Control device for power converter

Abstract

The objective is to provide a control device for a power conversion device that maintains the normally-off state of transistors, has low losses, and can suppress degradation of its lifespan. [Solution] A control device for a power converter, wherein the power converter has a transistor, and the control device for a power converter increases the difference between the threshold voltage and the gate voltage of the transistor as the temperature of the transistor decreases.

Description

Technical Field

[0001] The present invention relates to a control device for a power conversion device.

Background Art

[0002] As power semiconductors, gallium nitride (GaN)-based semiconductors and silicon carbide (SiC)-based semiconductors are used (for example, Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is required to drive the power semiconductor of the power conversion device with low loss. However, increasing the drive voltage may shorten the life of the element. Lowering the threshold voltage may cause the element to be in the normally-on state. Therefore, an object is to provide a control device for a power conversion device that maintains the normal-off of the transistor, has low loss, and suppresses deterioration of the life.

Means for Solving the Problems

[0005] The above object can be achieved by a control device for a power conversion device, wherein the power conversion device has a transistor, and the lower the temperature of the transistor, the greater the difference between the threshold voltage and the gate voltage of the transistor.

[0006] The gate voltage may be increased as the temperature of the transistor is lower.

[0007] If the temperature is lower than the first temperature, the gate voltage may be set to the first voltage; if the temperature is equal to or greater than the first temperature but lower than the second temperature, the gate voltage may be set to the second voltage which is lower than the first voltage; and if the temperature is equal to or greater than the second temperature, the gate voltage may be set to the third voltage which is lower than the second voltage.

[0008] The lower the temperature of the transistor, the smaller the turn-on gate resistance of the transistor may be.

[0009] If the temperature is lower than the fourth temperature, the turn-on gate resistance may be set to a first resistance value; if the temperature is higher than the fourth temperature and lower than the fifth temperature, the turn-on gate resistance may be set to a second resistance value higher than the first resistance value; and if the temperature is higher than the fifth temperature, the turn-on gate resistance may be set to a third resistance value higher than the second resistance value. [Effects of the Invention]

[0010] This invention provides a control device for a power conversion device that maintains the normally-off state of transistors, has low losses, and suppresses degradation of its lifespan. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1(a) is a schematic diagram of the power converter according to the first embodiment. Figure 1(b) is a block diagram illustrating the hardware configuration of the control device. [Figure 2] Figure 2 is a flowchart illustrating the process in the first embodiment. [Figure 3] Figures 3(a) and 3(b) illustrate voltage. [Figure 4] Figure 4(a) is a flowchart illustrating the process in the second embodiment. Figure 4(b) is a diagram illustrating the voltage. [Modes for carrying out the invention]

[0012] <First Embodiment> The control device of the power converter according to this embodiment will now be described with reference to the drawings. Figure 1(a) is a schematic diagram of the power converter 100 according to the first embodiment. The power converter 100 is mounted on a vehicle, for example, and converts power between a battery and a motor. The power converter 100 includes a transistor 10, a drive circuit 20, a temperature sensor 22, and a control device 30.

[0013] Transistor 10 is a normally-off field-effect transistor (FET), and is a HEMT (High Electron Mobility Transistor) formed from, for example, a gallium nitride (GaN) semiconductor. Transistor 10 has a gate electrode 12, a source electrode 14, and a drain electrode 16.

[0014] The drive circuit 20 is electrically connected to the gate electrode 12 of the transistor 10, has a power supply, and applies a gate voltage Vg to the gate electrode 12. When the gate voltage Vg is less than the threshold voltage Vth, the transistor 10 is off. When the gate voltage Vg becomes equal to or greater than the threshold voltage Vth, the transistor 10 switches from off to on.

[0015] The control device 30 is a control device for the power converter 100 and includes an arithmetic unit such as a CPU (Central Processing Unit), and memory devices such as RAM (Random Access Memory) and ROM (Read Only Memory). The control device 30 performs various controls by executing programs stored in the ROM and memory devices. The control device 30 is electrically connected to the temperature sensor 22 and the drive circuit 20.

[0016] The control device 30 includes a temperature acquisition unit 32, a voltage control unit 34, and a gate resistance control unit 36. The temperature sensor 22 detects the temperature of the transistor 10. The temperature acquisition unit 32 acquires the temperature of the transistor 10 from the temperature sensor 22. The voltage control unit 34 controls the drive circuit 20 and changes the gate voltage Vg according to the temperature. The gate resistance control unit 36 controls the turn-on gate resistance of the transistor 10.

[0017] FIG. 1(b) is a block diagram illustrating the hardware configuration of the control device 30. The control device 30 includes a CPU (Central Processing Unit) 40, a RAM (Random Access Memory) 42, a ROM (Read Only Memory) 43, a storage device 44, and an interface 46. The CPU 40, the RMA 42, the ROM 43, the storage device 44, and the interface 46 are connected to each other by a bus or the like. The RAM 42 is a volatile memory that temporarily stores programs and data. The storage device 44 is a solid state drive (SSD) such as a flash memory, a hard disk drive (HHD), or the like. The storage device 44 stores programs and the like.

