A fast shutdown system and control method thereof

Abstract

The present invention discloses a fast shutdown system and a control method thereof, and relates to the technical field of photovoltaic grid-connected power generation. The present invention mainly includes a short-circuit shutdown circuit configured on the output side of a photovoltaic module and a DC bypass circuit configured on the output side of a photovoltaic string. The short-circuit shutdown circuit mainly includes a first switch, a second switch, an energy storage element, a first control module, and a first auxiliary power supply. The connection between the photovoltaic module and the photovoltaic string is automatically shut down in the event of a short circuit, and short-circuit detection is required to reconnect after shutdown. The short-circuit shutdown circuit of each component is short-circuited or reduced in voltage through a DC bypass circuit including a third switch and a resistance element to achieve fast shutdown, which can meet the safety requirements of the photovoltaic system for fast shutdown, and has low cost, high reliability and safety.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid-connected power generation, and in particular to a rapid shutdown system for photovoltaic components in a photovoltaic grid-connected power generation system, and a rapid shutdown control method. Background Art

[0002] In recent years, photovoltaic power generation has achieved unprecedented rapid development in the world, including China, and has been widely installed on the roofs of residential houses, industrial and commercial buildings. When photovoltaic modules are illuminated, there is a DC high voltage in the string. When a fire occurs in a building, firefighters cannot spray water to extinguish the fire. They can only rescue after all the modules are burned out, causing property losses or threatening personal safety.

[0003] For safety reasons, Italy's safety warning states that firefighters are absolutely not allowed to perform firefighting operations when a building is energized. Germany has also taken the lead in implementing fire safety standards and has also explicitly stipulated that additional DC disconnect devices need to be added between the inverter and the components in the photovoltaic power generation system. In addition, German insurance companies also have clear regulations that personal injuries caused to firefighters by energized photovoltaic power stations during the firefighting process will not be compensated. The American Fire Protection Association has revised the National Electrical Code to require that in residential photovoltaic power generation systems: in the event of an emergency, after the AC grid-connected port of the photovoltaic power generation system is disconnected, the maximum voltage at the DC end shall not exceed 80V.

[0004] The laws and regulations on safe electricity use in European and American countries have been extended to the field of photovoltaic power generation. For example, the National Electrical Code (NEC) NEC2017--690.12 (B) of the United States requires that photovoltaic systems installed on or above the top of a building must have a rapid shutdown function. It also puts forward requirements for the shutdown speed and the voltage between the internal and external conductors of the photovoltaic array and between the conductors and the earth after shutdown. Specifically, within 30 seconds after the rapid shutdown device is activated, the voltage is ≤ 30V outside the 1 meter range of the photovoltaic array, and the voltage is ≤ 80V within the 1 foot (30.5 cm) range of the photovoltaic array.

[0005] In order to meet the requirements of the above NEC2017--690.12 (B) clause, the photovoltaic system needs to have a fast shutdown function at the component level. In the prior art, in order to achieve the fast shutdown function at the component level, the shutdown controller needs to continuously send a heartbeat communication signal, or the shutdown control module located on the DC bus needs to send a periodic excitation pulse source; and in these two solutions, not only the corresponding sending module needs to be added to the photovoltaic inverter system, but also an additional receiving module needs to be set in the photovoltaic component's switch or power optimizer. Since the above fast shutdown device relies on power carrier communication (PLC), it is subject to the attenuation problem of signal transmission of power carrier communication. The number and length of photovoltaic component strings acted on by each set of fast shutdown devices are limited, which not only increases the cost of the photovoltaic system and the system's self-consumption of electricity, but also increases more signal source sending and receiving module failure points.

[0006] Due to the existence of the above-mentioned problems, when realizing the shutdown at the photovoltaic module level, it is inevitable to face problems such as high cost and reliability. At the same time, the simple shutdown function will generate self-consumption of electricity of the shutdown device. Therefore, it is currently difficult to apply commercially in China, resulting in safety production risks in my country's photovoltaic power generation industry. Summary of the invention

