An online impedance testing device and method for high-power equipment in a DC power grid

Abstract

The present invention provides an online impedance testing device and method for high-power equipment in a DC power grid. The testing device is connected to the DC side of the high-power equipment to be tested. When the equipment is connected to the power grid for operation, a small current signal is injected into the equipment by frequency sweeping, and the impedance characteristics are calculated by measuring the voltage-frequency characteristics of the equipment. The function of online impedance testing of high-power equipment in a DC power grid operating under various working conditions is realized, and the differential mode impedance characteristics and common mode impedance characteristics of the equipment are tested respectively by changing the wiring method. The present invention ensures the safety of personnel and equipment through DC blocking capacitors and isolation transformers. The present invention is suitable for testing scenarios where the equipment to be tested contains a DC port and the frequency is below 1 MHz. By adjusting the energy storage and power devices to adapt to the current and voltage range of the power grid, the structure is simple, easy to manufacture and operate, with fewer additional devices, low requirements for the test site, and strong engineering practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic compatibility, and in particular relates to an online impedance testing device and method for high-power equipment in a direct current grid. Background Art

[0002] Traditional impedance testing methods such as resonance method and direct measurement method are aimed at the impedance characteristics of the equipment when it is offline. However, for devices such as large motors and switching power supplies, their working modes under different working conditions and the nonlinearity of the circuits make their impedance characteristics when they are online vary greatly compared to the offline state. In scenarios where the impedance characteristics of the equipment are required to be high, such as the electromagnetic compatibility simulation design of the equipment and the prediction of system electromagnetic interference, the impedance characteristics of the offline state can no longer restore the electromagnetic compatibility performance of the equipment after it is connected to the power grid.

[0003] The current online measurement methods include the insertion loss method and the dual current probe method. Since the insertion loss method requires a filter element to be connected in series in the circuit, it is not suitable for impedance testing under high voltage and high current conditions. The dual current probe method cannot directly obtain the interference voltage of the device and requires the use of LISN. When there is a large current in the line, there are high requirements for the signal source and LISN. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an online impedance testing device and method for high-power equipment in a DC power grid, which are used for online impedance testing of high-power equipment in a DC power grid under various operating conditions.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: an online impedance test device for high-power equipment in a direct current grid, comprising a signal source, a power amplifier, a current limiting resistor, a transformer, a direct current blocking capacitor, a current sensor, a voltage divider test device, and a spectrum analyzer; the signal output end of the signal source is connected to the signal input end of the power amplifier for generating a frequency sweep signal; the signal output end of the power amplifier is connected to the primary coil of the transformer after being connected in series with a current limiting resistor, the power amplifier is used to amplify and inject signals, and the current limiting resistor is used to prevent the output end of the power amplifier from short-circuiting and burning; the secondary coil of the transformer is connected to the direct current bus after being connected in series with a direct current blocking capacitor, the transformer is used to isolate the grid to protect the high-power equipment to be tested, and the direct current blocking capacitor is used to isolate the high voltage of the direct current grid, protect the signal injection device and personnel safety; the current sensor penetrates the direct current bus to measure the real-time current at the test point; the measuring end of the voltage divider test device is connected in parallel between the positive and negative poles of the direct current bus to measure the real-time voltage at the test point; the signal output end of the current sensor and the signal output end of the voltage divider test device are respectively connected to the signal input end of the spectrum analyzer; the power supply end of the high-power equipment to be tested is connected to the direct current bus.

[0006] According to the above scheme, the current sensor is a Rogowski coil, which includes a soft non-metallic open-and-closed ring frame and a coil wound on the open-and-closed ring frame, which is used to avoid metal attraction caused by a strong magnetic field generated by a large current; it also includes a hollow probe, which is connected to the protruding end of the coil, so as to avoid probe saturation caused by a large DC current; the current sensor measures the differential mode current and common mode current of the high-power device to be tested by changing the winding method of the coil.

