Optimizer short-circuit protection circuit, photovoltaic power generation system and control method thereof

Abstract

The present invention discloses a short-circuit protection circuit of an optimizer, a photovoltaic power generation system and a control method thereof, and relates to the technical field of photovoltaic grid-connected power generation. The short-circuit protection circuit can be configured in a photovoltaic power optimizer, which includes a first switch, a second switch and an energy storage element. When any of the first switch and the second switch are turned off, the connection between the photovoltaic unit and the power acquisition system is disconnected. The separate conduction of the first switch and the second switch allows the energy storage element to be connected to the power acquisition system after taking power from the photovoltaic unit. The operating voltage of the auxiliary power supply is lower than the shutdown voltage. The switch can disconnect the connection of the photovoltaic component to the outside, and use the energy storage element to perform a short-circuit test, and keep the optimizer turned off before the short circuit is eliminated. The present invention can realize the automatic disconnection of the short circuit, and the parallel arc can be automatically shut down and eliminated at the optimizer, and can be safely self-started in the case where the optimizer is shut down due to other factors other than the short circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid-connected power generation, and in particular to a short-circuit protection circuit configured in a photovoltaic power optimizer, a photovoltaic power generation system configured with the photovoltaic power optimizer, and a control method thereof capable of solving short-circuit and arc faults. Background Art

[0002] The DC input end of the current grid-connected photovoltaic system is generally a DC system with a system voltage of 500V-1500V formed by photovoltaic cells connected in series and parallel. Therefore, arc faults will occur when insulation damage, loose metal joints, component aging, animal bites, etc. occur. DC arcs are different from AC arcs. The current does not cross the zero point, so the arc cannot be extinguished automatically. Once the arc is not handled in time, it often causes economic losses or possible personal safety losses. DC arcing is an important safety issue for photovoltaic systems and needs to be taken seriously.

[0003] DC arcs can be divided into parallel DC arcs and serial DC arcs according to the location where they are generated. Serial arc faults are mainly caused by connecting line arc faults caused by factors such as poor contact between the connectors between photovoltaic cells and the connecting terminals of the DC combiner box and inverter, and broken DC cables. Parallel arc faults are mainly caused by insulation damage and can be divided into ground arcs and line-to-line arcs. The DC circuit that generates parallel arcs can be considered to be short-circuited. The short-circuit current of photovoltaic cells is related to the irradiation temperature and is difficult to detect and determine. Even if the arc detection device installed in the inverter or DC combiner box detects the existence of an arc fault in the circuit and disconnects the photovoltaic DC circuit, it can only eliminate the serial arc, but not the parallel arc. Because even after the DC circuit loop is disconnected, the ground and line-to-line loops caused by insulation damage still exist.

[0004] In order to eliminate parallel arc faults, the prior art is to disconnect the external power supply of the photovoltaic cell by installing a photovoltaic power optimizer or a switch at the output end of the photovoltaic cell. When an arc or short circuit fault occurs, a central controller is used to continuously send a heartbeat communication signal, or a shutdown control module located on the DC bus is used to send a periodic excitation pulse source to control the power optimizer or switch to shut down the output of the photovoltaic cell, so that it stops generating electricity; when the safety fault disappears, each photovoltaic cell power photovoltaic power optimizer or switch is reopened to enable the photovoltaic cell to which it is connected to output electrical energy. In the two solutions of the prior art, not only does it need to add a corresponding sending module in the photovoltaic inverter system, but it also needs to set an additional receiving module in the photovoltaic cell switch or power photovoltaic power optimizer, which not only increases the cost of the photovoltaic system and the self-consumption of the system, but also adds new signal source sending and receiving module failure points. Summary of the invention

[0005] In order to solve the defects of the prior art, the main purpose of the present invention is to provide a short-circuit protection circuit configured in a photovoltaic power optimizer. The photovoltaic power generation system configured with the photovoltaic power optimizer can realize automatic shutdown protection during short circuit through the photovoltaic power optimizer, and automatically start after the short circuit condition is relieved; on the other hand, on the basis of realizing rapid arc fault detection and arc extinguishing of the shutdown circuit on the DC side of the photovoltaic power generation system, reduce the signal source receiving module of the shutdown circuit in the photovoltaic cell and the signal source sending module in the photovoltaic inverter system. On the whole, not only the cost of rapid shutdown of arc and short circuit protection is reduced, but also the safety and reliability of the photovoltaic power generation system are improved.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides a short-circuit protection circuit of an optimizer, the optimizer comprising a power conversion module, a control module and an auxiliary power supply, the input end of the power conversion module can be connected to the output end of a photovoltaic unit, the output end of the power conversion module can be connected to a power acquisition system, the auxiliary power supply is connected to the output end of the photovoltaic unit and connected to the control module, the control module is controlled to be connected to the power conversion module, and the optimizer is also configured with a short-circuit protection circuit;

[0008] The short circuit protection circuit comprises a first switch component, a second switch component and an energy storage element, and the control module is connected to the first switch component and the second switch component by controlling the switch signal;

[0009] The first switch and the second switch are connected to a connection loop between the photovoltaic unit and the power acquisition system. When either of the first switch and the second switch is turned off, the connection between the photovoltaic unit and the power acquisition system is disconnected. The energy storage element is connected between the first switch and the second switch. When the first switch is turned on, the photovoltaic unit and the energy storage element are connected. When the second switch is turned on, the energy storage element and the power acquisition system are connected.

