Three-phase motor driving circuit and variable frequency motor driver

Abstract

The application provides a three-phase motor driving circuit and a variable-frequency motor driver, and relates to the technical field of motor driving control, and comprises an upper bridge arm and a lower bridge arm which are composed of power switching devices, wherein the power switching devices are internally integrated with body diodes; each power switching device of the lower bridge arm is reversely connected in parallel with a freewheeling element at both ends; and the forward conduction voltage drop of the freewheeling element is lower than that of the body diode of the power switching device. The application eliminates the risk of driving chip lockout, ensures reliable control, eliminates motor abnormal sound, significantly reduces freewheeling loss, and is cost-optimal, highly reliable, low-carbon and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of motor drive control technology, and more specifically, to a three-phase motor drive circuit and a variable frequency motor driver. Background Technology

[0002] With the development of power electronics technology, especially the application of wide-bandgap semiconductor devices, motor drive systems are evolving towards higher efficiency, higher power density, and higher switching frequencies. SiC MOSFETs, as a third-generation semiconductor power device, are increasingly widely used in three-phase motor drive circuits and variable frequency motor drivers due to their excellent performance, including high voltage resistance, high temperature resistance, fast switching speed, and low switching losses. However, in practical applications, SiC MOSFETs integrate a body diode. In a typical voltage-source three-phase inverter topology, when the motor windings require freewheeling, the current flows through the body diode of the lower-arm SiC MOSFET, resulting in a generally high forward voltage drop, typically around 4V, and even higher in some models.

[0003] Existing three-phase motor drive circuits and variable frequency motor drivers containing such circuits often experience malfunctions due to the high forward voltage drop of the SiC MOSFET body diode. In bridge drive circuits, the freewheeling current in the lower arm body diode generates a significant negative voltage spike at the VS terminal of the drive chip. Since the forward voltage drop of the SiC MOSFET body diode is as high as 4V, this negative voltage amplitude often exceeds the negative voltage tolerance limit of most drive chips. This can cause the drive chip to latch up, preventing it from correctly responding to the input PWM control signal, and even leading to output signal loss and logic disorder. This results in unstable motor control and abnormal noise. Because the drive chip's response to the PWM signal is unreliable, the current waveform of the motor windings will be distorted, leading to increased torque ripple, causing unstable motor operation and noticeable electromagnetic noise, severely impacting the user experience and reliability of the product. Furthermore, high freewheeling losses reduce system efficiency. The forward voltage drop of the body diode, which is as high as 4V, will bring significant freewheeling conduction losses. Especially under the conditions of light load or low speed operation of the motor, the proportion of freewheeling is relatively large. This loss will significantly reduce the overall energy efficiency of the variable frequency motor driver, which is not conducive to energy conservation and emission reduction. Summary of the Invention

[0004] The present invention aims to solve the problems of abnormal operation of the drive chip in the existing three-phase motor drive circuit and the variable frequency motor driver containing the circuit, which affects the stability of motor control and has high freewheeling loss.

[0005] To solve the above problems, the present invention provides a three-phase motor drive circuit, including an upper bridge arm and a lower bridge arm composed of power switching devices, wherein the power switching devices integrate a body diode. Each power switching device in the lower bridge arm has a freewheeling element connected in antiparallel across its two ends; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the diode inside the power switching device.

[0006] The three-phase motor drive circuit provided by this invention has, but is not limited to, the following beneficial effects compared to the prior art: In this invention, a fast recovery diode is connected in anti-parallel across each SiC MOSFET in the lower bridge arm of a three-phase motor drive circuit composed of SiC MOSFETs. This solves the problem of unstable motor control and even abnormal noise caused by SiC MOSFETs in current three-phase motor drive circuits and variable frequency motor driver control systems.

[0007] This invention eliminates the risk of driver chip lock-up and ensures reliable control: by connecting a low-dropout freewheeling element in parallel with the lower bridge arm, the negative voltage amplitude at the VS terminal is reduced from above 4V to below 2V, falling completely within the safe operating range of most driver chips. This avoids the problem of driver chips locking up or not responding to PWM signals due to excessive negative voltage, thus ensuring the absolute stability of motor control.

