Electric drive system and control method thereof

Abstract

The invention provides an electric drive system and a control method thereof.The input end of an inverter unit of the electric drive system is connected with a power supply unit, the output end of the inverter unit is connected with a drive motor, the inverter unit comprises three single-phase inverters, and each single-phase inverter comprises two hybrid power devices; each hybrid power device is formed by connecting an Si-IGBT power device, an MOS power device based on a target semiconductor material and a fly-wheel diode in parallel, the Si-IGBT power device and the MOS power device jointly achieve forward inversion output of the electric drive system, the MOS power device and the fly-wheel diode jointly achieve current follow current of the electric drive system, and the control unit controls the driving module through the driving module. And controlling the inversion unit to enter a forward inversion output state or a reverse follow current state. Therefore, the MOS power device based on the target semiconductor material is reused to replace part of the freewheeling diode for freewheeling, the use specification of the freewheeling diode can be reduced, and thus the cost and the size of the power module are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of electric drive systems for electric vehicles, and more specifically, to an electric drive system and a control method thereof. Background Art

[0002] At present, the inverter power devices used in the electric drive system of electric vehicles are mainly Si-IGBT (silicon insulated gate bipolar transistor) and SiC-MOS (metal oxide semiconductor field effect transistor based on silicon carbide material). Si-IGBT has the characteristics of low cost and low on-state voltage, while SiC-MOS has the characteristics of low switching loss and fast switching speed. In order to reduce costs and improve efficiency, researchers in the industry have proposed a power device solution of hybrid parallel connection of Si-IGBT and SiC-MOS. However, the current technical research on hybrid power devices mainly uses freewheeling diodes for freewheeling when the power module is reversely freewheeling, which makes the use of freewheeling diodes require large specifications, resulting in high costs and volume. Summary of the invention

[0003] The purpose of the present application is to provide an electric drive system and a control method thereof, aiming to solve the problem that the reverse freewheeling mode of the power module of the electric drive system in the related art has large requirements for the use of freewheeling diodes, resulting in high cost and volume.

[0004] In a first aspect, the present application provides an electric drive system, comprising a power supply unit, an inverter unit, a drive motor, a control unit and a drive module; wherein: the input end of the inverter unit is connected to the power supply unit, and the output end of the inverter unit is connected to the drive motor; the inverter unit comprises three single-phase inverters, each single-phase inverter comprises two hybrid power devices, and each hybrid power device is composed of a Si-IGBT power device, a MOS power device based on a target semiconductor material and a freewheeling diode in parallel; the inverter unit is used to realize the forward inverter output of the electric drive system through the Si-IGBT power device and the MOS power device, and to realize the reverse freewheeling of the electric drive system through the MOS power device and the freewheeling diode; the control unit is used to control the inverter unit to enter a forward inverter output state or a reverse freewheeling state through the drive module.

[0005] In the above implementation process, an electric drive system is provided, wherein the input end of the inverter unit of the electric drive system is connected to the power supply unit, and the output end is connected to the drive motor. The inverter unit includes three single-phase inverters, each of which includes two hybrid power devices, and each of which is composed of a Si-IGBT power device, a MOS power device based on the target semiconductor material, and a freewheeling diode in parallel, wherein the Si-IGBT power device and the MOS power device jointly realize the forward inverter output of the electric drive system, and the MOS power device and the freewheeling diode jointly realize the current freewheeling of the electric drive system, and the control unit controls the inverter unit to enter the forward inverter output state or the reverse freewheeling state through the driving module. In this way, the MOS power device based on the target semiconductor material is reused to replace part of the freewheeling diode for freewheeling, which can reduce the use specifications of the freewheeling diode, thereby reducing the cost and volume of the power module.

[0006] Furthermore, in some examples, the target semiconductor material includes any one of the following: SiC, GaN.

[0007] In the above implementation process, optional types of MOS power devices based on target semiconductor materials are provided.

[0008] Furthermore, in some examples, the control unit is specifically used to: when the electric drive system enters the freewheeling stage, control the MOS power device to remain in the off state, and control the freewheeling diode to perform current freewheeling; after the electric drive system enters the freewheeling stage, control the MOS power device and the freewheeling diode to jointly perform current freewheeling; at the end of the freewheeling stage, control the MOS power device to turn off, and then control the Si-IGBT power device and the MOS power device to jointly perform inverter output.

