltaic module to be less than the power bus current, communication data such as the operating data of the shutdown device is coupled to the power bus by the high-frequency switching of the bypass device, to implement the communication transmitting function of the shutdown device.
As an implementation of the present invention, the monitoring unit 133 monitors the input voltage Vin of the shutdown device, and outputs an input state detection signal to the power control unit 131. The power control unit 131 generates the freewheeling control signal according to the input state detection signal, the operating mode of the shutdown device, and the data transmitting state signal. The power control unit 131 further generates the power control signal according to the input state detection signal, the operating mode of the shutdown device, the data transmitting state signal, and the power bus current. The amplitude of the power control signal is correlate with the power bus current, and the freewheeling control signal is a set value. The modulation unit 132 modulates the power control signal and the first communication signal to generate the first composite control signal, and modulates the freewheeling control signal and the first communication signal to generate the second composite control signal. The duty cycle of the first composite control signal is determined by the power bus current, and the duty cycle of the second composite control signal is a predetermined value. The drive unit 136 deals with the first composite control signal and the second composite control signal respectively, to obtain a first drive signal and a second drive signal. The first drive signal controls the switching device 1221, and the second drive signal controls the bypass device 1222.
As an implementation of the present invention, when detecting that the input voltage Vin of the shutdown device is less than a voltage threshold, the monitoring unit 133 determines that the input state of the input port 10 of the shutdown device is abnormal, otherwise determines that the input state of the input port 10 of the shutdown device is normal. When the input state of the input port 10 of the shutdown device is abnormal, the power control unit 131 outputs the power control signal to control the switching device 1221 to be in an off state, and outputs the freewheeling control signal to control the bypass device 1222 to be in an always-on state or a high-frequency switching state. After a second preset time period, the power control signal output by the power control unit 131 controls the switching device 1221 to be turned on, and the output freewheeling control signal controls the bypass device 1222 to be turned off. For example, the second preset time period is set to 5 mins. When the input voltage Vin of the shutdown device is greater than a threshold voltage for more than a third preset time period, the input state of the input port 10 of the shutdown device is switched to a normal state, otherwise the input state of the input port 10 of the shutdown device remains abnormal. For example, the third preset time period is set to 100 ms.
As an implementation of the present invention, an initial operating mode after the shutdown device is powered on is the safe disconnection mode, and when receiving the permission to operate instruction, the comprehensive control unit 134 switches the operating mode of the shutdown device to the normal operating mode. When the comprehensive control unit 134 does not receive the permission to operate instruction within a first preset time period, or receives the rapid shutdown instruction, the comprehensive control unit switches the operating mode of the shutdown device to the safe disconnection mode. When the shutdown device is in the normal operating mode, if the comprehensive control unit 134 receives the data collection instruction, the comprehensive control unit packages the operating data of the shutdown device into the first data packet and provides the first data packet to the protocol processing unit 135. The protocol processing unit 135 encapsulates the first data packet into the first communication signal, provides the first communication signal to the modulation unit 132, and sets the data transmitting state signal to represent a busy state. In this case, if the input state of the input port 10 of the shutdown device is normal, the power control unit 131 adjusts the amplitude of the power control signal according to the power bus current. The modulation unit 132 modulates the first communication signal and the power control signal into the first composite control signal. The first composite control signal controls the switching device 1221 to work in a high-frequency switching state, and the second composite control signal controls the bypass device 1222 to be in an off state. When the transmitting of the first data packet is completed, the protocol processing unit 135 sets the data transmitting state signal to represent an idle state, the power control unit 131 adjusts the power control signal to a first preset value, in this case, the first composite control signal controls the switching device 1221 to be in an always-on state, and the second composite control signal controls the bypass device 1222 to remain in the off state; if the input state of the input port 10 of the shutdown device is abnormal, the modulation unit 132 modulates the first communication signal and the freewheeling control signal to generate the second composite control signal, the second composite control signal controls the bypass device 1222 to work in the high-frequency switching state, and the first composite control signal controls the switching device 1221 to be in an off state; and when the transmitting of the first data packet is completed, the second composite control signal controls the state of the bypass device 1222 to switch to the always-on state. When the operating mode of the shutdown device is the safe disconnection mode, the first composite control signal controls the switching device 1221 to be in an off state, and the second composite control signal controls the bypass device 1222 to be in an off state.
