An insulation detection circuit and an insulation detection method

Abstract

The embodiment of the present application discloses an insulation detection circuit and an insulation detection method, which comprises: a rectifier unit for converting a three-phase commercial power input voltage into a direct current input voltage to charge a pre-charging unit; the pre-charging unit provides a working voltage for the insulation detection circuit; an insulation detection unit connected to two poles of a direct current bus of a frequency converter, under the control of a first control signal and a second control signal output by the frequency converter, respectively adjusts a positive pole voltage and a negative pole voltage of the direct current bus to a first positive pole voltage and a first negative pole voltage; under the control of the first control signal, the second control signal and a third control signal, the positive pole voltage and the negative pole voltage are adjusted to a second positive pole voltage and a second negative pole voltage. In this way, the embodiment of the present application can detect the insulation fault of the energy storage system at the power-on moment of the three-phase alternating current commercial power, judge whether the insulation impedance is normal, prevent the electric shock of personnel and the damage of machine equipment caused by the system insulation fault, and improve the safety of the system.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of industrial frequency converters, and in particular to an insulation detection circuit and an insulation detection method. Background Technology

[0002] The most important function of a frequency converter is to regulate the speed of an AC motor. It offers excellent speed regulation, versatile performance, safety and reliability, simple operation, and system versatility. Because of these advantages, it is applicable to many industries and has been widely promoted. It is commonly used in the power, oil and gas drilling, building materials, and coal industries. However, in harsh environments, the UVW three-phase wires of traditional frequency converters are prone to damage. This is especially true for some construction machinery cranes that draw power from three-phase AC mains. The rectified UVW three-phase wires are far from the drive motor, and when the insulation breaks, it can easily cause electric shock, endangering lives. Therefore, designing a circuit capable of detecting insulation faults in the system is crucial.

[0003] Currently, conventional frequency converters typically only use a leakage protection switch added to the AC input side to protect the equipment and prevent damage caused by direct contact between the downstream active line and the PE. Summary of the Invention

[0004] To solve the above-mentioned technical problems, one technical solution adopted in this invention is: providing an insulation detection circuit applied to a frequency converter. This circuit includes a rectifier unit, a pre-charge unit, and an insulation detection unit. The rectifier unit is connected to the pre-charge unit and is used to convert the three-phase mains input voltage into a DC input voltage to charge the pre-charge unit. The pre-charge unit is connected to the insulation detection unit and stops charging when the output voltage reaches a preset voltage, and provides a working voltage to the insulation detection unit. The insulation detection unit is connected to the two poles of the DC bus of the frequency converter. Responding to the working voltage, the insulation detection unit adjusts the positive voltage of the DC bus to a first positive voltage and adjusts the negative voltage of the DC bus to a first negative voltage under the control of a first control signal and a second control signal output by the frequency converter. Under the control of the first control signal, the second control signal, and a third control signal output by the frequency converter, the insulation detection unit adjusts the positive voltage to a second positive voltage and adjusts the negative voltage to a second negative voltage.

[0005] In some embodiments, the pre-charge unit includes a positive main relay, a negative main contactor, a pre-charge relay, a pre-charge resistor, and a bus capacitor. The first terminal of the pre-charge relay is connected to the positive output terminal of the rectifier unit, the second terminal of the pre-charge relay is connected to the first terminal of the pre-charge resistor, and the second terminal of the pre-charge resistor is connected to the first terminal of the bus capacitor. The first terminal of the positive main relay is connected to the first terminal of the pre-charge relay, and the second terminal of the positive main relay is connected to the second terminal of the pre-charge resistor. The first terminal of the negative main contactor is connected to the negative output terminal of the rectifier unit, and the second terminal of the negative main contactor is connected to the second terminal of the bus capacitor. The first terminal of the bus capacitor is connected to the first terminal of the insulation detection unit, and the second terminal of the bus capacitor is connected to the second terminal of the insulation detection unit.

