Junction temperature fluctuation smoothing control method for hybrid devices considering active regulation of driving voltage

Abstract

The present invention discloses a hybrid device junction temperature fluctuation smoothing control method considering active drive voltage regulation, comprising the following steps: step S1, after setting the load current, calculating the MOSFET and IGBT losses under different drive voltages within the actual given range through a loss model; step S2, using the load current effective value as a restriction condition, judging whether the converter working condition belongs to light load or heavy load; step S3, actively regulating the drive voltage according to the determined load working condition: if it is light load, the actual drive voltage of SiC MOSFET and Si IGBT is equal to the drive voltage that maximizes the loss of the hybrid device, and if it is heavy load, the actual drive voltage of SiC MOSFET and Si IGBT is equal to the drive voltage that minimizes the loss of the hybrid device. The present invention can reduce the junction temperature fluctuation of the hybrid device when the load changes and reduce the total loss of the device.

Description

Technical Field

[0001] The invention belongs to the technical field of junction temperature control of switching devices, and relates to a method for smoothly controlling junction temperature fluctuation of a hybrid device taking active regulation of a driving voltage into consideration. Background Art

[0002] Si IGBT devices have the advantages of large current capacity, low on-state voltage drop, fast switching speed, low driving power consumption and simple control circuit, but they also have disadvantages such as low switching frequency, high switching loss and low junction temperature range. SiC MOSFET can greatly improve the performance of power electronic devices such as power conversion efficiency and power density due to its extremely low on-resistance, higher switching speed and switching frequency, but its current carrying capacity is poor and its cost is high. In order to complement the advantages of the two, SiC MOSFET and Si IGBT are connected in parallel to form a Si / SiC hybrid device. During the switching process, the optimal turn-on and turn-off delays are used to minimize the loss of the hybrid device, reducing the device cost while increasing the device power density.

[0003] Some scholars have proposed to use SiC MOSFET to turn on before Si IGBT and turn off later than Si IGBT to achieve zero voltage switching of Si IGBT, so as to reduce the loss of hybrid devices. On this basis, other scholars have proposed a minimum loss switching mode based on variable turn-off delay to optimize the efficiency of the converter. However, this mode is prone to cause SiC MOSFET junction temperature imbalance. If the load condition fluctuates over a large range, such as from light load to heavy load, it will cause a huge thermal stress shock inside the SiC MOSFET, endangering the reliability of the hybrid device converter. Therefore, measures need to be taken to reduce or smooth this thermal shock.

[0004] Traditional methods to suppress device junction temperature fluctuations include variable frequency temperature regulation, adding buffer circuits, adjusting load current, etc., but such junction temperature smoothing strategies for the system operation layer have the disadvantage of affecting the power quality on the output side. By adjusting the drive circuit parameters, the device junction temperature fluctuations can be effectively suppressed without affecting the converter output waveform. Based on this, some studies have achieved junction temperature smoothing by adjusting the drive voltage, while also having the advantage of reducing device losses. However, the strategy of achieving junction temperature smoothing for the drive voltage is currently limited to a single device, and no scholar has studied the ability of the drive voltage to regulate the junction temperature in a hybrid device. At the same time, since the hybrid device is composed of a Si IGBT and a SiC MOSFET in parallel, the drive voltages of the two devices will affect the switching characteristics of the hybrid device, which deepens the complexity of exploring the influence of the drive voltage on device losses. Summary of the invention

[0005] To achieve the above objectives, the present invention provides a method for smoothly controlling junction temperature fluctuation of a hybrid device taking into account active regulation of driving voltage, so as to reduce junction temperature fluctuation of the hybrid device when load changes and reduce total device loss.