When the input state of the input port 10 of the shutdown device is abnormal, the second composite control signal controls the bypass device to work in the high-frequency switching state, a corresponding fundamental component of the output voltage is generate at the output port 11 of the shutdown device. Under the excitation of the fundamental component of the output voltage, a corresponding fundamental current ripple is generated on the power bus, thereby coupling the first communication signal containing operating data to the power bus, generating the current ripple signal carrying operating data on the power bus, and implementing an objective of data transmitting by the shutdown device. The principle is the same as that of the first embodiment of the present invention. This is not repeated herein. When the input state of the input port 10 of the shutdown device is normal, data is transmitted by using the switching device 1221. The principle is the same as that of the first embodiment. This is not repeated herein.
When the shutdown device is in the safe disconnection mode, the switching device 1221 and the bypass device 1222 are in an off state, and the photovoltaic module accessing the input port 10 is disconnected from the power bus. The output of the photovoltaic module is in an open circuit state, the output power is close to zero, and the output voltage and power of the shutdown device are limited. When the shutdown device is in the normal operating mode and the input state of the input port 10 of the shutdown device is normal, the switching device 1221 is in the always-on state or the high-frequency switching state, the bypass device 1222 is in the off state, and the photovoltaic module connected to the input port 10 is connected to the power bus. The output power of the photovoltaic module is controlled by the power bus current and the duty cycle of the first composite control signal. When the shutdown device is in the normal operating mode and the input state of the input port 10 of the shutdown device is abnormal, the switching device 1221 is in the off state, the photovoltaic module accessing the input port 10 is disconnected from the power bus, the bypass device 1222 is in an on state, and the power bus current passes through the bypass device 1222. When the shutdown device transmits data, the bypass device 1222 is in the high-frequency switching state, and couples the operating data that needs to be transmitted by the shutdown device to the power bus.
As an implementation of the present invention, the switching device 1221 may be located between a high electric potential terminal of the input port 10 and a high electric potential terminal of the output port 11, or between a low electric potential terminal of the input port 10 and a low electric potential terminal of the output port 11. This implementation is described by using an example in which the switching device 1221 is located between a low electric potential terminal of the input port 10 and a low electric potential terminal of the output port 11.
In summary, when the abnormal output of the photovoltaic module connected to the input port of the shutdown device causes a maximum output current of photovoltaic module shutdown to be less than a power bus current, and when the switching device of the shutdown module is turned off, in this embodiment, through modulation and control of the bypass device of the shutdown device, and the bypass device is controlled to work in the high-frequency switching state, thereby implementing data transmitting of the shutdown device under an abnormal working condition, and improving environmental suitability of the shutdown device.
The present invention provides a communication method for a shutdown device, which may be applied to the above-mentioned shutdown device. However, the invention is not limited to the example. The communication method for embodiments of the present invention may be applied to any other shutdown device to which the present invention may be applied. The communication method for a shutdown device includes:
The operating data of the shutdown device is collected and obtained, the operating data of the shutdown device is packaged into a first data packet, and the first data packet is encapsulated into the first communication signal according to a predetermined communication protocol. The shutdown device generates the power control signal according to the power bus current, and modulates the first communication signal and the power control signal, to generate the first composite control signal. The first composite control signal controls the switching device 1221 to perform a high-frequency switching. By the high-frequency switching of the switching device 1221 under the control of the first composite control signal, a corresponding fundamental component of the output voltage is generated at an output port of the shutdown device, and under the excitation of the fundamental component of the output voltage, a corresponding fundamental current ripple is generated on the power bus, in other words, a current ripple signal carrying operating data is generated on the power bus, to implement a data transmitting function of the shutdown device.
Further, an amplitude of the power control signal is adjusted according to a power bus current of the shutdown device, and a duty cycle of the first composite control signal is further controlled, to keep a peak value of a voltage ripple at the input port of the shutdown device within a predetermined ripple threshold.
Further, the duty cycle of the first composite control signal is positively correlate with the power bus current, the larger the power bus current is, the larger the duty cycle is, and conversely, the smaller the duty cycle is.