[0007] According to the above scheme, the voltage division test device includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor, a second capacitor, a circuit breaker switch, a discharge switch, and a short-circuit switch; the circuit breaker switch includes a linked first switch and a second switch, the first switch, the first resistor, the discharge switch, and the second switch are sequentially connected in series and then connected in parallel between the positive and negative electrodes of the DC bus, the first switch is connected in series to the positive electrode of the DC bus, and the second switch is connected in series to the negative electrode of the DC bus; the first capacitor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, and the second capacitor are sequentially connected in series and then connected in parallel to the series connection of the first resistor and the discharge switch. The short-circuit switch includes a fourth switch and a fifth switch which are linked, the fourth switch is connected in parallel to the two ends of the series circuit of the second resistor and the third resistor, and the fifth switch is connected in parallel to the two ends of the series circuit of the fourth resistor and the fifth resistor; the connection point between the first capacitor and the second resistor leads to a first differential mode voltage terminal, and the connection point between the fifth resistor and the second capacitor leads to a second differential mode voltage terminal; the connection point between the third resistor and the fourth resistor leads to a common mode voltage terminal, and is connected to ground through a sixth resistor in series; the voltage divider test device is connected in parallel to the DC power grid in a high impedance state, and the differential mode voltage and common mode voltage of the high-power device to be tested are measured respectively by changing the switch closing mode.

[0008] Furthermore, the first resistor is 10 kΩ, the second resistor, the third resistor, the fourth resistor, and the fifth resistor are all 470 Ω, the sixth resistor is 20 kΩ, and the first capacitor and the second capacitor are both 10 uF.

[0009] Furthermore, when used to measure the differential mode current of the high-power device to be tested, the two ends of the secondary coil of the transformer are connected in parallel between the positive and negative poles of the DC bus, and the single-pole DC bus is inserted into the current sensor; the signal input end of the spectrum analyzer is respectively connected to the first differential mode voltage terminal and the second differential mode voltage terminal of the voltage divider test device;

[0010] When used to measure the common-mode current of the high-power device to be tested, one end of the secondary coil of the transformer is grounded, and the other end is connected to the positive and negative poles of the DC bus through parallel DC-isolating capacitors; the positive and negative poles of the DC bus are inserted into the current sensor; the signal input end of the spectrum analyzer is connected to the common-mode voltage terminal of the voltage divider test device.

[0011] An online impedance testing method for a high-power device in a DC power grid comprises the following steps:

[0012] S1: When the high-power device to be tested is powered off, an online impedance test device for a DC power grid high-power device is built, including a signal source, a power amplifier, a current limiting resistor, a transformer, a DC blocking capacitor, a current sensor, a voltage divider test device, and a spectrum analyzer; the signal output end of the signal source is connected to the signal input end of the power amplifier; the signal output end of the power amplifier is connected in series with a current limiting resistor and then connected to the primary coil of the transformer; the secondary coil of the transformer is connected in series with a DC blocking capacitor and then connected to the DC bus; the DC bus is inserted into the current sensor; the measuring end of the voltage divider test device is connected in parallel between the positive and negative poles of the DC bus; the signal output end of the current sensor and the signal output end of the voltage divider test device are respectively connected to the signal input end of the spectrum analyzer; the power supply end of the high-power device to be tested is connected to the DC bus; the test device is connected to the DC side of the high-power device to be tested;

[0013] S2: The high-power device to be tested is connected to the power grid, and a low current signal is injected into the high-power device to be tested by frequency sweeping; the voltage frequency-amplitude characteristics of the high-power device to be tested are measured;

[0014] S3: Calculate the impedance characteristics of the high-power device to be tested.

[0015] Furthermore, when testing the differential mode impedance characteristics of the high-power device to be tested,

[0016] The step S1 further includes the following specific steps:

[0017] S11: Connect the two ends of the transformer's secondary coil in parallel between the positive and negative poles of the DC bus.

[0018] S12: A single-pole DC bus is inserted into the current sensor;

[0019] S13: the signal input terminal of the spectrum analyzer is respectively connected to the first differential mode voltage terminal and the second differential mode voltage terminal of the voltage division test device;

[0020] S14: Keep the circuit breaker switch, the discharge switch and the short-circuit switch of the voltage dividing test device in the off state;

[0021] In the step S2, the specific steps are:

[0022] S21: After the high-power device to be tested is powered on and runs stably, the circuit breaker switch of the voltage division test device is closed. After the charging time t=5RC, the capacitor charging process ends. At this time, there is no DC high voltage at the differential mode terminal;

[0023] S22: Turn on the signal source and the power amplifier, set the frequency range and amplitude of the signal output by the signal source, and make the signal source work in the sine sweep mode;

[0024] S23: using a spectrum analyzer to read a voltage spectrum between a first differential mode voltage terminal and a second differential mode voltage terminal of the voltage divider test device, and reading a current spectrum from a current sensor;

