Insulation resistance detection method, power conversion device and photovoltaic system

Abstract

The invention provides an insulation resistance detection method, a power conversion device and a photovoltaic system, which have the advantages of simple circuit and few elements, and can effectively simplify the detection process and reduce the cost. The method comprises the following steps: controlling a direct-current conversion circuit to be in a non-working state, controlling a switch to be switched on, and obtaining a first bus voltage on a positive direct-current bus and a first voltage to ground between a negative direct-current bus and a protection ground; controlling the direct-current conversion circuit to be in a working state, and obtaining a second bus voltage on the positive direct-current bus and a second voltage to ground between the negative direct-current bus and the protection ground; according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistance, obtaining a reciprocal sum of insulation resistance between the plurality of direct-current power supplies and the protection ground; and judging whether the insulation impedance between the plurality of direct-current power supplies and the protection ground is abnormal according to the reciprocal sum of the insulation impedance.

Description

Technical Field

[0001] The present application relates to the technical field of circuit detection, and in particular to an insulation impedance detection method, a power conversion device and a photovoltaic system. Background Art

[0002] There is impedance between the positive and negative terminals of all inputs and the earth. For example, there is impedance between the positive and negative terminals of various electrical equipment and power generation equipment and the earth, which is also called insulation impedance to the earth. Under normal circumstances, the insulation impedance of the equipment to the earth is very large and will not cause harm to people. However, when an abnormal situation occurs, the insulation impedance to the earth becomes very small, which may endanger people's lives and property. Therefore, it is necessary to test the insulation impedance of the equipment to the earth. The insulation impedance test to the earth is also called ISO (Insulation System Observation) test.

[0003] ISO detection is particularly important in photovoltaic systems. The principle of ISO detection in photovoltaic systems is: by detecting the positive pole (PV+) to ground voltage and the negative pole (PV-) to ground voltage of each photovoltaic (PV) power generation device, and calculating the resistance of PV+ to ground and the resistance of PV- to ground respectively. If the resistance value on either side is lower than the threshold, it means that the insulation impedance in the system is abnormal. At present, most of the related technologies use the "unbalanced bridge method" to perform ISO detection on photovoltaic power generation equipment, that is, multiple detection resistors and relays are connected in parallel to the photovoltaic power generation equipment, and the positive and negative poles of the photovoltaic power generation equipment are dynamically measured by opening and closing the relays to measure the ground resistance and ground voltage, thereby analyzing and judging whether there is an abnormality in the insulation impedance to ground.

[0004] However, with the increase in photovoltaic power generation equipment, the relevant technology needs to simultaneously increase relays and detection resistors, making the detection more complicated, and increasing the number of relays and detection resistors is not conducive to reducing costs. Summary of the invention

[0005] In view of the above, it is necessary to provide an insulation impedance detection method, a power conversion device and a photovoltaic system, which have a simple circuit and few components, can effectively simplify the detection process and reduce costs.

[0006] In a first aspect, the present application provides an insulation impedance detection method, which is applied to a power conversion device. The power conversion device includes a DC conversion circuit, a positive DC bus, a negative DC bus, and an insulation impedance detection circuit. The positive DC bus is used to connect the positive input terminals of multiple DC power supplies through the DC conversion circuit, and the negative DC bus is used to connect the negative input terminals of multiple DC power supplies and connect to a protective ground. The insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus. The insulation impedance detection circuit includes a detection resistor and a switch. The insulation impedance detection method includes: controlling the DC conversion circuit to be in a non-working state and controlling the switch to be turned on; when the DC conversion circuit is in a non-working state, the insulation impedance detection circuit is connected to the positive input terminals of multiple DC power supplies and connected to a protective ground. When the DC conversion circuit is in a non-working state and the switch is turned on, a first bus voltage on the positive DC bus and a first voltage to ground between the negative DC bus and the protective ground are obtained; the DC conversion circuit is controlled to be in a working state; when the DC conversion circuit is in a working state and the switch is turned on, a second bus voltage on the positive DC bus and a second voltage to ground between the negative DC bus and the protective ground are obtained; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is obtained according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistance; and whether the insulation impedances between the multiple DC power supplies and the protective ground are abnormal is determined according to the reciprocal sum of the insulation impedances.

