Converter

Abstract

The present application discloses a converter, the converter includes a bidirectional conversion circuit, a detection circuit and a voltage detection module, the detection circuit includes a first resistor, a second resistor, a third resistor, a first switch and a second switch, the first end of the first resistor is electrically connected to the DC positive 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 DC negative end of the bidirectional conversion circuit; the connection point between the first resistor and the second resistor is electrically connected to the DC negative 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 voltage detection module is configured to collect the DC negative end voltage of the bidirectional conversion circuit to the ground. The converter of the present application can realize the detection of insulation impedance to the ground, and can also improve the sensitivity, accuracy and response speed of the converter short circuit detection to the ground.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a converter. Background Art

[0002] With the rapid development of renewable energy, the safety and reliability of energy storage systems, as an important part of smart grids, have received widespread attention. Energy storage systems are usually composed of battery packs, BMS (battery management system), PCS (energy storage converter) and AC mains. During the operation of the energy storage system, PCS, as one of the key devices, is responsible for realizing energy conversion and control between battery packs and AC mains.

[0003] In practical applications, various factors such as equipment aging, environmental impact, and human error may cause a short circuit to ground fault on the AC side of the PCS. This fault will not only affect the normal operation of the energy storage system, but may also threaten the safety of equipment and personnel. Therefore, the detection method of the short circuit to ground on the AC side of the PCS is of great significance to ensure the safety and reliability of the energy storage system. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the purpose of the present application is to provide a converter, which can detect the insulation impedance of the converter port to the ground.

[0005] To achieve the above objectives, this application adopts the following technical solutions:

[0006] 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 supply; the converter also includes: a detection circuit, 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 DC positive 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 DC negative end of the bidirectional conversion circuit; the detection circuit also includes a first switch and a second switch, the connection point between the first resistor and the second resistor is electrically connected to the DC negative 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 also includes a voltage detection module, the voltage detection module is configured to collect the DC negative end of the bidirectional conversion circuit to ground voltage.

[0007] The above-mentioned converter controls the closed or open 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 under different conditions, and then detects the voltage under different current loops to infer the magnitude and direction of the current, and collects the DC negative terminal to ground voltage through the voltage detection module, and then combines the magnitude and direction of the current and the DC negative terminal to ground voltage to detect the insulation impedance of the converter port to ground.

[0008] In one embodiment, the converter further includes: a control module, which is used to control the switching state of at least the first switch and the second switch; a processing module, which is used to calculate the insulation resistance of the DC positive terminal to ground and the insulation resistance of the DC negative terminal to ground of the converter based on 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 an off-grid state, the first switch is closed and the second switch is disconnected, the voltage measured by the voltage detection module; the second voltage is: when the converter is in an off-grid state, the first switch and the second switch are both closed, the voltage measured by the voltage detection module.

[0009] In one embodiment, the processing module calculates the insulation resistance of the DC positive terminal to ground and the insulation resistance of the DC negative terminal to ground according to the following formula:

[0010] U a / (R n / / R)=(U 1 -U a ) / (R p / / 2R) ;

[0011] U b / (R n / / R / / R)=(U 1 -U b ) / R p ;

[0012] In the formula, U a represents the first voltage, U b represents the second voltage, U 1 Indicates the DC source voltage connected to the DC side of the converter, R p Indicates the insulation resistance of the DC positive terminal of the converter to ground.R n represents the insulation resistance of the DC negative terminal of the converter to the ground. The resistance values ​​of the first resistor, the second resistor and the third resistor are R .

[0013] In one embodiment, the processing module is also used to determine the AC phase short circuit condition or calculate the insulation impedance of the AC phase to the ground based on the third voltage collected by the voltage detection module; wherein the third voltage is: when the converter is in a grid-connected state, the first switch is closed and the second switch is disconnected, and any relative power supply of the grid to the converter, the voltage measured by the voltage detection module.

[0014] In one embodiment, the processing module is also used to determine whether any AC phase of the converter is short-circuited based on the maximum change of the third voltage collected by the voltage detection module within a preset time; in response to the maximum change being less than or equal to a first preset threshold, it is determined that the insulation performance of the corresponding AC phase of the converter to the ground is normal.

[0015] In one embodiment, the first preset threshold is 0.2 times the peak-to-peak value of the AC voltage of the phase.

