SiC MOSFET tube junction temperature control method and circuit based on lossless buffer circuit switch trajectory adjustment and simulation platform

Abstract

The application discloses a SiC MOSFET tube junction temperature control method and circuit based on lossless buffer circuit switch trajectory adjustment and a simulation platform. First, a SiC MOSFET tube junction temperature control circuit is constructed, then it is judged whether the SiC MOSFET tube junction temperature needs to be cooled, if the SiC MOSFET tube junction temperature needs to be cooled, the Si-based MOSFET switch is controlled to be turned on at the time when the SiC MOSFET device is turned off, and at the same time, the switch trajectory is adjusted by controlling the turning-on time of the Si-based MOSFET switch at the time when the SiC MOSFET device is turned off; if loss control is needed, the Si-based MOSFET switch is controlled to be turned off, and the simulation circuit is used to verify the junction temperature control circuit and the method. The junction temperature control method combines the buffer circuit with the junction temperature control, and the junction temperature is smoothly controlled by the characteristics of the Si-based MOSFET. The circuit can actively control the switch trajectory of the SiC MOSFET, realize loss control, further realize smooth junction temperature control, and achieve the purpose of prolonging the service life of the device.

Description

Technical Field

[0001] This invention relates to the technical field of power electronic conversion and power device reliability, and in particular to a method, circuit, and simulation platform for controlling the junction temperature of SiC MOSFETs based on lossless buffer circuit switching trajectory adjustment. Background Technology

[0002] Power semiconductor devices play a crucial role in power electronic converters. Among them, SiC MOSFETs, as switching elements in various power supply applications, are rapidly expanding their use, primarily due to their faster switching speeds. Because of the rapid changes in voltage and current during switching, the inductance of the device's own package and the wiring inductance of surrounding circuitry become significant, leading to voltage and current oscillations and overshoots between the drain and source, resulting in junction temperature fluctuations and power losses.

[0003] Meanwhile, due to the high-speed switching action and losses of the device, the device is subjected to great thermal stress due to junction temperature changes. Therefore, junction temperature control measures are needed to reduce or smooth the fluctuation of its junction temperature, thereby improving the reliability of the device.

[0004] For example, in the patent application number CN2015100185040, entitled "A power device junction temperature control circuit and active thermal management method", although the device junction temperature is achieved through a buffer absorption circuit, energy is consumed in the resistor during the adjustment process. This is a buffer circuit adjustment with energy loss, which reduces the energy conversion efficiency of the power converter.

[0005] For example, in the patent application number CN201710211737.1, entitled "A Junction Temperature Smoothing Method and Circuit Based on Adjusting IGBT Turn-Off Trajectory", although it is a junction temperature smoothing method based on adjusting IGBT turn-off trajectory, it also belongs to the method of smoothing junction temperature through a lossy buffer circuit.

[0006] Therefore, a junction temperature regulation method and circuit that produces no energy loss or only a very small amount of energy loss is needed. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method, circuit and simulation platform for controlling the junction temperature of SiC MOSFET based on the switching trajectory adjustment of a passive buffer circuit. This method is based on the switching trajectory of a passive buffer circuit to adjust and achieve the control of the loss and junction temperature of SiC MOSFET.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] The present invention provides a method for controlling the junction temperature of SiC MOSFETs based on lossless buffer circuit switching trajectory adjustment, comprising the following steps:

[0010] A SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment is constructed. The lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts;

[0011] Determine and adjust the junction temperature of the SiC MOSFET: During the period when the junction temperature is estimated to be low, control the Si-based MOSFET switch to turn off, so that the SiC MOSFET operates in a hard-switching state; during the period when the junction temperature is estimated to be high, control the Si-based MOSFET switch to turn on when the SiC MOSFET device is turned off, so as to reduce the turn-off loss of the SiC MOSFET.

[0012] Furthermore, the control of the Si-based MOSFET switch is achieved by adjusting the turn-on time of the Si-based MOSFET switch when the SiC MOSFET device is turned off, thereby changing the connection time of the buffer circuit and thus changing the switching trajectory.

