Three-phase inverter SiC-MOSFET on-state voltage on-line monitoring circuit and method

Abstract

The three-phase inverter SiC-MOSFET on-state voltage on-line monitoring circuit comprises two monitoring units symmetrically installed on an upper bridge arm and a lower bridge arm of a three-phase inverter, and each monitoring unit comprises a signal trigger circuit, a sampling isolation circuit, a modulation circuit, a data processing circuit, a sampling resistor and a sampling gating module. The number of the signal trigger circuits and the number of the sampling resistors are both three. The monitoring unit is installed on an upper bridge arm or a lower bridge arm of the three-phase inverter, three signal trigger circuits of the monitoring unit are respectively connected in parallel to three SiC-MOSFETs of the upper bridge arm or the lower bridge arm after being respectively connected with a sampling resistor, one ends of the three sampling resistors share the positive electrode and the negative electrode of direct-current side voltage, and the other ends of the three sampling resistors share the positive electrode and the negative electrode of direct-current side voltage. Three input ends of the sampling gating module are respectively connected with the other ends of the three sampling resistors; and the sampling gating module, the sampling isolation circuit and the data processing circuit are electrically connected in sequence. The complexity of the circuit structure can be reduced, and the circuit size is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of online monitoring of SiC-MOSFET characteristic parameters, and in particular to an online monitoring circuit and method for on-state voltage of a three-phase inverter SiC-MOSFET. Background Art

[0002] Among the many studies dedicated to improving the reliability of power devices, the real-time online monitoring technology of SiC-MOSFET characteristic parameters is becoming a hot topic and focus of current research. Among them, the "on-state voltage", that is, the voltage tolerance of the power semiconductor in the fully on state, has become an important parameter for evaluating the degree of degradation of power semiconductor devices, estimating junction temperature, and implementing protection strategies. Therefore, in order to accurately monitor the health of power devices and ensure the reliability and stability of the efficient operation of electronic devices, it is very important to accurately measure and control their on-state voltage.

[0003] At present, the most widely used SiC-MOSFET on-state voltage measurement circuit in the industry is Figure 1 As shown in FIG. 1 , it is mainly composed of a signal trigger circuit, a sampling isolation circuit, a modulation circuit and a data processing circuit, wherein the signal trigger circuit is composed of a MOS tube VT 1. Resistance R 1 and isolated power supply E constitute, VT 1 is turned on, by collecting R 1 The voltage across the two ends can be used to obtain the on-state voltage of the SiC-MOSFET. The on-state voltage measurement process is not limited to simple voltage reading, but also needs to cover comprehensive measurements from the cut-off state voltage stress signal to the rated voltage range of the semiconductor device. To meet this requirement, traditional SiC-MOSFET on-state voltage measurement circuits are mostly designed at the component level, and an independent isolated power supply must be configured for each power device. During the measurement, these circuits need to be connected to the two power terminals of the power switch respectively. If applied to a three-phase inverter, it means that more connection terminals are required. In addition, in order to ensure the accuracy of the measurement, each phase leg needs to be equipped with a reference ground, which means that the on-state voltage monitoring of each power device needs to rely on an independent sampling optocoupler isolator, such as Figure 2 As shown in the figure, each power device of the three-phase inverter requires a complete on-state voltage measurement circuit, which not only greatly increases the demand for ADC sampling channels, but also makes the structure of the data sampling system more complicated. Therefore, although the traditional SiC-MOSFET on-state voltage measurement circuit shows certain advantages in performance, unfortunately, the circuit complexity it brings is significantly increased, which not only increases the size of the circuit, but also leads to an increase in the overall cost, becoming a major bottleneck restricting its widespread application. Summary of the invention

[0004] In order to reduce the complexity of the circuit structure and reduce the circuit size, the present invention provides a three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit and method.