[0006] The technical solution adopted by the present invention is a method for smoothly controlling junction temperature fluctuation of a hybrid device taking into account active regulation of driving voltage, comprising the following steps:

[0007] Step S1, after setting the load current, the MOSFET and IGBT losses under different driving voltages within the actual given range are calculated by the loss model, and the driving voltage mode that maximizes and minimizes the MOSFET loss is determined. The driving voltage mode that maximizes the hybrid device loss is recorded as: V GM =V loss_max_MOS 、V GT =V loss_max_IGBT , the loss is minimized to V GM =V loss_min_MOS 、V GT =V loss_min_IGBT And the corresponding device steady-state junction temperature is obtained through the thermal network model;

[0008] Step S2, using the load current effective value as a limiting condition to determine whether the converter operating condition is light load or heavy load;

[0009] Step S3: Actively adjust the drive voltage according to the determined load condition: if the load is light, use V GM =V loss_max_MOS 、V GT =V loss_max_IGBT mode makes SiC MOSFET loss the highest, achieving the goal of raising SiC MOSFET junction temperature; if it is heavy load, V GM =V loss_min_MOS 、V GT =V loss_min_IGBT mode to minimize SiC MOSFET losses and reduce its junction temperature;

[0010] Where V GM 、V GT They are the actual driving voltages of SiC MOSFET and Si IGBT respectively; V loss_max_MOS 、V loss_max_IGBT are the driving voltages that maximize the losses of SiC MOSFET and Si IGBT in the hybrid device, V loss_min_MOS 、V loss_min_IGBT They are the driving voltages that minimize the losses of SiC MOSFET and Si IGBT in the hybrid device, respectively.

[0011] Furthermore, the calculation formula for MOSFET and IGBT losses in step S1 is:

[0012]

[0013]

[0014] Where P loss_MOS , P loss_IGBT are the total losses of SiC MOSFET and Si IGBT respectively; P on_IGBT , P cond_IGBT , P off_IGBT are the turn-on, conduction and turn-off losses of Si IGBT respectively; P on_MOS , P cond_MOS , P off_MOS They are the turn-on, conduction, and turn-off losses of SiC MOSFET respectively; V th is the turn-on voltage of Si IGBT; P on_hard_MOS , P on_hard_IGBT are the hard turn-on losses of SiCMOSFET and Si IGBT respectively; P off_hard_MOS is the hard turn-off loss of SiC MOSFET; P res_IGBT is the residual turn-off loss of Si IGBT; m, n, a, b, c, d, k1, k2, g, c1, c2, u are all coefficients related to the load current, and e is a natural constant.

[0015] Furthermore, the calculation formula of the device junction temperature in step S1 is:

[0016]

[0017] Where, T j_MOS , T j_IGBT are the junction temperatures of SiC MOSFET and Si IGBT, respectively. th_(j-c)_MOS , Z th_(j-c)_IGBT Respectively represent the junction-to-case thermal impedance of SiC MOSFET and Si IGBT; T c is the case temperature of the device.

[0018] Furthermore, the method for determining the converter operating condition in step S2 is:

[0019] Assume the rated current is I F , the load current value is obtained through the current sampler. When the load current value is lower than I F When the load current value is higher than I F It is judged as overloaded.

[0020] Furthermore, in step S3:

[0021] If there is no load fluctuation and the load is always light or heavy, the drive voltage mode corresponding to the minimum loss is maintained to ensure the efficiency of the converter.

[0022] The beneficial effects of the present invention are:

[0023] The present invention utilizes active regulation of the driving voltage to effectively reduce the junction temperature swing of the SiC MOSFET in the hybrid device caused by load fluctuations, and at the same time reduces the overall loss of the hybrid device to a certain extent, and reduces the thermal stress impact of the junction temperature fluctuation on the device under the premise of ensuring the efficiency of the converter, which is beneficial to extend the life of the hybrid device. Compared with the traditional minimum loss control strategy, the active regulation strategy of the driving voltage of the present invention can effectively suppress the junction temperature fluctuation of SiC MOSFET; compared with the heavy load reliability control strategy, the two have basically the same effect on suppressing the junction temperature fluctuation, but the method proposed by the present invention can significantly reduce the loss and improve the efficiency of the hybrid device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 Schematic diagram of the junction temperature control principle of an embodiment of the present invention.