[0013] The present invention provides a SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment, comprising a lossless buffer circuit and a SiC MOSFET, wherein the lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s Transformer T R Diodes Ds1 and Ds2, and capacitor Cdc;

[0014] The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts;

[0015] The negative terminal of diode Ds1 is connected to transformer T R One side is connected, and the positive terminal of the diode Ds1 is connected to the buffer capacitor C. s Connect to the common connection point of the Si-based MOSFET switch Ts;

[0016] The positive terminal of diode Ds2 is connected to transformer T R One side is connected, and the negative terminal of the diode Ds2 is connected to the buffer capacitor C. s Connect to the common connection point of the SiC MOSFET;

[0017] The transformer T R The other end of the diode Ds1 is connected to the capacitor Cdc and the common connection point of the SiC MOSFET, respectively.

[0018] The transformer T R The other end of the diode Ds2 is connected to the common connection point of the capacitor Cdc and the other end of the SiC MOSFET.

[0019] Furthermore, the control of the Si-based MOSFET switch is achieved by adjusting the turn-on time of the Si-based MOSFET switch when the SiC MOSFET device is turned off, thereby changing the connection time of the buffer circuit and thus changing the switching trajectory.

[0020] The present invention provides a simulation platform for SiC device operating conditions in electric vehicle inverters based on a method for controlling the junction temperature of SiC MOSFETs using a lossless buffer circuit switching trajectory adjustment.

[0021] DC power supply and DC side filter capacitor, left bridge arm SiC switch group of electric vehicle inverter, right bridge arm SiC switch group of electric vehicle inverter, AC side output inductor, electric vehicle inverter control circuit, lossless buffer circuit junction temperature control unit.

[0022] The DC power supply and DC-side filter capacitor are used to provide power to the circuit. The filter capacitor is used to provide instantaneous peak power and reduce current harmonics at the switching frequency, ensuring that the bus voltage is stable near the given value, making the system output more stable.

[0023] The left bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit. It works in conjunction with the right bridge arm SiC switch group to realize the conversion from DC to AC.

[0024] The right bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit. It works in conjunction with the left bridge arm SiC switch group to realize the conversion from DC to AC.

[0025] The AC-side output inductor is used to simulate the operating conditions of the electric vehicle inverter, enabling the inverter to operate normally.

[0026] The electric vehicle inverter control circuit is used to control the switching state of the SiC switch groups of the left and right bridge arms of the electric vehicle inverter, so that the circuit works in a stable state, controls the AC side output current to track the reference value, and simulates the current change flowing through the SiC MOSFET under the actual operating conditions of the electric vehicle.

[0027] The lossless buffer circuit junction temperature control unit is used to realize loss control and junction temperature control of SiC MOSFET devices.

[0028] The SiC switch group of the left bridge arm and the SiC switch group of the electric vehicle inverter are connected in parallel.

[0029] One end of the AC-side output inductor is located at the common connection point of the SiC switch group on the left bridge arm of the electric vehicle inverter.

[0030] The other end of the AC output inductor is located at the common connection point of the SiC switch group on the right axle arm of the electric vehicle inverter.

[0031] The electric vehicle inverter control circuit is connected to the AC side output inductor;

[0032] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the left axle arm of the electric vehicle inverter.

[0033] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the right axle arm of the electric vehicle inverter.

[0034] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the DC power supply and the DC side filter capacitor.

[0035] Furthermore, one end of the DC power supply and DC-side filter capacitor, the SiC switch group of the left bridge arm of the electric vehicle inverter, the SiC switch group of the right bridge arm of the electric vehicle inverter, the AC-side output inductor, the electric vehicle inverter control circuit, and the junction temperature control unit of the lossless buffer circuit are respectively connected to ground.

