Control device for power conversion device
By dynamically adjusting the gate voltage and on-gate resistance according to temperature changes, the contradiction between low loss and extended lifespan of transistors is resolved, achieving both low loss and extended lifespan under different temperature conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2025-11-05
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies struggle to reduce losses and suppress lifetime degradation while maintaining transistors in a normally off state, especially when using GaN-based semiconductors, where a reduction in the threshold voltage may lead to a normally on state.
By dynamically adjusting the gate voltage and on-gate resistance through temperature sensing, the gate voltage and on-gate resistance values are set in different temperature ranges according to the transistor temperature changes, so as to maintain the transistor in a normal off state, reduce losses and suppress gate leakage current.
This technology achieves both reduced losses and suppression of transistor lifespan reduction under different temperature conditions, maintaining low losses while avoiding normal conduction and extending transistor lifespan.
Smart Images
Figure CN122026698A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a control device for a power conversion device. Background Technology
[0002] Gallium nitride (GaN) semiconductors and silicon carbide (SiC) semiconductors are used as power semiconductors (e.g., Patent Document 1, etc.).
[0003] Patent Document 1: Japanese Patent Application Publication No. 2014-229823 Summary of the Invention
[0004] Power semiconductors in power conversion devices require low-loss operation. However, increasing the drive voltage may shorten the device's lifespan. Conversely, lowering the threshold voltage causes the device to remain in a normally on state. Therefore, the object of this invention is to provide a control device for a power conversion device that maintains the transistor in a normally off state with low loss and suppresses lifespan reduction.
[0005] The above objective 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 lower the temperature of the transistor, the higher the gate voltage can be.
[0007] When the temperature is lower than a first temperature, the gate voltage is set to a first voltage. When the temperature is higher than the first temperature but lower than a second temperature, the gate voltage is set to a second voltage lower than the first voltage. When the temperature is higher than the second temperature, the gate voltage is set to a third voltage lower than the second voltage.
[0008] The lower the temperature of the transistor, the smaller the gate resistance of the transistor.
[0009] When the temperature is lower than the fourth temperature, the on-gate resistor is set to the first resistance value; when the temperature is higher than the fourth temperature but lower than the fifth temperature, the on-gate resistor is set to the second resistance value, which is higher than the first resistance value; when the temperature is higher than the fifth temperature, the on-gate resistor is set to the third resistance value, which is higher than the second resistance value.
[0010] Invention Effects
[0011] A control device for a power conversion device is provided, which can maintain the transistor in a normally closed state with low loss and suppress reduced lifespan. Attached Figure Description
[0012] Figure 1 (a) is a schematic structural diagram of the power conversion device according to the first embodiment. Figure 1 (b) is a block diagram illustrating the hardware structure of the control device.
[0013] Figure 2 This is a flowchart illustrating the process in the first embodiment.
[0014] Figure 3 (a) and Figure 3 (b) is a diagram illustrating voltage.
[0015] Figure 4 (a) is a flowchart illustrating the process in the second embodiment. Figure 4 (b) is a diagram illustrating voltage. Detailed Implementation
[0016] <First Embodiment>
[0017] Hereinafter, the control device of the power conversion device of this embodiment will be described with reference to the accompanying drawings. Figure 1 (a) is a schematic structural diagram of the power conversion device 100 according to the first embodiment. The power conversion device 100 is mounted, for example, in a vehicle, and converts power between a battery and a motor. The power conversion device 100 includes a transistor 10, a drive circuit 20, a temperature sensor 22, and a control device 30.
[0018] Transistor 10 is a normally-off field-effect transistor (FET), such as a high-electron-mobility transistor (HEMT) formed of gallium nitride (GaN) based semiconductors. Transistor 10 has a gate electrode 12, a source electrode 14, and a drain electrode 16.
[0019] The driving 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 turned off. When the gate voltage Vg becomes greater than or equal to the threshold voltage Vth, the transistor 10 switches from being off to being on.
[0020] The control device 30 is the control device for the power conversion device 100, and includes an arithmetic unit such as a central processing unit (CPU), random access memory (RAM), and read-only memory (ROM). The control device 30 performs various controls by executing programs stored in the ROM or the memory devices. The control device 30 is electrically connected to the temperature sensor 22 and the drive circuit 20.
[0021] The control device 30 includes a temperature acquisition unit 32, a voltage control unit 34, and a gate resistance control unit 36. A 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 to change the gate voltage Vg according to the temperature. The gate resistance control unit 36 controls the on-state gate resistance of the transistor 10.