[0007] In some embodiments, whether the insulation impedance between multiple DC power supplies and the protective ground is abnormal is judged based on the reciprocal sum of the insulation impedance, including: if the reciprocal sum of the insulation impedance is less than the reciprocal of the rated impedance of the DC power supply, then the insulation impedance is abnormal; if the reciprocal sum of the insulation impedance is not less than the reciprocal of the rated impedance of the DC power supply, then the insulation impedance is normal.

[0008] In some embodiments, the reciprocal sum of the insulation impedances between multiple DC power supplies and the protective ground is obtained according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor, including: obtaining a first current expression according to the first bus voltage, the first voltage to ground and the detection resistor; the first current expression is related to the bus voltage of the positive DC bus, the voltage to ground of the negative DC bus, the detection resistor, and the insulation impedance between the multiple DC power supplies and the protective ground; obtaining a second current expression according to the second bus voltage, the second voltage to ground and the detection resistor; the second current expression is related to the bus voltage of the positive DC bus, the voltage to ground of the negative DC bus, the detection resistor, and the insulation impedance between the multiple DC power supplies and the protective ground; according to the first current expression and the second current expression, the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is calculated.

[0009] In some embodiments, the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is inversely proportional to the resistance value of the detection resistor; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is positively correlated with the first bus voltage; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is negatively correlated with the second bus voltage; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is negatively correlated with the first voltage to ground; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is positively correlated with the second voltage to ground.

[0010] The second aspect of the present application provides a power conversion device, which includes: a DC conversion circuit, a positive DC bus, a negative DC bus, an insulation impedance detection circuit and a controller, wherein the positive DC bus is used to connect the positive input terminals of multiple DC power supplies through the DC conversion circuit, the negative DC bus is used to connect the negative input terminals of multiple DC power supplies and connect to the protective ground, the insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus, and the insulation impedance detection circuit includes a detection resistor and a switch; the controller is used to control the operating state of the DC conversion circuit and control the conduction state of the switch, and when the DC conversion circuit is in a non-operating state .... When the DC conversion circuit is in the working state and the switch is turned on, a first bus voltage on the positive DC bus and a first voltage to ground between the negative DC bus and the protective ground are obtained, and when the DC conversion circuit is in the working state and the switch is turned on, a second bus voltage on the positive DC bus and a second voltage to ground between the negative DC bus and the protective ground are obtained; the controller is also used to obtain the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistance, and judge whether the insulation impedances between the multiple DC power supplies and the protective ground are abnormal according to the reciprocal sum of the insulation impedances.

[0011] In some embodiments, the controller determines whether the insulation impedance between multiple DC power supplies and the protective ground is abnormal based on the reciprocal of the insulation impedance, including: if the reciprocal of the insulation impedance is less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is abnormal; if the reciprocal of the insulation impedance is not less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is normal.

[0012] The third aspect of the present application provides a photovoltaic system, including: multiple DC power supplies, a power conversion device and an inverter device; the power conversion device includes: a DC conversion circuit, a positive DC bus, a negative DC bus, an insulation impedance detection circuit and a controller, the positive DC bus is used to connect the positive input terminals of multiple DC power supplies through the DC conversion circuit, the negative DC bus is used to connect the negative input terminals of multiple DC power supplies and connect to the protective ground, the insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus, the insulation impedance detection circuit includes a detection resistor and a switch, the positive DC bus and the negative DC bus are respectively connected to the positive input terminal and the negative input terminal of the inverter device; the controller is used to control the operation of the DC conversion circuit The controller controls the conduction state of the switch, and when the DC conversion circuit is in a non-working state and the switch is turned on, obtains a first bus voltage on the positive DC bus and a first voltage to ground between the negative DC bus and the protective ground, and when the DC conversion circuit is in a working state and the switch is turned on, obtains a second bus voltage on the positive DC bus and a second voltage to ground between the negative DC bus and the protective ground; the controller is also used to obtain the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor, and judges whether the insulation impedances between the multiple DC power supplies and the protective ground are abnormal according to the reciprocal sum of the insulation impedances.

[0013] In some embodiments, the controller determines whether the insulation impedance between multiple DC power supplies and the protective ground is abnormal based on the reciprocal of the insulation impedance, including: if the reciprocal of the insulation impedance is less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is abnormal; if the reciprocal of the insulation impedance is not less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is normal.

[0014] In some embodiments, the DC power source includes a photovoltaic power source.