[0016] In one embodiment, in response to the maximum change being greater than a second preset threshold, it is determined that the corresponding AC phase of the converter is short-circuited to ground, and the second preset threshold is greater than the first preset threshold.

[0017] In one embodiment, the second preset threshold is 0.7 times the peak-to-peak value of the AC voltage of the phase.

[0018] In one embodiment, the processing module is further used to calculate the insulation impedance to ground of the corresponding AC phase of the converter according to the following formula:

[0019] （U 4 +U n ） / R ac +(U 1 -U 2 ) / R p1 =U 2 / R n1 ;

[0020] In the formula, U 1 represents the DC source voltage connected to the DC side of the converter, U 2 represents the third voltage,U 4 represents the phase voltage, U n Indicates the voltage between the neutral line and the ground. R p1 =R p / / (R 1 +R 2 ) , R p represents the insulation resistance of the DC positive terminal of the converter to ground, R 1 represents the resistance value of the first resistor, R 2 represents the resistance value of the second resistor, R n1 =R n / / R 3 , R n represents the insulation resistance of the DC negative terminal of the converter to ground, R 3 represents the resistance value of the third resistor, R ac is the equivalent insulation resistance of the AC phase to ground.

[0021] In one embodiment, the processing module is used to calculate the insulation impedance to ground of any AC phase of the converter by the following formula:

[0022] ;

[0023] In the formula, U n Indicates the voltage between the neutral line N and the ground PE. U 1 represents the battery voltage connected to the DC side of the converter, U 2i Indicates i The third voltage at the time, U 4i Indicates i The phase voltage of the first phase at the moment, U 5i Indicates i The phase voltage of the second phase at the moment, U 6i Indicates i The phase voltage of the third phase at the moment, R p1 = R p / / 2R, Rn1 = R n / / R, R p represents the insulation resistance of the DC positive terminal of the converter to ground, R n represents the insulation resistance of the DC negative terminal of the converter to ground, R represents the resistance values ​​of the first resistor, the second resistor and the third resistor, R ac1 is the first phase-to-ground equivalent insulation impedance of the converter, R ac2 is the second phase-to-ground equivalent insulation impedance of the converter, R ac3 is the third phase-to-ground equivalent insulation impedance of the converter; i represents the sampling time, i =1, 2, 3, the time interval between each of the sampling moments is not equal to the period of the three-phase alternating current or an integer multiple of the period. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a converter provided in an embodiment of the present application;

[0025] Figure 2 A schematic diagram of the structure of another converter provided in an embodiment of the present application;

[0026] Figure 3 A schematic diagram of an equivalent circuit for detecting the insulation resistance of a DC positive terminal to ground provided in an embodiment of the present application;

[0027] Figure 4 A schematic diagram of an equivalent circuit for detecting the insulation resistance of a DC negative terminal to ground provided in an embodiment of the present application;

[0028] Figure 5 A waveform diagram of a third voltage provided in an embodiment of the present application;

[0029] Figure 6 A flow chart for determining whether a current transformer is short-circuited to ground provided in an embodiment of the present application;

[0030] Figure 7 A circuit diagram of a converter provided in an embodiment of the present application;

[0031] Figure 8 A schematic diagram of an equivalent circuit for detecting insulation impedance of an AC phase to ground provided in an embodiment of the present application;

[0032] Fig. 9 Schematic diagram of an equivalent circuit for detecting the insulation impedance of three AC phases to ground provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the specific implementation manner of the present application will be clearly and completely described below in conjunction with the drawings in the implementation manner of the present application.

[0034] In order to improve the safety and reliability of the system, 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. In addition, the converter also 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 DC positive 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 DC negative end of the bidirectional conversion circuit; the detection circuit also includes a first switch and a second switch, the connection point between the first resistor and the second resistor is electrically connected to the DC negative 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 also includes a voltage detection module, and the voltage detection module is configured to collect the DC negative end of the bidirectional conversion circuit to ground voltage; the present application does not limit the specific connection method of the voltage detection module, which can be as follows Figure 1 As shown, it can be directly connected between the DC negative terminal and the ground to detect the voltage between the DC negative terminal and the ground. Figure 2 As shown, the voltage of the DC negative terminal to the ground is calculated by detecting the voltage of other points. The converter controls the closed or open 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 under different conditions, and then detects the voltage under different current loops to infer the magnitude and direction of the current, and collects the voltage of the DC negative terminal to the ground through the voltage detection module, and then detects the insulation impedance of the converter port to the ground in combination with the magnitude and direction of the current and the voltage of the DC negative terminal to the ground, and then determines whether there is a short circuit to the ground.