[0007] In order to solve the defects existing in the prior art, the main purpose of the present invention is to provide a rapid shutdown system for photovoltaic components in a photovoltaic grid-connected power generation system and a control method for rapid shutdown. On the one hand, the present invention reduces the heartbeat or periodic excitation pulse signal source receiving module in the photovoltaic shut-off device and the power optimizer, and the signal source sending module in the photovoltaic inverter system, and realizes the component-level shutdown of the photovoltaic system at low cost and high reliability, and reduces the voltage inside and outside the photovoltaic array to a safe range in a very short time. On the other hand, the present invention can be used with simple steps and reliable implementation. After the fault is eliminated, photovoltaic power generation can be restored conveniently and quickly, and when applied to a photovoltaic power optimizer, it can also provide a photovoltaic system with shielding to recover power generation losses and prevent component hot spots and DC arc fault points, solving the problem that the current photovoltaic component-level shutdown is difficult to commercialize on a large scale.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] The present invention provides a rapid shutdown system in one aspect, which is configured in a photovoltaic power acquisition system, wherein the photovoltaic power acquisition system includes a photovoltaic series body composed of a plurality of photovoltaic units connected in series, and the rapid shutdown system includes a short-circuit shutdown circuit configured on the output side of the photovoltaic unit, and a DC bypass circuit configured on the output side of the photovoltaic series body, wherein the output ends of the plurality of short-circuit shutdown circuits are connected in series as the output end of the photovoltaic series body;

[0010] The short-circuit shutdown circuit includes a first switch, a second switch, an energy storage element, a first control module and a first auxiliary power supply; the first switch and the second switch are connected to the connection loop between the photovoltaic unit and the photovoltaic series body, and when any of the first switch and the second switch is turned off, the connection between the photovoltaic unit and the photovoltaic series body is disconnected; the energy storage element is connected between the first switch and the second switch, and the conduction of the first switch can connect the photovoltaic unit and the energy storage element, and the conduction of the second switch can connect the energy storage element and the photovoltaic series body; the first auxiliary power supply is electrically connected to the output end of the photovoltaic unit and is connected to the first control module for power supply, and the first control module is connected to the first switch and the second switch by a switch signal;

[0011] The DC bypass circuit includes a third switch element and a resistance element connected in series, which are connected in parallel at the output side of the photovoltaic series body;

[0012] After the third switch is turned on, each first auxiliary power source is turned off at least because the voltage is lower than the operation requirement, so that any of the first switch and the second switch is turned off, and the connection between the photovoltaic unit and the photovoltaic series body is disconnected;

[0013] At least when the first auxiliary power supply is restarted due to the DC bypass circuit, the first control module controls the conduction of the first switch element and the second switch element separately, so that the energy storage element is connected to the photovoltaic series body after taking power from the photovoltaic unit, and obtains and determines whether the short-circuit condition is met based on the change of the electrical parameters of the energy storage element. Before determining that the short circuit is released, each short-circuit shutdown circuit keeps the photovoltaic unit and the photovoltaic series body disconnected.

[0014] The above-mentioned rapid shutdown system may optionally include that the third switch element is a normally closed switch element, and the DC bypass circuit also includes a second control module and a second auxiliary power supply, the second auxiliary power supply is electrically connected to the output side of the inverter system or the DC combiner box, the second auxiliary power supply is electrically connected to the second control module, and the second control module is controlled to be connected to the third switch element.

[0015] The above-mentioned rapid shutdown system may optionally include that the DC bypass circuit further includes a manual switch element, and the manual switch element can control the conduction of the third switch element.

[0016] The above-mentioned fast shutdown system may optionally include that the short-circuit shutdown circuit is configured in a photovoltaic power optimizer, which includes a power conversion module, a control module and an auxiliary power supply, the first control module serves as the control module of the optimizer, the first auxiliary power supply serves as the auxiliary power supply of the optimizer, and the first switch element, the second switch element and the energy storage element are configured on the positive and negative circuits of the power conversion module; when the optimizer operates normally, the first control module sets the electrical parameters of the output end of the photovoltaic unit at the maximum power point, and when the optimizer is started, the first control module controls the first switch element, the second switch element and the energy storage element to perform short-circuit detection.