[0005] In order to solve the above technical problems, the present invention adopts the following technical methods: an online monitoring circuit for the on-state voltage of a three-phase inverter SiC-MOSFET, comprising two monitoring units symmetrically installed on the upper bridge arm and the lower bridge arm of the three-phase inverter, wherein the monitoring unit comprises a signal trigger circuit, a sampling isolation circuit, a modulation circuit, and a data processing circuit, and the monitoring unit further comprises a sampling resistor and a sampling gating module having three input terminals and one output terminal. In one monitoring unit, the number of the signal trigger circuit and the number of the sampling resistor are both three; A monitoring unit installed on an upper bridge arm or a lower bridge arm of a three-phase inverter, wherein the three signal trigger circuits are respectively connected in parallel to the three SiC-MOSFETs of the upper bridge arm or the lower bridge arm after each of the three signal trigger circuits is connected to a sampling resistor, and one end of the three sampling resistors is connected to the positive electrode or the negative electrode of the DC side voltage, and the three input ends of the sampling gating module are respectively connected to the other ends of the three sampling resistors, and the sampling gating module, the sampling isolation circuit, the modulation circuit, and the data processing circuit are electrically connected in sequence; When only one SiC-MOSFET in the upper arm or lower arm of the three-phase inverter is turned on, the corresponding monitoring unit starts to monitor the on-state voltage of the SiC-MOSFET, that is, the signal trigger circuit connected to the SiC-MOSFET is turned on, and the sampling gating module collects the voltage across the sampling resistor connected to the turned-on signal trigger circuit. The voltage is then transmitted to the sampling isolation circuit, the modulation circuit, and the data processing circuit in sequence. After processing and calculation, the on-state voltage value of the SiC-MOSFET is obtained.

[0006] Furthermore, the sampling gating module includes three zener diodes. When the sampling gating module is installed on the upper bridge arm or the lower bridge arm of the three-phase inverter, the cathodes or anodes of the three zener diodes are respectively led out as the three input ends of the sampling gating module, and the anodes or cathodes of the three zener diodes are connected in line and led out as the output end of the sampling gating module.

[0007] Furthermore, the signal trigger circuit includes an NMOS tube, a voltage-dividing resistor and an isolated power supply. When the signal trigger circuit is installed on the upper bridge arm or the lower bridge arm of the three-phase inverter, the drain of the NMOS tube is connected to the positive or negative pole of the DC side voltage after passing through the sampling resistor, the gate of the NMOS tube is connected to the positive pole of the isolated power supply, and the source of the NMOS tube is connected to the voltage-dividing resistor and then connected to the midpoint of the bridge arm of the three-phase inverter together with the negative pole of the isolated power supply.

[0008] Preferably, the ratio of the sampling resistor to the voltage dividing resistor is greater than 10.

[0009] As another aspect of the present invention, a three-phase inverter SiC-MOSFET on-state voltage online monitoring method is provided, which uses the above-mentioned three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit to collect the three-phase inverter SiC-MOSFET on-state voltage, specifically: When only one SiC-MOSFET in the upper arm or lower arm of the three-phase inverter is turned on, the corresponding monitoring unit starts to monitor the on-state voltage of the SiC-MOSFET, that is, the signal trigger circuit connected to the SiC-MOSFET is turned on, and the sampling gating module collects the voltage across the sampling resistor connected to the turned-on signal trigger circuit. The voltage is then transmitted to the sampling isolation circuit, the modulation circuit, and the data processing circuit in sequence for processing. Finally, the data processing circuit combines the working waveform of the three-phase inverter and the ratio between the sampling resistor and the voltage divider resistor to calculate the on-state voltage value of the SiC-MOSFET.