[0035] In the related art, the detection of short-circuit faults on the AC side of energy storage converters mainly adopts traditional electrical quantity measurement and comparison methods. However, traditional methods are usually based on threshold judgment, and some weak short-circuit faults to the ground may not be detected in time, resulting in low detection sensitivity. Moreover, due to the large amount of harmonics and noise interference 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 faults in real time. The converter provided in the present application can not only realize the detection of insulation impedance to the ground through the setting and control of the first switch and the second switch, but also improve the sensitivity, accuracy and response speed of the converter short-circuit detection to the ground.

[0036] The converter according to the embodiment of the present application is described in detail below with reference to the accompanying drawings.

[0037] Figure 1 is a schematic diagram of the structure of the converter 100 of this embodiment, as shown in Figure 1 As shown, 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 to a DC power source 201 through the DC port 121 to receive or output DC power. The converter 100 is connected to an AC power source 202 through the AC port 122 to receive or output AC power. The bidirectional conversion circuit 12 is used to realize bidirectional conversion of power between the DC power source 201 and the AC power source 202.

[0038] 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 may be, but are not limited to, a relay or a contactor, an IGBT (Insulate-Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and the like.

[0039] 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 DC positive end of the bidirectional conversion circuit 12, and the DC positive end is equivalent to the positive electrode 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, and the second end of the third resistor 113 is electrically connected to the DC negative end of the bidirectional conversion circuit 12, and the DC negative end is equivalent to the negative electrode of the DC power supply 201. The connection point between the first resistor 111 and the second resistor 112 is electrically connected to the DC negative terminal of the bidirectional conversion circuit 12 through the second switch 115, and 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 to control the current path of the detection circuit 11 and form different current loops, thereby enabling the detection circuit 11 to detect the current flow and voltage state in the converter 100.

[0040] The voltage detection module 13 is configured to collect the voltage between the DC negative terminal of the bidirectional conversion circuit 12 and the ground. The working state of the converter 100, such as the voltage level, polarity and possible fault conditions, can be determined through the voltage between the DC negative terminal and the ground.

[0041] According to the above description, the converter 100 of this embodiment controls the closed or open state of the first switch 114 and the second switch 115, so that the first resistor 111, the second resistor 112 and the third resistor 113 in the detection circuit 11 form different current loops under different conditions, and then detects the voltage under different current loops to infer the magnitude and direction of the current, and collects the DC negative terminal to ground voltage through the voltage detection module 13, and then detects the insulation impedance of the DC port / AC port of the converter 100 to the ground in combination with the magnitude and direction of the current and the DC negative terminal to the ground voltage, and then determines whether there is a short circuit to the ground, thereby improving the safety and reliability of the converter 100. And the sensitivity, accuracy and response speed of the short circuit to the ground detection using this circuit are high.

[0042] In an optional embodiment, if Figure 2 As shown, it is a structural schematic diagram of the converter 100 of this embodiment. The converter 100 also includes a control module 14 and a processing module 15. The control module 14 is used to control the switching state of at least 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 to the ground and the insulation resistance of the DC negative terminal to the ground 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. The first voltage is: when the converter 100 is in an off-grid state, the first switch 114 is closed and the second switch 115 is disconnected, the voltage measured by the voltage detection module 13; the second voltage is: when the converter 100 is in an off-grid state, the first switch 114 and the second switch 115 are both closed, the voltage measured by the voltage detection module 13.

[0043] Specifically, when the converter 100 is in an off-grid state, the control module 14 controls the first switch 114 to be in a closed state, the second switch 115 to be in an 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 ground is as follows: Figure 3 As shown in the figure, R 1 represents the first resistor 111, R 2 represents the second resistor 112, R 3 represents the third resistor 113, 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 electrode of the DC power supply 201 to the ground. R nIt 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 electrode of the DC power supply 201 to the ground. U 1 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:

[0044] U a / (R n / / R)=(U 1 -U a ) / (R p / / 2R) Formula (1);

[0045] In the formula, U a represents the first voltage, U 1 represents the voltage of the DC power source 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 .