[0036] Furthermore, the junction temperature control unit of the lossless buffer circuit adopts a SiC MOSFET junction temperature control simulation circuit based on the switching trajectory adjustment of the lossless buffer circuit.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention provides a method, circuit, and simulation circuit for controlling the junction temperature of SiC MOSFETs based on lossless buffer circuit switching trajectory adjustment. It combines a buffer circuit with junction temperature control, utilizing the characteristics of Si-based MOSFETs by replacing the diodes in the passive buffer circuit with the Si-based MOSFETs. By controlling the switching of the Si-based MOSFETs, smooth junction temperature control can be achieved. This circuit provides an active method for controlling the loss adjustment and junction temperature of SiC MOSFETs. This method achieves loss control by controlling the switching trajectory of the passive buffer circuit, further realizing smooth junction temperature control, thereby extending the device's lifespan.

[0039] The junction temperature control method and circuit proposed in this invention achieve loss control of SiCMOSFET by controlling the Si-based MOSFET switch. During loss regulation, the turn-on time of the Si-based MOSFET switch when the SiC MOSFET device is turned off can be adjusted, thereby changing the connection time of the buffer circuit and thus altering the switching trajectory. This enables smooth control of junction temperature fluctuations, while simultaneously improving device reliability and extending device lifespan.

[0040] The method for adjusting the junction temperature of a device using the switching trajectory of a buffer circuit provided by this invention avoids energy loss of the power device during energy conversion. It is a lossless buffer circuit for adjusting the junction temperature, avoiding the energy consumption of the resistor in the traditional junction temperature adjustment process. Therefore, the method provided by this invention theoretically has no energy consumption on the resistor, thereby improving the energy conversion efficiency of the power converter.

[0041] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0042] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration:

[0043] Figure 1 This is a flowchart of a SiC MOSFET junction temperature control method based on lossless buffer circuit switching trajectory adjustment.

[0044] Figure 2 The turn-off trajectory curves of SiC MOSFET devices under different switching states are shown.

[0045] Figure 3 This is a simulation circuit for SiC MOSFET junction temperature control based on lossless buffer circuit switching trajectory adjustment.

[0046] Figure 4 This is a block diagram of a SiC inverter with a junction temperature control unit containing a lossless buffer circuit.

[0047] Figure 5a This is a circuit diagram of a SiC inverter containing a junction temperature control unit with a lossless buffer circuit.

[0048] Figure 5b This is a schematic diagram of energy feedback during the discharge of a SiC device.

[0049] Figure 6 The switching waveforms (Id and Vds) of the SiC MOSFET are shown without lossless buffer control.

[0050] Figure 7 To employ lossless buffer control, the waveform changes of the Si-based MOSFET switch are observed when the SiC MOSFET is turned off.

[0051] Figure 8 To employ lossless buffer control, the change in the switching waveform of the Si-based MOSFET switch is delayed when the SiC MOSFET is turned off.

[0052] Figure 9 This is the junction temperature waveform of the device when the load current is constant.

[0053] Figure 10 The waveforms represent the load current variation and the device junction temperature.

[0054] Figure 11 The waveform of the junction temperature of the SiC MOSFET changes before and after temperature regulation.

[0055] In the diagram, 1 represents the DC power supply and DC side filter capacitor, 2 represents the SiC switch group of the left bridge arm of the electric vehicle inverter, 3 represents the SiC switch group of the right bridge arm of the electric vehicle inverter, 4 represents the AC side output inductor, 5 represents the electric vehicle inverter control circuit, and 6 represents the lossless buffer circuit control unit. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0057] Example 1

[0058] like Figure 1 As shown, Figure 1The flowchart illustrates a method for controlling the junction temperature of a SiC MOSFET based on the adjustment of the switching trajectory using a lossless buffer circuit. This embodiment provides a method for controlling the junction temperature of a SiC MOSFET based on the adjustment of the switching trajectory using a lossless buffer circuit, which includes the following steps:

[0059] A SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment is constructed. The lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts;

[0060] In this embodiment, the source of the Si-based MOSFET switch Ts is connected in series with one end of the drain of the SiC MOSFET; the drain of the Si-based MOSFET switch Ts is connected to the buffer capacitor C. s One end is connected to the buffer capacitor C. s The other end is connected to one end of the source of the SiC MOSFET. In the circuit of this embodiment, the gate of the Si-based MOSFET switch Ts is floating with the gate of the SiC MOSFET.

