Converter

Abstract

A converter (100), comprising: a bidirectional conversion circuit (12), a detection circuit (11), and a voltage detection module (13). The detection circuit (11) comprises a first resistor (111), a second resistor (112), a third resistor (113), a first switch (114), and a second switch (115). A first terminal of the first resistor (111) is electrically connected to a direct current positive terminal of the bidirectional conversion circuit (12). A second terminal of the first resistor (111) is connected to a first terminal of the second resistor (112). A second terminal of the second resistor (112) is connected to a first terminal of the third resistor (113). A second terminal of the third resistor (113) is electrically connected to a direct current negative terminal of the bidirectional conversion circuit (12). A connection point between the first resistor (111) and the second resistor (112) is electrically connected to the direct current negative terminal of the bidirectional conversion circuit (12) via the second switch (115), and a connection point between the second resistor (112) and the third resistor (113) is grounded via the first switch (114). The voltage detection module (13) is configured to acquire a voltage between the direct current negative terminal of the bidirectional conversion circuit (12) and ground. The converter (100) enables detection of insulation impedance to ground, and the sensitivity, accuracy, and response speed of the converter (100) in detecting ground short circuits can also be improved.

Description

Converter

[0001] The present application claims priority to the Chinese patent application No. 202411288519.4, filed on September 13, 2024, and entitled "Converter", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of power electronics, in particular to a converter. BACKGROUND

[0003] With the rapid development of renewable energy, the safety and reliability of energy storage systems as an important part of smart grids have attracted widespread attention. Energy storage systems are usually composed of battery packs, BMS (battery management system), PCS (energy storage converter) and AC mains, etc. During the operation of the energy storage system, the PCS, as one of the key devices, is responsible for 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 influence, human operation errors, etc., the AC side of the PCS may occur a ground short circuit fault. This fault not only affects the normal operation of the energy storage system, but also may pose a threat to the safety of equipment and personnel. Therefore, the ground short circuit detection method of the AC side of the PCS is of great significance to ensure the safety and reliability of the energy storage system. SUMMARY

[0005] In order to solve the problems of the prior art, the purpose of the present application is to provide a converter which can realize the detection of the insulation impedance of the converter port to the ground.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The application provides a converter, which comprises a bidirectional conversion circuit, the bidirectional conversion circuit comprises a direct current port and an alternating current port, and the bidirectional conversion circuit is used for bidirectional conversion of direct / alternating current power supply; the converter further comprises a detection circuit, the detection circuit comprises a first resistor, a second resistor and a third resistor, a first end of the first resistor is electrically connected to a direct current positive end of the bidirectional conversion circuit, a second end of the first resistor is connected with a first end of the second resistor, a second end of the second resistor is connected with a first end of the third resistor, and a second end of the third resistor is electrically connected to a direct current negative end of the bidirectional conversion circuit; the detection circuit further comprises a first switch and a second switch, 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 converter further comprises a voltage detection module, and the voltage detection module is configured to collect a direct current negative end-to-ground voltage of the bidirectional conversion circuit.

[0008] The converter described above controls the closing or opening state 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 cases, then the voltage under different current loops is detected, the size and direction of the current are inferred, and the direct current negative end-to-ground voltage is collected through the voltage detection module, so that the ground insulation impedance of the converter port can be detected in combination with the size and direction of the current and the direct current negative end-to-ground voltage. BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a structural schematic diagram of a converter provided by an embodiment of the application;

[0010] Fig. 2 is a structural schematic diagram of another converter provided by an embodiment of the application;

[0011] Fig. 3 is an equivalent circuit schematic diagram for detecting a direct current positive end-to-ground insulation resistance provided by an embodiment of the application;

[0012] Fig. 4 is an equivalent circuit schematic diagram for detecting a direct current negative end-to-ground insulation resistance provided by an embodiment of the application;

[0013] Fig. 5 is a waveform schematic diagram of a third voltage provided by an embodiment of the application;

[0014] Fig. 6 is a judgment flowchart of a converter ground short circuit provided by an embodiment of the application;

[0015] Fig. 7 is a circuit schematic diagram of a converter provided by an embodiment of the application;

[0016] Fig. 8 is an equivalent circuit schematic diagram for detecting an alternating current phase-to-ground insulation impedance provided by an embodiment of the application;

[0017] Fig. 9 is an equivalent circuit schematic diagram for detecting three-phase-to-ground insulation impedance according to an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the personnel in the art better understand the scheme of the present application, the technical scheme in the specific embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application.