[0006] In some embodiments, the insulation detection unit includes a first or third detection resistor, a second detection resistor, and a fourth detection resistor, as well as a first or third relay, a second relay, and a fourth relay. The first terminal of the second relay is connected to the positive output terminal of the pre-charge unit; the second terminal of the second relay is connected to the first terminal of the second detection resistor; the second terminal of the second detection resistor is connected to the second terminal of the fourth detection resistor to form a first connection point, which is grounded; the first terminal of the fourth detection resistor is connected to the second terminal of the fourth relay; and the first terminal of the fourth relay is connected to the negative output terminal of the pre-charge unit. The first terminal of the first relay is connected to the first terminal of the second relay; the second terminal of the first relay is connected to the first terminal of the first detection resistor; and the second terminal of the first detection resistor is connected to the first connection point. The first terminal of the third relay is connected to the first terminal of the fourth relay; the second terminal of the third relay is connected to the first terminal of the third detection resistor; and the second terminal of the third detection resistor is connected to the first connection point.

[0007] In some embodiments, the second relay closes in response to the first control signal, the fourth relay closes in response to the second control signal, and the first relay or the third relay closes in response to the third control signal.

[0008] In some embodiments, the rectifier unit includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, wherein a first end of the first switch is connected to a second end of the fourth switch, a second end of the first switch is connected to a second end of the second switch, and a first end of the fourth switch is connected to a first end of the fifth switch; a first end of the second switch is connected to a second end of the fifth switch, a second end of the second switch is connected to a second end of the third switch, and a first end of the fifth switch is connected to a first end of the sixth switch; a first end of the third switch is connected to a second end of the sixth switch, a second end of the third switch is connected to the positive input terminal of the precharge unit, and a first end of the sixth switch is connected to the negative input terminal of the precharge unit.

[0009] In some embodiments, the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch may be diodes, MOSFETs, and IGBTs.

[0010] In some embodiments, the preset voltage is the product of the DC input voltage and 0.95.

[0011] To solve the above-mentioned technical problems, another technical solution adopted in the embodiments of the present invention is: providing an insulation detection method, applied to the insulation detection circuit as described above, the method comprising: when a three-phase mains input voltage is detected, closing the negative main contactor and the pre-charge relay to start charging the bus capacitor; when the voltage across the bus capacitor is detected to reach a preset voltage, disconnecting the negative main contactor and the pre-charge relay; closing the second relay and the fourth relay to collect the first positive voltage and the first negative voltage respectively; closing the third relay or the first relay to collect the second positive voltage and the second negative voltage respectively; calculating the positive-to-ground impedance and the negative-to-ground impedance of the DC bus based on the first positive voltage, the first negative voltage, the second positive voltage, and the second negative voltage respectively; detecting whether the positive-to-ground impedance or the negative-to-ground impedance is less than a preset resistance value; if not, closing the positive main relay and the negative main contactor; if yes, determining that the inverter has an insulation fault.

[0012] In some embodiments, the positive electrode impedance to ground is calculated using the following formula:

[0013] R+=R2×C / (R2-C),

[0014] C = R3 × (BA),

[0015] A = VBUS1+ / VBUS1-,

[0016] B = VBUS²+ / VBUS²-

[0017] Wherein, R+ is the positive terminal impedance to ground, R2 is the second detection resistor, R3 is the third detection resistor, VBUS1+ is the first positive terminal voltage, VBUS1- is the first negative terminal voltage, VBUS2+ is the second positive terminal voltage, and VBUS2- is the second negative terminal voltage.

[0018] In some embodiments, the negative electrode impedance to ground is calculated using the following formula:

[0019] R-=R4×D / (R4-D),

[0020] D = R3 × (BA) / A,

[0021] Wherein, R- is the negative electrode impedance to ground, and R4 is the fourth detection resistor.

[0022] In some embodiments, the preset resistance is 500 kilohms.

