Photovoltaic energy storage inverter and control method thereof

Abstract

The embodiment of the invention discloses a photovoltaic energy storage inverter and a control method thereof, relates to the technical field of energy, and solves the problem of how to determine parallel impedance to ground of the photovoltaic energy storage inverter and a photovoltaic array when the photovoltaic energy storage inverter is powered on for self-test at night, the photovoltaic array has no output voltage, or the output voltage of the photovoltaic array is unstable. And the grid connection problem of the photovoltaic energy storage inverter is controlled. Specifically, a controller in the photovoltaic energy storage inverter is used for controlling a switch tube in a Boost circuit to be in a conducting state under the condition that the voltage output by a photovoltaic array is smaller than or equal to a voltage threshold value and an energy storage device outputs the voltage to a direct current bus positive electrode and a direct current bus negative electrode. And under the condition that the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a proportional threshold value, controlling the output of the inverter circuit to establish connection with the power grid. And under the condition that the ratio of the negative bus voltage to the positive bus voltage is smaller than a proportion threshold value, controlling the output of the inverter circuit to be disconnected from the power grid.

Description

Technical Field

[0001] The present application relates to the field of energy technology, and in particular to a photovoltaic energy storage inverter and a control method thereof. Background Art

[0002] The photovoltaic energy storage inverter is used to convert the direct current provided by the photovoltaic array into alternating current during the day, or to convert the direct current provided by the energy storage device into alternating current at night, and transmit the alternating current to the grid or load, so that the photovoltaic energy storage inverter can transmit electric energy to the grid or load during the day or at night. When the photovoltaic energy storage inverter is connected to the grid, it is necessary to meet the requirements of the International Electrotechnical Commission (IEC) 62109-2 grid connection standard for the insulation impedance of the photovoltaic array to the ground.

[0003] When the photovoltaic energy storage inverter performs self-test during the day, the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array can be determined according to the output voltage of the photovoltaic array and the bus voltage between the positive pole of the DC bus and the negative pole of the DC bus in the photovoltaic energy storage inverter. The parallel impedance to ground can be regarded as the insulation impedance to ground of the photovoltaic array. Based on the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array, the photovoltaic energy storage inverter is controlled to be connected to the grid.

[0004] However, when the photovoltaic energy storage inverter is turned on for self-test at night and the photovoltaic array has no output voltage, or the output voltage of the photovoltaic array is unstable, how to determine the parallel impedance of the photovoltaic energy storage inverter and the photovoltaic array to the ground, and control the photovoltaic energy storage inverter to be connected to the grid based on the parallel impedance of the photovoltaic energy storage inverter and the photovoltaic array to the ground, becomes an urgent problem to be solved. Summary of the invention

[0005] The embodiment of the present application provides a photovoltaic energy storage inverter and a control method thereof, which solves the problem of how to determine the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array and control the photovoltaic energy storage inverter to be connected to the grid when the photovoltaic energy storage inverter is powered on for self-test at night and the photovoltaic array has no output voltage, or the output voltage of the photovoltaic array is unstable.

[0006] In order to achieve the above purpose, the embodiment of the present application adopts the following technical solution:

[0007] In a first aspect of an embodiment of the present application, a photovoltaic energy storage inverter is provided, comprising a Boost circuit, a first resistor, a second resistor, a positive pole of a DC bus, a negative pole of a DC bus, an inverter circuit and a controller. The input of the Boost circuit is used to connect to a photovoltaic array, the output of the Boost circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, the first resistor and the second resistor are connected in series between the positive pole of the DC bus and the negative pole of the DC bus, the connection point of the first resistor and the second resistor is used to connect to a protective ground wire, the input of the inverter circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, and the output of the inverter circuit is used to connect to a power grid. The positive pole of the DC bus and the negative pole of the DC bus are also used to connect the positive pole and the negative pole of the energy storage device. The controller is used to control the switch tube in the Boost circuit to be in a conducting state when the voltage output by the photovoltaic array is less than or equal to the voltage threshold and the energy storage device outputs a voltage to the positive pole of the DC bus and the negative pole of the DC bus. The controller is also used to obtain the bus voltage and the negative bus voltage. The bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus. The controller is also used to control the output of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to the proportional threshold. The positive bus voltage is the difference between the bus voltage and the negative bus voltage. The controller is also used to control the output of the inverter circuit to disconnect from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than the proportional threshold.

[0008] Based on this solution, compared with the prior art in which the photovoltaic energy storage inverter needs to obtain three voltages such as the bus voltage when performing a self-check at night to detect the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array, in this solution, the controller obtains the bus voltage and the negative bus voltage. Since the resistance value of the first resistor is fixed, the ratio of the negative bus voltage to the positive bus voltage can be equivalent to the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array. The controller controls the photovoltaic energy storage inverter to be connected to the grid according to the ratio of the negative bus voltage to the positive bus voltage, which is equivalent to the controller controlling the photovoltaic energy storage inverter to be connected to the grid according to the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array. There are inevitable errors in each voltage detection process, and the voltages that need to be detected in this application are fewer, thereby improving the detection accuracy of the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array. At the same time, compared with the prior art in which the photovoltaic energy storage inverter and the photovoltaic array are powered on for self-test at night and the parallel impedance to the ground is detected, since the photovoltaic array has no light and no output voltage, when the relay is closed, the port capacitor corresponding to the photovoltaic array in the photovoltaic energy storage inverter is charged, and the capacitance of the port capacitor is large, resulting in a large time constant of the charging circuit corresponding to the port capacitor. In this solution, when the controller controls the switch tube in the Boost circuit to be in the on state, the capacitance between the positive DC bus and the negative DC bus and the protective ground wire is smaller, and the time constant is smaller, so that the bus voltage and the negative bus voltage can be stabilized faster, and the controller can use less time to determine the ratio of the negative bus voltage to the positive bus voltage, and can use less time to determine the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array, and the detection time is shorter. Therefore, when the controller controls the photovoltaic energy storage inverter to be connected to the grid according to the ratio of the negative bus voltage to the positive bus voltage, the safety of the photovoltaic energy storage inverter can be improved, the grid connection speed or startup speed of the photovoltaic energy storage inverter can be increased, and damage to the photovoltaic energy storage inverter can be avoided, or the photovoltaic energy storage inverter can be connected to the grid at a lower efficiency.

[0009] In combination with the first aspect, in a possible implementation, the controller is specifically used to obtain the bus voltage and the negative bus voltage when the on-time of the switch tube in the Boost circuit is greater than or equal to the time threshold.

[0010] Based on this solution, the controller obtains the bus voltage and the negative bus voltage when the conduction time of the switch tube in the Boost circuit is greater than or equal to the time threshold, so that the controller can obtain more stable bus voltage and negative bus voltage, and the controller can more accurately determine the ratio of the negative bus voltage to the positive bus voltage, which is equivalent to more accurately determining the parallel impedance to the ground of the photovoltaic energy storage inverter and the photovoltaic array, and can more safely control the photovoltaic energy storage inverter to be connected to the grid.

[0011] In combination with the first aspect, in a possible implementation method, the controller is specifically used to obtain the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and to obtain the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold.

[0012] Based on this solution, the controller obtains the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and obtains the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold, so that the controller can obtain more stable bus voltage and negative bus voltage, and the controller can more accurately determine the ratio of the negative bus voltage to the positive bus voltage, which is equivalent to more accurately determining the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array, and more safely controlling the photovoltaic energy storage inverter to be connected to the grid.

[0013] In combination with the first aspect, in a possible implementation, the photovoltaic energy storage inverter further includes a third resistor and a first switch connected in parallel between the first resistor and the protective ground wire. The controller is also used to control the first switch to be in a closed state when the switch tube in the Boost circuit is in a conducting state.

[0014] Optionally, the type of the first switch includes a relay, an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor. The embodiment of the present application does not limit the specific type of the first switch.

[0015] Based on this solution, by setting a third resistor and a first switch connected in parallel between the first resistor and the protective ground wire, when the photovoltaic energy storage inverter is connected to the grid, the controller controls the first switch to be in an off state, so that the current flowing through the first resistor is small, which can reduce the loss of the photovoltaic energy storage inverter and improve efficiency. When the insulation impedance to the ground of the first photovoltaic array is near Vmax / 30mA, and the resistance value of the first resistor and the resistance value of the third resistor (or the resistance value between the positive DC bus and the protective ground wire) are orders of magnitude different from the insulation impedance to the ground of the first photovoltaic array, it will lead to a large detection error and low detection accuracy. Therefore, when the photovoltaic energy storage inverter is powered on for self-test at night, it is necessary to detect the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array. When the controller controls the switch tube in the Boost circuit to be in the on state, the controller controls the first switch to be in the closed state. At this time, the third resistor is short-circuited, and the resistance value of the first resistor is small. The resistance value of the first resistor is close to the insulation impedance to ground of the first photovoltaic array and there is no extreme difference in quantity, thereby ensuring the detection accuracy of the parallel impedance to ground when it is close to the requirements of the insulation impedance to ground corresponding to the photovoltaic energy storage inverter in the IEC 62109-2 grid-connected standard.

[0016] In combination with the first aspect, in a possible implementation, the photovoltaic energy storage inverter further includes a fourth resistor and a second switch connected in parallel between the second resistor and the protective ground wire. The controller is also used to control the second switch to be in a closed state and the first switch to be in an open state when the voltage output by the photovoltaic array is greater than the voltage threshold, so as to obtain the first negative bus voltage. After obtaining the first negative bus voltage, the first switch is controlled to be in a closed state and the second switch is controlled to be in an open state to obtain the second negative bus voltage.

[0017] Optionally, the type of the second switch includes a relay, an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor. The embodiment of the present application does not limit the specific type of the second switch.