[0019] In order to improve system safety and reliability, the embodiment of the present application provides a converter, which includes a bidirectional conversion circuit. The bidirectional conversion circuit includes a direct current port and an alternating current port, and the bidirectional conversion circuit is used for bidirectional conversion of direct current / alternating current power supply. 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. A first end of the first resistor is electrically connected to a direct current positive 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 direct current negative 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 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 converter further includes a voltage detection module, which is configured to collect a direct current negative end-to-ground voltage of the bidirectional conversion circuit. The specific connection mode of the voltage detection module is not limited in the present application. For example, the voltage detection module can be directly connected between the direct current negative end and the ground to detect the direct current negative end-to-ground voltage, as shown in Fig. 1, or the voltage detection module can calculate the direct current negative end-to-ground voltage by detecting other point voltages, as shown in Fig. 2. The converter controls the closing or opening state 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 cases. Then, the voltage under different current loops is detected, the size and direction of the current are inferred, and the direct current negative end-to-ground voltage is collected through the voltage detection module. Then, the converter port-to-ground insulation impedance is detected by combining the size and direction of the current and the direct current negative end-to-ground voltage, and then it is judged 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 the traditional electrical quantity measurement and comparison method. However, the traditional method is usually based on threshold judgment, and for some weak ground short-circuit faults, it may not be able to detect in time, resulting in low detection sensitivity. Moreover, due to the existence of a large amount of harmonics and noise interference in the power grid, the traditional method is prone to misjudgment. The traditional method needs a certain time to complete the measurement and comparison process of the electrical quantity, and cannot respond to the fault in real time. The converter provided in the present application can not only realize the detection of the ground insulation impedance, but also improve the sensitivity, accuracy and response speed of the ground short-circuit detection of the converter through the setting and control of the first switch and the second switch.

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

[0022] FIG. 1 is a structural schematic diagram of the converter 100 of the present embodiment. As shown in FIG. 1, the converter 100 includes a bidirectional conversion circuit 12, a detection circuit 11 and a voltage detection module 13. The bidirectional conversion circuit 12 includes a DC port 121 and an AC port 122. The converter 100 is connected with a DC power supply 201 through the DC port 121 to receive or output DC power, and is connected with an AC power supply 202 through the AC port 122 to receive or output AC power. The bidirectional conversion circuit 12 is used to realize the bidirectional conversion of the electrical 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. The first switch 114 and the second switch 115 can be, but are not limited to, relays or contactors, IGBTs (Insulate-Gate Bipolar Transistor), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistor) and the like.

[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 direct current positive end of the bidirectional conversion circuit 12, the direct current positive end is equivalent to the positive pole of the direct current power supply 201, the second end of the first resistor 111 is connected with the first end of the second resistor 112, the second end of the second resistor 112 is connected with the first end of the third resistor 113, the second end of the third resistor 113 is electrically connected to the direct current negative end of the bidirectional conversion circuit 12, the direct current negative end is equivalent to the negative pole of the direct current power supply 201. The connection point between the first resistor 111 and the second resistor 112 is electrically connected to the direct current negative end 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 the closed or open state, so as to control the current path of the detection circuit 11, form different current loops, and thus realize the detection of the current flowing condition and voltage state of the current transformer 100 by the detection circuit 11.

[0025] The voltage detection module 13 is configured to collect the voltage between the direct current negative end and the ground of the bidirectional conversion circuit 12, and the voltage between the direct current negative end and the ground can determine the working state of the current transformer 100, such as voltage level, polarity and possible fault condition.

[0026] According to the above description, the current transformer 100 of the embodiment can make 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 by controlling the closed or open state of the first switch 114 and the second switch 115, then detect the voltage under different current loops, infer the size and direction of the current, and collect the voltage between the direct current negative end and the ground through the voltage detection module 13, and then combine the size and direction of the current and the voltage between the direct current negative end and the ground to detect the insulation impedance of the direct current port / alternating current port to the ground of the current transformer 100, and then determine whether there is a ground short circuit condition, thereby improving the safety and reliability of the current transformer 100. The sensitivity, accuracy and response speed of the circuit for detecting ground short circuit are high.

