Differential mode and common mode impedance testing method and device for high-power electrical equipment

Abstract

The invention discloses a differential-mode and common-mode impedance testing method and device for high-power electrical equipment, relates to the technical field of impedance testing of the high-power electrical equipment, and aims to solve the problems that an existing testing method needs to be powered off, interference is strong, online impedance cannot be obtained, and synchronous testing of differential-mode and common-mode impedance cannot be considered. The device comprises a switch module, an impedance adjusting module, a grounding interface, a testing interface and a connecting cable, a common-mode or differential-mode impedance testing loop can be selectively constructed by switching the on-off state of a switch, and normal operation of high-power electrical equipment is not affected after the common-mode or differential-mode impedance testing loop is connected. The test method is realized through the following steps of firstly completing connection between the device and the equipment; during common-mode testing, a corresponding loop is built, three sets of known external common-mode impedances are set, corresponding common-mode currents are collected, and the common-mode impedances are calculated; the loop is switched during the differential mode test, the impedance setting and current acquisition process is repeated, and the differential mode impedance is calculated; and finally outputting test data. The method supports the online test of the high-power electrical equipment, is high in test precision and strong in anti-interference capability, can quickly obtain common-mode and differential-mode impedance parameters, provides reliable data support for filter design and electromagnetic compatibility optimization, and is suitable for the high-power electrical equipment such as a generator set, a permanent magnet motor, an inverter power supply and the like.

Description

Technical Field

[0001] This application relates to the field of electromagnetic compatibility technology for power systems, and in particular to a method and apparatus for testing the differential-mode and common-mode impedance of high-power electrical equipment. Background Technology

[0002] High-power electrical equipment such as generator sets, permanent magnet motors, and inverters can introduce harmonic interference into the power grid. To suppress this interference and improve power quality, filters are typically used. However, to design a suitable filter that avoids adding extra interference frequencies and resonant points to the power grid, it is necessary to know the impedance of the high-power electrical equipment itself. The impedance of high-power electrical equipment is divided into differential-mode impedance and common-mode impedance. Differential-mode impedance refers to the impedance formed when interference flows between phases of the power grid and propagates in opposite directions between phases; common-mode impedance refers to the impedance formed when interference flows between phases and ground and propagates in the same direction between phases.

[0003] Common methods for measuring the differential-mode and common-mode impedance of high-power electrical equipment are divided into offline and online measurements. Offline measurement refers to directly testing the impedance characteristics of the equipment using an impedance analyzer or network analyzer when the equipment is powered off. However, since the equipment is not running, this method cannot obtain the true impedance of the equipment during operation, and the accuracy of the measured impedance characteristics is limited. Online measurement typically uses the signal injection method, which involves injecting signals of different frequencies into the interference source end of the equipment and observing the disturbance on the load side. This method requires injecting signals into the equipment, the impact of which is unknown, and places high demands on the equipment emitting the signals, such as power amplifiers, making it difficult to implement. Summary of the Invention

[0004] To address the limitations of offline impedance characteristic measurement methods for high-power electrical equipment, which have limited accuracy, and the fact that online measurement methods have unknown impacts on the equipment and are difficult to implement, this invention proposes a method and apparatus for testing the differential-mode and common-mode impedances of high-power electrical equipment.

[0005] This invention proposes a method and apparatus for testing differential-mode and common-mode impedance of high-power electrical equipment. The apparatus can realize six different external differential-mode and common-mode impedance access forms through switching. By measuring the change of interference when different external impedances are changed, and combining the algorithm, the differential-mode and common-mode impedance of high-power electrical equipment can be measured.

[0006] This invention provides a differential-mode and common-mode impedance testing device for high-power electrical equipment, the testing device comprising:

[0007] The access unit includes two access modules with identical structures. Each access module includes an access point, an access switch, and a first resistor connected in series.

[0008] The resistor switching unit includes two resistor switching modules with the same structure. Each resistor switching module includes a second resistor connected in parallel, a resistor short-circuit switch, and a resistor access switch and a third resistor connected in series. One end of each of the two resistor switching modules is connected to the first resistor of the two access modules respectively.

[0009] The voltage divider and differential mode unit includes a first node, a fourth resistor, a second node, a fifth resistor, a third node and a differential mode voltage switch connected in series. The two ends of the voltage divider and differential mode unit are respectively connected to the other ends of the two resistor switching modules of the resistor switching unit.