[0025] S24: Adjust the gain of the power amplifier so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the high-power device to be tested and the DC bus, so that the spectrum of the voltage and current within the sweep range measured by the spectrum analyzer covers the spectrum of the interference signal; the voltage measured at this time is the differential mode voltage U of the injected signal at the output end of the high-power device to be tested d Frequency-amplitude characteristics; the measured current is the differential mode current I of the injected signal at the output end of the high-power device to be tested d Frequency-amplitude characteristics;

[0026] In the step S3, the specific steps are:

[0027] According to the measured differential mode voltage U d and differential mode current I d The frequency-amplitude characteristic curve is used to calculate the differential mode impedance Z of the high-power device under test under certain working conditions. d Frequency characteristics.

[0028] Furthermore, when testing the common mode impedance characteristics of the high power device to be tested,

[0029] The step S1 further includes the following specific steps:

[0030] S11: One end of the secondary coil of the transformer is grounded, and the other end is connected to the positive and negative poles of the DC bus through parallel DC blocking capacitors;

[0031] S12: The positive and negative electrodes of the current sensor are inserted into the DC bus;

[0032] S13: The signal input terminal of the spectrum analyzer is connected to the common mode voltage terminal of the voltage divider test device;

[0033] S14: Keep the circuit breaker switch, the discharge switch and the short-circuit switch of the voltage dividing test device in the off state;

[0034] In the step S2, the specific steps are:

[0035] S21: After the high-power device to be tested is powered on and runs stably, the circuit breaker switch of the voltage division test device is closed. After the charging time t=5RC, the capacitor charging process ends. At this time, there is no DC high voltage at the differential mode terminal;

[0036] S22: Turn on the signal source and the power amplifier, set the frequency range and amplitude of the signal output by the signal source, and make the signal source work in the sine sweep mode;

[0037] S23: close the short-circuit switch of the voltage divider test device, use a spectrum analyzer to read the voltage spectrum between the common mode terminal and the ground wire of the voltage divider test device, and read the current spectrum from the current sensor;

[0038] S24: Adjust the gain of the power amplifier so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the high-power device to be tested and the DC bus, so that the spectrum of the voltage and current within the sweep range measured by the spectrum analyzer covers the spectrum of the interference signal; the voltage measured at this time is the common mode voltage U of the injected signal at the output end of the high-power device to be tested c Frequency-amplitude characteristics; the measured current is the common-mode current I of the injected signal at the output end of the high-power device to be tested c Frequency-amplitude characteristics;

[0039] In the step S3, the specific steps are:

[0040] According to the measured common mode voltage U c and common mode current I c The common mode impedance Z of the high-power device to be tested under certain working conditions is calculated by using the frequency-amplitude characteristic curve c Frequency characteristics.

[0041] A computer storage medium stores a computer program executable by a computer processor, wherein the computer program executes an online impedance testing method for a high-power device in a direct current grid.

[0042] The beneficial effects of the present invention are:

[0043] 1. The present invention provides an online impedance test device and method for high-power equipment in a DC power grid. The test device is connected to the DC side of the high-power equipment to be tested. When the equipment is connected to the power grid, a small current signal is injected into the equipment by frequency sweeping, and the impedance characteristics are calculated by measuring the voltage-frequency characteristics of the equipment. The function of online impedance testing of high-power equipment in a DC power grid operating under various working conditions is realized, and the differential mode impedance characteristics and common mode impedance characteristics of the equipment are tested respectively by changing the wiring mode.

[0044] 2. The present invention ensures the safety of personnel and equipment through DC blocking capacitors and isolation transformers.

[0045] 3. The present invention is applicable to the test scenarios where the device under test contains a DC port and the frequency is below 1 MHz. It adapts to the current and voltage range of the power grid by adjusting the energy storage and power devices. It has a simple structure, is easy to manufacture and operate, has fewer additional devices, has low requirements for the test site, and has strong engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a general block diagram of the differential mode impedance test according to an embodiment of the present invention.

[0047] Figure 2 It is a general block diagram of the common mode impedance test according to an embodiment of the present invention.

[0048] Figure 3 Schematic diagram of a method for implementing a current sensor according to an embodiment of the present invention.

[0049] Figure 4 1 is a circuit and device diagram of a voltage divider test device according to an embodiment of the present invention.