[0018] By the CPU 40 executing the program stored in the RAM 42, the temperature acquisition unit 32, the voltage control unit 34, and the gate resistance control unit 36 are realized in the control device 30. Each part of the control device 30 may be hardware such as a circuit.

[0019] FIG. 2 is a flowchart illustrating the processing in the first embodiment. The temperature acquisition unit 32 acquires the temperature of the transistor 10 from the temperature sensor 22 (step S10). The voltage control unit 34 controls the gate voltage based on the temperature of the transistor 10 (step S12). The processing ends here.

[0020] FIG. 3(a) is a diagram illustrating voltage. The horizontal axis represents the temperature of transistor 10. The vertical axis represents the voltage of transistor 10. The dashed line in the figure represents the threshold voltage Vth of transistor 10. The dotted line represents the gate voltage Vg in the comparative example, and the gate voltage Vg is a constant value regardless of temperature. The solid line represents the gate voltage Vg in the first embodiment. The gate voltage Vg in the first embodiment changes depending on temperature, being higher at lower temperatures and lower at higher temperatures. The gate voltage Vg changes linearly with temperature, for example.

[0021] The power loss during the driving of transistor 10 depends on the difference (Vg - Vth) between the gate voltage Vg and the threshold voltage Vth. The larger Vg - Vth is, the smaller the loss becomes. If the gate voltage Vg is increased, Vg - Vth also increases, and the loss is reduced. However, an increase in the gate voltage Vg may deteriorate the lifespan of transistor 10. More specifically, as the gate voltage Vg increases, the gate leakage current increases. When the gate leakage current increases, the lifespan of the transistor becomes shorter. The higher the temperature, the larger the gate leakage current. Therefore, if the gate voltage Vg is increased in a high-temperature environment, the gate leakage current increases significantly, and the lifespan of transistor 10 is likely to deteriorate.

[0022] By reducing the threshold voltage Vth, Vg - Vth can also be widened. However, due to the decrease in the threshold voltage Vth, transistor 10 may enter the normally-on state. In particular, the threshold voltage Vth of GaN-HEMT is smaller compared to other transistors. Therefore, it is difficult to further reduce the threshold voltage Vth in a normally-off GaN-HEMT.

[0023] According to the first embodiment, as shown in Figure 3(a), the voltage control unit 34 increases the gate voltage Vg and increases Vg-Vth as the temperature of the transistor 10 decreases. By increasing Vg-Vth, the losses of the transistor 10 are reduced. In particular, the gate voltage Vg increases under low temperature and room temperature conditions, making it possible to drive the transistor 10 with low loss. As the temperature increases, the gate voltage Vg decreases. Therefore, the gate leakage current does not increase easily. The degradation of the lifespan of the transistor 10 is suppressed.

[0024] As shown in Figure 3(a), the threshold voltage Vth does not change with temperature and remains approximately constant. Transistor 10 maintains a normally-off state.

[0025] As shown in Figure 3(a), the gate voltage Vg changes continuously. The gate voltage Vg is proportional to the temperature, with Vg being larger at lower temperatures and smaller at higher temperatures. The gate voltage Vg may change linearly with respect to temperature or nonlinearly. The temperature of the transistor 10 may be detected by the temperature sensor 22, or it may be estimated from the surrounding environment and operating conditions.

[0026] (modified version) The same configuration as in the first embodiment will not be explained. Figure 3(b) is a diagram illustrating the voltages. The temperature thresholds are T1 (first temperature) and T2 (second temperature). T2 is higher than T1. Of the gate voltages in Figure 3(b), Vg1 (first voltage) is the highest. Vg2 (second voltage) is lower than Vg1 and higher than Vg3 (third voltage). Vg is the lowest.

[0027] The voltage control unit 34 controls the gate voltage Vg according to the temperature, changing the gate voltage Vg in steps (step S12 in Figure 2). When the temperature is lower than T1, the voltage control unit 34 sets the gate voltage to Vg1. When the temperature is greater than or equal to T1 and less than T2, the voltage control unit 34 sets the gate voltage to Vg2. When the temperature is greater than or equal to T2, the voltage control unit 34 sets the gate voltage to Vg3.

[0028] In the modified configuration, the voltage control unit 34 changes the gate voltage Vg in three stages according to the temperature, setting it to one of Vg1, Vg2, or Vg3. When the temperature is lower than T1, the voltage control unit 34 sets the gate voltage to the highest value, Vg1. As Vg-Vth increases, the loss of the transistor 10 is reduced. As the temperature rises, the voltage control unit 34 lowers the gate voltage to Vg2, and then further to Vg3. The gate leakage current decreases, and the degradation of the lifespan is suppressed.