[0010] In some embodiments, the test c device further includes:

[0011] The grounding module includes a sixth resistor and a grounding switch for controlling the grounding of the sixth resistor. The grounding module is connected to the voltage divider and differential mode unit near one end of the differential mode voltage switch.

[0012] In some embodiments, the testing apparatus further includes:

[0013] The voltage divider and differential mode short-circuit switch is connected to both ends of the voltage divider and differential mode unit.

[0014] In some embodiments, the resistance of the first resistor is 10kΩ;

[0015] The resistance of the second resistor is 20kΩ;

[0016] The resistance of the third resistor is 20kΩ;

[0017] The resistance of the fourth resistor is 1kΩ;

[0018] The fifth resistor has a resistance of 9kΩ;

[0019] The sixth resistor has a resistance of 20kΩ.

[0020] This invention provides a method for testing the differential-mode and common-mode impedance of high-power electrical equipment, based on the testing apparatus described in any of the above embodiments, the method comprising:

[0021] Test preparation phase:

[0022] Connect the two access points of the test device to the two ends of the load of the high-power electrical equipment to confirm that the high-power electrical equipment is in normal operating condition.

[0023] Common-mode impedance test:

[0024] Set the access switch, grounding switch, voltage divider and differential mode short circuit switch to normally closed, and set the differential mode voltage switch to normally open to construct a common mode impedance test circuit;

[0025] By controlling the resistor short-circuit switch and resistor access switch of the resistor switching unit, the resistance value of the test device is changed, and three sets of external common-mode impedances Zcm_in1, Zcm_in2, and Zcm_in3 are obtained. The external common-mode currents Icm1, Icm2, and Icm3 under the corresponding impedances are collected by the current probes respectively.

[0026] The common-mode impedance Zcm of high-power electrical equipment is determined based on Zcm_in1, Zcm_in2, Zcm_in3 and Icm1, Icm2, Icm3;

[0027] Differential-mode impedance testing:

[0028] Set the access switch and the differential mode voltage switch to normally closed, and set the voltage divider and differential mode short circuit switch and the grounding switch to normally open to construct a differential mode impedance test circuit;

[0029] By controlling the resistor short-circuit switch and resistor access switch of the resistor switching unit, the resistance value of the test device is changed, and three sets of external differential mode impedances Zdm_in1, Zdm_in2, and Zdm_in3 are obtained. The load-side differential mode currents Idm_l1, Idm_l2, and Idm_l3 under the corresponding impedances are collected by the current probe.

[0030] The differential mode impedance Zdm of high-power electrical equipment is determined based on Zdm_in1, Zdm_in2, Zdm_in3 and Idm_l1, Idm_l2, Idm_l3.

[0031] In some embodiments, determining the common-mode impedance Zcm of the high-power electrical equipment based on Zcm_in1, Zcm_in2, Zcm_in3, and Icm1, Icm2, and Icm3 includes:

[0032]

[0033] By solving the system of equations, we can obtain

[0034]

[0035] Z cm_l =-(I cm1* I cm2* Z cm_in1* Z cm_in3 -I cm1* I cm3* Z cm_in1 *Z cm_in2 -I cm1* I cm2* Z cm_in2* Z cm_in3 +I cm2* I cm3* Z cm_in1*Z cm_in2 +I cm2* I cm3* Z cm_in1* Z cm_in3 ) / (I cm1* I cm2* Z cm_in1 -I cm1* I cm2* Z cm_in2 -I cm1* I cm3* Z cm_in1 +I cm1* I cm3* Z cm_in3 +I cm2* I cm3* Z cm_in2 -I cm2* I cm3* Z cm_in3 ).

[0036] In some embodiments, determining the differential-mode impedance Zdm of the high-power electrical equipment based on Zdm_in1, Zdm_in2, Zdm_in3, and Idm_l1, Idm_l2, and Idm_l3 includes:

[0037]

[0038] By solving the system of equations, we can obtain:

[0039]

[0040] Utilizing the technological achievements of this invention, a test device and a method for simultaneously measuring the differential-mode and common-mode impedances of high-power electrical equipment can be developed. By switching different switches on the test device, different external impedances can be achieved without introducing additional interference or resonant points, thus having no impact on the equipment. Furthermore, by combining test data and software programs while the equipment is powered on, accurate measurement of the differential-mode and common-mode impedances of any high-power electrical equipment can be achieved, laying the foundation for subsequent filter design. Attached Figure Description

[0041] The accompanying drawings illustrate, by way of example and not limitation, the various embodiments discussed herein.

