Insulation resistance detection circuit and detection method of photovoltaic inverter and photovoltaic inverter

Abstract

The invention discloses an insulation resistance detection circuit and detection method of a photovoltaic inverter and the photovoltaic inverter. A first switch is arranged between a first photovoltaic input end and a direct current bus; a second switch is arranged between the second photovoltaic input end and the direct current bus; the impedance detection bridge circuit comprises a first bridge arm and a second bridge arm, the first bridge arm comprises a first impedance and a third impedance which are connected in series, the second bridge arm comprises a second impedance and a fourth impedance which are connected in series, and the first bridge arm and the second bridge arm are both connected to the positive electrode and the negative electrode of a direct current bus. The midpoint of the first bridge arm and the midpoint of the second bridge arm are both connected to the protection ground, the first impedance is connected to the midpoint of the first bridge arm through the third switch, and the third impedance is connected to the midpoint of the first bridge arm through the fourth switch. The detection circuit and the detection method provided by the embodiment of the invention are both suitable for the photovoltaic insulation impedance under the condition that the photovoltaic input voltage is greater than, equal to or less than the DC bus voltage, and the accurate measurement of the photovoltaic insulation impedance is realized.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to an insulation impedance detection circuit and detection method of a photovoltaic inverter and a photovoltaic inverter. Background Art

[0002] Since photovoltaic modules are installed outdoors, they are greatly affected by the outdoor environment. After a long period of exposure to the sun and rain, the aging of photovoltaic modules and other problems will cause the insulation impedance of the photovoltaic modules to change. It is different from the insulation impedance during the initial installation, which can easily cause the DC bus of the photovoltaic inverter to discharge to the ground. In severe cases, the photovoltaic inverter may be damaged.

[0003] At present, most solutions detect the insulation impedance through the DC bus. Based on the unbalanced bridge principle, the unbalanced bridge is generated by controlling the on and off of the relay to achieve the measurement purpose. This solution has two disadvantages. One is that the calculation process is relatively complicated when multiple equations need to be calculated before and after the relay switch is closed. The other is that due to the presence of diodes in the circuit, when the photovoltaic input voltage is less than the DC bus voltage, the insulation impedance detection will be inaccurate. Summary of the invention

[0004] The embodiments of the present application provide an insulation impedance detection circuit, a detection method and a photovoltaic inverter for a photovoltaic inverter, which are suitable for the photovoltaic insulation impedance when the photovoltaic input voltage is greater than, equal to or less than the DC bus voltage, and realize accurate measurement of the photovoltaic insulation impedance.

[0005] In a first aspect, an embodiment of the present application provides an insulation impedance detection circuit for a photovoltaic inverter, comprising:

[0006] a first photovoltaic input terminal, wherein a first switch is arranged between the first photovoltaic input terminal and the DC bus;

[0007] a second photovoltaic input terminal, wherein a second switch is arranged between the second photovoltaic input terminal and the DC bus;

[0008] An impedance detection bridge circuit includes a first bridge arm and a second bridge arm, wherein the first bridge arm includes a first impedance and a third impedance connected in series, and the second bridge arm includes a second impedance and a fourth impedance connected in series, the first bridge arm and the second bridge arm are both connected to the positive and negative poles of a DC bus, the midpoint of the first bridge arm and the midpoint of the second bridge arm are both connected to a protective ground, the first impedance is connected to the midpoint of the first bridge arm through a third switch, and the third impedance is connected to the midpoint of the first bridge arm through a fourth switch.

[0009] In some embodiments, the insulation impedance detection circuit also includes a first boost circuit and a second boost circuit, the positive pole of the first photovoltaic input terminal, the first switch, the first boost circuit and the positive pole of the DC bus are connected in sequence, and the positive pole of the second photovoltaic input terminal, the second switch, the second boost circuit and the negative pole of the DC bus are connected in sequence.

[0010] In some embodiments, the first boost circuit includes a first diode, a second diode, a first inductor and a first switch tube, and the second boost circuit includes a third diode, a fourth diode, a second inductor and a second switch tube;

[0011] The series branch of the first inductor and the second diode is connected in parallel with the first diode, and the connection point of the first inductor and the second diode is connected to the negative pole of the DC bus through the first switch tube; the series branch of the second inductor and the fourth diode is connected in parallel with the third diode, and the connection point of the second inductor and the fourth diode is connected to the negative pole of the DC bus through the second switch tube.

[0012] In some embodiments, the insulation impedance detection circuit also includes a first voltage detection module, a second voltage detection module, a third voltage detection module and a fourth voltage detection module; the first voltage detection module is used to detect the voltage value of the negative voltage of the first photovoltaic input terminal relative to the DC bus, the second voltage detection module is used to detect the voltage value of the negative voltage of the second photovoltaic input terminal relative to the DC bus, the three voltage detection modules are used to detect the voltage value of the positive voltage of the DC bus, and the fourth detection module is used to detect the voltage value of the negative voltage of the protective ground relative to the DC bus.

[0013] In a second aspect, an embodiment of the present application provides an insulation impedance detection method of an insulation impedance detection circuit, which is applied to the insulation impedance detection circuit of the first aspect, and the method includes:

[0014] When the voltage of the first photovoltaic input terminal or the voltage of the second photovoltaic input terminal is less than the voltage of the DC bus, switch to the first switch combination, the second switch combination, the third switch combination and the fourth switch combination respectively;

[0015] A first relational expression obtained under the first switch combination and a second relational expression obtained under the second switch combination are combined to obtain a first insulation impedance corresponding to the first photovoltaic input terminal and a third insulation impedance corresponding to the protective ground;

[0016] The third relational expression obtained under the third switch combination and the fourth relational expression obtained under the fourth switch combination are combined to obtain a second insulation impedance corresponding to the second photovoltaic input terminal and a third insulation impedance corresponding to the protective ground;

[0017] When any one of the first insulation impedance, the second insulation impedance, and the third insulation impedance is less than a first preset impedance value, an insulation impedance abnormal fault is prompted;

[0018] Wherein, the first switch combination is that the second switch and the fourth switch are turned off, the first switch and the third switch are turned on, and the first relational expression is an equation of the first insulation impedance and the third insulation impedance obtained according to Kirchhoff's law;

[0019] The second switch combination is that the second switch and the third switch are turned off, the first switch and the fourth switch are turned on, and the second relational expression is an equation of the first insulation impedance and the third insulation impedance obtained according to Kirchhoff's law;

[0020] The third switch combination is that the first switch and the fourth switch are turned off, the second switch and the third switch are turned on, and the third relational expression is an equation of the second insulation impedance and the third insulation impedance obtained according to Kirchhoff's law;

[0021] The fourth switch combination is that the first switch and the third switch are turned off, the second switch and the fourth switch are turned on, and the fourth relational expression is an equation of the second insulation impedance and the third insulation impedance obtained according to Kirchhoff's law.

