Non-contact measurement method of power device switching voltage based on differential electric field coupling

Abstract

The present invention is a non-contact measurement method for the switch voltage of a power device based on differential electric field coupling, comprising a differential electric field coupling probe and a differential signal processing circuit; the differential electric field coupling probe uses a PCB board as a carrier, the PCB board contains at least four layers of metal plate structure, which are respectively a shielding layer No. 1, a measuring layer, a sensing layer and a shielding layer No. 2 from top to bottom, and each layer is separated by an insulating medium; an array of through holes is provided in the middle of the PCB board, and the PCB board is divided into a left and a right part, so that the left half of the measuring layer and the left half of the sensing layer form a sensing end No. 1 and form a coupling capacitor No. 1, and the right half of the measuring layer and the right half of the sensing layer form a sensing end No. 2 and form a coupling capacitor No. 2; the measuring layers of the two sensing ends are both connected to the power device, and the sensing layers of the two sensing ends are both connected to the input end of the differential signal processing circuit. The probe measures the potential signals at two points to be measured of the power device through the two sensing ends, without considering the common ground problem, and has a wider range of applicable occasions.

Description

Technical Field

[0001] The present invention belongs to the technical field of power device voltage sensing, and in particular to a non-contact measurement method for a power device switch voltage based on differential electric field coupling. Background Art

[0002] Accurately measuring the switching voltage of power devices is a prerequisite for calculating switching losses, extracting junction temperature, real-time status detection, and reliability assessment. Therefore, switching voltage measurement plays an important role in power electronic systems. Wide bandgap semiconductor devices are widely used in power electronic systems due to their advantages such as high switching speed, high thermal conductivity, and high critical breakdown field strength. They provide a basis for the optimized design of power electronic systems and the high-frequency, miniaturization, and high-efficiency development of power modules. At the same time, they also put forward requirements for voltage probes such as high bandwidth, low intrusion, high voltage resistance, high anti-interference, and integration.

[0003] At present, common voltage probes have the following main problems in measuring the switching voltage of power devices. First, when measuring the switching voltage, the oscilloscope probe needs to be in direct contact with the circuit under test, so it is inevitable to introduce parasitic parameters into the main circuit. The input resistance and input capacitance of the oscilloscope probe are the main parasitic parameters introduced. The lower the input resistance, the more obvious the load effect of the oscilloscope probe on the main circuit, and the input capacitance will cause phase shifts in waveforms of different frequencies. As the frequency increases, the phase shift gradually increases, resulting in delays in the measured voltage signal and even distortion. Second, traditional single-ended probes need to consider the common ground problem and cannot measure the voltage of any port. For example, when using a single-ended probe to measure the switching voltage of the upper arm of a bridge circuit, the ground wire of the single-ended probe is connected to the midpoint of the bridge circuit, that is, the drain of the lower MOSFET, and the ground of the high-voltage power supply is connected to the source of the lower MOSFET. Since the high-voltage power supply and the ground of the single-ended probe are at the same potential, the lower arm of the bridge circuit is short-circuited, thereby changing the topological structure of the main circuit, and may also generate unexpected large currents, resulting in damage to experimental instruments or devices, causing unnecessary economic losses. Third, traditional differential probes are expensive and have low bandwidth, which cannot meet the switching voltage measurement requirements of power devices at high switching speeds. When measuring the switching voltage of a power device with a rise time of 10ns, in order to accurately measure its switching voltage waveform, the bandwidth of the differential probe needs to reach hundreds of MHz or more. Taking the Tek P5200 as an example, its price is as high as 10,000 yuan and its bandwidth is only 100MHz, which cannot meet the measurement requirements. Fourth, the test hook of the traditional high-voltage differential probe is large in size and cannot cope with the test environment of high-power density power electronic systems. Summary of the invention

[0004] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a non-contact measurement method for the switching voltage of a power device based on differential electric field coupling.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A non-contact measurement method for a power device switch voltage based on differential electric field coupling comprises a differential electric field coupling probe and a differential signal processing circuit; the differential electric field coupling probe uses a PCB board as a carrier, the PCB board contains at least four layers of metal plate structure, which are respectively a No. 1 shielding layer, a measuring layer, a sensing layer and a No. 2 shielding layer from top to bottom, and each layer is separated by an insulating medium; an array of through holes is arranged in the middle of the PCB board, and the PCB board is divided into a left and a right part, so that the left half of the measuring layer and the left half of the sensing layer constitute a No. 1 sensing end and form a No. 1 coupling capacitor, and the right half of the measuring layer and the right half of the sensing layer constitute a No. 2 sensing end and form a No. 2 coupling capacitor; the through hole is a copper hole groove, and the upper and lower ends of the through hole are respectively connected to the No. 1 shielding layer and the No. 2 shielding layer; the measuring layers of the two sensing ends are respectively connected to the power device, and the sensing layers of the two sensing ends are respectively connected to the input end of the differential signal processing circuit, and the sensing end is used to collect the changing voltage at the connection point between the measuring layer and the power device.