[0029] <Second Embodiment> The same configuration as in the first embodiment will not be explained. Figure 4(a) is a flowchart illustrating the process in the second embodiment. The temperature acquisition unit 32 acquires the temperature of the transistor 10 from the temperature sensor 22 (step S10). The gate resistance control unit 36 ​​controls the turn-on gate resistance based on the temperature of the transistor 10 (step S14). The process is then completed.

[0030] The gate resistance control unit 36 ​​changes the turn-on gate resistance Rg in three steps, for example. The temperature thresholds for transistor 10 are T4 (fourth temperature) and T5 (fifth temperature). T4 is lower than T5. When the temperature is lower than T4, the gate resistance control unit 36 ​​sets the turn-on gate resistance to Rg1 (first resistance value). When the temperature is T4 or higher and lower than T5, the gate resistance control unit 36 ​​sets the turn-on gate resistance to Rg2 (second resistance value). When the temperature is T5 or higher, the gate resistance control unit 36 ​​sets the turn-on gate resistance to Rg3 (third resistance value). Of the turn-on gate resistances, Rg1 is the lowest. Rg2 is higher than Rg1 and lower than Rg3. Rg3 is the highest.

[0031] Figure 4(b) illustrates voltage. The dashed line represents the threshold voltage Vth. The dotted line represents the gate voltage Vg. The threshold voltage Vth and gate voltage Vg are constant values. The solid line represents the surge voltage Vgs. The surge voltage Vgs is generated when transistor 10 is switched on and off and is the voltage applied to the gate electrode 12. The higher the turn-on gate resistance Rg, the smaller the surge voltage Vgs. The lower the turn-on gate resistance Rg, the larger the surge voltage Vgs. Of the surge voltages in Figure 4(b), Vgs1 is the highest. Vgs2 is lower than Vgs1 and higher than Vgs3. Vgs3 is the lowest.

[0032] The gate resistance control unit 36 ​​controls the turn-on gate resistance according to the temperature (step S14 in Figure 4(a)). When the temperature is lower than T4, the turn-on gate resistance is Rg1. Because the turn-on gate resistance is low, the surge voltage is high and becomes Vgs1. When the temperature is T4 or higher and lower than T5, the turn-on gate resistance is higher than Rg1 and becomes Rg2. Because the turn-on gate resistance is higher, the surge voltage becomes lower than Vgs1 and becomes Vgs2. When the temperature is T5 or higher, the turn-on gate resistance is higher than Rg2 and becomes Rg3. The surge voltage becomes lower than Vgs2 and becomes Vgs3.

[0033] According to the second embodiment, the lower the temperature, the smaller the turn-on gate resistance Rg the gate resistance control unit 36 ​​makes. As the turn-on gate resistance Rg decreases, the surge voltage Vgs applied to the gate electrode 12 increases. Since Vgs-Vth becomes larger, the transistor 10 can be driven with low loss. As the temperature increases, the turn-on gate resistance Rg increases, so the surge voltage Vgs decreases. The gate leakage current does not increase easily. The degradation of the transistor 10's lifespan is suppressed.

[0034] As shown in Figure 4(b), the threshold voltage Vth does not change with temperature and remains approximately constant. Transistor 10 maintains a normally-off state.

[0035] Since the turn-on gate resistance Rg changes in three stages, the surge voltage Vgs also changes in three stages. The turn-on gate resistance Rg may change continuously. The surge voltage Vgs also changes continuously. The turn-on gate resistance Rg may change linearly or nonlinearly with respect to temperature. The surge voltage Vgs changes linearly or nonlinearly.

[0036] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of Symbols]

[0037] 10 Transistor, 12 Token electrode, 14 Source electrode, 16 Drain electrode, 20 Drive circuit, 22 Temperature sensor, 30 Control device, 32 Temperature acquisition unit, 34 Voltage control unit, 36 Gate resistance control unit, 100 Power converter

Claims

1. A control device for a power converter, The power converter has a transistor, A control device for a power conversion device that increases the difference between the threshold voltage and gate voltage of the transistor as the temperature of the transistor decreases.

2. The control device for a power conversion device according to claim 1, wherein the gate voltage is increased as the temperature of the transistor decreases.

3. If the temperature is lower than the first temperature, the gate voltage is set to the first voltage. If the temperature is equal to or greater than the first temperature and lower than the second temperature, the gate voltage is set to a second voltage that is lower than the first voltage. The control device for a power converter according to claim 2, wherein if the temperature is equal to or greater than the second temperature, the gate voltage is set to a third voltage lower than the second voltage.

4. The control device for a power conversion device according to claim 1 or 2, wherein the lower the temperature of the transistor, the smaller the turn-on gate resistance of the transistor.

5. If the aforementioned temperature is lower than the fourth temperature, the turn-on gate resistance is set to the first resistance value. If the temperature is higher than the fourth temperature and lower than the fifth temperature, the turn-on gate resistance is set to a second resistance value that is higher than the first resistance value. The control device for a power converter according to claim 4, wherein if the temperature is higher than the fifth temperature, the turn-on gate resistance is set to a third resistance value higher than the second resistance value.

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