[0022] In some embodiments, the first relational expression is:

[0023]

[0024] The second relational expression is:

[0025]

[0026] The third relational expression is:

[0027]

[0028] The fourth relational expression is:

[0029]

[0030] Wherein, BUS+ is the positive voltage of the DC bus, PE1, PE2, PE3, and PE4 are the protective ground voltages of the circuit corresponding to the four switch combinations respectively, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R1, R2, R3, and R4 are the first impedance, the second impedance, the third impedance, and the fourth impedance respectively, and RZ1, RZ2, and RZ3 are the first insulation impedance, the second insulation impedance, and the third insulation impedance respectively.

[0031] In some embodiments, the method further comprises:

[0032] When the voltage of the first photovoltaic input terminal and the voltage of the second photovoltaic input terminal are both greater than the voltage of the DC bus, switching to the fifth switch combination and the sixth switch combination respectively;

[0033] The fifth relational expression obtained under the fifth switch combination and the sixth relational expression obtained under the sixth switch combination are combined to obtain the positive voltage insulation impedance and the negative voltage insulation impedance of the DC bus;

[0034] When the positive voltage insulation impedance or the negative voltage insulation impedance of the DC bus is less than the second preset impedance value, an abnormal insulation impedance fault is prompted;

[0035] The fifth switch combination is that the first switch, the second switch and the third switch are closed, and the fourth switch is open, and the fifth relational expression is an equation for obtaining the insulation impedance of the DC bus according to Kirchhoff's law;

[0036] The sixth switch combination is that the first switch, the second switch and the fourth switch are closed, and the third switch is open, and the sixth relationship is an equation for obtaining the insulation impedance of the DC bus according to Kirchhoff's law.

[0037] In some embodiments, the method further comprises:

[0038] When the voltage of the first photovoltaic input terminal and the voltage of the second photovoltaic input terminal are both greater than the voltage of the DC bus, switching to the seventh switch combination, the fifth switch combination and the sixth switch combination respectively;

[0039] The first insulation impedance, the second insulation impedance and the third insulation impedance are obtained by combining the seventh relational expression obtained under the seventh switch combination, the eighth relational expression obtained under the fifth switch combination and the ninth relational expression obtained under the sixth switch combination;

[0040] When any one of the first insulation impedance, the second insulation impedance and the third insulation impedance is less than a first preset impedance value, an abnormal insulation impedance fault is prompted;

[0041] The seventh switch combination is that the first switch and the second switch are closed, and the third switch and the fourth switch are opened, and the seventh relational expression is an equation for obtaining the first insulation impedance, the second insulation impedance, and the third insulation impedance according to Kirchhoff's law;

[0042] The fifth switch combination is that the first switch, the second switch and the third switch are closed, and the fourth switch is open, and the eighth relational expression is an equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law;

[0043] The sixth switch combination is that the first switch, the second switch and the fourth switch are closed, and the third switch is open, and the ninth relationship is an equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law.

[0044] In a third aspect, an embodiment of the present application provides a controller comprising at least one processor and a memory for communicating with the at least one processor; the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the insulation impedance detection method as described in the second aspect.

[0045] In a fourth aspect, an embodiment of the present application provides a photovoltaic inverter, comprising the insulation impedance detection circuit of the first aspect and the controller of the third aspect.

[0046] The insulation impedance detection circuit, detection method and photovoltaic inverter of the embodiment of the present application have at least the following beneficial effects: a first switch is set between the first photovoltaic input terminal and the DC bus, and a second switch is set between the second photovoltaic input terminal and the DC bus. The first switch and the second switch can be combined with the third switch and the fourth switch in the impedance detection bridge circuit to form a variety of switch combinations; when the photovoltaic input voltage is less than the DC bus voltage, in order to simplify the calculation process of the first insulation impedance of the first photovoltaic input terminal and the second insulation impedance of the second photovoltaic input terminal, when measuring the impedance, the second switch is disconnected so that the second insulation impedance is equivalent to infinity, thereby obtaining a first relational expression and a second relational expression that are independent of the second insulation impedance, and the first insulation impedance and the second insulation impedance are obtained by combining them. The third insulation impedance of the protective ground, disconnecting the first switch makes the first insulation impedance equivalent to infinity, and then obtaining a third relationship and a fourth relationship that are independent of the first insulation impedance, and obtaining the second insulation impedance and the third insulation impedance after combined, by comparing the first insulation impedance, the second insulation impedance and the third insulation impedance obtained by the above two calculations with the first preset impedance value, it can be determined whether an insulation impedance abnormality occurs; the insulation impedance is calculated by the method of the present application, and the calculation is simpler than the solution of solving the insulation impedance by a set of three-variable equations in the prior art, and is suitable for the photovoltaic insulation impedance when the photovoltaic input voltage is greater than, equal to or less than the DC bus voltage, especially when the photovoltaic input voltage is less than or equal to the DC bus voltage, thereby realizing accurate measurement of the photovoltaic insulation impedance.

[0047] Other features and advantages of the present application will be described in the following specification, and in part will be obvious from the specification, or will be understood by implementing the present application. The objectives and other advantages of the present application can be realized and obtained by the structures specifically pointed out in the specification, claims and drawings. Brief Description of the Drawings

[0048] Figure 1 is a schematic diagram of module connections of an insulation impedance detection circuit provided by an embodiment of the present application;

[0049] Figure 2 is a schematic circuit diagram of an insulation impedance detection circuit provided by an embodiment of the present application;

[0050] Figure 3 is a flowchart of a method for an insulation impedance detection method provided by an embodiment of the present application;

[0051] Figure 4 is a schematic circuit diagram of another insulation impedance detection circuit provided by an embodiment of the present application;

[0052] Figure 5 is a flowchart of a method for another insulation impedance detection method provided by an embodiment of the present application;

[0053] Figure 6 is a flowchart of a method for another insulation impedance detection method provided by an embodiment of the present application;

[0054] Figure 7 is a schematic diagram of modules of a controller provided by an embodiment of the present application. Detailed Description of the Embodiments

[0055] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Additionally, the features, operations or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are necessary sequences unless it is stated that a certain sequence must be followed.

[0056] In the description of this application, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0057] The serial numbers of the components in this document, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings).

[0058] As a new type of clean energy, household photovoltaic storage has become the main development direction. The core equipment used in household photovoltaic storage is photovoltaic inverter and energy storage converter. Photovoltaic panels convert solar energy into direct current, while our home and commercial electrical equipment usually use alternating current. Photovoltaic inverter is a device that converts the direct current generated by solar photovoltaic panels into alternating current to meet our home, commercial or industrial electricity needs.

[0059] In the field of photovoltaic grid-connected power generation, the insulation impedance of photovoltaic power sources to the ground is often tested. Since photovoltaic arrays are installed outdoors and are greatly affected by the environment, long-term exposure to the sun and rain, aging of photovoltaic components, lightning strikes and other problems can cause changes in insulation impedance. Reduced insulation impedance changes can cause discharge of the DC bus to the ground, which may damage the photovoltaic inverter in severe cases.

