Converter

Abstract

The converter comprises a bidirectional conversion circuit, a detection circuit and a voltage detection module, the detection circuit comprises a first resistor, a second resistor, a third resistor, a first switch and a second switch, and the first end of the first resistor is electrically connected to the direct current positive end of the bidirectional conversion circuit; the second end of the first resistor is connected with the first end of the second resistor, the second end of the second resistor is connected with the first end of the third resistor, and the second end of the third resistor is electrically connected to the direct current negative end of the bidirectional conversion circuit; a connection point between the first resistor and the second resistor is electrically connected to the direct current negative end of the bidirectional conversion circuit through the second switch, and a connection point between the second resistor and the third resistor is grounded through the first switch; the voltage detection module is configured to collect the voltage to ground of the direct current negative end of the bidirectional conversion circuit. According to the converter, detection of ground insulation resistance can be realized, and sensitivity, accuracy and response speed of ground short circuit detection of the converter can be improved.

Description

[0001] This application claims the priority of a Chinese patent application titled "Converter", with the application number 202411288519.4 and filed with the Chinese Patent Office on September 13, 2024. The entire content of which is incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and particularly to a converter. Background Art

[0003] With the rapid development of renewable energy, energy storage systems, as an important part of smart grids, have received extensive attention for their safety and reliability. An energy storage system usually consists of a battery pack, a BMS (Battery Management System), a PCS (Power Conversion System for Energy Storage), and AC mains. During the operation of the energy storage system, the PCS, as one of the key devices, is responsible for realizing the energy conversion and control between the battery pack and the AC mains.

[0004] In practical applications, due to various factors such as equipment aging, environmental impact, and human operation errors, a ground short - circuit fault may occur on the AC side of the PCS. This kind of fault will not only affect the normal operation of the energy storage system, but also pose a threat to the safety of equipment and personnel. Therefore, the method for detecting the ground short - circuit of the AC side of the PCS is of great significance for ensuring the safety and reliability of the energy storage system. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the purpose of this application is to provide a converter that can detect the insulation impedance between the converter port and the ground.

[0006] To achieve the above purpose, this application adopts the following technical solutions:

[0007] The present application provides a converter, the converter includes a bidirectional conversion circuit, the bidirectional conversion circuit includes a DC port and an AC port, and the bidirectional conversion circuit is used for bidirectional conversion of AC / DC power supplies; the converter further includes: a detection circuit, the detection circuit includes a first resistor, a second resistor and a third resistor, a first end of the first resistor is electrically connected to a positive DC end of the bidirectional conversion circuit, a second end of the first resistor is connected to a first end of the second resistor, a second end of the second resistor is connected to a first end of the third resistor, and a second end of the third resistor is electrically connected to a negative DC end of the bidirectional conversion circuit; the detection circuit further includes a first switch and a second switch, a connection point between the first resistor and the second resistor is electrically connected to the negative DC end of the bidirectional conversion circuit through the second switch, and a connection point between the second resistor and the third resistor is grounded through the first switch; the converter further includes a voltage detection module, and the voltage detection module is configured to collect the voltage of the negative DC end of the bidirectional conversion circuit with respect to the ground.

[0008] The above-mentioned converter controls the on / off states of the first switch and the second switch, so that the first resistor, the second resistor and the third resistor in the detection circuit form different current loops in different situations, then detects the voltages under different current loops, infers the magnitude and direction of the current, and collects the voltage of the negative DC end with respect to the ground through the voltage detection module. Furthermore, by combining the magnitude and direction of the current and the voltage of the negative DC end with respect to the ground, the insulation impedance of the converter port with respect to the ground can be detected. Description of the Drawings

[0009] Figure 1 It is a schematic structural diagram of a converter provided by an embodiment of the present application;

[0010] Figure 2 It is a schematic structural diagram of another converter provided by an embodiment of the present application;

[0011] Figure 3 It is a schematic diagram of an equivalent circuit for detecting the insulation resistance of the positive DC end with respect to the ground provided by an embodiment of the present application;

[0012] Figure 4 It is a schematic diagram of an equivalent circuit for detecting the insulation resistance of the negative DC end with respect to the ground provided by an embodiment of the present application;

[0013] Figure 5 It is a waveform diagram of a third voltage provided by an embodiment of the present application;

[0014] Figure 6 It is a flowchart for judging the ground short circuit of the converter provided by an embodiment of the present application;

[0015] Figure 7 It is a circuit schematic diagram of the converter provided by an embodiment of the present application;

[0016] Figure 8 This is a schematic diagram of an equivalent circuit for detecting the insulation impedance of an AC phase-to-ground in an embodiment of the present application;

[0017] Figure 9 This is a schematic diagram of an equivalent circuit for detecting the insulation impedance of three AC phase-to-ground in an embodiment of the present application. Detailed implementation manners

[0018] To enable those skilled in the art to better understand the solution of the present application, the technical solutions in the specific implementation manners of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the implementation manners of the present application.