[0023] The beneficial effects of the embodiments of the present invention are as follows: Unlike the prior art, the embodiments of the present invention can detect insulation faults in the energy storage system at the moment of power-on of three-phase AC mains power, determine whether the insulation impedance is normal, prevent electric shock to personnel and damage to machinery and equipment caused by system insulation faults, and improve the safety of the system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an insulation detection circuit provided by an embodiment of the present invention;

[0025] Figure 2 This is a circuit topology diagram of a rectifier unit provided by an embodiment of the present invention;

[0026] Figure 3 This is a circuit topology diagram of a pre-charge unit provided in an embodiment of the present invention;

[0027] Figure 4 This is a circuit topology diagram of an insulation detection unit provided by an embodiment of the present invention;

[0028] Figure 5 This is a circuit topology diagram of another insulation detection unit provided in an embodiment of the present invention;

[0029] Figure 6 This is a circuit topology diagram of an insulation detection circuit provided by an embodiment of the present invention;

[0030] Figure 7 This is a circuit topology diagram of another insulation detection circuit provided by an embodiment of the present invention;

[0031] Figure 8 This is a schematic flowchart of an insulation testing method provided by an embodiment of the present invention. Detailed Implementation

[0032] To facilitate understanding of this application, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected" to another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. The terms "upper," "lower," "inner," "outer," "bottom," etc., used in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0034] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0035] Regarding leakage protection measures for frequency converters, the following solutions exist:

[0036] 1. One solution involves adding a residual current device (RCD) on the AC input side. Typically, the RCD used in frequency converters has a leakage current of 200mA. When the system leakage current exceeds 200mA, the AC input is disconnected to protect downstream equipment. The drawback of this solution is that it only protects against short circuits and insulation faults caused by large leakage currents. Since the safe current flowing through a human body is 30mA at power frequency, the RCD may not disconnect in time in the event of an electric shock, leading to a safety accident. Therefore, traditional frequency converters generally lack electric shock protection; they can only protect equipment from damage and detect insulation faults with large leakage currents.

[0037] 2. Another approach is to add an isolated DC-DC power supply to the DC side of the frequency converter. Insulation resistance is calculated using the balanced bridge principle at the isolated DC output. By connecting resistors of different values ​​in series with the DC ± and PE terminals, the voltage across these resistors changes when an insulation fault occurs. Monitoring this voltage allows for the detection of insulation faults. The disadvantage of this approach is the need for an additional isolated DC-DC power supply, especially for high-power DC-DC converters, which significantly increases cost and size, and greatly reduces reliability.

[0038] 3. Another method is to add an isolated DC-DC power supply to the DC side of the frequency converter. A low-frequency signal is injected into the DC ± bus, generating a symmetrical square wave signal internally. This signal is then connected to an insulation resistance monitor to form a measurement circuit, which measures the insulation resistance RF between the DC high-voltage system and the chassis. The magnitude of RF is calculated by collecting the voltage across the sampling resistor. The disadvantage of this approach is that it requires an additional isolated DC-DC power supply, especially for high-power DC-DC power supplies, significantly increasing cost and size, and greatly reducing reliability.

[0039] In order to facilitate the detection of insulation faults in frequency converters and prevent electric shock to personnel, this invention provides a low-cost and convenient insulation fault detection method that can detect insulation faults in the system before the frequency converter is in operation, thus preventing electric shock to personnel and equipment damage caused by broken insulation wires.

[0040] In some embodiments of this application, an insulation detection circuit is proposed for use in a frequency converter, and its structural schematic diagram is shown below. Figure 1 As shown, the insulation detection circuit includes a rectifier unit 100, a precharge unit 200, and an insulation detection unit 300.

[0041] The rectifier unit 100 is connected to the precharge unit 200. The rectifier unit 100 is used to convert the three-phase mains input voltage RST into a DC input voltage to charge the precharge unit 200.

[0042] The pre-charge unit 200 is connected to the insulation detection unit 300. The pre-charge unit 200 stops charging when the output voltage reaches the preset voltage and provides the working voltage to the insulation detection unit 300.

[0043] The insulation detection unit 300 is connected to the positive DC+ and negative DC- terminals of the inverter's DC bus. In response to the operating voltage, the insulation detection unit 300 adjusts the positive voltage of the DC bus to the first positive voltage and the negative voltage of the DC bus to the first negative voltage under the control of the first control signal and the second control signal output by the inverter; under the control of the first control signal, the second control signal and the third control signal output by the inverter, it adjusts the positive voltage to the second positive voltage and the negative voltage to the second negative voltage.

[0044] In some embodiments of this application, a preset voltage V ref DC input voltage V in The product of V and 0.95 is V. ref =0.95V in .