As an implementation of the present invention, the method further includes:
When the shutdown device is in the normal operating mode, if it is monitored that the input voltage of the shutdown device is less than the voltage threshold, it is determined that the input state of the input port of the shutdown device is abnormal. When the first data packet needs to be transmitted, the first communication signal and the freewheeling control signal are modulated to generate the second composite control signal. The second composite control signal controls the bypass device 1222 to work in the high-frequency switching state, and the first composite control signal controls the switching device 1221 to be in an off state. A corresponding fundamental component of the output voltage is generated on the output port 11 of the shutdown device, and a corresponding fundamental current ripple is generated on the power bus, thereby coupling the first communication signal containing the operating data of the shutdown device to the power bus, and implementing an objective of data transmitting to the outside by the shutdown device when the input port is abnormal. When the transmitting of the first data packet is completed, the second composite control signal controls the state of the bypass device 1222 to switch to an always-on state.
A control module 13 is configured to modulate a power control signal and a first communication signal, to generate a first composite control signal, where the power control signal adjusts an output power of the first direct-current power supply coupled to the first input port 20, and the first composite control signal controls the first switching device 2221 to work in a high-frequency switching state, to superimpose a current ripple signal including the first communication signal onto the power bus; and
The second shutdown module 32 is connected in series to a high electric potential output terminal or a low electric potential output terminal of the first shutdown module 22. This application provides a description by using an example of the second shutdown module 32 connected in series to the high electric potential output terminal of the first shutdown module 22. An operating mode of the first shutdown module 22 is the same as an operating mode of the shutdown module of the shutdown device in the first embodiment. The similarities are not described again, and only the differences will be introduced herein.
As an implementation of the present invention, the control module 13 further includes a switching control unit 138, configured to generate a switching control signal that controls the switching of the second switching device 3221 according to an operating mode of the shutdown device. The working state of the second switching device 3221 includes an off state and an always-on state. The operating mode of the shutdown device includes a safe disconnection mode and a normal operating mode.
An initial operating mode after the shutdown device is powered on is the safe disconnection mode, and when receiving the permission to operate instruction, the comprehensive control unit 134 switches the operating mode of the shutdown device to the normal operating mode. When the comprehensive control unit 134 does not receive the permission to operate instruction within a first preset time period, or receives the rapid shutdown instruction, the comprehensive control unit switches the operating mode of the shutdown device to the safe disconnection mode.
As an implementation of the present invention, when the shutdown device is in the normal operating mode, if the comprehensive control unit 134 receives the data collection instruction, the comprehensive control unit 134 packages the operating data of the shutdown device into the first data packet and provides the first data packet to the protocol processing unit 135, and the protocol processing unit 135 encapsulates the first data packet into the first communication signal, and sets the data transmitting state signal to represent a busy state. The power control unit 131 adjusts the amplitude of the power control signal according to the power bus current. The modulation unit 132 modulates the first communication signal and the power control signal, to generate the first composite control signal. In this case, the first composite control signal controls the first switching device 2221 to work in the high-frequency switching state, and the switching control signal controls the second switching device 3221 to be in the always-on state. When the transmitting of the first data packet is completed, the protocol processing unit 135 sets the data transmitting state signal to represent an idle state, the power control unit 131 adjusts the power control signal to a first preset value, in this case, the first composite control signal controls the first switching device 2221 to be in an always-on state, and the switching control signal controls the second switching device 3221 to remain in the always-on state. When the shutdown device is in the safe disconnection mode, the power control unit 131 adjusts the power control signal to a second preset value, in this case, the first composite control signal controls the first switching device 2221 to be in an off state, and the switching control signal controls the second switching device 3221 to be in an off state.