[0010] At least when the operating voltage of the auxiliary power source is lower than the shutdown voltage, any one of the first switch element and the second switch element will be turned off, and the connection between the photovoltaic unit and the power acquisition system will be disconnected;

[0011] At least when the operating voltage of the auxiliary power supply is higher than the starting voltage, the control module controls the conduction of the first switch and the second switch respectively and separately, so that the energy storage element is connected to the power acquisition system after taking power from the photovoltaic unit, and obtains and determines whether the short-circuit condition is met according to the difference in electrical parameters of the energy storage element. After determining that the short-circuit condition is not met, the first switch and the second switch are turned on at the same time to try to restore the connection between the photovoltaic unit and the power acquisition system after a short-circuit test.

[0012] The above-mentioned short-circuit protection circuit may optionally include that the energy storage element is a capacitor element connected in parallel to the positive and negative circuits of the power conversion module, and the control module obtains and determines whether the short-circuit condition is met based on the voltage parameter difference of the capacitor element.

[0013] The above-mentioned short-circuit protection circuit may optionally include: the power conversion module is a Buck step-down type, Boost step-up type or Boost-Buck step-down type DC chopper circuit with an output capacitor; the output capacitor serves as an energy storage element of the short-circuit protection circuit;

[0014] During the short-circuit test, the control module collects and records the voltage parameters of the output capacitor connected to the photovoltaic unit to obtain electricity, and the voltage parameters of the output capacitor connected to the power acquisition system, so as to obtain the voltage parameter difference for determining whether the short-circuit condition is met;

[0015] Alternatively, the DC chopper circuit further has an input capacitor, and the control module acquires a voltage parameter difference for determining whether the short-circuit condition is met by respectively collecting a voltage parameter of the input capacitor and a voltage parameter of the output capacitor when the output capacitor is conducted to the power acquisition system.

[0016] The above-mentioned short-circuit protection circuit may optionally include that the power conversion module is a Buck step-down, Boost step-up or Boost-Buck step-down DC chopper circuit having a switching element, the first switch element is a switching element connected in series on the positive or negative loop in the DC chopper circuit, the second switch element is a switching element connected in series on the positive or negative loop between the output end of the DC chopper circuit and the output end of the optimizer, and at least one of the first switch element and the second switch element is a normally open switch element.

[0017] The above-mentioned short-circuit protection circuit can optionally include that the power conversion module is a Buck step-down DC chopper circuit, which includes an input capacitor, a switching element as the first switching device, an inductor, a freewheeling diode, and an output capacitor as the energy storage element; the first switching device, the inductor, and the second switching device are sequentially connected in series to the positive path of the DC chopper circuit, the positive and negative poles of the freewheeling diode are connected in parallel between the first switching device and the inductor, the positive and negative poles of the input capacitor are connected in parallel between the input end of the power conversion module and the first switching device, and the positive and negative poles of the output capacitor are connected in parallel between the inductor and the second switching device; a bypass diode is connected in parallel between the positive and negative poles of the second switching device and the output end of the power conversion module.

[0018] The above-mentioned short-circuit protection circuit may optionally include that the control module includes a control unit, a collection unit, a calculation unit, a judgment unit, a counting unit, a driving unit and a communication unit for controlling the operation of the short-circuit protection circuit;

[0019] The control unit is used to control the second switch to remain off, and then control the first switch to be turned on, so that the energy storage element obtains power from the photovoltaic unit, and control the first switch to be turned off, and then control the second switch to be turned on, so that the energy storage element is connected to the power acquisition system;

[0020] The acquisition unit is used to collect electrical parameter information of the energy storage element when it acquires power and is connected to the power acquisition system;

[0021] The computing unit is used to obtain the difference in electrical parameter information in the power state and in the system access state;

[0022] The judgment unit is used to judge the electrical parameter information parameter and drive the control unit to perform corresponding operations;

[0023] The control unit controls the first switch element and the second switch element to be turned on simultaneously by the switch quantity when it is determined that there is no short circuit; controls the first switch element and the second switch element to be turned off by the switch quantity when it is determined that there is a definite short circuit; and performs short circuit detection again by the control unit after a delay setting time when it is determined that there is an uncertain short circuit;

[0024] The counting unit counts the number of times the control unit is executed due to an uncertain short circuit, and determines that a short circuit is determined when the number exceeds a preset number;

[0025] The driving unit controls the turning off and on of the first switch and the second switch with driving power according to the switch quantity control command;

[0026] The control module further includes a communication unit, which alarms the power acquisition system after determining that a short circuit is confirmed.

[0027] The above short-circuit protection circuit may optionally include: the control module is further used to control the power conversion module to perform power conversion;

[0028] The acquisition unit is used to collect voltage and current parameters at the output end of the photovoltaic unit;

[0029] The computing unit is used to calculate the power parameter from the voltage and current parameters;

[0030] The judging unit is used to judge the change characteristics of the power parameter and drive the control unit to perform corresponding operations;

[0031] The control unit is used to output a pulse modulation signal according to the change of the power parameter;

[0032] The driving unit is used to control the operation of the switch element of the power conversion module with a pulse-modulated driving signal to set the electrical parameter of the output end of the photovoltaic unit at the maximum power point.

[0033] The present invention accordingly provides a control method for the above short-circuit protection circuit, the method comprising:

[0034] At least in the case of a short circuit, the short circuit protection circuit disconnects the first switch element and / or the second switch element because the operating voltage of the auxiliary power supply is lower than the shutdown voltage;

[0035] At least after the short circuit is disconnected, the auxiliary power supply operating voltage reaches the starting voltage again, and the control module performs the short circuit test steps:

[0036] Controlling the second switch element to remain off, and then controlling the first switch element to be turned on, so that the energy storage element obtains power from the photovoltaic unit;

[0037] Acquiring electrical parameter information of the energy storage element in the power acquisition state;

[0038] Controlling the first switch to be turned off, and then controlling the second switch to be turned on, so that the energy storage element is connected to the power acquisition system;

[0039] Obtaining electrical parameter information of energy storage elements when connected to the system;

[0040] Compare the differences in obtaining electrical parameter information of the energy storage element in the power state and in the system access state;

[0041] Determine the difference in electrical parameter information:

[0042] If the difference in the electrical parameter information is within the first preset difference limit, it is determined that there is no short circuit condition in the connected system, and the first switch element and the second switch element are turned on at the same time to restore the operation of the optimizer;

[0043] If the difference in the electrical parameter information is between the first preset difference limit and the second preset difference limit, the connected system is in an uncertain short circuit state, and the short circuit test step is performed again after a delay setting time;

[0044] If the difference in the electrical parameter information is outside the second preset difference limit, it is determined that a short circuit condition exists in the connected system, and the first switch element and / or the second switch element are controlled to be closed.