[0050] Figure 5 4 is a differential mode voltage spectrum diagram of an embodiment of the present invention.

[0051] Figure 6 4 is a differential mode current spectrum diagram of an embodiment of the present invention.

[0052] Figure 7 4 is a differential mode impedance spectrum characteristic diagram of an embodiment of the present invention.

[0053] Figure 8 4 is a comparison chart of differential mode test accuracy of an embodiment of the present invention.

[0054] Fig. 9 4 is a common mode voltage spectrum diagram of an embodiment of the present invention.

[0055] Fig.10 4 is a common-mode current spectrum diagram of an embodiment of the present invention.

[0056] Fig.11 4 is a common-mode impedance spectrum characteristic diagram of an embodiment of the present invention.

[0057] Fig.12 4 is a comparison chart of common mode test accuracy of an embodiment of the present invention.

[0058] In the figure: 1. Signal source; 2. Power amplifier; 3. Current limiting resistor; 4. Transformer; 5. DC blocking capacitor; 6. Current sensor; 7. Voltage divider test device. DETAILED DESCRIPTION

[0059] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0060] See also Figure 1 and Figure 2 The embodiment of the present invention includes a signal source 1 for generating a frequency sweep signal, a power amplifier 2 for signal injection, a current limiting resistor 3 for preventing the output end of the power amplifier 2 from short-circuiting and burning, a transformer 4 for isolating power grid protection, a DC blocking capacitor 5 for isolating DC high voltage, a current sensor 6 for measuring the real-time current at the test point, and a voltage divider test device 7 for measuring the real-time voltage at the test point;

[0061] The signal source 1 generates a frequency sweep signal, which is amplified by the power amplifier 2 and then injected into the device under test through the isolation transformer 4. The DC blocking capacitor 5 is used to isolate the high voltage of the DC power grid and protect the signal injection device and personnel safety. The current limiting resistor 3 is used to prevent the output end of the power amplifier 2 from short circuiting.

[0062] The current sensor 6 is a Rogowski coil, and its frame is made into a soft non-metallic open-and-closed structure. On the one hand, it is convenient for winding installation, and on the other hand, the strong magnetic field generated by the large current will cause the metal to attract. The use of non-metallic materials can avoid this situation. At the same time, the probe is developed into a hollow structure to ensure that the large DC current does not cause the probe saturation. By changing the winding method of the coil, the differential mode current and the common mode current of the device to be tested can be measured respectively.

[0063] The voltage-dividing test device 7 is a self-developed voltage measuring device, which can change the switch closing mode to measure the differential mode voltage and common mode voltage of the device under test respectively; the device itself is in a high-impedance state, and when connected in parallel to the DC power grid, it has little impact on the device under test.

[0064] Taking the impedance characteristic test of a motor as an example, an online impedance test method for a DC power grid high-power device of the present invention comprises the following steps:

[0065] 1. Differential mode impedance characteristic test

[0066] Step 1: When the motor is off, press Figure 1 Arrangement is performed, using signal source 1 to connect power amplifier 2, and current limiting resistor 3 is connected in series at the output end of power amplifier 2. Power amplifier 2 is isolated from the DC grid through isolation transformer 4, and DC isolation capacitor 5 is used to further isolate the DC high voltage to ensure safety. At this time, it is ensured that neither signal source 1 nor power amplifier 2 outputs signals.

[0067] Step 2: Attach the current sensor 6 Figure 3 The medium differential mode current test winding method is arranged on a single pole bus at the output end of the motor.

[0068] Step 3: According to the attached Figure 4 , connect the DC+ and DC- ends of the voltage dividing test device 7 to the positive bus and the negative bus respectively, and keep the circuit breaker switch, the discharge switch and the short-circuit switch in the disconnected state.

[0069] Step 4: After the motor is put into use and runs stably, the circuit breaker switch of the voltage divider test device 7 is closed. After the charging time t=5RC, the capacitor charging process is basically completed. At this time, there is no DC high voltage at the differential mode terminal, ensuring the safety of personnel.

[0070] Step 5: Turn on signal source 1 and power amplifier 2, set the frequency range and amplitude of the output signal of signal source 1, and make signal source 1 work in sine sweep mode.

[0071] Step 6: Use a spectrum analyzer to read the voltage spectrum from the differential mode terminals of the voltage divider test device 7 , and read the current spectrum from the current sensor 6 .

