High switching frequency inverter based on silicon carbide MOSFET

Abstract

The invention belongs to the field of power electronics, relates to the technical field of inverter design, and provides a silicon carbide MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor)-based high-switching-frequency inverter which comprises a parallel S C inverter, a direct-current bus capacitor and a DSP (Digital Signal Processor) controller. The parallel Si C inverter comprises a plurality of parallel bidirectional bridge arm inverters, and the output end of each bidirectional bridge arm inverter is connected with a Hall sensor CT. And one end of the direct current bus capacitor is connected with the positive terminal of the parallel Si C inverter, and the other end of the direct current bus capacitor is connected with the negative terminal of the parallel Si C inverter. The DSP controller comprises a plurality of driving circuits, a current sampling circuit and a PWM control signal conversion circuit. According to the inverter, under the condition that the power frequency of the inverter is ensured and the quality of the output waveform is not influenced, the volume and the weight of the filter inductor and the filter capacitor are greatly reduced, and the requirement of product weight limitation is met.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, relates to the technical field of inverter design, and particularly relates to a high-switching-frequency inverter based on silicon carbide MOSFETs. Background Art

[0002] The main devices of an inverter are power switches such as IGBTs and MOSFETs. By controlling the power switches, the DC-AC conversion function is achieved. In the key weight distribution of the inverter, the weights of the filter inductor and filter capacitor account for a relatively large proportion. To achieve the goal of high power density, there is a higher demand for the switching frequency of the switching devices. Usually, the inverter needs to operate at a higher frequency to reduce the volume of the filter.

[0003] When IGBTs are selected as the power switches in high-power inverters, their switching speed is generally 10 kHz, and large losses will be brought due to the tail current during turn-off. The losses of IGBTs will be even greater when operating above 10 kHz. When SiC MOSFETs are selected, there is almost no reverse recovery current, resulting in small turn-off losses. Moreover, the operating frequency of SiC MOSFETs can reach 200 kHz or even the MHz level. After the operating frequency is increased, not only can the losses be reduced, but also the volume and weight of the filter inductor and filter capacitor can be reduced, the power density can be increased. At the same time, with higher stress tolerance and better high-temperature operating ability, it means that SiC MOSFETs can improve the reliability of the inverter.

[0004] However, there are still some limitations in applying SiC MOSFETs to high-power inverters at present. For example, the current-carrying capacity of SiC MOSFETs is small, and they need to be used in parallel when the power is large. And the stable control of SiC MOSFETs at high switching frequencies in inverters is also an urgent problem to be solved. Summary of the Invention

[0005] To realize the application of SiC MOSFETs in inverters, the present invention discloses a high-switching-frequency inverter based on silicon carbide MOSFETs. The rated power of this inverter is 15 kW, and by adopting the method of paralleling SiC MOSFETs, the current-carrying capacity is increased to improve the power of the inverter. When the switching frequency is set at 30 kHz, without affecting the quality of the output waveform, the volume and weight of the filter inductor and filter capacitor can be reduced, and the volume and weight of the inverter can be reduced to meet the requirements of product weight limitations. Specifically, the high-switching-frequency inverter based on silicon carbide MOSFETs disclosed by the present invention includes a paralleled SiC inverter, a DC bus capacitor, and a DSP controller.

[0006] Among them, the parallel SiC inverter includes a plurality of parallel bidirectional bridge arm inverters, and a Hall sensor CT is connected to the output end of each bidirectional bridge arm inverter.

[0007] One end of the DC bus capacitor is connected to the positive terminal of the parallel SiC inverter, and the other end of the DC bus capacitor is connected to the negative terminal of the parallel SiC inverter.

[0008] The DSP controller includes a plurality of drive circuits, a current sampling circuit, and a PWM control signal conversion circuit. One of the drive circuits is connected to each bidirectional bridge arm inverter, and the current sampling circuit is connected to the Hall sensor CT.

[0009] Further, the parallel SiC inverter includes three parallel bidirectional bridge arm inverters, and each bidirectional bridge arm inverter includes an upper bridge arm power switch tube and a lower bridge arm power switch tube.