[0017] The above-mentioned fast shutdown system may optionally include that the power conversion module is a Buck type or Boost type or Boost-Buck type DC chopper circuit with an output capacitor; the output capacitor serves as an energy storage element of the short-circuit shutdown circuit;

[0018] During the short-circuit test, the first control module collects and records the voltage parameters of the output capacitor being connected to the photovoltaic unit to obtain electricity, and the voltage parameters of the output capacitor being connected to the power acquisition system, to obtain the voltage parameter difference used to determine whether the short-circuit condition is met;

[0019] Alternatively, the DC chopper circuit further has an input capacitor, and the first control module acquires a voltage parameter difference for determining whether a 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;

[0020] The first switch element is a switch element connected in series on a positive or negative loop in a DC chopper circuit, and the second switch element 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. At least one of the first switch element and the second switch element is a normally open switch element.

[0021] The above-mentioned fast shutdown system may optionally include that the power conversion module is a step-down Buck DC chopper circuit, which includes an input capacitor, a switching element as the first switching device, an inductor, 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 loops 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 electrodes of the output capacitor are connected in parallel between the inductor and the second switching device.

[0022] The above-mentioned rapid shutdown system may optionally have the energy storage element being a capacitor element connected in parallel to the positive and negative connection circuits of the photovoltaic unit and the photovoltaic series body, and the first control module obtaining and judging whether the short-circuit condition is met based on the difference in voltage parameters of the capacitor element before and after drawing power from the photovoltaic unit and connecting to the photovoltaic series body.

[0023] The above-mentioned rapid shutdown system may optionally include that the first control module includes a control unit, a collection unit, a calculation unit, a judgment unit, a counting unit and a driving unit for controlling the operation of the short-circuit shutdown circuit;

[0024] 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;

[0025] 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;

[0026] The computing unit is used to obtain the difference in electrical parameter information in the power state and in the system access state;

[0027] The judgment unit is used to judge the electrical parameter information parameter and drive the control unit to perform corresponding operations;

[0028] 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;

[0029] 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;

[0030] The driving unit controls the turning off and on of the first switch element and the second switch with driving power according to the switching value control command.

[0031] The present invention accordingly provides a control method for the above-mentioned rapid shutdown system, the method comprising:

[0032] At least when the photovoltaic power acquisition system fails and shuts down or actively controls the photovoltaic power acquisition system to shut down, control the third switch element to conduct and connect the photovoltaic series body to the resistance element;

[0033] The resistance element makes the operating voltage of the first auxiliary power supply of each short-circuit shutdown circuit lower than the shutdown voltage, thereby disconnecting the first switch element and / or the second switch element;

[0034] At least when the photovoltaic power acquisition system is shut down due to a fault or the photovoltaic power acquisition system is actively controlled to shut down, and the auxiliary power supply is restarted, the first control module performs the short circuit test step:

[0035] 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;

[0036] Acquiring electrical parameter information of the energy storage element in the power acquisition state;

[0037] 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;

[0038] Obtaining electrical parameter information of energy storage elements when connected to the system;

[0039] Compare the differences in obtaining electrical parameter information of the energy storage element in the power state and in the system access state;

[0040] Determine the difference in electrical parameter information:

[0041] If the difference in the electrical parameter information is within the first preset difference limit, it is determined that there is no short circuit 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;

[0042] 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 situation, and the short circuit test step is performed again after the delay setting time;

[0043] If the difference in the electrical parameter information is outside the second preset difference limit, it is determined that a short circuit exists in the connected system, and the first switch element and / or the second switch element are controlled to be closed.

[0044] The control method described above may optionally further include: performing a first count on the situation where the difference in the electrical parameter information is between the first preset difference limit and the second preset difference, and if the first count satisfies that the continuous short circuit uncertain short circuit situation reaches a preset number of times, determining that the connected system has a short circuit situation, and controlling the first switch element and / or the second switch element to be closed;

[0045] Establishing a communication connection between the optimizer and the power acquisition system, and after determining that the connected system has a short circuit, alarming and / or reporting a repair to the power acquisition system;

[0046] 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;