[0007] Furthermore, when the power device is a MOSFET tube, the measurement layer of one sensing end is connected to the drain of the MOSFET tube, and the measurement layer of the other sensing end is connected to the source of the MOSFET tube; when the power device is an IGBT, the measurement layer of one sensing end is connected to the collector of the IGBT, and the measurement layer of the other sensing end is connected to the emitter of the IGBT.

[0008] Furthermore, the radius of the through hole is 0.1-1 mm, and the through hole spacing is 0.1-0.5 mm.

[0009] Furthermore, the differential signal processing circuit includes a voltage restoration circuit, a voltage follower circuit and a differential operation circuit; the voltage restoration circuit includes grounding capacitors C3 and C4, grounding resistors R1 and R2, the voltage follower circuit includes an operational amplifier No. 1 and an operational amplifier No. 2, and the differential operation circuit includes resistors R3 to R6 and an operational amplifier No. 3;

[0010] The first coupling capacitor C1 is connected to the positive input terminal of the first operational amplifier, one end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the positive input terminal of the first operational amplifier, and the other end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the ground; the output terminal of the first operational amplifier is connected to the inverting input terminal to realize negative feedback; the second coupling capacitor C2 is connected to the positive input terminal of the second operational amplifier, one end of the grounding resistor R2 and the grounding capacitor C4 connected in parallel is connected to the positive input terminal of the second operational amplifier, and the grounding resistor R2 and the grounding capacitor C4 are connected in parallel. The other end of the resistor R4 is connected to the output end of the operational amplifier No. 2, and the other end is connected to the inverting input end of the operational amplifier No. 3 to achieve negative feedback. One end of the resistor R3 is connected to the output end of the operational amplifier No. 1, and the other end is connected to the non-inverting input end of the operational amplifier No. 3. One end of the resistor R5 is connected to the non-inverting input end of the operational amplifier No. 3, and the other end is grounded. One end of the resistor R4 is connected to the output end of the operational amplifier No. 2, and the other end is connected to the inverting input end of the operational amplifier No. 3. One end of the resistor R6 is connected to the inverting input end of the operational amplifier No. 3, and the other end is connected to the output end of the operational amplifier No. 3.

[0011] Furthermore, when the number of layers of the PCB board is greater than four, the multilayer structure located in the middle constitutes a multilayer electric field coupling structure in the form of alternating arrangement of measurement layers and sensing layers, and coupling capacitors are formed between adjacent measurement layers and sensing layers. The coupling capacitors of the entire sensing end are equivalent to multiple coupling capacitors in parallel.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. Since the single-ended probe measures the voltage to ground of one point of the power device, it will be constrained by the common ground problem during the voltage measurement process, and cannot meet the measurement requirements of the power device under different working conditions. For example, when using a single-ended probe to measure the switching voltage of the upper bridge arm of the bridge circuit, the ground wire of the single-ended probe is connected to the drain of the lower bridge arm MOSFET tube, and the ground of the high-voltage power supply is connected to the source of the lower bridge arm MOSFET tube. Since the high-voltage power supply and the ground of the single-ended probe are at the same potential, the lower bridge arm of the bridge circuit is short-circuited, thereby changing the topology of the main circuit. Therefore, the differential electric field coupling probe of the present application includes two sensing ends, which respectively measure the potential signals at the two points to be measured of the power device, and then the terminal voltage of the power device is obtained by subtracting the two potential signals through the differential signal processing circuit, without considering the common ground problem, and is applicable to a wider range of occasions.