[0018] Based on this solution, by arranging a fourth resistor and a second switch connected in parallel between the second resistor and the protective ground wire, the photovoltaic energy storage inverter can adopt the method of the prior art of self-checking during the daytime to detect the parallel impedance of the photovoltaic energy storage inverter and the photovoltaic array to the ground. During the daytime self-check, the parallel impedance of the photovoltaic energy storage inverter and the photovoltaic array to the ground is detected, so that the controller can control the photovoltaic energy storage inverter to be connected to the grid when the parallel impedance of the photovoltaic energy storage inverter and the photovoltaic array to the ground meets the insulation impedance requirements corresponding to the photovoltaic energy storage inverter in the IEC62109-2 grid-connection standard. The safety of the photovoltaic energy storage inverter can be improved, the damage of the photovoltaic energy storage inverter can be avoided, and the photovoltaic energy storage inverter can be prevented from being connected to the grid at a lower efficiency.

[0019] The second aspect of the embodiment of the present application provides a control method for a photovoltaic energy storage inverter, which is applied to a photovoltaic energy storage inverter, and the method includes: when the voltage output by the photovoltaic array is less than or equal to the voltage threshold, and the energy storage device outputs voltage to the positive pole of the DC bus and the negative pole of the DC bus, the switch tube in the Boost circuit is controlled to be in a conductive state. Obtain the bus voltage and the negative bus voltage, the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus. When the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to the proportional threshold, the output of the inverter circuit is controlled to establish a connection with the power grid, and the positive bus voltage is the difference between the bus voltage and the negative bus voltage. When the ratio of the negative bus voltage to the positive bus voltage is less than the proportional threshold, the output of the inverter circuit is controlled to be disconnected from the power grid. The input of the Boost circuit is used to connect to the photovoltaic array, the output of the Boost circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, the first resistor and the second resistor are connected in series between the positive pole of the DC bus and the negative pole of the DC bus, the connection point of the first resistor and the second resistor is used to connect to the protective ground wire, the input of the inverter circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, and the positive pole of the DC bus and the negative pole of the DC bus are also used to connect the positive pole and the negative pole of the energy storage device.

[0020] In combination with the second aspect, in a possible implementation, the above-mentioned acquisition of the bus voltage and the negative bus voltage includes: acquiring the bus voltage and the negative bus voltage when the conduction time of the switch tube in the Boost circuit is greater than or equal to the time threshold.

[0021] In combination with the second aspect, in a possible implementation method, the above-mentioned acquisition of the bus voltage and the negative bus voltage includes: acquiring the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and acquiring the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold.

[0022] In combination with the second aspect, in a possible implementation, the photovoltaic energy storage inverter also includes a third resistor and a first switch arranged in parallel between the first resistor and the protective ground wire, and the method also includes: when the switch tube in the Boost circuit is controlled to be in an on state, controlling the first switch to be in a closed state.

[0023] In combination with the second aspect, in a possible implementation, the photovoltaic energy storage inverter further includes a fourth resistor and a second switch connected in parallel between the second resistor and the protective ground wire, and the method further includes: when the voltage output by the photovoltaic array is greater than the voltage threshold, controlling the second switch to be in a closed state and controlling the first switch to be in an open state to obtain a first negative bus voltage. After obtaining the first negative bus voltage, controlling the first switch to be in a closed state and controlling the second switch to be in an open state to obtain a second negative bus voltage.

[0024] In a third aspect of the embodiment of the present application, a photovoltaic power generation system is provided, which includes a photovoltaic energy storage inverter and an energy storage device connected to the photovoltaic energy storage inverter. The photovoltaic energy storage inverter includes a Boost circuit, a first resistor, a second resistor, a DC bus positive pole, a DC bus negative pole, an inverter circuit and a controller. The input of the Boost circuit is used to connect to the photovoltaic array, the output of the Boost circuit is connected to the DC bus positive pole and the DC bus negative pole, the first resistor and the second resistor are connected in series between the DC bus positive pole and the DC bus negative pole, the connection point of the first resistor and the second resistor is used to connect to the protective ground wire, the input of the inverter circuit is connected to the DC bus positive pole and the DC bus negative pole, and the output of the inverter circuit is used to connect to the power grid. The DC bus positive pole and the DC bus negative pole are also used to connect the positive pole and the negative pole of the energy storage device. The controller is used to control the switch tube in the Boost circuit to be in a conducting state when the voltage output by the photovoltaic array is less than or equal to the voltage threshold and the energy storage device outputs voltage to the DC bus positive pole and the DC bus negative pole. The controller is also used to obtain the bus voltage and the negative bus voltage. The bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus. The controller is also used to control the output of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to the proportional threshold. The positive bus voltage is the difference between the bus voltage and the negative bus voltage. The controller is also used to control the output of the inverter circuit to disconnect from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than the proportional threshold.

[0025] In combination with the third aspect, in a possible implementation, the controller is specifically used to obtain the bus voltage and the negative bus voltage when the on-time of the switch tube in the Boost circuit is greater than or equal to the time threshold.

[0026] In combination with the third aspect, in a possible implementation method, the controller is specifically used to obtain the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and to obtain the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold.

[0027] In conjunction with the third aspect, in a possible implementation, the photovoltaic energy storage inverter further includes a third resistor and a first switch that are arranged in parallel and connected between the first resistor and the protective ground wire. The controller is also used to control the first switch to be in a closed state when the switch tube in the Boost circuit is in a conducting state.

[0028] In combination with the third aspect, in a possible implementation, the photovoltaic energy storage inverter further includes a fourth resistor and a second switch connected in parallel between the second resistor and the protective ground wire. The controller is also used to control the second switch to be in a closed state and the first switch to be in an open state when the voltage output by the photovoltaic array is greater than the voltage threshold, so as to obtain the first negative bus voltage. After obtaining the first negative bus voltage, the first switch is controlled to be in a closed state and the second switch is controlled to be in an open state to obtain the second negative bus voltage.

[0029] The description of the second and third aspects in this application can refer to the detailed description of the first aspect; and the beneficial effects of the second and third aspects can refer to the analysis of the beneficial effects of the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of an application scenario of a photovoltaic energy storage inverter provided in an embodiment of the present application;

[0031] Figure 2 is an equivalent circuit diagram of a pure light inverter;

[0032] Figure 3 is an equivalent circuit diagram of a photovoltaic energy storage inverter;

[0033] Figure 4 An equivalent circuit diagram of a photovoltaic energy storage inverter provided in an embodiment of the present application;

[0034] Figure 5 An equivalent circuit diagram of another photovoltaic energy storage inverter provided in an embodiment of the present application;

[0035] Figure 6 An equivalent circuit diagram of another photovoltaic energy storage inverter provided in an embodiment of the present application;

[0036] Figure 7 An equivalent circuit diagram of another photovoltaic energy storage inverter provided in an embodiment of the present application;

[0037] Figure 8 An equivalent circuit diagram of another photovoltaic energy storage inverter provided in an embodiment of the present application;

[0038] Fig. 9 A schematic diagram of a flow chart of an insulation impedance detection method provided in an embodiment of the present application;

[0039] Fig.10 A flowchart of another insulation impedance detection method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0040] The following will discuss the making and use of each embodiment in detail. However, it should be understood that many applicable inventive concepts provided by this application can be implemented in a variety of specific environments. The specific embodiments discussed are only used to illustrate the specific ways to implement and use this description and this technology, and do not limit the scope of this application.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0042] Various circuits or other components may be described or referred to as being "configured to" perform one or more tasks. In this case, "configured to" is used to imply structure by indicating that the circuit / component includes structure (e.g., circuitry) that performs the one or more tasks during operation. Thus, even when the specified circuit / component is not currently operational (e.g., not turned on), the circuit / component may be referred to as being configured to perform the task. Circuits / components used with the phrase "configured to" include hardware, such as circuits that perform an operation, etc.

[0043] The technical scheme in the embodiment of the present application will be described below in conjunction with the accompanying drawings in the embodiment of the present application. In the present application, "at least one" refers to one or more, and "multiple" refers to two or more. "And / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or its similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c or a, b and c, where a, b and c can be single or multiple. In addition, in the embodiment of the present application, the words "first", "second" and the like do not limit the quantity and order.

[0044] In this application, the words "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the words "exemplary" or "for example" is intended to present the related concepts in a concrete way.

[0045] Before introducing the embodiments of the present application, the technical terms and background technologies involved in the present application are first introduced.

[0046] Photovoltaic (PV) module: A device used to convert solar energy into electrical energy.

[0047] Photovoltaic array: A photovoltaic array includes at least one photovoltaic component. When a photovoltaic array includes multiple photovoltaic components, the multiple photovoltaic components can be connected in series, or connected in parallel, or some of the multiple photovoltaic components can be connected in series and the rest can be connected in parallel.

[0048] Grid connection: Technically, it refers to the physical connection between a generator set or power plant (field, station) or direct dispatch user and the power grid. Management-wise, it refers to the establishment of a dispatch relationship between it and the power grid dispatching organization.

[0049] Protective earth (PE): A protective earth wire is a safety conductor, also known as a ground wire. It is used to connect the metal casing of electrical equipment or other potentially energized parts to the ground wire to prevent electric shock accidents.

[0050] Analog ground (AGND): used for grounding analog circuits, providing a stable reference point for analog signals.

[0051] Pure solar inverter: This pure solar inverter is used to connect to the photovoltaic array, receive the DC power provided by the photovoltaic array, convert the DC power into AC power and transmit it to the grid or load. This pure solar inverter operates in grid connection during the day.