[0047] 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.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention uses a DC bypass circuit to short-circuit or connect a resistor in parallel to the photovoltaic series body to reduce the voltage, so that the auxiliary power supply in the photovoltaic module equipped with the short-circuit shutdown circuit stops running at least because the voltage is lower than the shutdown voltage. At the same time, the switch of the short-circuit shutdown circuit automatically disconnects the connection between the photovoltaic module and the photovoltaic series body to achieve rapid shutdown; at the same time, when the auxiliary power supply is restarted after the disconnection, the control module of the short-circuit shutdown circuit will first maintain the connection between the photovoltaic module and the photovoltaic series body disconnected, and use the principle that the energy storage element will produce an electrical parameter change when a short circuit exists to perform short-circuit detection; during the detection process, the photovoltaic module and the power acquisition circuit are kept disconnected to ensure that the photovoltaic module does not receive external Output power; When the circuit is shut down due to a short circuit caused by other reasons, it will automatically restart after short circuit detection, realizing the intelligence of the photovoltaic grid-connected system; The rapid shutdown process does not require the setting of a heartbeat or periodic excitation pulse signal for communication in the switch or optimizer, reducing the setting of the receiving module and the sending module, reducing the cost, and realizing the rapid shutdown of the photovoltaic power generation system to the photovoltaic components with high reliability, and reducing the voltage inside and outside the photovoltaic array to a safe range in a very short time, meeting the safety regulations of NEC2017-690.12 (B); Only a small amount of power from the energy storage element is used for testing, and the measurement process is safe and reliable, and will not burden the system.

[0050] (2) The third switch element of the present invention is a normally closed switch element. When the inverter system is operating normally, the third switch element needs to be controlled to be turned off to maintain operation. However, when the inverter system shuts down due to a fault or actively shuts down, the third switch element automatically turns on due to the shutdown of the second auxiliary power supply, and then cooperates with the short-circuit shutdown circuit to quickly disconnect each photovoltaic module from the system. At the same time, the resistor element can reduce the output voltage of the photovoltaic string to a safe range, and quickly consume the electrical energy of the inverter input capacitor and various energy storage devices in the photovoltaic string, thereby improving the safety of the photovoltaic power generation system after shutdown.

[0051] (3) The present invention can configure the short-circuit shutdown circuit in the photovoltaic power optimizer. On the one hand, the photovoltaic power optimizer can make the photovoltaic module operate at the maximum power point to improve the efficiency of power generation; on the other hand, the short-circuit shutdown 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 shutdown 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 module and sending module, reducing the manufacturing cost of the power generation system.

[0052] The present invention will be further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A schematic diagram of the structure of a rapid shutdown system according to an embodiment of the present invention;

[0054] Figure 2 It is a structural schematic diagram of a short-circuit shutdown circuit according to an embodiment of the present invention;

[0055] Figure 3 It is a structural schematic diagram of a photovoltaic power optimizer equipped with a short-circuit shutdown circuit according to an embodiment of the present invention;

[0056] Figure 4 This is a schematic diagram of a short-circuit shutdown control structure of a first control module according to an embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of a power conversion control structure of a first control module according to an embodiment of the present invention;

[0058] Figure 6 It is a structural schematic diagram of a photovoltaic inverter system equipped with a DC bypass circuit according to an embodiment of the present invention;

[0059] Figure 7 The figure is a flow chart of a control method for a short-circuit shutdown circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0060] 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.

[0061] like Figure 1As shown, a fast shutdown system according to an embodiment of the present invention is configured in a photovoltaic grid-connected power generation system, which includes a photovoltaic series body composed of a plurality of photovoltaic units in series. The photovoltaic unit is a photovoltaic module A in this embodiment, and in other implementations, it can also be a photovoltaic string B containing a plurality of photovoltaic modules A, or a series body of some photovoltaic cells in a photovoltaic module A. The photovoltaic series body corresponds to the photovoltaic string B in this embodiment. The fast shutdown system includes a short-circuit shutdown circuit E4 and a DC bypass circuit P.

[0062] refer to Figure 1 , the output side of the photovoltaic component A is connected to a short-circuit shutdown circuit E4, and the output ends of many short-circuit shutdown circuits E4 are connected in series as the output end of the photovoltaic string B. There are multiple photovoltaic components A, and A-1, A-2, ..., An in the figure; the number of short-circuit shutdown circuits E4 corresponds. E-1, E-2, ..., En in the figure are power optimizers E, each power optimizer E is equipped with a short-circuit shutdown circuit E4, there are multiple photovoltaic strings B, and the output ends of multiple photovoltaic strings B are connected to the photovoltaic inverter system J. In other embodiments, the photovoltaic string B can also be connected to the input end of the DC combiner box, and the output end of the DC combiner box is connected to the inverter system J. The DC bypass circuit P is configured on the output side of the photovoltaic string B. In this embodiment, it is specifically configured in the inverter system J, and in other embodiments, it can also be configured in the DC combiner box. The short-circuit shutdown circuit E4 can be configured separately to run at the output end of the photovoltaic component A or configured in the power optimizer E.