[0008] This invention eliminates motor noise: because the drive signal is complete and accurate, the distortion of the motor winding current waveform is greatly reduced, the torque pulsation is reduced, and the electromagnetic noise caused by current distortion is completely eliminated.

[0009] This invention significantly reduces freewheeling losses: the forward voltage drop of the external freewheeling element is much lower than that of the SiC MOSFET body diode, reducing conduction losses by more than 50% during freewheeling. For variable frequency motors that operate for extended periods, such as washing machines, air conditioners, and fans, the cumulative energy savings are considerable.

[0010] This invention offers optimal cost and high reliability: Employing an asymmetric topology, it adds only three low-dropout diodes to the lower bridge arm, eliminating the need for additional components in the upper bridge arm, changes to the driver chip, or complex negative voltage circuitry. Compared to a full-arm parallel design, it reduces cost by 50%; compared to a negative voltage circuit design, the circuit is simpler and more reliable.

[0011] This invention is low-carbon and environmentally friendly: it achieves significant low-carbon benefits during the usage phase; on the other hand, the high efficiency characteristics of SiC MOSFET itself are fully utilized, contributing to the achievement of the "dual carbon" goal.

[0012] Furthermore, a three-phase motor drive circuit includes an upper bridge arm and a lower bridge arm composed of SiC MOSFETs; Each SiC MOSFET in the lower bridge arm has a freewheeling element connected in antiparallel across its terminals; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the SiC MOSFET body diode.

[0013] Furthermore, the SiC MOSFET of the lower bridge arm integrates a body diode, and the freewheeling element is an external fast recovery diode, which is connected in anti-parallel between the drain and source of the SiC MOSFET.

[0014] Furthermore, the SiC MOSFET in the upper bridge arm integrates a body diode.

[0015] Furthermore, the forward voltage drop of the freewheeling element is less than 2V, or less than 50% of the forward voltage drop of the bulk diode.

[0016] Furthermore, the lower bridge arm is composed of three SiC MOSFETs, each of which has a freewheeling element connected in antiparallel across its terminals.

[0017] Furthermore, the SiC MOSFET of the lower bridge arm is a SiC MOSFET without a built-in body diode.

[0018] Furthermore, the freewheeling element is a fast recovery diode or a Schottky diode.

[0019] A variable frequency motor driver includes the above-mentioned three-phase motor drive circuit and a drive chip, wherein the drive chip is electrically connected to the three-phase terminals of the motor through the three-phase motor drive circuit.

[0020] Furthermore, three of the output terminals of the driver chip are respectively connected to the gates of three MOS transistors in the upper bridge arm of the three-phase motor drive circuit; The other three output terminals of the driver chip are respectively connected to the gates of the three MOS transistors in the lower bridge arm of the three-phase motor drive circuit; The sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are connected one-to-one. The three connection points between the sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are electrically connected to the three-phase terminals of the motor, respectively. A freewheeling element is provided between the source and drain of the three MOSFETs in the lower bridge arm. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a circuit topology for a three-phase motor drive circuit of a variable frequency motor driver according to an embodiment of the present invention. Figure 2 This is a schematic diagram of another circuit topology of the three-phase motor drive circuit of the variable frequency motor driver according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application are described clearly and completely below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," "comprise," etc., in the specification, claims, and accompanying drawings of this application are open-ended terms, indicating that a method comprises one or more steps, or an apparatus comprises one or more elements, but do not exclude the inclusion of other steps or elements. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or primary / secondary relationship. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0025] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0026] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0027] See Figure 1 An embodiment of the present invention provides a three-phase motor drive circuit, comprising an upper bridge arm and a lower bridge arm composed of power switching devices, wherein the power switching devices integrate a body diode. Each power switching device in the lower bridge arm has a freewheeling element connected in antiparallel across its two ends; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the diode inside the power switching device.