[0019] To improve the system safety and reliability, an embodiment of the present application provides a converter, which includes a bidirectional conversion circuit. The bidirectional conversion circuit includes a DC port and an AC port, and the bidirectional conversion circuit is used for bidirectional conversion of AC / DC power supplies. Moreover, the converter further includes a detection circuit and a voltage detection module. The detection circuit includes a first resistor, a second resistor, and a third resistor. The first end of the first resistor is electrically connected to the positive DC end of the bidirectional conversion circuit, the second end of the first resistor is connected to the first end of the second resistor, the second end of the second resistor is connected to the first end of the third resistor, and the second end of the third resistor is electrically connected to the negative DC end of the bidirectional conversion circuit; the detection circuit further includes a first switch and a second switch. The connection point between the first resistor and the second resistor is electrically connected to the negative DC end of the bidirectional conversion circuit through the second switch, and the connection point between the second resistor and the third resistor is grounded through the first switch; the converter further includes a voltage detection module, and the voltage detection module is configured to collect the voltage of the negative DC end of the bidirectional conversion circuit with respect to the ground; the specific connection manner of the voltage detection module in the present application is not limited. It can be directly connected between the negative DC end and the ground as shown in Figure 1 to detect the voltage of the negative DC end with respect to the ground, or it can be calculated by detecting the voltage of other points as shown in Figure 2 . By controlling the on / off states of the first switch and the second switch, the first resistor, the second resistor, and the third resistor in the detection circuit form different current loops under different circumstances, and then the voltages under different current loops are detected to infer the magnitude and direction of the current. The voltage of the negative DC end with respect to the ground is collected through the voltage detection module, and then combined with the magnitude and direction of the current and the voltage of the negative DC end with respect to the ground, the insulation impedance of the converter port with respect to the ground is detected, and then it is determined whether there is a ground short circuit.

[0020] In the related art, the detection of the AC side to ground short - circuit fault of the energy storage converter mainly adopts traditional electrical quantity measurement and comparison methods. However, traditional methods usually rely on threshold judgment and may not be able to detect some weak ground short - circuit faults in time, resulting in low detection sensitivity. Moreover, due to the existence of a large number of harmonics and noise interferences in the power grid, traditional methods are prone to misjudgment. Traditional methods require a certain amount of time to complete the measurement and comparison process of electrical quantities and cannot respond to the occurrence of faults in real - time. The converter provided in this application, through the setting and control of the first switch and the second switch, can not only detect the ground insulation impedance, but also improve the sensitivity, accuracy and response speed of the converter's ground short - circuit detection.

[0021] The converter of the embodiment of the present application will be described in detail below with reference to the accompanying drawings.

[0022] Figure 1 It is a schematic structural diagram of the converter 100 of this embodiment, as Figure 1 shown. The converter 100 includes a bidirectional conversion circuit 12, a detection circuit 11, and a voltage detection module 13. Among them, the bidirectional conversion circuit 12 includes a DC port 121 and an AC port 122. The converter 100 is connected to a DC power supply 201 through the DC port 121 to receive or output DC electric energy. The converter 100 is connected to an AC power supply 202 through the AC port 122 to receive or output AC electric energy. The bidirectional conversion circuit 12 is used to realize the bidirectional conversion of electric energy between the DC power supply 201 and the AC power supply 202.

[0023] The detection circuit 11 includes a first resistor 111, a second resistor 112, a third resistor 113, a first switch 114, and a second switch 115. Among them, the first switch 114 and the second switch 115 can be, but are not limited to, relays or contactors, IGBTs (Insulate - Gate Bipolar Transistors), MOSFETs (Metal - Oxide - Semiconductor Field - Effect Transistors), etc.

[0024] Specifically, the first resistor 111, the second resistor 112, and the third resistor 113 are connected in series. The first end of the first resistor 111 is electrically connected to the positive DC terminal of the bidirectional conversion circuit 12. The positive DC terminal is equivalent to the positive pole of the DC power supply 201. The second end of the first resistor 111 is connected to the first end of the second resistor 112. The second end of the second resistor 112 is connected to the first end of the third resistor 113. The second end of the third resistor 113 is electrically connected to the negative DC terminal of the bidirectional conversion circuit 12. The negative DC terminal is equivalent to the negative pole of the DC power supply 201. The connection point between the first resistor 111 and the second resistor 112 is electrically connected to the negative DC terminal of the bidirectional conversion circuit 12 through the second switch 115. The connection point between the second resistor 112 and the third resistor 113 is grounded through the first switch 114. The first switch 114 and the second switch 115 can change the series or parallel connection relationship of the first resistor 111, the second resistor 112, and the third resistor 113 by switching between the closed and open states, so as to control the current path of the detection circuit 11 and form different current loops, thereby realizing the detection of the current flow and voltage state in the converter 100 by the detection circuit 11.

