High-voltage capacitor charging and discharging circuit and charging and discharging method for power device test

Abstract

The invention provides a high-voltage capacitor charging and discharging circuit and method for testing a power device, and the circuit achieves the controllable connection between a high-voltage power supply and a testing circuit through the arrangement of a high-voltage relay group, and enables a system to be flexibly switched among a charging state, a charging disconnection state and an electric quantity recovery state. The high-voltage power supply charges the power device test circuit and the high-voltage capacitor bank; in a charging disconnection state, the high-voltage power supply and the test circuit are completely disconnected, so that interference signals and potential safety hazards possibly caused by the fact that the high-voltage power supply continuously supplies power to the test circuit are avoided; and in the electric quantity recovery state, the high-voltage power supply is disconnected and electric energy discharge is carried out on the high-voltage capacitor bank. According to the three-state switching design scheme, the safety problem of long-term connection between the high-voltage power supply and the test circuit in the traditional test system is effectively solved. In addition, the discharged electric energy can be used as the power supply voltage of the driving circuit, so that the test safety is ensured, and the recycling of the residual electric energy is realized.

Description

Technical Field

[0001] The present invention relates to the field of circuit testing, and in particular to a high-voltage capacitor charging and discharging circuit and a charging and discharging method for power device testing. Background Art

[0002] With the continuous improvement of the withstand voltage and power level of power semiconductor devices (IGBT, SiC MOSFET, GaN HEMT, etc.), their characteristic test devices need to use high-voltage power supplies with higher voltage levels and high-voltage capacitors with larger capacity. In the existing conventional test methods, the test circuit is directly connected to the high-voltage power supply, which not only causes the test circuit and the device to be tested to be in a high-voltage state for a long time, which poses a safety hazard, but also when the test circuit fails, the instantaneous release of energy stored in the large-capacity capacitor may cause circuit damage; in addition, the residual electric energy in the high-voltage capacitor after the test is generally limited by a parallel current limiting resistor to limit its discharge current, and the capacitor energy is released and consumed in the form of Joule heat. It cannot be discharged directly by short-circuiting the two poles of the capacitor, otherwise the instantaneous current is too large, which can easily cause device damage. In the test of power semiconductor devices, due to the diversity of test conditions and the large number of test times required, high-voltage and large-capacity capacitors need to be frequently charged and discharged, and such a repetitive process will cause a lot of energy waste. Summary of the invention

[0003] The invention provides a high-voltage capacitor charging and discharging circuit and a charging and discharging method for power device testing, thereby improving the safety of power device testing.

[0004] The present invention discloses a high-voltage capacitor charging and discharging circuit for power device testing, comprising: A high-voltage relay group, the input end of which is electrically connected to the high-voltage power supply, and the output end of which is electrically connected to the power device test circuit through a high-voltage capacitor group; the high-voltage relay group can switch between a charging state, a charging disconnection state, and an electric power recovery state; When the high-voltage relay group is switched to a charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; When the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit performs a voltage parameter test on the high-voltage capacitor group; When the high-voltage relay group is switched to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor group is discharged; The relay drive circuit is electrically connected to the high-voltage relay group and is used to control the high-voltage relay group to switch between a charging state, a charging disconnection state and an electric power recovery state.

[0005] Furthermore, it also includes a sampling circuit; The sampling circuit includes a voltage sampling resistor and an isolation voltage sampling circuit; The voltage sampling resistor is connected in parallel to both ends of the high-voltage capacitor group and is used to collect the voltage signal of the high-voltage capacitor group; The input end of the isolation voltage acquisition circuit is connected in parallel with the voltage sampling resistor, and the output end is electrically connected to the driving circuit.

[0006] Furthermore, the drive circuit includes: an isolating switch drive circuit, a first input end of which is connected to the first output end of the single-chip microcomputer main control circuit, and an output end is connected to the capacitor output switch in the high-voltage capacitor group; the input end of the single-chip microcomputer main control circuit is connected to the output end of the isolation voltage acquisition circuit; the second output end of the single-chip microcomputer main control circuit is connected to the input end of the relay drive circuit, and the output end of the relay drive circuit is electrically connected to the high-voltage relay group; the single-chip microcomputer main control circuit is also interconnected with the communication interface circuit.

[0007] Furthermore, it also includes: an isolated energy recovery circuit, the input end of the isolated energy recovery circuit is connected in parallel with the high-voltage capacitor group, and the output end outputs the power supply voltage to the communication interface circuit, the single-chip microcomputer main control circuit and the relay drive circuit through a step-down voltage stabilization circuit.