[0027] In an optional embodiment, as shown in FIG. 2, a structure diagram of the converter 100 of the embodiment, the converter 100 further comprises a control module 14 and a processing module 15, the control module 14 is configured to control at least the switching state of the first switch 114 and the second switch 115, and the processing module 15 is configured to calculate the DC positive terminal-to-ground insulation resistance and the DC negative terminal-to-ground insulation resistance of the converter 100 according to the DC source voltage, and the first voltage and the second voltage collected by the voltage detection module 13, wherein the first voltage is the voltage measured by the voltage detection module 13 when the converter 100 is in an off-grid state, the first switch 114 is closed, and the second switch 115 is open, and the second voltage is the voltage measured by the voltage detection module 13 when the converter 100 is in the off-grid state, and the first switch 114 and the second switch 115 are both closed.

[0028] Specifically, in the case where the converter 100 is in the off-grid state, the control module 14 controls the first switch 114 to be in the closed state, the second switch 115 to be in the open state, and the connection point between the second resistor 112 and the third resistor 113 to be grounded, at this time, the equivalent circuit for detecting the ground insulation impedance of the converter 100 is shown in FIG. 3, wherein R1 represents the first resistor 111, R2 represents the second resistor 112, R3 represents the third resistor 113, R p represents the DC positive terminal-to-ground insulation resistance of the converter 100, and is equivalent to the positive electrode-to-ground insulation impedance of the DC power supply 201, R n represents the DC negative terminal-to-ground insulation resistance of the converter 100, and is equivalent to the negative electrode-to-ground insulation impedance of the DC power supply 201. U1 represents the voltage on both sides of the DC power supply 201, and is 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 collected by the voltage detection module 13 on both sides of the third resistor 113 can be represented 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 DC positive terminal-to-ground insulation resistance of the converter 100, R n represents the DC negative terminal-to-ground insulation resistance of the converter 100, 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 an off-grid state, the control module 14 controls the first switch 114 and the second switch 115 to be in a closed state, so that the connection point between the first resistor 111 and the second resistor 112 is connected to the negative terminal of the DC, 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 ground insulation impedance of the converter 100 is shown in FIG. 4. The second voltage across the third resistor 113 collected by the voltage detection module 13 can be represented 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 DC positive terminal insulation resistance of the converter 100, R n represents the DC negative terminal insulation resistance of the converter 100, and 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 detection circuit 11 detects the DC source voltage, which causes a current to flow through the detection circuit 11. Since the 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. Further, according to the first voltage and the second voltage under different states at the same point, the DC positive terminal insulation resistance and the DC negative terminal insulation resistance of the converter 100 are calculated by combining formula (1) and formula (2).

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

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

[0037] When the converter 100 is an energy storage converter, the energy storage converter can be applied in an energy storage system, the direct current power supply 201 can be a battery, the energy storage converter is connected between the battery pack and the power grid or the load, the energy storage converter can convert the direct current of the battery into alternating current to supply the power grid or the alternating current load, and the energy storage converter can rectify the alternating current of the power grid into direct current to charge the battery.

[0038] When the converter 100 is a photovoltaic converter, the photovoltaic converter can be applied in a photovoltaic system, the direct current power supply 201 can be a solar cell, the photovoltaic converter is connected between the solar cell pack and the power grid, and the photovoltaic converter can convert the direct current voltage of the solar cell pack into an alternating current voltage of a common frequency to supply the power grid.

[0039] According to the above description, the converter 100 of the embodiment can be an energy storage converter or a photovoltaic converter, and can be applied in a corresponding energy storage system or photovoltaic system to avoid damage to the direct current power supply 201 of the system caused by the ground short circuit and the personnel safety problem caused by the 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 ground short circuit of the alternating current phase or calculate the insulation impedance of the alternating current phase to ground according to the third voltage collected by the voltage detection module; wherein the third voltage is the voltage detected by the voltage detection module 13 when the converter 100 is in the grid-connected state, the first switch 114 is closed, the second switch 115 is open, and the power grid supplies power to the converter 100 through any phase.