[0045] In some embodiments of this application, a rectifier unit is provided, which includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first terminal of the first switch is connected to the second terminal of the fourth switch, the second terminal of the first switch is connected to the second terminal of the second switch, and the first terminal of the fourth switch is connected to the first terminal of the fifth switch. The first terminal of the second switch is connected to the second terminal of the fifth switch, the second terminal of the second switch is connected to the second terminal of the third switch, and the first terminal of the fifth switch is connected to the first terminal of the sixth switch. The first terminal of the third switch is connected to the second terminal of the sixth switch, the second terminal of the third switch is connected to the positive input terminal of a pre-charge unit, and the first terminal of the sixth switch is connected to the negative input terminal of the pre-charge unit.

[0046] It should be noted that the types of the first, second, third, fourth, fifth, and sixth switching transistors include diodes, MOSFETs, and IGBTs, etc.

[0047] In some embodiments of this application, a rectifier unit 100 is provided, using a diode as a switching transistor as an example. Its circuit topology is shown below. Figure 2 As shown, the rectifier unit 100 specifically includes a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, and a sixth diode D6.

[0048] In this configuration, the anode of the first diode D1 is connected to the cathode of the fourth diode D4, the cathode of the first diode D1 is connected to the cathode of the second diode D2, and the anode of the fourth diode D4 is connected to the anode of the fifth diode D5.

[0049] The anode of the second diode D2 is connected to the cathode of the fifth diode D5, the cathode of the second diode D2 is connected to the cathode of the third diode D3, and the anode of the fifth diode D5 is connected to the anode of the sixth diode D6.

[0050] The anode of the third diode D3 is connected to the cathode of the sixth diode D6, the cathode of the third diode D3 is connected to the positive input terminal of the precharge unit 200, and the anode of the sixth diode D6 is connected to the negative input terminal of the precharge unit 200.

[0051] Diodes D1, D2, D3, D4, D5, and D6 form a passive rectifier bridge, converting the three-phase AC input voltage RST into a DC input voltage to charge the pre-charge unit 200.

[0052] In some embodiments of this application, the circuit topology of the pre-charge unit 200 is as follows: Figure 3 As shown, the pre-charge unit 200 specifically includes a positive main relay K6, a negative main contactor K7, a pre-charge relay K5, a pre-charge resistor R5, and a bus capacitor C1.

[0053] The first terminal of the precharge relay K5 is connected to the positive output terminal of the rectifier unit 100, the second terminal of the precharge relay K5 is connected to the first terminal of the precharge resistor R5, and the second terminal of the precharge resistor R5 is connected to the first terminal of the bus capacitor C1.

[0054] The first terminal of the positive main relay K6 is connected to the first terminal of the precharge relay K5, and the second terminal of the positive main relay K6 is connected to the second terminal of the precharge resistor R5. The first terminal of the negative main contactor K7 is connected to the negative output terminal of the rectifier unit 100, and the second terminal of the negative main contactor K7 is connected to the second terminal of the bus capacitor C1.

[0055] The first end of the bus capacitor C1 is connected to the first end of the insulation detection unit 300, and the second end of the bus capacitor C1 is connected to the second end of the insulation detection unit 300.

[0056] In some embodiments of this application, an insulation detection unit 300 is proposed, the circuit topology of which is shown below. Figure 4 As shown, the insulation detection unit 300 specifically includes a third detection resistor R3, a second detection resistor R2 and a fourth detection resistor R4, as well as a third relay K3, a second relay K2 and a fourth relay K4.

[0057] In this configuration, the first end of the second relay K2 is connected to the positive output terminal of the precharge unit 200, the second end of the second relay K2 is connected to the first end of the second detection resistor R2, the second end of the second detection resistor R2 is connected to the second end of the fourth detection resistor R4 to form a first connection point A, the first connection point A is grounded, the first end of the fourth detection resistor R4 is connected to the second end of the fourth relay K4, and the first end of the fourth relay K4 is connected to the negative output terminal of the precharge unit 200.

[0058] The first terminal of the second relay K2 is connected to the positive terminal DC+ of the inverter's DC bus, and the first terminal of the fourth relay K4 is connected to the negative terminal DC- of the inverter's DC bus.