[0015] In some embodiments, the DC conversion circuit includes a BOOST boost circuit.

[0016] In some embodiments, the switch comprises a relay.

[0017] This application has the following technical effects:

[0018] 1. The insulation impedance detection method, power conversion device and photovoltaic system of the present application control the working state of the DC conversion circuit and obtain multiple voltages of the positive and negative DC bus bars. There is no need to add resistors and relays to obtain the multiple voltages required for insulation impedance detection. Compared with the "unbalanced bridge method", the circuit is simpler and has fewer components, which can effectively simplify the detection process and reduce costs.

[0019] 2. The insulation impedance detection method, power conversion device and photovoltaic system of the present application can quickly determine whether the insulation impedance to ground of multiple DC power supplies is abnormal based on the relationship between multiple voltages and the insulation impedance to ground of DC power supplies. If the insulation impedance to ground of multiple DC power supplies is normal, there is no need to detect the insulation impedance to ground of each DC power supply, thereby improving the working efficiency of the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a photovoltaic system according to an embodiment of the present application.

[0021] Figure 2 It is a circuit schematic diagram when the DC conversion circuit is in a non-working state during the process of detecting the insulation impedance of a DC power supply in an embodiment of the present application.

[0022] Figure 3 It is a circuit schematic diagram of a DC conversion circuit in a working state during the process of detecting the insulation impedance of a DC power supply in an embodiment of the present application.

[0023] Figure 4 It is a flow chart of the insulation impedance detection method of an embodiment of the present application. DETAILED DESCRIPTION

[0024] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example" and the like are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "or", "for example" and the like is intended to present related concepts in a concrete manner.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field in the embodiments of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. It should be understood that in the embodiments of the present application, unless otherwise specified, " / " means or. For example, A / B can represent A or B. "And / or" in the embodiments of the present application is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. "At least one" means one or more. "Multiple" means two or more than two. For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c, a, b and c seven situations.

[0026] It should also be noted that the terms "first" and "second" in the specification, claims and drawings of the present application are used to distinguish similar objects rather than to describe a specific order or sequence.

[0027] The principle of ISO detection in conventional photovoltaic systems is: by detecting the PV+ voltage to ground and the PV- voltage to ground, the resistance of PV+ to ground and the resistance of PV- to ground are calculated respectively. If the resistance value on either side is lower than the threshold, it means that the insulation impedance in the system is abnormal. Among them, PV (Photovoltaic) refers to photovoltaic power generation equipment. During detection, photovoltaic power generation equipment is used as a power supply to other equipment, so it is also called DC power supply or DC input. PV+ and PV- are the positive and negative poles of the DC power supply respectively. At present, most of the related technologies use the "unbalanced bridge method" to perform ISO detection on the DC power supply, that is, multiple detection resistors and relays are connected in parallel to the DC power supply, and the positive and negative poles of the DC power supply are dynamically measured by opening and closing the relay to measure the ground resistance and ground voltage of the DC power supply, thereby analyzing and judging whether there is an abnormality in the insulation impedance to ground.

[0028] The more DC power supplies there are, the better, because this allows people to get more electricity through DC power supplies. However, when performing ISO detection in related technologies, the increase in DC power supplies requires the simultaneous increase of relays and detection resistors, making the detection more cumbersome, and increasing the number of relays and detection resistors is not conducive to reducing costs. For example, a method for detecting impedance from multiple DC inputs to ground seen in the "unbalanced bridge method" includes installing detection resistors on multiple DC power supplies, installing relays on multiple DC power supplies, disconnecting the relays, obtaining the voltage of the positive and negative poles of the DC bus, and then closing the relays to obtain the voltage of the positive and negative poles of the DC power bus. According to the two sets of voltages, the mathematical expression of the conductivity value containing the impedance to ground is determined, and finally the range of the impedance value to ground is determined, thereby completing the insulation impedance to ground. In this related technology, the number of detection resistors and relays needs to be the same as the number of DC power supplies, which leads to a complex circuit structure and a cumbersome detection process, which is not conducive to reducing costs.

[0029] To this end, the embodiments of the present application provide an insulation impedance detection method, a power conversion device, and a photovoltaic system, which have a simple circuit and few components, and can effectively simplify the detection process and reduce costs.

[0030] Some embodiments will be described below in conjunction with the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other if there is no conflict.

