SiC variable-frequency power supply for high-voltage series resonance withstand voltage test

Abstract

The invention discloses a SiC variable-frequency power supply for a high-voltage series resonance withstand voltage test. The SiC variable-frequency power supply comprises a control module, a driving module, a three-phase rectifier bridge, a filter capacitor bank, a SiC inverter bridge and an outlet filter, the control module is used for logic control and clock control, and obtains a feedback signal of the capacitive voltage divider as a voltage reference; the driving module is used for performing voltage isolation on a power supply circuit and a driving signal and transmitting a control signal through a photoelectric isolation method, and the control signal is amplified and then drives a grid electrode of the MOSFET; the three-phase rectifier bridge is used for rectifying input three-phase alternating current into single-phase direct current, the filter capacitor bank is used for filtering the single-phase direct current, the SiC inverter bridge is used for rectifying the filtered single-phase direct current into alternating current, and the outlet filter is used for filtering the alternating current.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation state detection of electric power equipment, and more particularly to a SiC variable frequency power supply for high voltage series resonance withstand voltage test. Background Art

[0002] Before new high-voltage electrical equipment is put into operation, it is necessary to conduct a withstand voltage test to verify its insulation performance in order to improve the reliability of the equipment during operation. During the withstand voltage test, the voltage applied to the equipment can reach hundreds to thousands of kilovolts. However, due to the large equivalent capacitance of equipment such as high-voltage switches and high-voltage cables, it is necessary to use a series resonance pressurization method to pressurize. Series resonant withstand voltage equipment usually consists of a variable frequency power supply, an excitation transformer, a resonant inductor, and a voltage divider. The working principle of the series resonant withstand voltage device can be described as a resonant circuit formed by a resonant inductor and a capacitive test load, and a resonant frequency voltage is applied by a variable frequency power supply. After the voltage is isolated and output by an excitation transformer, it is applied to the resonant circuit to form a high voltage on the test capacitor. All the energy in the device pressurization process comes from the variable frequency power supply. The energy conversion efficiency and waveform distortion rate of the variable frequency power supply significantly affect the equipment operation efficiency.

[0003] The publication number is CN114337312A, and the name is a variable frequency power supply for induction and partial discharge tests of power transformers, including: first to third sub-frequency variable power supplies (A, B, C), first to third output terminals (OUT1, OUT2, OUT3); the first terminal (A1) of the first sub-frequency variable power supply is configured to be connected to the first output terminal, and the second terminal (A2) is configured to be connected to the second or third output terminal; the third terminal (B1) of the second sub-frequency variable power supply is configured to be connected to the first or second output terminal, and the fourth terminal (B2) is configured to be connected to the third output terminal; the fifth terminal (C1) of the third sub-frequency variable power supply is configured to be connected to the first or third output terminal, and the sixth terminal (C2) is configured to be connected to the first or third output terminal.

[0004] The publication number is CN118677271A, and the name is a variable frequency power supply and its control method; wherein the variable frequency power supply includes a grid-side filter unit, a first power unit, a second power unit and a load-side filter unit; the two ends of the first power unit are respectively provided with a first grid-side on-off control unit and a first load-side on-off control unit; the two ends of the second power unit are respectively provided with a second grid-side on-off control unit and a second load-side on-off control unit; the first end of the grid-side filter unit is connected to the first grid-side on-off control unit and the second grid-side on-off control unit, and the second end of the grid-side filter unit is used to connect to the power grid; the first end of the load-side filter unit is connected to the first load-side on-off control unit and the second load-side on-off control unit, and the second end of the load-side filter unit is used to connect to the load device.

[0005] However, existing variable frequency power supplies all use silicon-based IGBTs as basic components, which have the disadvantages of slow breaking speed, high breaking loss, and large on-resistance.

[0006] Therefore, how to provide a SiC variable frequency power supply for high-voltage series resonant withstand voltage test, which, compared with traditional withstand voltage devices, has a smaller device size, lower energy loss, and lower waveform distortion rate, and can be applied to withstand voltage tests of high-voltage switches and high-voltage cable equipment is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0007] In view of this, the present invention provides a SiC variable frequency power supply for high voltage series resonant withstand voltage test, aiming to solve the technical problems that the existing variable frequency power supplies all use silicon-based IGBT as basic components, with slow breaking speed, high breaking loss and large on-resistance.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A SiC variable frequency power supply for high voltage series resonant withstand voltage test, comprising: a control module, a drive module, a three-phase rectifier bridge, a filter capacitor bank, a SiC inverter bridge and an outlet filter;

[0010] The three-phase rectifier bridge is electrically connected to the filter capacitor bank, the filter capacitor bank is electrically connected to the SiC inverter bridge, the SiC inverter bridge is electrically connected to the outlet filter, the drive module is signal-connected to the SiC inverter bridge, and the drive module is signal-connected to the control module;

[0011] The control module is used for logic control and clock control, and obtains the feedback signal of the capacitive voltage divider as a voltage reference;

[0012] The driving module is used to perform voltage isolation on the power supply circuit and the driving signal, and transmit the control signal through a photoelectric isolation method, and the control signal is amplified to drive the gate of the MOSFET;

[0013] The three-phase rectifier bridge is used to rectify the input three-phase alternating current into single-phase direct current, the filter capacitor group is used to filter the single-phase direct current, the SiC inverter bridge is used to rectify the filtered single-phase direct current into alternating current, and the outlet filter is used to filter the alternating current.