[0063] Specifically, in this embodiment, the short-circuit shutdown circuit E4 includes a first switch S1, a second switch S2, an energy storage element C, a first control module E2, and a first auxiliary power supply E3. The first switch S1 and the second switch S2 are connected in series on the positive circuit connecting the photovoltaic component A and the photovoltaic string B. The first switch S1 and the second switch S2 can disconnect the power generation circuit of the photovoltaic component A. In this embodiment, the energy storage element C is a capacitor element R connected in parallel on the connected circuit between the first switch S1 and the second switch S2. 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 of the inductor. When the first switch S1 is turned on, the capacitor element R is connected to the photovoltaic component A; when the second switch S2 is turned on, the capacitor element R is connected to the photovoltaic string B. The first auxiliary power supply E3 is connected in parallel to the positive and negative circuits of 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 voltage of the positive and negative circuits is lower than the voltage of the first auxiliary power supply E3, the first control module E2 stops running, and the first switch S1 and the second switch S2 become disconnected, so that the connection circuit between the photovoltaic component A and the photovoltaic string B connected to it is disconnected. After the first switch S1 and the second switch S2 are turned off, the first auxiliary power supply E3 will be isolated from the short circuit of the external circuit and restore the power from the photovoltaic component A. The first control module E2 controls the conduction of the first switch S1 and the second switch S2 separately, so that the capacitor is connected to the power acquisition system after drawing power from the photovoltaic component A, obtains and determines whether the short circuit condition is met based on the difference in the voltage parameters at both ends of the capacitor, and only turns on the first switch S1 and the second switch S2 at the same time after determining that the short circuit condition is not met, and restores the connection between the photovoltaic unit and the photovoltaic string B. The short-circuit shutdown circuit E4 of the present invention, on the one hand, utilizes the first switch element S1 and the second switch element 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 element S1 and the second switch element S2, and uses the energy storage element C to test whether the external circuit is short-circuited.

[0064] refer to Figure 1 and 6, in conjunction with the short-circuit shutdown circuit E4, the DC bypass circuit P of the present invention is configured in the photovoltaic inverter system J, which includes a third switch S3, a resistor element, a second control module H, a second auxiliary power supply Q and a manual switch K. The photovoltaic inverter system J includes a Boost boost conversion circuit J1 and an inverter circuit J2. The conversion circuit J1 is connected to each photovoltaic string B, obtains the power at the output end of the photovoltaic string B and converts it into another electrical parameter of power output to the inverter circuit J2, and the inverter circuit J2 inverts the DC power into AC power and supplies it to the grid. The third switch S3 and the resistor element are connected in series, and their output ends are connected in parallel to the input end of the conversion circuit J1. In this embodiment, the third switch S3 is a P-type normally closed field effect switch tube M3, and in other embodiments it can also be a normally closed relay, or other normally closed fully controlled semiconductor switch elements.

[0065] It should be noted that the resistance element is a power resistor with a small resistance value. When connected to the photovoltaic string B into a loop, it can not only make each first auxiliary power supply E3 lower than the shutdown voltage, but also reduce the output voltage of the photovoltaic string B to within the safety requirement. At the same time, it can quickly consume the power of the input capacitor of the conversion circuit and the power of each output capacitor in the photovoltaic string B, further ensuring the safety of the system after shutdown.

[0066] It should be noted that the input end of the second auxiliary power supply Q is connected to the AC side of the inverter system J, the output end of the second auxiliary power supply Q is connected to the second control module H, the second control module H is controlled to be connected to the third switch S3, the conversion circuit J1 and the inverter circuit J2, and the second control module H is connected to the input of the manual switch K. The manual switch K is an emergency shutdown button. When the manual switch K is actively pressed, the second control module H controls the switch in the inverter circuit J2 to turn off, so that the inverter system J stops running, and the connection between the inverter system J and the power grid is cut off, the second auxiliary power supply Q will stop operating, and further stop the second control module H, while the third switch S3 remains in the on state due to the loss of drive, so as to achieve the rapid shutdown of each photovoltaic component A in an emergency. When the inverter system J stops due to other reasons, the second auxiliary power supply Q will lose power acquisition and shut down, and the second control module H will be shut down, and the third switch S3 will lose drive and turn on, so as to achieve the rapid shutdown of each photovoltaic component A in an emergency.