[0008] Furthermore, the isolated electric energy recovery circuit includes a flyback voltage stabilization circuit, which includes a flyback transformer S1, an NMOS tube Q1, a PWM chip, a high-voltage capacitor C1, a rectifier diode D1, a current sampling resistor R1, an optocoupler OC1 and a filter capacitor C2; One end of the primary winding of the flyback transformer S1 is connected to the positive electrode of the high-voltage capacitor C1 group through the high-voltage relay group (specifically the third high-voltage relay), and the other end of the primary winding is connected to the drain of the NMOS tube Q1; the source of the NMOS tube Q1 is connected to the current feedback terminal 2 of the PWM chip, and is connected to the emitter of the phototransistor in the optical coupler OC1 through the current sampling resistor R1, and the gate is connected to the PWM output terminal 1 of the PWM chip. One end of the secondary winding of the flyback transformer S1 is connected to the positive electrode of the high-voltage capacitor C1 group through the high-voltage relay group (specifically the third high-voltage relay), and the other end of the primary winding is connected to the drain of the NMOS tube Q1; the source of the NMOS tube Q1 is connected to the current feedback terminal 2 of the PWM chip, and is connected to the emitter of the phototransistor in the optical coupler OC1 through the current sampling resistor R The rectifier diode D1 is connected to the positive output end of the isolated energy recovery circuit, and the other end of the secondary winding of the flyback transformer S1 is connected to the negative output end of the isolated energy recovery circuit; the filter capacitor C2 is connected in parallel between the cathode and the negative output end of the rectifier diode D1; the voltage feedback end 4 of the PWM chip is connected to the collector of the phototransistor in the optocoupler OC1, and the power supply input end 3 of the PWM chip is connected to the positive output end of the rectifier diode D2 connected to the other secondary winding of the flyback transformer S1.

[0009] Furthermore, the isolated electric energy recovery circuit also includes a constant current circuit, which includes a constant current chip, a digital potentiometer, an energy storage capacitor C4 and a current limiting inductor L1; The input end of the constant current chip is connected to one end of the secondary winding of the flyback transformer S1 through the rectifier diode D1; the output end of the constant current chip is connected to the positive output end of the isolated electric energy recovery circuit, and a current limiting inductor L1 is also connected in parallel between the input and output ends of the constant current chip, the adjustment end of the constant current chip is connected to the adjustable resistance end of the digital potentiometer, and the clock end and data end of the digital potentiometer are respectively connected to the main control circuit of the single-chip microcomputer; the energy storage capacitor C4 is connected in parallel between the positive output end and the negative output end.

[0010] Further, the high-voltage relay group includes a high-voltage relay group, and the high-voltage relay group includes a first relay control switch, a second relay and a third relay control switch; The input ends of the first relay and the second relay are connected to the high voltage power supply, and the output ends are connected to the high voltage capacitor bank and the power device test circuit; The input end of the third relay is connected to the high-voltage capacitor bank, and the output end is connected to the isolated electric energy recovery circuit.

[0011] Furthermore, it also includes a buck-stabilizing circuit, the input end of the buck-stabilizing circuit is connected to the output end of the isolated electric energy recovery circuit, and the output end of the buck-stabilizing circuit is connected to the single-chip microcomputer main control circuit.

[0012] Furthermore, the high-voltage capacitor group includes a plurality of high-voltage capacitors connected in parallel, the positive electrodes of the plurality of high-voltage capacitors are connected to the high-voltage relay group, and the negative electrodes are grounded through capacitor output switches.

[0013] This embodiment also provides a high-voltage capacitor charging and discharging method for power device testing, the method adopts the above-mentioned high-voltage capacitor charging and discharging circuit for power device testing, and the method includes: When the high-voltage relay group is switched to a charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; When the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit is tested by the amount of electricity stored on the high-voltage capacitor; When the high-voltage relay group switches to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor is discharged; Wherein, the high voltage relay group includes a first relay, a second relay and a third relay; When the high-voltage relay group is in a charging state, the first relay and the second relay are closed, and the third relay is opened; When charging is completed, the high-voltage relay group is in a disconnected state, and the first relay, the second relay and the third relay are all disconnected; When the test is completed, the high-voltage relay group is in a power recovery state, the first relay and the second relay are disconnected, and the third relay is closed.