[0025] The voltage detection module 13 is configured to collect the voltage of the negative DC terminal of the bidirectional conversion circuit 12 with respect to the ground. Through the voltage between the negative DC terminal and the ground, the working state of the converter 100, such as the voltage level, polarity, and possible fault conditions, can be determined.

[0026] According to the above description, for the converter 100 of this embodiment, by controlling the closed or open state of the first switch 114 and the second switch 115, the first resistor 111, the second resistor 112, and the third resistor 113 in the detection circuit 11 form different current loops in different situations. Then, by detecting the voltage under different current loops, the magnitude and direction of the current are inferred. And the voltage detection module 13 collects the voltage of the negative DC terminal with respect to the ground. Furthermore, by combining the magnitude and direction of the current and the voltage of the negative DC terminal with respect to the ground, the insulation impedance of the DC port / AC port of the converter 100 with respect to the ground is detected, and thus it can be determined whether there is a ground short - circuit situation, improving the safety and reliability of the converter 100. Moreover, the sensitivity, accuracy, and response speed of using this circuit to detect ground short - circuit are relatively high.

[0027] In an optional embodiment, as Figure 2As shown, it is a schematic structural diagram of the converter 100 according to this embodiment. The converter 100 further includes a control module 14 and a processing module 15. The control module 14 is used to control at least the switching states of the first switch 114 and the second switch 115. The processing module 15 is used to calculate the insulation resistance of the DC positive terminal of the converter 100 to the ground and the insulation resistance of the DC negative terminal of the converter 100 to the ground according to the DC source voltage, as well as the first voltage and the second voltage collected by the voltage detection module 13. Wherein, the first voltage is: when the converter 100 is in the off-grid state, the voltage measured by the voltage detection module 13 when the first switch 114 is closed and the second switch 115 is open. The second voltage is: when the converter 100 is in the off-grid state, the voltage measured by the voltage detection module 13 when both the first switch 114 and the second switch 115 are closed.

[0028] Specifically, when the converter 100 is in the off-grid state, the control module 14 controls the first switch 114 to be in the closed state and the second switch 115 to be in the open state, and the connection point between the second resistor 112 and the third resistor 113 is grounded. At this time, the equivalent circuit for detecting the insulation impedance of the converter 100 to the ground is as Figure 3 shown. In the figure, R1 represents the first resistor 111, R2 represents the second resistor 112, R3 represents the third resistor 113, and R p represents the insulation resistance of the DC positive terminal of the converter 100 to the ground, which is also equivalent to the insulation impedance of the positive pole of the DC power supply 201 to the ground. R n represents the insulation resistance of the DC negative terminal of the converter 100 to the ground, which is also equivalent to the insulation impedance of the negative pole of the DC power supply 201 to the ground. U1 represents the voltage across the DC power supply 201, which is also equivalent to the DC source voltage connected to the DC side of the inverter. Assuming that the resistance values of the first resistor 111, the second resistor 112, and the third resistor 113 are all R, the first voltage across the third resistor 113 collected by the voltage detection module 13 can be expressed by the following formula:

[0029] U a / (R n / / R)=(U1 - U a ) / (R p / / 2R) Formula (1);

[0030] In the formula, U a represents the first voltage, U1 represents the voltage of the DC power supply 201 connected to the DC side of the converter 100, R p represents the insulation resistance of the DC positive terminal of the converter 100 to the ground, R n represents the insulation resistance of the DC negative terminal of the converter 100 to the ground, and the resistance values of the first resistor 111, the second resistor 112, and the third resistor 113 are all R.

[0031] When the converter 100 is in the off-grid state, the control module 14 controls the first switch 114 and the second switch 115 to be both in the closed state, so that the connection point between the first resistor 111 and the second resistor 112 is connected to the DC negative terminal, and the connection point between the second resistor 112 and the third resistor 113 is grounded. At this time, the equivalent circuit for detecting the insulation impedance of the converter 100 to the ground is as Figure 4 shown. The second voltage across the third resistor 113 collected by the voltage detection module 13 can be expressed by the following formula:

[0032] U b / (R n / / R / / R)=(U1-U b ) / R p Formula (2);

[0033] In the formula, U b represents the second voltage, U1 represents the DC source voltage connected to the DC side of the converter 100, R p represents the insulation resistance of the positive DC terminal of the converter 100 to the ground, R n represents the insulation resistance of the negative DC terminal of the converter 100 to the ground. The resistance values of the first resistor 111, the second resistor 112, and the third resistor 113 are all R.