[0042] Figure 1 This is a schematic diagram of a high-power electrical device.

[0043] Figure 2 For common-mode current loops of high-power electrical equipment;

[0044] Figure 3 To simplify the common-mode circuit for high-power electrical equipment;

[0045] Figure 4 Circuit diagram of a differential-mode and common-mode impedance testing device for high-power electrical equipment;

[0046] Figure 5 The common-mode circuit and equivalent diagram after the test device is connected to the circuit;

[0047] Figure 6 For differential mode current loops in high-power electrical equipment;

[0048] Figure 7 To simplify the differential mode circuit of high-power electrical equipment;

[0049] Figure 8 The differential mode circuit and equivalent diagram after the test device is connected to the circuit;

[0050] Figure 9 This is a physical image of a device for testing the differential and common mode impedances of high-power electrical equipment. Detailed Implementation

[0051] In order to gain a more detailed understanding of the features and technical content of the embodiments of this application, the implementation of the embodiments of this application will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for reference and illustration only and are not intended to limit the embodiments of this application.

[0052] In the embodiments described in this application, it should be noted that, unless otherwise stated and limited, the term "connection" should be interpreted broadly. For example, it can be an electrical connection, or a connection between two internal components. It can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above term according to the specific circumstances.

[0053] It should be noted that the terms "first," "second," and "third" used in the embodiments of this application are merely used to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first," "second," and "third" can be interchanged in a specific order or sequence where permitted. It should be understood that the objects distinguished by "first," "second," and "third" can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in an order other than those illustrated or described herein.

[0054] A schematic diagram of a high-power electrical equipment is shown below. Figure 1 As shown, the casing is grounded via a grounding cable. Due to the presence of a common-mode voltage source in high-power electrical equipment, such as... Figure 2As shown, common-mode current forms a loop through the equipment and ground, thus generating common-mode current. Because the frequency and energy of common-mode interference from high-power electrical equipment are relatively high, it can flow into other sensitive equipment through the ground loop, which is detrimental to the normal operation of the system. To model and suppress common-mode current, it is necessary to clarify the common-mode impedance of the high-power electrical equipment and design corresponding filters based on the impedance. For example... Figure 3 As shown, according to Thevenin's law, the common-mode circuit is simplified, where U cm For common-mode voltage, I cm For common-mode current, Z cm Z represents the common-mode impedance to ground of high-power electrical equipment. cm l This is the load's impedance to ground.

[0055] Therefore, we can conclude that:

[0056]

[0057] Among them, only the common-mode current I cm It can be obtained through testing, U cm Z cm_l Since both are unknown, the common-mode impedance of high-power electrical equipment cannot be determined. The circuit diagram of the differential-mode and common-mode impedance testing device for high-power electrical equipment designed in conjunction with this invention is shown below. Figure 4 As shown in the image, and in the actual product picture. Figure 9 As shown.

[0058] like Figure 4 The differential-mode and common-mode testing device for high-power electrical equipment described in this application embodiment includes:

[0059] The access unit 110 includes two access modules with the same structure, namely the first access module 111 and the second access module 112 with the same structure. The access module includes an access position, an access switch S1 and a first resistor R1 connected in series. Here, the access position includes the first access position 1 and the second access position 2, which are respectively set in the first access module 111 and the second access module 112.

[0060] The resistor switching unit 120 includes two resistor switching modules with the same structure, namely a first resistor switching module 121 and a second resistor module 122 with the same structure. Each resistor switching module includes a second resistor R2 connected in parallel, a resistor short-circuit switch S2, and a resistor access switch S3 and a third resistor R3 connected in series. One end of each resistor switching module is connected to the first resistor of the two access modules respectively. The first resistor switching module 121 is connected to the first access module 111, and the second resistor module 122 is connected to the second access module 112.

[0061] The voltage divider and differential mode unit 130 includes a first node a, a fourth resistor R4, a second node b, a fifth resistor R5, a third node c and a differential mode voltage switch S4 connected in series. The two ends of the voltage divider and differential mode unit 130 are respectively connected to the other ends of the two resistor switching modules of the resistor switching unit 120.

[0062] The grounding module 140 includes a sixth resistor R6 and a grounding switch S6 for controlling the grounding of the sixth resistor R6. The grounding module 140 is connected to one end of the differential mode voltage switch S4 of the voltage divider and differential mode unit 130.

[0063] The voltage divider and differential mode short-circuit switch S5 is connected to both ends of the voltage divider and differential mode unit 130.