[0045] The above-mentioned short-circuit protection circuit control method may optionally further include:

[0046] A first count is performed on the condition where the difference in electrical parameter information is between a first preset difference limit and a second preset difference. If the first count satisfies that the continuous uncertain short-circuit condition reaches a preset number of times, it is determined that a short-circuit condition exists in the connected system, and the first switch element and / or the second switch element is controlled to be closed.

[0047] Establishing a communication connection between the optimizer and the power acquisition system, and after determining that the connected system has a short circuit condition, alarming and / or reporting a repair to the power acquisition system;

[0048] When attempting to restore the connection between the photovoltaic unit and the power acquisition system after the short-circuit test, the control module collects and records the voltage parameters of the output capacitor connected to the photovoltaic unit to obtain electricity, and the voltage parameters of the output capacitor connected to the power acquisition system, so as to obtain the voltage parameter difference for determining whether the short-circuit condition is met;

[0049] Alternatively, the DC chopper circuit further has an input capacitor, and the control module acquires a voltage parameter difference for determining whether the short-circuit condition is met by respectively collecting a voltage parameter of the input capacitor and a voltage parameter of the output capacitor when the output capacitor is conducted to the power acquisition system.

[0050] On the other hand, the present invention also provides a photovoltaic power generation system, including a plurality of photovoltaic units, the output end of the photovoltaic unit is connected to the input end of an optimizer, the output ends of the plurality of optimizers are connected in series to form a photovoltaic series body, the output end of the photovoltaic series body is connected to the DC input side of the inverter or the input end of the DC combiner box, the optimizer is configured with the above-mentioned short-circuit protection circuit, and also includes an arc fault detection device, the arc fault detection device is configured on the output side of the photovoltaic series body, and when an arc is detected, the connection of the photovoltaic series body to the inverter or the DC combiner box is cut off.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The present invention uses a short-circuit protection circuit. When a short circuit occurs at the output end of the optimizer, the auxiliary power supply will stop supplying power due to low voltage, and the switch will automatically disconnect the connection between the photovoltaic cell and the power acquisition system, thereby realizing shutdown protection during a short circuit. At the same time, during the startup process of the optimizer, the principle that the energy storage element will produce an electrical parameter change when a short circuit occurs is used to detect whether there is a short circuit before restarting the optimizer. At least two switch elements are provided on the connection loop between the photovoltaic cell and the power acquisition circuit. When the switch elements are turned on alone, the energy storage element can be powered from the photovoltaic cell and connected to the power acquisition system, respectively. The electrical parameter change of the energy storage element is detected to determine whether there is a short circuit. During the detection process, the photovoltaic cell and the power acquisition circuit remain disconnected, ensuring that the photovoltaic cell does not output power to the outside before the short circuit condition is resolved. When a short circuit or parallel fault occurs, the optimizer responds quickly, isolates the photovoltaic cell from the power acquisition system, and uses only a small amount of power from the energy storage element for testing. The measurement process is safe and reliable, and does not cause a burden on the system. When a safety fault occurs, the output of the photovoltaic cell can be quickly shut down. After the safety fault is eliminated, each photovoltaic cell can resume power generation.

[0053] (2) The present invention configures the short-circuit protection circuit in the photovoltaic power optimizer. On the one hand, the photovoltaic power optimizer can make the photovoltaic cell operate at the maximum power point to improve the efficiency of power generation; on the other hand, the short-circuit protection circuit can use the control module of the optimizer to collect, calculate, judge and control when shutting down and starting up, and can also use the switch and energy storage element in the power conversion module of the optimizer. Compared with the optimizer of the Buck topology structure, it is equivalent to adding a second switch at the output end of the power conversion module, making the short-circuit protection circuit simple in structure and easy to implement, which greatly improves the safety and reliability of power generation on the basis of low cost. Compared with traditional shut-off devices and optimizers, it also reduces the dedicated receiving modules and sending modules, reducing the manufacturing cost of the power generation system.

[0054] (3) The photovoltaic power generation system of the present invention can extinguish the fault arc in the first place in the initial stage of arc generation in view of the difference between parallel arc and serial arc, thereby avoiding more serious damage. When a parallel DC arc occurs, the short-circuit protection circuit configured in the power optimizer of each photovoltaic cell automatically extinguishes the arc, and the optimizer is disconnected from the external system before the short-circuit fault is resolved, so as to quickly eliminate the parallel arc without relying on the arc fault detection device, and there is no need to configure a device for receiving carrier signals in each power optimizer, thus saving costs; when a serial DC arc occurs, the serial arc is eliminated in the first place by disconnecting the DC circuit of the DC combiner box or inverter.