[0014] Furthermore, the control module is specifically:

[0015] The control module includes a main control chip and an analog-to-digital conversion circuit. The main control chip has built-in ARM module and FPGA module. The ARM module is used for logic control, and the FPGA is used for clock control. The system clock is 50MHz, the signal period adjustment accuracy is 20ns, and the frequency adjustment accuracy is 0.002Hz. The analog-to-digital conversion circuit is connected to the feedback signal of the capacitor voltage divider, and the voltage signal is collected and input into the main control chip as a voltage reference. The main control chip is set with four I / O output ports to output control signals to the drive module.

[0016] Furthermore, the driving module is specifically:

[0017] The driving module includes an isolated power supply circuit and a driving circuit, and the output signal of the driving module is directly connected to the gate of the MOSFET in the SiC inverter bridge;

[0018] The isolated power supply circuit includes four transformers, which transmit energy through magnetic circuit connection to achieve potential isolation. The drive circuit adopts a photoelectric isolation method to transmit a control signal through an optical signal. The control signal is amplified by the drive circuit and obtains energy to drive the MOSFET, which is then output to the gate of the MOSFET as a drive signal.

[0019] Furthermore, the three-phase rectifier bridge is specifically:

[0020] It includes six diodes with a rated conduction current of 500A, a rated voltage of 500V and a short-time withstand current of 800A.

[0021] Furthermore, the filter capacitor bank is specifically:

[0022] The filter capacitor group includes a current limiting inductor and a filter capacitor. The current limiting inductor is used to prevent excessive transient current from damaging the diode of the three-phase rectifier bridge. The current limiting inductor is 10μH and the filter capacitor is 10mF. The presence of the current limiting inductor ensures that the maximum transient current value is less than 600A at the moment the three-phase power supply is connected.

[0023] Furthermore, the parameters of the filter capacitor are:

[0024] C≥5f / R

[0025] Where f is the frequency and R is the load resistance.

[0026] Furthermore, the SiC inverter bridge is specifically:

[0027] The SiC inverter bridge includes four SiC-based MOSFETs with anti-parallel diode structures, which are composed of a half bridge composed of D1 and D2 and a half bridge composed of D3 and D4. A capacitor is connected in parallel between the drain of D1 and the source of D2, and a capacitor is connected in parallel between the drain of D3 and the source of D4 to absorb the overvoltage generated at both ends of the stray inductance on the line when the MOSFET is turned off.

[0028] Furthermore, the modulation method of the SiC inverter bridge is:

[0029] Adopt SPWM modulation, the modulation signal is formed by the intersection of the modulation wave and the carrier signal, the modulation wave is the target sine wave, the carrier is a triangle wave, when the sine modulation signal is greater than the triangle wave signal, the modulation signal output is high level, otherwise the output is low level;

[0030] When the modulation signal output is a high level, the MOSFETs numbered D1 and D4 in the SiC inverter bridge are turned on, and when the modulation signal output is a low level, the MOSFETs numbered D2 and D3 in the SiC inverter bridge are turned on.

[0031] Furthermore, the modulation signal is specifically:

[0032] The modulated signal includes the fundamental component, carrier harmonics and sideband harmonics, among which the fundamental component is only related to the angular frequency ω of the modulated wave. m The carrier harmonics are related to the angular frequency ω of the carrier signal. c The sideband harmonics are related to ω c and ω m All are related;

[0033] The fundamental component is:

[0034]

[0035] The carrier harmonics are:

[0036]

[0037] The sideband harmonics are:

[0038]

[0039] In the formula, Q km is the amplitude of the modulated wave, E is the amplitude of the modulated signal, and J0(x) is the 0th-order Bessel function.

[0040] Furthermore, the outlet filter is a low-pass filter with a cut-off frequency of 400 Hz and a cut-off frequency of 500 Hz.