[0031] In the embodiments of this application, please refer to Figure 1 The photovoltaic system 1 may include: a plurality of DC power sources 11 , a power conversion device 12 and an inverter device 13 .

[0032] The positive input terminal and the negative input terminal of the DC power supply 11 are connected to the power conversion device 12 , and the DC power supply 11 is used to output DC power to the power conversion device 12 .

[0033] In this embodiment, the DC power supply 11 may adopt a photovoltaic power generation device. Photovoltaic power generation equipment is used to convert solar energy into DC power. It is understandable that in other embodiments and other application scenarios, the DC power supply 11 may not be limited to a photovoltaic power supply, for example, it may also include a wind power supply, a hydropower supply or other power supplies that convert different forms of energy into electrical energy. A wind power supply refers to a power supply device that converts the mechanical energy carried by wind power into electrical energy, and a hydropower supply refers to a power supply device that converts the mechanical energy carried by water power into electrical energy.

[0034] In the embodiments of this application, please refer to Figure 1 and Figure 2 The DC power supply 11 can be set to n, where n is a positive integer not less than 2, for example, n=2, 3, 4 or a larger value, which can be selected according to actual conditions.

[0035] It is understandable that if Figure 2 As shown, when there are n DC power supplies 11, the impedances of the positive and negative terminals of the first DC power supply 11a to the ground are R1+ and R1-, respectively, and the impedances of the positive and negative terminals of the second DC power supply 11b to the ground are R2+ and R2-, respectively. By analogy, the impedances of the positive and negative terminals of the nth DC power supply 11n to the ground are Rn+ and Rn-, respectively. Since the negative input terminals of each DC power supply 11 are directly connected to the protective ground PE, each protective ground PE can use the same as a reference, so the impedances from the negative input terminals of each DC power supply 11 to the protective ground PE can be regarded as parallel impedances, set to R 并 -, that is, R 并 - is the parallel impedance of R1-, R2-, R3-, ... The input voltages of the n DC power sources 11 are V1, V2, ..., Vn, respectively.

[0036] The power conversion device 12 includes a DC conversion circuit 121 , a positive DC bus (ie, BUS+), a negative DC bus (ie, BUS−), a controller 122 , and an insulation impedance detection circuit 123 .

[0037] The DC conversion circuit 121 is connected to the positive DC bus and the negative DC bus, and can be connected to the inverter device 13 through the positive DC bus and the negative DC bus. The inverter device 13 can also be connected to the load or the AC grid 2. The DC conversion circuit 121 can be used to convert the DC power output by the DC power supply 11 into another DC power and provide it to the inverter device 13. The inverter device 13 then inverts the DC power output by the DC conversion circuit 121 into AC power and provides it to the load or the AC grid 2.

[0038] In the embodiment of the present application, the DC conversion circuit 121 may include at least one of a BUCK step-down circuit, a BOOST step-up circuit, and a BUCK-BOOST step-up / step-down circuit, and is used to perform voltage conversion operations such as step-down, step-up, or step-up / step-down on multiple DC power sources 11. In this embodiment, the DC conversion circuit 121 is a BOOST step-up circuit.

[0039] In the embodiment of the present application, the positive DC bus is used to connect one side of the DC conversion circuit 121, the other side of the DC conversion circuit 121 is connected to the positive input terminal of multiple DC power supplies 11, the negative DC bus is used to connect the negative input terminal of multiple DC power supplies 11, and the negative DC bus is also used to connect the protective ground PE. The positive DC bus is also connected to the positive input terminal of the inverter device 13, and the negative DC bus is also connected to the negative input terminal of the inverter device 13. Among them, the protective ground PE is also called the safety ground, which refers to the zero point position that ensures the safety of the circuit, and sometimes also refers to the earth.

[0040] The operation state of the DC conversion circuit 121 includes a working state and a non-working state. Figure 2 The voltage of the plurality of DC power supplies 11 remains unchanged when in working state (indicated by a dotted frame in FIG. Figure 3 The voltages of the plurality of DC power supplies 11 may be transformed.

[0041] In the embodiment of the present application, the insulation impedance detection circuit 123 is connected in parallel between the positive DC bus and the negative DC bus. Figure 1 As shown, the insulation impedance detection circuit 123 includes a detection resistor R and a switch RY. The detection resistor R and the switch are connected in series and connected between the positive DC bus and the negative DC bus, so that the insulation impedance detection of multiple DC power supplies 11 can be used.

