Hybrid switch circuit of series SiC MOSFET, experimental platform system and power board

Abstract

The invention provides a switching circuit of series SiC MOSFETs, an experiment platform system and a power board, the switching circuit comprises two SiC MOSFETs and a Si IGBT, and the two SiC MOSFETs are connected in series and then are connected with the Si IGBT in parallel. And a closed-loop voltage-sharing control scheme is adopted, so that the non-uniform turn-off voltage between the series MOS tubes is overcome, and the voltage balance of the hybrid switch is ensured. According to the switch, on the premise that the power density, the efficiency, the voltage level and other characteristics of a traditional switch device are improved, optimization design in the aspects of a driving scheme, circuit layout and the like is completed, and performance optimization of the power device under the working conditions of high frequency and high load is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of switch circuits, and in particular relates to a hybrid switch circuit of series-connected SiC MOSFETs, an experimental platform system, and a power board. Background Art

[0002] The most widely used and researched power device is Si IGBT, which has high current handling capability and is usually used for high-power control drivers, especially motor drives that require large rated current devices. However, its switching speed is slow, especially the tail current during shutdown limits the switching frequency. SiC MOSFET can significantly improve system efficiency due to its excellent characteristics, but its cost is high and its voltage resistance and current carrying capacity are weak. At present, aerospace, aviation, shipbuilding and other fields have higher requirements for power devices. Using the respective advantages of SiC MOSFET and Si IGBT to form a hybrid switch is a solution.

[0003] In the existing technology, in order to improve the current level of SiC MOSFET, the current carrying capacity of Si IGBT is used to form a SiC / Si hybrid switch, and Si IGBT and SiC MOSFET are connected in parallel to provide most of the advantages of SiC device switching characteristics, and the cost is much lower than that of the full SiC solution. The main goal of hybrid switch design optimization is to achieve efficiency improvement while reducing the current level of the SiC MOSFET used, and to minimize costs while ensuring switch safety.

[0004] Chinese patent CN201910323061.4, named as series resonant dual active bridge circuit based on Si IGBT and SiC MOSFET hybrid switch, connects a single SiC MOSFET in parallel with Si IGBT to form a hybrid switch, and is designed to be applied in H-bridge circuit. The structure is as follows Figure 1 As shown. This method greatly improves the current carrying capacity of SiC MOSFET and completes the working mode judgment. However, the voltage level and cost of the switch will be completely subject to the selected SiC MOSFET chip, and it is difficult to flexibly change the design scheme and device parameters after they are selected. Chinese patent CN202310848095.1, named a hybrid switch structure of SiC MOSFET, SiIGBT and Si MOSFET, adds a low-voltage Si MOSFET, solves the IGBT tail current problem while controlling costs, and improves reliability. However, the parasitic parameters and characteristics of the three devices are different, and there is a risk of device overheating and damage due to uneven voltage, and the application scenarios are limited. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of power devices and hybrid switches in the prior art in circuits and driving schemes, and to utilize the performance advantages of SiC MOSFET and the cost advantages of Si IGBT to form a hybrid switch circuit. A closed-loop voltage-balanced control scheme is adopted to overcome the uneven turn-off voltage between series-connected MOS tubes and ensure the voltage balance of the hybrid switch. On the premise of improving the power density, efficiency, voltage level and other characteristics of traditional switch devices, the switch completes the optimized design of driving schemes, circuit layout and other aspects, and realizes the performance optimization of power devices under high frequency and high load conditions.

[0006] The present invention proposes a hybrid switch circuit combining SiC MOSFET and Si IGBT, which is composed of an IGBT and two MOSFETs. Two SiC MOSFETs are connected in series to increase the voltage level and then a Si IGBT is connected in parallel.

[0007] Furthermore, the present invention needs to calculate the mathematical formula between the driving time difference and the voltage difference between the tubes, and complete the voltage adjustment by adding a delay to achieve voltage equalization control.

[0008] Furthermore, the present invention designs the driving circuits of SiC MOSFET and Si IGBT respectively. For Si IGBT, UCC5320E is selected to provide a single-channel driving signal, and bypass capacitors are set at the input and output pins to suppress the disturbance introduced by the external power supply circuit and the resonance caused by factors such as line capacitance and inductance. When selecting the chip for the series branch, it is necessary to ensure that the output current level is high enough and the driving delay is as small as possible. The UCC21520 driver chip is selected to provide two outputs, and a resistor is inserted between the input control terminals to ensure that the two tubes are triggered at the same time.

