A leakage detection method for a high-voltage inverter with a power unit in series

Abstract

The present invention discloses a leakage detection method for a high-voltage inverter with a power unit connected in series. The midpoint of the three-phase output terminal of the high-voltage inverter's main circuit is connected to a power supply, and the current between the power supply and the midpoint is detected to determine whether a leakage fault exists. The present invention can effectively detect leakage in the secondary winding of a multi-level high-voltage inverter with power units connected in series, or in the cable at the secondary winding output end, to provide leakage protection and improve the safety of the high-voltage inverter's operation.

Description

Technical Field

[0001] The present invention relates to a high-voltage frequency converter with power units connected in series, and in particular to a leakage detection method for a high-voltage frequency converter with power units connected in series. Background Art

[0002] The multi-level high-voltage inverter with power units in series is the most widely used type of high-voltage inverter in the market, and its output voltage mainly includes 3.3kV, 6kV, 10kV, etc. Figure 1 This is a schematic diagram of the main circuit of a 10kV voltage level power unit series multi-level high-voltage inverter. Figure 1 The middle T is a rectifier phase-shifting transformer, which includes a primary 10kV high-voltage winding, 24 three-phase windings with a line voltage of 690V, and 1 three-phase winding with a line voltage of 380V. Figure 1 A1-A8, B1-B8, C1-C8 are power units. The schematic diagram of the power unit is as follows: Figure 2 As shown in Figure 1. The output terminals L2 of power units A8, B8, and C8 are connected together, with the connection point being called the midpoint. The output terminals L1 of power units A1, B1, and C1 are the output terminals of this type of high-voltage inverter. The line voltage between the output terminals is 10kV. The output terminals L2 of A1 are connected in series with the output terminals L1 of A8, the output terminals L2 of B1 are connected in series with the output terminals L1 of B8, and the output terminals L2 of C1 are connected in series with the output terminals L1 of C8. The 24 secondary windings of the phase-shifting transformer are connected to the input terminals of the 24 power units, respectively.

[0003] The characteristic of the multi-level high-voltage inverter with power units in series is that high-voltage output is formed by connecting power units in series, and different voltage outputs can be formed by changing the number of each series-connected power unit.

[0004] There has been no good detection method for leakage in the secondary winding and the cable at the output end of the secondary winding of a multi-level high-voltage inverter with power units connected in series, which poses a threat to the safe operation of the multi-level high-voltage inverter with power units connected in series. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a leakage detection method for a power unit connected in series with a high-voltage inverter, so as to perform leakage protection and improve the safety of the high-voltage inverter operation.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is a leakage detection method for a power unit connected in series with a high-voltage inverter. The midpoint of the three-phase output end of the high-voltage inverter main circuit is connected to the power supply, and the current between the power supply and the midpoint is detected to determine whether there is a leakage fault.

[0007] In the leakage detection method described above, the high-voltage inverter includes a main circuit and a leakage detection module. The main circuit includes a phase-shifting transformer on the input side and three power unit groups constituting a three-phase output. Each power unit group is composed of a plurality of power units connected in series. The first output ends of the three power unit groups are connected together to form the midpoint. The leakage detection module includes a power supply and a current sampling circuit. One end of the power supply is connected to the midpoint of the three-phase output ends of the main circuit, and the other end is grounded. The current sampling circuit samples the current output by the power supply, and the sampling signal output end of the current sampling circuit is the leakage signal output end of the leakage detection module.

[0008] In the leakage detection method described above, the current sampling circuit includes a current transformer, the line of the DC power supply output circuit passes through the current transformer, and the output end of the current transformer is the leakage signal output end of the leakage detection module.

[0009] In the leakage detection method described above, the leakage detection module includes a first resistor and a second resistor. The power supply is a DC power supply. The first end of the first resistor is connected to the midpoint, the second end is connected to the first end of the second resistor, and the second end of the second resistor is grounded. The positive electrode of the DC power supply is connected to the second end of the first resistor, and the negative electrode is grounded. The current transformer is arranged between the positive electrode of the DC power supply and the second end of the first resistor.