[0059] The first terminal of the third relay K3 is connected to the first terminal of the fourth relay K4, the second terminal of the third relay K3 is connected to the first terminal of the third detection resistor R3, and the second terminal of the third detection resistor R3 is connected to the first connection point A.

[0060] Based on the aforementioned rectifier unit 100, precharge unit 200, and insulation detection unit 300, the circuit topology of the insulation detection circuit provided in this embodiment of the invention is as follows: Figure 6 As shown, the connection relationships within the rectifier unit 100, precharge unit 200, and insulation detection unit 300 have been described in the above embodiments and will not be repeated here.

[0061] Unless otherwise specified, the precharge relay K5, positive main relay K6, negative main contactor K7, third relay K3, second relay K2 and fourth relay K4 are in the open circuit state by default.

[0062] It should be noted that the cathode of the third diode D3 is connected to the first terminal of the precharge relay K5, and the anode of the sixth diode D6 is connected to the first terminal of the negative main contactor K7; the first terminal of the bus capacitor C1 is connected to the first terminal of the second relay K2, and the second terminal of the bus capacitor C1 is connected to the first terminal of the fourth relay K4.

[0063] When the rectifier unit 100 receives the three-phase mains input voltage RST, it passively converts the three-phase mains input voltage RST into a DC input voltage and outputs it to the pre-charge unit 200. At this time, the negative main contactor K7 and the pre-charge relay K5 are closed, causing the rectifier unit 100 to output a DC input voltage V. in Charge the bus capacitor C1. When the voltage across the bus capacitor C1 reaches the preset voltage, disconnect the negative main contactor K7 and the pre-charge relay K5 to stop charging.

[0064] The pre-charge unit 200 further supplies power to the insulation detection unit 300, and the positive terminal impedance of the DC bus to ground is equivalent to R+, and the negative terminal impedance of the DC bus to ground is equivalent to R-.

[0065] Close the second relay K2 and the fourth relay K4, and collect the voltage on the positive terminal impedance R+, which is recorded as the first positive terminal voltage VBUS1+; collect the voltage on the negative terminal impedance R-, which is recorded as the first negative terminal voltage VBUS1-.

[0066] Let A = V BUS1+ / V BUS1- =(R2 / / R + ) / (R4 / / R - )=C / D,(1)

[0067] Therefore, A = C / D, (2)

[0068] At this point, close the third relay K3 again, collect the voltage on the positive terminal impedance R+ to ground, and record it as the second positive terminal voltage VBUS2+; collect the voltage on the negative terminal impedance R- to ground, and record it as the second negative terminal voltage VBUS2-.

[0069] Let B = V BUS2+ / V BUS2- =(R2 / / R + ) / (R4 / / R - / / R3), (3)

[0070] Then we have, B=C / (D / / R3)=(A×D) / (D / / R3), (4)

[0071] Combining equations (1), (2), (3), and (4), we have:

[0072] A = V BUS1+ / V BUS1- (5)

[0073] B = V BUS2+ / V BUS2- (6)

[0074] C = R3 × (BA), (7)

[0075] D = R3 × (BA) / A, (8)

[0076] R + =R²×C / (R²-C), (9)

[0077] R - =R4×D / (R4-D), (10)

[0078] The above formula can be used to calculate the positive and negative impedances of the DC bus to ground. By setting a preset resistance value, if either the positive or negative impedance to ground is lower than the preset resistance value, an insulation fault is considered to exist, and no relays will be activated and an insulation fault will be reported. If both the positive and negative impedances to ground are greater than the preset resistance value, an insulation fault is considered to exist, and the positive main relay K6 and the negative main contactor K7 can be activated to perform subsequent operations.

[0079] In some embodiments of this application, another insulation detection unit 300 is proposed, the circuit topology of which is shown below. Figure 5 As shown, the insulation detection unit 300 specifically includes a first detection resistor R1, a second detection resistor R2 and a fourth detection resistor R4, as well as a first relay K1, a second relay K2 and a fourth relay K4.

[0080] In this configuration, the first end of the second relay K2 is connected to the positive output terminal of the precharge unit 200, the second end of the second relay K2 is connected to the first end of the second detection resistor R2, the second end of the second detection resistor R2 is connected to the second end of the fourth detection resistor R4 to form a first connection point A, the first connection point A is grounded, the first end of the fourth detection resistor R4 is connected to the second end of the fourth relay K4, and the first end of the fourth relay K4 is connected to the negative output terminal of the precharge unit 200.