[0041] Specifically, in a normal case, the voltage and the current of each phase of the alternating current phase are balanced, and once a ground short circuit occurs in a phase, the voltage of the phase will decrease, and the current will significantly increase. Therefore, 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 voltage on both sides of the third resistor 113 at this time as the third voltage, so that the ground short circuit of the alternating current phase can be determined according to the third voltage. Moreover, in this current loop, combined with the detected third voltage, the insulation impedance of the alternating current phase to ground can be calculated by using Ohm's law, Kirchhoff's current law and other circuit laws.

[0042] According to the above description, the converter 100 of the embodiment can realize the detection of the short circuit of the AC phase to ground of the converter 100 or the detection of the insulation impedance of the AC phase to ground by controlling the first switch 114 to be closed and the second switch 115 to be opened by the control module 14 when the converter 100 is in the grid-connected state and collecting the third voltage by the voltage detection module 13.

[0043] In an optional 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 variation of the third voltage collected by the voltage detection module 13 within a preset time, and determine that the ground insulation performance of the corresponding AC phase of the converter 100 is normal in response to the maximum variation being less than or equal to a first preset threshold.

[0044] The preset time can be set as a short time window, for example, several seconds to several minutes. The preset time can be set to an appropriate value through multiple experiments to avoid misjudgment caused by too long or too short time. The maximum variation represents the maximum fluctuation amplitude of the third voltage within the preset time, which reflects the instability of the voltage within the preset time. The first preset threshold is used to warn the change problem of the third voltage, and the first preset threshold can be 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 on both sides of the third resistor 113. Further, within the preset time, the voltage detection module 13 continuously collects the third voltage to obtain the maximum value and the minimum value of the voltage at the point, and calculates the difference between the two to obtain the maximum variation of the third voltage, so as to determine whether the AC port 122 of the converter 100 is short-circuited to ground.

[0046] Further, when the maximum variation is less than or equal to the first preset threshold, it indicates that the third voltage is relatively stable and no abnormal state occurs, and therefore, it is determined that the ground insulation performance of the corresponding AC phase of the converter 100 is normal, i.e., any AC phase of the converter 100 does not exist short-circuit.

[0047] According to the above description, the converter 100 of the embodiment can prevent the short circuit problem of the converter 100, improve the stability and safety of the converter 100 during grid-connected operation, by controlling the first switch 114 to be closed and the second switch 115 to be opened when the converter 100 is in the grid-connected state, the voltage detection module 13 collecting the maximum variation of the third voltage within a preset time, and the processing module 15 determining that the corresponding AC phase of the converter 100 has normal insulation performance to ground and that there is no short circuit in any AC phase of the converter 100 when the maximum variation is less than or equal to the first preset threshold value.

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

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

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

[0051] Specifically, when the maximum variation of the third voltage is greater than the second preset threshold value, it is indicated that the variation of the third voltage is large, and it is determined that the corresponding AC phase of the converter 100 is short-circuited to ground. Furthermore, the connection with the AC phase that has a fault can be automatically disconnected, or an alarm information can be sent to notify the maintenance team to check and repair.

[0052] According to the above description, the converter 100 of the embodiment can further prevent the short circuit problem of the converter 100, so as to take protective measures in time, avoid serious short circuit faults, and further improve the stability and safety of the converter 100 during grid-connected operation, by setting the second preset threshold value and determining that the corresponding AC phase of the converter 100 is short-circuited to ground when the maximum variation is greater than the second preset threshold value.

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

[0054] For example, it is assumed that the peak voltage of a phase AC voltage of the converter 100 is Vb, and the maximum variation of the phase AC voltage is 2Vb, the first preset threshold is 0.4Vb, and the second preset threshold is 1.4Vb. The waveform diagram of the third voltage is shown in FIG. 5. In the diagram, the red ripple is the waveform diagram of the third voltage under normal circumstances, and the maximum variation of the ripple is less than 0.4Vb. The green ripple is the waveform diagram of the third voltage when there is a short circuit problem with respect to the ground of the AC phase, and the maximum variation of the ripple is greater than 1.4Vb. As can be seen, when the maximum variation is less than 0.4Vb, the ripple variation of the third voltage is relatively stable, and there is no abnormal state, and the AC phase of the converter 100 does not have a short circuit. When the maximum variation is greater than 1.4Vb, the third voltage is approximately equal to the phase voltage, and it can be determined that the AC phase of the converter 100 has a short circuit with respect to the ground.