[0061] The junction temperature of the SiC MOSFET is determined and adjusted. During the estimated period of high junction temperature, the Si-based MOSFET switch is controlled to turn on when the SiC MOSFET is turned off, thereby reducing the turn-off loss of the SiC MOSFET. At the same time, the switching trajectory can be changed and the magnitude of the turn-off loss can be adjusted by controlling the on-time of the Si-based MOSFET when the SiC MOSFET is turned off. During the estimated period of low junction temperature, the Si-based MOSFET switch is controlled to turn off, so that the SiC MOSFET operates in a hard-switching state, where the loss is the greatest.

[0062] In this embodiment, the estimated high junction temperature refers to the period during which the load current remains constant.

[0063] In this embodiment, the estimated low junction temperature refers to the time period during which the load current decreases.

[0064] Junction temperature fluctuations in power devices are mainly related to low-frequency junction temperature fluctuations, which are primarily caused by large-scale random fluctuations in the input and output power of the power converter. When the load current decreases, the junction temperature of the device will drop significantly, and the junction temperature can be predicted by the change in load current.

[0065] By comparing the junction temperature waveforms of the device with and without a constant load current, it was found that the junction temperature waveform decreases significantly with a small change in load current. The junction temperature of the device can be estimated based on the magnitude of the load current change.

[0066] By adjusting the losses of SiC MOSFET devices through Si-based MOSFET switches, the device can be cooled down by reducing losses when the junction temperature is high, and heated up by increasing losses when the junction temperature is low. This can reduce junction temperature fluctuations and is used when smoothing junction temperature fluctuations is required. It also reduces the thermal stress on the device, improves the device's reliability, and extends its lifespan.

[0067] Figure 2 This is the turn-off trajectory curve of a SiC MOSFET device under different switching states. During the use of power electronic switching devices, hard switching leads to significant switching losses, and the inductive components of the circuit induce voltage spikes. The higher the switching frequency and the faster the turn-off, the higher this induced voltage. This voltage applied across the switching device can easily cause it to break down. Therefore, soft switching is necessary during the use of power electronic switching devices.

[0068] Soft switching refers to the switching process that utilizes soft-switching technology. An ideal soft-switching process involves the current or voltage first dropping to zero, and then slowly rising back to its off-state value, resulting in near-zero switching losses. Adding a buffer circuit to a SiC MOSFET device can reduce its turn-off losses and alter its turn-off trajectory.

[0069] Because the turn-off trajectory of the SiC MOSFET device can be adjusted in the buffer circuit, the turn-off trajectory can be adjusted by changing the turn-on time of the Si-based MOSFET switch in this lossless buffer junction temperature control circuit. The diagram shows the turn-off trajectory states of the SiC MOSFET device under different Si-based MOSFET switch turn-on times, with large buffers indicating greater turn-off losses and a turn-off trajectory closer to a hard-switching state.

[0070] Example 2

[0071] The SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment provided in this embodiment includes a lossless buffer circuit and a SiC MOSFET.

[0072] The lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s Transformer T R Diode Ds1, Diode Ds2, Capacitor Cdc;

[0073] The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts.

[0074] The negative terminal of diode Ds1 is connected to transformer T R One side is connected, and the positive terminal of the diode Ds1 is connected to the buffer capacitor C. s Connect to the common connection point of the Si-based MOSFET switch Ts;

[0075] The positive terminal of diode Ds2 is connected to transformer T R One side is connected, and the negative terminal of the diode Ds2 is connected to the buffer capacitor C. s Connect to the common connection point of the SiC MOSFET;

[0076] The transformer T R The other end of the diode Ds1 is connected to the capacitor Cdc and the common connection point of the SiC MOSFET, respectively.

[0077] The transformer T R The other end of the diode Ds2 is connected to the common connection point of the capacitor Cdc and the other end of the SiC MOSFET.

[0078] In this embodiment, the negative terminal of diode Ds1 and the positive terminal of diode Ds2 are connected to transformer T. R At both ends on the same side, the transformer T R The two ends on the other side are connected to the capacitor Cdc, and simultaneously connected to the drain and source of the SiC MOSFET.