[0081] The first terminal of the second relay K2 is connected to the positive terminal DC+ of the inverter's DC bus, and the first terminal of the fourth relay K4 is connected to the negative terminal DC- of the inverter's DC bus.

[0082] The first terminal of the first relay K1 is connected to the first terminal of the second relay K2, the second terminal of the first relay K1 is connected to the first terminal of the first detection resistor R1, and the second terminal of the first detection resistor R1 is connected to the first connection point A.

[0083] Based on the aforementioned rectifier unit 100, precharge unit 200, and another insulation detection unit 300, the circuit topology of the insulation detection circuit provided in this embodiment of the invention is as follows: Figure 7 As shown, the connection relationships within the rectifier unit 100, precharge unit 200, and insulation detection unit 300 have been described in the above embodiments and will not be repeated here.

[0084] Unless otherwise specified, the precharge relay K5, positive main relay K6, negative main contactor K7, first relay K1, second relay K2 and fourth relay K4 are in the open circuit state by default.

[0085] It should be noted that the cathode of the third diode D3 is connected to the first terminal of the precharge relay K5, and the anode of the sixth diode D6 is connected to the first terminal of the negative main contactor K7; the first terminal of the bus capacitor C1 is connected to the first terminal of the second relay K2, and the second terminal of the bus capacitor C1 is connected to the first terminal of the fourth relay K4.

[0086] When the rectifier unit 100 receives the three-phase mains input voltage RST, it passively converts the three-phase mains input voltage RST into a DC input voltage and outputs it to the pre-charge unit 200. At this time, the negative main contactor K7 and the pre-charge relay K5 are closed, causing the rectifier unit 100 to output a DC input voltage V. in Charge the bus capacitor C1. When the voltage across the bus capacitor C1 reaches the preset voltage, disconnect the negative main contactor K7 and the pre-charge relay K5 to stop charging.

[0087] The pre-charge unit 200 further supplies power to the insulation detection unit 300, and the positive terminal impedance of the DC bus to ground is equivalent to R+, and the negative terminal impedance of the DC bus to ground is equivalent to R-.

[0088] Close the second relay K2 and the fourth relay K4, and collect the voltage on the positive terminal impedance R+, which is recorded as the first positive terminal voltage VBUS1+; collect the voltage on the negative terminal impedance R-, which is recorded as the first negative terminal voltage VBUS1-.

[0089] Let E = V BUS1- / V BUS1+ =(R4 / / R - ) / (R2 / / R + )=G / H,(11)

[0090] Therefore, E = G / H, (12)

[0091] At this point, close the first relay K1 again, collect the voltage on the positive terminal impedance R+ to ground, and record it as the second positive terminal voltage VBUS2+; collect the voltage on the negative terminal impedance R- to ground, and record it as the second negative terminal voltage VBUS2-.

[0092] Let F = V BUS2- / V BUS2+ =(R4 / / R - ) / (R2 / / R + / / R1), (13)

[0093] Then we have F = G / (H / / R1) = (E×H) / (H / / R1), (14)

[0094] Combining equations (11), (12), (13), and (14), we have:

[0095] E = V BUS1- / V BUS1+ (15)

[0096] F = V BUS2- / V BUS2+ (16)

[0097] G = R1 × (FE), (17)

[0098] H = R1 × (FE) / E, (18)

[0099] R + =R2×H / (R2-H), (19)

[0100] R - =R4×G / (R4-G), (20)

[0101] The above formula can be used to calculate the positive and negative impedances of the DC bus to ground. By setting a preset resistance value, if either the positive or negative impedance to ground is lower than the preset resistance value, an insulation fault is considered to exist, and no relays will be activated and an insulation fault will be reported. If both the positive and negative impedances to ground are greater than the preset resistance value, an insulation fault is considered to exist, and the positive main relay K6 and the negative main contactor K7 can be activated to perform subsequent operations.