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

[0056] The insulation impedance can evaluate the insulation performance of the converter 100, and the insulation impedance reflects the limiting ability of the converter 100 to the current, i.e., the ability to prevent the current from flowing through unintended paths (such as the battery shell or connecting components). A higher insulation impedance indicates better insulation performance, because it means that it is more difficult for the current to flow through unintended paths. On the contrary, a lower insulation impedance may indicate that there is an insulation problem, such as damage to the battery shell, loosening or corrosion of the connecting components, etc., which can all cause current leakage and affect the safety and performance of the converter 100. Therefore, the ground insulation impedance of the input AC phase of the converter 100 can be calculated by the processing module 15 to effectively evaluate the insulation performance of the converter 100 with respect to the ground, and potential insulation problems can be found and handled in a timely manner. If the ground insulation impedance is very low, even close to 0, it indicates that a short circuit with respect to the ground has occurred.

[0057] For example, as shown in FIG. 6, a flowchart for determining whether the converter 100 has a short circuit with respect to the ground includes the following steps:

[0058] Step S601, the voltage detection module 13 collects the third voltage and the maximum variation of the third voltage in the preset time.

[0059] Step S602, the processing module 15 judges whether the maximum variation is less than or equal to the first preset threshold value; if the result is yes, step S603 is executed, and if the 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 variation is greater than the second preset threshold value; if the result is yes, step S605 is executed, and if the 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 ground.

[0064] It should be understood that the above-mentioned various forms of flow can be reordered, added or deleted steps. For example, each step described in the present application can be executed in parallel, sequentially or in different order, as long as the desired results of the technical solutions of the present application can be achieved, which is not limited herein.

[0065] Further, as shown in FIG. 7, it is a circuit schematic diagram of the converter 100. Among them, the DC power supply 201 is a battery connected to the DC side of the illustrated converter 100, BAT+ represents the positive electrode of the battery, BAT- represents the negative electrode 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 of the positive DC end of the converter 100 to ground, n represents the equivalent insulation resistance of the negative DC end of the converter 100 to ground.

[0066] As shown in FIG. 7, one use scenario of the embodiment is that, before the direct current power supply 201 is connected to the inverter 100, the detection circuit 11 detects the direct current source voltage, the direct current source voltage makes the current flow through the detection circuit 11, and because the current flows through the third resistor 113, a voltage value of the third resistor 113 relative to the ground PE is generated, therefore, the voltage detection module 13 collects the voltage of both sides of the third resistor 113 at this time as the second voltage. Further, according to the first voltage and the second voltage under different states of the same point, combined with formula (1) and formula (2), the direct current positive terminal-to-ground insulation resistance and the direct current negative terminal-to-ground insulation resistance of the inverter 100 are calculated; if the insulation impedance meets the insulation requirement, then the switch tubes K3 and K4 are controlled to be closed to realize the electrical connection between the battery and the inverter. Another use scenario is that, when the inverter is working normally, because the detection circuit 11 is also connected to the direct current source voltage, therefore, through the control of the first switch and the second switch, the insulation impedance can be detected in time, when it is detected that the insulation impedance does not meet the insulation requirement, the switch tubes K3 and K4 are controlled to be opened to prevent safety risks.

[0067] According to the circuit diagram, the first switch 114 can be controlled by the control module 14 to be in a closed state, the second switch 115 can be controlled by the control module 14 to be in an open state, the third voltage and the maximum change of the third voltage within a preset time can be collected by the voltage detection module 13, and further, the processing module 15 can judge the ground insulation performance of the corresponding alternating current phase of the inverter 100, whether there is a ground short circuit of the corresponding alternating current phase of the inverter 100, and calculate the ground insulation impedance of the corresponding alternating current phase of the inverter 100 according to the maximum change.