[0052] Photovoltaic energy storage inverter: It can also be referred to as a photovoltaic storage inverter. The photovoltaic energy storage inverter is used to connect the photovoltaic array and the energy storage device. When connected to the grid during the day, the photovoltaic energy storage inverter is used to receive the DC power provided by the photovoltaic array, convert the DC power into AC power and transmit it to the grid or load. When connected to the grid at night, the photovoltaic energy storage inverter is used to receive the DC power provided by the energy storage device, convert the DC power into AC power and transmit it to the grid or load.

[0053] Photovoltaic inverters include pure solar inverters and photovoltaic energy storage inverters, which are used in photovoltaic power generation systems. Figure 1 As shown, it is a schematic diagram of an application scenario of a photovoltaic energy storage inverter 100 provided in an embodiment of the present application. The photovoltaic energy storage inverter 100 is applied to a photovoltaic power generation system 200, and the photovoltaic power generation system 200 also includes an energy storage device 300 connected to the photovoltaic energy storage inverter 100, and the photovoltaic energy storage inverter 100 is used to connect to a first photovoltaic array 400, and the photovoltaic energy storage inverter 100 is also used to connect to a power grid / load 500.

[0054] During the day, when the first photovoltaic array 400 provides direct current to the photovoltaic energy storage inverter 100, the photovoltaic energy storage inverter 100 is used to convert the direct current into alternating current and transmit it to the grid / load 500. At night, when the energy storage device 300 provides direct current to the photovoltaic energy storage inverter 100, the photovoltaic energy storage inverter 100 is used to convert the direct current into alternating current and transmit it to the grid / load 500.

[0055] The IEC 62109-2 grid-connected standard requires that the insulation resistance of the photovoltaic array connected to the photovoltaic inverter to the ground is greater than or equal to the system maximum voltage Vmax / 30 milliamperes (mA). The system maximum voltage is the highest voltage level that needs to be considered when designing and testing the photovoltaic inverter. For example, for a single-phase photovoltaic inverter with a system maximum voltage of 600V, the insulation resistance of the photovoltaic array connected to the single-phase photovoltaic inverter to the ground needs to be greater than or equal to 20 (600 / 30) kilo-ohms (kΩ). For a three-phase photovoltaic inverter with a system maximum voltage of 1000V, the insulation resistance of the photovoltaic array connected to the three-phase photovoltaic inverter to the ground needs to be greater than or equal to 33.3 (1000 / 30) kΩ.

[0056] Since the more resistors are connected in parallel, the smaller the total resistance value, when the PV inverter is connected to the grid, the parallel impedance to ground of the PV inverter and the PV array (also called equivalent impedance to ground) can be regarded as the insulation impedance to ground of the PV array. When the parallel impedance to ground meets the requirements of the insulation impedance to ground in the IEC 62109-2 grid-connected standard, the insulation impedance to ground of the PV array will also meet the requirements of the insulation impedance to ground in the IEC 62109-2 grid-connected standard. It is possible to determine whether the PV inverter meets the grid-connected standard based on the parallel impedance to ground of the PV inverter and the PV array.

[0057] The positive and negative poles of the photovoltaic modules in the photovoltaic array are insulated from the protective ground wire. The impedance between the positive and negative poles of the photovoltaic modules and the protective ground wire is generally greater than or equal to 40 megohms (MΩ). The impedance between the positive and negative poles of the photovoltaic modules and the protective ground wire can also be called the insulation impedance of the photovoltaic modules to the ground. As the number of photovoltaic modules in series or parallel in the photovoltaic array increases, which can also be called the increase in the number of photovoltaic module cascades, the insulation impedance of the photovoltaic modules to the ground will decrease slightly, which will cause the insulation impedance of the photovoltaic array to the ground to decrease slightly. When the photovoltaic modules in the photovoltaic array are cracked, the sealing is poor and water enters, the insulation cables are aged, or the poor construction quality causes leakage in the connection cables of the photovoltaic modules, the insulation impedance of the photovoltaic modules to the ground will decrease significantly, resulting in a significant decrease in the insulation impedance of the photovoltaic array to the ground. When the insulation impedance of the photovoltaic array to the ground decreases significantly, the parallel impedance of the photovoltaic inverter and the photovoltaic array to the ground will decrease significantly, and the leakage current in the photovoltaic inverter will increase. When the leakage current in the photovoltaic inverter increases, the possibility of damage to the photovoltaic inverter will increase, resulting in a decrease in the efficiency of the photovoltaic inverter. Therefore, the controller in the photovoltaic inverter needs to detect the parallel impedance to ground of the photovoltaic inverter and the photovoltaic array before the photovoltaic inverter is connected to the grid or during the power-on self-test. When the parallel impedance to ground of the photovoltaic inverter and the photovoltaic array does not meet the requirements of the insulation impedance to ground in the IEC 62109-2 grid-connection standard, the photovoltaic inverter is controlled not to be connected to the grid, thereby improving the safety of the photovoltaic inverter, avoiding damage to the photovoltaic inverter, and preventing the photovoltaic inverter from being connected to the grid at a lower efficiency.

[0058] like Figure 2 The figure shows an equivalent circuit diagram of a pure light inverter 600 . The pure light inverter 600 includes a Boost circuit 610 , a first resistor R1 , a second resistor R2 , a third resistor R3 , a fourth resistor R4 , a first relay K1 , a second relay K2 and an inverter circuit 620 .

[0059] The two input terminals of the boost circuit 610 are used to connect the positive and negative electrodes of the first photovoltaic array 400, the two output terminals of the boost circuit 610 are respectively connected to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the two input terminals of the inverter circuit 620 are respectively connected to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the output terminal of the inverter circuit 620 is used to connect to the power grid / load 500, and the DC bus negative electrode BUS- can also be used as a simulated ground. The insulation impedance of the first photovoltaic array 400 to the ground is equivalent to the fifth resistor R5 and the sixth resistor R6 connected in parallel with the first photovoltaic array 400, and the connection point of the fifth resistor R5 and the sixth resistor R6 is equivalent to being connected to the protective ground wire PE.

[0060] The boost circuit 610 includes a capacitor C, an inductor L, a diode D and a switch tube Q. The connection relationship of the components in the boost circuit 610 can be referred to Figure 2 The circuit topology of the Boost circuit in the prior art is not described in detail in the embodiments of the present application.

[0061] One end of the first resistor R1 is connected to the DC bus positive electrode BUS+, the other end of the first resistor R1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to the protective ground line PE, and the first relay K1 is connected in parallel with the second resistor R2. One end of the third resistor R3 is connected to the protective ground line PE, the other end of the third resistor R3 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is connected to the DC bus negative electrode BUS-, and the second relay K2 is connected in parallel with the third resistor R3.

[0062] Reference Figure 1 The resistor R0 is the equivalent resistance of the remaining circuits in the pure light inverter 600, except the Boost circuit 610, the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the first relay K1 and the second relay K2. One end of the resistor R0 is connected to the protective ground wire PE, and the other end of the resistor R0 is connected to the negative electrode BUS- of the DC bus.

[0063] The resistance values ​​of the resistor R0, the first resistor R1 to the fourth resistor R4 in the pure solar inverter 600 can be determined in advance by detection or experiment, etc. The first resistor R1 to the fourth resistor R4, the first relay K1 and the second relay K2 are used to detect the parallel impedance to ground of the pure solar inverter 600 and the first photovoltaic array 400, or the insulation impedance to ground of the first photovoltaic array 400.

[0064] Specifically, when the first relay K1 is disconnected and the second relay K2 is closed, the fifth resistor R5 and the sixth resistor R6 of the first photovoltaic array 400 satisfy the following formula:

[0065]

[0066] Among them, U PVA is the output voltage of the first photovoltaic array 400, the first voltage U1 is the voltage between the protective ground wire PE and the negative pole of the DC bus BUS- when the first relay K1 is disconnected and the second relay K2 is closed, U BUS is the bus voltage between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, R0 to R2 and R4 to R6 represent the resistance value of each resistor, and “ / / ” indicates calculation according to the resistor parallel formula.

[0067] When the first relay K1 is closed and the second relay K2 is open, the insulation impedance of the first photovoltaic array 400 to ground, the fifth resistor R5 and the sixth resistor R6, satisfy the following formula:

[0068]

[0069] The second voltage U2 is the voltage between the protective ground wire PE and the negative electrode BUS- of the DC bus when the first relay K1 is closed and the second relay K2 is opened, and R3 represents the resistance value of the third resistor R3.

[0070] By combining the above two equations, the sum of the reciprocal of the fifth resistor R5 and the reciprocal of the sixth resistor R6 of the ground insulation impedance of the first photovoltaic array 400 can be obtained, which satisfies the following formula:

[0071]

[0072] According to this formula, the insulation resistance of the first photovoltaic array 400 to the ground can be obtained.

[0073] The parallel impedance to ground of the pure solar inverter 600 and the first photovoltaic array 400 satisfies the following formula:

[0074]

[0075] Wherein, R100 is the parallel impedance of the pure solar inverter 600 and the first photovoltaic array 400 to the ground.

[0076] According to the above two formulas, it can be understood that the controller in the pure solar inverter 600 first obtains the bus voltage U BUS , the first voltage U1 and the second voltage U2, and then use the above two formulas, according to the resistance values ​​of the resistor R0, the first resistor R1 to the fourth resistor R4, and the bus voltage U BUS , the first voltage U1 and the second voltage U2 are calculated, and the inverse of the calculated result can be taken to determine the parallel impedance R100 to the ground of the pure light inverter 600 and the first photovoltaic array 400. When the parallel impedance R100 to the ground does not meet the requirements of the insulation impedance to the ground corresponding to the pure light inverter 600 in the IEC 62109-2 grid-connected standard, the controller in the pure light inverter 600 controls the pure light inverter 600 not to be grid-connected, thereby improving the safety of the pure light inverter 600, avoiding damage to the pure light inverter 600, and avoiding the pure light inverter 600 from being grid-connected at a lower efficiency.