[0041] The above technical solution includes at least the following technical effects:

[0042] It can be seen from the above technical solution that the present invention discloses a SiC variable frequency power supply for high-voltage series resonant withstand voltage test. Compared with the prior art, the present invention proposes to use SiC power electronic devices as the basic components of the variable frequency source, and its starting speed, breaking loss and on-resistance are significantly improved compared with silicon-based devices, which can significantly improve the energy utilization of the device and reduce the distortion rate of the inverter output waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0044] Figure 1 The present invention is a schematic diagram of the overall structure of a SiC variable frequency power supply for high voltage series resonance withstand voltage test.

[0045] Figure 2 The present invention is a schematic structural diagram of a SiC variable frequency power supply control module for high voltage series resonance withstand voltage test.

[0046] Figure 3 The present invention is a schematic structural diagram of a SiC variable frequency power supply drive module for high voltage series resonance withstand voltage test.

[0047] Figure 4 The present invention is a schematic structural diagram of a SiC variable frequency power supply inverter bridge for high voltage series resonance withstand voltage test.

[0048] Figure 5 The present invention is a structural schematic diagram of the SPWM modulation principle of a SiC variable frequency power supply for high voltage series resonance withstand voltage test.

[0049] Among them, 1 is a control module, 2 is a drive module, 3 is a three-phase rectifier bridge, 4 is a filter capacitor group, 5 is a SiC inverter bridge, 6 is an export filter, 11 is a main control chip, 12 is an analog-to-digital conversion circuit, 21 is an isolated power supply circuit, and 22 is a drive circuit. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] See attached Figure 1-5 The embodiment of the present invention discloses a SiC variable frequency power supply for high voltage series resonant withstand voltage test, comprising: a control module 1, a drive module 2, a three-phase rectifier bridge 3, a filter capacitor bank 4, a SiC inverter bridge 5 and an outlet filter 6;

[0052] The three-phase rectifier bridge 3 is electrically connected to the filter capacitor group 4, the filter capacitor group 4 is electrically connected to the SiC inverter bridge (5), the SiC inverter bridge 5 is electrically connected to the outlet filter 6, the drive module 2 is signal-connected to the SiC inverter bridge 5, and the drive module 2 is signal-connected to the control module 1;

[0053] The control module 1 is used for logic control and clock control, and obtains the feedback signal of the capacitor voltage divider as a voltage reference;

[0054] The driving module 2 is used to perform voltage isolation on the power supply circuit and the driving signal, and transmit the control signal through the photoelectric isolation method. The control signal is amplified to drive the gate of the MOSFET;

[0055] The three-phase rectifier bridge 3 rectifies the input three-phase AC power into single-phase DC power, the filter capacitor group 4 filters the single-phase DC power, the SiC inverter bridge 5 rectifies the filtered single-phase DC power into AC power, and the outlet filter 6 filters the AC power.

[0056] To further optimize the above technical solution, the control module 1 is specifically:

[0057] The control module 1 includes a main control chip 11 and an analog-to-digital conversion circuit 12. The main control chip 11 has an ARM module and an FPGA module built in. The ARM module is used for logic control, and the FPGA is used for clock control. The system clock is 50MHz, the signal period adjustment accuracy is 20ns, and the frequency adjustment accuracy is 0.002Hz. The analog-to-digital conversion circuit 12 is connected to the feedback signal of the capacitor voltage divider, and the voltage signal is collected and input into the main control chip 11 as a voltage reference. The main control chip is set with four I / O output ports to output control signals to the drive module 2.

[0058] To further optimize the above technical solution, the driving module 2 is specifically:

[0059] The driving module 2 includes an isolated power supply circuit 21 and a driving circuit 22, and the output signal of the driving module is directly connected to the gate of the MOSFET in the SiC inverter bridge 5;

[0060] The isolated power supply circuit 21 includes four transformers, which transmit energy through magnetic circuit connections to achieve potential isolation. The drive circuit 22 adopts a photoelectric isolation method to transmit a control signal through an optical signal. The control signal is amplified by the drive circuit 22 and obtains the energy to drive the MOSFET and is output to the gate of the MOSFET as a drive signal.

[0061] In order to further optimize the above technical solution, the three-phase rectifier bridge 3 is specifically:

[0062] It includes six diodes with a rated conduction current of 500A, a rated voltage of 500V and a short-time withstand current of 800A.

[0063] In order to further optimize the above technical solution, the filter capacitor group 4 is specifically:

[0064] The filter capacitor group 4 includes a current limiting inductor and a filter capacitor. The current limiting inductor is used to prevent excessive transient current from damaging the diode of the three-phase rectifier bridge 3. The current limiting inductor is 10μH and the filter capacitor is 10mF. The existence of the current limiting inductor ensures that the maximum transient current value is less than 600A at the moment when the three-phase power supply is connected.

[0065] To further optimize the above technical solution, the parameters of the filter capacitor are:

[0066] C≥5f / R

[0067] Where f is the frequency and R is the load resistance.