[0068] Further, the input of two alternating current phases of the inverter 100 is disconnected, and the first switch K1 is closed and the second switch K2 is opened by the control module 14, and the equivalent circuit is shown in FIG. 8. Wherein, R ac is the equivalent insulation impedance of the alternating current phase to the ground, and the processing module 15 can calculate the ground insulation impedance of the corresponding alternating current phase of the inverter 100 by the following formula:

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

[0070] In the formula, U1 represents the direct current source voltage connected to the direct current side of the inverter 100, such as the output voltage of the energy storage battery or the output voltage of the 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, and R p1 =R p(R1+R2), R1 represents the resistance value of the first resistor, R2 represents the resistance value of the second resistor, R p represents the DC positive terminal-to-ground insulation resistance of the converter 100, R n1 =R n / / R3, R3 represents the resistance value of the third resistor, R n represents the DC negative terminal-to-ground insulation resistance of the converter 100, R ac is the equivalent insulation impedance of the AC phase to ground.

[0071] According to the above description, in the embodiment, by disconnecting the input of two AC phases of the converter 100, the control module 14 controls the first switch 114 to be closed and the second switch 115 to be disconnected, to form an equivalent circuit of the equivalent insulation impedance of one AC phase to ground, and combines the detected DC source voltage, the third voltage, the midpoint-to-ground voltage, and the phase voltage, and obtains the insulation impedance of the AC phase to ground through the calculation of formula (3), which improves the accuracy of the obtained insulation impedance to ground. Further, the detected AC-to-ground equivalent insulation impedance can also be used to judge the short circuit risk of the AC-to-ground, which is beneficial to improve the safety of the system.

[0072] In an optional embodiment, the third voltage and the phase voltage of the three phases at multiple sampling time points are collected by the voltage detection module 13 at intervals, so as to simultaneously detect the insulation impedance of the three AC phases of the converter 100 to ground. The equivalent circuit for detecting the insulation impedance of the three AC phases of the converter 100 to ground is shown in FIG. 9, wherein R ac1 is the equivalent insulation impedance of the first phase of the converter 100 to ground, R ac2 is the equivalent insulation impedance of the second phase of the converter 100 to ground, and R ac3 is the equivalent insulation impedance of the third phase of the converter 100 to ground. Specifically, the processing module 15 calculates the insulation impedance of any AC phase of the converter 100 to ground through the following formula:

[0073] In the formula, U n represents the voltage of the neutral line N to ground PE, U1 represents the battery voltage connected to the DC side of the converter 100, U 2i represents the third voltage at the i-th time point, U 4i represents the phase voltage of the first phase at the i-th time point, U 5i represents the phase voltage of the second phase at the i-th time point, and U 6i represents the phase voltage of the third phase at the i-th time point, R p1 =R p / / 2R, R n1 =R n / / R, R p represents the DC positive terminal-to-ground insulation resistance of the converter 100, R nrepresents the DC negative terminal-to-ground insulation resistance of the converter 100, R represents the resistance values of the first resistor 111, the second resistor 112 and the third resistor 113, R ac1 is the first phase-to-ground equivalent insulation impedance of the converter 100, R ac2 is the second phase-to-ground equivalent insulation impedance of the converter 100, R ac3 is the third phase-to-ground equivalent insulation impedance of the converter 100; i represents a sampling time, i = 1, 2, 3, and the time interval of each sampling time is not equal to the period of the three-phase alternating current or an integer multiple of the period. According to the above description, the converter 100 of the embodiment can collect the third voltage at multiple sampling times and the phase voltages of the three phases through the voltage detection module 13, and simultaneously obtain the ground equivalent insulation impedance of the three phases through formula (4) in the case that the time interval of each sampling time is not equal to the period of the three-phase alternating current or an integer multiple of the period, thereby improving the accuracy and efficiency of obtaining the ground insulation impedance; and R p , R n can be calculated through formulas (1) and (2). The embodiment does not need to detect the leakage current through the current sensor to determine the AC side ground short circuit, which is beneficial to save detection cost, and does not need to disconnect the connection of other phase lines, and is suitable for real-time monitoring. Through the embodiment, the detection of the DC side ground insulation impedance and the AC side ground insulation impedance can be realized, and the embodiment has the characteristics of low detection cost and high universality.