[0014] Compared with the prior art, the present invention has at least the following technical effects: This solution realizes a controllable connection between the high-voltage power supply and the test circuit by setting up a high-voltage relay group, so that the system can flexibly switch between the charging state, the charging disconnection state and the power recovery state: in the charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; in the charging disconnection state, the connection between the high-voltage power supply and the test circuit is completely disconnected, avoiding the interference signal and safety hazards that may be caused by the high-voltage power supply continuously supplying power to the test circuit; in the power recovery state, the high-voltage power supply is disconnected and the high-voltage capacitor group is discharged at the same time, which not only ensures the safety of the test, but also realizes the recycling of the remaining electric energy. This three-state switching design effectively solves the safety problem of the long-term connection between the high-voltage power supply and the test circuit in the traditional test system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structure of a high-voltage capacitor charging and discharging circuit for power device testing in Embodiment 1 of the present invention; Figure 2 It is a schematic diagram of the opening and closing of the switch in the high-voltage relay group when the circuit in the first embodiment of the present invention is in the charging state; Figure 3 It is a schematic diagram of the opening and closing of the switch in the high-voltage relay group when the circuit is in the power recovery state in the first embodiment of the present invention; Figure 4 It is a schematic diagram of the opening and closing of the switch in the high-voltage relay group when the circuit is in the charging disconnection state in the first embodiment of the present invention; Figure 5 Schematic diagram of capacitor voltage charge and discharge curve in Embodiment 1 of the present invention; Figure 6 It is a schematic diagram of the structure of the isolated electric energy recovery circuit in the second embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following is a description of the high-voltage capacitor charging and discharging circuit and charging and discharging method for power device testing of the present invention in conjunction with a schematic diagram, wherein a preferred embodiment of the present invention is shown, and it should be understood that those skilled in the art can modify the present invention described herein, while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art, and not as a limitation of the present invention.

[0017] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and in non-precise proportions, and are only used to facilitate and clearly assist in illustrating the purpose of the embodiments of the present invention.

[0018] Embodiment 1 Please refer to Figure 1 This embodiment discloses a high-voltage capacitor charging and discharging circuit for power device testing, which specifically includes a high-voltage relay group.

[0019] Specifically, the input end of the high-voltage relay group is electrically connected to the high-voltage power supply, and the output end is electrically connected to the power device test circuit through the high-voltage capacitor group; the high-voltage relay group can switch between the charging state, the charging disconnection state and the power recovery state. The relay drive circuit is electrically connected to the high-voltage relay group, and is used to control the high-voltage relay group to switch between the charging state, the charging disconnection state and the power recovery state.

[0020] Among them, the specific switching method is: when the high-voltage relay group is switched to the charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; when the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit performs a voltage parameter test of the high-voltage capacitor group; when the high-voltage relay group is switched to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor group is discharged.

[0021] It can be seen that this embodiment realizes a controllable connection between the high-voltage power supply and the test circuit by setting a high-voltage relay group, so that the circuit can be flexibly switched between the charging state, the charging disconnection state and the power recovery state: in the charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; in the charging disconnection state, the connection between the high-voltage power supply and the test circuit is completely disconnected, avoiding interference signals and safety hazards that may be caused by the high-voltage power supply continuously supplying power to the test circuit; in the power recovery state, the high-voltage power supply is disconnected and the high-voltage capacitor group is discharged at the same time, which not only ensures the safety of the test, but also realizes the recycling of the remaining electric energy. This three-state switching design effectively solves the safety problem of the long-term connection between the high-voltage power supply and the test circuit in the traditional test system.

[0022] In this embodiment, the high-voltage power supply cannot directly charge the high-voltage capacitor, otherwise the instantaneous current will be too large, causing damage to the high-voltage power supply or the high-voltage capacitor. In order to avoid the above problem, this embodiment also provides a charging current limiting circuit.

[0023] Specifically, the input end of the charging current limiting circuit is connected to the high-voltage power supply, and the output end is connected to the high-voltage relay group.

[0024] In a specific embodiment, the charging current limiting circuit can adopt a charging current limiting circuit such as an RC charging current limiting circuit (composed of a power resistor and a capacitor), an LC charging current limiting circuit (composed of a current limiting inductor and a capacitor), and a constant current source chip. Those skilled in the art can select different charging current limiting circuits according to circuit cost, circuit energy loss, switching efficiency, etc.

[0025] In this embodiment, the high-voltage capacitor group includes a plurality of high-voltage capacitors connected in parallel, the positive electrodes of the plurality of high-voltage capacitors are connected to the high-voltage relay group, and the negative electrodes are grounded through capacitor output switches.

[0026] In a specific embodiment, the number of the high-voltage capacitors can be 2-5, preferably 3; when 3 high-voltage capacitors are used, the total capacitance of the three capacitors in parallel is 3 times the capacity of a single capacitor, which can meet the electrical energy requirements of most power device tests; the number of high-voltage capacitors can be flexibly adjusted according to the actual test voltage and test electrical energy requirements. Specifically, when the test electrical energy requirement is low, it can be reduced to 2 or 1 high-voltage capacitors. When a higher test electrical energy is required, it can be increased to 4 or 5 high-voltage capacitors in parallel to increase the capacity of the capacitor bank.