[0042] The switch RY may include an electronic switch such as a semiconductor switch, a relay or a contactor. In this embodiment, the switch RY adopts a relay. The DC power supply 11 can be tested for insulation impedance to ground by cooperating with the relay and the detection resistor R. When not testing, the relay is disconnected and the detection resistor R is not connected, which does not affect the normal operation of the DC input. When testing, the relay is closed.

[0043] In some embodiments, the insulation impedance detection circuit 123 may further include a detection voltmeter Vi, which may be disposed between the negative DC bus and the protective ground PE. Alternatively, the insulation impedance detection circuit may not include a voltmeter, that is, the voltmeter is independent of the insulation impedance detection circuit, and the insulation impedance detection circuit may be connected to the voltmeter in communication and obtain detection data of the voltmeter from the voltmeter. Of course, in some other embodiments, the voltmeter may also be replaced by a voltage detection circuit, which may be independently disposed or integrated in the controller.

[0044] In the embodiment of the present application, the controller 122 can control the DC conversion circuit 121 to be in a non-operating state and the switch RY to be turned on, or control the DC conversion circuit 121 to be in an operating state and the switch RY to be turned on. Controlling the switch RY to be turned on means controlling the switch RY such as a relay to be turned on (i.e., the switch RY is closed) when insulation impedance detection of multiple DC power sources 11 is required, thereby obtaining multiple voltages required for detection through the insulation impedance detection circuit 123.

[0045] Further, when the DC conversion circuit 121 is in a non-operating state and the switch RY is turned on, the controller 122 can also obtain a first bus voltage on the positive DC bus and a first ground voltage between the negative DC bus and the protective ground PE. Figure 2 When the controller 122 controls the BOOST boost circuit to be in a non-working state, the first bus voltage from the positive DC bus to the protective ground PE is Vb1. During detection, the controller 122 controls the relay RY to close, and the first ground voltage from the negative DC bus to the protective ground PE is Vg1.

[0046] When the DC conversion circuit 121 is in operation and the switch RY is turned on, the controller 122 can obtain the second bus voltage on the positive DC bus and the second ground voltage between the negative DC bus and the protective ground PE. Figure 3 When the controller 122 controls the BOOST boost circuit to be in working state, the second bus voltage from the positive DC bus to the protective ground PE is Vb2. During detection, the controller 122 controls the relay RY to close, and the second ground voltage from the negative DC bus to the protective ground PE is Vg2.

[0047] The first bus voltage and the second bus voltage can be obtained by sampling the inverter device 13. Specifically, the controller 122 can obtain the first bus voltage and the second bus voltage by sampling the input terminal voltage of the inverter device 12. The first voltage to ground and the second voltage to ground can be obtained by detecting the voltage meter Vi.

[0048] In the embodiment of the present application, the controller 122 can obtain the reciprocal sum of the insulation impedances between multiple DC power supplies 11 and the protective ground PE based on the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor R.

[0049] Specifically, the reciprocals of R1+, R2+…Rn+ are G1, G2…Gn, R 并 - is the reciprocal of G0. When the BOOST boost circuit is in a non-operating state, the controller 122 can obtain the following first current expression based on Kirchhoff's current law according to the first bus voltage, the first ground voltage and the detection resistor R:

[0050] Vg1×(G0)=(V1-Vg1)×G1+(V2-Vg1)×G2+…+(Vn-Vg1)×Gn+(Vb1-Vg1) / R (1)

[0051] When the BOOST boost circuit is in operation, the controller 122 can obtain the following second current expression based on Kirchhoff's current law according to the second bus voltage, the second ground voltage and the detection resistor R:

[0052] Vg2×(G0)=(V1-Vg2)×G1+(V2-Vg2)×G2+…+(Vn-Vg2)×Gn+(Vb2-Vg2) / R (2)

[0053] Furthermore, the controller 122 can calculate the reciprocal sum of the insulation impedances between the plurality of DC power supplies 11 and the protective ground PE according to the first current expression and the second current expression, that is, the following formula can be obtained through formula (1) and formula (2):

[0054] G0+G1+G2+……+Gn=(Vb1-Vg1-Vb2+Vg2) / R(Vg1-Vg2) (3)