[0046] 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 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 follows: Figure 4 The second voltage across the third resistor 113 collected by the voltage detection module 13 can be expressed by the following formula:

[0047] U b / (R n / / R / / R)=(U 1 -U b ) / R p Formula (2);

[0048] In the formula, Ub represents the second voltage, U 1 represents the DC source voltage 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 .

[0049] When the DC source 201 is connected to the inverter 100, the DC source voltage appears in the detection circuit 11, and the DC source voltage causes 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 voltages on both sides of the third resistor 113 at this time as the second voltage. Then, according to the first voltage and the second voltage under different states at the same point, combined with formula (1) and formula (2), the DC positive terminal insulation resistance to ground and the DC negative terminal insulation resistance to ground of the converter 100 are calculated.

[0050] According to the above description, the converter 100 of this embodiment controls the closed or open state of the first switch 114 and the second switch 115 through the control module 14 to form different current loops, and collects voltages in different states through the voltage detection module 13, and then calculates and processes multiple voltages and multiple resistances through the processing module 15 to obtain the insulation resistance of the DC positive end to the ground and the insulation resistance of the DC negative end to the ground of the converter 100, thereby further improving the detection sensitivity and detection accuracy of the insulation impedance of the converter 100 to the ground.

[0051] 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 this embodiment.

[0052] When the inverter 100 is an energy storage inverter, the energy storage inverter can be applied to the energy storage system, the DC power supply 201 can be a battery, and the energy storage inverter is connected between the battery group and the power grid or the load. The energy storage inverter can invert the DC power of the battery into AC power and transmit it to the power grid or use it for the AC load. The energy storage inverter can also rectify the AC power of the power grid into DC power to charge the battery.

[0053] When the inverter 100 is a photovoltaic inverter, the photovoltaic inverter can be applied to a photovoltaic system, the DC power supply 201 can be a solar cell, the photovoltaic inverter is connected between the solar cell group and the power grid, and the photovoltaic inverter can convert the DC voltage of the solar cell group into an AC voltage of a common frequency for use in the power grid.

[0054] According to the above description, the inverter 100 of this embodiment can be an energy storage inverter or a photovoltaic inverter, which can be applied to the corresponding energy storage system or photovoltaic system to avoid damage to the DC power supply 201 of the system due to a short circuit to the ground and personnel safety issues caused by a short circuit to the ground, thereby improving the safety and reliability of the energy storage system or photovoltaic system.

[0055] In an optional embodiment, the processing module 15 is further used to determine the AC phase short circuit condition or calculate the insulation impedance of the AC phase to the ground according to the third voltage collected by the voltage detection module; wherein the third voltage is: when the converter 100 is in a grid-connected state, the first switch 114 is closed and the second switch 115 is disconnected, and any relative power supply of the grid to the converter 100 is supplied, the voltage measured by the voltage detection module 13;

[0056] Specifically, under normal circumstances, the voltage and current of each phase of the AC phase are balanced, and once a phase is short-circuited to the ground, the voltage of the phase will decrease, and the current will increase significantly. Therefore, when the converter 100 is in a grid-connected state, when any phase of the grid supplies power to the converter 100, the control module 14 controls the first switch 114 to be in a closed state and the second switch 115 to be in an 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 AC phase short circuit to the ground can be judged according to the third voltage. Moreover, under this set current loop, combined with the detected third voltage, using Ohm's law, Kirchhoff's current theorem and other circuit laws, the insulation impedance of the AC phase to the ground can be calculated.

[0057] According to the above description, the converter 100 of this embodiment realizes AC phase-to-ground short circuit detection of the converter 100 or detects the insulation impedance of the AC phase to ground by controlling the control module 14 to close the first switch 114 and disconnect the second switch 115 when the converter 100 is in the grid-connected state, and the voltage detection module 13 collects the third voltage.

[0058] In an optional embodiment, the processing module 15 is also used to determine whether any AC phase of the converter 100 is short-circuited based on the maximum change in the third voltage collected by the voltage detection module 13 within a preset time, and in response to the maximum change being less than or equal to a first preset threshold, determine that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal.