[0060] The insulation impedance test of the photovoltaic inverter is a test of the insulation performance of the inverter's internal circuit and insulation materials. Through the insulation impedance test of the photovoltaic inverter, problems such as insulation material damage, water infiltration, and insulation degradation can be discovered in a timely manner so that appropriate repair or replacement measures can be taken. This helps to ensure the safety and performance of the photovoltaic inverter and ensure the normal power generation operation of the photovoltaic system.

[0061] At present, most products use the insulation impedance detection of positive and negative busbars to ground, which is mostly based on the unbalanced bridge principle. By controlling the on and off of the relay, an unbalanced bridge is generated to achieve the measurement purpose. However, this detection method requires multiple equations to be calculated before and after the relay switch is closed. The calculation process is relatively complicated and there may be situations where the calculation cannot be made. In addition, due to the presence of diodes in the circuit, when the photovoltaic input voltage is less than the DC bus voltage, the insulation impedance detection will be inaccurate.

[0062] Based on this, embodiments of the present application provide an insulation impedance detection circuit, a detection method, and a photovoltaic inverter for photovoltaic insulation impedance in cases where the photovoltaic input voltage is greater than, equal to, or less than the DC bus voltage, especially when the photovoltaic input voltage is less than or equal to the DC bus voltage, thereby enabling accurate measurement of the photovoltaic insulation impedance.

[0063] First of all, a photovoltaic inverter is an inverter that can convert the variable DC voltage generated by photovoltaic solar panels into AC power with the commercial power frequency, which can be fed back into the commercial power transmission system or used for an off-grid power grid; while a battery energy storage converter can control the charging and discharging processes of the battery, perform AC-DC conversion, and directly supply power to AC loads in the absence of a power grid.

[0064] Insulation impedance detection is a test method used to evaluate the insulation performance of electrical equipment or electrical systems. It determines the quality and reliability of insulation by measuring the resistance between the insulation material or insulation structure and the ground. If the insulation impedance is low, there may be damage to the insulation material, water ingress, or other faults, which may lead to electrical equipment failures or electric shock risks. By regularly performing insulation impedance tests, insulation problems can be detected and discovered in a timely manner, so as to take appropriate repair or insulation improvement measures.

[0065] The insulation impedance detection circuit, detection method, and photovoltaic inverter of the photovoltaic inverter will be described below with reference to the accompanying drawings:

[0066] Refer to Figure 1 as shown Figure 1 is a schematic diagram of the module connection of an insulation impedance detection circuit provided by an embodiment of the present application, including a first photovoltaic input terminal, a first switch K3 is provided between the first photovoltaic input terminal and the DC bus; a second photovoltaic input terminal, a second switch K4 is provided between the second photovoltaic input terminal and the DC bus; an impedance detection bridge circuit, including a first bridge arm and a second bridge arm, the first bridge arm includes a first impedance R1 and a third impedance R3 connected in series, the second bridge arm includes a second impedance R2 and a fourth impedance R4 connected in series, both the first bridge arm and the second bridge arm are connected between the positive and negative poles of the DC bus, the midpoints of the first bridge arm and the second bridge arm are both connected to the protective ground, the first impedance R1 is connected to the midpoint of the first bridge arm through a third switch K1, and the third impedance R3 is connected to the midpoint of the first bridge arm through a fourth switch K2.

[0067] It should be noted that the first photovoltaic input terminal and the second photovoltaic input terminal serve as the interfaces of the photovoltaic input power supply, transmitting the DC electric energy generated by the photovoltaic power generation system; the first switch K3 and the second switch K4 are used to control the connection between the photovoltaic input terminal and the DC bus. By controlling the closing and opening of the switches, the connection state of the circuit can be switched; the first arm and the second arm form a bridge circuit for impedance detection. The first arm consists of a first impedance R1 and a third impedance R3 connected in series, and the second arm consists of a second impedance R2 and a fourth impedance R4 connected in series; the first impedance R1, the second impedance R2, the third impedance R3, and the fourth impedance R4 are impedance elements in the bridge circuit. Among them, each impedance can be formed by connecting multiple resistors in series according to the impedance value required for testing; the protective ground is connected to the midpoint of the first arm and the second arm for protecting the circuit and equipment; the third switch K1 and the fourth switch K2 are used to control the connection of the first impedance R1 and the third impedance R3. By controlling the closing and opening of the switches, the connection or disconnection of the impedance can be controlled. On this basis, according to the testing requirements, controlling the closing and opening of the first switch K3, the second switch K4, the third switch K1, and the fourth switch K2 corresponds to four testing situations.

[0068] In an embodiment of the present application, the first switch K3 and the second switch K4 are in the closed state in the initial state, connecting the photovoltaic input terminal to the DC bus. The third switch K1 and the fourth switch K2 are in the open state in the initial state, and the impedance is not connected to the bridge circuit. When the voltage PV1 of the first photovoltaic input terminal or the voltage PV2 of the second photovoltaic input terminal is less than the voltage of the DC bus, the second switch K4 is opened to cut off the connection between the second photovoltaic input terminal and the DC bus, and the third switch K1 is closed to measure parameters such as the voltages PV1 and PV2 of the photovoltaic input terminal, the positive voltage of the DC bus, and the protective ground voltage PE in the current state, and then obtain their relationships. Then, the third switch K1 is controlled to open and the fourth switch K2 is closed, and the voltages PV1 and PV2 of the photovoltaic input terminal, the positive voltage of the DC bus, and the protective ground voltage PE in the current state are measured again, and then obtain their relationships; the first switch K3, the second switch K4, the third switch K1, and the fourth switch K2 are reset to the initial state, the first switch K3 is controlled to open to cut off the connection between the first photovoltaic input terminal and the DC bus, and the third switch K1 is closed to measure parameters such as the voltages PV1 and PV2 of the photovoltaic input terminal, the positive voltage of the DC bus, and the protective ground voltage PE in the current state, and then obtain their relationships. Then, the third switch K1 is controlled to open and the fourth switch K2 is closed, and the voltages PV1 and PV2 of the photovoltaic input terminal, the positive voltage of the DC bus, and the protective ground voltage PE in the current state are measured again, and then obtain their relationships. By solving the simultaneous equations, the insulation impedance is calculated. By comparing the insulation impedance obtained in the above manner with the preset impedance value, it can be determined whether there is an abnormal insulation impedance.

[0069] ReferenceFigure 2 As shown Figure 2 This is a schematic circuit diagram of an insulation impedance detection circuit provided by an embodiment of the present application.

[0070] In some embodiments, the insulation impedance detection circuit further includes a first boost circuit and a second boost circuit. The positive pole of the first photovoltaic input terminal, the first switch K3, the first boost circuit, and the positive pole of the DC bus are connected in sequence. The positive pole of the second photovoltaic input terminal, the second switch K4, the second boost circuit, and the negative pole of the DC bus are connected in sequence.