[0014] 2. During the measurement process, the inductive layer of the probe will not come into direct contact with the power device, which can effectively reduce the invasiveness of the probe. Since the differential electric field coupling probe uses the PCB board as a carrier, the differential electric field coupling probe and the differential signal processing circuit can be integrated on the PCB board. The differential electric field coupling probe and the differential signal processing circuit have no direct electrical connection with the PCB board of the power device, which further reduces the invasiveness while meeting the integrated development of power electronic systems. The differential electric field probe is composed of a PCB circuit board, has a simple structure, and has a millimeter-level volume, which can realize voltage measurement in a narrow space. The probe has the characteristics of high bandwidth, low intrusion, high voltage resistance, small size, high anti-interference and voltage isolation. It can meet the measurement requirements of the dynamic voltage of power devices in high power density power electronic systems, and provide important information support for the reliable operation, optimized design, life prediction, and switching loss calculation of power devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the measurement principle diagram of the present invention;

[0016] Figure 2 This is the structural diagram of the differential electric field coupling probe;

[0017] Figure 3 is a topological diagram of a differential signal processing circuit;

[0018] Figure 4 is the lumped parameter model of a single-ended electric field coupling probe;

[0019] Figure 5 This is the schematic diagram of the differential operation circuit. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods, but the protection scope of the present application is not limited thereto.

[0021] The present invention discloses a non-contact measurement method for the switching voltage of a power device based on differential electric field coupling. The method collects a potential signal during the switching process of the power device through a differential electric field coupling probe. After the potential signal is processed by a differential signal processing circuit, an attenuated voltage signal during the switching process of the power device is obtained and displayed on an oscilloscope.

[0022] like Figure 2As shown, the differential electric field coupling probe uses a PCB board as a carrier, and the PCB board contains at least four layers of metal plate structure, which are respectively a shielding layer No. 1, a measuring layer, a sensing layer and a shielding layer No. 2 from top to bottom, and each layer is separated by an insulating medium, and the shielding layer, the measuring layer and the sensing layer are all realized by copper cladding; an array of through holes is provided in the middle position of the PCB board, and the PCB board is divided into a left and a right part, so that the left half of the measuring layer and the left half of the sensing layer constitute a sensing end No. 1, and form a coupling capacitor No. 1, and the right half of the measuring layer and the right half of the sensing layer constitute a sensing end No. 2, and form a coupling capacitor No. 2; the through hole is a copper hole groove, and the upper and lower ends of the through hole are respectively connected to the shielding layer No. 1 and the shielding layer No. 2; the through hole is to shield the electric field between the two sensing ends, so as to achieve the purpose of suppressing interference, and avoid the formation of an additional coupling capacitor between the two sensing ends, resulting in the mutual interference of the two voltage signals obtained by the two sensing ends;

[0023] The measuring layers of the two sensing ends are respectively connected to the power device, and the sensing layers of the two sensing ends are respectively connected to the input end of the differential signal processing circuit; during the switching process of the power device, a changing potential signal appears on the measuring layer of the sensing end, and the changing potential signal is obtained through the coupling capacitor, so the sensing end is used to collect the changing voltage at the connection point between the measuring end and the power device; the differential signal processing circuit processes the voltage obtained by coupling the two coupling capacitors to obtain the switching voltage of the power device; when the power device is a MOSFET tube, the measuring layer of one of the sensing ends is connected to the drain of the MOSFET tube (i.e., the power device to be tested point 1), and the measuring layer of the other sensing end is connected to the source of the MOSFET tube (i.e., the power device to be tested point 2); when the power device is an IGBT, the measuring layer of one of the sensing ends is connected to the collector of the IGBT (i.e., the power device to be tested point 1), and the measuring layer of the other sensing end is connected to the emitter of the IGBT (i.e., the power device to be tested point 2).

[0024] like Figure 3 As shown, the differential signal processing circuit includes a voltage restoration circuit, a voltage follower circuit and a differential operation circuit; the voltage restoration circuit includes grounding capacitors C3 and C4, grounding resistors R1 and R2, the voltage follower circuit includes an operational amplifier No. 1 and an operational amplifier No. 2, and the differential operation circuit includes resistors R3 to R6 and an operational amplifier No. 3;