[0059] Among them, the preset time can be set to a short time window, such as a few seconds to a few minutes. The preset time can be set to a suitable value after multiple experiments to avoid misjudgment that may be caused by being too long or too short. The maximum change 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 of the change problem of the third voltage. The first preset threshold can be specifically set according to historical data and experience.

[0060] Specifically, when the converter 100 is in a grid-connected state, the control module 14 controls the first switch 114 to be in a closed state and the second switch 115 to be in an 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. Then, within a preset time, the voltage detection module 13 continuously collects the third voltage, obtains the maximum value and the minimum value of the voltage at the point, and obtains the difference between the two by calculation, that is, the maximum variation of the third voltage, to determine whether the AC port 122 of the converter 100 is short-circuited to the ground.

[0061] Furthermore, when the maximum change is less than or equal to the first preset threshold, it indicates that the third voltage is relatively stable and no abnormal state occurs. Therefore, it is judged that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal, that is, there is no short circuit in any AC phase of the converter 100.

[0062] According to the above description, the converter 100 of this embodiment controls the first switch 114 to close and the second switch 115 to open when the converter 100 is in a grid-connected state, the voltage detection module 13 collects the maximum change of the third voltage within a preset time, and the processing module 15 determines that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal when the maximum change is less than or equal to the first preset threshold value, and determines that there is no short circuit in any AC phase of the converter 100, thereby preventing possible short circuit problems in the converter 100 and improving the stability and safety of the converter 100 during grid-connected operation.

[0063] In an optional embodiment, the first preset threshold is 0.2 times the peak-to-peak value of the AC voltage of the phase. For example, if the peak-to-peak value of the AC voltage of a phase is Va, then the first preset threshold is 0.2Va. When the maximum change is less than or equal to 0.2 times the AC voltage of the 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.

[0064] In an optional embodiment, in response to the maximum change amount being greater than a second preset threshold, it is determined that the corresponding AC phase of the converter 100 is short-circuited to ground, and the second preset threshold is greater than the first preset threshold.

[0065] The second preset threshold is used to indicate that the change of the third voltage has a large fluctuation, which is likely caused by a fault in the converter 100. The second preset threshold can be specifically set according to historical experience, safety standards, and application environment, etc. For example, the first preset threshold is set to 10V, and the second preset threshold is set to 250V.

[0066] Specifically, when the maximum change in the third voltage is greater than the second preset threshold, it indicates that the change in the third voltage is large, and it is judged that the corresponding AC phase of the converter 100 is short-circuited, and the connection with the faulty AC phase can be automatically disconnected, or an alarm message can be issued to notify the maintenance team to conduct inspection and repair.

[0067] According to the above description, the converter 100 of this embodiment sets a second preset threshold value, and when the maximum change amount is greater than the second preset threshold value, determines that the corresponding AC phase of the converter 100 is short-circuited, thereby further preventing the short-circuit problem existing in the converter 100, so as to take protective measures in time to avoid serious short-circuit faults, and further improve the stability and safety of the converter 100 during grid-connected operation.

[0068] In an optional embodiment, the second preset threshold is 0.7 times the peak-to-peak value of the AC voltage of the phase. For example, if the peak-to-peak value of the AC voltage of a phase is Va, the first preset threshold is 0.2Va and the second preset threshold is 0.7Va. When the maximum change is greater than 0.7Va, it is determined that the corresponding AC phase of the converter 100 has a short circuit problem to better maintain the stability of the operation of the converter 100.

[0069] For example, assuming that the peak voltage of a phase AC voltage of the converter 100 is Vb, the maximum change of the phase AC voltage is 2Vb, the first preset threshold is 0.4 Vb, and the second preset threshold is 1.4 Vb, then the waveform of the third voltage is as follows: Figure 5 As shown. The red ripple in the figure is the waveform of the third voltage under normal conditions, and the maximum variation of the ripple is less than 0.4Vb. The green ripple in the figure is the waveform of the third voltage when there is a short circuit problem between the AC phase and the ground, and the maximum variation of the ripple is greater than 1.4Vb. It can be seen that when the maximum variation is less than 0.4Vb, the ripple variation of the third voltage is relatively stable, no abnormal state occurs, and there is no short circuit in the AC phase of the converter 100; 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 is short-circuited to the ground.