[0077] However, when the resistance value of the fifth resistor R5 of the first photovoltaic array 400 is small, the output voltage U PVA will be very close to the first voltage U1 / second voltage U2 mentioned above. PVA-U1) and (U PVA -U2) is close to 0, and there are inevitable detection errors in the actual voltage detection process. When the above method is used to detect the parallel impedance to ground R100, a very large error will be generated. At the same time, for the scenario where the photovoltaic energy storage inverter is powered on for self-test at night, the above-mentioned method of detecting the parallel impedance to ground R100 when the first photovoltaic array 400 has a stable output voltage is used. When the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array is detected at night, there are problems of inaccurate detection and long detection time. When the photovoltaic energy storage inverter is controlled to be connected to the grid based on the parallel impedance to ground of the photovoltaic energy storage inverter and the photovoltaic array obtained by the detection, the safety of the photovoltaic energy storage inverter is poor, and the photovoltaic energy storage inverter may be damaged, or connected to the grid with lower efficiency.

[0078] Specifically, Figure 3 FIG. 7 is an equivalent circuit diagram of a photovoltaic energy storage inverter 700. Figure 2 The equivalent circuit of the pure solar inverter 600 shown is the same, and the embodiments of the present application will not be repeated here. The circuit topology of the photovoltaic energy storage inverter 700 is different from the circuit topology of the above-mentioned pure solar inverter 600 in that the DC bus positive pole BUS+ and the DC bus negative pole BUS- in the photovoltaic energy storage inverter 700 are also used to connect with the positive pole and negative pole of the energy storage device 300 to obtain the DC power provided by the energy storage device 300 at night.

[0079] When the photovoltaic energy storage inverter 700 is powered on for self-test at night, the first photovoltaic array 400 will have no output voltage or output a relatively small voltage. When the first photovoltaic array 400 has a stable output voltage, the method of detecting the parallel impedance R100 to the ground is adopted. When the photovoltaic energy storage inverter 700 and the first photovoltaic array 400 are powered on for self-test at night, the parallel impedance R200 to the ground is detected, which includes the following process:

[0080] Reference Figure 3 When the first relay K1 is closed and the second relay K2 is open, the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- will charge the capacitor C. Figure 3 As shown in the loop P in FIG. 1 , the current outputted from the DC bus positive electrode BUS+ will sequentially pass through the first resistor R1 , the first relay K1 , the fifth resistor R5 and the capacitor C to the DC bus negative electrode BUS-, thereby charging the capacitor C.

[0081] However, when the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- charge the capacitor C, the voltage of the first photovoltaic array 400 will be unstable, resulting in the voltage between the protective ground wire PE and the DC bus negative electrode BUS- being unstable, and it will take a long time to recover stability. Taking the charging circuit of capacitor C as an example when the first relay K1 is closed and the second relay K2 is disconnected, since the time constant of the charging circuit is (R1+R5)×C, the capacitance of capacitor C is large, and the time constant of the charging circuit is large, it will take a long time for the voltage of the first photovoltaic array 400 to recover stability. If the voltage between the protective ground wire PE and the DC bus negative electrode BUS- when the voltage of the first photovoltaic array 400 is not stable is used to calculate the parallel impedance R200 to the ground of the photovoltaic energy storage inverter 700 and the first photovoltaic array 400, the parallel impedance R200 to the ground cannot be accurately detected. If the voltage between the protection ground wire PE and the negative pole of the DC bus BUS- is used to calculate the parallel impedance R200 to the ground after the voltage of the first photovoltaic array 400 is stabilized, it will take a long time to complete the impedance detection.

[0082] In summary, when the first photovoltaic array 400 has a stable output voltage, the method of detecting the parallel impedance to the ground R100 is adopted. At night, when the first photovoltaic array 400 has no output voltage or outputs a small voltage, when the photovoltaic energy storage inverter 700 and the parallel impedance to the ground R200 of the first photovoltaic array 400 are detected, there are problems of inaccurate impedance detection and long detection time. When the photovoltaic energy storage inverter 700 is controlled to be connected to the grid according to the parallel impedance to the ground R200, the safety of the photovoltaic energy storage inverter 700 is poor, and the photovoltaic energy storage inverter 700 may be damaged, or connected to the grid with lower efficiency.

[0083] In order to solve this problem, the embodiment of the present application provides a photovoltaic energy storage inverter, which is powered on and self-checked at night. When the photovoltaic energy storage inverter and the photovoltaic array are detected in parallel to the ground, less voltage needs to be detected, thereby improving the detection accuracy of the photovoltaic energy storage inverter and the photovoltaic array in parallel to the ground. According to the photovoltaic energy storage inverter and the photovoltaic array in parallel to the ground impedance, when the photovoltaic energy storage inverter is controlled to be connected to the grid, the safety of the photovoltaic energy storage inverter can be improved, damage to the photovoltaic energy storage inverter can be avoided, or the photovoltaic energy storage inverter can be connected to the grid at a lower efficiency. At the same time, the loop time constant during detection is small, which can reduce the detection time.

[0084] like Figure 4 , which is an equivalent circuit diagram of a photovoltaic energy storage inverter 100 provided in an embodiment of the present application. The photovoltaic energy storage inverter 100 includes a Boost circuit 110, a first resistor R1, a second resistor R2, a DC bus positive electrode BUS+, a DC bus negative electrode BUS-, an inverter circuit 120 and a controller 130.

[0085] The input of the boost circuit 110 is used to connect the first photovoltaic array 400, the output of the boost circuit 110 is connected to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the first resistor R1 and the second resistor R2 are connected in series between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the connection point of the first resistor R1 and the second resistor R2 is used to connect to the protective ground wire PE, the input of the inverter circuit 120 is connected to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, and the output of the inverter circuit 120 is used to connect to the power grid / load 500. The DC bus positive electrode BUS+ and the DC bus negative electrode BUS- are also used to connect the positive electrode and the negative electrode of the energy storage device 300. The insulation impedance of the first photovoltaic array 400 to the ground is equivalent to the fifth resistor R5 and the sixth resistor R6 connected in parallel with the first photovoltaic array 400, and the connection point of the fifth resistor R5 and the sixth resistor R6 is equivalent to being connected to the protective ground wire PE.

[0086] Reference Figure 4 The boost circuit 110 includes a capacitor C, an inductor L, a diode D and a switch tube Q. The connection relationship of the components in the boost circuit 110 can be referred to Figure 4 The circuit topology of the Boost circuit in the prior art is not described in detail in the embodiments of the present application.

[0087] Optionally, the switch tube Q includes an insulate-gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET), which is not limited in the present embodiment. Figure 4 In the embodiment of the present application, an example is given for illustrative description by taking the switch tube Q including a metal oxide semiconductor field effect transistor.

[0088] Reference Figure 4 , the resistor R0 is the equivalent resistance of the remaining circuits in the photovoltaic energy storage inverter 100 except the Boost circuit 110, the first resistor R1 and the second resistor R2. One end of the resistor R0 is connected to the protective ground wire PE, and the other end of the resistor R0 is connected to the negative pole BUS- of the DC bus. Among them, the resistance values ​​of the resistor R0, the first resistor R1 and the second resistor R2 can be determined in advance by detection or experiment. The resistor R0, the first resistor R1 and the second resistor R2 are used to detect the parallel impedance to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400.

[0089] When the photovoltaic energy storage inverter 100 is powered on and self-checked at night, the voltage output by the first photovoltaic array 400 is less than or equal to the voltage threshold, and the energy storage device 300 outputs voltage to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the controller 130 is used to control the switch tube Q in the Boost circuit 110 to be in the on state, and the specific value of the voltage threshold is not limited in the embodiment of the present application. Thus, it can be avoided that when the voltage or current of the DC power output by the first photovoltaic array 400 is large, the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state, resulting in a short circuit between the positive and negative electrodes of the first photovoltaic array 400, and further causing damage to the switch tube or other devices, which can improve the reliability of the photovoltaic energy storage inverter 100.

[0090] At this time, if Figure 4 As shown in the loop T in FIG, the current output from the DC bus positive electrode BUS+ first passes through the first resistor R1, and then a part of the current passes through the fifth resistor R5, the inductor L and the switch tube Q to the DC bus negative electrode BUS-, and the other part of the current passes through the sixth resistor R6 to the DC bus negative electrode BUS-. The fifth resistor R5 and the sixth resistor R6 are equivalently connected in parallel between the protective ground wire PE and the DC bus negative electrode BUS-. Figure 5 The insulation impedance of the first photovoltaic array 400 to the ground can be equivalent to a resistor Rm, and the resistance value of Rm satisfies the formula Rm=R5 / / R6, where Rm, R5 and R6 represent the resistance values ​​of each resistor.

[0091] Continue to refer to Figure 5 , at this time, the first parallel impedance to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 satisfies the following formula:

[0092] Z1=R1 / / R1*V PE / (V BUS -V PE )

[0093] Wherein, Z1 is the first parallel impedance to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, R1 is the resistance value of the first resistor R1, V BUS is the bus voltage, the bus voltage V BUS is the absolute value of the voltage difference between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, V PE is the negative bus voltage, the negative bus voltage V PE It is the absolute value of the voltage difference between the protective ground wire PE and the negative pole of the DC bus BUS-.