[0027] In addition, it is understandable that during the test process, storing too much electrical energy in the high-voltage capacitor is more likely to cause damage to the power device under test, and at the same time cause waste of excess electrical energy. It is necessary to flexibly adjust the energy charged by the high-voltage capacitor according to specific test conditions to achieve the purpose of optimization.

[0028] According to the capacitor energy formula , under a specific test voltage, the energy stored in the high-voltage capacitor is proportional to the capacitance value. In this embodiment, when a small-capacitance capacitor is needed, you can choose to turn on only one capacitor output switch; when a large-capacitance capacitor is needed, you can choose to turn on multiple capacitor switches; the capacitor output switch (the figure is only for illustration, the actual object can be a power switch device such as a thyristor, IGBT or MOSFET) is operated instantly through the control circuit, eliminating the risk of electric shock to the operator and greatly improving the test efficiency.

[0029] In this embodiment, the high voltage relay group includes a first relay control switch, a second relay and a third relay control switch.

[0030] The input ends of the first relay and the second relay are connected to the high-voltage power supply, and the output ends are connected to the high-voltage capacitor group and the power device test circuit; the input end of the third relay is connected to the high-voltage capacitor group, and the output end is connected to the isolated energy recovery circuit.

[0031] For details, please refer to Figure 2-Figure 4 When in the charging state, the first relay control switch and the second relay are closed, and the third relay control switch is opened, so that the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group.

[0032] When in the charging disconnect state, the first relay control switch, the second relay and the third relay control switch are all disconnected, so that the power device test circuit is isolated from the high voltage power supply to perform a voltage parameter test.

[0033] When in the power recovery state, the first relay control switch and the second relay are disconnected, and the third relay control switch is closed, so that the high-voltage capacitor group is connected to the isolated power recovery circuit to achieve power recovery.

[0034] In this embodiment, in the charging disconnection state, the first relay control switch, the second relay and the third relay control switch are all disconnected, rather than just disconnecting the first relay control switch or the second relay. The benefits brought about by this are: avoiding the high-voltage power supply loop from introducing additional interference into the test circuit, ensuring the accuracy of the test results of the test circuit, greatly reducing the workload of interference analysis on the test results, and improving the test efficiency.

[0035] In this embodiment, the high-voltage capacitor charging and discharging circuit for the power device test further includes a sampling circuit.

[0036] Please refer to Figure 1Specifically, the sampling circuit includes a voltage sampling resistor and an isolated voltage sampling circuit; the voltage sampling resistor is connected in parallel to both ends of the high-voltage capacitor group for collecting the voltage signal of the high-voltage capacitor group; the input end of the isolated voltage collection circuit is connected in parallel with the voltage sampling resistor, and the output end is electrically connected to the microcontroller main control circuit.

[0037] In a specific embodiment, the isolated voltage sampling circuit can use an ISO124 chip with a high-voltage isolation function, whose high-voltage end pin is connected to a voltage sampling resistor for collecting voltage signals, and whose low-voltage end pin is directly connected to an AD port of a single-chip microcomputer in a single-chip microcomputer connection circuit, and the electrical isolation of the high-voltage end and the low-voltage end is achieved through isolation barrier technology, which can provide ±1000V common-mode voltage isolation. Of course, those skilled in the art can also select different types of chips with high-voltage isolation functions according to actual conditions.

[0038] In another specific embodiment, the voltage sampling resistor can be a 1MΩ precision metal film resistor, which has good temperature characteristics and stability. The sampling circuit not only realizes the accurate acquisition of high-voltage signals, but also ensures the safety of signal acquisition through the isolation operational amplifier. Of course, those skilled in the art can also select resistors of different types and specifications according to actual conditions.

[0039] Please continue to refer to Figure 1 In this embodiment, the driving circuit includes an isolating switch driving circuit, a single chip microcomputer main control circuit and a relay driving circuit.

[0040] Specifically, the isolation switch driving circuit has a first input end connected to the single-chip main control circuit, and an output end connected to the high-voltage capacitor output switch; the output end of the single-chip main control circuit is connected to the input end of the relay driving circuit, and the output end of the relay driving circuit is electrically connected to the high-voltage relay group. The single-chip main control circuit controls the state switching of the high-voltage relay group through the relay driving circuit according to the size of the voltage signal collected by the isolation voltage collection circuit.