[0067] It can be understood that the short-circuit shutdown circuit E4 disconnects the photovoltaic component A due to other factors in conjunction with the short circuit of the non-DC bypass circuit P, which can be automatically started after short-circuit detection. After the first switch S1 and the second switch S2 are turned off, the first auxiliary power supply E3 will be isolated from the short circuit of the external circuit and restore the power from the photovoltaic component A. The first control module E2 controls the conduction of the first switch S1 and the second switch S2 separately, so that the capacitor is connected to the power acquisition system after taking power from the photovoltaic component A, and obtains and determines whether the short-circuit condition is met based on the difference in voltage parameters at both ends of the capacitor. Before determining that the short circuit is released, each short-circuit shutdown circuit E4 keeps the photovoltaic component A and the photovoltaic string B disconnected, and only conducts the first switch S1 and the second switch S2 at the same time after determining that the short-circuit condition is not met, and restores the connection between the photovoltaic unit and the power acquisition system.

[0068] As a feature of an embodiment of the present invention, a fast shutdown system including a short-circuit shutdown circuit E4 and a DC bypass circuit P can meet the requirements of safety regulations 690.12 (B) in the face of emergency active shutdown and sudden shutdown due to faults, and can realize automatic shutdown of the photovoltaic array and reduce the voltage of the photovoltaic string B to below the safety requirement. In the face of the shutdown of the photovoltaic component A caused by other factors other than short circuit, the short-circuit shutdown circuit E4 can realize automatic startup after short-circuit detection, and there is no need to establish communication between the photovoltaic component A and the central control. Overall, a simple and low-cost circuit structure is used to realize the fast shutdown and safe self-start of the photovoltaic component A of the photovoltaic grid-connected power generation system.

[0069] like Figure 2 As shown, a photovoltaic power optimizer E configured with the short-circuit shutdown circuit E4 according to an embodiment of the present invention, the optimizer E includes a power conversion module E1, a control module and an auxiliary power supply. It can be understood that when the short-circuit shutdown circuit E4 is configured in the photovoltaic power optimizer E, the control module and the auxiliary power supply can be shared with the optimizer E to simplify the circuit structure and reduce the hardware cost. In this embodiment, the short-circuit shutdown circuit E4 has a first control module E2 as a control module of the optimizer E, a first auxiliary power supply E3 as an auxiliary power supply of the optimizer E, and a first switch S1, a second switch S2 and an energy storage element C are configured on the positive and negative circuits of the power conversion module E1; when the optimizer E is operating normally, the first control module E2 sets the electrical parameters of the output end of the photovoltaic component A at the maximum power point, and when the optimizer E is started, the first control module E2 controls the first switch S1, the second switch S2 and the energy storage element C to perform short circuit detection. Among them, the power conversion module E1 can be a Buck type or a Boost type or a Boost-Buck type DC chopper circuit.

[0070] like Figure 3The figure shows a specific BUCK step-down photovoltaic power optimizer E equipped with the short-circuit shutdown circuit E4. Figure 2 Based on the circuit structure of the optimizer E, since the structure of the DC chopper circuit has a switch element and a capacitor, the short-circuit shutdown circuit E4 and the optimizer E can also share the first switch element S1 and the capacitor element R.

[0071] 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 connected in series in sequence 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 transistors. 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 toward the output side of PV+, the drain of the first switch tube M1 and the second switch tube M2 are connected toward 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 first control module E2. The auxiliary capacitor and the input capacitor C1 are respectively connected in parallel on 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. Among them, the input capacitor C1 and the output capacitor C2 are used for filtering of the chopper circuit, the first switch tube M1 controls the chopping conversion of the photovoltaic component A to the inductor L, and the freewheeling diode D1 is used to maintain the output level.

[0072] 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 shutdown circuit E4; the output capacitor C2 serves as the energy storage element C of the short-circuit shutdown 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 shutdown circuit E4. Among them, the short-circuit shutdown 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 through the bypass diode D2.

[0073] 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.