[0010] The three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit provided by the present invention has a simple structure, can realize the rapid identification of the conduction of the power tube of the three-phase inverter and the rapid and accurate extraction of the on-state voltage of the power tube. Specifically, the present invention does not need to add a new power supply and does not need a control signal from an industrial control chip. By adding a sampling resistor with a common bus reference potential and a sampling gating module with a three-select-one gating capability, the overall circuit structure is cleverly simplified, the circuit size is reduced, and the required sampling isolation and ADC sampling channels are significantly reduced, thereby effectively reducing the complexity and cost of the monitoring circuit used in the three-phase inverter. At the same time, the present invention hardly affects the switching speed of the original device, and maintains the accuracy and reliability of the SiC-MOSFET on-state voltage measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the topology diagram of the traditional SiC-MOSFET on-state voltage online monitoring circuit; Figure 2 The topology diagram of the connection between the three-phase inverter and the traditional SiC-MOSFET on-state voltage online monitoring circuit; Figure 3 This is a topology diagram of an online monitoring circuit for the on-state voltage of a three-phase inverter SiC-MOSFET according to the present invention; Figure 4 This is the working waveform of the three-phase inverter. DETAILED DESCRIPTION

[0012] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0013] like Figure 1 As shown in the traditional SiC-MOSFET on-state voltage online monitoring circuit, when the power tube to be measured T 1 When in the off state, the voltage on the DC side is directly applied to T 1, i.e. point a ( T 1 drain) and point b ( T 1) will form a significant voltage difference. According to the connection between the monitoring circuit and the main circuit, the voltage difference between point a and point b will act on the internal circuit of the monitoring circuit. It can be seen that in the monitoring circuit, the isolated power supply of the signal trigger circuit E The voltage is 2.5V (isolated power supply E By power tube T 1 drive circuit power supply, such as Figure 1 As shown), while the MOS tube VT The threshold voltage of 1 is usually in the range of 0.7V~1.5V, which means that under normal circumstances, VT 1 is conducting. VT 1 is turned on, then the voltage difference between points a and b will form a current path in the signal trigger circuit, and the current flows from point a through VT 1. Then through R 1 flows back to point b. Since a current loop is created, the current will flow through the resistor R 1 generates voltage, which will cause the potential of point C to rise in a short time. As the potential of point C increases, VT 1 The voltage between the gate and point c is not enough to drive VT 1 conduction, that is VT 1 will be turned off and the current loop will be disconnected.

[0014] When the power tube to be measured T When 1 is in the on state, since its on-state voltage is extremely low, usually between 200mV and 300mV, the potential difference between points a and b is also kept at a very low level. VT 1 is turned on and a current path is formed, but due to the low voltage, the current value is also correspondingly small, and the resistance R The voltage on 1 will not be too significant, which means that the potential at point c will not be very large. VT 1 The potential difference between the gate and point C can still make VT 1 Keep the conduction state, thereby maintaining the current path. At this time, directly measure R 1The voltage across the two ends can be obtained VT 1 is the on-state voltage when it is turned on.

[0015] According to the above analysis of the working principle of the traditional monitoring circuit, the present invention intends to add a resistor to the signal trigger circuit. By designing the resistance value of the added resistor and the original resistor, it is only necessary to measure the voltage across the added resistor to accurately know the magnitude of the on-state voltage of the power tube to be measured. In order to make the overall circuit structure simpler when the monitoring circuit is applied to a three-phase inverter, the present invention also intends to design a module that can select one of the three resistors for voltage sampling, which can significantly reduce the number of required sampling isolation and data processing circuits. Based on this, the present invention provides a three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit, which is as follows: like Figure 3 As shown, a three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit includes two monitoring units symmetrically installed on the upper bridge arm and the lower bridge arm of the three-phase inverter.