[0010] Furthermore, both the upper bridge arm power switch tube and the lower bridge arm power switch tube include two parallel SiC MOSFET power switch tubes.

[0011] Further, the DC bus capacitor includes a first capacitor C1 and a second capacitor C2 connected in series. The first capacitor C1 is connected to the positive terminal of the parallel SiC inverter, and the second capacitor C2 is connected to the negative terminal of the parallel SiC inverter.

[0012] Furthermore, both the first capacitor C1 and the second capacitor C2 are formed by a plurality of capacitors connected in parallel.

[0013] Further, a filter inductor L is connected in series with the Hall sensor CT.

[0014] Further, the drive circuit includes a voltage on-off control chip, and a PWM control signal generation chip is connected to the output end of the voltage on-off control chip.

[0015] Furthermore, the voltage on-off control chip is used to generate an on voltage signal or an off voltage signal for the bidirectional bridge arm inverter, and the PWM control signal generation chip is used to generate a PWM upper bridge arm control signal and a PWM lower bridge arm control signal for controlling the bidirectional bridge arm inverter according to the on voltage signal or the off voltage signal.

[0016] Further, the DSP controller includes a plurality of voltage sampling circuits. One end of the voltage sampling circuit is connected to one bidirectional bridge arm inverter in the parallel SiC inverter, and the other end is connected to another bidirectional bridge arm inverter in the parallel SiC inverter.

[0017] Furthermore, the DSP controller includes a fault judgment module, which is used to judge faults according to the current collected by the current sampling circuit and the current threshold.

[0018] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification at least include: The high-switching-frequency inverter based on silicon carbide MOSFET designed by the present invention, through the parallel SiC inverter formed by multiple parallel bidirectional bridge arm inverters, combined with the DC bus capacitor and the DSP controller, can achieve a switching frequency of up to 30 kHz, a power of up to 15 kW, and its efficiency can reach more than 95% during full-power operation. And when ensuring that the output waveform remains unchanged, the selected filter inductor and filter capacitor have smaller capacity, volume and weight. Compared with the traditional IGBT inverter, the quality of its filter inductor and capacitor is reduced by 5 kg, and the output voltage distortion is still within 3%. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0020] Figure 1 It is a schematic structural diagram of a high-switching-frequency inverter based on silicon carbide MOSFET disclosed in the embodiments of the present invention;

[0021] Figure 2 It is a main topological structure diagram of the parallel SiC inverter disclosed in the embodiments of the present invention;

[0022] Figure 3 It is a schematic diagram of the drive circuit disclosed in the embodiments of the present invention;

[0023] Figure 4 It is a schematic diagram of the voltage sampling circuit disclosed in the embodiments of the present invention;

[0024] Figure 5 It is a schematic diagram of the current sampling circuit disclosed in the embodiments of the present invention;

[0025] Figure 6 It is the main program operation flow of the high-switching-frequency inverter based on silicon carbide MOSFET disclosed in the embodiments of the present invention;

[0026] Figure 7 It is the control flow of the operation of the high-switching-frequency inverter based on silicon carbide MOSFET disclosed in the embodiments of the present invention. Detailed Embodiments

[0027] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0028] The following specific examples illustrate the implementation manners of the present application. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features of the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0029] An embodiment of the present invention discloses a high-switching-frequency inverter based on a silicon carbide MOSFET. Refer to Figure 1 As shown, the inverter includes a parallel SiC inverter, a DC bus capacitor, and a DSP controller. The parallel SiC inverter includes a plurality of parallel bidirectional bridge arm inverters, and a Hall sensor CT is connected to the output end of each bidirectional bridge arm inverter. One end of the DC bus capacitor is connected to the positive connection terminal of the parallel SiC inverter, and the other end of the DC bus capacitor is connected to the negative connection terminal of the parallel SiC inverter. The DSP controller includes a plurality of drive circuits, a current sampling circuit, and a PWM control signal conversion circuit. One drive circuit is connected to each bidirectional bridge arm inverter, and the current sampling circuit is connected to the Hall sensor CT.