[0009] Experimental verification shows that even under the condition of uneven auxiliary branch voltage, the efficiency and loss performance of the hybrid switch is still better than that of the pure Si IGBT switch. After voltage balancing, the dynamic performance of the hybrid switch is further improved and the amplitude increases with the increase of output power and frequency. In addition, the hybrid switch has better application effect in medium and high power scenarios, which further amplifies the advantages brought by its efficiency improvement.

[0010] The beneficial effects of the present invention are as follows:

[0011] 1. The present invention proposes a SiC MOSFET / Si IGBT hybrid switch circuit, which combines the advantages of the switching characteristics of the two devices to improve the dynamic performance of the switch device, reduce the switch cost, and improve the terminal voltage adaptability of the two devices;

[0012] 2. The present invention designs a voltage balancing strategy to solve the problem of uneven voltage in series SiC MOSFETs, derives the mathematical relationship between voltage difference and drive delay, transmits the voltage difference between the two ends of the tube to the main control chip, and completes voltage balance within a few adjustment cycles. This method has a simple circuit structure, strong applicability, and can quickly complete voltage balance control;

[0013] 3. The present invention sets a support capacitor in the circuit layout, reduces the distance between devices during arrangement, and keeps the switch devices away from the board edge, thereby minimizing the interference of the bus high-voltage signal on the hybrid switch, avoiding the problem of uneven parasitic parameters caused by the arrangement of the switch devices, and ensuring the smooth execution of the designed control scheme;

[0014] 4. Compared with existing solutions at home and abroad, the circuit of the present invention can realize high-performance and high-efficiency operation of power switching devices, achieve the purpose of reducing costs and increasing efficiency, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention:

[0016] Figure 1 It is a common hybrid switch structure in the prior art;

[0017] Figure 2 is a switch structure of a series SiC MOSFET according to an embodiment of the present invention;

[0018] Figure 3 is a schematic diagram of two tubes in series according to an embodiment of the present invention;

[0019] Figure 4 Schematic diagram of the turn-off process of two-tube series-connected SiC MOSFETs according to an embodiment of the present invention;

[0020] Figure 5 This is the SiC MOSFET voltage-sharing closed-loop control schematic;

[0021] Figure 6 It is a schematic diagram of the hybrid switch driving scheme and the commutation process;

[0022] Figure 7 This is a schematic diagram of SiC MOSFET series branch driving;

[0023] Figure 8 It is a schematic diagram of the hybrid switch experimental platform;

[0024] Fig. 9 It is a schematic diagram of the hybrid switch power board layout. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0026] This embodiment provides a hybrid switch circuit of a series SiC MOSFET, which connects two SiC MOSFETs in series to increase the voltage level and then connects a Si IGBT in parallel. Figure 2 The parasitic parameters of the same SiC MOSFET may also be different, and the different parasitic parameters will produce gate drive delay td, which will eventually lead to uneven voltage division during the shutdown process.

[0027] Furthermore, the present invention provides a mathematical formula between the driving time difference and the voltage difference between the tubes, and completes the voltage adjustment by adding a delay to achieve voltage balance control. Figure 3 As shown, the upper tube is set as 1 tube and the lower tube is set as 2 tubes.

[0028] The turn-off process of two SiC MOSFETs in series is as follows: Figure 4 As shown. Assuming that the two tubes are forward-conducting before being turned off, tube 1 is turned off at time t0, and tube 2 is turned off td later than tube 1. The rapid voltage rise from t2 to t3 and the rapid current drop from t3 to t4 are two important stages, which have the most profound impact on the voltage change. It can be seen from the waveform of the turn-off process that the final voltage unevenness is dominated by the rapid voltage rise stage.

[0029] Through model derivation and calculation, td and △V are approximately linearly related. To solve the problem of voltage unevenness, the proportional coefficient between td and △V is calculated, and the closed-loop transfer function model (Formula 2) is determined by the charge difference between the two switch tubes (Formula 1). The gate drive delay between the two tubes is adjusted by voltage closed-loop control. The principle is as follows Figure 5 shown.

[0030]

[0031] Among them, △Q is the charge difference between the two tubes, Vmiller1 and Vmiller1 are the Miller platform voltages of the two tubes, Vth is the threshold voltage, g is the transconductance, Id is the terminal current, Vds1 and Vds2 are the terminal voltages of the two tubes, ioss is the output current, Δt is the driving delay time, △V is the voltage difference between the two tubes, and i d is the drain current, C OSS is the output capacitor.