[0055] It can be obtained from formula (3) that the reciprocal sum of the insulation impedances between the multiple DC power supplies 11 and the protective ground PE is inversely proportional to the resistance value of the detection resistor R, the reciprocal sum of the insulation impedances between the multiple DC power supplies 11 and the protective ground PE is positively correlated with the first bus voltage, the reciprocal sum of the insulation impedances between the multiple DC power supplies 11 and the protective ground PE is negatively correlated with the second bus voltage, the reciprocal sum of the insulation impedances between the multiple DC power supplies 11 and the protective ground PE is negatively correlated with the first voltage to ground, and the reciprocal sum of the insulation impedances between the multiple DC power supplies 11 and the protective ground PE is positively correlated with the second voltage to ground.

[0056] Moreover, as long as the insulation impedance between any at least one DC power supply 11 and the protective earth PE is less than the rated impedance of the DC power supply 11, that is, the insulation impedance of at least one DC power supply 11 is abnormal, the sum of the reciprocals of the insulation impedances between multiple DC power supplies 11 and the protective earth PE will be less than the reciprocal of the rated impedance of the DC power supply 11. Therefore, it can be determined that the insulation impedances between multiple DC power supplies 11 and the protective earth PE are abnormal.

[0057] On the contrary, if the insulation impedance between all DC power supplies 11 and the protective earth PE is greater than the rated impedance of the DC power supplies 11, that is, the insulation impedance of all DC power supplies 11 is normal, the sum of the reciprocals of the insulation impedances between multiple DC power supplies 11 and the protective earth PE can be no less than the reciprocal of the rated impedance of the DC power supplies 11, then it can be determined that the insulation impedance between multiple DC power supplies 11 and the protective earth PE is normal.

[0058] For example, assuming that the insulation resistance of multiple DC power supplies 11 to ground is 50kΩ, when G0+G1+G2+…+Gn<1 / 50000, the insulation resistance of at least one of the DC power supplies 11 to ground is less than 50kΩ. When G0+G1+G2+…+Gn≥1 / 50000, the insulation resistance of all multiple DC power supplies 11 to ground is greater than 50kΩ. Therefore, any insulation resistance of any one of the multiple DC power supplies 11 to ground less than 50kΩ (i.e., unqualified) can be detected by the controller of the present application.

[0059] Based on the above power conversion device and photovoltaic system, the present application embodiment also provides an insulation impedance detection method. Figure 4 , the insulation impedance detection method of the embodiment of the present application may include:

[0060] Step S100, controlling the DC conversion circuit to be in a non-operating state, and controlling the switch to be turned on.

[0061] The DC conversion circuit being in a non-working state means that the operating state of the BOOST boost circuit is controlled to be a non-working state, and the control switch is turned on, that is, the control relay is closed.

[0062] Step S200, when the DC conversion circuit is in a non-operating state and the switch is turned on, obtaining a first bus voltage on the positive DC bus and a first ground voltage between the negative DC bus and the protective ground.

[0063] The first bus voltage from the positive DC bus to the protective ground is Vb1, and the first ground voltage from the negative DC bus to the protective ground is Vg1.

[0064] Step S300, controlling the DC conversion circuit to be in a working state, wherein the DC conversion circuit being in a working state means controlling the operation state of the BOOST boost circuit to be in a working state.

[0065] Step S400, when the DC conversion circuit is in working state and the switch is turned on, obtaining a second bus voltage on the positive DC bus and a second ground voltage between the negative DC bus and the protective ground.

[0066] The second bus voltage from the positive DC bus to the protective ground is Vb2, and the second ground voltage from the negative DC bus to the protective ground is Vg2.

[0067] Step S500, obtaining the reciprocal sum of insulation impedances between a plurality of DC power supplies and a protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and a detection resistor.