[0074] like Figure 4 and 5 As shown, it is a structural diagram of the first control module E2 according to an embodiment of the present invention. The first 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 arranged at the collection position, amplified by an amplifier and processed by a processor into an operational electrical signal. The calculation unit 23 can be arranged in the processor to calculate the collected electrical parameters. The judgment unit 24 can be arranged in the processor to judge the short circuit situation or the current power situation according to the result of the calculation. The control unit 21 can be arranged in the processor, including under the triggering operation condition, such as the initial start after power is obtained, to perform the corresponding short circuit detection control; it also includes performing the corresponding control operation 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 a second control module H is configured in the inverter system J or the DC combiner box. The second control module H is configured with a communication device that matches the optimizer E. When a short circuit fault occurs, the first control module E2 can alarm the second control module H through the communication unit 27.

[0075] Specific reference Figure 4In 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 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 The control unit 21 performs 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 control unit 21 controls the first switch tube M1 and the second switch tube M2 to be 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 second control module H after determining that there is a definite short circuit.

[0076] Specific reference Figure 5 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.

[0077] like Figure 7 FIG. 1 is a fast shutdown control flow of a fast shutdown system according to an embodiment of the present invention. The method is as follows:

[0078] In the DC bypass circuit P of the inverter system J, if the output end of the inverter system J is disconnected, the second auxiliary power supply Q and the second control module H are shut down, and the third switch element S3 loses drive and remains on; or, if the manual switch element K is pressed, the third switch element S3 will be driven to remain on. The photovoltaic string B and the resistance element will be connected to form a loop, and the resistance element will make the operating voltage of the first auxiliary power supply E3 of each short-circuit shutdown circuit E4 lower than the shutdown voltage, and disconnect the first switch element S1 and / or the second switch element S2. When the photovoltaic component A is disconnected, the first auxiliary power supply E3 is restarted, and the first control module E2 remains off, achieving rapid shutdown.

[0079] In terms of the short-circuit shutdown circuit E4 of the photovoltaic component A, when power is first obtained after the auxiliary power supply is turned off and the control module is running, the startup optimizer E tested by the short-circuit condition is executed. The short-circuit detection step includes: 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, and 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%:

[0080] 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 situation, and after a delay of 3 minutes, the optimizer E is started again after the short circuit test. The situation is counted for the first time. If the uncertain short circuit situation reaches 3 times during 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; 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. 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.

[0081] 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.

[0082] It is worth noting that the short-circuit shutdown circuit E4 of the present invention has a restart function after short-circuit detection. When the short-circuit shutdown circuit E4 is disconnected due to the DC bypass circuit P being in the on state, the optimizer E will be shut down after the above-mentioned short-circuit detection step. In this case, after the cause of the rapid shutdown is eliminated, the optimizer E is restarted after the second control module H actively sends a start instruction. In the face of short-circuit faults such as parallel arc factors, the optimizer E will automatically shut down without manual switch K or AC side disconnection, and will shut down due to failure to pass the short-circuit test. In the face of shutdown after dark and the next morning, the auxiliary power supply reaches the starting voltage for the first time, and the optimizer E will smoothly pass the short-circuit detection and automatically turn on. When the optimizer E is interrupted due to other non-short-circuit faults such as overcurrent, the optimizer E will be able to restart and run through short-circuit detection. In summary, safe self-starting is achieved through the short-circuit shutdown circuit E4, and rapid shutdown of the photovoltaic module A is achieved on the basis of reducing the communication hardware settings.