[0022] Figure 1 (b) is a block diagram illustrating the hardware structure of the control device 30. The control device 30 includes a Central Processing Unit (CPU) 40, Random Access Memory (RAM) 42, Read Only Memory (ROM) 43, a storage device 44, and an interface 46. The CPU 40, RAM 42, ROM 43, storage device 44, and interface 46 are interconnected via a bus, etc. RAM 42 is volatile memory that temporarily stores programs and data. The storage device 44 is a solid-state drive (SSD) such as flash memory, a hard disk drive (HDD), etc. The storage device 44 stores programs, etc.
[0023] The CPU 40 executes the program stored in RAM 42, thereby implementing the temperature acquisition unit 32, voltage control unit 34, and gate resistor control unit 36 in the control device 30. Each part of the control device 30 can be hardware such as circuits.
[0024] Figure 2 This is a flowchart illustrating the process 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 process ends here.
[0025] Figure 3(a) is a graph illustrating the voltage. The horizontal axis represents the temperature of transistor 10. The vertical axis represents the voltage of transistor 10. The dashed line in the graph represents the threshold voltage Vth of transistor 10. The dotted line represents the gate voltage Vg in the comparative example, which is a constant value independent of temperature. The solid line represents the gate voltage Vg in the first embodiment. The gate voltage Vg in the first embodiment varies with temperature, being higher at low temperatures and lower at high temperatures. The gate voltage Vg varies linearly with respect to temperature, for example.
[0026] The power loss during the operation of transistor 10 depends on the difference between the gate voltage Vg and the threshold voltage Vth (Vg-Vth). A larger Vg-Vth results in lower losses. Increasing the gate voltage Vg increases Vg-Vth, thus reducing losses. However, increasing the gate voltage Vg may reduce the lifetime of transistor 10. More specifically, a higher gate voltage Vg increases the gate leakage current. Increased gate leakage current shortens the transistor's lifetime. Higher temperatures result in higher gate leakage current. Therefore, increasing the gate voltage Vg at high temperatures leads to a significant increase in gate leakage current, which can easily reduce the lifetime of transistor 10.
[0027] By reducing the threshold voltage Vth, Vg-Vth can also be increased. However, due to the reduction in the threshold voltage Vth, transistor 10 may become normally turned on. In particular, the threshold voltage Vth of GaN-HEMT is smaller compared to other transistors. Therefore, in a normally turned-off GaN-HEMT, it is difficult to further reduce the threshold voltage Vth.
[0028] According to the first embodiment, such as Figure 3 As shown in (a), the lower the temperature of transistor 10, the higher the gate voltage Vg and the larger Vg-Vth become in the voltage control unit 34. By increasing Vg-Vth, the losses of transistor 10 are reduced. In particular, since the gate voltage Vg increases under conditions such as low temperature and room temperature, transistor 10 can be driven with low losses. The higher the temperature, the lower the gate voltage Vg. Therefore, the gate leakage current is less likely to increase. The reduction in the lifetime of transistor 10 is suppressed.
[0029] like Figure 3 As shown in (a), the threshold voltage Vth does not change with temperature and is a nearly constant value. Transistor 10 remains in a normally off state.
[0030] like Figure 3 As shown in (a), the gate voltage Vg changes continuously. The gate voltage Vg is proportional to the temperature; the lower the temperature, the larger Vg is, and the higher the temperature, the smaller Vg is. The gate voltage Vg can change linearly or non-linearly with respect to temperature. The temperature of transistor 10 can be detected by temperature sensor 22, or it can be estimated based on the surrounding environment and operating conditions.
[0031] (Variation example)
[0032] Descriptions of structures identical to those in the first embodiment are omitted. Figure 3 (b) is a diagram illustrating the voltage. The temperature thresholds are set as T1 (temperature 1) and T2 (temperature 2). T2 is higher than T1. Figure 3 In (b), Vg1 (the first voltage) is the highest among the gate voltages. Vg2 (the second voltage) is lower than Vg1 but higher than Vg3 (the third voltage). Vg is the lowest.
[0033] The voltage control unit 34 controls the gate voltage Vg according to the temperature, causing the gate voltage Vg to change in stages. Figure 2 (Step S12). When the temperature is below T1, the voltage control unit 34 sets the gate voltage to Vg1. When the temperature is above T1 but below T2, the voltage control unit 34 sets the gate voltage to Vg2. When the temperature is above T2, the voltage control unit 34 sets the gate voltage to Vg3.
[0034] According to a modified example, the voltage control unit 34 varies the gate voltage Vg in three stages based on temperature, set to any one of Vg1, Vg2, and Vg3. When the temperature is below T1, the voltage control unit 34 sets the gate voltage to the highest value, Vg1. Since Vg-Vth increases, the losses of the transistor 10 are reduced. As the temperature rises, the voltage control unit 34 lowers the gate voltage to Vg2, and further to Vg3. Gate leakage current decreases, and lifetime reduction is suppressed.