[0071] It can be understood that the first boost circuit is used to extract electrical energy from the first photovoltaic input terminal and boost and output it. When the first switch K3 is closed, the positive pole of the first photovoltaic input terminal is connected to the first boost circuit, and the DC electrical energy generated at the photovoltaic input terminal will undergo a certain boost process through the boost circuit, and a high-voltage signal will be generated at the output terminal of the boost circuit. The second boost circuit is used to extract electrical energy from the second photovoltaic input terminal and boost and output it. When the second switch K4 is closed, the positive pole of the second photovoltaic input terminal is connected to the second boost circuit, and the DC electrical energy generated at the photovoltaic input terminal will undergo a certain boost process through the boost circuit, and a high-voltage signal will be generated at the output terminal of the boost circuit. The function of these two boost circuits is to convert the DC electrical energy generated at the photovoltaic input terminal into a signal with a higher voltage for subsequent use.

[0072] In some embodiments, the first boost circuit includes a first diode D1, a second diode D3, a first inductor L3, and a first switching tube Q7. The second boost circuit includes a third diode D2, a fourth diode D4, a second inductor L4, and a second switching tube Q8. The series branch of the first inductor L3 and the second diode D3 is connected in parallel with the first diode D1. The connection point of the first inductor L3 and the second diode D3 is connected to the negative pole of the DC bus through the first switching tube Q7. The series branch of the second inductor L4 and the fourth diode D4 is connected in parallel with the third diode D2. The connection point of the second inductor L4 and the fourth diode D4 is connected to the negative pole of the DC bus through the second switching tube Q8.

[0073] It can be understood that the series branch of the first inductor L3 and the second diode D3 is connected in parallel with the first diode D1. There is a shared connection point between the first inductor L3 and the second diode D3, and it is connected to the negative pole of the DC bus through the first switching tube Q7. The series branch of the second inductor L4 and the fourth diode D4 is connected in parallel with the third diode D2. There is a shared connection point between the second inductor L4 and the fourth diode D4, and it is connected to the negative pole of the DC bus through the second switching tube Q8.

[0074] In some embodiments, the insulation impedance detection circuit also includes a first voltage detection module, a second voltage detection module, a third voltage detection module and a fourth voltage detection module; the first voltage detection module is used to detect the voltage value of the negative voltage of the first photovoltaic input terminal relative to the DC bus, the second voltage detection module is used to detect the voltage value of the negative voltage of the second photovoltaic input terminal relative to the DC bus, the three voltage detection modules are used to detect the voltage value of the positive voltage of the DC bus, and the fourth detection module is used to detect the voltage value of the negative voltage of the protective ground relative to the DC bus.

[0075] It should be noted that the first voltage detection module connects the detection point to the first photovoltaic input terminal, and at the same time connects the corresponding reference point to the negative pole of the DC bus; the connection method of the second voltage detection module is similar to that of the first voltage detection module, connecting the detection point to the second photovoltaic input terminal, and connecting the reference point to the negative pole of the DC bus; the third voltage detection module connects the detection point to the DC bus, and the reference point to the protective ground; the fourth voltage detection module connects the detection point to the protective ground, and the reference point to the negative pole of the DC bus.

[0076] Reference Figure 3 As shown, Figure 3 A method flow chart of an insulation impedance detection method provided in an embodiment of the present application.

[0077] A method for insulation impedance detection, the method may include but is not limited to the following steps:

[0078] Step S310, when the voltage of the first photovoltaic input terminal or the voltage of the second photovoltaic input terminal is less than the voltage of the DC bus, switch to the first switch combination, the second switch combination, the third switch combination and the fourth switch combination respectively;

[0079] Step S320, combining a first relational expression obtained under the first switch combination and a second relational expression obtained under the second switch combination to obtain a first insulation impedance corresponding to the first photovoltaic input terminal and a third insulation impedance corresponding to the protective ground;

[0080] Step S330, combining a third relational expression obtained under the third switch combination and a fourth relational expression obtained under the fourth switch combination to obtain a second insulation impedance corresponding to the second photovoltaic input terminal and a third insulation impedance corresponding to the protective ground;

[0081] Step S340: When any one of the first insulation impedance, the second insulation impedance and the third insulation impedance is less than the first preset impedance value, an insulation impedance abnormality fault is prompted.

[0082] It should be noted that the first switch combination is that the second switch K4 and the fourth switch K2 are disconnected, and the first switch K3 and the third switch K1 are closed. The first relational expression is an equation of the first insulation impedance RZ1 and the third insulation impedance RZ3 obtained according to Kirchhoff's law; the second switch combination is that the second switch K4 and the third switch K1 are disconnected, and the first switch K3 and the fourth switch K2 are closed. The second relational expression is an equation of the first insulation impedance RZ1 and the third insulation impedance RZ3 obtained according to Kirchhoff's law; the third switch combination is that the first switch K3 and the fourth switch K2 are disconnected, and the second switch K4 and the third switch K1 are closed. The third relational expression is an equation of the second insulation impedance RZ2 and the third insulation impedance RZ3 obtained according to Kirchhoff's law; the fourth switch combination is that the first switch K3 and the third switch K1 are disconnected, and the second switch K4 and the fourth switch K2 are closed. The fourth relational expression is an equation of the second insulation impedance RZ2 and the third insulation impedance RZ3 obtained according to Kirchhoff's law.

[0083] In some embodiments, when the insulation impedance detection circuit is controlled to switch to the first switch combination, that is, when the second switch K4 and the fourth switch K2 are disconnected and the first switch K3 and the third switch K1 are closed, the voltage values of the negative voltage of the first photovoltaic input terminal relative to the DC bus, the negative voltage of the second photovoltaic input terminal relative to the DC bus, the positive voltage of the DC bus, and the negative voltage of the protective ground relative to the DC bus are respectively detected by the first voltage detection module, the second voltage detection module, the third voltage detection module, and the fourth voltage detection module. After detecting these voltage values and obtaining the first relational expression according to Kirchhoff's law, after obtaining the first relational expression, the insulation impedance detection circuit is controlled to switch to the second switch combination, that is, the second switch K4 and the third switch K1 are disconnected and the first switch K3 and the fourth switch K2 are closed, and the second relational expression is obtained according to the above parameter detection and Kirchhoff's law. Since both the first relational expression and the second relational expression are obtained when the second switch K4 is disconnected, the first relational expression and the second relational expression have nothing to do with the second insulation impedance RZ2. By solving the equations simultaneously, the first insulation impedance RZ1 corresponding to the first photovoltaic input terminal and the third insulation impedance RZ3 corresponding to the protective ground can be obtained.