[0068] To further optimize the above technical solution, the SiC inverter bridge 5 is specifically:

[0069] The SiC inverter bridge 5 includes four SiC-based MOSFETs with anti-parallel diode structures, which are composed of a half bridge composed of D1 and D2 and a half bridge composed of D3 and D4. A capacitor is connected in parallel between the drain of D1 and the source of D2, and a capacitor is connected in parallel between the drain of D3 and the source of D4 to absorb the overvoltage generated at both ends of the stray inductance on the line when the MOSFET is turned off.

[0070] In order to further optimize the above technical solution, the modulation method of the SiC inverter bridge 5 is:

[0071] Adopt SPWM modulation, the modulation signal is formed by the intersection of the modulation wave and the carrier signal, the modulation wave is the target sine wave, the carrier is a triangle wave, when the sine modulation signal is greater than the triangle wave signal, the modulation signal output is high level, otherwise the output is low level;

[0072] When the modulation signal output is at a high level, the MOSFETs numbered D1 and D4 in the SiC inverter bridge 5 are turned on, and when the modulation signal output is at a low level, the MOSFETs numbered D2 and D3 in the SiC inverter bridge 5 are turned on.

[0073] To further optimize the above technical solution, the modulation signal is specifically:

[0074] The modulated signal includes the fundamental component, carrier harmonics and sideband harmonics, among which the fundamental component is only related to the angular frequency ω of the modulated wave. mThe carrier harmonics are related to the angular frequency ω of the carrier signal. c The sideband harmonics are related to ω c and ω m All are related;

[0075] The fundamental component is:

[0076]

[0077] The carrier harmonics are:

[0078]

[0079] The sideband harmonics are:

[0080]

[0081] In the formula, Q km is the amplitude of the modulated wave, E is the amplitude of the modulated signal, and J0(x) is the 0th-order Bessel function.

[0082] To further optimize the above technical solution, the outlet filter 6 is a low-pass filter with a conduction frequency of 400 Hz and a cut-off frequency of 500 Hz.

[0083] Specific implementation method Figure 1 As shown in the figure, the SiC variable frequency power supply used for high-voltage series resonant withstand voltage test consists of 6 parts, namely control module 1, drive module 2, three-phase rectifier bridge 3, filter capacitor group 4, SiC inverter bridge 5, and export filter 6. The SiC variable frequency power supply needs to be used with a full set of series resonant withstand voltage devices. When conducting a withstand voltage test on high-voltage power equipment, the excitation transformer, resonant inductor, capacitor voltage divider and capacitive test product must be connected to the variable frequency power supply. The low-voltage signal collected by the low-voltage arm of the capacitor voltage divider is connected to the control module as a feedback signal, which serves as the basis for adjusting the control signal. The input end of the variable frequency power supply is a three-phase AC mains power supply. The maximum rated output power of the variable frequency power supply is 200kVA, and the rated current of the power supply should exceed 300A.

[0084] Control module 1 Figure 2 As shown, it consists of two parts, namely the main control chip 11 and the analog-to-digital conversion circuit 12. The main control chip selects the ZYNQ7010 chip of Xilinx Company, with built-in ARM module and FPGA module. The ARM module is responsible for logic control, and the FPGA is responsible for clock control. The system clock is 50MHz, the signal cycle adjustment accuracy is 20ns, and the frequency adjustment accuracy is 0.002Hz. The analog-to-digital conversion circuit 12 is connected to the feedback signal of the capacitor voltage divider, and the voltage signal is collected and input into the main control chip as a voltage reference. The main control chip is set with four I / O output ports to output control signals to the drive module.

[0085] The driving module 2 consists of an isolated power supply circuit 21 and a driving circuit 22. Since the output signal of the driving module is directly connected to the gate of the MOSFET in the SiC inverter bridge, and the four SiC MOSFETs are not grounded, there is a potential difference, so both the power supply circuit and the driving signal need to be voltage isolated. The isolated power supply circuit is implemented through four transformers, and the energy is transmitted through the magnetic circuit connection to achieve potential isolation. The driving circuit part adopts a photoelectric isolation method, and the control signal is transmitted through an optical signal. After the control signal is amplified by the driving circuit and has the energy to drive the MOSFET, it is output to the gate of the MOSFET as a driving signal.

[0086] The three-phase rectifier bridge consists of six diodes with a rated conduction current of 500A and a rated voltage of 500V, which can meet the three-phase rectification requirements of the mains.

[0087] The filter capacitor group consists of a current-limiting inductor and a filter capacitor. The current-limiting inductor prevents the transient current from being too large and damaging the diodes of the three-phase rectifier bridge. The short-time withstand current of the rectifier bridge is 800A, so the current-limiting inductor is set to 10μH and the filter capacitor is set to 10mF. The existence of the current-limiting inductor can ensure that the maximum transient current value is less than 600A at the moment when the three-phase power supply is connected.