[0030] Further, the parallel SiC inverter includes three parallel bidirectional bridge arm inverters. Each bidirectional bridge arm inverter includes an upper bridge arm power switch tube and a lower bridge arm power switch tube. Further still, both the upper bridge arm power switch tube and the lower bridge arm power switch tube include two parallel SiC MOSFET power switch tubes. The upper / lower bridge arm power switch tubes adopt the method of switch parallel connection, which can improve the output power of the inverter.

[0031] During specific implementation, refer to Figure 2As shown in the figure, it is the main topological structure diagram of a parallel SiC inverter. The three parallel bidirectional leg inverters can be named as the A-phase bidirectional leg inverter, the B-phase bidirectional leg inverter, and the C-phase bidirectional leg inverter respectively. The structures of the A-phase bidirectional leg inverter, the B-phase bidirectional leg inverter, and the C-phase bidirectional leg inverter are the same. Each phase leg consists of 4 power switches. Taking the A-phase bidirectional leg inverter as an example, there are two parallel power switches S1 and S2 on its upper leg, and two parallel power switches S3 and S4 on its lower leg. When the inverter is working, the turn-on time and turn-off time of power switch S1 and power switch S2 are the same, and the turn-on time and turn-off time of power switch S3 and power switch S4 are the same, that is, the PWM control signals of power switch S1 and power switch S2 are the same, and the PWM control signals of power switch S3 and power switch S4 are the same, ensuring that power switch S1 and power switch S2, power switch S3 and power switch S4 achieve current sharing during the working process, preventing the situation of uneven current in the two parallel switches, and reducing the overheating loss and damage caused by excessive current in the switches. The connection method of the switching tubes of the B-phase and C-phase bidirectional leg inverters can refer to that of the A-phase bidirectional leg inverter.

[0032] Furthermore, referring to Figure 1 and Figure 2 As shown, the DC bus capacitor mainly plays the roles of DC energy storage and voltage stabilization, including a series-connected first capacitor C1 and second capacitor C2. The first capacitor C1 is connected to the positive terminal of the parallel SiC inverter, and the second capacitor C2 is connected to the negative terminal of the parallel SiC inverter. Further, both the first capacitor C1 and the second capacitor C2 are formed by paralleling multiple capacitors.

[0033] In the embodiment of the present invention, the DSP controller mainly realizes the sampling of the output current and voltage, transmits the sampled parameters to the DSP control core to participate in the control, realizes the control algorithm of the inverter to output PWM signals, and converts the PWM into the drive signals of the power devices. It also has a communication interface, which is connected to the upper computer, and realizes signal transmission through a communication conversion circuit to achieve the online debugging function.

[0034] Furthermore, a filter inductor L is connected in series with the Hall sensor CT. Referring to Figure 1 As shown, the Hall sensors CT connected to the A-phase bidirectional leg inverter, the B-phase bidirectional leg inverter, and the C-phase bidirectional leg inverter are CT1, CT2, and CT3 respectively, and the filter inductors L are L4, L5, and L6 respectively.

[0035] In specific implementation, the current sampling circuit includes collecting the current of each bidirectional bridge arm inverter, that is, sampling the A-phase current, B-phase current, and C-phase current. Their sampling conditioning circuits are exactly the same, so the A-phase is taken as an example for introduction. See Figure 5 As shown, the current detection circuit samples the current through a Hall sensor. The measurement range of the Hall sensor is 50A (that is, 5V voltage of the Hall sensor represents 50A current). The current is converted into a proportional voltage signal through the Hall sensor as the input of the conditioning circuit, and the range of the input voltage is 0-5V. The maximum analog input voltage of the DSP controller is 3.3V, so a voltage dividing resistor is used to obtain an electrical signal reduced by 0.6 times, and then an operational amplifier and RC filtering are used to filter out the clutter in the signal.