[0055] The present invention will be further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of a short-circuit protection circuit configured in an optimizer according to an embodiment of the present invention;

[0057] Figure 2 It is a schematic structural diagram of an optimizer circuit with a short-circuit protection circuit according to an embodiment of the present invention;

[0058] Figure 3 A schematic diagram of a short-circuit protection control structure of a control module according to an embodiment of the present invention;

[0059] Figure 4 A schematic diagram of a power conversion control structure of a control module according to an embodiment of the present invention;

[0060] Figure 5 A schematic flow chart of a control method for a short-circuit protection circuit according to an embodiment of the present invention;

[0061] Figure 6 is a schematic structural diagram of a photovoltaic power generation system according to an embodiment of the present invention;

[0062] Figure 7It is a schematic diagram of an arc fault occurring in a local structure of a photovoltaic power generation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0064] like Figure 1 As shown, it is a short-circuit protection circuit configured in a photovoltaic power optimizer according to an embodiment of the present invention. The optimizer E is composed of a power conversion module E1, a control module E2 and an auxiliary power supply E3. The input end of the power conversion module E1 is connected to the output of the photovoltaic unit through an interface, and the output ends of many power conversion modules E1 are connected in series through the interface to the power acquisition system. The photovoltaic unit described in this embodiment is a photovoltaic module A. In other implementations, it can also be a photovoltaic string B containing multiple photovoltaic modules A, or a series body of some photovoltaic cells in a photovoltaic module A. The power conversion module E1 is used to transform the electrical parameter of the input end of the photovoltaic module A, and output another electrical parameter at the output end of the power conversion module E1. The control module E2 is connected to the power conversion module E1 and can control the electrical parameter conversion process of the power conversion module E1. The auxiliary power supply E3 is electrically connected to the photovoltaic module A, and is connected to the control module E2 for power supply to power the operation of the control module E2.

[0065] Specifically, in this embodiment, reference Figure 1, the short-circuit protection circuit E4 includes a first switch S1, a second switch S2 and an energy storage element C. The first switch S1 and the second switch S2 are connected in series to the positive circuit of the optimizer E, and the first switch S1 or the second switch S2 can disconnect the circuit. In this embodiment, the energy storage element C is a capacitor element connected in parallel to the positive and negative circuits between the first switch S1 and the second switch S2. When the first switch S1 is turned on alone, the capacitor element is connected to the photovoltaic component A; when the second switch S2 is turned on alone, the capacitor element is connected to the photovoltaic string B. The auxiliary power supply E3 is connected in parallel to the positive and negative circuits at the output end of the photovoltaic component A, and the first switch S1 and the second switch S2 are normally open switches. When a short circuit or other conditions occur and the positive and negative circuit voltages are lower than the operating voltage of the auxiliary power supply E3, the control module E2 stops running, and the first switch S1 and the second switch S2 become disconnected, and then the connection circuit between the photovoltaic component A and the power acquisition system is disconnected. After the first switch S1 and the second switch S2 are turned off, the auxiliary power source E3 will be isolated from the external circuit, and the short-circuit condition of the auxiliary power source E3 will be eliminated, and the power from the photovoltaic module A will be restored. The control module E2 controls the conduction of the first switch S1 and the second switch S2 separately, so that the capacitor element is connected to the power acquisition system after drawing power from the photovoltaic module A, and obtains and determines whether the short-circuit condition is met according to the difference in voltage parameters at both ends of the capacitor element, and only when it is determined that the short-circuit condition is not met, the first switch S1 and the second switch S2 are simultaneously turned on to restore the connection between the photovoltaic unit and the power acquisition system.

[0066] It can be understood that the short-circuit protection circuit E4 of the present invention, on the one hand, utilizes the first switch component S1 and the second switch component S2 to automatically shut down and perform short-circuit protection when a short circuit occurs in the power acquisition system; on the other hand, it utilizes the on-off control of the first switch component S1 and the second switch component S2, and uses the energy storage element C to test whether the external circuit is short-circuited. Compared with the existing, this embodiment utilizes the control module E2 of the optimizer E to achieve automatic shutdown and automatic safety start-up of the photovoltaic component A when short-circuited, simplifies the safety protection structure of the photovoltaic power generation system, and also simplifies the difficulty of setting up distributed system communications. In other embodiments, the energy storage element C can also be an inductor, and whether the external circuit is short-circuited is determined by measuring the current or energy storage status of the inductor.

[0067] like Figure 2As shown, a short-circuit protection circuit E4 according to an embodiment of the present invention is configured in a BUCK step-down photovoltaic power optimizer E. The power conversion module E1 of the optimizer E is a Buck type DC chopper circuit structure with an output capacitor C2. It can be understood that the power conversion module E1 can also be a Boost type or Boost-Buck type DC chopper circuit. The power conversion module E1 includes an input capacitor C1, a first switch tube M1, an inductor L, a freewheeling diode D1, an output capacitor C2, a second switch tube M2 and a bypass diode D2. The first switch tube M1, the inductor L and the second switch tube M2 are sequentially connected in series on the positive path PV+ of the DC chopper circuit. More specifically, the first switch tube M1 and the second switch tube M2 are n-type normally open switch field effect tubes. In other embodiments, the first switch tube M1 and the second switch tube M2 can also be other fully controlled switch tubes. The source of the first switch tube M1 and the second switch tube M2 are connected to the output side of PV+, the drain of the first switch tube M1 and the second switch tube M2 are connected to the input side of PV+, and the gates of the first switch tube M1 and the second switch tube M2 are respectively connected to the control module E2. The auxiliary capacitor element and the input capacitor C1 are respectively connected in parallel to the positive path PV+ and the negative path PV- of the DC chopper circuit, and are located between the input end of the DC chopper circuit and the second switch tube M2. The anode of the freewheeling diode D1 is connected to the negative loop PV-, and the cathode of the freewheeling diode D1 is connected to the positive loop PV+, and is located between the first switch tube M1 and the inductor. The output capacitor C2 is connected in parallel to PV+ and PV- of the DC chopper circuit, and is located between the inductor L and the second switch tube M2. The bypass diode D2 is connected in parallel to PV+ and PV- of the DC chopper circuit, and is located between the second switch tube M2 and the output end of the DC chopper circuit. The input capacitor C1 and the output capacitor C2 are used for filtering of the chopper circuit, the first switch tube M1 controls the chopper conversion of the photovoltaic component A to the inductor L, and the freewheeling diode D1 is used to maintain the output level.