[0016] like Figure 3 As shown in the figure, the monitoring unit installed on the upper bridge arm of the three-phase inverter includes three signal trigger circuits, three sampling resistors, a sampling gating module, a sampling isolation circuit, a modulation circuit, and a data processing circuit; the first signal trigger circuit includes an NMOS tube M 1. Voltage divider resistor R 1 and isolated power supply E 1, M 1 Drain through sampling resistor R 1* Then connect it to the positive pole of the DC voltage. M 1 Gate and E 1's positive connection, M 1 Source connection R 1 after E 1 is connected to the midpoint of the three-phase inverter bridge arm; the second signal trigger circuit includes an NMOS tube M 3. Voltage divider resistor R 3 and isolated power supply E 3. M 3. Drain through sampling resistor R 3* Then connect it to the positive pole of the DC voltage. M 3 gate and E 3's positive connection, M 3 Source connection R 3 after and E The negative electrodes of 3 are connected to the midpoint of the three-phase inverter bridge arm; the third signal trigger circuit includes an NMOS tube M 5. Voltage divider resistor R 5 and isolated power supply E 5. M 5. Drain through sampling resistor R 5*Then connect it to the positive pole of the DC voltage. M 5 Gate and E 5's positive connection, M 5 Source connection R 5 after E The negative poles of 5 are connected to the midpoint of the three-phase inverter bridge arm; the sampling and gating module includes three voltage stabilizing diodes D 1. D 3. D 5. D 1's cathode is connected to R 1* and M 1 between, D The cathode of 3 is connected to R 3* and M 3. D The cathode of 5 is connected to R 5* and M 5, D 1. D 3. D The anodes of 5 are connected in common line and then led out as output terminals to be connected to the input terminals of sampling isolation circuit; the output terminals of sampling isolation circuit are connected to the input terminals of modulation circuit; the data processing circuit comprises an ADC converter and an FPGA chip connected in sequence, and the output terminals of modulation circuit are connected to the ADC converter.

[0017] like Figure 3 As shown in the figure, the monitoring unit installed in the lower bridge arm of the three-phase inverter includes three signal trigger circuits, three sampling resistors, a sampling gating module, a sampling isolation circuit, a modulation circuit, and a data processing circuit; the first signal trigger circuit includes an NMOS tube M 2. Voltage divider resistor R 2 and isolated power supply E 2, M 2 Drain through sampling resistor R 2* Then connect it to the negative pole of the DC voltage. M 2 Gate and E 2's positive connection, M 2 Source connection R 2 after and E 2 are connected to the midpoint of the three-phase inverter bridge arm; the second signal trigger circuit includes an NMOS tube M 4. Voltage divider resistor R 4 and isolated power supply E 4. M 4 Drain through sampling resistor R 4* Then connect it to the negative pole of the DC voltage. M 4 gate andE 4's positive connection, M 4 Source connection R 4 After E The negative electrodes of 4 are connected to the midpoint of the three-phase inverter bridge arm; the third signal trigger circuit includes an NMOS tube M 6. Voltage divider resistor R 6 and isolated power supply E 6. M 6 Drain through sampling resistor R 6* Then connect it to the negative pole of the DC voltage. M 6 gate and E 6's positive connection, M 6 Source connection R 6 and E The negative poles of 6 are connected to the midpoint of the three-phase inverter bridge arm; the sampling and gating module includes three voltage stabilizing diodes D 2. D 4. D 6. D 2's cathode is connected to R 2* and M 2, D The cathode of 4 is connected to R 4* and M 4 between, D The cathode of 6 is connected to R 6* and M 6 between, D 2. D 4. D The anodes of 6 are connected in parallel and then led out as output terminals to be connected to the input terminals of the sampling isolation circuit; the output terminals of the sampling isolation circuit are connected to the input terminals of the modulation circuit; the data processing circuit includes an ADC converter and an FPGA chip connected in sequence, and the output terminals of the modulation circuit are connected to the ADC converter.

[0018] It is worth mentioning that, when designing the signal trigger circuit, the present invention cleverly sets the ratio between the sampling resistor and the voltage-dividing resistor to a larger value of at least greater than 10, ensuring that the resistance of the sampling resistor is much larger than the voltage-dividing resistor, so that the on-state voltage of the power tube to be measured basically falls on the sampling resistor. In response to the voltage-dividing problem caused by the voltage-dividing resistor, the subsequent data processing circuit can adopt effective means such as voltage compensation in the specific calculation to accurately compensate the extracted on-state voltage.