[0072] Step 7: Adjust the gain of power amplifier 2 so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the motor and the power grid, that is, the spectrum of the voltage and current within the sweep frequency range measured by the spectrum analyzer can cover the spectrum of the interference signal. The voltage measured at this time is the differential mode voltage U of the injected signal at the motor output end. d Frequency characteristics, such as Figure 5 The measured current is the differential mode current I of the injected signal at the motor output end. d Frequency characteristics, such as Figure 6 shown.

[0073] Step 8: Based on the measured differential mode voltage U d and current I d The frequency-amplitude characteristic curve can be used to obtain the differential mode impedance Z of the motor under certain working conditions. d Frequency characteristics, such as Figure 7 shown.

[0074] Will Figure 7 The differential mode impedance characteristics obtained by the test are used as the impedance input for the simulation. Figure 8 As shown, the error between the two in the first three main harmonics is less than 5dB.

[0075] 2. Common mode impedance characteristics test

[0076] Step 1: When the motor is off, press Figure 2 Arrangement is made, using signal source 1 to connect power amplifier 2, and current limiting resistor 3 is connected in series at the output end of power amplifier 2. The input end of isolation transformer 4 is connected to power amplifier 2, the output end is single-ended to ground, and the other end is connected to the midpoint between two DC blocking capacitors 5. At this time, it is ensured that neither signal source 1 nor power amplifier 2 outputs a signal.

[0077] Step 2: Attach the current sensor 6 Figure 3 The common mode current test winding method is arranged on the positive and negative busbars at the output end of the motor.

[0078] Step 3, step 4, step 5 are the same as the differential mode impedance characteristic test

[0079] Step 6: Close the short-circuit switch of the voltage divider test device 7 , use a spectrum analyzer to read the voltage spectrum between the common mode terminal and the ground terminal of the voltage divider test device 7 , and read the current spectrum from the current sensor 6 .

[0080] Step 7: Adjust the gain of power amplifier 2 so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the motor and the power grid, that is, the spectrum of the voltage and current within the sweep range measured by the spectrum analyzer can cover the spectrum of the interference signal. The voltage measured at this time is the common mode voltage U of the injected signal at the motor output end. c Frequency characteristics, such as Fig. 9 The measured current is the common mode current I of the injected signal at the motor output end. c Frequency characteristics, such as Fig.10 Shown

[0081] Step 8: Based on the measured common mode voltage U c and current I c The frequency-amplitude characteristic curve can be used to obtain the common-mode impedance Z of the motor under certain working conditions. c Frequency characteristics, such as Fig.11 shown.

[0082] Will Fig.11 The common mode impedance characteristics obtained by the test are used as the impedance input for the simulation. Fig.12 As shown, the error between the two in the first three main harmonics is less than 5dB.

[0083] The above is a preferred embodiment of the present invention, which is intended to illustrate the typical application of the present invention. The differential mode impedance and common mode impedance tests of the motor are specific implementations of this patent. In addition, this patent is also applicable to other devices under test such as switching power supplies, motors, etc. Due to the diversity of impedance test devices, characteristics of the devices under test and field test conditions, the implementation method of the present invention has greater flexibility, so the present invention should not be limited to the contents disclosed in this embodiment and the accompanying drawings. Therefore, any equivalent or modification that is completed without departing from the spirit disclosed in the present invention, such as changing the sensor type, changing the test frequency range, replacing some devices of the device, implementing some functions of the device, improving or enhancing measures, etc., all fall within the scope of protection of the present invention.

[0084] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. An online impedance test device for high-power equipment in a DC power grid, characterized in that: It includes a signal source, a power amplifier, a current limiting resistor, a transformer, a DC blocking capacitor, a current sensor, a voltage divider test device, and a spectrum analyzer; the signal output end of the signal source is connected to the signal input end of the power amplifier for generating a frequency sweep signal; the signal output end of the power amplifier is connected to the primary coil of the transformer after being connected in series with a current limiting resistor, the power amplifier is used to amplify and inject signals, and the current limiting resistor is used to prevent the output end of the power amplifier from short-circuiting and burning; the secondary coil of the transformer is connected to the DC bus after being connected in series with a DC blocking capacitor, the transformer is used to isolate the power grid to protect the high-power equipment to be tested, and the DC blocking capacitor is used to isolate the high voltage of the DC grid, protect the signal injection device and personnel safety; the DC bus is penetrated into the current sensor to measure the real-time current at the test point; the measuring end of the voltage divider test device is connected in parallel between the positive and negative poles of the DC bus to measure the real-time voltage at the test point; the signal output end of the current sensor and the signal output end of the voltage divider test device are respectively connected to the signal input end of the spectrum analyzer; the power supply end of the high-power equipment to be tested is connected to the DC bus.