[0094] It can be understood that the controller 130 obtains and calculates the bus voltage V BUS and negative bus voltage V PE, the first parallel impedance Z1 to ground can be determined, and the controller 130 can control the photovoltaic energy storage inverter 100 to be connected to the grid according to the first parallel impedance Z1 to ground, or control the photovoltaic energy storage inverter 100 not to be connected to the grid. Since the resistance value of the first resistor R1 is fixed, the negative bus voltage V PE The ratio of the positive bus voltage to the positive bus voltage can be equivalent to the first parallel impedance Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 to the ground. The controller 130 can also be based on the negative bus voltage V PE The ratio of the positive bus voltage to the positive bus voltage controls the photovoltaic energy storage inverter 100 to be connected to the grid, or controls the photovoltaic energy storage inverter 100 not to be connected to the grid. The positive bus voltage is the bus voltage V BUS and negative bus voltage V PE The controller 130 obtains the bus voltage V BUS and negative bus voltage V PE The specific process can refer to the prior art, and the embodiments of the present application are not limited to this.

[0095] In a possible embodiment, the controller 130 is further configured to: PE When the ratio of the positive bus voltage V is greater than or equal to the ratio threshold, the output of the inverter circuit 120 is controlled to establish a connection with the grid / load 500 to control the photovoltaic energy storage inverter 100 to be connected to the grid. The controller 130 is also used to connect the negative bus voltage V PE When the ratio of the positive bus voltage to the positive bus voltage is less than the proportional threshold, the output of the inverter circuit 120 is controlled to be disconnected from the grid / load 500 to control the photovoltaic energy storage inverter 100 not to be grid-connected. The specific value of the proportional threshold is not limited in the embodiment of the present application. The proportional threshold is related to the insulation impedance requirement corresponding to the photovoltaic energy storage inverter 100 in the IEC62109-2 grid-connected standard, so that the controller 130 controls the output of the inverter circuit 120 to be disconnected from the grid / load 500 according to the negative bus voltage V PE The ratio of the positive bus voltage and the proportional threshold value can improve the safety of the photovoltaic energy storage inverter 100 when controlling the photovoltaic energy storage inverter 100 to be connected to the grid, avoid damage to the photovoltaic energy storage inverter 100, and avoid the photovoltaic energy storage inverter 100 being connected to the grid with lower efficiency.

[0096] In one possible embodiment, referring to Figure 5 Since the resistance values ​​of the resistor R0, the first resistor R1 and the second resistor R2 are known, the insulation impedance to ground of the first photovoltaic array 400 can also be determined according to the first parallel impedance to ground Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, and the resistance values ​​of the resistor R0, the first resistor R1 and the second resistor R2. The controller 130 can control the photovoltaic energy storage inverter 100 to be connected to the grid according to the insulation impedance to ground of the first photovoltaic array 400.

[0097] It can be understood that, in the above-mentioned method of detecting the parallel impedance R100 to the ground when the first photovoltaic array 400 has a stable output voltage, when the self-check is started at night and the parallel impedance R200 to the ground of the photovoltaic energy storage inverter 700 and the first photovoltaic array 400 is detected, the controller in the photovoltaic energy storage inverter 700 needs to obtain the bus voltage U BUS , the first voltage U1 and the second voltage U2 are compared. In the embodiment of the present application, the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE , the first parallel impedance Z1 to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 is determined according to the two voltages and the resistance value of the first resistor R1. There are inevitable errors in the process of each voltage detection, and the voltages that need to be detected in the present application are less, so the detection accuracy of the first parallel impedance Z1 to ground can be improved. At the same time, compared with the above-mentioned detection of the parallel impedance to ground R200, when the first relay K1 is closed and the second relay K2 is disconnected, the time constant of the charging circuit is (R1+R5)×C. In the embodiment of the present application, when the self-test is started at night and the first parallel impedance Z1 to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 is detected, the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state, and the capacitance between the positive pole BUS+ of the DC bus and the negative pole BUS- of the DC bus and the protective ground wire PE is smaller, and the time constant is smaller, so that the bus voltage V BUS and negative bus voltage V PE It can be stabilized faster, and the controller 130 can use less time to determine the first parallel impedance Z1 to the ground, and the detection time is shorter.

[0098] In a possible embodiment, the controller 130 is specifically configured to: when the on-time of the switch tube Q in the Boost circuit 110 is greater than or equal to the time threshold, obtain the bus voltage V BUS and negative bus voltage V PE , the embodiment of the present application does not limit the specific value of the time threshold. Thus, the controller 130 can obtain a more stable bus voltage V BUS and negative bus voltage V PE , the controller 130 can more accurately determine the first parallel impedance Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 to ground, or more accurately determine the negative bus voltage V PE and the positive bus voltage.

[0099] In a possible embodiment, the controller 130 is specifically configured to: when the voltage fluctuation between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- is less than or equal to the bus voltage fluctuation threshold, obtain the bus voltage V BUS, when the voltage fluctuation between the protective ground wire PE and the DC bus negative pole BUS- is less than or equal to the negative bus voltage fluctuation threshold, obtain the negative bus voltage V PE , the embodiment of the present application does not limit the specific values ​​of the bus voltage fluctuation threshold and the negative bus voltage fluctuation threshold. Thus, the controller 130 can obtain a more stable bus voltage V BUS and negative bus voltage V PE , the controller 130 can more accurately determine the first parallel impedance Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 to ground, or more accurately determine the negative bus voltage V PE and the positive bus voltage.

[0100] In a possible embodiment, the controller 130 is specifically used to: when the on-time of the switch tube Q in the Boost circuit 110 is greater than or equal to the time threshold, and the voltage fluctuation between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- is less than or equal to the bus voltage fluctuation threshold, obtain the bus voltage V BUS When the voltage fluctuation between the protective ground wire PE and the DC bus negative pole BUS- is less than or equal to the negative bus voltage fluctuation threshold, the negative bus voltage V is obtained. PE Thus, the controller 130 can obtain a more stable bus voltage V BUS and negative bus voltage V PE , the controller 130 can more accurately determine the first parallel impedance Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 to ground, or more accurately determine the negative bus voltage V PE and the positive bus voltage.

[0101] In a possible embodiment, the photovoltaic energy storage inverter 100 may include a Boost circuit 110, or may include multiple Boost circuits 110, and the multiple Boost circuits 110 are used to connect to multiple photovoltaic arrays. The embodiment of the present application does not limit the specific number of Boost circuits 110 included in the photovoltaic energy storage inverter 100. Figure 6In (a), the embodiment of the present application takes the photovoltaic energy storage inverter 100 including two Boost circuits 110, wherein the two input ends of one Boost circuit 110 are used to connect to the positive and negative poles of the first photovoltaic array 400, and the two input ends of the other Boost circuit 110 are used to connect to the positive and negative poles of the second photovoltaic array 800, and the two output ends of the two Boost circuits 110 are respectively connected to the positive pole BUS+ of the DC bus and the negative pole BUS- of the DC bus, as an example for exemplary description. The insulation impedance of the second photovoltaic array 800 to the ground is equivalent to the seventh resistor R7 and the eighth resistor R8 connected in parallel with the second photovoltaic array 800, and the connection point of the seventh resistor R7 and the eighth resistor R8 is equivalent to being connected to the protective ground wire PE.

[0102] When the photovoltaic energy storage inverter 100 includes two Boost circuits 110, the photovoltaic energy storage inverter 100 is powered on for self-test at night, and the energy storage device 300 outputs voltage to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the controller 130 is used to control the switch tubes Q in the two Boost circuits 110 to be in the on state. Figure 6 As shown in the loop J in (a), the fifth resistor R5 and the sixth resistor R6 are equivalently connected in parallel between the protection ground wire PE and the negative pole of the DC bus BUS-, and the seventh resistor R7 and the eighth resistor R8 are equivalently connected in parallel between the protection ground wire PE and the negative pole of the DC bus BUS-. Figure 6 In (b), the insulation impedance of the two photovoltaic arrays to the ground can be equivalent to a resistor Rn, and the resistance value of the resistor Rn satisfies the formula Rn=R5 / / R6 / / R7 / / R8, where R5 to R8 represent the resistance values ​​of each resistor.

[0103] Continue to refer to Figure 6 , at this time, the second parallel impedance to ground of the photovoltaic energy storage inverter 100, the first photovoltaic array 400 and the second photovoltaic array 800 satisfies the following formula:

[0104] Z2=R1 / / R1*V PE1 / (V BUS -V PE1 )

[0105] Wherein, Z2 is the second parallel impedance to ground of the photovoltaic energy storage inverter 100, the first photovoltaic array 400 and the second photovoltaic array 800, R1 is the resistance value of the first resistor R1, and the bus voltage V BUS This is the absolute value of the voltage difference between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- at this time, the negative bus voltage V PE1 The absolute value of the voltage difference between the protective ground wire PE and the negative pole BUS- of the DC bus at this time. It can be understood that the controller 130 obtains the bus voltage V BUSand negative bus voltage V PE1 , and according to the bus voltage V BUS and negative bus voltage V PE1 The resistance value of the first resistor R1 and the resistance value of the first resistor R1 can determine the second parallel impedance Z2 to the ground of the photovoltaic energy storage inverter 100, the first photovoltaic array 400 and the second photovoltaic array 800 at this time. The controller 130 can control the photovoltaic energy storage inverter 100 to be connected to the grid according to the second parallel impedance Z2 to the ground, or control the photovoltaic energy storage inverter 100 not to be connected to the grid. Since the resistance value of the first resistor R1 is fixed, the controller 130 can also control the photovoltaic energy storage inverter 100 to be connected to the grid according to the ratio of the negative bus voltage VPE to the positive bus voltage, or control the photovoltaic energy storage inverter 100 not to be connected to the grid, and the positive bus voltage is the difference between the bus voltage VBUS and the negative bus voltage VPE.

[0106] When the photovoltaic energy storage inverter 100 includes more Boost circuits 110, and the more Boost circuits 110 are respectively connected to multiple photovoltaic arrays, when the photovoltaic energy storage inverter 100 is powered on for self-test at night, the process of the controller 130 determining the parallel impedance to ground of the photovoltaic energy storage inverter 100 and multiple photovoltaic arrays can refer to the above description, and the embodiments of the present application will not be repeated here.