[0064] In some embodiments, the first resistor R1 has a resistance of 10kΩ.

[0065] The second resistor R2 has a resistance of 20kΩ.

[0066] The third resistor R3 has a resistance of 20kΩ.

[0067] The fourth resistor, R4, has a resistance of 1kΩ.

[0068] The fifth resistor, R5, has a resistance of 9kΩ.

[0069] The sixth resistor, R6, has a resistance of 20kΩ.

[0070] When testing the common-mode impedance of high-power electrical equipment, S1, S5, and S6 are normally closed, and S4 is normally open. The test device is connected to the circuit. The schematic diagram and equivalent diagram are shown below. Figure 5 As shown.

[0071] The common-mode voltage source and common-mode internal resistance of high-power electrical equipment do not change with external impedance; they are only related to the internal composition of the equipment. By changing the value of the resistor in the impedance testing device, i.e., changing the Z-axis in the equivalent circuit diagram... cm_in The following formula can be obtained:

[0072]

[0073] Among them I cm1 I cm2 I cm3 Z can be obtained through current probe testing. cm_in1 Z cm_in2 Z cm_in3 All are known. By solving the system of equations and running the software program, we can obtain:

[0074]

[0075] Z cm_l =-(I cm1* Icm2* Z cm_in1* Z cm_in3 -I cm1* I cm3* Z cm_in1 *Z cm_in2 -I cm1* I cm2* Z cm_in2* Z cm_in3 +I cm2* I cm3* Z cm_in1* Z cm_in2 +I cm2* I cm3* Z cm_in1*

[0076] Z cm_in3 ) / (I cm1* I cm2* Z cm_in1 -I cm1* I cm2* Z cm_in2 -I cm1* I cm3* Z cm_in1 +I cm1* I cm3* Z cm_in3 +I cm2* I cm3* Z cm_in2 -I cm2* I cm3* Z cm_in3 ).

[0077] Due to the presence of differential mode current sources in high-power electrical equipment, such as Figure 6 As shown, common-mode current forms a loop through the phases of the equipment, resulting in differential-mode current. Because the energy of differential-mode interference in high-power electrical equipment is significant, it can flow into other sensitive equipment through the phase-to-phase connections, hindering the normal operation of the system. To suppress differential-mode current, it is necessary to clarify the differential-mode impedance of the high-power electrical equipment and design appropriate filters based on the impedance. For example... Figure 7 As shown, according to Thevenin's law, the common-mode circuit is simplified, where Udm is the differential-mode current source, Idm is the differential-mode current, Zdm is the differential-mode impedance of the high-power electrical equipment, and Zdm_l is the load impedance.

[0078] Therefore, we can conclude that:

[0079]

[0080] Among them, only the differential mode current I dm_l It can be obtained through testing, I dm Z dm_lSince both are unknown, the differential-mode impedance of the high-power electrical equipment cannot be determined. A high-power electrical equipment differential-mode and common-mode impedance testing device is connected. When testing the differential-mode impedance of the high-power electrical equipment, normally closed S1 and S4, and normally open S5 and S6, are used. The schematic diagram and equivalent diagram are shown below. Figure 8 As shown.

[0081] The differential mode current source and differential mode internal resistance of high-power electrical equipment do not change with external impedance; they are only related to the internal composition of the equipment. By changing the value of the resistor in the impedance testing device, i.e., changing the Z-axis in the equivalent circuit diagram... dm_in The following formula can be obtained:

[0082]

[0083] Among them I dm_l1 I dm_l2 I dm_l3 Z can be obtained through current probe testing. dm_in1 Z dm_in2 Z dm_in3 All are known. By solving the system of equations and running the program, we can obtain:

[0084]

[0085] Utilizing the technological achievements of this invention, a test device and a method for simultaneously measuring the differential-mode and common-mode impedances of high-power electrical equipment can be developed. By switching different switches on the test device, different external impedances can be achieved without introducing additional interference or resonant points, thus having no impact on the equipment. Furthermore, by combining test data and software programs while the equipment is powered on, accurate measurement of the differential-mode and common-mode impedances of any high-power electrical equipment can be achieved, laying the foundation for subsequent filter design.

[0086] The technical solutions described in the embodiments of this application can be combined arbitrarily without conflict.