When the shutdown device is in the safe disconnection mode, both the first switching device 2221 and the second switching device 3221 are in an off state, the photovoltaic module accessing the first input port 20 is disconnected from the power bus, and the photovoltaic module accessing the second input port 30 is disconnected from the power bus. The output of the photovoltaic module is in an open circuit state, the output power is close to zero, and the output voltage and power of the shutdown device are limited. When the shutdown device is in the normal operating mode, the first switching device 2221 is in the always-on state or the high-frequency switching state, the second switching device 3221 is in the always-on state, the photovoltaic module accessing the first input port 20 is connected to the power bus, and the photovoltaic module accessing the second input port 30 is connected to the power bus. The output power of the photovoltaic module accessing the first input port 20 is controlled by both the power bus current and the duty cycle of the first composite control signal. The output power of the photovoltaic module accessing the second input port 30 is controlled by the power bus current.
As an implementation of the present invention, the first switching device 2221 may be located between a high electric potential terminal of the first input port 20 and a high electric potential terminal of the output port 11, or may be located between a low electric potential terminal of the first input port 20 and a low electric potential terminal of the output port 11. The second switching device 3221 may be located between a high electric potential terminal of the second input port 30 and a high electric potential terminal of the output port 11, or may be located between a low electric potential terminal of the second input port 30 and a low electric potential terminal of the output port 11. This implementation is described by using an example in which the first switching device 2221 is located between a high electric potential terminal of the first input port 20 and a high electric potential terminal of the output port 11 and the second switching device 3221 is located between a high electric potential terminal of the second input port 30 and a high electric potential terminal of the output port 11.
The shutdown device in this embodiment includes a plurality of input ports, which is a multi-input topology, and may select a switching device corresponding to any input port to work in the high-frequency switching state, for coupling the operating data of the shutdown device to the power bus to perform data transmitting. A plurality of switching devices share one control module, which may improve the integration level and power density of the shutdown device, and significantly reduce the production cost of a product.
In an embodiment of the present invention as shown in
The main controller 72 includes a power line carrier transceiver and a current transformer, a power line carrier signal (namely, the current ripple signal) coupled to the power bus by the shutdown device 71 is extracted by the current transformer, after demodulating and parsing the power line carrier signal by the power line carrier transceiver, a first data packet transmitted by each shutdown device 71 is obtained, the first data packet includes the operating data of the shutdown device 41. A second data packet including the control instructions of the shutdown device transmitted by the main controller 72 is encapsulated and modulated by the power line carrier transceiver, then coupled to the power bus through the current transformer and transmitted to each shutdown device 71 through the power bus.
The main controller 72 performs point-to-point communication with each shutdown device 71 in a master-slave polling manner. The main controller 72 regularly transmits control instructions to collect the operating data of the shutdown device 71, and controls the operating mode of the shutdown device. The control instructions of the main controller 72 include a permission to operate instruction, used for controlling an operating state of the photovoltaic system. When the permission to operate instruction is sent normally, if each shutdown device 71 normally receives the permission to operate instruction, each shutdown device 71 is in the normal operating mode, the switching device of the shutdown device is in the always-on state or the high-frequency switching state, the photovoltaic modules are normally connected in series to the power bus, and the photovoltaic system is in the normal operating state; and when transmitting of the permission to operate instruction stops for a time period longer than a definite time period, each shutdown device 71 switches to the safe disconnection mode, and the switching device of each shutdown device 71 is in an off state. The photovoltaic module 70 at the input port of the shutdown device 71 is disconnected from the power bus, the power bus is quickly discharged to keep its voltage below a safe value within a specified time period, and the photovoltaic system is in the safe disconnection mode.
The shutdown device 71 extracts the power line carrier signal transmitted by the main controller 72 to the power bus through an internal RLC decoupling circuit, and obtains a polling instruction transmitted by the main controller through conditioning, demodulating, and parsing the power line carrier signal. If a collection address of the polling instruction matches an address of the shutdown device 71, the shutdown device 71 processes the collected operating data to generate the first composite control signal by the internal protocol processing unit, the power control unit, and the modulation unit. The switching device of the shutdown device 71 receives the first composite control signal and works in the high-frequency switching state, thereby the power line carrier signal carrying the operating data of the shutdown device 71 is injected into the power bus, and coupled to the main controller 72 through the power bus, so the main controller 72 may obtain the operating data of the shutdown device 71.
Although the preferred implementations of the present invention have been disclosed for illustrative purposes, a person of ordinary skill in the art will appreciate that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the present invention as disclosed in the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/124879 | 10/20/2021 | WO |