[0107] In the photovoltaic energy storage inverter 100 provided in the embodiment of the present application, when the first photovoltaic array 400 has a stable output voltage, the parallel impedance R100 to the ground is detected. When the photovoltaic energy storage inverter 700 and the first photovoltaic array 400 are detected during the self-test at night, the controller in the photovoltaic energy storage inverter 700 needs to obtain the bus voltage U BUS , the first voltage U1 and the second voltage U2 are compared, and the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE , since the resistance value of the first resistor R1 is fixed, the ratio of the negative bus voltage VPE to the positive bus voltage can be equivalent to the first parallel impedance to ground Z1. The controller 130 controls the photovoltaic energy storage inverter 100 to be connected to the grid according to the ratio of the negative bus voltage VPE to the positive bus voltage, which is equivalent to the controller 130 controlling the photovoltaic energy storage inverter 100 to be connected to the grid according to the first parallel impedance to ground Z1. There are inevitable errors in each voltage detection process, and the voltage that needs to be detected in the present application is less, so that the detection accuracy of the first parallel impedance to ground Z1 can be improved. At the same time, compared with the above-mentioned detection of the parallel impedance to ground R200, when the first relay K1 is closed and the second relay K2 is disconnected, the time constant of the charging circuit is (R1+R5)×C. In the embodiment of the present application, when the power-on self-test is performed at night and the first parallel impedance to ground Z1 is detected, the capacitance between the positive pole of the DC bus BUS+ and the negative pole of the DC bus BUS- and the protective ground wire PE is smaller, and the time constant is smaller, so that the bus voltage VBUS and negative bus voltage V PE It can be stabilized faster, the controller 130 can use less time to determine the ratio of the negative bus voltage VPE to the positive bus voltage, and can use less time to determine the first parallel impedance Z1 to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, and the detection time is shorter. Therefore, when the controller 130 controls the photovoltaic energy storage inverter 100 to be connected to the grid according to the ratio of the negative bus voltage VPE to the positive bus voltage, it can improve the safety of the photovoltaic energy storage inverter 100, improve the grid connection speed or startup speed of the photovoltaic energy storage inverter 100, and avoid damage to the photovoltaic energy storage inverter 100, or connect to the grid with lower efficiency.

[0108] In a possible embodiment, in addition to requiring that the insulation impedance of the photovoltaic array connected to the photovoltaic inverter is greater than or equal to the system maximum voltage Vmax / 30mA, the IEC 62109-2 grid-connected standard also requires the detection accuracy of the insulation impedance of the photovoltaic array to the ground when it is near Vmax / 30mA. According to the formula satisfied by the above-mentioned first parallel impedance to the ground Z1, when the insulation impedance of the first photovoltaic array 400 to the ground is near Vmax / 30mA, and the resistance value of the first resistor R1 is large, and there is an order of magnitude difference between the resistance value of the first resistor R1 and the insulation impedance of the first photovoltaic array 400 to the ground, when the resistance value of the first parallel impedance to the ground Z1 is determined according to the above formula, it will lead to a relatively large detection error. When the resistance value of the first resistor R1 is small, when the photovoltaic energy storage inverter 100 is grid-connected, the current flowing through the first resistor R1 is large, which will lead to high losses and low efficiency of the photovoltaic energy storage inverter 100.

[0109] To solve this problem, Figure 7 As shown, the photovoltaic energy storage inverter 100 provided in the embodiment of the present application further includes a third resistor R3 and a first switch Y1 which are arranged in parallel and connected between the first resistor R1 and the protective ground line PE.

[0110] When the photovoltaic energy storage inverter 100 is connected to the grid, the controller 130 controls the first switch Y1 to be in an off state, and the sum of the resistance values ​​of the first resistor R1 and the third resistor R3 is large, so that the current flowing through the first resistor R1 is small, which can reduce the loss of the photovoltaic energy storage inverter 100 and improve efficiency.

[0111] Reference Figure 7When the insulation impedance of the first photovoltaic array 400 to the ground is near Vmax / 30mA, and the resistance value of the first resistor R1 and the resistance value of the third resistor R3 (or the resistance value between the positive pole of the DC bus BUS+ and the protective ground wire PE) are orders of magnitude different from the insulation impedance of the first photovoltaic array 400 to the ground, it will lead to a large detection error and a low detection accuracy. When the photovoltaic energy storage inverter 100 is powered on for self-test at night, it is necessary to detect the first parallel impedance to ground Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400. When the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state, the controller 130 controls the first switch Y1 to be in the closed state. At this time, the third resistor R3 is short-circuited, and the resistance value of the first resistor R1 is small. The resistance value of the first resistor R1 is close to the insulation impedance to ground of the first photovoltaic array 400, and there is no extreme difference in quantity, thereby ensuring the detection accuracy of the first parallel impedance to ground Z1 when it is close to the insulation impedance to ground corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connected standard.

[0112] In a possible embodiment, when selecting specific resistance values ​​of the first resistor R1 and the third resistor R3, they can be selected according to the requirements of the insulation impedance to ground corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connected standard, thereby ensuring the detection accuracy of the first parallel impedance to ground Z1 when it is close to the requirements of the insulation impedance to ground corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connected standard.

[0113] Optionally, the type of the first switch Y1 includes a relay, an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor. The embodiment of the present application does not limit the specific type of the first switch Y1. The embodiment of the present application takes the first switch Y1 as a relay as an example for illustrative description.

[0114] In the photovoltaic energy storage inverter 100 provided in the embodiment of the present application, by setting a third resistor R3 and a first switch Y1 connected in parallel between the first resistor R1 and the protective ground wire PE, when the photovoltaic energy storage inverter 100 is connected to the grid, the controller 130 controls the first switch Y1 to be in an off state, so that the current flowing through the first resistor R1 is small, which can reduce the loss of the photovoltaic energy storage inverter 100 and improve efficiency. When the insulation impedance to ground of the first photovoltaic array 400 is near Vmax / 30mA, and the resistance value of the first resistor R1 and the resistance value of the third resistor R3 (or the resistance value between the DC bus positive electrode BUS+ and the protective ground wire PE) are orders of magnitude different from the insulation impedance to ground of the first photovoltaic array 400, it will lead to a large detection error and low detection accuracy. Therefore, when the photovoltaic energy storage inverter 100 is powered on for self-test at night, it is necessary to detect the first parallel impedance to ground Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400. When the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state, the controller 130 controls the first switch Y1 to be in the closed state. At this time, the third resistor R3 is short-circuited, and the resistance value of the first resistor R1 is small. The resistance value of the first resistor R1 is close to the insulation impedance to ground of the first photovoltaic array 400, and there is no extreme difference in quantity. Therefore, the detection accuracy of the first parallel impedance to ground Z1 can be ensured when it is close to the insulation impedance to ground requirement corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connected standard.

[0115] In a possible embodiment, Figure 8 As shown, the photovoltaic energy storage inverter 100 provided in the embodiment of the present application further includes a fourth resistor R4 and a second switch Y2 which are arranged in parallel and connected between the second resistor R2 and the protective ground wire PE.

[0116] When the photovoltaic energy storage inverter 100 is powered on and self-tested during the day, and the voltage output by the first photovoltaic array 400 is greater than the voltage threshold, the controller 130 is also used to control the second switch Y2 to be in a closed state and the first switch Y1 to be in an open state, and obtain the bus voltage V BUS , and the first negative bus voltage V between the protective ground wire PE and the negative pole of the DC bus BUS- PE2 . When obtaining the first negative bus voltage V PE2 Afterwards, the controller 130 is further used to control the first switch Y1 to be in a closed state and the second switch Y2 to be in an open state to obtain a second negative bus voltage V between the protective ground wire PE and the negative electrode BUS- of the DC bus. PE3 , the resistance of the first resistor R1, the resistance of the second resistor R2, the resistance of the third resistor R3, the resistance of the fourth resistor R4, the bus voltage V BUS , the first negative bus voltage V PE2 and the second negative bus voltage V PE3Used to determine the third parallel impedance Z3 to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400. Figure 2 and Figure 8 It can be understood that at this time, the equivalent circuit of the photovoltaic energy storage inverter 100 is the same as the equivalent circuit of the above-mentioned pure light inverter 600. The photovoltaic energy storage inverter 100 can adopt the method of detecting the parallel impedance R100 to the ground when the above-mentioned first photovoltaic array 400 has a stable output voltage, and detect the third parallel impedance Z3 to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 during the day. The specific process can refer to the specific process of detecting the parallel impedance R100 to the ground when the above-mentioned first photovoltaic array 400 has a stable output voltage, and the embodiments of the present application will not be repeated here.

[0117] Optionally, the type of the second switch Y2 includes a relay, an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor. The embodiment of the present application does not limit the specific type of the second switch Y2. The embodiment of the present application uses the second switch Y2 as a relay as an example for illustrative description.

[0118] In the photovoltaic energy storage inverter 100 provided in the embodiment of the present application, by providing a fourth resistor R4 and a second switch Y2 connected in parallel between the second resistor R2 and the protective ground wire PE, the photovoltaic energy storage inverter 100 can adopt the above-mentioned method of detecting the parallel impedance R100 to the ground when the first photovoltaic array 400 has a stable output voltage, and detect the third parallel impedance Z3 to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 during the day, so that the controller 130 can control the photovoltaic energy storage inverter 100 to be connected to the grid when the third parallel impedance Z3 to the ground meets the insulation impedance requirement corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connection standard, which can improve the safety of the photovoltaic energy storage inverter 100, avoid damage to the photovoltaic energy storage inverter 100, and avoid the photovoltaic energy storage inverter 100 being connected to the grid at a lower efficiency.