[0010] In the leakage detection method described above, the leakage detection module includes a filter circuit connected between the positive electrode of the DC power supply and the second end of the first resistor.

[0011] In the leakage detection method described above, the power unit includes a rectifier and filter circuit, a DC bus and an H-bridge inverter. The front stage of the rectifier and filter circuit is connected to the secondary winding of the phase-shifting transformer, the rear stage of the rectifier and filter circuit is connected to the front stage of the DC bus, the rear stage of the DC bus is connected to the front stage of the H-bridge inverter, and the rear stage of the H-bridge inverter serves as the output end of the power unit; the rectifier and filter circuit includes a filter resistor.

[0012] The present invention can effectively detect leakage of the secondary winding of a multi-level high-voltage inverter with power units connected in series or leakage of a cable at the output end of the secondary winding, so as to perform leakage protection and improve the safety of the high-voltage inverter operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] Figure 1 This is a circuit diagram of a main circuit of a high-voltage inverter in which a power unit is connected in series with the power unit according to an embodiment of the present invention.

[0015] Figure 2 This is a circuit diagram of a power unit connected in series with a high-voltage inverter main circuit and a leakage detection module according to an embodiment of the present invention.

[0016] Figure 3 This is a working principle diagram of a leakage detection circuit in which a power unit is connected in series with a high-voltage inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The structure and principle of the power unit in series with the high voltage inverter in the embodiment of the present invention are as follows Figure 2 and Figure 3 As shown, it includes a main circuit and a leakage detection module JY. The main circuit includes a phase-shifting transformer on the input side and three power unit groups that form a three-phase output. Each power unit group consists of eight power units connected in series. The first output terminals of the three power unit groups are connected together, forming the midpoint of the main circuit's three-phase output.

[0018] The power unit includes a three-phase full-bridge rectifier and filter circuit, a DC bus, and an H-bridge inverter. The three-phase full-bridge rectifier and filter circuit includes rectifier diodes DR1-DR6, filter capacitor C1, and filter resistor RE1. The H-bridge inverter includes four switching transistors V1-V4.

[0019] The front stage of the rectifier and filter circuit is connected to the secondary winding of the phase-shifting transformer, the rear stage of the rectifier and filter circuit is connected to the front stage of the DC bus, the rear stage of the DC bus is connected to the front stage of the H-bridge inverter, and the rear stage of the H-bridge inverter serves as the output end of the power unit.

[0020] The leakage detection module JY includes resistors R1 and R2, a DC switching power supply G1, a filter circuit LC1, and a current sampling circuit. The current sampling circuit includes a high-precision current sensor TA1 and a signal processing circuit ZH1.

[0021] The line passes through the current transformer, and the output end of the current transformer is the leakage signal output end of the leakage detection module JY.

[0022] The first terminal of resistor R1 is connected to the midpoint of the three-phase output of the main circuit, and the second terminal is connected to the first terminal of resistor R2. The second terminal of resistor R2 is grounded. The positive terminal of the DC switching power supply G1 is connected to the second terminal of resistor R1 through the filter circuit LC1, and the negative terminal is grounded. A high-precision current sensor TA1 is placed between the positive terminal of the DC switching power supply G1 and the filter circuit LC1. The connection between the positive terminal of the DC switching power supply G1 and the filter circuit LC1 passes through the current transformer (current sensor) TA1.

[0023] A high-precision current sensor TA1 is connected between the positive electrode of the DC power supply and the second end of the resistor R1 . The current signal detected by the high-precision current sensor TA1 is processed by the signal processing circuit ZH1 and then sent to the controller.

[0024] The working principle of leakage detection circuit is as follows Figure 3As shown, the terminals of the leakage detection module JY include a detection input, a ground terminal, a DC switching power supply input terminal, and a detection output terminal. The detection input terminal (the first terminal of resistor R1) is connected to the midpoint of the three-phase AC output, the ground terminal (the second terminal of resistor R2) is connected to the earth, the input terminal of the DC switching power supply G1 is connected to a single-phase AC 80-265V AC power supply, and the detection output terminal is connected to the inverter controller.