[0088] The selection of filter capacitors refers to the empirical formula:

[0089] C≥5f / R

[0090] Where f is the frequency, here the AC ripple of the three-phase rectification is 300Hz, and R is the load resistance, which is calculated as 1Ω.

[0091] The SiC inverter bridge consists of four SiC-based MOSFETs with anti-parallel diode structures. Compared with traditional silicon-based switching devices, it has smaller switching losses, smaller conduction losses and faster switching speeds. The inverter bridge consists of a half bridge composed of D1 and D2 and a half bridge composed of D3 and D4. A capacitor is connected in parallel between the drain of D1 and the source of D2, and a capacitor is connected in parallel between the drain of D3 and the source of D4 to absorb the overvoltage generated at both ends by the stray inductance on the line when the MOSFET is turned off.

[0092] Since the frequency SiC device can achieve a higher frequency breaking speed, the SPWM modulation method can be used here. Figure 5 As shown in the figure, the modulation signal is formed by the intersection of the modulation wave and the carrier signal. The modulation wave is the target sine wave, and the carrier is a triangular wave. When the sine modulation signal is greater than the triangular wave signal, the modulation signal output is a high level, otherwise it is a low level. The ratio of the triangular carrier signal to the sine modulation signal is called the frequency modulation ratio. In order to reduce the distortion rate of the waveform, the frequency modulation ratio is set to 20.

[0093] When the modulation signal output is high level, Figure 4 When the MOSFETs numbered D1 and D4 in the middle inverter bridge are turned on and the modulation signal output is low level, Figure 4 The MOSFETs numbered D2 and D3 in the middle inverter bridge are turned on.

[0094] The modulation signal is composed of three frequency components, namely the fundamental component, carrier harmonics and sideband harmonics. The fundamental component is only related to the angular frequency ω of the modulation wave. m The carrier harmonics are related to the angular frequency ω of the carrier signal. c The sideband harmonics are related to ω c and ω m Are relevant.

[0095] The fundamental component can be described as:

[0096]

[0097] In the formula, Q km is the amplitude of the modulation wave, and E is the amplitude of the modulation signal.

[0098] The carrier harmonics can be described as:

[0099]

[0100] The sideband harmonics can be described as:

[0101]

[0102] Since the pressure frequency range of the series resonant withstand voltage is 30Hz~300Hz, the modulation wave frequency is also 30Hz~300Hz, and the carrier frequency range is 600Hz~6000Hz. Based on the above three equations, except for the fundamental component, most of the harmonic components are higher than the carrier frequency.

[0103] The outlet filter 6 is a low-pass filter with a cut-off frequency of 400 Hz and a cut-off frequency of 500 Hz.

[0104] The control module 1 adds automatic frequency sweeping and automatic pressurization functions. The frequency sweeping frequency is 30Hz to 300Hz. The frequency sweeping process can be described as follows:

[0105] Step 1: Set the sweep voltage amplitude Vmax.

[0106] Step 2: Set the modulation wave amplitude to one twentieth of the amplitude, sweep the frequency in the sweep frequency range with a step length of 0.5Hz, collect the voltage value through the feedback channel, and obtain the three frequency points with the largest voltage value. During the sweep process, if the voltage amplitude exceeds Vmax, stop the sweep immediately, reduce the modulation wave amplitude by half, and start the sweep again.

[0107] Step 3: Sweep again between the three frequency points obtained in step 2 with a sweep step of 0.02Hz, collect voltage values ​​through the feedback channel, and obtain the three frequency points with the largest voltage values. During the sweep process, if the voltage amplitude exceeds Vmax, stop the sweep immediately, halve the modulation wave amplitude, and start the sweep again.

[0108] Step 4: Sweep again between the three frequency points obtained in step 3 with a sweep step of 0.002Hz, collect the voltage value through the feedback channel, and obtain the frequency point with the maximum voltage value. During the sweep process, if the voltage amplitude exceeds Vmax, stop the sweep immediately, reduce the modulation wave amplitude by half, and start the sweep again.

[0109] After the above four steps, the resonant frequency point can be found with an accuracy of 0.002Hz.

[0110] The automatic pressurization function can be described as:

[0111] Step 1: Set the pressurization process, including the pressurization voltage value and the pressurization time of each voltage.

[0112] Step 2: Apply pressure at the frequency resonance point obtained by frequency sweeping, and observe the voltage value in real time through the feedback signal channel. Figure 5 The amplitude of the modulation wave is used to adjust the voltage. If a voltage drop occurs during the voltage application process, it means that a breakdown or a resonant circuit detunes, and the SiC frequency conversion source stops working immediately.