[0070] In an optional embodiment, in response to the maximum change being greater than the first preset threshold value, and the maximum change being less than or equal to the second preset threshold value, the processing module 15 calculates the insulation impedance to ground of the corresponding AC phase of the converter 100. Of course, the processing module 15 may also be used to directly calculate the insulation impedance to ground of the corresponding AC phase of the converter 100 without first performing a short circuit judgment.

[0071] Among them, the insulation impedance can evaluate the insulation performance of the converter 100, and the insulation impedance reflects the converter 100's ability to limit current, that is, the ability to prevent current from passing through unexpected paths (such as battery housings or connecting parts). A higher insulation impedance indicates better insulation performance, because it means that it is more difficult for current to flow through unexpected paths. On the contrary, a lower insulation impedance may indicate the presence of insulation problems, such as damage to the battery housing, looseness or corrosion of connecting parts, etc., all of which may cause current leakage, thereby affecting the safety and performance of the converter 100. Therefore, the processing module 15 can be used to calculate the insulation impedance of the input AC phase of the converter 100 to the ground, so as to effectively evaluate the insulation performance of the converter 100 to the ground, and to promptly discover and deal with potential insulation problems. If the insulation impedance to the ground is very low, or even close to 0, it indicates that a short circuit to the ground has occurred.

[0072] For example, Figure 6 As shown, it is a flow chart for judging whether the converter 100 is short-circuited to ground, which specifically includes the following steps:

[0073] Step S601: The voltage detection module 13 collects a third voltage and a maximum variation of the third voltage within a preset time.

[0074] Step S602, the processing module 15 determines whether the maximum change is less than or equal to the first preset threshold; if the judgment result is yes, execute step S603, if the judgment result is no, execute step S604.

[0075] Step S603: Determine that the insulation performance of the corresponding AC phase of the converter 100 to the ground is normal.

[0076] Step S604, the processing module 15 determines whether the maximum change amount is greater than the second preset threshold; if the judgment result is yes, execute step S605, if the judgment result is no, execute step S606.

[0077] Step S605 : The processing module 15 calculates the insulation impedance of the corresponding AC phase of the converter 100 to ground.

[0078] Step S606: Determine that the corresponding AC phase of the converter 100 is short-circuited to ground.

[0079] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this application can be executed in parallel, sequentially or in different orders, as long as the expected results of the technical solution of this application can be achieved, and this document does not limit this.

[0080] Furthermore, if Figure 7 , which is a circuit diagram of the converter 100. The DC power supply 201 is a battery connected to the DC side of the converter 100, BAT+ represents the positive electrode of the battery, BAT- represents the negative electrode of the battery, R 1 represents the first resistor 111, R 2 represents the second resistor 112, R 3 represents the third resistor 113, K 1 represents the first switch 114, K 2 represents the second switch 115, R p represents the equivalent insulation resistance of the DC positive terminal of the converter 100 to the ground, R n It represents the equivalent insulation resistance of the DC negative terminal of the converter 100 to the ground.

[0081] like Figure 7 As shown, one use scenario of this embodiment is that before the DC power supply 201 is connected to the inverter 100, the detection circuit 11 appears the DC source voltage, and the DC source voltage causes the 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 voltages on both sides of the third resistor 113 at this time as the second voltage. Then, according to the first voltage and the second voltage under different states at the same point, combined with formula (1) and formula (2), the DC positive terminal insulation resistance to ground and the DC negative terminal insulation resistance to ground of the converter 100 are calculated; if the insulation impedance meets the insulation requirements, 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 DC source voltage, the insulation impedance can be detected in time by controlling the first switch and the second switch. When it is detected that the insulation impedance does not meet the insulation requirements, the switch tubes K3 and K4 are controlled to be disconnected to prevent safety risks.

[0082] According to the circuit diagram, the control module 14 can be used to control the first switch 114 to be in a closed state and the second switch 115 to be in an open state, and the voltage detection module 13 can be used to collect the third voltage and the maximum change 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 the corresponding AC phase of the converter 100 is short-circuited to the ground, and calculates the insulation impedance of the corresponding AC phase of the converter 100 to the ground based on the maximum change.