[0068] It should be noted that the first switch tube M1 constitutes an element of a Buck type DC chopper circuit, which can be used to control the power conversion of the DC chopper circuit with a pulse modulation signal (pulse width modulation PWM or pulse frequency modulation PFM), and at the same time serves as the first switch element S1 of the short-circuit protection circuit E4; the output capacitor C2 serves as the energy storage element C of the short-circuit protection circuit E4; the second switch tube M2 is added on the output side of the DC chopper circuit, serving as the second switch element S2 of the short-circuit protection circuit E4. Among them, the short-circuit protection circuit E4 and the DC chopper circuit have common components, realizing the simplified circuit of the photovoltaic power optimizer E. Among them, the bypass diode D2 serves as the current of the photovoltaic string B when the optimizer E is turned off, and the bypass diode D2 can be turned on.

[0069] It should be noted that there are differences in the electrical parameters of the energy storage element C under the two control states of the switch. On the one hand, under the two control states, the voltage parameters of the output capacitor C2 when connected to the photovoltaic component A are collected and recorded respectively, and compared with the voltage parameters of the output capacitor C2 when connected to the photovoltaic string B, so as to obtain the voltage difference of the output capacitor C2 during the short-circuit test process. On the other hand, a filtered input capacitor C1 is provided at the input end of the DC chopper circuit to prevent the fluctuating current of the power conversion from reversely affecting the photovoltaic component A. When the output capacitor C2 is connected to the photovoltaic string B, the voltage parameters of the input capacitor C1 and the output capacitor C2 are collected and compared to obtain the voltage difference of the output capacitor C2 during the short-circuit test process. In the latter solution, the output storage process can be reduced, while reducing the errors of the previous and subsequent measurements.

[0070] like Figure 3 and 4 As shown, it is a structural diagram of the control module E2 according to an embodiment of the present invention. The control module E2 includes a control unit 21, a collection unit 22, a calculation unit 23, a judgment unit 24, a counting unit 25, a driving unit 26 and a communication unit 27. Among them, the collection unit 22 can collect the current parameter Ipv and the voltage parameter Vpv at the input end of the power conversion module, and the output capacitor C2, that is, the voltage parameter Vout at the output end of the power conversion module. The collection is realized by a sensor set at the collection position, amplified by an amplifier and processed by a processor into an operational electrical signal. The calculation unit 23 can be set in the processor to calculate the collected electrical parameters. The judgment unit 24 can be set in the processor to judge the short circuit condition or the current power condition according to the result of the calculation. The control unit 21 can be set in the processor, including under the triggering operation condition, such as the initial start after power is obtained, to perform corresponding short circuit detection control; it also includes performing corresponding control operations according to the judged structure. The counting unit 25 can be set in the processor to measure a certain result of the judgment unit 24, or to measure a certain operation of the control unit 21, and output the result when the set counting limit is reached, or reset under the set conditions. The communication unit 27 can be Zibee or WIFI or Bluetooth wireless communication, and the centralized control module HE2 is configured in the inverter system J or the DC combiner box. The centralized control module HE2 is configured with a communication device matching the optimizer E. When a short circuit fault occurs, the control module E2 can alarm the centralized control module HE2 through the communication unit 27.

[0071] Specific reference Figure 3In the control process of restarting the optimizer E after the short-circuit test, specifically, the control unit 21 is used to control the second switch tube M2 to remain turned off, and then control the first switch tube M1 to be turned on, so that the output capacitor C2 obtains power from the photovoltaic unit, and controls the first switch tube M1 to be turned off, and then controls the second switch tube M2 to be turned on, so that the output capacitor C2 is connected to the power acquisition system; the collection unit 22 is used to collect the voltage parameter information of the output capacitor C2 when obtaining power and connecting to the power acquisition system; the calculation unit 23 is used to obtain the difference in voltage parameter information in the power state and in the system connection state; the judgment unit 24 is used to judge the voltage parameter information parameters, and drive the control unit 21 to execute the corresponding operation; when it is determined that there is no short circuit, the control unit 21 controls the first switch tube M1 and the second switch tube M2 to be turned on at the same time by the switch quantity; when it is determined that there is a definite short circuit, the first switch tube M1 and the second switch tube M2 are turned off by the switch quantity; when it is determined that there is an uncertain short circuit, the control unit 21 performs short circuit detection again after a delay setting time; the counting unit 25 counts the number of executions of the control unit 21 executed due to an uncertain short circuit, and when the number exceeds the preset number, it is determined to be a definite short circuit; the driving unit 26 controls the turning off and on of the first switch tube M1 and the second switch by the driving power according to the switch quantity control command; the communication unit 27 alarms the centralized control module HE2 after determining that there is a definite short circuit.

[0072] Specific reference Figure 4 In the control process of power conversion when the optimizer E is operating normally, specifically, the acquisition unit 22 is used to collect the voltage and current parameters of the output end of the photovoltaic unit; the operation unit 23 is used to calculate the power parameter from the voltage and current parameters; the judgment unit 24 is used to judge the change characteristics of the power parameter and drive the control unit 21 to perform corresponding operations; the control unit 21 is used to output a pulse modulation signal according to the change of the power parameter; the driving unit 26 is used to control the operation of the switch element of the power conversion module E1 with the pulse modulated driving signal to set the electrical parameter of the output end of the photovoltaic unit at the maximum power point.