[0102] Unlike existing technologies, the embodiments of this invention can detect insulation faults in the energy storage system the instant three-phase AC mains power is applied, and determine whether the insulation impedance is normal. This can prevent electric shock to personnel and damage to machinery and equipment caused by system insulation faults, thus improving system safety. Compared to the leakage current prevention measures listed in Scheme 1 of the existing frequency converters, the solution provided in this application can detect insulation faults with small leakage currents, accurate to 2mA. Compared to Schemes 2 and 3, the solution provided in this application is lower in cost, smaller in size, and more operable.

[0103] Based on the insulation detection circuit provided in any of the above embodiments, the present invention also provides an insulation detection method, which includes the following specific steps, and its flowchart is shown below. Figure 8 As shown:

[0104] Step S100: When the three-phase mains input voltage is detected, close the negative main contactor and the pre-charge relay to start charging the bus capacitor.

[0105] Step S200: When the voltage across the bus capacitor is detected to reach the preset voltage, disconnect the negative main contactor and the pre-charge relay.

[0106] In this embodiment of the application, the preset voltage V ref =0.95V in V in This is the DC input voltage.

[0107] Step S300: Close the second and fourth relays to collect the first positive voltage and the first negative voltage, respectively.

[0108] Step S400: Close the third relay or the first relay to collect the second positive voltage and the second negative voltage respectively.

[0109] Step S500: Calculate the positive-to-ground impedance and negative-to-ground impedance of the DC bus based on the first positive voltage, the first negative voltage, the second positive voltage, and the second negative voltage.

[0110] Specifically, if the insulation detection circuit includes a third relay, the positive-to-ground impedance R+ and negative-to-ground impedance R- of the DC bus are calculated using equations (5), (6), (7), (8), (9), and (10), respectively; if the insulation detection circuit includes a first relay, the positive-to-ground impedance R+ and negative-to-ground impedance R- of the DC bus are calculated using equations (15), (16), (17), (18), (19), and (20), respectively.

[0111] Step S600: Detect whether the impedance of the positive terminal to ground or the impedance of the negative terminal to ground is less than the preset resistance value.

[0112] If yes, proceed to step S720; otherwise, proceed to step S720.

[0113] In some embodiments of this application, the preset resistance value is 500 kilohms.

[0114] Step S710: Close the positive main relay and the negative main contactor.

[0115] Step S720: Determine that there is an insulation fault in the frequency converter.

[0116] Specifically, when the positive-to-ground impedance or negative-to-ground impedance is less than 500 kΩ, it is determined that there is an insulation fault in the frequency converter, so no relays are activated and the insulation fault is reported.

[0117] Unlike existing technologies, the embodiments of the present invention can detect insulation faults in the energy storage system at the moment of power-on of three-phase AC mains power, and determine whether the insulation impedance is normal. This can prevent electric shock to personnel and damage to machinery and equipment caused by system insulation faults, thereby improving the safety of the system.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above. For the sake of brevity, they are not provided in detail; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An insulation detection circuit applied to a frequency converter, characterized by, The circuit includes: a rectifier unit, a precharge unit, and an insulation detection unit, wherein, The rectifier unit is connected to the pre-charge unit, and the rectifier unit is used to convert the three-phase mains input voltage into a DC input voltage to charge the pre-charge unit; The pre-charge unit is connected to the insulation detection unit. The pre-charge unit includes a bus capacitor. When the bus capacitor is charged to the point where the output voltage reaches a preset voltage, charging stops, and the pre-charge unit provides the working voltage to the insulation detection unit. The insulation detection unit is connected to the two poles of the DC bus of the frequency converter. The insulation detection unit uses the bus capacitor after the pre-charge unit stops charging as its working power source. Within a specific time window after the pre-charge unit stops charging and before the positive main relay and negative main contactor of the frequency converter close, in response to the working voltage, the insulation detection unit adjusts the positive voltage of the DC bus to the first positive voltage and the negative voltage of the DC bus to the first negative voltage under the control of the first control signal and the second control signal output by the frequency converter; and adjusts the positive voltage to the second positive voltage and the negative voltage to the second negative voltage under the control of the first control signal, the second control signal and the third control signal output by the frequency converter.