[0068] In some embodiments, step S500 further includes: obtaining a first current expression according to the first bus voltage, the first voltage to ground and the detection resistor, and obtaining a second current expression according to the second bus voltage, the second voltage to ground and the detection resistor; and calculating the reciprocal sum of the insulation impedances between the plurality of DC power supplies and the protective ground according to the first current expression and the second current expression. Specifically including:

[0069] The reciprocals of R1+, R2+…Rn+ are G1, G2…Gn, R 并 - is the reciprocal of G0. The controller can obtain a first current expression according to the first bus voltage, the first voltage to ground and the detection resistor. Specifically, according to Kirchhoff's current law, the following formula can be obtained when the BOOST boost circuit is in a non-working state:

[0070] Vg1×(G0)=(V1-Vg1)×G1+(V2-Vg1)×G2+…+(Vn-Vg1)×Gn+(Vb1-Vg1) / R (1)

[0071] The controller can obtain a second current expression according to the second bus voltage, the second voltage to ground and the detection resistor. Specifically, according to Kirchhoff's current law, the following expression can be obtained when the BOOST boost circuit is in the working state:

[0072] Vg2×(G0)=(V1-Vg2)×G1+(V2-Vg2)×G2+…+(Vn-Vg2)×Gn+(Vb2-Vg2) / R (2)

[0073] In some embodiments, the controller can calculate the reciprocal sum of the insulation impedances between the plurality of DC power supplies and the protective ground according to the first current expression and the second current expression. Specifically, the controller can calculate the following formula using formula (1) and formula (2):

[0074] G0+G1+G2+……+Gn=(Vb1-Vg1-Vb2+Vg2) / R(Vg1-Vg2) (3)

[0075] Step S600: determining whether the insulation impedances between the plurality of DC power supplies and the protective ground are abnormal based on the sum of the inverses of the insulation impedances.

[0076] In some embodiments, step S600 further includes: if the sum of the reciprocals of the insulation impedances is less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is abnormal; if the sum of the reciprocals of the insulation impedances is not less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is normal.

[0077] In summary, the insulation impedance detection method, power conversion device 12 and photovoltaic system 1 of the present application, by controlling the working state of the DC conversion circuit 121 and obtaining multiple voltages of the positive and negative DC busbars, do not need to add resistors and relays to obtain multiple voltages required for insulation impedance detection. Compared with the "unbalanced bridge method", the circuit is simpler and has fewer components, which can effectively simplify the detection process and reduce costs. In addition, based on the relationship between multiple voltages and the insulation impedance to ground of the DC power supply 11, the present application can quickly determine whether the insulation impedance to ground of multiple DC power supplies 11 is abnormal. If the insulation impedance to ground of multiple DC power supplies 11 is normal, there is no need to detect the insulation impedance to ground of each DC power supply 11, thereby improving the working efficiency of the photovoltaic system 1.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A method for detecting insulation impedance, characterized in that: Applied to a power conversion device, the power conversion device includes a DC conversion circuit, a positive DC bus, a negative DC bus and an insulation impedance detection circuit, the positive DC bus is used to connect the positive input terminals of multiple DC power supplies through the DC conversion circuit, the negative DC bus is used to connect the negative input terminals of multiple DC power supplies and connect to a protective ground, the insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus, and the insulation impedance detection circuit includes a detection resistor and a switch; The insulation impedance detection method comprises: Controlling the DC conversion circuit to be in a non-working state, and controlling the switch to be turned on; When the DC conversion circuit is in the non-working state and the switch is turned on, obtaining a first bus voltage on the positive DC bus and a first ground voltage between the negative DC bus and the protective ground; Controlling the DC conversion circuit to be in working state; When the DC conversion circuit is in the working state and the switch is turned on, obtaining a second bus voltage on the positive DC bus and a second ground voltage between the negative DC bus and the protective ground; Obtaining a sum of reciprocals of insulation impedances between the plurality of DC power supplies and the protection ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground, and the detection resistor; Whether the insulation impedances between the plurality of DC power supplies and the protection ground are abnormal is determined according to the reciprocal sum of the insulation impedances.

2. The insulation impedance detection method according to claim 1, characterized in that: The step of judging whether the insulation impedances between the plurality of DC power supplies and the protection ground are abnormal based on the reciprocal of the insulation impedance includes: If the sum of the reciprocals of the insulation impedances is less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is abnormal; If the sum of the reciprocals of the insulation impedances is not less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is normal.