[0041] In a specific embodiment, the single-chip microcomputer main control circuit includes a single-chip microcomputer, and the single-chip microcomputer can at least achieve the following technical effects: collect the high-voltage capacitor voltage signal output by the isolation voltage acquisition circuit in real time through the AD port, and perform digital filtering processing; judge the charging state of the high-voltage capacitor group according to the comparison result of the collected voltage value and the preset threshold; output the control signal to the isolation switch drive circuit through the IO port, and change the capacitance value in the high-voltage capacitor group through the isolation switch drive circuit; and control and adjust the discharge speed of the high-voltage capacitor by setting the constant current value of the power recovery circuit. All operations can be completed by the single-chip microcomputer main control circuit autonomously, or through the communication interface circuit, the host computer issues corresponding instructions and executes corresponding operations.

[0042] Please refer to Figure 5 In the above specific embodiment, after setting the charging specified voltage, undervoltage specified voltage and safety voltage value in the single chip microcomputer, the capacitor voltage is compared with these three voltages to control the high voltage relay group to switch the corresponding state. In addition, the single chip microcomputer can also send corresponding charging completion, undervoltage, and discharge completion signals for indication. Each signal can be set to an indicator light, and the color of the indicator light can be designed to be different. At this time, the user can intuitively know the current voltage state and perform corresponding operations; the host computer can also judge the working state according to the signal sent by the single chip microcomputer through the control communication interface, and send corresponding operation instructions to realize online automatic operation.

[0043] In another specific embodiment, the isolation switch driving circuit includes a capacitor output switch and a switch control device, wherein a power switch device such as a thyristor, IGBT or MOSFET can be used as the capacitor output switch, and a simple isolation driving circuit such as an optocoupler can realize the control of the high-voltage side power switch by the single-chip microcomputer. Since the opening and closing frequency of the capacitor output switch (which can be a power switch device such as a thyristor, IGBT or MOSFET) in this device is low, there is no need to use a complex driving circuit. The input end of the optocoupler is connected to the IO port of the single-chip microcomputer, and the output end is connected to the control end of the power switch device. The safe conversion of the low-voltage control signal to the high-voltage drive signal is realized through the principle of photoelectric isolation, and the closing and disconnection of the power switch device are controlled.

[0044] Preferably, the driving circuit also includes a communication interface circuit: used to realize digital communication between the device and other equipment, such as using commonly used communication interface chips such as 232 and 485, and when necessary, it can be interconnected with a single-chip microcomputer to achieve online automatic operation.

[0045] Preferably, a manual operation circuit is further included: in some test cases, the relay can be manually opened and closed by the standby manual operation circuit to switch between different states of the high voltage circuit without the need for single chip microcomputer control. The operating device can be a button or a switch.

[0046] In this embodiment, the relay drive circuit is used to provide sufficient drive current to the relay coil according to the control signal. At the same time, the drive circuit also includes measures such as optocoupler isolation, state feedback, decoupling capacitors and overcurrent protection to improve the reliability and anti-interference ability of the circuit, and realize precise timing control of the relay through the single-chip microcomputer.

[0047] In a specific embodiment, the relay driving circuit can use a triode or Darlington transistor array chip as a driving element, wherein the triode driving solution requires a freewheeling diode to be connected in parallel at both ends of the coil for protection, while the Darlington transistor array solution has the advantages of high integration and few peripheral components. Those skilled in the art can select different relay driving circuits according to actual conditions.

[0048] In this embodiment, an isolated electric energy recovery circuit is also included, the input end of the isolated electric energy recovery circuit is connected in parallel with the high-voltage capacitor group, and the output end is electrically connected to the single-chip microcomputer main control circuit.

[0049] The inventor found that by converting the energy of the high-voltage capacitor into the low-voltage power supply end of the device, the electric energy can be recycled. However, the voltage on the high-voltage capacitor is generally very high, and the voltage on the low-voltage power supply end is obviously low. At the same time, in order to meet the isolation requirements of electrical safety and have a higher energy conversion efficiency, the switching power supply topology is a suitable choice. In this regard, the inventor designed the following isolated energy recovery circuit: Please refer to Figure 6 The isolated electric energy recovery circuit includes a flyback voltage stabilization circuit, and the flyback voltage stabilization circuit includes a flyback transformer S1, an NMOS tube Q1, a PWM chip, a high-voltage capacitor C1, a rectifier diode D1, a current sampling resistor R1, an optocoupler OC1 and a filter capacitor C2.