[0034] When the DC source 201 is connected to the inverter 100, the DC source voltage appears in the detection circuit 11. This DC source voltage causes current to flow through the detection circuit 11. Since current flows through the third resistor 113, a voltage value relative to the ground PE is generated on the third resistor 113. Therefore, the voltage detection module 13 collects the voltage across the third resistor 113 at this time as the second voltage. Furthermore, based on the first voltage and the second voltage in different states at the same point, and combining Formula (1) and Formula (2), the insulation resistance of the positive DC terminal of the converter 100 to the ground and the insulation resistance of the negative DC terminal of the converter 100 to the ground are calculated.

[0035] According to the above description, the converter 100 of this embodiment controls the on or off states of the first switch 114 and the second switch 115 through the control module 14 to form different current loops, and the voltage detection module 13 collects the voltages in different states. Furthermore, the processing module 15 calculates and processes multiple voltages and multiple resistors to obtain the insulation resistance of the positive DC terminal of the converter 100 to the ground and the insulation resistance of the negative DC terminal of the converter 100 to the ground, further improving the detection sensitivity and detection accuracy of the insulation impedance of the converter 100 to the ground.

[0036] In an alternative embodiment, the converter 100 is an energy storage converter or a photovoltaic converter to improve the applicability of the converter 100 of this embodiment.

[0037] When the converter 100 is an energy storage converter, the energy storage converter can be applied to an energy storage system. The DC power supply 201 can be a storage battery. The energy storage converter is connected between the battery bank and the power grid or load. The energy storage converter can invert the DC power of the storage battery into AC power and transmit it to the power grid or supply it to an AC load. The energy storage converter can also rectify the AC power of the power grid into DC power to charge the storage battery.

[0038] When the converter 100 is a photovoltaic converter, the photovoltaic converter can be applied to a photovoltaic system. The DC power supply 201 can be a solar cell. The photovoltaic converter is connected between the solar cell bank and the power grid. The photovoltaic converter can convert the DC voltage of the solar cell bank into an AC voltage with a common frequency for use by the power grid.

[0039] According to the above description, the converter 100 of this embodiment can be an energy storage converter or a photovoltaic converter, and can be applied to the corresponding energy storage system or photovoltaic system to avoid damage to the DC power supply 201 of the system caused by ground short - circuit and personnel safety problems caused by ground short - circuit, thereby improving the safety and reliability of the energy storage system or photovoltaic system.

[0040] In an optional embodiment, the processing module 15 is further configured to determine the AC - to - ground short - circuit condition or calculate the insulation impedance between the AC phase and the ground according to the third voltage collected by the voltage detection module; wherein, the third voltage is: when the converter 100 is in the grid - connected state, the voltage measured by the voltage detection module 13 when the first switch 114 is closed and the second switch 115 is open, and any phase of the power grid supplies power to the converter 100.

[0041] Specifically, under normal circumstances, the voltages and currents of each phase of the AC phase are balanced. Once a ground short - circuit occurs in a certain phase, the voltage of that phase will decrease, and the current will increase significantly. Therefore, when the converter 100 is in the grid - connected state, when any phase of the power grid supplies power to the converter 100, the control module 14 controls the first switch 114 to be in the closed state and the second switch 115 to be in the open state, so that the connection point between the second resistor 112 and the third resistor 113 is grounded. The voltage detection module 13 collects the voltage across the third resistor 113 at this time as the third voltage, so that the AC - to - ground short - circuit condition can be determined according to the third voltage. Moreover, in this set current loop, combined with the detected third voltage, using Ohm's law, Kirchhoff's current law and other circuit laws, the insulation impedance between the AC phase and the ground can be calculated.

[0042] According to the above description, when the converter 100 of this embodiment is in the grid-connected state, the control module 14 controls the first switch 114 to close and the second switch 115 to open, and the voltage detection module 13 collects the third voltage, so as to realize the detection of the AC phase-to-ground short circuit of the converter 100 or the detection of the insulation impedance between the AC phase and the ground.

[0043] In an alternative embodiment, the processing module 15 is further configured to determine whether any AC phase of the converter 100 is short-circuited according to the maximum change amount of the third voltage collected by the voltage detection module 13 within a preset time. In response to the maximum change amount being less than or equal to the first preset threshold, it is determined that the ground insulation performance of the corresponding AC phase of the converter 100 is normal.

[0044] Among them, the preset time can be set as a short time window, such as several seconds to several minutes. The preset time can be set to a suitable value through multiple experiments to avoid misjudgment caused by being too long or too short. The maximum change amount represents the maximum fluctuation amplitude of the third voltage within the preset time, reflecting the instability of the voltage within the preset time. The first preset threshold is used to warn about the change problem of the third voltage, and the first preset threshold can be specifically set according to historical data and experience.