[0028] In this embodiment, in the three-phase motor drive circuit composed of SiC MOSFETs, a fast recovery diode is connected in anti-parallel across the drain and source terminals of each SiC MOSFET with a body diode in the lower bridge arm. The forward voltage drop of the parallel fast recovery diode, i.e., the freewheeling diode, is less than 2V, or less than 50% of the forward voltage drop of the body diode in the SiC MOSFET. Thus, during freewheeling, the body diode conducts, and the reverse voltage at the VS terminal of the DRIVE driver chip is clamped by the diode and will not exceed 2V, significantly lower than the 4V or higher reverse voltage at the VS terminal when using the body diode for freewheeling. Therefore, there is no problem of excessive negative voltage at the VS terminal, which will not cause the driver chip to lock out and fail to respond to the PWM signal, ensuring stable motor control and reliable operation even with abnormal noise, while minimizing freewheeling damage.

[0029] See Figure 2 This invention discloses a three-phase motor drive circuit, comprising an upper bridge arm and a lower bridge arm composed of SiC MOSFETs. Each SiC MOSFET in the lower bridge arm has a freewheeling element connected in antiparallel across its terminals; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the SiC MOSFET body diode.

[0030] In this embodiment, in the three-phase motor drive circuit composed of SiC MOSFETs, the upper bridge arm uses SiC MOSFETs with integrated body diodes in each SiC MOSFET, while the lower bridge arm uses SiC MOSFETs without integrated body diodes in each SiC MOSFET. A fast recovery diode is connected in anti-parallel across the drain and source of each SiC MOSFET in the lower bridge arm. The forward voltage drop of the parallel fast recovery diode, i.e., the freewheeling diode, is less than 2V. Because the reverse voltage at the VS terminal of the DRIVE driver chip is clamped by the diode, it will not exceed 2V. At this time, there will be no problem of excessive negative voltage at the VS terminal, preventing the driver chip from blocking and failing to respond to the PWM signal. This ensures stable motor control and reliable operation, even with issues like abnormal noise, and minimizes freewheeling damage.

[0031] In this invention, a fast recovery diode is connected in anti-parallel across each SiC MOSFET in the lower bridge arm of a three-phase motor drive circuit composed of SiC MOSFETs. This solves the problem of unstable motor control and even abnormal noise caused by SiC MOSFETs in current three-phase motor drive circuits and variable frequency motor driver control systems.

[0032] This invention solves the problems of motor instability and even abnormal noise in current SiC MOSFET applications in three-phase motor drive circuits and variable frequency motor driver control systems. Simultaneously, it reduces lower bridge arm freewheeling losses, enabling the variable frequency motor to continuously save energy during long-term operation. Taking a variable frequency washing machine with 300 cycles per year and a 10-year lifespan as an example, the cumulative energy savings far exceed the material savings in manufacturing, achieving significant low-carbon benefits during use. This invention eliminates the risk of driver chip lock-up and ensures reliable control: by connecting a low-dropout freewheeling element in parallel with the lower bridge arm, the negative voltage amplitude at the VS terminal is reduced from above 4V to below 2V, falling completely within the safe operating range of most driver chips. This avoids the problem of driver chips locking up or not responding to PWM signals due to excessive negative voltage, thus ensuring the absolute stability of motor control.

[0033] This invention eliminates motor noise: because the drive signal is complete and accurate, the distortion of the motor winding current waveform is greatly reduced, the torque pulsation is reduced, and the electromagnetic noise caused by current distortion is completely eliminated.

[0034] This invention significantly reduces freewheeling losses: the forward voltage drop of the external freewheeling element is much lower than that of the SiC MOSFET body diode, reducing conduction losses by more than 50% during freewheeling. For variable frequency motors that operate for extended periods, such as washing machines, air conditioners, and fans, the cumulative energy savings are considerable.

[0035] This invention offers optimal cost and high reliability: Employing an asymmetric topology, it adds only three low-dropout diodes to the lower bridge arm, eliminating the need for additional components in the upper bridge arm, changes to the driver chip, or complex negative voltage circuitry. Compared to a full-arm parallel design, it reduces cost by 50%; compared to a negative voltage circuit design, the circuit is simpler and more reliable.