[0025] like Figure 3 As shown, the negative pole of the switching power supply DC switching power supply G1 is connected to the ground, the filter circuit LC1 is used to filter out the AC component in the circuit, and the high-precision current sensor TA1 is used to detect the current flowing through the circuit. The output of the high-precision current sensor TA1 is a voltage signal, and the output voltage signal is proportional to the current flowing through.

[0026] When there is no leakage, the DC switching power supply G1, filter circuit LC1, and resistor R2 form a current loop. The current flowing through the high-precision current sensor TA1 in this loop is stable, and the output voltage of the high-precision current sensor TA1 is stable. When leakage occurs in the secondary winding of the phase-shifting transformer or the output cable, in addition to the loop formed by the DC switching power supply G1, filter circuit LC1, and resistor R2, the DC switching power supply G1, filter circuit LC1, resistor R2, and the components from the midpoint to the inverter leakage point also form a loop. At this time, the current flowing through the high-precision current sensor TA1 increases rapidly, and the output voltage of the high-precision current sensor TA1 also increases rapidly. By properly setting the output voltage threshold of the high-precision current sensor TA1, it is possible to determine whether leakage occurs in the secondary winding of the inverter's phase-shifting transformer or the output cable. Alternatively, the output voltage of the high-precision current sensor TA1 is connected to the inverter controller, and through A / D conversion, the impedance to ground of the secondary winding of the phase-shifting transformer and the output cable can be calculated.

[0027] by Figure 3 The leakage of the input line C11 of the A8 power unit to the ground is taken as an example to illustrate the leakage detection principle of the present invention. When the secondary winding or cable is short-circuited to the ground or leaks, the signal source will Figure 3 The dotted path in the figure forms a path, that is, the current flows out of the DC switching power supply G1, passes through the filter circuit LC1, the resistor R1, the body diode D1 of the switch tube, the filter resistor RE1, the rectifier diode DR6 and the fuse F2, and flows into the ground. The current value of this loop is superimposed on the stable value of the current flowing through the high-precision current sensor TA1, causing the total current to exceed the set threshold. At this time, the inverter controller sends a leakage fault signal.

Claims

1. A method for detecting leakage of a power unit connected in series with a high-voltage inverter, characterized in that: The midpoint of the three-phase output end of the main circuit of the high-voltage frequency converter is connected to the power supply, and the magnitude of the current between the power supply and the midpoint is detected to determine whether there is a leakage fault; the high-voltage frequency converter includes the main circuit and the leakage detection module, the main circuit includes a phase-shifting transformer on the input side and three power unit groups constituting the three-phase output, each power unit group is composed of a plurality of power units connected in series; the first output ends of the three power unit groups are connected together to form the midpoint; the leakage detection module includes a first resistor, a second resistor, a DC switching power supply, a filter circuit and a current sampling circuit; the current sampling circuit includes a current sensor and a signal processing circuit The first end of the first resistor is connected to the midpoint of the three-phase output of the main circuit, the second end is connected to the first end of the second resistor, and the second end of the second resistor is grounded; the positive pole of the DC switching power supply is connected to the second end of the first resistor through the filter circuit, and the negative pole is grounded; the current sensor is arranged between the positive pole of the DC switching power supply and the filter circuit, and the connection between the positive pole of the DC switching power supply and the filter circuit is connected between the positive pole of the DC power supply and the second end of the first resistor and passes through the current sensor. The current signal detected by the current sensor is processed by the signal processing circuit and sent to the controller; the output end of the current transformer is the leakage signal output end of the leakage detection module.

2. The leakage detection method according to claim 1, characterized in that: The power unit includes a rectifier and filter circuit, a DC bus and an H-bridge inverter. The front stage of the rectifier and filter circuit is connected to the secondary winding of the phase-shifting transformer, the rear stage of the rectifier and filter circuit is connected to the front stage of the DC bus, the rear stage of the DC bus is connected to the front stage of the H-bridge inverter, and the rear stage of the H-bridge inverter serves as the output end of the power unit; the rectifier and filter circuit includes a filter resistor.

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