[0084] In some embodiments, when controlling the insulation impedance detection circuit to switch to the third switch combination, i.e., the first switch K3 and the fourth switch K2 are open, and the second switch K4 and the third switch K1 are closed, the voltage values of the negative voltage of the first photovoltaic input terminal relative to the DC bus, the negative voltage of the second photovoltaic input terminal relative to the DC bus, the positive voltage of the DC bus, and the negative voltage of the protective ground relative to the DC bus are respectively detected through the first voltage detection module, the second voltage detection module, the third voltage detection module, and the fourth voltage detection module. After detecting these voltage values and obtaining the third relationship according to Kirchhoff's law, after obtaining the third relationship, the insulation impedance detection circuit is controlled to switch to the fourth switch combination, i.e., the first switch K3 and the third switch K1 are open, and the second switch K4 and the fourth switch K2 are closed. According to the above parameter detection and Kirchhoff's law, the fourth relationship is obtained. Since both the third relationship and the fourth relationship are obtained when the first switch K3 is open, the third relationship and the fourth relationship have nothing to do with the first insulation impedance RZ1. By solving the equations simultaneously, the second insulation impedance RZ2 corresponding to the second photovoltaic input terminal and the third insulation impedance RZ3 corresponding to the protective ground can be obtained.

[0085] It should be noted that the insulation impedance is an index used to evaluate the insulation performance of the insulating material in the circuit, and is usually used to detect whether there is insulation breakage or aging of the insulating material. When any one of the first insulation impedance RZ1, the second insulation impedance RZ2, or the third insulation impedance RZ3 is less than the first preset impedance value, this may indicate an abnormal fault in the insulation impedance, which may lead to insulation breakage or poor insulation performance in the circuit. When an abnormal fault in the insulation impedance is detected, measures should be taken in a timely manner for repair and maintenance to ensure the normal operation of the circuit and the safety of personnel.

[0086] In some embodiments, the first relationship is:

[0087]

[0088] The second relationship is:

[0089]

[0090] The third relationship is:

[0091]

[0092] The fourth relationship is:

[0093]

[0094] Wherein, BUS+ is the positive voltage of the DC bus, PE1, PE2, PE3, and PE4 are the protective ground voltages of the circuit corresponding to the four switch combinations respectively, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R1, R2, R3, and R4 are the first impedance, second impedance, third impedance, and fourth impedance respectively, and RZ1, RZ2, and RZ3 are the first insulation impedance, second insulation impedance, and third insulation impedance respectively.

[0095] It should be noted that R1 / / R2 is the parallel connection of R1 and R2, specifically R1*R2 / (R1 + R2), and the same applies to R3 / / R4 described above.

[0096] It can be understood that the first relationship, the second relationship, the third relationship, and the fourth relationship are obtained from the parameters measured in the four switch combinations of the corresponding first switch combination, second switch combination, third switch combination, and fourth switch combination, and according to Kirchhoff's law, the sum of all currents entering a certain node is equal to the sum of all currents leaving this node.

[0097] In some embodiments, when the insulation impedance detection circuit switches to the first switch combination, according to Kirchhoff's law, the current passing through the parallel circuit of the first impedance R1 and the second impedance R2 and the first insulation impedance RZ1 is equal to the current passing through the third insulation impedance RZ3 and the fourth impedance R4, and the first relationship is obtained; when the insulation impedance detection circuit switches to the second switch combination, according to the current passing through the second impedance R2 and the first insulation impedance RZ1 is equal to the current passing through the third insulation impedance RZ3 and the parallel circuit of the third impedance R3 and the fourth impedance R4, the second relationship is obtained; when the insulation impedance detection circuit switches to the third switch combination, according to the current passing through the parallel circuit of the first impedance R1 and the second impedance R2 and the second insulation impedance RZ2 is equal to the current passing through the third insulation impedance RZ3 and the fourth impedance R4, the third relationship is obtained; when the insulation impedance detection circuit switches to the fourth switch combination, according to the current passing through the second impedance R2 and the second insulation impedance RZ2 is equal to the current passing through the third insulation impedance RZ3 and the parallel circuit of the third impedance R3 and the fourth impedance R4, the fourth relationship is obtained.

[0098] Referring to Figure 4 and Figure 5 as shown, Figure 4 is a circuit schematic diagram of another insulation impedance detection circuit provided by an embodiment of the present application, Figure 5 is a method flowchart of another insulation impedance detection method provided by an embodiment of the present application.

[0099] An insulation impedance detection method, which is applied when the voltages of the first photovoltaic input terminal and the second photovoltaic input terminal are both greater than the voltage of the DC bus. The method may include but is not limited to the following steps:

[0100] Step S510: When the voltages of both the first photovoltaic input terminal and the second photovoltaic input terminal are greater than the voltage of the DC bus, switch to the fifth switch combination and the sixth switch combination respectively.

[0101] Step S520: Combine the fifth relationship obtained under the fifth switch combination and the sixth relationship obtained under the sixth switch combination to obtain the positive voltage insulation impedance and negative voltage insulation impedance of the DC bus.

[0102] Step S530: When the positive voltage insulation impedance or negative voltage insulation impedance of the DC bus is less than the second preset impedance value, prompt an abnormal insulation impedance fault.

[0103] It should be noted that, as Figure 4 shown, the fifth switch combination is that the first switch K3, the second switch K4, and the third switch K1 are closed, and the fourth switch K2 is open. The fifth relationship is the equation of the insulation impedance of the DC bus obtained according to Kirchhoff's law. The sixth switch combination is that the first switch K3, the second switch K4, and the fourth switch K2 are closed, and the third switch K1 is open. The sixth relationship is the equation of the insulation impedance of the DC bus obtained according to Kirchhoff's law.

[0104] It should be noted that, as Figure 4 shown, the positive voltage insulation impedance RB+ of the DC bus is equivalent to the insulation impedance of the parallel circuit of the first insulation impedance RZ1 and the second insulation impedance RZ2, and the negative voltage insulation impedance RB- of the DC bus is equivalent to the third insulation impedance RZ3.

[0105] In some embodiments, when the voltages PV1 of the first photovoltaic input terminal and PV2 of the second photovoltaic input terminal are both greater than the voltage of the DC bus, control the insulation impedance detection circuit to switch to the fifth switch combination. Through the third voltage detection module and the fourth voltage detection module, detect the voltage value of the positive voltage of the DC bus and the voltage value of the negative voltage of the protective ground relative to the DC bus at this time, and according to the current passing through the parallel circuit of the first impedance R1, the second impedance R2, and the positive voltage insulation impedance RB+ of the DC bus is equal to the current passing through the parallel circuit of the fourth impedance R4 and the negative voltage insulation impedance RB- of the DC bus, obtain the fifth relationship:

[0106]

[0107] where BUS+ is the positive voltage of the DC bus, PE is the protective ground voltage of the circuit, R1, R2, and R4 are the first impedance, the second impedance, and the fourth impedance respectively, RB+ is the positive voltage insulation impedance of the DC bus, and RB- is the negative voltage insulation impedance of the DC bus.