[0050] One end of the primary winding of the flyback transformer S1 is connected to the positive electrode of the high-voltage capacitor C1 group through the high-voltage relay group (specifically the third high-voltage relay), and the other end of the primary winding is connected to the drain of the NMOS tube Q1; the source of the NMOS tube Q1 is connected to the current feedback terminal 2 of the PWM chip, and is connected to the emitter of the phototransistor in the optical coupler OC1 through the current sampling resistor R1, and the gate is connected to the PWM output terminal 1 of the PWM chip. One end of the secondary winding of the flyback transformer S1 is connected to the positive electrode of the high-voltage capacitor C1 group through the high-voltage relay group (specifically the third high-voltage relay), and the other end of the primary winding is connected to the drain of the NMOS tube Q1; the source of the NMOS tube Q1 is connected to the current feedback terminal 2 of the PWM chip, and is connected to the emitter of the phototransistor in the optical coupler OC1 through the current sampling resistor R The rectifier diode D1 is connected to the positive output end of the isolated energy recovery circuit, and the other end of the secondary winding of the flyback transformer S1 is connected to the negative output end of the isolated energy recovery circuit; the filter capacitor C2 is connected in parallel between the cathode and the negative output end of the rectifier diode D1; the voltage feedback end 4 of the PWM chip is connected to the collector of the phototransistor in the optocoupler OC1, and the power supply input end 3 of the PWM chip is connected to the positive output end of the rectifier diode D2 connected to the other secondary winding of the flyback transformer S1.

[0051] In addition, the isolated electric energy recovery circuit also includes a constant current circuit, which includes a constant current chip, a digital potentiometer, an energy storage capacitor C4 and a current limiting inductor L1.

[0052] The voltage detection terminal 6 of the constant current chip is connected to one end of the secondary winding of the flyback transformer S1 through the rectifier diode D1; the output terminal 8 of the constant current chip is connected to the positive output terminal of the isolated energy recovery circuit, and a current limiting inductor L1 is also connected in parallel between the input terminal 5 and the output terminal 8 of the constant current chip. The adjustment terminal 7 of the constant current chip is connected to the adjustable resistance terminal of the digital potentiometer, and the clock terminal and data terminal of the digital potentiometer are respectively connected to the microcontroller main control circuit through the I2C data bus; the energy storage capacitor C4 is connected in parallel between the positive output terminal and the negative output terminal.

[0053] Specifically, in the above-mentioned isolated energy recovery circuit, in the flyback topology (discontinuous current mode), during the conduction time of the NMOS tube Q1, the high-voltage bus does not provide energy to the load, but only provides current to the current-limiting inductor L1 to store energy. During the off time of the NMOS tube Q1, the high-voltage bus is disconnected, and the current-limiting inductor L1 releases energy to the load. Therefore, in the flyback topology (discontinuous current mode), the high-voltage bus is only connected to the current-limiting inductor L1. Since the current of the current-limiting inductor L1 cannot change suddenly, there will be no instantaneous high current on the high-voltage bus. At the same time, the flyback topology has few components and low cost, which is suitable as an energy recovery circuit for the high-voltage capacitor C1.

[0054] However, the fluctuation of the output load of the flyback topology will affect the discharge speed of the high-voltage capacitor C1: if the output load is too large, it will cause the discharge to be too fast, affecting the service life of the capacitor. Therefore, a constant current chip is added to the output end to limit the output current to prevent the high-voltage capacitor C1 from discharging too fast; if the output load is too small, it will cause the discharge to be too slow, increasing safety hazards and affecting the test efficiency. Therefore, a large-capacity energy storage capacitor C4 is placed after the constant current output to absorb the energy discharged by the high-voltage capacitor C1. In actual use, if the capacity is not enough, the high-voltage capacitor C1 still discharges too slowly. Low-voltage and large-capacity energy storage components such as supercapacitors and lithium batteries can also be used.

[0055] Preferably, the isolated electric energy recovery circuit also includes: a current limiting resistor R2 and a clamping protection diode D3, one end of the current limiting resistor R2 is connected between the rectifier diode D1 and the voltage detection terminal 6 of the constant current chip, and the other end is connected to the cathode of the clamping protection diode D3, and the clamping protection diode D3 is connected in series with the light-emitting diode in the optocoupler.

[0056] After recovering the electric energy, the isolated energy recovery circuit inputs the excess electric energy into low-voltage control circuits such as the microcontroller main control circuit, relay drive circuit and communication interface circuit, thereby providing a stable DC voltage for the microcontroller main control circuit.

[0057] It can be seen that in this embodiment, the isolated energy recovery circuit recovers excess electric energy to provide a stable DC voltage for low-voltage control circuits such as the microcontroller main control circuit, relay drive circuit and communication interface circuit, thereby achieving efficient use of electric energy and reducing the complexity and cost of power supply design.