2. The on-line impedance test device for high-power equipment in a DC power grid according to claim 1, characterized in that: The current sensor is a Rogowski coil, which includes a soft non-metallic open-and-closed ring frame and a coil wound on the open-and-closed ring frame to avoid metal attraction caused by a strong magnetic field generated by a large current; it also includes a hollow probe, which is connected to the protruding end of the coil to avoid probe saturation caused by a large DC current; the current sensor measures the differential mode current and common mode current of the high-power device to be tested by changing the winding method of the coil.

3. The on-line impedance test device for high-power equipment in a DC power grid according to claim 1, characterized in that: The voltage division test device includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor, a second capacitor, a circuit breaker switch, a discharge switch, and a short-circuit switch; the circuit breaker switch includes a first switch and a second switch that are linked together, the first switch, the first resistor, the discharge switch, and the second switch are sequentially connected in series and then connected in parallel between the positive and negative electrodes of the DC bus, the first switch is connected in series with the positive electrode of the DC bus, and the second switch is connected in series with the negative electrode of the DC bus; the first capacitor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, and the second capacitor are sequentially connected in series and then connected in parallel to both ends of the series circuit of the first resistor and the discharge switch; the short-circuit switch includes a fourth switch and a fifth switch that are linked together, the fourth switch is connected in parallel to both ends of the series circuit of the second resistor and the third resistor, and the fifth switch is connected in parallel to both ends of the series circuit of the fourth resistor and the fifth resistor; the connection point between the first capacitor and the second resistor leads to a first differential mode voltage terminal, and the connection point between the fifth resistor and the second capacitor leads to a second differential mode voltage terminal; the connection point between the third resistor and the fourth resistor leads to a common mode voltage terminal, and is grounded through the sixth resistor in series; The voltage divider test device is connected in parallel to the DC power grid in a high-impedance state, and the differential-mode voltage and common-mode voltage of the high-power device to be tested are measured by changing the switch closing mode.

4. The on-line impedance test device for high-power equipment in a DC power grid according to claim 3, characterized in that: The first resistor is 10 kΩ, the second resistor, the third resistor, the fourth resistor, and the fifth resistor are all 470 Ω, the sixth resistor is 20 kΩ, and the first capacitor and the second capacitor are both 10 uF.

5. An online impedance test device for high-power equipment in a DC power grid according to claim 2 or 3, characterized in that: When used to measure the differential mode current of high-power equipment to be tested, The two ends of the secondary coil of the transformer are connected in parallel between the positive and negative poles of the DC bus. A single-pole DC bus is inserted into the current sensor; The signal input terminal of the spectrum analyzer is respectively connected to the first differential mode voltage terminal and the second differential mode voltage terminal of the voltage division test device; When used to measure the common mode current of high power equipment under test, One end of the secondary coil of the transformer is grounded, and the other end is connected to the positive and negative poles of the DC bus through parallel DC blocking capacitors; The positive and negative poles of the DC bus are inserted into the current sensor; The signal input terminal of the spectrum analyzer is connected to the common mode voltage terminal of the voltage divider test device.

6. A testing method for an online impedance testing device for a DC power grid high-power device based on any one of claims 1 to 5, characterized in that: The following steps are involved: S1: When the high-power device to be tested is powered off, an online impedance test device for a DC power grid high-power device is built, including a signal source, a power amplifier, a current limiting resistor, a transformer, a DC blocking capacitor, a current sensor, a voltage divider test device, and a spectrum analyzer; the signal output end of the signal source is connected to the signal input end of the power amplifier; the signal output end of the power amplifier is connected in series with a current limiting resistor and then connected to the primary coil of the transformer; the secondary coil of the transformer is connected in series with a DC blocking capacitor and then connected to the DC bus; the DC bus is inserted into the current sensor; the measuring end of the voltage divider test device is connected in parallel between the positive and negative poles of the DC bus; the signal output end of the current sensor and the signal output end of the voltage divider test device are respectively connected to the signal input end of the spectrum analyzer; the power supply end of the high-power device to be tested is connected to the DC bus; the test device is connected to the DC side of the high-power device to be tested; S2: The high-power device to be tested is connected to the power grid, and a low current signal is injected into the high-power device to be tested by frequency sweeping; the voltage frequency-amplitude characteristics of the high-power device to be tested are measured; S3: Calculate the impedance characteristics of the high-power device to be tested.