[0079] In this embodiment, the source of the Si-based MOSFET switch Ts is connected in series with one end of the drain of the SiC MOSFET; the drain of the Si-based MOSFET switch Ts is connected to the buffer capacitor C. s One end is connected to the buffer capacitor C. s The other end is connected to one end of the source of the SiC MOSFET. In the circuit of this embodiment, the gate of the Si-based MOSFET switch Ts is floating with the gate of the SiC MOSFET.

[0080] The embodiment provided Figure 3 The working principle of a SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment is presented, wherein... Figure 3 (a) is the basic unit. Figure 3In (b), when the SiC MOSFET (switch S in the figure) is turned off, the buffer capacitor Cs is charged and the Si-based MOSFET switch (switch Ts in the figure) is turned on. By adjusting the turn-on time of the Si-based MOSFET, the turn-off delay time of the SiC MOSFET can be adjusted, thereby achieving the purpose of adjusting the turn-off loss and regulating the junction temperature.

[0081] Figure 3 When the SiC MOSFET is turned on (Si-based MOSFET is turned off, normal buffering), the buffer capacitor Cs discharges, and the buffer capacitor discharges to the power supply side through the diode Ds and the transformer TR.

[0082] The circuit provided in this embodiment mainly controls the connection time of the buffer circuit by controlling the turn-on time of the Si-based MOSFET, thereby achieving loss regulation of the SiC MOSFET.

[0083] Example 3

[0084] This embodiment constructs a simulation platform for measuring the operating conditions of SiC MOSFETs in electric vehicle inverters based on the principle of a SiC MOSFET junction temperature control simulation circuit based on lossless buffer circuit switching trajectory adjustment. Figure 4 , Figure 5a , Figure 5b As shown, Figure 4 The schematic diagram of a SiC inverter with a junction temperature control unit containing a lossless buffer circuit is shown. Figure 5a This is a circuit diagram of a SiC inverter with a junction temperature control unit and a lossless buffer circuit. The SiC device operating condition simulation platform for the electric vehicle inverter mainly includes a DC power supply and DC-side filter capacitor, a SiC switch group for the left bridge arm of the electric vehicle inverter, a SiC switch group for the right bridge arm of the electric vehicle inverter, an AC-side output inductor, an electric vehicle inverter control circuit, and a junction temperature control unit with a lossless buffer circuit.

[0085] The DC power supply and DC-side filter capacitor are used to provide power to the circuit. The filter capacitor is used to provide instantaneous peak power and reduce current harmonics at the switching frequency, ensuring that the bus voltage is stable near the given value, making the system output more stable.

[0086] The left bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit. It works in conjunction with the right bridge arm SiC switch group to realize the conversion from DC to AC.

[0087] The right bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit. It works in conjunction with the left bridge arm SiC switch group to realize the conversion from DC to AC.

[0088] The AC-side output inductor is used to simulate the operating conditions of the electric vehicle inverter, enabling the inverter to operate normally.

[0089] The electric vehicle inverter control circuit is used to control the switching state of the SiC switch group of the left and right bridge arms of the electric vehicle inverter, so that the circuit works in a stable state, controls the AC side output current to track the reference value, and simulates the current change flowing through the SiC MOSFET under the actual operating conditions of the electric vehicle.

[0090] The lossless buffer circuit junction temperature control unit is used to realize loss control and junction temperature control of SiC MOSFET devices.

[0091] The SiC switch group of the left bridge arm and the SiC switch group of the electric vehicle inverter are connected in parallel.

[0092] One end of the AC-side output inductor is located at the common connection point of the SiC switch group on the left bridge arm of the electric vehicle inverter.

[0093] The other end of the AC output inductor is located at the common connection point of the SiC switch group on the right axle arm of the electric vehicle inverter.

[0094] The electric vehicle inverter control circuit is connected to the AC side output inductor;

[0095] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the left axle arm of the electric vehicle inverter.