[0083] Further, the input of two AC phases of the converter 100 is disconnected, and the first switch K is closed through the control module 14. 1 , disconnect the second switch K 2 , the equivalent circuit formed is as follows Figure 8 As shown. Among them, R ac The processing module 15 can calculate the insulation impedance of the corresponding AC phase of the converter 100 to the ground by the following formula:

[0084] （U 4 +U n ） / R ac +(U 1 -U 2 ) / R p1 =U 2 / R n1 Formula (3);

[0085] In the formula, U 1 represents the DC source voltage connected to the DC side of the converter 100, such as the output voltage of an energy storage battery or a solar cell, U 2 represents the third voltage, U 4 represents the phase voltage, U n Indicates the voltage between the neutral line N and the ground PE. R p1 =R p / / (R 1 +R 2 ) , R 1 represents the resistance value of the first resistor, R 2represents the resistance value of the second resistor, R p represents the insulation resistance of the DC positive terminal of the converter 100 to the ground, R n1 = R n / / R 3 , R 3 represents the resistance value of the third resistor, R n represents the insulation resistance of the DC negative terminal of the converter 100 to the ground, R ac is the equivalent insulation resistance of the AC phase to ground.

[0086] According to the above description, in this embodiment, by disconnecting the input of two 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 AC phase to the ground, and combining the detected DC source voltage, the third voltage, the midpoint voltage to the ground, and the phase voltage, and calculating the insulation impedance of the AC phase to the ground by formula (3), the accuracy of the obtained insulation impedance to the ground is improved. Furthermore, the short circuit risk of AC to the ground can also be judged by the detected AC equivalent insulation impedance to the ground, which is conducive to improving the safety of the system.

[0087] In an optional embodiment, the voltage detection module 13 collects the third voltage and the phase voltage of the three phases at multiple sampling moments at intervals, and the insulation impedance of the three-phase AC phase of the converter 100 to the ground can be detected simultaneously. The equivalent circuit for detecting the insulation impedance of the three-phase AC phase of the converter 100 to the ground is as follows: Fig. 9 As shown, 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. Specifically, the processing module 15 calculates the insulation impedance of any AC phase of the converter 100 to ground by the following formula:

[0088] Formula (4);

[0089] In the formula, U n Indicates the voltage between the neutral line N and the ground PE. U 1 represents the battery voltage connected to the DC side of the converter 100, U 2i Indicates i The third voltage at the moment,U 4i Indicates i The phase voltage of the first phase at the moment, U 5i Indicates i The phase voltage of the second phase at the moment, U 6i Indicates i The phase voltage of the third phase at the moment, R p1 = R p / / 2R, R n1 = R n / / R, 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, 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 the sampling time, i =1, 2, 3, the time interval of each sampling moment is not equal to the cycle of the three-phase alternating current or an integer multiple of the cycle. According to the above description, the converter 100 of this embodiment, when the time interval of each sampling moment is not equal to the cycle of the three-phase alternating current or an integer multiple of the cycle, collects the third voltage and the phase voltage of the three phases at multiple sampling moments through the voltage detection module 13, and simultaneously obtains the equivalent insulation impedance of the three phases to the ground through formula (4), thereby improving the accuracy and efficiency of obtaining the insulation impedance to the ground; and R p , R n It can be calculated by formula (1) and (2). In this embodiment, there is no need to use a current sensor to detect leakage current to determine whether the AC side is short-circuited to the ground, which is conducive to saving detection costs, and there is no need to disconnect the connection of other phase lines, which is suitable for real-time monitoring. Through this embodiment, the insulation impedance of the DC side to the ground and the insulation impedance of the AC side to the ground can be detected, which has the characteristics of low detection cost and high versatility.

[0090] In the description of this application, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0091] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0092] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the claims attached to this application.