[0108] In some embodiments, after the fifth relationship is obtained, the insulation impedance detection circuit is controlled to switch to the sixth switch combination, and the voltage value of the positive voltage of the DC bus and the voltage value of the negative voltage of the protection ground relative to the DC bus are detected through the third voltage detection module and the fourth voltage detection module, and the current of the parallel circuit of the positive voltage insulation impedance RB+ of the DC bus through the second impedance R2 is equal to the current of the parallel circuit of the negative voltage insulation impedance RB- of the DC bus through the third impedance R3, the fourth impedance R4 and the DC bus, The sixth relationship is obtained:

[0109]

[0110] Wherein, BUS+ is the positive voltage of the DC bus, PE1' is the protection ground voltage of the circuit, R1, R3 and R4 are the first impedance, the third impedance and the fourth impedance respectively, RB+ is the positive voltage insulation impedance of the DC bus, and RB- is the negative voltage insulation impedance of the DC bus.

[0111] In some embodiments, by combining the fifth and sixth equations, the positive voltage insulation impedance RB+ and the negative voltage insulation impedance RB- of the DC bus are calculated and compared with the second preset impedance value. If one of them is less than the second preset impedance value, it indicates that there is an abnormal fault in the insulation impedance, which may cause insulation damage or poor insulation performance in the circuit.

[0112] In some embodiments, when the voltage PV1 of the first photovoltaic input terminal or the voltage PV2 of the second photovoltaic input terminal is less than the voltage of the DC bus, Figure 4 In the insulation impedance detection circuit, since the positive voltage insulation impedance RB+ of the DC bus is equivalent to the insulation impedance of the parallel circuit of the first insulation impedance RZ1 and the second insulation impedance RZ2, after the insulation impedance detection circuit is controlled to switch to the first switch combination, the positive voltage insulation impedance RB+ of the DC bus is equivalent to the first insulation impedance RZ1, and the negative voltage insulation impedance RB- of the DC bus is equivalent to the third insulation impedance RZ3. Therefore, a variation of the fifth relation can be obtained:

[0113]

[0114] Among them, BUS+ is the positive voltage of the DC bus, PE1' is the protection ground voltage of the circuit, R1, R2 and R4 are the first impedance, the second impedance and the fourth impedance respectively, RZ1 is the first insulation impedance, and RB- is the negative voltage insulation impedance of the DC bus.

[0115] In some embodiments, after the variation of the fifth relational expression is obtained, the insulation impedance detection circuit is controlled to switch the second switch combination, so that a variation of the sixth relational expression can be obtained:

[0116]

[0117] Among them, BUS+ is the positive voltage of the DC bus, PE1' is the protection ground voltage of the circuit, R1, R3 and R4 are the first impedance, the third impedance and the fourth impedance respectively, RZ1 is the first insulation impedance, and RB- is the negative voltage insulation impedance of the DC bus.

[0118] In some embodiments, the first insulation resistance RZ1 and the third insulation resistance RZ3 are calculated by combining the modified equations of the fifth relational expression and the modified equations of the sixth relational expression.

[0119] In some embodiments, after the insulation impedance detection circuit is controlled to switch to the third switch combination, the positive voltage insulation impedance RB+ of the DC bus is equivalent to the second insulation impedance RZ2, and the negative voltage insulation impedance RB- of the DC bus is equivalent to the third insulation impedance RZ3. Therefore, another variation of the fifth relational expression can be obtained:

[0120]

[0121] Wherein, BUS+ is the positive voltage of the DC bus, PE1' is the protection ground voltage of the circuit, R1, R2 and R4 are the first impedance, the second impedance and the fourth impedance respectively, RZ2 is the second insulation impedance, and RB- is the negative voltage insulation impedance of the DC bus.

[0122] In some embodiments, the insulation impedance detection circuit is controlled to switch to the fourth switch combination, and another variation of the sixth relational equation can be obtained:

[0123]

[0124] Among them, BUS+ is the positive voltage of the DC bus, PE1' is the protection ground voltage of the circuit, R1, R3 and R4 are the first impedance, the third impedance and the fourth impedance respectively, RZ2 is the second insulation impedance, and RB- is the negative voltage insulation impedance of the DC bus.

[0125] It can be understood that the second insulation impedance RZ2 and the third insulation impedance RZ3 are calculated by using the simultaneous variant equations.

[0126] It should be noted that insulation impedance is an indicator used to evaluate the insulation performance of insulating materials in circuits, and is usually used to detect whether there is insulation damage or aging of insulating materials. When any of the first insulation impedance RZ1, the second insulation impedance RZ2, or the third insulation impedance RZ3 is less than the first preset impedance value, this may indicate that there is an abnormal fault in the insulation impedance, which may cause insulation damage or poor insulation performance in the circuit. When an abnormal insulation impedance fault is detected, timely measures should be taken for inspection and maintenance to ensure the normal operation of the circuit and the safety of personnel.

[0127] Reference Figure 6 As shown,Figure 6 A method flow chart of another insulation impedance detection method provided in an embodiment of the present application.

[0128] The method is applied when the voltage PV1 of the first photovoltaic input terminal and the voltage PV2 of the second photovoltaic input terminal are both greater than the voltage of the DC bus. The method may include but is not limited to the following steps:

[0129] Step S610, when the voltage of the first photovoltaic input terminal and the voltage of the second photovoltaic input terminal are both greater than the voltage of the DC bus, switching to the seventh switch combination, the fifth switch combination and the sixth switch combination respectively;

[0130] Step S620, combining the seventh relational expression obtained under the seventh switch combination, the eighth relational expression obtained under the fifth switch combination, and the ninth relational expression obtained under the sixth switch combination to obtain the first insulation impedance, the second insulation impedance, and the third insulation impedance;

[0131] Step S630: When any one of the first insulation impedance, the second insulation impedance and the third insulation impedance is less than the first preset impedance value, an insulation impedance abnormality fault is prompted.

[0132] It should be noted that the seventh switch combination is that the first switch K3 and the second switch K4 are closed, the third switch K1 and the fourth switch K2 are disconnected, and the seventh relationship is the equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law; the fifth switch combination is that the first switch K3, the second switch K4 and the third switch K1 are closed, and the fourth switch K2 is disconnected, and the eighth relationship is the equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law; the sixth switch combination is that the first switch K3, the second switch K4 and the fourth switch K2 are closed, and the third switch K1 is disconnected, and the ninth relationship is the equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law.

[0133] In some embodiments, when the voltage PV1 of the first photovoltaic input terminal and the voltage PV2 of the second photovoltaic input terminal are both greater than the voltage of the DC bus, the insulation impedance detection circuit is controlled to switch to the seventh switch combination, and the voltage value of the negative voltage of the first photovoltaic input terminal relative to the DC bus, the voltage value of the negative voltage of the second photovoltaic input terminal relative to the DC bus, the voltage value of the positive voltage of the DC bus, and the voltage value of the negative voltage of the protective ground relative to the DC bus are respectively detected through the first voltage detection module, the second voltage detection module, the third voltage detection module, and the fourth voltage detection module. According to the sum of the currents passing through the second impedance R2, the first insulation impedance RZ1, and the second insulation impedance RZ2 being equal to the sum of the currents passing through the third insulation impedance RZ3 and the fourth impedance RZ4, the seventh relationship is obtained:

[0134]

[0135] Among them, BUS+ is the positive voltage of the DC bus, PE is the protection ground voltage of the circuit, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R1 and R2 are the first impedance and the fourth impedance respectively, RZ1, RZ2 and RZ3 are the first insulation impedance, the second insulation impedance and the third insulation impedance respectively.