[0036] This invention is low-carbon and environmentally friendly: it achieves significant low-carbon benefits during the usage phase; on the other hand, the high efficiency characteristics of SiC MOSFET itself are fully utilized, contributing to the achievement of the "dual carbon" goal.

[0037] Furthermore, the SiC MOSFET of the lower bridge arm integrates a body diode, and the freewheeling element is an external fast recovery diode, which is connected in anti-parallel between the drain and source of the SiC MOSFET.

[0038] The typical forward voltage drop of the SiC MOSFET body diode in this invention is around 4V, while the voltage drop of an external fast recovery diode is typically less than 2V (even as low as 0.7~0.9V). During freewheeling, the current preferentially flows through the external diode with the lower voltage drop, clamping the negative voltage of the VS terminal (switching node) to ground from above -4V to below -2V. Topology 1 solves the core pain point caused by the high voltage drop of the SiC MOSFET body diode in the simplest and most reliable way without increasing device complexity and cost, while retaining the body diode as a safety backup.

[0039] Furthermore, the SiC MOSFET in the upper bridge arm integrates a body diode.

[0040] This invention does not add any components to the upper bridge arm. Compared to the full-bridge parallel scheme, the number of external diodes is reduced by 50%, from 6 to 3. Simultaneously, it reduces PCB layout area and surface mount processing costs, resulting in a more significant overall cost advantage. When the lower bridge arm is off and the upper bridge arm is not yet on, the motor winding current needs to flow from the positive terminal of the DC bus to the switching node VS. At this time, the current flows through the body diode of the upper bridge arm, from the source to the drain, i.e., forward conduction. This freewheeling path does not generate a negative voltage problem at the VS terminal because the cathode of the upper bridge arm body diode is the positive terminal of the DC bus, and the anode is the VS terminal, thus preventing a negative voltage impact on the driver chip.

[0041] Furthermore, the forward voltage drop of the freewheeling element is less than 2V, or less than 50% of the forward voltage drop of the SiC MOSFET body diode.

[0042] This invention quantitatively guarantees that the negative voltage at the VS terminal of the driver chip does not exceed 2V, completely eliminating the risk of latch-up; it reduces freewheeling conduction loss by more than 50%, achieving significant long-term energy savings; it provides more than twice the engineering safety margin, accommodating changes in all operating conditions; it allows the selection of low-cost general-purpose diodes, reducing BOM costs; it forms a clear and strong patent protection boundary, preventing competitors from circumventing it; and ultimately achieves a comprehensive competitive advantage of high reliability, high efficiency, low cost, and low carbon emissions.

[0043] Furthermore, the lower bridge arm is composed of three SiC MOSFETs, and each SiC MOSFET is connected in antiparallel to the freewheeling element.

[0044] This invention provides full three-phase coverage, ensuring that any freewheeling phase passes through a low-voltage-drop path, with no technical blind spots; The three-phase drive chip operates symmetrically with balanced current, resulting in smoother motor operation; current losses are reduced, achieving optimal overall energy saving; the unified three-phase circuit structure simplifies the entire process of design, procurement, production, and testing; it prevents system collapse due to single-phase failures, improving the reliability level of industrial applications; and it achieves complete protection using only 3 diodes, at half the cost of a full-bridge parallel solution.

[0045] Furthermore, the SiC MOSFET of the lower bridge arm is a SiC MOSFET without a built-in body diode, and its freewheeling path is entirely provided by the freewheeling element.

[0046] This invention completely eliminates a series of parasitic problems caused by body diodes, such as reverse recovery loss, EMI, thermal runaway risk, and gate oscillation; the negative voltage at the VS terminal is strictly equal to the voltage drop of the external diode, providing the highest safety margin for the driver chip; the freewheeling element and power switching device are completely decoupled, allowing independent selection of the optimal external diode; it is not limited by the reverse recovery of the body diode, supports ultra-high frequency operation of 50kHz~500kHz and above, and significantly reduces the size of magnetic components; there is no dual-path thermal competition or thermal runaway risk, making it suitable for harsh applications such as automotive and aerospace; the freewheeling waveform is clean, the cost of the EMI filter is reduced, and the system immunity is improved.