[0096] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the right axle arm of the electric vehicle inverter.

[0097] The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the DC power supply and the DC side filter capacitor.

[0098] The DC power supply and DC side filter capacitor, the SiC switch group of the left bridge arm of the electric vehicle inverter, the SiC switch group of the right bridge arm of the electric vehicle inverter, the AC side output inductor, the electric vehicle inverter control circuit, and one end of the junction temperature control unit of the lossless buffer circuit are respectively connected to ground.

[0099] In this embodiment, the junction temperature control unit of the lossless buffer circuit adopts a SiC MOSFET junction temperature control simulation circuit based on the switching trajectory adjustment of the lossless buffer circuit.

[0100] In this embodiment, the energy is fed back to the power supply side when the buffer capacitor discharges, ideally with no energy loss during the energy conversion process. This overcomes the problem of energy consumption in the regulated power transistor during junction temperature adjustment in existing lossy buffer circuits, and also overcomes the energy loss of SiC MOSFETs during discharge. Figure 3 , Figure 5a and Figure 5b The side where the capacitor Cdc is located. When discharging, electrical energy is fed back to the power supply side, such as... Figure 5b The bolded line is shown in the image. Figure 4 This is a block diagram of a SiC inverter with a lossless buffer circuit and junction temperature control unit. First, the load current is acquired and processed, and then compared with a given reference current through a comparator and a compensation controller for output. The compensation controller is used to adjust the system stability, eliminate steady-state errors, and improve control accuracy. The PWM modulation module generates the pulse wave drive signal required by the MOSFETs. The drive module amplifies the control pulse signal of the switching transistors generated by the control circuit to effectively drive the switching transistors, while reducing switching losses and improving overall efficiency and reliability. S1 and S2 are the SiC switching groups of the left bridge arm of the inverter, and S3 and S4 are the SiC switching groups of the right bridge arm. S1 and S4 are turned on simultaneously, as are S2 and S3. The pulse waveforms of S1 and S4 are complementary to those of S2 and S3, but to ensure normal operation of the inverter, the complementary pulse waveforms contain a certain dead time.

[0101] Among them, S1 in the SiC switch group of the left bridge arm is connected to the Si-based MOSFET switch T in series. s1 and buffer capacitor C s1 Connection; where, Si-based MOSFET switch T s1 The source of the SiC MOSFET is connected in series with one end of the drain of the SiC MOSFET; the Si-based MOSFET switch T s1 The drain and buffer capacitor C s1 One end is connected to the buffer capacitor C. s1 The other end is connected to one source terminal of the SiC MOSFET. In this embodiment, the Si-based MOSFET switch T... s1 The gate of the SiC MOSFET is left floating. The connection method between S2 in the left bridge arm SiC switch group and S3 and S4 in the right bridge arm SiC switch group and the snubber circuit is the same.

[0102] This embodiment utilizes an electric vehicle inverter SiC device operating condition simulation platform to conduct experiments according to the following steps:

[0103] First, the transformation curves of drain current (Id) and drain-source voltage (Vds) during device switching are tested without lossless buffer control. Figure 6 This is a curve showing the transformation of drain current (Id) and drain-source voltage (Vds) during switching of a SiC MOSFET device without passive buffer control.

[0104] Figure 6 To prevent changes in the switching waveforms (Id and Vds) of the SiC MOSFET without using lossless buffer control, the method described in this invention, which adjusts the switching trajectory based on a passive buffer circuit to control device losses, is employed. The test uses a lossless buffer circuit. The Si-based MOSFET switch is controlled to turn on at the instant the SiC MOSFET is turned off, at which point the SiC MOSFET loss is minimized. Conversely, the Si-based MOSFET switch is controlled to turn on with a delay when the SiC MOSFET is turned off, resulting in higher losses.

[0105] Figure 7 The change in the switching waveform of the SiC MOSFET before and after the SiC MOSFET turns on at the moment of its turn-off is controlled by a lossless buffer. Figure 8 The change in the switching waveform of the Si-based MOSFET switch before and after the SiC MOSFET is delayed when it is turned on is controlled by a lossless buffer.