[0019] Next, the working principle of the above-mentioned three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit provided by the present invention is described in detail, that is, the three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit method provided by the present invention, specifically: like Figure 4 The three-phase inverter working waveform shown in the figure shows that at the same time, the power tube of the upper bridge arm may be in a single-tube or double-tube conducting state. In order to accurately extract the on-state voltage of a certain power tube every time, the monitoring method provided by the present invention needs to combine the working waveform of the three-phase inverter and the three-selection gating capability of the sampling gating module to extract the on-state voltage.

[0020] Figure 4 The working areas ①, ③, ⑤ and other similar areas of the three-phase inverter are in the negative half of the working waveform. These areas are for extracting the on-state voltage of the three power tubes in the upper bridge arm of the three-phase inverter. Figure 3 Power tube T 1 conduction as an example, when T 1 is in the on state, while T 3. T 5 When in the off state, the working area of ​​the three power tubes of the upper bridge arm is located at Figure 4 Area ① in the figure means that only the current in phase A is positive, while the currents in phases B and C are negative. That is to say, in the circuit, the current will flow through T 1Inflow and utilization T 3. T 5 body diode for freewheeling. Due to the sampling resistor in the monitoring circuit R 1* , R 3* , R 5* The left ends of the two terminals are connected to the same reference potential point a. According to the current path, R 1* Point d on the right has a low potential relative to the reference potential, while R 3* Point e on the right and R 5* Point f on the right has a relatively high potential. Since the potentials of points e and f are higher than that of point d, a certain voltage difference will be generated between them according to the current path, which will cause the Zener diode to D 3. D 5 was penetrated, and D 1 is in the on state. At this time, the potential of point b is pulled down to the same potential as point d. Therefore, by measuring the voltage of ports a and b, we can directly know R 1* Similarly, when the three-phase inverter works in regions ③ and ⑤, the potentials at points e and f will be selected respectively, thereby extracting T 3. T 5 on-state voltage.

[0021] Figure 4The working areas ②, ⑥, ④ and other similar areas of the three-phase inverter are in the positive half of the working waveform. These areas are for extracting the on-state voltage of the three power tubes in the lower bridge arm of the three-phase inverter. Figure 4 Take the working area ④ in the figure as an example. Although both phases A and C are positive at this time, according to the working principle of the three-phase inverter, the currents of phases A and C flow into the load, and the current of phase B flows out of the load. At this time, the corresponding situation of the power tube is: T 1. T 5 conduction, T 3 is turned off, but the two power tubes in the same bridge arm are turned on at 180°. T 4 is on, then the current flows from the load side T 4 forms a loop, and for T 2. T 6 is the diode freewheeling, that is, for the lower bridge arm, the potential at point m is higher than that at point g, while the potentials at points l and n are lower than that at point g, so a potential difference will be formed between point m and points l and n, which leads to D 4 is turned on, so that the potential of point h is consistent with that of point m, then the T 4. Similarly, for regions ② and ⑥, select T 2 and T 6 on-state voltage.

[0022] To sum up, when only one power tube in the upper bridge arm or lower bridge arm of the three-phase inverter is turned on, the sampling and selection module of the upper bridge arm or lower bridge arm will select and follow the low potential of the upper bridge arm d, e, f or the high potential of the lower bridge arm l, m, n.

[0023] After collecting the required voltage signal in the above manner, the sampling isolation circuit of the upper bridge arm or the lower bridge arm will receive the voltage signal through the upper bridge arm b, c ends or the lower bridge arm g, h ends and perform electrical isolation, and then forward it to the modulation circuit for modulation. The modulated voltage signal is finally forwarded to the data processing circuit for processing and calculation. In the data processing circuit, the ADC converter first performs analog-to-digital conversion on the modulated voltage signal, and then the FPGA chip combines the working waveform of the three-phase inverter and the ratio between the sampling resistor and the voltage divider resistor to calculate the electrical signal after the analog-to-digital conversion, and finally obtains the on-state voltage of the above-mentioned conductive power tube.