[0058] Furthermore, in this embodiment, a buck-stabilizing circuit is also included, wherein the input end of the buck-stabilizing circuit is connected to an external power supply, and the output end is connected to the microcontroller main control circuit. The buck-stabilizing circuit is used to convert the energy recovered by the isolated power recovery circuit into a DC voltage required by the microcontroller main control circuit.

[0059] In a specific embodiment, the XL1401 switching buck regulator chip is used as the buck regulator circuit to reduce the supply voltage to 5V, and then power is supplied to the single-chip microcomputer main control circuit, the isolation voltage acquisition circuit and the isolation switch drive circuit.

[0060] Embodiment 2 This embodiment provides a method for charging and discharging a high-voltage capacitor C1 for power device testing, using a high-voltage capacitor C1 charging and discharging circuit for power device testing disclosed in Embodiment 1. The specific method includes: S1. When the high-voltage relay group is switched to the charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor C1 group.

[0061] S2. When the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit uses the voltage on the high-voltage capacitor C1 to perform a test.

[0062] S3. When the high-voltage relay group switches to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor C1 is discharged.

[0063] Specifically, in step S1, when the high-voltage relay group is in a charging state, the first relay and the second relay are closed, and the third relay is disconnected, and at this time, the charging circuit is turned on. In this state, the high-voltage circuit charges the high-voltage capacitor group, and the sampling circuit monitors the charging voltage. When the voltage reaches the specified value, the communication interface circuit sends a charging completion signal to the upper computer, indicating that the test work can be carried out.

[0064] In step S2, when the test can be performed, the high-voltage relay group is charged and is in a disconnected state, and the first relay, the second relay and the third relay are all disconnected; the test circuit can use the electric energy stored in the high-voltage capacitor C1 to perform pulse testing.

[0065] In step S3, after the test is completed, the sampling circuit continues to monitor the voltage. When the voltage is less than the specified value, the communication interface circuit sends an undervoltage signal to the upper computer, indicating that the power is too low. At this time, if it is necessary to test immediately, repeat step S1 and continue to charge the high-voltage capacitor bank until the test is completed. Otherwise, the first relay and the second relay are disconnected, and the third relay is closed, so that the residual electric energy on the capacitor is collected and released into the buck voltage stabilization circuit through the isolation electric energy recovery circuit, and then the electric energy is output to the single-chip microcomputer main control circuit, the isolation voltage acquisition circuit and the isolation switch drive circuit through the buck voltage stabilization circuit, thereby providing a stable power supply for these circuits.

[0066] In a specific embodiment, in the isolated energy recovery circuit, in order to avoid damage to the high-voltage capacitor C1 due to excessive discharge, the maximum discharge current must be limited. At the same time, in order to meet the safety of electricity use and the needs of high-frequency test operation, in this embodiment, the discharge speed of the isolated energy recovery circuit is adjusted by adjusting the constant current value input to the isolated energy recovery circuit through the single-chip microcomputer main control circuit. The capacity parameters of the current limiting inductor L1 can also be adjusted, the turns ratio of the flyback transformer S1 can be set, or the duty cycle of the PWM can be changed, so that the isolated energy recovery circuit can complete the discharge of the energy storage capacitor within 3 to 5 seconds.

[0067] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high voltage capacitor charging and discharging circuit for power device testing, characterized in that: include: A high-voltage relay group, the input end of which is electrically connected to the high-voltage power supply, and the output end of which is electrically connected to the power device test circuit through a high-voltage capacitor group; The high-voltage relay group can switch between a charging state, a charging disconnection state and an electric power recovery state; When the high-voltage relay group is switched to a charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; When the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit performs a voltage parameter test on the high-voltage capacitor group; When the high-voltage relay group is switched to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor group is discharged; The drive circuit is electrically connected to the high-voltage relay group and is used to control the high-voltage relay group to switch between a charging state, a charging disconnection state and an electric power recovery state.

2. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 1, characterized in that: Also includes a sampling circuit; The sampling circuit includes a voltage sampling resistor and an isolation voltage sampling circuit; The voltage sampling resistor is connected in parallel to both ends of the high-voltage capacitor group and is used to collect the voltage signal of the high-voltage capacitor group; The input end of the isolation voltage acquisition circuit is connected in parallel with the voltage sampling resistor, and the output end is electrically connected to the driving circuit.

3. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 2, characterized in that: The driving circuit comprises: An isolating switch driving circuit, whose input end is connected to the first output end of the single-chip microcomputer main control circuit, and whose output end is connected to the capacitor output switch in the high-voltage capacitor bank; The input end of the single chip microcomputer main control circuit is connected to the output end of the isolation voltage acquisition circuit; The second output terminal of the single chip microcomputer main control circuit is connected to the input terminal of the relay drive circuit; The output end of the relay drive circuit is electrically connected to the high voltage relay group; The single chip microcomputer main control circuit is also interconnected with the communication interface circuit.

4. The high-voltage capacitor charging and discharging circuit for power device testing as claimed in claim 3, characterized in that: Also includes: An isolated electric energy recovery circuit, wherein the input end of the isolated electric energy recovery circuit is connected in parallel with the high-voltage capacitor group, and the output end outputs the supply voltage to the communication interface circuit, the single-chip microcomputer main control circuit and the relay drive circuit through a step-down voltage stabilization circuit.

5. The high-voltage capacitor charging and discharging circuit for power device testing as claimed in claim 4, characterized in that: The isolated electric energy recovery circuit includes a flyback voltage stabilization circuit, which includes a flyback transformer S1, an NMOS tube Q1, a PWM chip, a high-voltage capacitor C1, a rectifier diode D1, a current sampling resistor R1, an optocoupler OC1 and a filter capacitor C2; One end of the primary winding of the flyback transformer S1 is connected to the positive electrode of the high-voltage capacitor C1 group through the high-voltage relay group, and the other end of the primary winding is connected to the drain of the NMOS tube Q1; the source of the NMOS tube Q1 is connected to the emitter of the phototransistor in the optocoupler OC1 and the ground end of the PWM chip through the current sampling resistor R1, and the gate is connected to the output end of the PWM chip, one end of the secondary winding of the flyback transformer S1 is connected to the positive output end of the isolated electric energy recovery circuit through the rectifier diode D1, and the other end of the secondary winding of the flyback transformer S1 is connected to the negative output end of the isolated electric energy recovery circuit; the filter capacitor C2 is connected in parallel between the cathode and the negative output end of the rectifier diode D1; the feedback input end of the PWM chip is connected to the collector of the phototransistor in the optocoupler OC1.

6. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 5, characterized in that: The isolated electric energy recovery circuit also includes a constant current circuit, which includes a constant current chip, a digital potentiometer, an energy storage capacitor C4 and a current limiting inductor L1; The voltage detection end of the constant current chip is connected to one end of the secondary winding of the flyback transformer S1 through the rectifier diode D1; the output end of the constant current chip is connected to the positive output end of the isolated energy recovery circuit, and a current limiting inductor L1 is also connected in parallel between the input and output ends of the constant current chip. The adjustment end of the constant current chip is connected to the adjustable resistance end of the digital potentiometer, and the clock end and data end of the digital potentiometer are respectively connected to the main control circuit of the single-chip microcomputer; the energy storage capacitor C4 is connected in parallel between the positive output end and the negative output end.

7. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 4, characterized in that: The high voltage relay group includes a first relay, a second relay and a third relay; The input ends of the first relay and the second relay are connected to the high voltage power supply, and the output ends are connected to the high voltage capacitor bank and the power device test circuit; The input end of the third relay is connected to the high-voltage capacitor bank, and the output end is connected to the isolated electric energy recovery circuit.

8. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 1, characterized in that: It also includes a charging current limiting circuit, the input end of which is connected to the high-voltage power supply, and the output end of which is connected to the high-voltage relay group.

9. The high-voltage capacitor charging and discharging circuit for power device testing according to claim 1, characterized in that: The high-voltage capacitor group includes a plurality of high-voltage capacitors connected in parallel, the positive electrodes of the plurality of high-voltage capacitors are connected to the high-voltage relay group, and the negative electrodes are grounded through capacitor output switches.

10. A high-voltage capacitor charging and discharging method for power device testing, characterized in that: When the high-voltage relay group is switched to a charging state, the high-voltage power supply charges the power device test circuit and the high-voltage capacitor group; When the high-voltage relay group is switched to the charging disconnection state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the power device test circuit is tested by the amount of electricity stored on the high-voltage capacitor; When the high-voltage relay group switches to the power recovery state, the connection between the high-voltage power supply and the power device test circuit is disconnected, and the electric energy on the high-voltage capacitor is discharged; Wherein, the high voltage relay group includes a first relay, a second relay and a third relay; When the high-voltage relay group is in a charging state, the first relay and the second relay are closed, and the third relay is opened; When charging is completed, the high-voltage relay group is in a disconnected state, and the first relay, the second relay and the third relay are all disconnected; When the test is completed, the high-voltage relay group is in a power recovery state, the first relay and the second relay are disconnected, and the third relay is closed.

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