[0025] The first coupling capacitor C1 is connected to the positive input terminal of the first operational amplifier, one end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the positive input terminal of the first operational amplifier, and the other end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the ground; the parallel grounding resistor R1 and the grounding capacitor C3 perform attenuation and restoration processing on the potential signal coupled to the first coupling capacitor C1, and transmit it to the first operational amplifier, and the output terminal of the first operational amplifier is connected to the inverting input terminal to realize negative feedback, forming a voltage follower; similarly, the second coupling capacitor C2 is connected to the positive input terminal of the second operational amplifier, one end of the grounding resistor R2 and the grounding capacitor C4 connected in parallel is connected to the positive input terminal of the second operational amplifier, and the other end of the grounding resistor R2 and the grounding capacitor C4 connected in parallel is grounded; the parallel grounding resistor R2 and the grounding capacitor C4 are connected in parallel. The ground capacitor C4 performs attenuation and restoration processing on the potential signal coupled to the No. 2 coupling capacitor C2, and transmits it to the No. 2 operational amplifier; the output end of the No. 2 operational amplifier is connected to the inverting input end to realize negative feedback, forming another voltage follower; the voltage follower has a large input impedance and a small output impedance, which can reduce the impact on the signal source and has a certain buffering and isolation effect; one end of the resistor R3 is connected to the output end of the No. 1 operational amplifier, and the other end is connected to the non-inverting input end of the No. 3 operational amplifier; one end of the resistor R5 is connected to the non-inverting input end of the No. 3 operational amplifier, and the other end is grounded; one end of the resistor R4 is connected to the output end of the No. 2 operational amplifier, and the other end is connected to the inverting input end of the No. 3 operational amplifier; one end of the resistor R6 is connected to the inverting input end of the No. 3 operational amplifier, and the other end is connected to the output end of the No. 3 operational amplifier. The resistance values ​​of resistors R3 and R4 are equal, and the resistance values ​​of resistors R5 and R6 are equal. The attenuation multiple of the differential signal can be adjusted by adjusting the resistance ratio of resistors R5 and R3. The potential signal obtained by coupling two coupling capacitors passes through the differential operation circuit to obtain the terminal voltage of the power device. The differential signal processing circuit transmits the terminal voltage of the power device to the oscilloscope, and then dynamically displays the voltage of the power device during the switching process in the oscilloscope.

[0026] The number of layers of the PCB board is an even number greater than four, preferably 4, 6, or 8 layers; the multilayer structure located in the middle forms a multilayer electric field coupling structure in the form of alternating arrangement of measurement layers and sensing layers, and coupling capacitors are formed between adjacent measurement layers and sensing layers. Therefore, the coupling capacitor of the entire sensing end can be equivalent to multiple coupling capacitors in parallel. The multilayer electric field coupling structure can increase the coupling capacitance value under the condition that the areas of the sensing layer and the measurement layer remain unchanged. The larger the coupling capacitance value, the larger the voltage obtained by coupling, thereby improving the sensitivity of the differential electric field coupling probe and allowing the attenuation multiple of the differential electric field coupling probe to have a larger selection range.

[0027] The radius of the through hole is in the range of 0.1 to 1 mm, and the through hole spacing is in the range of 0.1 to 0.5 mm. To ensure that the through hole has good suppression capability, the smaller the radius of the through hole and the denser the spacing, the better the shielding effect.

[0028] Regarding the coupling capacitance between the measuring layer and the sensing layer, firstly, the coupling capacitance value can be adjusted by changing the area of ​​the measuring layer and the sensing layer; secondly, the coupling capacitance value can be adjusted by changing the spacing between the measuring layer and the sensing layer by changing the PCB manufacturing process, while the condition that the insulating medium is not broken down needs to be met; thirdly, the coupling capacitance value can also be adjusted by changing the type of insulating medium between the PCB layers.

[0029] The shielding layer is realized by fully copper-cladding the PCB and is located at the top and bottom layers of the PCB board. The shielding layer is larger than the area of ​​the measuring layer and the sensing layer and completely surrounds the measuring layer and the sensing layer. Both shielding layers are connected to the ground of the differential signal processing circuit to improve the ability of the differential electric field coupling probe to suppress external electromagnetic interference.

[0030] Figure 4 It is the lumped parameter model of the single-ended electric field coupling probe. The single-ended electric field coupling probe consists of a sensing end and a processing circuit. A coupling capacitor C is formed between the measuring layer and the sensing layer of the sensing end. coupling ; V ds is the terminal voltage across the power device under test, C d , R d are the grounding capacitance and grounding resistance of the processing circuit, V dot To process the inductive voltage output by the circuit; coupling capacitor C coupling Usually several hundred fF, grounding capacitance is pF level, grounding resistance R d More than 500MΩ; Figure 4 It can be deduced that the transfer function of the single-ended electric field coupling probe is:

[0031]

[0032] In the formula, j represents the imaginary unit, ω represents the angular frequency;

[0033] When ω(C d +C coupling )R d >>1, the transfer function of the single-ended electric field coupling probe is:

[0034]

[0035] Figure 5 This is the schematic diagram of the differential operation circuit. Operational amplifier No. 1 and operational amplifier No. 2 meet the virtual short and virtual break principle under negative feedback conditions. Under the condition of R3 / / R5=R4 / / R6, the output voltage of the differential electric field coupling probe is:

[0036]

[0037] Where Vi+ 、V i- Respectively represent the output voltages of the two operational amplifiers of the voltage follower circuit;

[0038] When R3=R4, the output voltage is proportional to the voltage difference, and the output voltage of the differential electric field coupling probe is further equivalent to:

[0039]

[0040] The output voltage of the differential signal processing circuit is the terminal voltage of the power device after attenuation. The oscilloscope digitally restores the output voltage of the differential signal processing circuit and displays the terminal voltage of the power device in real time on the oscilloscope during the switching process of the power device.