[0045] Specifically, when the converter 100 is in the grid-connected state, the control module 14 controls the first switch 114 to be in the closed state and the second switch 115 to be in the open state, so that the connection point between the second resistor 112 and the third resistor 113 is grounded, and the voltage detection module 13 collects the third voltage across the third resistor 113. Furthermore, within the preset time, the voltage detection module 13 continuously collects the third voltage, obtains the maximum value and the minimum value of the voltage at this point, and calculates the difference between the two, that is, the maximum change amount of the third voltage, to determine whether the AC port 122 of the converter 100 is short-circuited to the ground.

[0046] Furthermore, when the maximum change amount is less than or equal to the first preset threshold, it indicates that the third voltage is relatively stable and no abnormal state has occurred. Therefore, it is determined that the ground insulation performance of the corresponding AC phase of the converter 100 is normal, that is, there is no short circuit in any AC phase of the converter 100.

[0047] According to the above description, when the converter 100 of this embodiment is in the grid-connected state, the control module 14 controls the first switch 114 to close and the second switch 115 to open. The voltage detection module 13 collects the maximum change amount of the third voltage within a preset time. When the maximum change amount is less than or equal to the first preset threshold, the processing module 15 determines that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal and there is no short circuit in any AC phase of the converter 100, thereby preventing the possible short circuit problem of the converter 100 and improving the stability and safety of the converter 100 during grid-connected operation.

[0048] In an alternative embodiment, the first preset threshold is 0.2 times the peak-to-peak value of the AC voltage of this phase. For example, if the peak-to-peak value of the AC voltage of a certain phase is Va, then the first preset threshold is 0.2Va. When the maximum change amount is less than or equal to 0.2 times the AC voltage of this phase, it is considered that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal and there is no short circuit risk.

[0049] In an alternative embodiment, in response to the maximum change amount being greater than the second preset threshold, it is determined that the corresponding AC phase of the converter 100 is short-circuited to the ground, and the second preset threshold is greater than the first preset threshold.

[0050] Wherein, the second preset threshold is used to indicate that the change of the third voltage has a large fluctuation, which is very likely caused by a fault of the converter 100. The second preset threshold can be specifically set according to historical experience, safety standards, application environment, etc. For example, the first preset threshold is set to 10V and the second preset threshold is set to 250V.

[0051] Specifically, when the maximum change amount of the third voltage is greater than the second preset threshold, it indicates that the change of the third voltage is large, and it is determined that the corresponding AC phase of the converter 100 is short-circuited to the ground. Furthermore, the connection to the faulty AC phase can be automatically disconnected, or an alarm message can be sent to notify the maintenance team for inspection and repair.

[0052] According to the above description, the converter 100 of this embodiment determines that the corresponding AC phase of the converter 100 is short-circuited to the ground by setting the second preset threshold and when the maximum change amount is greater than the second preset threshold, thereby further preventing the short circuit problem existing in the converter 100, so as to take protection measures in time to avoid serious short circuit faults and further improve the stability and safety of the converter 100 during grid-connected operation.

[0053] In an alternative embodiment, the second preset threshold is 0.7 times the peak-to-peak value of the AC voltage of that phase. For example, if the peak-to-peak value of the AC voltage of a certain phase is Va, the first preset threshold is 0.2Va, and the second preset threshold is 0.7Va. When the maximum change amount is greater than 0.7Va, it is determined that there is a short circuit problem between the corresponding AC phase of the converter 100 and the ground, so as to better maintain the stability of the operation of the converter 100.

[0054] Exemplarily, assume that the peak voltage of the AC voltage of a certain phase of the converter 100 is Vb, then the maximum change amount of the AC voltage of that phase is 2Vb, the first preset threshold is 0.4Vb, and the second preset threshold is 1.4Vb. Then the waveform diagram of the third voltage is as Figure 5 shown. Among them, the red ripple in the figure is the waveform diagram of the third voltage under normal conditions, and the maximum change amount of this ripple is less than 0.4Vb. The green ripple in the figure is the waveform diagram of the third voltage when there is a short circuit problem between the AC phase and the ground, and the maximum change amount of this ripple is greater than 1.4Vb. It can be seen that when the maximum change amount is less than 0.4Vb, the ripple change of the third voltage is relatively stable, and no abnormal state occurs, and there is no short circuit in the corresponding AC phase of the converter 100; when the maximum change amount is greater than 1.4Vb, the third voltage is approximately equal to the phase voltage, and it can be determined that the corresponding AC phase of the converter 100 is short-circuited to the ground.

[0055] In an alternative embodiment, in response to the maximum change amount being greater than the first preset threshold and the maximum change amount being less than or equal to the second preset threshold, the processing module 15 calculates the insulation impedance to the ground of the corresponding AC phase of the converter 100. Of course, the processing module 15 can also directly calculate the insulation impedance to the ground of the corresponding AC phase of the converter 100 without relying on the prior short circuit judgment.