[0009] In the above implementation process, when entering the freewheeling stage, in order to prevent the upper and lower bridge arms of the same half-bridge of the hybrid power device from being directly connected, the MOS power device remains in the off state, and the freewheeling diode alone realizes the current freewheeling; after entering the freewheeling stage, the MOS power device is turned on with zero voltage, and the current is freewheeling together with the freewheeling diode; at the end of the freewheeling stage, in order to prevent the upper and lower bridge arms of the same half-bridge of the hybrid power device from being directly connected, the MOS power device is first turned off with zero voltage, and the hybrid power device then performs inverter output, and the freewheeling diode realizes the current freewheeling during the process. In this way, the rationality and reliability of the freewheeling process of the MOS power device and the freewheeling diode are guaranteed.

[0010] Furthermore, in some examples, the usage specification of the freewheeling diode is determined according to the maximum allowable operating current of the drive motor and the maximum conduction current of the MOS power device.

[0011] In the above implementation process, appropriate freewheeling diode specifications are selected according to the maximum allowable operating current of the drive motor and the maximum on-current of the MOS power device to ensure circuit stability.

[0012] Furthermore, in some examples, a current acquisition module and a junction temperature estimation module are also included; the current acquisition module is arranged between the inverter unit and the drive motor, and is used to collect the current value of the three-phase current of the drive motor and transmit the current value to the control unit; the junction temperature estimation module is used to estimate the real-time junction temperature value of the Si-IGBT power device, the MOS power device and the freewheeling diode and feed it back to the control unit.

[0013] In the above implementation process, by monitoring the junction temperature and current of the MOS power device, the control unit can promptly detect potential over-temperature risks and take corresponding measures to intervene, thereby avoiding damage to the MOS power device due to overheating.

[0014] Furthermore, in some examples, the control unit is also used for: when the real-time junction temperature value of the MOS power device is less than the maximum junction temperature limit of the MOS power device, if the Si-IGBT power device and the MOS power device are in the off state, controlling the MOS power device and the freewheeling diode to jointly perform current freewheeling; when the real-time junction temperature value of the MOS power device is greater than the maximum junction temperature limit of the MOS power device, if the current value collected by the current acquisition module is greater than or equal to the maximum conduction current of the freewheeling diode, and the Si-IGBT power device and the MOS power device are in the off state, controlling the MOS power device and the freewheeling diode to jointly perform current freewheeling; if the current value collected by the current acquisition module is less than the maximum conduction current of the freewheeling diode, controlling the MOS power device to be turned off, and controlling the freewheeling diode to perform current freewheeling.

[0015] In the above implementation process, a control method for the joint freewheeling of a MOS power device and a freewheeling diode is provided, which effectively reduces the risk of overheating of the MOS power device.

[0016] Furthermore, in some examples, the maximum junction temperature limit of the MOS power device is determined based on the difference between the maximum allowable operating temperature of the MOS power device and the junction temperature rise value; the junction temperature rise value is estimated based on the forward output loss and reverse output loss of the MOS power device when the forward output current of the hybrid power device is maximum.

[0017] In the above implementation process, the junction temperature rise of the MOS power device is estimated based on the forward output loss and reverse freewheeling loss of the MOS power device when the forward output current of the hybrid device is maximum. Then, combined with the maximum allowable operating temperature of the MOS power device, the maximum junction temperature limit of the MOS power device is accurately calculated, laying a good foundation for avoiding overheating of the MOS power device.

[0018] Further, in some examples, the junction temperature rise value is the product of the power loss value calculated by the power loss model when the forward output current of the hybrid power device is the maximum and the heat dissipation thermal resistance parameter; the power loss model is expressed as the following formula:

[0019]

[0020] Among them, P m is the power loss value; I n , U n and E sw (I n , U n ) are respectively the test current, test voltage and test loss value of the MOS power device; f is the frequency of the MOS power device; U Dc is the power supply voltage; I m K is the forward current amplitude of the hybrid power device; m is the correction coefficient; T is the current cycle of the drive motor; u r 、u F are respectively the initial voltage drops of the MOS power device in forward conduction and reverse conduction; r r 、r F are respectively the internal resistance of the forward conduction and reverse conduction of the MOS power device; i r (t), i r (t) are the forward current and reverse current of the MOS power device respectively; D is the switching duty cycle of the MOS power device.