[0074] In the description of the present application, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. The meaning of "multiple" is two or more, unless otherwise specifically limited.

[0075] The technical features of the above embodiments can be combined in any way, and in order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0076] It should be understood that those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall fall within the protection scope of the appended claims of the present application.

Claims

1. A converter, comprising a bidirectional conversion circuit, the bidirectional conversion circuit comprising a direct current port and an alternating current port, the bidirectional conversion circuit being configured to perform bidirectional conversion between direct current and alternating current power supply; characterized in that the converter further comprising: a detection circuit, the detection circuit comprising a first resistor, a second resistor and a third resistor, a first end of the first resistor being electrically connected to a direct current positive end of the bidirectional conversion circuit, a second end of the first resistor being connected to a first end of the second resistor, a second end of the second resistor being connected to a first end of the third resistor, a second end of the third resistor being electrically connected to a direct current negative end of the bidirectional conversion circuit; the detection circuit further comprising a first switch and a second switch, a connection point between the first resistor and the second resistor being electrically connected to the direct current negative end of the bidirectional conversion circuit through the second switch, a connection point between the second resistor and the third resistor being grounded through the first switch; the converter further comprising a voltage detection module, the voltage detection module being configured to acquire a direct current negative end-to-ground voltage of the bidirectional conversion circuit; a control module, the control module being configured to control at least a switching state of the first switch and the second switch; a processing module, the processing module being configured to calculate a direct current positive end-to-ground insulation resistance and a direct current negative end-to-ground insulation resistance of the converter according to a direct current source voltage, a first voltage and a second voltage acquired by the voltage detection module, wherein the first voltage is a voltage measured by the voltage detection module when the converter is in an off-grid state, the first switch is closed and the second switch is opened; the second voltage is a voltage measured by the voltage detection module when the converter is in the off-grid state, the first switch and the second switch are both closed. 2.The converter of claim 1, wherein the processing module calculates the direct current positive end-to-ground insulation resistance and the direct current negative end-to-ground insulation resistance 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 ; In the formula, U a represents the first voltage, U b represents the second voltage, U1 represents the voltage of the direct current source connected to the direct current side of the converter, R p represents the direct current positive terminal-ground insulation resistance of the converter, R n represents the direct current negative terminal-ground insulation resistance of the converter, and the resistance values of the first resistance, the second resistance and the third resistance are all R.

3. The current transformer of claim 2, wherein, the processing module is further configured to determine an alternating current phase-to-ground short circuit condition according to a third voltage acquired by the voltage detection module; wherein the third voltage is a voltage measured by the voltage detection module when the converter is in a grid-connected state, the first switch is closed and the second switch is opened, and any phase of a power grid supplies power to the converter.

4. The current transformer of claim 3, wherein, the processing module is further configured to determine whether any alternating current phase of the converter is short-circuited according to a maximum variation of the third voltage acquired by the voltage detection module within a preset time; in response to the maximum variation being less than or equal to a first preset threshold, determining that a ground insulation performance of a corresponding alternating current phase of the converter is normal. 5.The converter of claim 4, wherein the first preset threshold is 0.2 times of a peak-to-peak value of the alternating current voltage of the phase. 6.The converter of claim 4, wherein in response to the maximum variation being greater than a second preset threshold, determining that the corresponding alternating current phase of the converter is short-circuited to the ground, the second preset threshold being greater than the first preset threshold. 7.The converter of claim 6, wherein The second preset threshold is 0.7 times of the peak-to-peak value of the phase alternating voltage.

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

9. The current transformer of claim 3, wherein, The processing module is configured to calculate the ground insulation impedance of any alternating current phase of the converter by the following formula: In the formula, U n represents the voltage of the neutral line to the ground, U1 represents the voltage of the battery connected to the direct current 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 direct current positive terminal of the converter to the ground, R n represents the insulation resistance of the direct current negative terminal of the converter to the ground, R represents the resistance 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 of each sampling moment is not equal to the period or an integer multiple of the period of the three-phase alternating current.

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