[0026] Figure 2 1 is a graph showing the relationship between SiC MOSFET loss and driving voltage in an embodiment of the present invention, wherein (a) is a graph showing the relationship between MOSFET turn-on loss and driving voltage, (b) is a graph showing the relationship between MOSFET conduction loss and driving voltage, and (c) is a graph showing the relationship between MOSFET turn-on + conduction loss and driving voltage.

[0027] Figure 3 1 is a graph showing the relationship between IGBT loss and driving voltage according to an embodiment of the present invention, wherein (a) is a graph showing the relationship between IGBT turn-on loss and driving voltage, (b) is a graph showing the relationship between IGBT conduction loss and driving voltage, and (c) is a graph showing the relationship between IGBT turn-on + conduction loss and driving voltage.

[0028] Figure 4 2 is a driving voltage mode diagram of an embodiment of the present invention, wherein (a) is a driving voltage mode diagram under heavy load, and (b) is a driving voltage mode diagram under light load.

[0029] Figure 5 This is the traditional driving voltage mode diagram.

[0030] Figure 6 It is a schematic diagram of current fluctuation of heavy load reliability control strategy.

[0031] Figure 7 1 and 12 are simulation result diagrams of different control strategies of the embodiments of the present invention, wherein (a) is a simulation result diagram of the minimum loss control strategy, (b) is a simulation result diagram of the heavy load reliability control strategy, and (c) is a simulation result diagram of the active drive voltage regulation strategy of the embodiments of the present invention.

[0032] Figure 8 Schematic diagram of a thermal network model of a hybrid device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0034] Without changing the system switching frequency and load current, the overall idea of ​​this embodiment to smooth the low-frequency junction temperature of SiC MOSFET is to reduce the loss of SiC MOSFET under heavy load conditions to reduce its junction temperature, and to increase the loss of SiC MOSFET under light load conditions to increase its junction temperature, thereby achieving junction temperature smoothing when the load fluctuates. Figure 1 As shown in the figure. j_MOS is the SiC MOSFET junction temperature, ΔE MOS is the loss change of SiC MOSFET before and after junction temperature adjustment, ΔE MOS A value greater than 0 indicates an increase in loss, and a value less than 0 indicates a decrease in loss.

[0035] Example

[0036] In this embodiment, the minimum value V of the driving voltage required for the SiC MOSFET and Si IGBT to be fully turned on is determined according to the actual device model selected. min , and the maximum driving voltage V to avoid oscillation max , so we choose to study the driving voltage V GM With V GT Range is V min ~V max This embodiment takes the range of 15V to 20V as an example, and conducts a double pulse test experiment based on the LTspice simulation platform to obtain the relationship between the device loss and the driving voltage under the condition that the load current effective value is 20A. Figure 2 shown.

[0037] Since the driving voltage has little effect on the device turn-off process, the change of turn-off loss is not discussed. Figure 2 It can be seen that:

[0038] 1) MOSFET drive voltage V GM When a certain time, due to V GT The increase in MOSFET dynamic current reduces, so the MOSFET turn-on loss E on_MOS With V GT The relationship between the conduction loss E cond_MOS With V GT The increase of is slightly reduced; its overall loss is consistent with the change law of opening loss.

[0039] 2) IGBT drive voltage V GT When E on_MOS With V GM The increase of decreases first and then increases. This is the superposition effect of the reduction of loss caused by the faster turn-on speed of MOSFET and the increase of loss caused by more load current flowing into MOSFET; E cond_MOS With V GM The change trend is positively correlated; its overall loss also increases with V GM The increase of first decreases and then increases.

[0040] Depend on Figure 2 It can be seen that V GM =15V, V GT =15V mode has the highest overall MOSFET loss. The drive voltage in this mode can be recorded as V GM =V loss_max_MOS 、V GT =V loss_max_IGBT , then in this embodiment V loss_max_MOS With V loss_max_IGBT Both are 15V; and V GM =15V, V GT = 20V mode can minimize the MOSFET loss, so this mode is recorded as V GM =V loss_min_MOS 、V GT =V loss_min_IGBT , this embodiment V loss_min_MOS Take 15V, V loss_min_IGBT Take 20 V. Therefore, these two modes can be considered to control the loss distribution and thus suppress the junction temperature fluctuation of the MOSFET.