[0113] Implementation 1: Basic Configuration and Startup

[0114] 1. Power connection and preliminary inspection

[0115] First, make the power connection and ensure that the SiC inverter power supply is connected to a stable three-phase AC mains power supply. The power line should meet the rated current requirements of the power supply to avoid line overheating under high load. Before connecting the power supply, make a preliminary inspection to ensure that all components are not damaged and all connection terminals are clean and free of corrosion.

[0116] 2. Module inspection and configuration

[0117] Check whether the control module 1, drive module 2, three-phase rectifier bridge 3, filter capacitor bank 4, SiC inverter bridge 5 and outlet filter 6 are correctly installed and connected. Make sure all connections are firm and in good contact. For each module, perform a detailed functional test to ensure that it can work properly before powering on.

[0118] 3. Control module settings

[0119] In the control module, ZYNQ series chips are used and the system clock is set to 50MHz to achieve a frequency modulation accuracy of 0.002Hz. This will ensure that the variable frequency power supply can be accurately adjusted within a wide frequency range to adapt to different test conditions. The control module is the core of the entire system and is responsible for coordinating and controlling the operations of all other modules.

[0120] 4. Drive module isolation and power supply

[0121] In the driver module, the power supply circuit and the drive signal are ensured to achieve voltage isolation through optocouplers and transformers. This isolation can protect the control module from high voltage shocks while ensuring clear signal transmission. The isolated power supply circuit is realized through four transformers, and the energy is transmitted through magnetic circuit connection to achieve potential isolation. The drive circuit part adopts the optoelectronic isolation method, and the control signal is transmitted through the optical signal. After the control signal is amplified in the drive circuit and has the energy to drive the MOSFET, it is output to the gate of the MOSFET as a drive signal.

[0122] 5. Rectification and filtering

[0123] The AC power is rectified into DC power through a three-phase rectifier bridge and filtered through a filter capacitor bank to reduce the ripple in the power supply and improve the power quality. The three-phase rectifier bridge consists of six diodes with a rated conduction current of 500A and a rated voltage of 500V, which can meet the three-phase rectification requirements of the mains. The filter capacitor bank consists of a current-limiting inductor and a filter capacitor. The current-limiting inductor prevents excessive transient current from damaging the diodes of the three-phase rectifier bridge. The short-term withstand current of the rectifier bridge is 800A, so the current-limiting inductor is set to 10μH and the filter capacitor is set to 10mF. The existence of the current-limiting inductor can ensure that the maximum transient current value is less than 600A at the moment when the three-phase power supply is connected.

[0124] 6. Inverter bridge configuration

[0125] Configure the SiC inverter bridge and use a full H-bridge inverter composed of four SiC MOSFETs. SiC MOSFET is particularly suitable for high-frequency applications due to its high-speed switching capability and low conduction loss. The inverter bridge consists of a half-bridge composed of D1 and D2 and a half-bridge composed of D3 and D4. A capacitor is connected in parallel between the drain of D1 and the source of D2, and a capacitor is connected in parallel between the drain of D3 and the source of D4 to absorb the overvoltage generated at both ends by the stray inductance on the line when the MOSFET is turned off.

[0126] 7. Filter settings

[0127] The outlet filter is set as a low-pass filter with a conduction frequency of 400Hz and a cut-off frequency of 500Hz to further purify the voltage waveform output by the inverter. The outlet filter 6 is a low-pass filter with a conduction frequency of 400Hz and a cut-off frequency of 500Hz, which can effectively reduce the impact of high-frequency harmonics on the test equipment.

[0128] 8. System startup and preliminary testing

[0129] After all hardware configuration and settings are completed, start the system and perform preliminary tests. First, check whether the power indicator is on, indicating that the power supply has been successfully connected. Then, perform a no-load test to ensure that the system can operate normally without load. In the no-load test, monitor the output voltage and current of the power supply to ensure that they are within the expected range.

[0130] 9. Load testing and adjustment

[0131] After the no-load test is successful, gradually increase the load and perform a load test. During the load test, closely monitor the output voltage and current of the power supply, as well as the temperature rise of the system. If any abnormalities are found, such as voltage or current outside the expected range, or the system temperature rise is too high, stop the test immediately and check and adjust the system settings.

[0132] Implementation Method 2: Pressure Withstand Test and Monitoring

[0133] 1. Connect the pressure-resistant device

[0134] When conducting a high-voltage series resonant withstand voltage test, the SiC variable frequency power supply must first be connected to a complete withstand voltage device, which includes an excitation transformer, a resonant reactor, a capacitive voltage divider, and a capacitive test piece.

[0135] The specific steps are as follows:

[0136] Connect the excitation transformer: Connect the output of the SiC variable frequency power supply to the input of the excitation transformer. The function of the excitation transformer is to increase the voltage output by the variable frequency power supply to the required test voltage.