[0032] By deriving the relationship between the voltage difference and the driving delay time, the PI algorithm is introduced to determine the closed-loop transfer function model. A delay link is generated by DSP in the control loop as the timing adjustment for the next period. The voltage between the drain and source of the two tubes is measured and the difference is compared with the reference voltage. If the current difference does not meet the threshold limit, the additional delay time is obtained through the relationship, and the signal is delayed and adjusted before triggering the switch again. Voltage balance is achieved through multiple adjustments.

[0033] The present invention provides a driving method for a hybrid switch circuit of a series SiC MOSFET, characterized in that the steps are as follows:

[0034] (1) Calculate the voltage between the drain and source of the two SiC MOSFETs, and subtract them to obtain the voltage difference △V;

[0035] (2) Compare △V with the reference voltage. If the current difference does not meet the threshold limit, the relationship is Calculate the drive delay time Δt, where i d is the drain current, C OSS is the output capacitor;

[0036] (3) After adjusting the signal delay, trigger the switch again and complete the voltage balance through multiple adjustments.

[0037] Furthermore, a high-voltage Si IGBT is connected in parallel at both ends of the series SiC MOSFET. The driving scheme and commutation process are as follows: Figure 6 As shown. In this scheme, switching losses are only generated at the beginning and end of the commutation process. In one cycle, the SiC MOSFET is switched twice and the Si IGBT is switched once. The auxiliary function of the MOS tube only works during the switching transition process and remains off during the conduction period of the main switch IGBT.

[0038] This method has four variables (t1-t4), which can be adjusted to minimize the conduction loss of SiC MOSFET, thereby reducing the selected chip area and compressing the switch cost. Special attention should be paid to the fact that there will be a large current oscillation when the MOSFET is turned on for the first time. During the period when the MOSFET is turned on alone, the load current flows through both ends of it. Its maximum pulse current and junction temperature should be estimated to prevent breakdown. In the model calculation, the switching loss is minimized, and the hybrid switch drive solution is optimized by changing the duration of t1-t4.

[0039] The off voltage imbalance coefficient α is defined as shown in (Formula 3), where △Vds is the voltage difference between the two MOSFET terminals, and Vcc is the circuit bus voltage. The current ratio γ is defined as the ratio of the rated current of the IGBT and the MOSFET at 25°C, as shown in (Formula 4). A higher current ratio can significantly reduce costs, but at the same time it brings more electrical and thermal stress to the SiC MOSFET. α has a greater impact on the loss of the hybrid switch. The peak current of the MOSFET is greatly affected by the current ratio, and as the ratio decreases, its overshoot current ratio increases. Whether it is the turn-on or turn-off process, extending the conduction time will also increase the current overshoot. The drive scheme should be flexibly adjusted to ensure the safe operation of each switch.

[0040]

[0041] The hybrid switch circuit consists of an IGBT and two MOSFETs, and the drive circuits of the two must be designed separately. For Si IGBT, UCC5320E is selected to provide a single-channel drive signal, and bypass capacitors are set at the input and output pins to suppress the disturbance introduced by the external power supply circuit and the resonance caused by factors such as line capacitance and inductance. When selecting the chip for the series branch, it is necessary to ensure that the output current level is high enough and the drive delay is as small as possible. The UCC21520 driver chip is selected to provide two outputs, and a resistor is inserted between the input control terminal (pins 1 and 2 of the chip) to ensure that the two tubes are triggered at the same time.

[0042] Series SiC MOSFET drive circuit Figure 7 The voltage-equalizing control driving circuit includes a voltage conversion chip U1, a DSP main control chip U2, a dual-channel isolation gate driving chip U3, filter circuits R1, R2, C1, C2, a voltage-equalizing resistor R3, turn-on resistors Ron1, Ron2, turn-off resistors Roff1, Roff2, breakdown diodes D1, D2, and SiC MOSFET tubes Q1, Q2.

[0043] The voltage conversion chip U1 converts the +15V input signal into a 15V / -5V voltage signal and transmits it to the driver chip U3. The DSP main control chip U2 receives the voltage difference signal between Q1 and Q2, and transmits it to U3 after passing through the voltage equalization resistor R3 and the filter circuit to control the voltage balance between the two tubes. R3 can ensure that the delay generated by the DSP is transmitted to the output terminals Vgs_1 and Vgs_2. The output drive signals Vgs_1 and Vgs_2 control the MOS tube switch through the on-off resistor, and the breakdown diodes D1 and D2 play a protective role.

[0044] The present invention provides an electrical connection and experimental platform system for a hybrid switch, the structure of which is as follows: Figure 8As shown. Experimental verification shows that even under the condition of uneven auxiliary branch voltage, the efficiency and loss performance of the hybrid switch is still better than that of the pure Si IGBT switch. After voltage balancing, the dynamic performance of the hybrid switch is further improved and the amplitude increases with the increase of output power and frequency. In addition, the hybrid switch has better application effect in medium and high power scenarios, which further amplifies the advantages brought by its efficiency improvement.