[0035] <Second Implementation>
[0036] Descriptions of structures identical to those in the first embodiment are omitted. 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 gate resistance based on the temperature of the transistor 10 (step S14). The process ends thereafter.
[0037] The gate resistance control unit 36, for example, changes the on-gate resistance Rg in three stages. The temperature thresholds of the transistor 10 are set to 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 on-gate resistance to Rg1 (first resistance value). When the temperature is above T4 but below T5, the gate resistance control unit 36 sets the on-gate resistance to Rg2 (second resistance value). When the temperature is above T5, the gate resistance control unit 36 sets the on-gate resistance to Rg3 (third resistance value). Of the on-gate resistances, Rg1 is the lowest. Rg2 is higher than Rg1 but lower than Rg3. Rg3 is the highest.
[0038] Figure 4 (b) is a diagram illustrating the voltages. The dashed line represents the threshold voltage Vth. The dotted line represents the gate voltage Vg. Both the threshold voltage Vth and the gate voltage Vg are constant values. The solid line represents the surge voltage Vgs. The surge voltage Vgs is generated when the switching transistor 10 is turned on / off and is the voltage applied to the gate electrode 12. The higher the on-gate resistance Rg, the smaller the surge voltage Vgs. The lower the on-gate resistance Rg, the larger the surge voltage Vgs. Figure 4 (b) Of the surge voltages, Vgs1 is the highest. Vgs2 is lower than Vgs1 but higher than Vgs3. Vgs3 is the lowest.
[0039] The gate resistance control unit 36 controls the gate resistance based on temperature. Figure 4 (a) Step S14). When the temperature is below T4, the on-gate resistance is Rg1. Due to the low on-gate resistance, the surge voltage becomes high, becoming Vgs1. When the temperature is above T4 but below T5, the on-gate resistance becomes Rg2, which is higher than Rg1. Due to the increased on-gate resistance, the surge voltage becomes Vgs2, which is lower than Vgs1. When the temperature is above T5, the on-gate resistance becomes Rg3, which is higher than Rg2. The surge voltage becomes Vgs3, which is lower than Vgs2.
[0040] According to the second embodiment, the lower the temperature, the smaller the on-gate resistance Rg is controlled by the gate resistance control unit 36. As the on-gate resistance Rg decreases, the surge voltage Vgs applied to the gate electrode 12 increases. Since Vgs-Vth increases, the transistor 10 can be driven with low loss. Because the higher the temperature, the higher the on-gate resistance Rg is, the lower the surge voltage Vgs becomes. The gate leakage current is less likely to increase. The reduction in the lifetime of the transistor 10 is suppressed.
[0041] like Figure 4 As shown in (b), the threshold voltage Vth does not change with temperature and is a nearly constant value. Transistor 10 remains in a normally off state.
[0042] The gate resistance Rg varies in three stages, therefore the surge voltage Vgs also varies in three stages. The gate resistance Rg can also vary continuously. The surge voltage Vgs also varies continuously. The gate resistance Rg can vary linearly or non-linearly with respect to temperature. The surge voltage Vgs varies linearly or non-linearly.
[0043] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to this specific embodiment. Various modifications and alterations can be made within the scope of the spirit of the present invention as set forth in the claims.
[0044] Symbol Explanation
[0045] 10-Transistor, 12-Gate 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 resistor control unit, 100-Power conversion device.
Claims
1. A control device for a power conversion device, characterized in that, The power conversion device has transistors. The lower the temperature of the transistor, the greater the difference between the threshold voltage and the gate voltage of the transistor.
2. The control device for the power conversion device according to claim 1, characterized in that, The lower the temperature of the transistor, the higher the gate voltage.
3. The control device for the power conversion device according to claim 2, characterized in that, When the temperature is lower than the first temperature, the gate voltage is set to the first voltage. When the temperature is above the first temperature and below the second temperature, the gate voltage is set to a second voltage that is lower than the first voltage. When the temperature is above the second temperature, the gate voltage is set to a third voltage that is lower than the second voltage.
4. The control device for the power conversion device according to claim 1 or 2, characterized in that, The lower the temperature of the transistor, the smaller the gate resistance of the transistor.
5. The control device for the power conversion device according to claim 4, characterized in that, When the temperature is lower than the fourth temperature, the on-gate resistor is set to the first resistance value. When the temperature is higher than the fourth temperature but lower than the fifth temperature, the on-gate resistance is set to a second resistance value that is higher than the first resistance value. When the temperature is higher than the fifth temperature, the on-gate resistance is set to a third resistance value that is higher than the second resistance value.