[0056] Among them, the insulation impedance can evaluate the insulation performance of the converter 100. The insulation impedance reflects the current-limiting ability of the converter 100, that is, the ability to prevent current from passing through unintended paths (such as the battery case or connecting components). A higher insulation impedance indicates better insulation performance because it means that it is more difficult for current to flow through unintended paths. On the contrary, a lower insulation impedance may indicate insulation problems, such as damage to the battery case, looseness or corrosion of connecting components, etc. These problems may cause current leakage, thus affecting the safety and performance of the converter 100. Therefore, the processing module 15 can be used to calculate the insulation impedance to the ground of the input AC phase of the converter 100 to effectively evaluate the quality of the insulation performance of the converter 100 to the ground, and timely discover and handle potential insulation problems. If the insulation impedance to the ground is very low or even close to 0, it indicates that a ground short circuit has occurred.

[0057] Exemplarily, as Figure 6As shown, it is a flowchart for judging whether the converter 100 is short-circuited to the ground, specifically including the following steps:

[0058] Step S601: The voltage detection module 13 collects the third voltage and the maximum change amount of the third voltage within a preset time.

[0059] Step S602: The processing module 15 judges whether the maximum change amount is less than or equal to the first preset threshold; if the judgment result is yes, step S603 is executed, and if the judgment result is no, step S604 is executed.

[0060] Step S603: It is determined that the ground insulation performance of the corresponding AC phase of the converter 100 is normal.

[0061] Step S604: The processing module 15 judges whether the maximum change amount is greater than the second preset threshold; if the judgment result is yes, step S605 is executed, and if the judgment result is no, step S606 is executed.

[0062] Step S605: The processing module 15 calculates the ground insulation impedance of the corresponding AC phase of the converter 100.

[0063] Step S606: It is determined that the corresponding AC phase of the converter 100 is short-circuited to the ground.

[0064] It should be understood that various forms of the flowcharts shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this application can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of this application can be achieved, and this is not limited herein.

[0065] Furthermore, as Figure 7 shown, it is a circuit schematic diagram of the converter 100. Among them, the DC power supply 201 is the battery connected to the DC side of the illustrated converter 100, BAT+ represents the positive pole of the battery, BAT- represents the negative pole of the battery, R1 represents the first resistor 111, R2 represents the second resistor 112, R3 represents the third resistor 113, K1 represents the first switch 114, K2 represents the second switch 115, R p represents the equivalent insulation resistance between the DC positive terminal of the converter 100 and the ground, and R n represents the equivalent insulation resistance between the DC negative terminal of the converter 100 and the ground.

[0066] As Figure 7As shown, one usage scenario of this embodiment is that before the DC power supply 201 is connected to the inverter 100, when the DC source voltage appears in the detection circuit 11, this DC source voltage causes current to flow through the detection circuit 11. Since current flows through the third resistor 113, a voltage value relative to the ground PE is generated on the third resistor 113. Therefore, the voltage detection module 13 collects the voltage across the third resistor 113 at this time as the second voltage. Furthermore, based on the first voltage and the second voltage at the same point under different states, and in combination with formulas (1) and (2), the insulation resistance of the positive DC terminal of the converter 100 to the ground and the insulation resistance of the negative DC terminal of the converter 100 to the ground are calculated. If the insulation impedance meets the insulation requirements, then control the switch tubes K3 and K4 to close to achieve the electrical connection between the battery and the inverter. Another usage scenario is that when the inverter is working normally, since the detection circuit 11 is also connected to the DC source voltage, the insulation impedance can be detected in a timely manner by controlling the first switch and the second switch. When it is detected that the insulation impedance does not meet the insulation requirements, control the switch tubes K3 and K4 to disconnect to prevent safety risks.

[0067] According to this circuit diagram, the control module 14 can control the first switch 114 to be in the closed state and the second switch 115 to be in the open state. The voltage detection module 13 collects the third voltage and the maximum change amount of the third voltage within a preset time. Then, the processing module 15 determines the insulation performance of the corresponding AC phase of the converter 100 to the ground, whether there is a short circuit to the ground in the corresponding AC phase of the converter 100, and calculates the insulation impedance of the corresponding AC phase of the converter 100 to the ground based on the maximum change amount.