[0045] The present invention provides a hybrid switch power board, the layout of which is as follows Fig. 9 As shown. The bus voltage first passes through the support capacitor to ensure the safety of the switching device. Two sets of hybrid switches are designed in the circuit so that it can work in the inverter function. Special attention should be paid to the layout of the Si IGBT and SiC MOSFET tube positions. They should be as far away from the high-voltage DC input terminal as possible on the board to reduce the power supply interference during the switching process. The lateral spacing between Si IGBT and SiC MOSFET should be minimized, and the two sets of switches should be arranged vertically on the same horizontal line to reduce mutual interference between devices.

[0046] The hybrid switch circuit combining SiC MOSFET and Si IGBT proposed in the present invention solves the voltage level matching problem of the traditional hybrid switch circuit. By analyzing the switch working process, a driving scheme with four time degrees of freedom is proposed, which shortens the conduction time of SiC MOSFET. The specifications of the selected devices in the hybrid switch can be adjusted through model calculation to reduce the switch cost and ensure the flexible application of the proposed switch circuit. A closed-loop voltage balancing control scheme based on drive delay is proposed to solve the problem of uneven voltage distribution of series branches in the designed circuit and ensure the safe operation of the switch circuit. An experimental platform is built, the hardware circuit layout is rationalized, and key components such as support capacitors and voltage balancing resistors are added to verify the improvement of the switching efficiency of the present invention.

[0047] Compared with existing solutions at home and abroad, the circuit of the present invention can realize high-performance and high-efficiency operation of power switch devices, achieve the purpose of reducing costs and increasing efficiency, and has a wide range of applications.

[0048] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hybrid switch circuit of a series SiC MOSFET, characterized in that: The switch circuit includes: two SiC MOSFETs and a Si IGBT, wherein the two SiC MOSFETs are connected in series and in parallel with the Si IGBT; wherein voltage adjustment is completed by driving delay, thereby realizing voltage equalization control.

2. A hybrid switch circuit of a series SiC MOSFET according to claim 1, characterized in that: A UCC5320E driver chip is used to provide a single-channel drive signal for the Si IGBT, and bypass capacitors are set at the input and output pins to suppress disturbances introduced by an external power supply circuit and resonance caused by factors such as line capacitance and inductance.

3. The hybrid switch circuit of a series SiC MOSFET according to claim 1, characterized in that: The voltage balancing control driving circuit of the SiCMOSFET series branch includes: a voltage conversion chip U1, a DSP main control chip U2, a dual-channel isolated gate drive chip U3, a filter circuit, a voltage balancing resistor R3, turn-on resistors Ron1 and Ron2, turn-off resistors Roff1 and Roff2, and breakdown diodes D1 and D2.

4. A hybrid switch circuit of a series SiC MOSFET according to claim 3, characterized in that: The dual-channel isolation gate driver chip U3 uses the UCC21520 driver chip.

5. A driving method for a hybrid switch circuit of a series SiC MOSFET according to any one of claims 1 to 4, characterized in that: Here are the steps: (1) Calculate the voltage between the drain and source of the two SiC MOSFETs, and subtract them to obtain the voltage difference △V; (2) Compare △V with the reference voltage. If the current difference does not meet the threshold limit, the relationship is Calculate the drive delay time Δt, where i d is the drain current, C OSS is the output capacitor; (3) After adjusting the signal delay, trigger the switch again and complete the voltage balance through multiple adjustments.

6. An experimental platform system comprising a hybrid switch circuit of a series SiC MOSFET according to any one of claims 1 to 4, characterized in that: It includes a DC source, a hybrid switching circuit, an IGBT driving circuit, a MOSFET driving circuit, and an external load.

7. A power board comprising a hybrid switch circuit of a series SiC MOSFET according to any one of claims 1 to 4, characterized in that: Including: supporting capacitors, two sets of hybrid switches; The supporting capacitor is used to ensure the safety of the switching device, and the two sets of hybrid switches enable the power board to work in the inverter function.

8. The power board according to claim 7, characterized in that: The hybrid switch circuit is far away from the high voltage DC input terminal.

9. The power board according to claim 7, characterized in that: The lateral spacing between the Si IGBT and the SiC MOSFET in the hybrid switch circuit should be as small as possible.

10. The power board according to claim 7, characterized in that: The two groups of mixing switches are arranged vertically on the same horizontal line.

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