[0073] like Figure 5 As shown, it is a flow chart of a control method of a short-circuit protection circuit configured in a photovoltaic power optimizer according to an embodiment of the present invention. The method comprises: obtaining power for the first time after the auxiliary power source E3 is turned off, and making the control module E2 run, executing the startup optimizer E after the short-circuit condition test. Specifically, when the photovoltaic power optimizer E is turned on after a power outage or restarted the next day after being shut down at night, before the optimizer E enters the working state, a circuit anti-short circuit detection is performed to avoid the risk of short circuit.

[0074] The first step is to control the second switch tube M2 to remain off, and then control the first switch tube M1 to be turned on, so that the input capacitor C1 and the output capacitor C1 obtain power from the photovoltaic component A, and detect and determine that the voltage values ​​of the two are close to the same. The second step is to control the first switch tube M1 to be turned off, and then control the second switch tube M2 to be turned on, so that the output capacitor C2 is connected to the photovoltaic string B, and the input capacitor C1 is blocked from the photovoltaic string B. The voltage value V1 of the input capacitor C1 at this time is collected, and the voltage value V2 of the output capacitor C2 at this time is collected; by comparing |V1-V2| / V2, the voltage information difference of the output capacitor C2 after being connected to the photovoltaic string B is obtained. The fourth step is to determine the relationship between |V1-V2| / V2 and the first preset difference limit of 10%, and the second preset difference limit of 50%:

[0075] If |V1-V2| / V2≤10%, it is determined that there is no short circuit in the connected system, and the first switch tube M1 and the second switch tube M2 are turned on at the same time, and the optimizer E is restored to operate; if 10%<|V1-V2| / V2<50%, the connected system is in an uncertain short circuit state, and after a delay of 3 minutes, the optimizer E is started again after the short circuit state test. The first count is performed on this state, and if the uncertain short circuit state reaches 3 times in the continuous short circuit test process, it is determined that there is a short circuit in the connected system, and the first switch tube M1 and the second switch are kept closed, and the power optimizer E is stopped from operating; if |V1-V2| / V2≥50%, it is determined that there is a short circuit in the connected system, and the first switch tube M1 and the second switch are kept closed, and the power optimizer E is stopped from operating. After determining that there is a short circuit in the connected system, an alarm and / or repair report is issued to the centralized control module HE2.

[0076] It should be noted that during the short-circuit detection process, there is an uncertain short-circuit range, and the short-circuit detection can be tried again. For example, the output voltage of the optimizer E is determined by the input capacitor C1 of the inverter. Before the input capacitor C1 has completed energy storage, there is a possibility of voltage change. In summary, the determination of the uncertain short-circuit range can reduce the shutdown of the optimizer E caused by short-circuit detection errors. At the same time, the determination of the uncertain short-circuit range can also reduce the impact and damage caused by the input capacitor C1 being connected to the photovoltaic power generation system during a short circuit.

[0077] like Figure 6As shown, it is a photovoltaic power generation system according to an embodiment of the present invention, which is composed of a photovoltaic module A, a power optimizer E, and a photovoltaic inverter system J. The output end of each photovoltaic module A is connected to a power optimizer E. There are multiple photovoltaic modules A, and A-1, A-2, ..., An in the figure; the number of power optimizers E corresponds to that, and E-1, E-2, ..., En in the figure. The output ends of the power optimizers E are connected in series to form a photovoltaic string B, that is, B-1, B-2, ..., Bm in the figure. The output end of the photovoltaic string B can be connected to the DC side of the inverter system J, or after being connected to the input end of the DC combiner box, the output end of the DC combiner box is connected to the output side of the inverter system J. In this embodiment, the photovoltaic string B is connected to the inverter system J. Each optimizer E is configured with the above-mentioned short-circuit protection circuit E4, and the inverter system J is configured with an arc fault detection device F and a centralized control module HE2. The arc fault detection device F is an arc fault detector (AFCI) and / or a residual current detection device (RCD), which is a common device for detecting arc faults in the prior art. It detects the characteristics of the electrical parameters of the connected circuit in the time domain and / or frequency domain, and determines whether a fault arc is generated. When the arc fault detection device F detects an arc, the inverter circuit can be controlled to shut down through the centralized control module HE2. The centralized control module HE2 can establish a wireless communication connection with each optimizer E to obtain the alarm information of each optimizer E, or send a startup instruction to the control module E2 of each optimizer E after maintenance, and actively control the startup of the optimizer E.

[0078] It is understandable that in the process of quickly eliminating arc faults in the photovoltaic power generation system, when the arc fault detection device F detects a serial arc, the inverter or DC combiner box will disconnect the output circuit of the photovoltaic string B to eliminate the serial arc. This solution can send a warning message to the photovoltaic inverter system J or the DC combiner box connected to the photovoltaic string B as soon as the arc occurs, thereby driving the photovoltaic inverter system J or the DC return box to disconnect the circuit that generates the serial arc, thereby extinguishing the arc as soon as possible to avoid more serious consequences.

[0079] When a parallel arc occurs, the optimizer E at the location where the parallel arc occurs will be shut down when the auxiliary power source E3 is lower than the operating voltage, and the optimizer E will be disconnected from the photovoltaic string B before determining that the short-circuit state is released to eliminate the parallel arc. This solution can detect the short-circuit condition, that is, the occurrence of the parallel arc, by the optimizer E equipped with the above-mentioned short-circuit protection circuit E4 and the control method using the above-mentioned short-circuit protection circuit E4 at the first time when the parallel arc occurs, and keep the first switch tube M1 and the second switch tube M2 turned off after the auxiliary power source E3 stops operating due to too low voltage, so as to extinguish the parallel arc at the first time, and will not start the optimizer E before the short-circuit condition is eliminated in the test. On the other hand, for the optimizer E that is restarted after being shut down due to other reasons, the optimizer E equipped with the above-mentioned short-circuit protection circuit E4 and the control method using the above-mentioned short-circuit protection circuit E4 can automatically start running after completing the short-circuit test without the need for a complex communication structure.