7. The testing method according to claim 6, characterized in that: When testing the differential mode impedance characteristics of the high-power device to be tested, The step S1 further includes the following specific steps: S11: Connect the two ends of the transformer's secondary coil in parallel between the positive and negative poles of the DC bus. S12: A single-pole DC bus is inserted into the current sensor; S13: the signal input terminal of the spectrum analyzer is respectively connected to the first differential mode voltage terminal and the second differential mode voltage terminal of the voltage division test device; S14: Keep the circuit breaker switch, the discharge switch and the short-circuit switch of the voltage dividing test device in the off state; In the step S2, the specific steps are: S21: After the high-power device to be tested is powered on and runs stably, the circuit breaker switch of the voltage division test device is closed. After the charging time t=5RC, the capacitor charging process ends. At this time, there is no DC high voltage at the differential mode terminal; S22: Turn on the signal source and the power amplifier, set the frequency range and amplitude of the signal output by the signal source, and make the signal source work in the sine sweep mode; S23: using a spectrum analyzer to read a voltage spectrum between a first differential mode voltage terminal and a second differential mode voltage terminal of the voltage divider test device, and reading a current spectrum from a current sensor; S24: Adjust the gain of the power amplifier so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the high-power device to be tested and the DC bus, so that the spectrum of the voltage and current within the sweep range measured by the spectrum analyzer covers the spectrum of the interference signal; the voltage measured at this time is the differential mode voltage U of the injected signal at the output end of the high-power device to be tested d Frequency-amplitude characteristics; the measured current is the differential mode current I of the injected signal at the output end of the high-power device to be tested d Frequency-amplitude characteristics; In the step S3, the specific steps are: According to the measured differential mode voltage U d and differential mode current I d The frequency-amplitude characteristic curve is used to calculate the differential mode impedance Z of the high-power device under test under certain working conditions. d Frequency characteristics.

8. The testing method according to claim 6, characterized in that: When testing the common mode impedance characteristics of the high power device to be tested, The step S1 further includes the following specific steps: S11: One end of the secondary coil of the transformer is grounded, and the other end is connected to the positive and negative poles of the DC bus through parallel DC blocking capacitors; S12: The positive and negative electrodes of the current sensor are inserted into the DC bus; S13: The signal input terminal of the spectrum analyzer is connected to the common mode voltage terminal of the voltage divider test device; S14: Keep the circuit breaker switch, the discharge switch and the short-circuit switch of the voltage dividing test device in the off state; In the step S2, the specific steps are: S21: After the high-power device to be tested is powered on and runs stably, the circuit breaker switch of the voltage division test device is closed. After the charging time t=5RC, the capacitor charging process ends. At this time, there is no DC high voltage at the differential mode terminal; S22: Turn on the signal source and the power amplifier, set the frequency range and amplitude of the signal output by the signal source, and make the signal source work in the sine sweep mode; S23: close the short-circuit switch of the voltage divider test device, use a spectrum analyzer to read the voltage spectrum between the common mode terminal and the ground wire of the voltage divider test device, and read the current spectrum from the current sensor; S24: Adjust the gain of the power amplifier so that the amplitude of the injected signal is greater than the intrinsic interference amplitude of the high-power device to be tested and the DC bus, so that the spectrum of the voltage and current within the sweep range measured by the spectrum analyzer covers the spectrum of the interference signal; the voltage measured at this time is the common mode voltage U of the injected signal at the output end of the high-power device to be tested c Frequency-amplitude characteristics; the measured current is the common-mode current I of the injected signal at the output end of the high-power device to be tested c Frequency-amplitude characteristics; In the step S3, the specific steps are: According to the measured common mode voltage U c and common mode current I c The common mode impedance Z of the high-power device to be tested under certain working conditions is calculated by using the frequency-amplitude characteristic curve c Frequency characteristics.

9. A computer storage medium, characterized in that: A computer program executable by a computer processor is stored therein, and the computer program executes an online impedance testing method for a high-power device in a DC power grid as claimed in any one of claims 6 to 8.

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