2. The circuit of claim 1, wherein, The pre-charge unit includes a positive main relay, a negative main contactor, a pre-charge relay, a pre-charge resistor, and a bus capacitor. The first terminal of the precharge relay is connected to the positive output terminal of the rectifier unit, the second terminal of the precharge relay is connected to the first terminal of the precharge resistor, and the second terminal of the precharge resistor is connected to the first terminal of the bus capacitor. The first terminal of the positive main relay is connected to the first terminal of the precharge relay, the second terminal of the positive main relay is connected to the second terminal of the precharge resistor, the first terminal of the negative main contactor is connected to the negative output terminal of the rectifier unit, and the second terminal of the negative main contactor is connected to the second terminal of the bus capacitor. The first end of the bus capacitor is connected to the first end of the insulation detection unit, and the second end of the bus capacitor is connected to the second end of the insulation detection unit.

3. The circuit of claim 1, wherein, The insulation detection unit includes a first or third detection resistor, a second detection resistor, and a fourth detection resistor, as well as a first or third relay, a second relay, and a fourth relay, wherein... The first end of the second relay is connected to the positive output terminal of the precharge unit, the second end of the second relay is connected to the first end of the second detection resistor, the second end of the second detection resistor is connected to the second end of the fourth detection resistor to form a first connection point, the first connection point is grounded, the first end of the fourth detection resistor is connected to the second end of the fourth relay, and the first end of the fourth relay is connected to the negative output terminal of the precharge unit. The first terminal of the first relay is connected to the first terminal of the second relay, the second terminal of the first relay is connected to the first terminal of the first sensing resistor, and the second terminal of the first sensing resistor is connected to the first connection point. The first terminal of the third relay is connected to the first terminal of the fourth relay, the second terminal of the third relay is connected to the first terminal of the third detection resistor, and the second terminal of the third detection resistor is connected to the first connection point.

4. The circuit of claim 3, wherein, The second relay closes in response to the first control signal, the fourth relay closes in response to the second control signal, and the first relay or the third relay closes in response to the third control signal.

5. The circuit of claim 1, wherein, The rectifier unit includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, wherein, The first end of the first switch is connected to the second end of the fourth switch, the second end of the first switch is connected to the second end of the second switch, and the first end of the fourth switch is connected to the first end of the fifth switch. The first end of the second switch is connected to the second end of the fifth switch, the second end of the second switch is connected to the second end of the third switch, and the first end of the fifth switch is connected to the first end of the sixth switch. The first end of the third switch is connected to the second end of the sixth switch, the second end of the third switch is connected to the positive input terminal of the precharge unit, and the first end of the sixth switch is connected to the negative input terminal of the precharge unit.

6. The circuit according to claim 5, wherein the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch are of the types of diodes, MOSFETs, and IGBTs.

7. The circuit according to any one of claims 1 to 6, characterized in that The preset voltage is the product of the DC input voltage and 0.

95.

8. An insulation detection method applied to the insulation detection circuit according to claim 7, characterized by, The method includes: When a three-phase mains input voltage is detected, the negative main contactor and the pre-charge relay are closed to start charging the bus capacitor. When the voltage across the bus capacitor reaches a preset voltage, the negative main contactor and the pre-charge relay are disconnected. Close the second and fourth relays to collect the first positive voltage and the first negative voltage, respectively. Close the third relay or the first relay to collect the second positive voltage and the second negative voltage, respectively. Calculate the positive-to-ground impedance and negative-to-ground impedance of the DC bus based on the first positive voltage, the first negative voltage, the second positive voltage, and the second negative voltage, respectively. Detect whether the impedance of the positive terminal to ground or the impedance of the negative terminal to ground is less than a preset value; If not, then close the positive main relay and the negative main contactor; If so, then it is determined that the frequency converter has an insulation fault.

9. The method of claim 8, wherein, The impedance of the positive electrode to ground is calculated using the following formula: ， ， ， ， wherein, is the positive electrode impedance to ground, is a second detection resistance, is a third detection resistance, is the first positive electrode voltage, is the first negative electrode voltage, is the second positive electrode voltage, is the second negative electrode voltage.

10. The method of claim 9, wherein, The impedance of the negative electrode to ground is calculated using the following formula: ， ， wherein, is the negative electrode impedance to ground, is the fourth detection resistance.

11. The method of claim 8, wherein, The preset resistance value is 500 kilohms.

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