[0080] like Figure 7As shown, it is a part of the photovoltaic power generation system according to an embodiment of the present invention. In the figure, arc faults occur at positions a to f. Among them, position a is a serial arc generated between the connection line or joint of the photovoltaic string B and the DC bus; position b is a serial arc generated at the disconnection of the connection line between the photovoltaic component A and the photovoltaic component A; position c is a serial arc generated at the connection of the DC bus, or at the disconnection of the connection joint of the single-line DC bus and the inverter system J. The arcs at positions a to c are serial arc faults. During the operation of the photovoltaic power generation system of the present invention, they will be detected by the arc fault detection device F, and the inverter will shut down its AC side switch to achieve the disconnection of the power acquisition system loop, and complete the first-time serial arc extinguishing. Among them, position d is a parallel arc caused by the damage between the two DC busbars, position e is a parallel arc generated at the connection between the positive and negative DC busbars and the inverter system J, and position f is a parallel arc generated by a DC busbar and the ground terminal. The arc at position d to f is a parallel arc fault. Even if it is detected by the arc fault detection device F and the power supply circuit of the entire photovoltaic power generation system is shut down, the local parallel arc can still be connected into a loop and obtain power from the photovoltaic assembly A in the loop, and the parallel arc still exists. In the operation process of the photovoltaic power generation system of the present invention, the parallel arc will cause the auxiliary power supply E3 in each optimizer E to short-circuit, and under the condition that the voltage is equal to or close to zero, the auxiliary power supply E3 is turned off, and the normally open first switch tube M1 and the second switch tube M2 are disconnected when the driving power is lost; at the same time, even if the auxiliary power supply E3 reaches the starting voltage again after disconnection, after the control module E2 is started, the switch tube will be kept disconnected for the first time, and the short-circuit test will be performed under the condition that the photovoltaic assembly A is disconnected from the external circuit throughout the process. After the optimizer E is disconnected, the photovoltaic assembly A and the DC circuit at the parallel arc position will be disconnected, so as to eliminate the parallel arc in the first time. In addition, before the short-circuit condition is resolved, the optimizer E will remain shut down until the maintenance personnel actively start the optimizer E after maintenance.

[0081] At the same time, under the influence of other factors, the control module E2 is restarted, such as the optimizer E is shut down due to darkness and then restarted the next morning, or the optimizer E is shut down and then restarted due to other factors such as overcurrent. Each photovoltaic component A will successfully pass the short-circuit test and automatically restart.

[0082] The above embodiments mainly describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A control method for controlling the operation of a short-circuit protection circuit of an optimizer, wherein the optimizer (E) comprises a power conversion module (E1), a control module (E2) and an auxiliary power supply (E3), wherein the input end of the power conversion module (E1) can be connected to the output end of a photovoltaic unit, the output end of the power conversion module (E1) can be connected to a power acquisition system, the auxiliary power supply (E3) is electrically connected to the output end of the photovoltaic unit and is connected to the control module (E2) for power supply, and the control module (E2) is control-connected to the power conversion module (E1), wherein: The optimizer (E) is also provided with a short circuit protection circuit (E4); The short-circuit protection circuit (E4) comprises a first switch component (S1), a second switch component (S2) and an energy storage element (C), and the control module (E2) is connected to the first switch component (S1) and the second switch component (S2) by controlling the switch signal; The first switch (S1) and the second switch (S2) are connected to a connection loop between a photovoltaic unit and a power acquisition system. When either the first switch (S1) or the second switch (S2) is turned off, the connection between the photovoltaic unit and the power acquisition system is disconnected. The energy storage element (C) is connected between the first switch (S1) and the second switch (S2). When the first switch (S1) is turned on, the photovoltaic unit and the energy storage element (C) are connected. When the second switch (S2) is turned on, the energy storage element (C) and the power acquisition system are connected. The method comprises: At least in the case of a short circuit, the short circuit protection circuit (E4) disconnects the first switch element (S1) and / or the second switch element (S2) because the operating voltage of the auxiliary power supply (E3) is lower than the shutdown voltage; At least after the short circuit is disconnected, the operating voltage of the auxiliary power supply (E3) reaches the starting voltage again, and the control module (E2) performs the short circuit test steps: Controlling the second switch (S2) to remain off, and then controlling the first switch (S1) to be on, so that the energy storage element (C) obtains power from the photovoltaic unit; Acquiring electrical parameter information of the energy storage element (C) in a power acquisition state; Controlling the first switch (S1) to be turned off, and then controlling the second switch (S2) to be turned on, so that the energy storage element (C) is connected to the power acquisition system; Acquiring electrical parameter information of the energy storage element (C) when it is connected to the system; Compare the differences in obtaining electrical parameter information of the energy storage element (C) in the power state and in the system access state; Determine the difference in electrical parameter information: If the difference in the electrical parameter information is within a first preset difference limit, it is determined that there is no short circuit condition in the connected system, and the first switch (S1) and the second switch (S2) are turned on at the same time, and the optimizer (E) is restored to operate; If the difference in the electrical parameter information is between the first preset difference limit and the second preset difference limit, the connected system is in an uncertain short circuit state, and the short circuit test step is performed again after a delay setting time; If the difference in the electrical parameter information is outside the second preset difference limit, it is determined that a short circuit condition exists in the connected system, and the first switch element (S1) and / or the second switch element (S2) are controlled to be closed.