[0119] Based on this, Fig. 9 As shown, the embodiment of the present application further provides an insulation impedance detection method, which is applied to the above-mentioned photovoltaic energy storage inverter 100, and the method includes steps S901-S904.

[0120] SS901. When the voltage output by the first photovoltaic array 400 is less than or equal to the voltage threshold and the energy storage device 300 outputs voltage to the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state.

[0121] S902, the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE, bus voltage V BUS is the absolute value of the voltage difference between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS-, the negative bus voltage V PE It is the absolute value of the voltage difference between the protective ground wire PE and the negative pole of the DC bus BUS-.

[0122] In a possible embodiment, the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE , including: when the on-time of the switch tube Q in the Boost circuit 110 is greater than or equal to the time threshold, the controller 130 obtains the bus voltage VBUS and the negative bus voltage VPE, and the embodiment of the present application does not limit the specific value of the time threshold. Thus, the controller 130 can obtain a more stable bus voltage VBUS and a negative bus voltage VPE, and the controller 130 can more accurately determine the first parallel impedance Z1 to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, or more accurately determine the ratio of the negative bus voltage VPE to the positive bus voltage.

[0123] In a possible embodiment, the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE , including: when the voltage fluctuation between the DC bus positive pole BUS+ and the DC bus negative pole BUS- is less than or equal to the bus voltage fluctuation threshold, the controller 130 obtains the bus voltage VBUS, and when the voltage fluctuation between the protective ground wire PE and the DC bus negative pole BUS- is less than or equal to the negative bus voltage fluctuation threshold, the controller 130 obtains the negative bus voltage VPE. The embodiment of the present application does not limit the specific values ​​of the bus voltage fluctuation threshold and the negative bus voltage fluctuation threshold. Thus, the controller 130 can obtain a more stable bus voltage VBUS and a negative bus voltage VPE, and the controller 130 can more accurately determine the first parallel impedance Z1 to the ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, or more accurately determine the ratio of the negative bus voltage VPE to the positive bus voltage.

[0124] In a possible embodiment, the controller 130 obtains the bus voltage V BUS and negative bus voltage V PE, including: when the on-time of the switch tube Q in the Boost circuit 110 is greater than or equal to the time threshold, and the voltage fluctuation between the DC bus positive electrode BUS+ and the DC bus negative electrode BUS- is less than or equal to the bus voltage fluctuation threshold, the controller 130 obtains the bus voltage VBUS, and when the voltage fluctuation between the protection ground wire PE and the DC bus negative electrode BUS- is less than or equal to the negative bus voltage fluctuation threshold, the controller 130 obtains the negative bus voltage VPE. Thus, the controller 130 can obtain a more stable bus voltage VBUS and negative bus voltage VPE, and the controller 130 can more accurately determine the first parallel impedance Z1 to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, or more accurately determine the ratio of the negative bus voltage VPE to the positive bus voltage.

[0125] S903, at the negative bus voltage V PE When the ratio of the positive bus voltage is greater than or equal to the ratio threshold, the controller 130 controls the output of the inverter circuit 120 to establish a connection with the grid / load 500, and the positive bus voltage is the bus voltage V BUS and negative bus voltage V PE difference.

[0126] S904, at the negative bus voltage V PE When the ratio to the positive bus voltage is less than the ratio threshold, the controller 130 controls the output of the inverter circuit 120 to be disconnected from the power grid / load 500 .

[0127] When executing the above steps S903 and S904, the controller 130 can PE The relationship between the ratio of the positive bus voltage and the proportional threshold is selected to execute one of the steps.

[0128] The insulation impedance detection method provided in the embodiment of the present application is compared with the above-mentioned method of detecting the parallel impedance R100 to the ground when the first photovoltaic array 400 has a stable output voltage. When the photovoltaic energy storage inverter 700 and the first photovoltaic array 400 are powered on for self-test at night, the controller in the photovoltaic energy storage inverter 700 needs to obtain the bus voltage UBUS, the first voltage U1 and the second voltage U2. Compared with the controller 130 obtaining the bus voltage VBUS and the negative bus voltage VPE, due to the first voltage The resistance value of resistor R1 is fixed, and the ratio of the negative bus voltage VPE to the positive bus voltage can be equivalent to the first parallel impedance to ground Z1. The controller 130 controls the photovoltaic energy storage inverter 100 to be connected to the grid according to the ratio of the negative bus voltage VPE to the positive bus voltage, which is equivalent to the controller 130 controlling the photovoltaic energy storage inverter 100 to be connected to the grid according to the first parallel impedance to ground Z1. There are inevitable errors in each voltage detection process, and the voltages that need to be detected in the present application are fewer, thereby improving the detection accuracy of the first parallel impedance to ground Z1. At the same time, compared with the above-mentioned detection of the parallel impedance to ground R200, when the first relay K1 is closed and the second relay K2 is disconnected, the time constant (R1+R5)×C of the charging circuit, in the embodiment of the present application, when the power-on self-check is performed at night and the first parallel impedance to ground Z1 is detected, the capacitance between the positive pole BUS+ of the DC bus and the negative pole BUS- of the DC bus and the protective ground wire PE is smaller, and the time constant is smaller, so that the bus voltage VBUS and the negative bus voltage VPE can be stabilized faster, and the controller 130 can use less time to determine the ratio of the negative bus voltage VPE to the positive bus voltage, and can use less time to determine the first parallel impedance to ground Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400, and the detection time is shorter. Therefore, when the controller 130 controls the photovoltaic energy storage inverter 100 to be connected to the grid according to the ratio of the negative bus voltage VPE to the positive bus voltage, the safety of the photovoltaic energy storage inverter 100 can be improved, the grid-connected speed or startup speed of the photovoltaic energy storage inverter 100 can be improved, and damage to the photovoltaic energy storage inverter 100 can be avoided, or the photovoltaic energy storage inverter 100 can be connected to the grid at a lower efficiency.

[0129] In a possible embodiment, when the photovoltaic energy storage inverter 100 is as follows Figure 7 When the photovoltaic energy storage inverter 100 is shown, Fig.10 As shown, the method further includes step S905, which can be executed simultaneously with the above step S901.

[0130] S905 , the controller 130 controls the first switch Y1 to be in a closed state while controlling the switch tube Q in the Boost circuit 110 to be in an on state.

[0131] In the insulation impedance detection method provided in the embodiment of the present application, when the photovoltaic energy storage inverter 100 is connected to the grid, the controller 130 controls the first switch Y1 to be in an off state, so that the current flowing through the first resistor R1 is small, which can reduce the loss of the photovoltaic energy storage inverter 100 and improve efficiency. When the insulation impedance to ground of the first photovoltaic array 400 is near Vmax / 30mA, and the resistance value of the first resistor R1 and the resistance value of the third resistor R3 (or the resistance value between the DC bus positive electrode BUS+ and the protective ground wire PE) are orders of magnitude different from the insulation impedance to ground of the first photovoltaic array 400, it will result in a large detection error and a low detection accuracy. Therefore, when the photovoltaic energy storage inverter 100 is powered on for self-test at night, it is necessary to detect the first parallel impedance to ground Z1 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400. When the controller 130 controls the switch tube Q in the Boost circuit 110 to be in the on state, the controller 130 controls the first switch Y1 to be in the closed state. At this time, the third resistor R3 is short-circuited, and the resistance value of the first resistor R1 is small. The resistance value of the first resistor R1 is close to the insulation impedance to ground of the first photovoltaic array 400, and there is no extreme difference in quantity. Therefore, the detection accuracy of the first parallel impedance to ground Z1 can be ensured when it is close to the insulation impedance to ground requirement corresponding to the photovoltaic energy storage inverter 100 in the IEC 62109-2 grid-connected standard.

[0132] In a possible embodiment, when the photovoltaic energy storage inverter 100 is as follows Figure 8 When the photovoltaic energy storage inverter 100 is shown, Fig.10 As shown, the method further includes steps S906-S907. When the photovoltaic energy storage inverter 100 is powered on for self-test at night, the above steps S901-S905 can be executed. When the photovoltaic energy storage inverter 100 is powered on for self-test during the day, the steps S906-S907 can be executed.

[0133] S906: When the voltage output by the first photovoltaic array 400 is greater than the voltage threshold, the controller 130 controls the second switch Y2 to be in a closed state and the first switch Y1 to be in an open state, and obtains the bus voltage V BUS , and the first negative bus voltage V between the protective ground wire PE and the negative pole of the DC bus BUS- PE2 .

[0134] S907, obtaining the first negative bus voltage V PE2 Afterwards, the controller 130 controls the first switch Y1 to be in a closed state and controls the second switch Y2 to be in an open state to obtain a second negative bus voltage V between the protective ground line PE and the negative electrode BUS- of the DC bus. PE3 .

[0135] The resistance of the first resistor R1, the resistance of the second resistor R2, the resistance of the third resistor R3, the resistance of the fourth resistor R4, and the bus voltage V BUS , the first negative bus voltage V PE2 and the second negative bus voltage V PE3 It is used to determine the third parallel impedance Z3 to ground of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 .

[0136] The insulation impedance detection method provided in the embodiment of the present application adopts the method of detecting the parallel impedance to ground R100 when the first photovoltaic array 400 has a stable output voltage, and detects the third parallel impedance to ground Z3 of the photovoltaic energy storage inverter 100 and the first photovoltaic array 400 during the day, so that the controller 130 can control the photovoltaic energy storage inverter 100 to be connected to the grid when the third parallel impedance to ground Z3 meets the insulation impedance requirement corresponding to the photovoltaic energy storage inverter 100 in the IEC62109-2 grid-connection standard, which can improve the safety of the photovoltaic energy storage inverter 100, avoid damage to the photovoltaic energy storage inverter 100, and avoid the photovoltaic energy storage inverter 100 being connected to the grid at a lower efficiency.