[0137] Connect the resonant reactor: Connect the output end of the excitation transformer to the resonant reactor. The resonant reactor and the test capacitor together form a resonant circuit.

[0138] Connect the capacitor voltage divider: Connect the capacitor voltage divider to the resonant circuit to measure the voltage on the test object. The low-voltage signal collected by the low-voltage arm of the capacitor voltage divider is connected to the control module as a feedback signal and serves as the basis for adjusting the control signal.

[0139] Connecting capacitive test product: Connect the capacitive test product (such as high-voltage cable or high-voltage switch) to the resonant circuit as the object of the withstand voltage test.

[0140] 2. Signal feedback and control

[0141] During the pressure test, real-time monitoring and feedback are the key to ensuring the safety and accuracy of the test. The specific steps are as follows:

[0142] Feedback signal acquisition: The low-voltage signal collected by the low-voltage arm of the capacitor voltage divider is connected to the control module as a feedback signal. The control module monitors the voltage and current of the test product in real time through these feedback signals.

[0143] Control signal adjustment: The control module adjusts the output voltage and frequency of the variable frequency power supply according to the feedback signal to ensure that the resonant circuit is always in the best resonant state. The control module uses FPGA and ARM chips, the FPGA part is responsible for clock control, and the ARM part is responsible for logic control.

[0144] Automatic frequency sweep: The control module has an automatic frequency sweep function to find the best resonant frequency point in the range of 30Hz to 300Hz. The specific steps include:

[0145] Set the sweep voltage amplitude Vmax.

[0146] Perform a preliminary frequency sweep within the sweep frequency range with a step size of 0.5 Hz, collect voltage values ​​through the feedback channel, and obtain the three frequency points with the largest voltage values.

[0147] Between the three frequency points obtained by the preliminary frequency sweep, the frequency is swept again with a step size of 0.02 Hz to obtain the three frequency points with the largest voltage values.

[0148] Finally, a fine frequency sweep is performed between the above three frequency points with a step size of 0.002 Hz to obtain the frequency point with the maximum voltage value.

[0149] 3. Automatic pressurization and safety monitoring

[0150] After finding the best resonant frequency point, perform the automatic pressure test. The specific steps are as follows:

[0151] Set pressurization parameters: Set the parameters of the pressurization process in the control module, including the pressurization voltage value and the pressurization time for each voltage.

[0152] Automatic pressurization: The control module automatically adjusts the output voltage of the variable frequency power supply according to the set parameters, so that the voltage on the test piece gradually increases to the set withstand voltage value. During the pressurization process, the voltage value is monitored in real time, and the voltage is precisely controlled by adjusting the amplitude of the SPWM modulation wave.

[0153] Safety monitoring: If a voltage drop occurs during the pressurization process, it means that the test product may have a breakdown or the resonant circuit is out of tune. At this time, the control module will immediately stop the operation of the variable frequency power supply to prevent further damage to the test product.

[0154] 4. Test data recording and analysis

[0155] During the voltage test, recording and analyzing the test data is an important part of evaluating the insulation performance of the test product. The specific steps are as follows:

[0156] Data recording: The control module records the voltage, current, frequency and other data in real time during the test. These data can be used for subsequent analysis and evaluation.

[0157] Data analysis: By analyzing the test data, the insulation performance and withstand voltage capability of the test product can be evaluated. If the test product does not break down during the withstand voltage test, it means that its insulation performance is good and it can withstand the set withstand voltage value.

[0158] Report generation: Generate a test report based on the test data, and record the test process, test parameters and test results in detail. The test report can serve as an important basis for equipment acceptance and quality assessment.

[0159] According to the design of the present invention, a SiC variable frequency power supply for high-voltage series resonant withstand voltage test adopts SiC power electronic devices as the basic components of the variable frequency source. Its starting speed, breaking loss and on-resistance are significantly improved compared with silicon-based devices, which can significantly improve the energy utilization of the device and reduce the distortion rate of the inverter output waveform. The frequency modulation accuracy achieved by the present invention is relatively high, reaching 0.002Hz, which can ensure that the system operates at the optimal resonance point. The present invention adopts SiC devices as switching devices, and the loss is reduced by two-thirds compared with traditional IGBT devices. Autonomous resonant frequency selection can be achieved. Compared with the traditional variable frequency power supply, the volume of the realized variable frequency power supply can be reduced by half.