[0041] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A non-contact measurement method for power device switch voltage based on differential electric field coupling, comprising a differential electric field coupling probe and a differential signal processing circuit; characterized in that: The differential electric field coupling probe uses a PCB board as a carrier. The PCB board contains at least four layers of metal plate structure, which are respectively a shielding layer No. 1, a measuring layer, a sensing layer and a shielding layer No. 2 from top to bottom, and each layer is separated by an insulating medium; an array of through holes is provided in the middle position of the PCB board, and the PCB board is divided into a left and a right part, so that the left half of the measuring layer and the left half of the sensing layer constitute a sensing end No. 1 and form a coupling capacitor No. 1, and the right half of the measuring layer and the right half of the sensing layer constitute a sensing end No. 2 and form a coupling capacitor No. 2; the through hole is a copper hole groove, and the upper and lower ends of the through hole are respectively connected to the shielding layer No. 1 and the shielding layer No. 2; the measuring layers of the two sensing ends are respectively connected to the power device, and the sensing layers of the two sensing ends are respectively connected to the input end of the differential signal processing circuit, and the sensing end is used to collect the changing voltage at the connection point between the measuring layer and the power device.

2. The non-contact measurement method of power device switch voltage based on differential electric field coupling according to claim 1, characterized in that: When the power device is a MOSFET tube, the measurement layer of one sensing end is connected to the drain of the MOSFET tube, and the measurement layer of the other sensing end is connected to the source of the MOSFET tube; when the power device is an IGBT, the measurement layer of one sensing end is connected to the collector of the IGBT, and the measurement layer of the other sensing end is connected to the emitter of the IGBT.

3. The non-contact measurement method of power device switch voltage based on differential electric field coupling according to claim 1, characterized in that: The radius of the through hole is 0.1-1 mm, and the through hole spacing is 0.1-0.5 mm.

4. The non-contact measurement method of power device switch voltage based on differential electric field coupling according to claim 1, characterized in that: The differential signal processing circuit includes a voltage restoration circuit, a voltage follower circuit and a differential operation circuit; the voltage restoration circuit includes grounding capacitors C3 and C4, grounding resistors R1 and R2, the voltage follower circuit includes an operational amplifier No. 1 and an operational amplifier No. 2, and the differential operation circuit includes resistors R3 to R6 and an operational amplifier No. 3; The first coupling capacitor C1 is connected to the positive input terminal of the first operational amplifier, one end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the positive input terminal of the first operational amplifier, and the other end of the grounding resistor R1 and the grounding capacitor C3 connected in parallel is connected to the ground; the output terminal of the first operational amplifier is connected to the inverting input terminal to realize negative feedback; the second coupling capacitor C2 is connected to the positive input terminal of the second operational amplifier, one end of the grounding resistor R2 and the grounding capacitor C4 connected in parallel is connected to the positive input terminal of the second operational amplifier, and the grounding resistor R2 and the grounding capacitor C4 are connected in parallel. The other end of the resistor R4 is connected to the output end of the operational amplifier No. 2, and the other end is connected to the inverting input end of the operational amplifier No. 3 to achieve negative feedback. One end of the resistor R3 is connected to the output end of the operational amplifier No. 1, and the other end is connected to the non-inverting input end of the operational amplifier No.

3. One end of the resistor R5 is connected to the non-inverting input end of the operational amplifier No. 3, and the other end is grounded. One end of the resistor R4 is connected to the output end of the operational amplifier No. 2, and the other end is connected to the inverting input end of the operational amplifier No.

3. One end of the resistor R6 is connected to the inverting input end of the operational amplifier No. 3, and the other end is connected to the output end of the operational amplifier No.

3.

5. The non-contact measurement method of power device switch voltage based on differential electric field coupling according to claim 1, characterized in that: When the number of layers of the PCB board is greater than four, the multi-layer structure in the middle forms a multi-layer electric field coupling structure in the form of alternating measurement layers and sensing layers. Coupling capacitors are formed between adjacent measurement layers and sensing layers, and the coupling capacitors of the entire sensing end are equivalent to multiple coupling capacitors in parallel.

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