[0068] Furthermore, disconnect the inputs of two of the AC phases of the converter 100, and through the control module 14, close the first switch K1 and open the second switch K2. The equivalent circuit formed is as Figure 8 shown. Among them, R ac is the equivalent insulation impedance of this AC phase to the ground. The processing module 15 can calculate the insulation impedance of the corresponding AC phase of the converter 100 to the ground through the following formula:

[0069] (U4 + U n ) / R ac + U1 / R p1 =U2 / R n1 Formula (3);

[0070] In the formula, U1 represents the DC source voltage connected to the DC side of the converter 100, such as the output voltage of a storage battery or the output voltage of a solar cell. U2 represents the third voltage. U4 represents the phase voltage. U n represents the voltage of the neutral line N to the ground PE. R p1 =R p / / (R1 + R2), where R1 represents the resistance value of the first resistor and R2 represents the resistance value of the second resistor, R p represents the insulation resistance of the positive DC terminal of the converter 100 to the ground, and R n1 = R n / / R3, where R3 represents the resistance value of the third resistor, and R n represents the insulation resistance of the negative DC terminal of the converter 100 to the ground, and R ac is the equivalent insulation impedance of this AC phase to the ground.

[0071] According to the above description, in this embodiment, by disconnecting the inputs of two of the three AC phases of the converter 100, the control module 14 controls the first switch 114 to close and the second switch 115 to open, forming an equivalent circuit of the equivalent insulation impedance of one of the AC phases to the ground. By combining the detected DC source voltage, the third voltage, the midpoint-to-ground voltage, and the phase voltage, and through the calculation of formula (3), the insulation impedance of this AC phase to the ground is obtained, improving the accuracy of the obtained insulation impedance to the ground. Further, the short-circuit risk of the AC to the ground can be judged based on the detected equivalent insulation impedance of the AC to the ground, which is beneficial to improving the system safety.

[0072] In an alternative embodiment, the voltage detection module 13 samples the third voltage and the phase voltages of the three phases at multiple sampling moments at intervals, and the insulation impedances of the three AC phases of the converter 100 to the ground can be detected simultaneously. The equivalent circuit for detecting the insulation impedances of the three AC phases of the converter 100 to the ground is as Figure 9 shown, where R ac1 is the equivalent insulation impedance of the first phase of the converter 100 to the ground, R ac2 is the equivalent insulation impedance of the second phase of the converter 100 to the ground, and R ac3 is the equivalent insulation impedance of the third phase of the converter 100 to the ground. Specifically, the processing module 15 calculates the insulation impedance of any AC phase of the converter 100 through the following formula:

[0073]

[0074] In the formula, U n represents the voltage of the neutral line N to the ground PE, U1 represents the voltage of the battery connected to the DC side of the converter 100, U 2i represents the third voltage at the i-th moment, U 4i represents the phase voltage of the first phase at the i-th moment, U 5i represents the phase voltage of the second phase at the i-th moment, U 6i represents the phase voltage of the third phase at the i-th moment, and R p1 = R p / / 2R, and R n1 = R n / / R, and R pRepresents the insulation resistance of the positive DC terminal of the converter 100 to the ground, R n Represents the insulation resistance of the negative DC terminal of the converter 100 to the ground, R represents the resistance values of the first resistor 111, the second resistor 112, and the third resistor 113, R ac1 Is the equivalent insulation impedance of the first phase of the converter 100 to the ground, R ac2 Is the equivalent insulation impedance of the second phase of the converter 100 to the ground, R ac3 Is the equivalent insulation impedance of the third phase of the converter 100 to the ground; i represents the sampling moment, i = 1, 2, 3, and the time interval between each sampling moment is not equal to the period of the three-phase alternating current or an integer multiple of the period. According to the above description, for the converter 100 of this embodiment, when the time interval between each sampling moment is not equal to the period of the three-phase alternating current or an integer multiple of the period, the voltage detection module 13 collects the third voltage at multiple sampling moments and the phase voltages of the three phases, and simultaneously obtains the equivalent insulation impedance of the three phases to the ground through formula (4), improving the accuracy and efficiency of obtaining the insulation impedance to the ground; while R p 、R n Can be calculated through formulas (1) and (2). This embodiment does not need to use a current sensor to detect the leakage current for AC side-to-ground short circuit judgment, which is beneficial to saving the detection cost, and does not need to disconnect the connections of other phase lines, and is suitable for real-time monitoring. Through this embodiment, the detection of the DC side insulation impedance to the ground and the AC side insulation impedance to the ground can be realized, and it has the characteristics of low detection cost and high versatility.

[0075] In the description of the present application, terms such as "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of these features. The meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0076] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0077] It should be understood that for those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the claims attached to this application.