[0047] Furthermore, the freewheeling element is a fast recovery diode or a Schottky diode.

[0048] The forward voltage drop of both fast recovery diodes and Schottky diodes (D) is far less than 2V, ensuring that the negative voltage at the VS terminal is clamped within a safe range, completely eliminating the risk of driver chip latch-up. Freewheeling losses are reduced by 65%~85%, resulting in cumulative energy savings of tens to hundreds of kilowatt-hours over a 10-year lifespan for variable frequency motors, demonstrating significant low-carbon benefits during their use. Both types of diodes are standard devices produced in large quantities, ensuring stable supply and reliability, requiring no custom development and allowing for rapid mass production.

[0049] A variable frequency motor driver includes the above-mentioned three-phase motor drive circuit and a drive chip, wherein the drive chip is electrically connected to the three-phase terminals of the motor through the three-phase motor drive circuit.

[0050] This invention fundamentally solves the core pain point: the negative voltage at the VS terminal is reduced from above -4V to below -1.5V, completely eliminating the driver chip latch-up problem, ensuring 100% complete response of the PWM signal, and transforming motor control from "intermittent instability" to "absolute stability." It significantly improves the user experience: electromagnetic noise is eliminated, reducing overall noise levels, and the motor operates quietly and smoothly, meeting the quiet requirements of high-end home appliances, industrial equipment, and electric vehicles. It offers substantial energy savings, low carbon emissions, and net carbon reduction, with environmental benefits during use far exceeding the slight increase in manufacturing costs. It provides high reliability, long lifespan, and a significantly reduced overall failure rate. It simplifies design and reduces costs: no negative voltage power supply or Miller clamping circuit is required.

[0051] Furthermore, three of the output terminals of the driver chip are respectively connected to the gates of three MOS transistors in the upper bridge arm of the three-phase motor drive circuit; The other three output terminals of the driver chip are respectively connected to the gates of the three MOS transistors in the lower bridge arm of the three-phase motor drive circuit; The sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are connected one-to-one. The three connection points between the sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are electrically connected to the three-phase terminals of the motor, respectively. A freewheeling element is provided between the source and drain of the three MOSFETs in the lower bridge arm.

[0052] In one specific embodiment of the circuit, the VB and VS terminals of the driver chip are directly connected to a capacitor C1, the VSS terminal of the driver chip is connected to the anode of diode D4 through a resistor R5, and the cathode of diode D4 is connected to the VB terminal of the driver chip. The HO terminal of the driver chip is connected to the gate of the MOS transistor SW1 in the upper bridge arm of the three-phase motor drive circuit through resistor R1. A resistor R2 is connected in parallel between the gate of MOSFET SW1 and the VS terminal of the driver chip; As mentioned above, the other two output terminals of the driver chip are connected to the gates of MOSFET SW2 and MOSFET SW3 respectively through the same circuit structure; one signal output terminal of the driver chip controls one MOSFET of the upper bridge arm. The LO terminal of the driver chip is connected to the gate of the MOS transistor SW4 in the lower bridge arm of the three-phase motor drive circuit through resistor R3; resistor R4 is connected in parallel between the gate and source of MOS transistor SW4. As mentioned above, the other two output terminals of the driver chip are connected to the gates of MOSFET SW5 and MOSFET SW6 respectively through the same circuit structure; one signal output terminal of the driver chip controls one MOSFET of the lower bridge arm. The COM terminal of the driver chip is grounded; The VS terminal of the driver chip is simultaneously connected to the source of MOSFET SW1 in the upper bridge arm, the drain of MOSFET SW4 in the lower bridge arm, and the first terminal of the three phases of the motor. The source of MOSFET SW2 in the upper bridge arm is simultaneously connected to the drain of MOSFET SW5 in the lower bridge arm and the second terminal of the three-phase terminals of the motor. The source of MOSFET SW3 in the upper bridge arm is connected to the drain of MOSFET SW6 in the lower bridge arm and the third terminal of the three-phase terminals of the motor. The source of MOSFET SW4 is connected to the positive terminal of diode D1, and the negative terminal of diode D1 is connected to the drain of MOSFET SW4. The source of MOSFET SW5 is connected to the positive terminal of diode D2, and the negative terminal of diode D2 is connected to the drain of MOSFET SW5. The source of MOSFET SW6 is connected to the positive terminal of diode D3, and the negative terminal of diode D3 is connected to the drain of MOSFET SW6. The drain of MOSFET SW1, the drain of MOSFET SW2, and the source and drain of MOSFET SW3 are all connected to the power supply Vbus. The source of MOSFET SW4, the source of MOSFET SW5, and the source of MOSFET SW6 are grounded.