3. The insulation impedance detection method according to claim 1, characterized in that: The step of obtaining the reciprocal sum of the insulation impedances between the plurality of DC power supplies and the protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor comprises: A first current expression is obtained according to the first bus voltage, the first voltage to ground and the detection resistor; the first current expression is related to the bus voltage of the positive DC bus, the voltage to ground of the negative DC bus, the detection resistor, and the insulation impedance between the plurality of DC power supplies and the protection ground; A second current expression is obtained according to the second bus voltage, the second voltage to ground and the detection resistor; the second current expression is related to the bus voltage of the positive DC bus, the voltage to ground of the negative DC bus, the detection resistor, and the insulation impedance between the plurality of DC power supplies and the protection ground; According to the first current expression and the second current expression, the reciprocal sum of the insulation impedances between the plurality of DC power supplies and the protective ground is calculated and obtained.

4. The insulation impedance detection method according to claim 1, characterized in that: The reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is inversely proportional to the resistance value of the detection resistor; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is positively correlated with the first bus voltage; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is negatively correlated with the second bus voltage; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is negatively correlated with the first voltage to ground; the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground is positively correlated with the second voltage to ground.

5. A power conversion device, characterized in that: The power conversion device comprises: a DC conversion circuit, a positive DC bus, a negative DC bus, an insulation impedance detection circuit and a controller, wherein the positive DC bus is used to connect the positive input terminals of a plurality of DC power supplies through the DC conversion circuit, the negative DC bus is used to connect the negative input terminals of the plurality of DC power supplies and to a protective ground, the insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus, and the insulation impedance detection circuit comprises a detection resistor and a switch; The controller is used to control the operating state of the DC conversion circuit and the conducting state of the switch, and when the DC conversion circuit is in a non-working state and the switch is turned on, obtain a first bus voltage on the positive DC bus and a first voltage to ground between the negative DC bus and the protective ground, and when the DC conversion circuit is in a working state and the switch is turned on, obtain a second bus voltage on the positive DC bus and a second voltage to ground between the negative DC bus and the protective ground; The controller is also used to obtain the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor, and to determine whether the insulation impedances between the multiple DC power supplies and the protective ground are abnormal according to the reciprocal sum of the insulation impedances.

6. The power conversion device according to claim 5, characterized in that: When the sum of the reciprocals of the insulation impedances is less than the reciprocal of the rated impedance of the DC power supply, the controller determines that the insulation impedance is abnormal; When the sum of the reciprocals of the insulation impedances is not less than the reciprocal of the rated impedance of the DC power supply, the controller determines that the insulation impedance is normal.

7. A photovoltaic system, characterized in that: include: Multiple DC power supplies, power conversion devices and inverter devices; The power conversion device comprises: a DC conversion circuit, a positive DC bus, a negative DC bus, an insulation impedance detection circuit and a controller, wherein the positive DC bus is used to connect the positive input terminals of a plurality of DC power supplies through the DC conversion circuit, the negative DC bus is used to connect the negative input terminals of a plurality of the DC power supplies and to a protective ground, the insulation impedance detection circuit is connected in parallel between the positive DC bus and the negative DC bus, the insulation impedance detection circuit comprises a detection resistor and a switch, and the positive DC bus and the negative DC bus are respectively connected to the positive input terminal and the negative input terminal of the inverter device; The controller is used to control the operating state of the DC conversion circuit and the conducting state of the switch, and when the DC conversion circuit is in a non-working state and the switch is turned on, obtain a first bus voltage on the positive DC bus and a first voltage to ground between the negative DC bus and the protective ground, and when the DC conversion circuit is in a working state and the switch is turned on, obtain a second bus voltage on the positive DC bus and a second voltage to ground between the negative DC bus and the protective ground; The controller is also used to obtain the reciprocal sum of the insulation impedances between the multiple DC power supplies and the protective ground according to the first bus voltage, the first voltage to ground, the second bus voltage, the second voltage to ground and the detection resistor, and to determine whether the insulation impedances between the multiple DC power supplies and the protective ground are abnormal according to the reciprocal sum of the insulation impedances.

8. The photovoltaic system according to claim 7, characterized in that: The controller determines whether the insulation impedance between the plurality of DC power supplies and the protection ground is abnormal according to the inverse of the insulation impedance, including: If the sum of the reciprocals of the insulation impedances is less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is abnormal; If the sum of the reciprocals of the insulation impedances is not less than the reciprocal of the rated impedance of the DC power supply, the insulation impedance is normal.

9. The photovoltaic system according to claim 7, characterized in that: The DC power source includes a photovoltaic power generation device.

10. The photovoltaic system according to claim 7, characterized in that: The DC conversion circuit includes a BOOST boost circuit.

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