[0041] Depend on Figure 3 The data shown show that:

[0042] 1) MOSFET drive voltage V GM When a certain value is reached, the IGBT turn-on loss Eon_IGBT With V GT The increase of first increases and then decreases. This is due to the mutual influence of the loss reduction caused by increasing the IGBT turn-on speed and the loss increase caused by more load current flowing into the IGBT; its conduction loss E cond_IGBT Under the combined effect of on-resistance and on-current, there is little change; the overall loss of IGBT is consistent with the change pattern of turn-on loss.

[0043] 2) IGBT drive voltage V GT When E on_IGBT With V GM decreases with the increase of E cond_IGBT With V GM The change trend is negatively correlated; its overall loss increases with V GM decreases with the increase of .

[0044] As can be seen from the above figure, V GM =15V, the total IGBT loss increases with V GT The change is very small, so V GT The adjustment will not cause a significant increase in IGBT losses, thus ensuring the overall efficiency of the hybrid converter.

[0045] Combined with the above analysis of MOSFET and IGBT, considering that the dynamic adjustment of the driving voltage will increase the hardware cost and design difficulty of the driving circuit, the present embodiment sets V GM Designed for 15V, V GT The regulation is only switched between 15V and 20V, that is, when V GM =V loss_max_MOS 、V GT =V loss_max_IGBT With V GM =V loss_min_MOS 、V GT =V loss_min_IGBT Active adjustment of the driving voltage between the two modes, such as Figure 4 shown.

[0046] In summary, under light load conditions, using V GM =15V, V GT = 15V mode makes SiC MOSFET loss the highest, achieving the goal of raising SiC MOSFET junction temperature; under heavy load conditions, V GM =15V, V GT =20V mode minimizes SiCMOSFET losses to reduce its junction temperature, and ultimately achieves low-frequency junction temperature smoothing of MOSFET while ensuring efficiency, which is called the active drive voltage regulation strategy.

[0047] In combination with the above embodiments, the present invention provides a universal method for smoothing junction temperature fluctuation of a hybrid device taking into account active regulation of a driving voltage, comprising the following steps:

[0048] 1) First, based on the loss model of the driving voltage and the typical thermal network model, the required driving voltage mode under light load and heavy load is selected. After setting the load current, the loss model is used to calculate the MOSFET and IGBT losses under different driving voltages within the actual given range, and the driving voltage mode that maximizes and minimizes the MOSFET loss is determined. The driving voltage mode that maximizes the loss is recorded as: V GM =V loss_max_MOS 、V GT =V loss_max_IGBT , the lowest loss is V GM =V loss_min_MOS 、V GT =V loss_min_IGBT And the corresponding device steady-state junction temperature is obtained through the thermal network model.

[0049] Among them, the hybrid device loss model can be divided into two parts: SiC MOSFET and Si IGBT. The loss calculation formula for the two is:

[0050]

[0051]

[0052] Where P loss_MOS , P loss_IGBT are the total losses of SiC MOSFET and Si IGBT respectively; P on_IGBT , P cond_IGBT , P off_IGBT are the turn-on, conduction and turn-off losses of Si IGBT respectively; P on_MOS , P cond_MOS , P off_MOS They are the turn-on, conduction, and turn-off losses of SiC MOSFET respectively; V GM 、V GT They are the driving voltages of SiC MOSFET and Si IGBT respectively; I MOS ,I IGBT are the conduction currents of SiC MOSFET and Si IGBT respectively; V th is the turn-on voltage of Si IGBT; P on_hard_MOS , P on_hard_IGBT They are the hard turn-on losses of SiC MOSFET and Si IGBT respectively; P off_hard_MOS is the hard turn-off loss of SiC MOSFET; P res_IGBTis the residual turn-off loss of SiIGBT; m, n, a, b, c, d, k1, k2, g, c1, c2, u are all coefficients related to the load current, and e is a natural constant.