[0137] Based on this, the embodiment of the present application also provides a photovoltaic power generation system, the circuit topology of the photovoltaic power generation system is as follows Figure 1 The circuit topology of the photovoltaic power generation system 200 shown in FIG. 1 includes a photovoltaic energy storage inverter 100 and an energy storage device 300 connected to the photovoltaic energy storage inverter 100. The photovoltaic energy storage inverter 100 is used to connect to at least one photovoltaic array. Figure 1 In the embodiment of the present application, the photovoltaic energy storage inverter 100 is used to connect with the first photovoltaic array 400 as an example for exemplary description. The equivalent circuit diagram of the photovoltaic energy storage inverter 100 is as follows: Figures 4 to 8 An equivalent circuit diagram of the photovoltaic energy storage inverter 100 shown in any of the accompanying drawings.

[0138] The above detailed description of the photovoltaic energy storage inverter 100 and the analysis of the beneficial effects can be correspondingly referred to the control method of the photovoltaic energy storage inverter 100 and the photovoltaic power generation system 200, and the embodiments of the present application will not be repeated here.

[0139] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A photovoltaic energy storage inverter, characterized in that: It includes a Boost circuit, a first resistor, a second resistor, a DC bus positive pole, a DC bus negative pole, an inverter circuit and a controller; The input of the Boost circuit is used to connect to the photovoltaic array, the output of the Boost circuit is connected to the positive electrode of the DC bus and the negative electrode of the DC bus, the first resistor and the second resistor are connected in series between the positive electrode of the DC bus and the negative electrode of the DC bus, the connection point of the first resistor and the second resistor is used to connect to the protective ground wire, the input of the inverter circuit is connected to the positive electrode of the DC bus and the negative electrode of the DC bus, and the output of the inverter circuit is used to connect to the power grid; The DC bus positive electrode and the DC bus negative electrode are also used to connect the positive electrode and negative electrode of the energy storage device; The controller is used to control the switch tube in the Boost circuit to be in a conducting state when the voltage output by the photovoltaic array is less than or equal to the voltage threshold and the energy storage device outputs voltage to the positive electrode of the DC bus and the negative electrode of the DC bus; The controller is further used to obtain a bus voltage and a negative bus voltage, wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus; The controller is further used to control the output of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, and the positive bus voltage is the difference between the bus voltage and the negative bus voltage; The controller is further used to control the output of the inverter circuit to be disconnected from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than a ratio threshold.

2. The photovoltaic energy storage inverter according to claim 1, characterized in that: The controller is specifically used to obtain the bus voltage and the negative bus voltage when the conduction time of the switch tube in the Boost circuit is greater than or equal to a time threshold.

3. The photovoltaic energy storage inverter according to claim 1 or 2, characterized in that: The controller is specifically used to obtain the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and to obtain the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold.

4. The photovoltaic energy storage inverter according to any one of claims 1 to 3, characterized in that: The photovoltaic energy storage inverter further includes a third resistor and a first switch which are arranged in parallel and connected between the first resistor and the protective ground wire; The controller is further configured to control the first switch to be in a closed state when controlling the switch tube in the Boost circuit to be in an on state.

5. The photovoltaic energy storage inverter according to claim 4, characterized in that: The photovoltaic energy storage inverter further includes a fourth resistor and a second switch which are arranged in parallel and connected between the second resistor and the protective ground wire; The controller is further configured to control the second switch to be in a closed state and the first switch to be in an open state when the voltage output by the photovoltaic array is greater than the voltage threshold, so as to obtain a first negative bus voltage; After acquiring the first negative bus voltage, the first switch is controlled to be in a closed state, and the second switch is controlled to be in an open state, so as to acquire a second negative bus voltage.

6. A control method for a photovoltaic energy storage inverter, characterized in that: Applied to a photovoltaic energy storage inverter, the method comprises: When the voltage output by the photovoltaic array is less than or equal to the voltage threshold, and the energy storage device outputs voltage to the positive pole of the DC bus and the negative pole of the DC bus, the switch tube in the Boost circuit is controlled to be in the on state; Obtaining a bus voltage and a negative bus voltage, wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus; When the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, controlling the output of the inverter circuit to establish a connection with a power grid, the positive bus voltage being the difference between the bus voltage and the negative bus voltage; When the ratio of the negative bus voltage to the positive bus voltage is less than a ratio threshold, controlling the output of the inverter circuit to be disconnected from the power grid; The input of the Boost circuit is used to connect to the photovoltaic array, the output of the Boost circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, the first resistor and the second resistor are connected in series between the positive pole of the DC bus and the negative pole of the DC bus, the connection point of the first resistor and the second resistor is used to connect to the protective ground wire, the input of the inverter circuit is connected to the positive pole of the DC bus and the negative pole of the DC bus, and the positive pole of the DC bus and the negative pole of the DC bus are also used to connect the positive pole and negative pole of the energy storage device.

7. The control method of the photovoltaic energy storage inverter according to claim 6, characterized in that: The obtaining of the bus voltage and the negative bus voltage comprises: When the on-time of the switch tube in the Boost circuit is greater than or equal to a time threshold, the bus voltage and the negative bus voltage are obtained.

8. The control method of the photovoltaic energy storage inverter according to claim 6 or 7, characterized in that: The obtaining of the bus voltage and the negative bus voltage comprises: When the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, the bus voltage is obtained; when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold, the negative bus voltage is obtained.

9. The control method of the photovoltaic energy storage inverter according to any one of claims 6 to 8, characterized in that: The photovoltaic energy storage inverter further includes a third resistor and a first switch which are arranged in parallel and connected between the first resistor and the protective ground line, and the method further includes: When the switch tube in the Boost circuit is controlled to be in an on state, the first switch is controlled to be in a closed state.

10. The control method of the photovoltaic energy storage inverter according to claim 9, characterized in that: The photovoltaic energy storage inverter further includes a fourth resistor and a second switch which are arranged in parallel and connected between the second resistor and the protective ground line, and the method further includes: When the voltage output by the photovoltaic array is greater than the voltage threshold, controlling the second switch to be in a closed state and controlling the first switch to be in an open state to obtain a first negative bus voltage; After acquiring the first negative bus voltage, the first switch is controlled to be in a closed state, and the second switch is controlled to be in an open state, so as to acquire a second negative bus voltage.

11. A photovoltaic power generation system, characterized in that: The photovoltaic power generation system includes a photovoltaic energy storage inverter and an energy storage device connected to the photovoltaic energy storage inverter, wherein the photovoltaic energy storage inverter includes a Boost circuit, a first resistor, a second resistor, a DC bus positive pole, a DC bus negative pole, an inverter circuit and a controller; The input of the Boost circuit is used to connect to the photovoltaic array, the output of the Boost circuit is connected to the positive electrode of the DC bus and the negative electrode of the DC bus, the first resistor and the second resistor are connected in series between the positive electrode of the DC bus and the negative electrode of the DC bus, the connection point of the first resistor and the second resistor is used to connect to the protective ground wire, the input of the inverter circuit is connected to the positive electrode of the DC bus and the negative electrode of the DC bus, and the output of the inverter circuit is used to connect to the power grid; The DC bus positive electrode and the DC bus negative electrode are also used to connect the positive electrode and negative electrode of the energy storage device; The controller is used to control the switch tube in the Boost circuit to be in a conducting state when the voltage output by the photovoltaic array is less than or equal to the voltage threshold and the energy storage device outputs voltage to the positive electrode of the DC bus and the negative electrode of the DC bus; The controller is further used to obtain a bus voltage and a negative bus voltage, wherein the bus voltage is the absolute value of the voltage difference between the positive pole of the DC bus and the negative pole of the DC bus, and the negative bus voltage is the absolute value of the voltage difference between the protective ground wire and the negative pole of the DC bus; The controller is further used to control the output of the inverter circuit to establish a connection with the power grid when the ratio of the negative bus voltage to the positive bus voltage is greater than or equal to a ratio threshold, and the positive bus voltage is the difference between the bus voltage and the negative bus voltage; The controller is further used to control the output of the inverter circuit to be disconnected from the power grid when the ratio of the negative bus voltage to the positive bus voltage is less than a ratio threshold.

12. The photovoltaic power generation system according to claim 11, characterized in that: The controller is specifically used to obtain the bus voltage and the negative bus voltage when the conduction time of the switch tube in the Boost circuit is greater than or equal to a time threshold.

13. The photovoltaic power generation system according to claim 11 or 12, characterized in that: The controller is specifically used to obtain the bus voltage when the voltage fluctuation between the positive pole of the DC bus and the negative pole of the DC bus is less than or equal to the bus voltage fluctuation threshold, and to obtain the negative bus voltage when the voltage fluctuation between the protective ground wire and the negative pole of the DC bus is less than or equal to the negative bus voltage fluctuation threshold.

14. The photovoltaic power generation system according to any one of claims 11 to 13, characterized in that: The photovoltaic energy storage inverter further includes a third resistor and a first switch which are arranged in parallel and connected between the first resistor and the protective ground wire; The controller is further configured to control the first switch to be in a closed state when controlling the switch tube in the Boost circuit to be in an on state.

15. The photovoltaic power generation system according to claim 14, characterized in that: The photovoltaic energy storage inverter further includes a fourth resistor and a second switch which are arranged in parallel and connected between the second resistor and the protective ground wire; The controller is further configured to control the second switch to be in a closed state and the first switch to be in an open state when the voltage output by the photovoltaic array is greater than the voltage threshold, so as to obtain a first negative bus voltage; After acquiring the first negative bus voltage, the first switch is controlled to be in a closed state, and the second switch is controlled to be in an open state, so as to acquire a second negative bus voltage.

Images