[0160] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0161] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A SiC variable frequency power supply for high voltage series resonance withstand voltage test, characterized in that: include: A control module (1), a drive module (2), a three-phase rectifier bridge (3), a filter capacitor group (4), a SiC inverter bridge (5) and an outlet filter (6); the three-phase rectifier bridge (3) is electrically connected to the filter capacitor group (4), the filter capacitor group (4) is electrically connected to the SiC inverter bridge (5), the SiC inverter bridge (5) is electrically connected to the outlet filter (6), the drive module (2) is signal-connected to the SiC inverter bridge (5), and the drive module (2) is signal-connected to the control module (1); The control module (1) is used for logic control and clock control, and obtains a feedback signal of a capacitive voltage divider as a voltage reference; The driving module (2) is used to perform voltage isolation on the power supply circuit and the driving signal, and transmit the control signal through a photoelectric isolation method, and the control signal is amplified to drive the gate of the MOSFET; The three-phase rectifier bridge (3) is used to rectify the input three-phase alternating current into single-phase direct current, the filter capacitor group (4) filters the single-phase direct current, the SiC inverter bridge (5) is used to rectify the filtered single-phase direct current into alternating current, and the outlet filter (6) is used to filter the alternating current.

2. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The control module (1) is specifically: The control module (1) comprises a main control chip (11) and an analog-to-digital conversion circuit (12); the main control chip (11) has an ARM module and an FPGA module built therein; the ARM module is used for logic control, and the FPGA is used for clock control; the system clock is 50 MHz, the signal period adjustment accuracy is 20 ns, and the frequency adjustment accuracy is 0.002 Hz; the analog-to-digital conversion circuit (12) receives a feedback signal from a capacitor voltage divider, collects a voltage signal, and inputs it into the main control chip (11) as a voltage reference; the main control chip is provided with four I / O output ports, and outputs a control signal to the drive module (2).

3. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The driving module (2) is specifically: The driving module (2) comprises an isolated power supply circuit (21) and a driving circuit (22), and an output signal of the driving module is connected to the gate of the MOSFET in the SiC inverter bridge (5); The isolated power supply circuit (21) comprises four transformers, which transmit energy through magnetic circuit connection. The drive circuit (22) adopts a photoelectric isolation method and transmits a control signal through an optical signal. The control signal is amplified by the drive circuit (22) to obtain energy for driving the MOSFET and then output as a drive signal to the gate of the MOSFET.

4. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The three-phase rectifier bridge (3) is specifically: It includes six diodes with a rated conduction current of 500A, a rated voltage of 500V and a short-time withstand current of 800A.

5. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The filter capacitor group (4) is specifically: The filter capacitor group (4) comprises a current limiting inductor and a filter capacitor. The current limiting inductor is used to prevent excessive transient current from damaging the diode of the three-phase rectifier bridge (3). The current limiting inductor is 10 μH and the filter capacitor is 10 mF. The existence of the current limiting inductor ensures that the maximum transient current value is less than 600 A at the moment when the three-phase power supply is connected.

6. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 5, characterized in that: The parameters of the filter capacitor are: C≥5f / R Where f is the frequency and R is the load resistance.

7. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The SiC inverter bridge (5) is specifically: The SiC inverter bridge (5) comprises four SiC-based MOSFETs with anti-parallel diode structures, and is composed of a half bridge composed of D1 and D2 and a half bridge composed of D3 and D4. A capacitor is connected in parallel between the drain of D1 and the source of D2, and a capacitor is connected in parallel between the drain of D3 and the source of D4, so as to absorb overvoltage generated at both ends of the MOSFET by stray inductance on the line when the MOSFET is turned off.

8. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 7, characterized in that: The modulation method of the SiC inverter bridge (5) is: Adopt SPWM modulation, the modulation signal is formed by the intersection of the modulation wave and the carrier signal, the modulation wave is the target sine wave, the carrier is a triangle wave, when the sine modulation signal is greater than the triangle wave signal, the modulation signal output is high level, otherwise the output is low level; When the modulation signal output is a high level, the MOSFETs numbered D1 and D4 in the SiC inverter bridge (5) are turned on, and when the modulation signal output is a low level, the MOSFETs numbered D2 and D3 in the SiC inverter bridge (5) are turned on.

9. A SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 8, characterized in that: The modulation signal is specifically: The modulated signal includes the fundamental component, carrier harmonics and sideband harmonics, among which the fundamental component is only related to the angular frequency ω of the modulated wave. m The carrier harmonics are related to the angular frequency ω of the carrier signal. c The sideband harmonics are related to ω c and ω m All are related; The fundamental component is: The carrier harmonics are: The sideband harmonics are: m=1, 2,…∞, n=1, 2…∞ In the formula, Q km is the amplitude of the modulated wave, E is the amplitude of the modulated signal, and J0(x) is the 0th-order Bessel function.

10. The SiC variable frequency power supply for high voltage series resonance withstand voltage test according to claim 1, characterized in that: The outlet filter (6) is a low-pass filter with a cut-off frequency of 400 Hz and a cut-off frequency of 500 Hz.

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