2. The control method according to claim 1, characterized in that: The method further comprises the steps of: A first count is performed on the condition that the difference of the electrical parameter information is between a first preset difference limit and a second preset difference, and if the first count satisfies that the continuous short-circuit uncertainty condition reaches a preset number of times, it is determined that the connected system has a short-circuit condition, and the first switch element (S1) and / or the second switch element (S2) are controlled to be closed; Establishing a communication connection between the optimizer (E) and the power acquisition system, and after determining that the connected system has a short circuit condition, alarming and / or reporting a repair to the power acquisition system; When attempting to restore the connection between the photovoltaic unit and the power acquisition system after the short-circuit test, the control module (E2) collects and records the voltage parameters of the output capacitor (C2) conducting to the photovoltaic unit to obtain electricity, and the voltage parameters of the output capacitor (C2) conducting to the power acquisition system, so as to obtain the voltage parameter difference used to determine whether the short-circuit condition is met; Alternatively, the DC chopper circuit further has an input capacitor (C1), and the control module (E2) acquires a voltage parameter difference for determining whether a short-circuit condition is met by respectively collecting a voltage parameter of the input capacitor (C1) and a voltage parameter of the output capacitor (C2) when the output capacitor (C2) is conducted to the power acquisition system.

3. The control method according to claim 1, characterized in that: The energy storage element (C) is a capacitor element connected in parallel to the positive and negative circuits of the power conversion module (E1), and the control module (E2) obtains and determines whether a short-circuit condition is met based on a voltage parameter difference of the capacitor element.

4. The control method according to claim 3, characterized in that: The power conversion module (E1) is a Buck step-down type, Boost step-up type or Boost-Buck step-down type DC chopper circuit having an output capacitor (C2); the output capacitor (C2) serves as an energy storage element (C) of a short-circuit protection circuit (E4).

5. The control method according to claim 1, characterized in that: The power conversion module (E1) is a Buck step-down type, Boost step-up type or Boost-Buck step-down type DC chopper circuit having a switch element, the first switch element (S1) is a switch element connected in series on a positive or negative loop in the DC chopper circuit, the second switch element (S2) is a switch element connected in series on a positive or negative loop between an output end of the DC chopper circuit and an output end of an optimizer (E), and at least one of the first switch element (S1) and the second switch element (S2) is a normally open switch element.

6. The control method according to claim 1, characterized in that: The power conversion module (E1) is a Buck step-down DC chopper circuit, comprising an input capacitor (C1), a switch element as the first switch element (S1), an inductor (L), and an output capacitor (C2) as the energy storage element (C); the first switch element (S1), the inductor (L), and the second switch element (S2) are sequentially connected in series to the positive path of the DC chopper circuit, the positive and negative electrodes of the input capacitor (C1) are connected in parallel between the input end of the power conversion module (E1) and the first switch element (S1), and the positive and negative electrodes of the output capacitor (C2) are connected in parallel between the inductor (L) and the second switch element (S2).

7. The control method according to claim 1, characterized in that: The control module (E2) comprises a control unit (21), a collection unit (22), a calculation unit (23), a judgment unit (24), a counting unit (25) and a driving unit (26) for controlling the operation of the short-circuit protection circuit (E4); The control unit (21) is used to control the second switch (S2) to remain off, and then control the first switch (S1) to be turned on, so that the energy storage element (C) obtains power from the photovoltaic unit, and to control the first switch (S1) to be turned off, and then control the second switch (S2) to be turned on, so that the energy storage element (C) is connected to the power acquisition system; The acquisition unit (22) is used to collect electrical parameter information of the energy storage element (C) when acquiring power and connecting to the power acquisition system; The computing unit (23) is used to obtain the difference in electrical parameter information in a power state and in a system access state; The judgment unit (24) is used to judge the electrical parameter information parameter and drive the control unit (21) to perform corresponding operations; The control unit (21) controls the first switch element (S1) and the second switch element (S2) to be turned on simultaneously by the switch quantity when it is determined that there is no short circuit; controls the first switch element (S1) and the second switch element (S2) to be turned off by the switch quantity when it is determined that there is a definite short circuit; and performs short circuit detection again by the control unit (21) after a set delay time when it is determined that there is an indeterminate short circuit; The counting unit (25) counts the number of times the control unit (21) is executed due to an uncertain short circuit, and when the number exceeds a preset number, it is determined to be a confirmed short circuit; The driving unit (26) controls the turning off and on of the first switch element (S1) and the second switch with driving power according to the switching quantity control command.

8. The control method according to claim 7, characterized in that: The control module (E2) further comprises a communication unit (27), and the communication unit (27) alarms the power acquisition system after determining that a short circuit has occurred; The control module (E2) is also used to control the power conversion module (E1) to perform power conversion; The collection unit (22) is used to collect voltage and current parameters at the output end of the photovoltaic unit; The computing unit (23) is used to calculate the power parameter from the voltage and current parameters; The judging unit (24) is used to judge the change characteristics of the power parameter and drive the control unit (21) to perform corresponding operations; The control unit (21) is used to output a pulse modulation signal according to a change in a power parameter; The driving unit (26) is used to control the operation of the switch element of the power conversion module (E1) with a pulse-modulated driving signal to set the electrical parameter at the output end of the photovoltaic unit at the maximum power point.

9. A photovoltaic power generation system using the control method according to any one of claims 1 to 8, comprising a plurality of photovoltaic units, the output end of the photovoltaic unit is connected to the input end of an optimizer (E), the output ends of the plurality of optimizers (E) are connected in series to form a photovoltaic series body, the output end of the photovoltaic series body is connected to the DC input side of the inverter or the input end of the DC combiner box, wherein: It also includes an arc fault detection device (F), which is configured at the output side of the photovoltaic series body and cuts off the connection between the photovoltaic series body and the inverter or DC combiner box when an arc is detected.

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