[0106] Next, test the temperature control effect of the circuit. First, simulate the circuit by controlling the load current to reduce the current amplitude to 18 in 0.1s-0.2s. Figure 10 This is the junction temperature waveform of the device when the load current changes. When the load current changes within 0.1s-0.2s, the junction temperature of the device changes significantly.

[0107] Figure 10 The load current changes and device junction temperature waveforms are controlled to simultaneously turn on the Si-based MOSFET when the SiC MOSFET is turned off during the 0s-0.1s and 0.2s-0.3s time periods, and the device operates in a buffer state during this time. During the 0.1s-0.2s time period, the Si-based MOSFET is turned off, and the device operates in a hard-switching state. Figure 10 The figure shows the junction temperature changes of the SiC MOSFET before and after temperature regulation. It can be seen that the overall junction temperature decreases during 0-0.1s and 0.2s-0.3s, while the junction temperature waveform increases during 0.1s-0.2s, achieving a smooth junction temperature control effect.

[0108] Figure 11 The change in the junction temperature waveform of the SiC MOSFET before and after temperature regulation shows that when temperature regulation is used, the switching loss of the SiC MOSFET device can be controlled by adjusting the turn-on time of the Si-based MOSFET switch when the SiC MOSFET is turned off.

[0109] pass Figure 7 Changes in the switching waveform of SiC MOSFETs under lossless buffer control, and Figure 11 The change in the junction temperature waveform of the SiC MOSFET shows that when the Si-based MOSFET switch is turned on when the SiC MOSFET is turned off, and the circuit is in a lossless buffer control state, it can effectively reduce current and voltage oscillations and overshoot, and reduce switching losses.

[0110] When the Si-based MOSFET is turned off, the device is in a hard-switching state, which can increase losses and adjust the junction temperature. At the same time, experimental verification shows that by adjusting the Si-based MOSFET to turn on when the SiC MOSFET is turned off, the turn-off trajectory of the SiC MOSFET main switch can be adjusted to adjust the turn-off loss and achieve the purpose of junction temperature control.

[0111] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for controlling the junction temperature of SiC MOSFETs based on lossless buffer circuit switching trajectory adjustment, characterized in that: Includes the following steps: A SiC MOSFET junction temperature control circuit based on lossless buffer circuit switching trajectory adjustment is constructed. The lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts; Determine and adjust the junction temperature of the SiC MOSFET: During the period when the junction temperature is estimated to be low, control the Si-based MOSFET switch to turn off, so that the SiC MOSFET operates in a hard-switching state; during the period when the junction temperature is estimated to be high, control the Si-based MOSFET switch to turn on when the SiC MOSFET device is turned off, so as to reduce the turn-off loss of the SiC MOSFET.

2. The SiC MOSFET junction temperature control method based on lossless buffer circuit switching trajectory adjustment as described in claim 1, characterized in that: The control of the Si-based MOSFET switch is achieved by adjusting the turn-on time of the Si-based MOSFET switch when the SiC MOSFET device is turned off, thereby changing the connection time of the buffer circuit and thus changing the switching trajectory.

3. A circuit implemented according to the SiC MOSFET junction temperature control method based on lossless buffer circuit switching trajectory adjustment as described in claim 1, characterized in that: It includes a lossless buffer circuit and a SiC MOSFET, wherein the lossless buffer circuit includes a Si-based MOSFET switch Ts and a buffer capacitor C. s ,transformer T R Diodes Ds1 and Ds2, and capacitor Cdc; The Si-based MOSFET switch Ts is connected in series with one end of the SiC MOSFET; the buffer capacitor C s One end is connected to the other end of the SiC MOSFET to form the first connection point, and the buffer capacitor C s The other end is connected to the other end of the Si-based MOSFET switch Ts to form a second connection point; The negative terminal of diode Ds1 is connected to the transformer. T R One end of one winding is connected, and the positive terminal of the diode Ds1 is connected to the buffer capacitor C. s Connect to the second connection point that is connected to the Si-based MOSFET switch Ts; The positive terminal of diode Ds2 is connected to the transformer. T R One end of the other winding is connected, and the negative terminal of the diode Ds2 is connected to the buffer capacitor C. s Connect to the first connection point of the SiC MOSFET; The capacitor Cdc is connected in parallel with the SiC MOSFET. One end of the SiC MOSFET is connected to one end of the capacitor Cdc to form a third connection point, and the other end of the SiC MOSFET is connected to the other end of the capacitor Cdc to form a fourth connection point. The transformer T R One end of one winding is connected to the negative terminal of diode Ds1, and the transformer T R The other end of one winding is connected to the capacitor Cdc and the third connection point of the SiC MOSFET. The transformer T R One end of the other winding is connected to the positive terminal of diode Ds2, and the transformer T R The other end of the other winding is connected to the capacitor Cdc and the fourth connection point of the SiC MOSFET.