[0036] Furthermore, see Figure 3 As shown, the drive circuit includes a voltage on-off control chip, and a PWM control signal generation chip is connected to the output end of the voltage on-off control chip. The voltage on-off control chip is used to generate the on-voltage signal or off-voltage signal of the bidirectional bridge arm inverter, and the PWM control signal generation chip is used to generate the PWM upper bridge arm control signal and PWM lower bridge arm control signal for controlling the bidirectional bridge arm inverter according to the on-voltage signal or the off-voltage signal.

[0037] In specific implementation, see Figure 3 As shown, it is a schematic diagram of the drive circuit of the A-phase bidirectional bridge arm inverter in the present invention. The drive circuit is mainly composed of a voltage on-off control chip U1 that generates on and off voltages and a PWM control signal generation chip U2 that generates opposite PWM control signals. The voltage on-off control chip U1 can select the QA123C-1803R3 isolation chip to build the drive circuit, which can generate the on-voltage of the switch tube of +18V and the reverse off-voltage of the switch tube of -3V. The PWM control signal generation chip U2 can select the NSi6801 B-DSWFR chip. The PWM control signal passes through the G channel, and the high level of the PWM control signal can be changed to +18V, and the low level can be changed to -3V. Through the PWM control signal generation chip U2, the PWM control signal can be changed into the PWM1 upper bridge arm control signal and the PWM2 lower bridge arm control signal. The PWM periods of these two signals are the same, but the on and off times are opposite, ensuring that the control of the SiC MOSFET power switch tubes of the upper and lower bridge arms of the A-phase is in the opposite state. Among them, the drive circuits of the B-phase and C-phase bidirectional bridge arm inverters are the same as that of the A-phase.

[0038] Further, the DSP controller includes a plurality of voltage sampling circuits. One end of each voltage sampling circuit is connected to one of the bidirectional bridge arm inverters in the parallel SiC inverter, and the other end is connected to another bidirectional bridge arm inverter in the parallel SiC inverter.

[0039] During specific implementation, refer to Figure 4 As shown, the output voltage detection circuit includes AB line voltage sampling, BC line voltage sampling, and AC line voltage sampling. Their sampling and conditioning circuits are exactly the same. In the embodiment of the present invention, the AB line voltage is taken as an example for introduction. The output voltage sampling circuit adopts a high-impedance differential sampling circuit, and the designed voltage sampling range is AC 0 - 250V. The input end of the output voltage sampling circuit is respectively connected to the A phase and the B phase. First, a voltage-dividing resistor is used to reduce the input voltage to within the range allowed by the operational amplifier chip. The output voltage is stepped down to within 3.3V required by the drive circuit through an operational amplifier circuit, and finally, an operational amplifier and RC filtering are used for processing.

[0040] Further, the DSP controller includes a fault judgment module, which is used to perform fault judgment based on the current collected by the current sampling circuit and the current threshold.

[0041] The main program of the present invention for the operation of a high-switching-frequency inverter based on silicon carbide MOSFET, that is, the operation flow is shown in Figure 6 As shown, it includes system initialization and a main loop program. After entering the main program of the silicon carbide MOSFET high-switching-frequency inverter, system initialization is first performed, mainly including the initialization of system parameters and the initialization of system states. Then, it enters the main loop program, which includes detecting faults, sampling and converting voltage and current values, running a modulation algorithm, and updating the PWM output drive signal. After entering the main loop program, the fault signal is detected in real time. If a fault signal appears, the main loop program is exited; if not, other program blocks are executed. The sampling and conversion of voltage and current values mainly convert the sampled analog voltage and current signals into digital signals recognizable by the DSP, and at the same time, scale the collected voltage and current signals to convert them into actual voltage and current values, and then perform algorithm operations. Running the modulation algorithm mainly runs the two-level inverter SVPWM algorithm and the double closed-loop control strategy, and then updates the output drive signal through these algorithms to achieve the control of the inverter.