[0021] In the above implementation process, a specific method for accurately and quickly calculating the junction temperature rise value of the MOS power device is provided.

[0022] In a second aspect, the present application provides a control method for an electric drive system as described in any one of the first aspects, which is applied to the control unit, including: obtaining a target signal of the electric drive system and a requirement of an external system; the target signal includes the current value of the three-phase current of the drive motor, and the real-time junction temperature values ​​of the Si-IGBT power device, the MOS power device and the freewheeling diode; and according to the target signal and the requirement of the external system, controlling the inverter unit to enter a forward inverter output state or a reverse freewheeling state through the drive module.

[0023] In a third aspect, the present application provides a vehicle, which includes an electric drive system as described in any one of the first aspects.

[0024] Other features and advantages disclosed in the present application will be described in the following description, or some features and advantages can be inferred or determined without doubt from the description, or can be learned by implementing the above-mentioned technology disclosed in the present application.

[0025] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic diagram of an electric drive system provided in an embodiment of the present application;

[0028] Figure 2 A schematic diagram of a curve showing the relationship between the on-state voltage drop and the on-state current of a hybrid device provided in an embodiment of the present application;

[0029] Figure 3 A flow chart of a control method of an electric drive system provided in an embodiment of the present application;

[0030] Figure 4 A schematic diagram of the overall architecture of a solution for realizing current freewheeling using SiC-MOS and a freewheeling diode provided in an embodiment of the present application;

[0031] Figure 5 A schematic diagram of the composition of a hybrid power device provided in an embodiment of the present application;

[0032] Figure 6A schematic diagram of a freewheeling control method provided in an embodiment of the present application;

[0033] Figure 7 A schematic diagram of a diode freewheeling flow direction provided in an embodiment of the present application;

[0034] Figure 8 A schematic diagram of the freewheeling flow direction of a diode and a MOS tube provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0036] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0037] As described in the background technology, the reverse freewheeling mode of the power module of the electric drive system in the related art has the problem that the specification requirements of the freewheeling diode are large, resulting in high cost and volume. Based on this, the embodiment of the present application provides a new electric drive system solution to solve the above problem.

[0038] Next, the embodiments of the present application are introduced:

[0039] like Figure 1 As shown, Figure 1 1 is a schematic diagram of an electric drive system provided in an embodiment of the present application, wherein the electric drive system includes a power supply unit 11, an inverter unit 12, a drive motor 13, a control unit 14 and a drive module 15, wherein: the input end of the inverter unit 12 is connected to the power supply unit 11, and the output end of the inverter unit 12 is connected to the drive motor 13; the inverter unit 12 includes three single-phase inverters, each of which includes two hybrid power devices 16, and each hybrid power device 16 is composed of a Si-IGBT power device 161, a MOS power device 162 based on a target semiconductor material, and a freewheeling diode 163 connected in parallel; the inverter unit 12 is used to realize the forward inverter output of the electric drive system through the Si-IGBT power device 161 and the MOS power device 162, and realize the reverse freewheeling of the electric drive system through the MOS power device 162 and the freewheeling diode 163; the control unit 14 is used to control the inverter unit to enter a forward inverter output state or a reverse freewheeling state through the drive module 15.

[0040] The above electric drive system can be applied to the motor drive control of electric vehicles. Of course, in some scenarios, the electric drive system can also be applied to other types of electric equipment, such as electric ships. In the above electric drive system, the power supply unit is a device that provides DC power to the drive system, which can be a power battery; the drive motor is the controlled object of the drive control system, which can be a three-phase synchronous motor or a three-phase asynchronous motor; the inverter unit is a three-phase inverter composed of six hybrid power devices, which can convert the DC power provided by the power supply unit into a three-phase current and output it to the drive motor. In this embodiment, the hybrid power device is composed of power semiconductor devices of different materials or structures connected in parallel. Specifically, each hybrid power device includes a Si-IGBT power device, a MOS power device based on the target semiconductor material, and a freewheeling diode, wherein the Si-IGBT power device and the MOS power device jointly realize the forward inverter output of the electric drive system, and the MOS power device and the freewheeling diode jointly realize the current freewheeling of the electric drive system. In this way, the MOS power device based on the target semiconductor material is reused to replace part of the freewheeling diode for freewheeling, which can reduce the use specifications of the freewheeling diode, thereby reducing the cost and volume of the power module.