[0087] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A differential mode and common mode impedance testing device for high power electrical equipment, characterized by, The test device comprises: an access unit comprising two access modules of the same structure, the access module comprising an access position, an access switch and a first resistor connected in series; a resistance switching unit comprising two resistance switching modules of the same structure, the resistance switching module comprising a second resistor, a resistance short-circuit switch and a resistance access switch and a third resistor connected in series, and the two resistance switching modules being connected at one end to the first resistor of the two access modules; a voltage dividing and differential mode unit comprising a first node, a fourth resistor, a second node, a fifth resistor, a third node and a differential mode voltage switch connected in series, and the voltage dividing and differential mode unit being connected at two ends to the other end of the two resistance switching modules of the resistance switching unit.

2. The differential mode and common mode impedance testing device for high power electrical equipment of claim 1, wherein, The test device further comprises: a grounding module comprising a sixth resistor and a grounding switch for controlling the grounding of the sixth resistor, and the grounding module being connected to the voltage dividing and differential mode unit near the end of the differential mode voltage switch.

3. The differential mode and common mode impedance testing device for high power electrical equipment of claim 2, wherein, The test device further comprises: a voltage dividing and differential mode short-circuit switch connected to the two ends of the voltage dividing and differential mode unit.

4. The differential mode and common mode impedance testing device for high power electrical equipment of claim 2, wherein, The first resistor has a resistance of 10kΩ; The second resistor has a resistance of 20kΩ; The third resistor has a resistance of 20kΩ; The fourth resistor has a resistance of 1kΩ; The fifth resistor has a resistance of 9kΩ; The sixth resistor has a resistance of 20kΩ.

5. A differential mode and common mode impedance testing method for a high-power electrical device, based on the test device according to any one of claims 1 to 4, the method comprising: a test preparation stage: connecting the two access positions of the test device to the two ends of the load of the high-power electrical device respectively, and confirming that the high-power electrical device is in a normal operating state; a common mode impedance testing stage: setting the access switch, the grounding switch and the voltage dividing and differential mode short-circuit switch to be normally closed, and setting the differential mode voltage switch to be normally open, to construct a common mode impedance testing circuit; controlling the resistance short-circuit switch and the resistance access switch of the resistance switching unit to change the resistance value of the test device, to obtain three groups of external common mode impedances Zcm_in1, Zcm_in2 and Zcm_in3, and using a current probe to collect external common mode currents Icm1, Icm2 and Icm3 under the corresponding impedances; determining the common mode impedance Zcm of the high-power electrical device according to Zcm_in1, Zcm_in2, Zcm_in3, Icm1, Icm2 and Icm3; a differential mode impedance testing stage: setting the access switch and the differential mode voltage switch to be normally closed, and setting the voltage dividing and differential mode short-circuit switch and the grounding switch to be normally open, to construct a differential mode impedance testing circuit; controlling the resistance short-circuit switch and the resistance access switch of the resistance switching unit to change the resistance value of the test device, to obtain three groups of external differential mode impedances Zdm_in1, Zdm_in2 and Zdm_in3, and using a current probe to collect load side differential mode currents Idm_l1, Idm_l2 and Idm_l3 under the corresponding impedances; determining the differential mode impedance Zdm of the high-power electrical device according to Zdm_in1, Zdm_in2, Zdm_in3, Idm_l1, Idm_l2 and Idm_l3.

6. The method of differential mode and common mode impedance testing of high power electrical equipment of claim 5, wherein, The common-mode impedance Zcm of the high-power electrical equipment is determined according to Zcm_in1, Zcm_in2, Zcm_in3, Icm1, Icm2 and Icm3, and includes: By solving the equation set, the following can be obtained where Z cm_l = - (I cm1* I cm2* Z cm_in1* Z cm_in3 - I cm1* I cm3* Z cm_in1 * Z cm_in2 - I cm1* I cm2* Z cm_in2* Z cm_in3 + I cm2* I cm3* Z cm_in1* Z cm_in2 + I cm2* I cm3* Z cm_in1* Z cm_in3 ) / (I cm1* I cm2* Z cm_in1 - I cm1* I cm2* Z cm_in2 - I cm1* I cm3* Z cm_in1 + I cm1* I cm3* Z cm_in3 + I cm2* I cm3* Z cm_in2 - I cm2* I cm3* Z cm_in3 ).

7. The method of differential mode and common mode impedance testing of high power electrical equipment of claim 5, wherein, The differential-mode impedance Zdm of the high-power electrical equipment is determined according to Zdm_in1, Zdm_in2, Zdm_in3, Idm_l1, Idm_l2 and Idm_l3, and includes: By solving the equation set, the following can be obtained:

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