[0042] The high-switching-frequency inverter based on silicon carbide MOSFET of the present invention is controlled by a general double closed-loop control method. Refer to Figure 7As shown, its control process mainly includes sector judgment, load voltage and current detection, double closed-loop control and PID regulation, calculation of vector action time and correction, and generation of drive signals. First, it judges the sector where the target vector is located to determine the basic space vectors for synthesizing the target vector. Then, it detects the load voltage and current, compares the detected voltage and current values with the set values of the voltage and current in the double closed-loop control, and then performs PID regulation to obtain the correction value of the target vector at the next moment. It calculates the vector action time based on the adjusted target vector, and then generates PWM drive signals according to the SVPWM algorithm.

[0043] The invented SiC MOSFET high-switching-frequency inverter based on the design, which is a parallel SiC inverter formed by multiple parallel bidirectional bridge arm inverters, combined with a DC bus capacitor and a DSP controller, can achieve a switching frequency of up to 30 kHz and a power of up to 15 kW. When operating at full power, its efficiency can reach over 95%. Moreover, while ensuring the output waveform remains unchanged, the selected filter inductor and filter capacitor have smaller capacity, volume, and weight. Compared with the traditional IGBT inverter, the quality of its filter inductor and capacitor is reduced by 5 kg, and the output voltage distortion is still within 3%.

[0044] Obviously, those skilled in the art should understand that the above description is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the embodiments of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high switching frequency inverter based on silicon carbide MOSFET, characterized in that: include: A parallel SiC inverter, wherein the parallel SiC inverter comprises a plurality of parallel bidirectional bridge arm inverters, and an output end of each bidirectional bridge arm inverter is connected to a Hall sensor CT; A DC bus capacitor, one end of which is connected to the positive terminal of the parallel SiC inverter, and the other end of which is connected to the negative terminal of the parallel SiC inverter; The DSP controller includes a plurality of drive circuits, a current sampling circuit and a PWM control signal conversion circuit. Each of the bidirectional bridge arm inverters is connected to one of the drive circuits, and the current sampling circuit is connected to the Hall sensor CT.

2. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The parallel SiC inverter includes three parallel bidirectional bridge arm inverters, and each of the bidirectional bridge arm inverters includes an upper bridge arm power switch tube and a lower bridge arm power switch tube.

3. The high switching frequency inverter based on silicon carbide MOSFET according to claim 2, characterized in that: The upper bridge arm power switch tube and the lower bridge arm power switch tube each include two parallel-connected SiC MOSFET power switch tubes.

4. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The DC bus capacitor includes a first capacitor C1 and a second capacitor C2 connected in series, the first capacitor C1 is connected to the positive terminal of the parallel SiC inverter, and the second capacitor C2 is connected to the negative terminal of the parallel SiC inverter.

5. The high switching frequency inverter based on silicon carbide MOSFET according to claim 4, characterized in that: The first capacitor C1 and the second capacitor C2 are both formed by connecting a plurality of capacitors in parallel.

6. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The Hall sensor CT is connected in series with a filter inductor L.

7. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The driving circuit comprises a voltage on-off control chip, and an output end of the voltage on-off control chip is connected to a PWM control signal generating chip.

8. The high switching frequency inverter based on silicon carbide MOSFET according to claim 7, characterized in that: The voltage on-off control chip is used to generate a turn-on voltage signal or a turn-off voltage signal for the bidirectional bridge arm inverter, and the PWM control signal generation chip is used to generate a PWM upper bridge arm control signal and a PWM lower bridge arm control signal for controlling the bidirectional bridge arm inverter according to the turn-on voltage signal or the turn-off voltage signal.

9. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The DSP controller includes a plurality of voltage sampling circuits, one end of the voltage sampling circuit is connected to one of the bidirectional bridge arm inverters in the parallel SiC inverters, and the other end of the voltage sampling circuit is connected to another bidirectional bridge arm inverter in the parallel SiC inverters.

10. The high switching frequency inverter based on silicon carbide MOSFET according to claim 1, characterized in that: The DSP controller comprises a fault judgment module, and the fault judgment module is used to perform fault judgment according to the current collected by the current sampling circuit and the current threshold.

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