Claims

1. A converter, the converter includes a bidirectional conversion circuit, the bidirectional conversion circuit includes a DC port and an AC port, and the bidirectional conversion circuit is used for bidirectional conversion of AC / DC power supplies; It is characterized in that, The converter further includes: A detection circuit, the detection circuit includes a first resistor, a second resistor and a third resistor, a first end of the first resistor is electrically connected to the positive DC end of the bidirectional conversion circuit, a second end of the first resistor is connected to a first end of the second resistor, a second end of the second resistor is connected to a first end of the third resistor, and a second end of the third resistor is electrically connected to the negative DC end of the bidirectional conversion circuit; The detection circuit further includes a first switch and a second switch, a connection point between the first resistor and the second resistor is electrically connected to the negative DC end of the bidirectional conversion circuit through the second switch, and a connection point between the second resistor and the third resistor is grounded through the first switch; The converter further includes a voltage detection module, and the voltage detection module is configured to collect the voltage of the negative DC end of the bidirectional conversion circuit with respect to the ground; A control module, the control module is used to at least control the switching states of the first switch and the second switch; A processing module, the processing module is used to calculate the insulation resistance of the positive DC end of the converter with respect to the ground and the insulation resistance of the negative DC end of the converter with respect to the ground according to the DC source voltage, and the first voltage and the second voltage collected by the voltage detection module, wherein, the first voltage is: when the converter is in the off-grid state, the voltage measured by the voltage detection module when the first switch is closed and the second switch is open; The second voltage is: when the converter is in the off-grid state, the voltage measured by the voltage detection module when both the first switch and the second switch are closed.

2. The converter according to claim 1, wherein, The processing module calculates the insulation resistance of the positive DC end with respect to the ground and the insulation resistance of the negative DC end with respect to the ground according to the following formula: U a / (R n / / R)=(U1 - U a ) / (R p / / 2R); U b / (R n / / R / / R)=(U1 - U b ) / R p ; Wherein, U a represents the first voltage, U b represents the second voltage, U1 represents the DC source voltage connected to the DC side of the converter, R p represents the insulation resistance of the positive DC terminal of the converter to the ground, R n represents the insulation resistance of the negative DC terminal of the converter to the ground, and the resistance values of the first resistor, the second resistor, and the third resistor are all R.

3. The converter according to claim 2, characterized in that, The processing module is further used to judge the situation of AC phase-to-ground short circuit according to the third voltage collected by the voltage detection module; wherein, the third voltage is: when the converter is in the grid-connected state, when the first switch is closed and the second switch is open, and any grid phase supplies power to the converter, the voltage measured by the voltage detection module.

4. The converter according to claim 3, characterized in that, The processing module is further used to judge whether any AC phase of the converter is short-circuited according to the maximum change amount of the third voltage collected by the voltage detection module within a preset time; In response to the maximum change amount being less than or equal to the first preset threshold, it is judged that the ground insulation performance of the corresponding AC phase of the converter is normal.

5. The converter according to claim 4, wherein, The first preset threshold is 0.2 times the peak-to-peak value of the AC voltage of this phase.

6. The converter according to claim 4, wherein, In response to the maximum change amount being greater than the second preset threshold, it is judged that the corresponding AC phase of the converter is short-circuited to the ground, and the second preset threshold is greater than the first preset threshold.

7. The converter according to claim 6, wherein, The second preset threshold is 0.7 times the peak-to-peak value of the AC voltage of this phase.

8. The converter according to claim 3, characterized in that, The processing module is further configured to calculate the insulation impedance to ground of the corresponding AC phase of the converter according to the following formula: (U4 + U n ) / R ac + U1 / R p1 = U2 / R n1 ; Wherein, U1 represents the DC source voltage connected to the DC side of the converter, U2 represents the third voltage, U4 represents the phase voltage, and U n represents the voltage of the neutral line to the ground, and R p1 = R p / / (R1 + R2), where R p represents the insulation resistance of the positive DC terminal of the converter to the ground, R1 represents the resistance value of the first resistor, R2 represents the resistance value of the second resistor, and R n1 = R n / / R3, where R n represents the insulation resistance of the negative DC terminal of the converter to the ground, R3 represents the resistance value of the third resistor, and R ac is the equivalent insulation impedance of this AC phase to the ground.

9. The converter according to claim 3, characterized in that, The processing module is configured to calculate the insulation impedance to ground of any AC phase of the converter according to the following formula: Wherein, U n represents the voltage of the neutral line to the ground, U1 represents the voltage of the battery connected to the DC side of the converter, U 2i represents the third voltage at the i-th moment, U 4i represents the phase voltage of the first phase at the i-th moment, U 5i represents the phase voltage of the second phase at the i-th moment, U 6i represents the phase voltage of the third phase at the i-th moment, R p1 = R p / / 2R, R n1 = R n / / R, R p represents the insulation resistance of the positive DC terminal of the converter to the ground, R n represents the insulation resistance of the negative DC terminal of the converter to the ground, R represents the resistance values of the first resistor, the second resistor and the third resistor, R ac1 is the equivalent insulation impedance of the first phase of the converter to the ground, R ac2 is the equivalent insulation impedance of the second phase of the converter to the ground, R ac3 is the equivalent insulation impedance of the third phase of the converter to the ground; i represents the sampling moment, i = 1, 2, 3, and the time interval between each sampling moment is not equal to the period of the three-phase alternating current or an integer multiple of the period.

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