[0136] In some embodiments, after the seventh relationship is obtained, the insulation impedance detection circuit is controlled to switch to the fifth switch combination, and the sum of the currents through the parallel circuit of the first impedance R1 and the second impedance R2, the first insulation impedance RZ1 and the second insulation impedance RZ2 are equal to the sum of the currents through the third insulation impedance RZ3 and the fourth impedance R4, and the eighth relationship is obtained:

[0137]

[0138] Among them, BUS+ is the positive voltage of the DC bus, PE is the protection ground voltage of the circuit, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R1, R2 and R4 are the first impedance, the second impedance and the fourth impedance respectively, and RZ1, RZ2 and RZ3 are the first insulation impedance, the second insulation impedance and the third insulation impedance respectively.

[0139] In some embodiments, after the eighth relationship is obtained, the insulation impedance detection circuit is controlled to switch to the sixth switch combination, and the eighth relationship is obtained according to the sum of the currents passing through the second impedance R2, the first insulation impedance RZ1, and the second insulation impedance RZ2 being equal to the sum of the currents passing through the third insulation impedance RZ3 and the parallel circuit of the third impedance R3 and the fourth impedance R4:

[0140]

[0141] Among them, BUS+ is the positive voltage of the DC bus, PE is the protection ground voltage of the circuit, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R2, R3 and R4 are the second impedance, the third impedance and the fourth impedance respectively, and RZ1, RZ2 and RZ3 are the first insulation impedance, the second insulation impedance and the third insulation impedance respectively.

[0142] It can be understood that the first insulation impedance RZ1, the second insulation impedance RZ2 and the third insulation impedance RZ3 are calculated by means of the simultaneous variant equations.

[0143] It should be noted that the insulation impedance is an index used to evaluate the insulation performance of insulating materials in a circuit, and is usually used to detect whether there is insulation breakage or aging of insulating materials. When any one of the first insulation impedance RZ1, the second insulation impedance RZ2, or the third insulation impedance RZ3 is less than the first preset impedance value, this may indicate an abnormal fault in the insulation impedance, which may lead to insulation breakage or poor insulation performance in the circuit. When an abnormal fault in the insulation impedance is detected, measures should be taken in a timely manner for repair and maintenance to ensure the normal operation of the circuit and the safety of personnel.

[0144] Referring to Figure 7 as shown, Figure 7 is a schematic diagram of the modules of a controller provided by an embodiment of the present application. The controller 700 includes:

[0145] A processor 710, which can be implemented by using a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, etc., and is used to execute relevant instructions to implement the technical solutions provided by the embodiments of the present application;

[0146] A memory 720, which can be implemented in the form of a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM), etc. The memory 720 can store an operating system and other application programs. When implementing the technical solutions provided by the embodiments of this specification through software or firmware, the relevant program codes are stored in the memory 720 and are called by the processor 710 to execute the technical solutions of the embodiments of the present application;

[0147] An input / output interface 730, which is used to implement information input and output;

[0148] A communication interface 740, which is used to implement communication interaction between this device and other devices, and can implement communication through a wired method (such as USB, network cable, etc.) or through a wireless method (such as mobile network, WIFI, Bluetooth, etc.);

[0149] A bus 750, which transmits information between the various components of the device (such as the processor 710, the memory 720, the input / output interface 730, and the communication interface 740);

[0150] Among them, the processor 710, the memory 720, the input / output interface 730, and the communication interface 740 are communicatively connected to each other inside the device through the bus 750.

[0151] An embodiment of the present application further provides a photovoltaic inverter, which includes the insulation impedance detection circuit and the controller described above.

[0152] In the present application, a first switch is set between the first photovoltaic input terminal and the DC bus, and a second switch is set between the second photovoltaic input terminal and the DC bus. The first switch and the second switch are combined with the third switch and the fourth switch in the impedance detection bridge circuit to form a variety of switch combinations; when the photovoltaic input voltage is less than the DC bus voltage, in order to simplify the calculation process of the first insulation impedance of the first photovoltaic input terminal and the second insulation impedance of the second photovoltaic input terminal, when measuring the impedance, the second switch is disconnected so that the second insulation impedance is equivalent to infinity, and then the first relationship and the second relationship that are independent of the second insulation impedance are obtained. After the first insulation impedance and the third insulation impedance of the protective ground are obtained by combining them, the first switch is disconnected so that the first insulation impedance and the third insulation impedance of the protective ground are obtained. An insulation impedance is equivalent to infinity, and then a third relationship and a fourth relationship that are independent of the first insulation impedance are obtained. The second insulation impedance and the third insulation impedance are obtained after being combined. By comparing the first insulation impedance, the second insulation impedance and the third insulation impedance obtained by the above two calculations with the first preset impedance value, it can be determined whether an insulation impedance abnormality occurs; the insulation impedance is calculated by the method of the present application, and the calculation is simpler than the solution of solving the insulation impedance by combining a set of three-variable equations in the prior art. It is suitable for the photovoltaic insulation impedance when the photovoltaic input voltage is greater than, equal to or less than the DC bus voltage, especially when the photovoltaic input voltage is less than or equal to the DC bus voltage, thereby realizing accurate measurement of the photovoltaic insulation impedance.

[0153] Those of ordinary skill in the art will understand that all or some of the steps and systems disclosed above can be implemented as software, firmware, hardware, and their appropriate combinations. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, it is well known to those of ordinary skill in the art that a communication medium typically includes computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0154] It should be understood that in this application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist at the same time. Among them, 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 (one) of the following" or its similar expression refers to any combination of these items, including any combination of single item (one) or plural items (ones). For example, at least one (one) of a, b, or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0155] In several embodiments provided by the present application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces, indirect couplings or communication connections of apparatuses or units, which can be electrical, mechanical, or other forms. The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0156] It should also be understood that the various embodiments provided by the embodiments of the present application can be arbitrarily combined to achieve different technical effects.

[0157] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present application.

Claims

1. An insulation impedance detection circuit for a photovoltaic inverter, characterized in that, it includes: A first photovoltaic input terminal, with a first switch arranged between the first photovoltaic input terminal and the DC bus; A second photovoltaic input terminal, with a second switch arranged between the second photovoltaic input terminal and the DC bus; An impedance detection bridge circuit, including a first bridge arm and a second bridge arm. The first bridge arm includes a first impedance and a third impedance connected in series, and the second bridge arm includes a second impedance and a fourth impedance connected in series. Both the first bridge arm and the second bridge arm are connected between the positive and negative poles of the DC bus. The midpoints of the first bridge arm and the second bridge arm are both connected to the protective ground. The first impedance is connected to the midpoint of the first bridge arm through a third switch, and the third impedance is connected to the midpoint of the first bridge arm through a fourth switch.