[0053] The thermal network model of the hybrid device is as follows Figure 8 As shown in Figure 2, the loss P of SiC MOSFET and Si IGBT is obtained by using the loss model. loss_MOS With P loss_IGBT , combined with the thermal network model shown in the figure, the corresponding device junction temperature can be obtained, and the calculation formula is:

[0054]

[0055] In the formula, Z th_(j-c)_MOS , Z th_(j-c)_IGBT Respectively represent the junction-to-case thermal impedance of SiC MOSFET and Si IGBT; T c is the case temperature of the device, which can be measured by a thermocouple.

[0056] 2) Using the load current effective value as the limiting condition, determine whether the converter operating condition is light load or heavy load. If it is light load, increase the MOSFET loss to increase its junction temperature; if it is heavy load, reduce the MOSFET loss to reduce its junction temperature.

[0057] The method for judging the working condition of the converter is as follows: Assume the rated current value is I F , the load current value is obtained through the current sampler. When the load current is lower than I F When the load current is higher than I F It is judged as overloaded.

[0058] 3) Actively adjust the drive voltage according to the determined load condition. If the load is light, use V GM =V loss_max_MOS 、V GT =V loss_max_IGBT mode makes SiC MOSFET loss the highest, achieving the goal of raising SiC MOSFET junction temperature; if it is heavy load, V GM =V loss_min_MOS 、V GT =V loss_min_IGBT This mode minimizes SiC MOSFET losses to reduce its junction temperature, and achieves low-frequency junction temperature smoothing of MOSFET while ensuring efficiency.

[0059] In this field, traditional control strategies include minimum loss control strategy and heavy load reliability control strategy, among which:

[0060] Minimum loss control strategy Figure 5As shown in Mode 1, the Si / SiC hybrid parallel devices are turned on at the same time. Since the SiC MOSFET switches quickly, the turn-on loss is minimal when both are turned on at the same time. The SiC MOSFET is turned off with a delay, so that the Si IGBT turns off at zero voltage to reduce the high turn-off loss caused by its tail current. The optimal turn-off delay is related to the load current. In this switching mode, the hybrid device can achieve the minimum loss.

[0061] The heavy load reliability control strategy consists of two different modes. When the load current is less than the safe operating area current I SOA Mode 1 is used to reduce device loss. When the load current is greater than the safe operating area current I SOA Mode 2 is used: the IGBT turn-on timing is advanced, but the MOSFET itself turns on faster, so the two complete the turn-on process together. The MOSFET and IGBT are turned off at the same time. Since the MOSFET turns off faster, the MOSFET is approximately turned off at zero voltage. This method can minimize the loss of SiCMOSFET when it is overloaded and balance its junction temperature. For details, see Figure 5-6 .

[0062] Based on a single-phase inverter, the advantages and disadvantages of the active driving voltage regulation strategy proposed in the present invention are compared with the traditional minimum loss control strategy and heavy-load reliability control strategy through simulation. The SiC MOSFET model is C2M0160120D, whose rated current is 12.5A; the Si IGBT model is IGW25N120H3, whose rated current is 25A, and the suppression effect of the junction temperature fluctuation by the active driving voltage regulation strategy is compared with the other two strategies. The effective value of the load current is set to 10A in the first 100s, 25A in 100-200s, and then reduced to 10A in 200-300s to simulate the fluctuating working conditions of light load and heavy load switching. Figure 7 As shown, the simulation results are as follows:

[0063] Table 1 Junction temperature smoothing effect and loss comparison control strategy under three strategies

[0064]

[0065]