[0083] 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 rapid shutdown system, wherein the rapid shutdown system is configured in a photovoltaic power acquisition system, wherein the photovoltaic power acquisition system comprises a photovoltaic series body composed of a plurality of photovoltaic units connected in series, wherein: The rapid shutdown system comprises a short-circuit shutdown circuit (E4) configured at the output side of the photovoltaic unit, and a DC bypass circuit (P) configured at the output side of the photovoltaic series body, and the output ends of the short-circuit shutdown circuits (E4) are connected in series as the output end of the photovoltaic series body; The short-circuit shutdown circuit (E4) comprises a first switch (S1), a second switch (S2), an energy storage element (C), a first control module (E2) and a first auxiliary power supply (E3); the first switch (S1) and the second switch (S2) are connected to a connection loop between a photovoltaic unit and a photovoltaic series body, and when any of the first switch (S1) and the second switch (S2) are turned off, the connection between the photovoltaic unit and the photovoltaic series body is disconnected; the energy storage element (C) is connected between the first switch (S1) and the second switch (S2), and the conduction of the first switch (S1) can connect the photovoltaic unit and the energy storage element (C), and the conduction of the second switch (S2) can connect the energy storage element (C) and the photovoltaic series body; the first auxiliary power supply (E3) is electrically connected to the output end of the photovoltaic unit and is connected to the first control module (E2) for power supply, and the first control module (E2) is connected to the first switch (S1) and the second switch (S2) by a switch signal; The DC bypass circuit (P) comprises a third switch element (S3) and a resistance element connected in series, which are connected in parallel at the output side of the photovoltaic series body; the method comprises: At least when the photovoltaic power acquisition system fails and shuts down or actively controls the photovoltaic power acquisition system to shut down, the third switch (S3) is controlled to be turned on and the photovoltaic series body is connected to the resistance element; The resistance element makes the operating voltage of the first auxiliary power supply (E3) of each short-circuit shutoff circuit (E4) lower than the shutoff voltage, thereby disconnecting the first switch element (S1) and / or the second switch element (S2); At least when the photovoltaic power acquisition system is shut down due to a fault or the photovoltaic power acquisition system is actively controlled to shut down, and the auxiliary power supply is restarted, the first 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 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 situation, and the short circuit test step is performed again after the 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 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: performing a first count on the situation where 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 uncertain short-circuit situation reaches a preset number of times, determining that the connected system has a short-circuit situation, and controlling the closing of the first switch element (S1) and / or the second switch element (S2); Establishing a communication connection between the optimizer (E) and the power acquisition system, and after determining that the connected system has a short circuit, 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 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 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 third switch element (S3) is a normally closed switch element, and the DC bypass circuit (P) also includes a second control module (H) and a second auxiliary power supply (Q), the second auxiliary power supply (Q) is electrically connected to the output side of the inverter system (J) or the DC combiner box, the second auxiliary power supply (Q) is electrically connected to the second control module (H), and the second control module (H) is controlled to be connected to the third switch element (S3).

4. The control method according to claim 1, characterized in that: The DC bypass circuit (P) further comprises a manual switch component (K), and the manual switch component (K) can control the conduction of the third switch component (S3).

5. The control method according to claim 1, characterized in that: The short-circuit shutdown circuit (E4) is configured in a photovoltaic power optimizer (E), and the optimizer (E) includes a power conversion module (E1), a control module and an auxiliary power supply. The first control module (E2) serves as the control module of the optimizer (E), the first auxiliary power supply (E3) serves as the auxiliary power supply of the optimizer (E), and the first switch component (S1), the second switch component (S2) and the energy storage element (C) are configured on the positive and negative circuits of the power conversion module (E1); when the optimizer (E) operates normally, the first control module (E2) sets the electrical parameters of the output end of the photovoltaic unit at the maximum power point, and when the optimizer (E) is started, the first control module (E2) controls the first switch component, the second switch component (S2) and the energy storage element (C) to perform short-circuit detection.

6. The control method according to claim 5, characterized in that: The power conversion module (E1) is a Buck type or Boost type or Boost-Buck type DC chopper circuit having an output capacitor (C2); the output capacitor (C2) serves as an energy storage element (C) of a short-circuit shutdown circuit (E4); The first switch element (S1) is a switch element connected in series on a positive or negative loop in a DC chopper circuit, and 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.

7. The control method according to claim 5, characterized in that: The power conversion module (E1) is a step-down Buck 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 loops 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).

8. The control method according to claim 1, characterized in that: The energy storage element (C) is a capacitor element (R) connected in parallel to the positive and negative connection circuits of the photovoltaic unit and the photovoltaic series body. The first control module (E2) obtains and determines whether the short-circuit condition is met based on the difference in voltage parameters of the capacitor element (R) before and after taking power from the photovoltaic unit and connecting to the photovoltaic series body.

9. The control method according to claim 1, characterized in that: The first 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 shutdown circuit (E4); The control unit (21) is used to control the second switch (S2) to remain turned 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 controls the first switch (S1) to be turned off, and then controls 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 switching on and off of the first switch element (S1) and the second switch with driving power according to the switching quantity control command.

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