2. The insulation impedance detection circuit according to claim 1, characterized in that, it further includes a first boost circuit and a second boost circuit. The positive pole of the first photovoltaic input terminal, the first switch, the first boost circuit, and the positive pole of the DC bus are connected in sequence. The positive pole of the second photovoltaic input terminal, the second switch, the second boost circuit, and the negative pole of the DC bus are connected in sequence.

3. The insulation impedance detection circuit according to claim 2, characterized in that, the first boost circuit includes a first diode, a second diode, a first inductor, and a first switching tube, and the second boost circuit includes a third diode, a fourth diode, a second inductor, and a second switching tube; The series branch of the first inductor and the second diode is connected in parallel with the first diode. The connection point of the first inductor and the second diode is connected to the negative pole of the DC bus through the first switching tube; the series branch of the second inductor and the fourth diode is connected in parallel with the third diode. The connection point of the second inductor and the fourth diode is connected to the negative pole of the DC bus through the second switching tube.

4. The insulation impedance detection circuit according to claim 1, characterized in that, it further includes a first voltage detection module, a second voltage detection module, a third voltage detection module, and a fourth voltage detection module; the first voltage detection module is used to detect the voltage value of the first photovoltaic input terminal relative to the negative voltage of the DC bus, the second voltage detection module is used to detect the voltage value of the second photovoltaic input terminal relative to the negative voltage of the DC bus, the third voltage detection module is used to detect the voltage value of the positive voltage of the DC bus, and the fourth detection module is used to detect the voltage value of the protective ground relative to the negative voltage of the DC bus.

5. An insulation impedance detection method for an insulation impedance detection circuit, characterized in that, applied to the insulation impedance detection circuit according to any one of claims 1 to 4, the method includes: When the voltage of the first photovoltaic input terminal or the voltage of the second photovoltaic input terminal is less than the voltage of the DC bus, switch to the first switch combination, the second switch combination, the third switch combination, and the fourth switch combination respectively; By combining the first relationship obtained under the first switch combination and the second relationship obtained under the second switch combination, the first insulation impedance corresponding to the first photovoltaic input terminal and the third insulation impedance corresponding to the protective ground are obtained; By combining the third relationship obtained under the third switch combination and the fourth relationship obtained under the fourth switch combination, the second insulation impedance corresponding to the second photovoltaic input terminal and the third insulation impedance corresponding to the protective ground are obtained; When any one of the first insulation impedance, the second insulation impedance, and the third insulation impedance is less than a first preset impedance value, an insulation impedance abnormal fault is prompted; Wherein, the first switch combination is that the second switch and the fourth switch are disconnected, the first switch and the third switch are closed, and the first relationship is an equation of the first insulation impedance and the third insulation impedance obtained according to Kirchhoff's law; The second switch combination is that the second switch and the third switch are disconnected, the first switch and the fourth switch are closed, and the second relationship is an equation of the first insulation impedance and the third insulation impedance obtained according to Kirchhoff's law; The third switch combination is that the first switch and the fourth switch are disconnected, the second switch and the third switch are closed, and the third relationship is an equation of the second insulation impedance and the third insulation impedance obtained according to Kirchhoff's law; The fourth switch combination is that the first switch and the third switch are disconnected, the second switch and the fourth switch are closed, and the fourth relationship is an equation of the second insulation impedance and the third insulation impedance obtained according to Kirchhoff's law.

6. The insulation impedance detection method according to claim 5, characterized in that, The first relationship is: The second relationship is: The third relationship is: The fourth relationship is: Wherein, BUS+ is the positive voltage of the DC bus, PE1, PE2, PE3, and PE4 are the protective ground voltages of the circuit under the corresponding four switch combinations respectively, PV1 is the voltage of the first photovoltaic input terminal, PV2 is the voltage of the second photovoltaic input terminal, R1, R2, R3, and R4 are the first impedance, the second impedance, the third impedance, and the fourth impedance respectively, and RZ1, RZ2, and RZ3 are the first insulation impedance, the second insulation impedance, and the third insulation impedance respectively.

7. The insulation impedance detection method according to claim 4, characterized in that, The method further includes: When the voltages of the first photovoltaic input terminal and the second photovoltaic input terminal are both greater than the voltage of the DC bus, switch to the fifth switch combination and the sixth switch combination respectively; By combining the fifth relationship obtained under the fifth switch combination and the sixth relationship obtained under the sixth switch combination, the positive voltage insulation impedance and the negative voltage insulation impedance of the DC bus are obtained; When the positive voltage insulation impedance or the negative voltage insulation impedance of the DC bus is less than a second preset impedance value, an insulation impedance abnormal fault is prompted; The fifth switch combination is that the first switch, the second switch and the third switch are closed, and the fourth switch is open, and the fifth relational expression is an equation for obtaining the insulation impedance of the DC bus according to Kirchhoff's law; The sixth switch combination is that the first switch, the second switch and the fourth switch are closed, and the third switch is open, and the sixth relationship is an equation for obtaining the insulation impedance of the DC bus according to Kirchhoff's law.

8. The insulation impedance detection method according to claim 4, It is characterized in that The method further comprises: When the voltage of the first photovoltaic input terminal and the voltage of the second photovoltaic input terminal are both greater than the voltage of the DC bus, switching to the seventh switch combination, the fifth switch combination and the sixth switch combination respectively; The first insulation impedance, the second insulation impedance and the third insulation impedance are obtained by combining the seventh relational expression obtained under the seventh switch combination, the eighth relational expression obtained under the fifth switch combination and the ninth relational expression obtained under the sixth switch combination; When any one of the first insulation impedance, the second insulation impedance and the third insulation impedance is less than a first preset impedance value, an abnormal insulation impedance fault is prompted; The seventh switch combination is that the first switch and the second switch are closed, and the third switch and the fourth switch are opened, and the seventh relational expression is an equation for obtaining the first insulation impedance, the second insulation impedance, and the third insulation impedance according to Kirchhoff's law; The fifth switch combination is that the first switch, the second switch and the third switch are closed, and the fourth switch is open, and the eighth relational expression is an equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law; The sixth switch combination is that the first switch, the second switch and the fourth switch are closed, and the third switch is open, and the ninth relationship is an equation for obtaining the first insulation impedance, the second insulation impedance and the third insulation impedance according to Kirchhoff's law.

9. A controller, It is characterized in that comprising at least one processor and a memory for communicatively connecting to the at least one processor; The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the insulation impedance detection method according to any one of claims 5 to 8.

10. A photovoltaic inverter, It is characterized in that It comprises the insulation impedance detection circuit as described in any one of claims 1 to 4 and the controller as described in claim 9.

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