Claims

1. A converter, comprising a bidirectional conversion circuit, the bidirectional conversion circuit comprising a DC port and an AC port, the bidirectional conversion circuit being used for bidirectional conversion of AC / DC power supply; It is characterized in that The converter further comprises: A detection circuit, the detection circuit comprising a first resistor, a second resistor and a third resistor, wherein a first end of the first resistor is electrically connected to a DC 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 DC negative end of the bidirectional conversion circuit; The detection circuit further includes a first switch and a second switch, wherein a connection point between the first resistor and the second resistor is electrically connected to a DC negative terminal 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, wherein the voltage detection module is configured to collect the voltage between the negative DC terminal of the bidirectional conversion circuit and the ground; The converter further comprises: A processing module, the processing module is used to determine the short circuit situation of the AC phase to the ground or to calculate the insulation impedance of the AC phase to the ground according to the third voltage collected by the voltage detection module; The third voltage is: when the converter is in a grid-connected state, the first switch is closed and the second switch is open, and any one side of the grid supplies power to the converter, the voltage measured by the voltage detection module; The processing module is used to calculate the insulation impedance of the corresponding AC phase of the converter to the ground according to the following formula: （U 4 +U n ） / R ac +(U 1 -U 2 ) / R p1 =U 2 / R n1 ； In the formula, U 1 represents the DC source voltage connected to the DC side of the converter, U 2 represents the third voltage, U 4 represents the phase voltage, U n Indicates the voltage from the neutral line to the ground. R p1 =R p / / (R 1 +R 2 ) , R p represents the insulation resistance of the DC positive terminal of the converter to ground, R 1 represents the resistance value of the first resistor, R 2 represents the resistance value of the second resistor, R n1 =R n / / R 3. R n represents the insulation resistance of the DC negative terminal of the converter to ground, R 3 represents the resistance value of the third resistor, R ac is the equivalent insulation resistance of the AC phase to ground; or, The processing module is used to calculate the insulation impedance of any AC phase of the converter to ground by the following formula: ； In the formula, U n Indicates the voltage from the neutral line to the ground. U 1 indicates the battery voltage connected to the DC side of the converter, U 2i Indicates i The third voltage at the time, U 4i Indicates i The phase voltage of the first phase at the moment, U 5i Indicates i The phase voltage of the second phase at the moment, U 6i Indicates i The phase voltage of the third phase at the moment, R p1 = R p / / 2R, R n1 = R n / / R, R p represents the insulation resistance of the DC positive terminal of the converter to ground, R n represents the insulation resistance of the DC negative terminal of the converter to ground, R represents the resistance values ​​of the first resistor, the second resistor and the third resistor, R ac1 is the first phase-to-ground equivalent insulation impedance of the converter, R ac2 is the second phase-to-ground equivalent insulation impedance of the converter, R ac3 is the third phase-to-ground equivalent insulation impedance of the converter; i represents the sampling time, i =1, 2, 3, the time interval between each of the sampling moments is not equal to the period of the three-phase alternating current or an integer multiple of the period.

2. The converter according to claim 1, characterized in that: The converter further comprises: A control module, the control module is used to control at least the switch state of the first switch and the second switch; The processing module is used to calculate the insulation resistance of the DC positive terminal to ground and the insulation resistance of the DC negative terminal to ground of the converter according to the DC source voltage and the first voltage and the second voltage collected by the voltage detection module. The first voltage is: when the converter is in an off-grid state, the first switch is closed and the second switch is open, the voltage measured by the voltage detection module; The second voltage is: when the converter is in an off-grid state and the first switch and the second switch are both closed, the voltage measured by the voltage detection module.

3. The converter according to claim 2, characterized in that: The processing module calculates the insulation resistance of the DC positive terminal to ground and the insulation resistance of the DC negative terminal to ground according to the following formula: U a / (R n / / R)=(U 1 -U a ) / (R p / / 2R) ； U b / (R n / / R / / R)=(U 1 -U b ) / R p ； In the formula, U a represents the first voltage, U b represents the second voltage, U 1 represents the DC source voltage connected to the DC side of the converter, R p Indicates the insulation resistance of the DC positive terminal of the converter to ground. R n represents the insulation resistance of the DC negative terminal of the converter to the ground. The resistance values ​​of the first resistor, the second resistor and the third resistor are R .

4. The converter according to claim 1, characterized in that: The processing module is also used to determine 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 being less than or equal to a first preset threshold, it is determined that the insulation performance of the corresponding AC phase of the converter to the ground is normal.

5. The converter according to claim 4, characterized in that: The first preset threshold is 0.2 times the peak-to-peak value of the AC voltage of the phase.

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

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

Images