4. The circuit as described in claim 3, characterized in that: The control of the Si-based MOSFET switch is achieved by adjusting the turn-on time of the Si-based MOSFET switch, which is during the turn-off period of the SiC MOSFET device, thereby changing the connection time of the buffer circuit to change the switching trajectory of the SiC MOSFET device.

5. A simulation platform for SiC device operating conditions in electric vehicle inverters, implemented according to the lossless buffer circuit switching trajectory adjustment SiC MOSFET junction temperature control method described in claim 1, is characterized in that: Includes DC power supply and DC side filter capacitor, left bridge arm SiC switch group of electric vehicle inverter, right bridge arm SiC switch group of electric vehicle inverter, AC side output inductor, electric vehicle inverter control circuit, and lossless buffer circuit junction temperature control unit. The DC power supply and DC-side filter capacitor are used to provide power to the circuit. The function of the filter capacitor is to provide instantaneous peak power and reduce current harmonics at the switching frequency, so as to ensure that the bus voltage is stable near the given value and make the system output more stable. The left bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit and works in conjunction with the right bridge arm SiC switch group to realize the conversion from DC to AC. The right bridge arm SiC switch group of the electric vehicle inverter is used to control the working state of the circuit. It works in conjunction with the left bridge arm SiC switch group to realize the conversion from DC to AC. The AC-side output inductor is used to simulate the operating conditions of the electric vehicle inverter, so that the inverter can operate normally. The electric vehicle inverter control circuit is used to control the switching state of the SiC switch group of the left and right bridge arms of the electric vehicle inverter, so that the circuit works in a stable state, controls the AC side output current to track the reference value, and simulates the current change flowing through the SiC MOSFET under the actual operating conditions of the electric vehicle. The lossless buffer circuit junction temperature control unit is used to realize loss control and junction temperature control of SiC MOSFET devices; The left bridge arm SiC switch group and the right bridge arm SiC switch group of the electric vehicle inverter are connected together. One end of the AC side output inductor is located at the common connection point of the SiC switch group on the left bridge arm of the electric vehicle inverter. The other end of the AC side output inductor is located at the common connection point of the SiC switch group on the right axle arm of the electric vehicle inverter. The electric vehicle inverter control circuit is connected to the AC side output inductor; The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the left axle arm of the electric vehicle inverter. The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the SiC switch group of the right axle arm of the electric vehicle inverter. The two ends of the junction temperature control unit of the lossless buffer circuit are respectively connected to the two ends of the DC power supply and the DC side filter capacitor.

6. The SiC device operating condition simulation platform for electric vehicle inverters as described in claim 5, characterized in that: The DC power supply and DC side filter capacitor, the SiC switch group of the left bridge arm of the electric vehicle inverter, the SiC switch group of the right bridge arm of the electric vehicle inverter, the AC side output inductor, the electric vehicle inverter control circuit, and one end of the junction temperature control unit of the lossless buffer circuit are respectively connected to ground.

7. The SiC device operating condition simulation platform for electric vehicle inverters as described in claim 5, characterized in that: The junction temperature control unit of the lossless buffer circuit adopts a SiC MOSFET junction temperature control circuit based on the switching trajectory adjustment of the lossless buffer circuit.

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