[0024] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0025] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit, comprising two monitoring units symmetrically installed on the upper bridge arm and the lower bridge arm of the three-phase inverter, wherein the monitoring unit comprises a signal trigger circuit, a sampling isolation circuit, a modulation circuit, and a data processing circuit, and is characterized in that: The monitoring unit also includes a sampling resistor and a sampling gating module having three input terminals and one output terminal. In one monitoring unit, the number of the signal trigger circuit and the number of the sampling resistor are both three; A monitoring unit installed on an upper bridge arm or a lower bridge arm of a three-phase inverter, wherein the three signal trigger circuits are respectively connected in parallel to the three SiC-MOSFETs of the upper bridge arm or the lower bridge arm after each of the three signal trigger circuits is connected to a sampling resistor, and one end of the three sampling resistors is connected to the positive electrode or the negative electrode of the DC side voltage, and the three input ends of the sampling gating module are respectively connected to the other ends of the three sampling resistors, and the sampling gating module, the sampling isolation circuit, the modulation circuit, and the data processing circuit are electrically connected in sequence; When only one SiC-MOSFET in the upper arm or lower arm of the three-phase inverter is turned on, the corresponding monitoring unit starts to monitor the on-state voltage of the SiC-MOSFET, that is, the signal trigger circuit connected to the SiC-MOSFET is turned on, and the sampling gating module collects the voltage across the sampling resistor connected to the turned-on signal trigger circuit. The voltage is then transmitted to the sampling isolation circuit, the modulation circuit, and the data processing circuit in sequence. After processing and calculation, the on-state voltage value of the SiC-MOSFET is obtained.

2. The three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit according to claim 1 is characterized in that: The sampling gating module includes three voltage-stabilizing diodes. When the sampling gating module is installed on the upper bridge arm or the lower bridge arm of the three-phase inverter, the cathodes or anodes of the three voltage-stabilizing diodes are respectively led out as the three input ends of the sampling gating module, and the anodes or cathodes of the three voltage-stabilizing diodes are collinearly led out as the output end of the sampling gating module.

3. The three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit according to claim 2, characterized in that: The signal trigger circuit includes an NMOS tube, a voltage-dividing resistor and an isolated power supply. When the signal trigger circuit is installed on the upper bridge arm or the lower bridge arm of the three-phase inverter, the drain of the NMOS tube is connected to the positive or negative electrode of the DC side voltage through the sampling resistor, the gate of the NMOS tube is connected to the positive electrode of the isolated power supply, and the source of the NMOS tube is connected to the voltage-dividing resistor and then connected to the midpoint of the bridge arm of the three-phase inverter together with the negative electrode of the isolated power supply.

4. The three-phase inverter SiC-MOSFET on-state voltage online monitoring circuit according to claim 3 is characterized in that: The ratio of the sampling resistor to the voltage dividing resistor is greater than 10.

5. A method for online monitoring of the on-state voltage of a three-phase inverter SiC-MOSFET, characterized in that: The on-state voltage of the three-phase inverter SiC-MOSFET is collected by using the on-state voltage online monitoring circuit of the three-phase inverter SiC-MOSFET according to any one of claims 1 to 4, specifically: When only one SiC-MOSFET in the upper arm or lower arm of the three-phase inverter is turned on, the corresponding monitoring unit starts to monitor the on-state voltage of the SiC-MOSFET, that is, the signal trigger circuit connected to the SiC-MOSFET is turned on, and the sampling gating module collects the voltage across the sampling resistor connected to the turned-on signal trigger circuit. The voltage is then transmitted to the sampling isolation circuit, the modulation circuit, and the data processing circuit in sequence. After processing and calculation, the on-state voltage value of the SiC-MOSFET is obtained.

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