[0066] From the above data, it can be seen that the active drive voltage adjustment strategy adopted in this embodiment can reduce the junction temperature fluctuation amplitude by 15.1°C and reduce the device loss by 7.73% compared with the minimum loss control strategy; compared with the heavy load reliability control strategy, the suppression effect of the two on the junction temperature fluctuation is only about 3°C ​​different, but the heavy load reliability control strategy increases the loss of the hybrid device by 14.106% compared with the active drive voltage adjustment strategy, thereby reducing the overall efficiency of the device. Therefore, by switching the drive voltage, the junction temperature fluctuation suppression can be achieved without increasing the device loss, effectively reducing the thermal stress impact inside the device under large load fluctuations, thereby extending the device life.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for smoothing junction temperature fluctuation of a hybrid device considering active regulation of driving voltage, characterized in that: The following steps are involved: Step S1, after setting the load current, the MOSFET and IGBT losses under different driving voltages within the actual given range are calculated by the loss model, and the driving voltage mode that maximizes and minimizes the MOSFET loss is determined. The driving voltage mode that maximizes the hybrid device loss is recorded as: V GM =V loss_max_MOS 、V GT =V loss_max_IGBT , the loss is minimized to V GM =V loss_min_MOS 、V GT =V loss_min_IGBT And the corresponding device steady-state junction temperature is obtained through the thermal network model; Step S2, using the load current effective value as a limiting condition to determine whether the converter operating condition is light load or heavy load; Step S3: Actively adjust the drive voltage according to the determined load condition: if the load is light, use V GM =V loss_max_MOS 、V GT =V loss_max_IGBT mode makes SiC MOSFET loss the highest, achieving the goal of raising SiC MOSFET junction temperature; if it is heavy load, V GM =V loss_min_MOS 、V GT =V loss_min_IGBT mode to minimize SiC MOSFET losses and reduce its junction temperature; Where V GM 、V GT They are the actual driving voltages of SiC MOSFET and Si IGBT respectively; V loss_max_MOS 、V loss_max_IGBT are the driving voltages that maximize the losses of SiC MOSFET and Si IGBT in the hybrid device, V loss_min_MOS 、V loss_min_IGBT They are the driving voltages that minimize the losses of SiC MOSFET and Si IGBT in the hybrid device, respectively.

2. A method for smoothly controlling junction temperature fluctuation of a hybrid device taking into account active regulation of driving voltage according to claim 1, characterized in that: The calculation formula for the MOSFET and IGBT losses in step S1 is: Where P loss_MOS , P loss_IGBT are the total losses of SiC MOSFET and Si IGBT respectively; P on_IGBT , P cond_IGBT , P off_IGBT are the turn-on, conduction and turn-off losses of Si IGBT respectively; P on_MOS , P cond_MOS , P off_MOS They are the turn-on, conduction, and turn-off losses of SiC MOSFET respectively; V th is the turn-on voltage of Si IGBT; P on_hard_MOS , P on_hard_IGBT They are the hard turn-on losses of SiC MOSFET and SiIGBT respectively; P off_hard_MOS is the hard turn-off loss of SiC MOSFET; P res_IGBT is the residual turn-off loss of Si IGBT; m, n, a, b, c, d, k1, k2, g, c1, c2, u are all coefficients related to the load current, and e is a natural constant.

3. A method for smoothly controlling junction temperature fluctuation of a hybrid device taking into account active regulation of driving voltage according to claim 1 or 2, characterized in that: The calculation formula of the device junction temperature in step S1 is: Where, T j_MOS 、T j_IGBT are the junction temperatures of SiC MOSFET and Si IGBT, respectively. th_(j-c)_MOS , Z th_(j-c)_IGBT Respectively represent the junction-to-case thermal impedance of SiC MOSFET and Si IGBT; T c is the case temperature of the device.

4. The method for smoothly controlling junction temperature fluctuation of a hybrid device taking into account active regulation of driving voltage according to claim 1, characterized in that: The method for determining the converter operating condition in step S2 is: Assume the rated current is I F , the load current value is obtained through the current sampler. When the load current value is lower than I F When the load current value is higher than I F It is judged as overloaded.

5. The method for smoothly controlling junction temperature fluctuation of a hybrid device considering active regulation of driving voltage according to claim 1, characterized in that: In step S3: If there is no load fluctuation and the load is always light or heavy, the drive voltage mode corresponding to the minimum loss is maintained to ensure the efficiency of the converter.

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