[0053] This invention utilizes a bootstrap capacitor C1 in conjunction with a pre-charge network D4+R5 to ensure safe upper bridge arm drive and smooth startup while saving costs. The gate drive network is comprehensive: R1 / R3 enables single-channel drive of multiple transistors in parallel, while R2 / R4 provides pull-down protection, collectively ensuring reliable switching and preventing false triggering. Three freewheeling diodes are connected in anti-parallel to the lower bridge arm, clamping the negative voltage at the VS terminal from -4V to below -1.5V, fundamentally solving the problems of driver chip latch-up and motor noise. System-level synergy: all circuit modules cooperate to form a complete, reliable, efficient, and low-EMI signal and power chain from the MCU to the motor windings.

[0054] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A three-phase motor drive circuit, characterized by, It includes an upper bridge arm and a lower bridge arm composed of power switching devices, wherein the power switching devices have a body diode integrated inside; Each power switching device in the lower bridge arm has a freewheeling element connected in antiparallel across its two ends; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the diode inside the power switching device.

2. A three-phase motor drive circuit, characterized by, This includes the upper and lower bridge arms, which are composed of SiC MOSFETs; Each SiC MOSFET in the lower bridge arm has a freewheeling element connected in antiparallel across its terminals; The forward voltage drop of the freewheeling element is lower than the forward voltage drop of the SiC MOSFET body diode.

3. The three-phase motor drive circuit of claim 2, wherein, The SiC MOSFET in the lower bridge arm integrates a body diode, and the freewheeling element is an external fast recovery diode, which is connected in antiparallel between the drain and source of the SiC MOSFET.

4. The three-phase motor drive circuit of claim 3, wherein, The SiC MOSFET in the upper bridge arm integrates a body diode.

5. The three-phase motor drive circuit of claim 1 or 2, wherein, The forward voltage drop of the freewheeling element is less than 2V, or less than 50% of the forward voltage drop of the bulk diode.

6. The three-phase motor drive circuit of claim 3, wherein, The lower bridge arm consists of three SiC MOSFETs, each with a freewheeling element connected in antiparallel across its terminals.

7. The three-phase motor drive circuit of claim 6, wherein, The SiC MOSFET in the lower bridge arm is a SiC MOSFET without a built-in body diode.

8. The three-phase motor drive circuit of claim 5, wherein, The freewheeling element is a fast recovery diode or a Schottky diode.

9. A variable frequency motor drive, characterized by, The three-phase motor drive circuit comprising any one of claims 1-8 further comprises a drive chip, wherein the drive chip is electrically connected to the three-phase terminals of the motor through the three-phase motor drive circuit.

10. The variable frequency motor drive of claim 9, wherein, Three of the output terminals of the driver chip are respectively connected to the gates of three MOS transistors in the upper bridge arm of the three-phase motor drive circuit. The other three output terminals of the driver chip are respectively connected to the gates of the three MOS transistors in the lower bridge arm of the three-phase motor drive circuit; The sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are connected one-to-one. The three connection points between the sources of the three MOSFETs in the upper bridge arm and the drains of the three MOSFETs in the lower bridge arm are electrically connected to the three-phase terminals of the motor, respectively. A freewheeling element is provided between the source and drain of the three MOSFETs in the lower bridge arm.

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