[0041] Among them, in the hybrid power device, the Si-IGBT power device may include a Si-IGBT transistor, or may be composed of multiple Si-IGBT transistors connected in parallel; accordingly, the MOS power device may include a MOS transistor based on the target semiconductor material, or may be composed of multiple MOS transistors based on the target semiconductor material connected in parallel; the freewheeling diode may include a fast recovery diode, or may be composed of multiple fast recovery diodes connected in parallel. The target semiconductor material here may include SiC, that is, the MOS power device based on the target semiconductor material may be a SiC-MOS power device. When the current is small, the SiC-MOS conduction voltage drop is low, most of the current flows through the SiC-MOS, and a small part flows through the freewheeling diode; when the current is large, the freewheeling diode conduction voltage drop is low, most of the current flows through the freewheeling diode, and a small part flows through the SiC-MOS. During the entire freewheeling process, the hybrid device freewheeling conduction voltage drop is the lower value of the conduction voltage drop of both SiC-MOS and the freewheeling diode, thereby reducing the reverse freewheeling loss. In other embodiments, the target semiconductor material here may also include GaN (gallium nitride), that is, the MOS power device based on the target semiconductor material may be a GaN-based MOS power device.

[0042] The comparison of freewheeling loss between hybrid devices and non-hybrid devices is as follows:

[0043] Assuming the same specification of non-hybrid devices, such as Si-IGBT independent modules, the number of freewheeling diodes connected in parallel in each bridge arm is n, and the maximum conduction current capability of the MOS tube is I m; The maximum freewheeling capability of the hybrid device is I n When the hybrid device uses SiC-MOS devices for freewheeling, the number of parallel diodes in each bridge arm is (I n -I m )n / I n When the hybrid devices are freewheeling together, the real-time current of the MOS tube is I mos , the real-time current of the diode is I D ;

[0044] Hybrid device common freewheeling conduction voltage drop V F =V F0 +I F *R F ; Hybrid device common freewheeling conduction loss E F =V F (I mos +I D )DT; where T is the switching period of the power device, D is the freewheeling duty cycle of the power device, V F0 With R F Obtained by fitting the on-state voltage drop curve in the power device manual, I F The calculation formula is as follows:

[0045]

[0046] Diode freewheeling solution conduction voltage drop V F1 =V F0 +(I mos +I D )*R F ;Diode freewheeling scheme conduction loss E F1 =V F1 (I mos +I D )DT;

[0047] When the hybrid devices are freewheeling together, according to the following Figure 2 The relationship between the on-state voltage drop and on-state current of the hybrid device shown in the figure shows the following relationship:

[0048]

[0049] exist Figure 2 In the figure, curve 21 is the relationship curve between the on-state voltage drop and the on-state current of the SiC-MOS power device, and curve 22 is the relationship curve between the on-state voltage drop and the on-state current of the freewheeling diode. The horizontal axis represents the on-state voltage drop, and the vertical axis represents the on-state current. The intersection of the two curves is (V0, I0). The maximum on-state voltage drop of the SiC-MOS power device is V m From the above relationship, we can get:

[0050]

[0051]

[0052] V F1 ≥V F

[0053] Thus we can get: E F1 >E F Based on the above freewheeling loss analysis, it can be seen that under the same current, the freewheeling conduction loss of the hybrid device is lower than the conduction loss of the freewheeling diode of the non-hybrid device.

[0054] In the above electric drive system, the drive module outputs positive voltage or negative voltage to the gate of the hybrid power device to turn on and off the power device; and the control unit sends corresponding instructions to the drive module according to the relevant signals of the electric drive system and the requirements of the external system, so as to control the inverter unit to enter the forward inverter output state or the reverse freewheeling state through the drive module. Among them, the drive module can be a drive circuit, and the control unit can be a motor controller (Motor Control Unit, MCU).

[0055] In some embodiments, the control unit is specifically used to: when the electric drive system enters the freewheeling stage, control the MOS power device to remain in the off state, and control the freewheeling diode to perform current freewheeling; after the electric drive system enters the freewheeling stage, control the MOS power device and the freewheeling diode to jointly perform current freewheeling; at the end of the freewheeling stage, control the MOS power device to turn off, and then control the Si-IGBT power device and the MOS power device to jointly perform inverter output. That is to say, when entering the freewheeling stage, the forward inverter output of the hybrid power device is not completely disconnected. Therefore, in order to prevent the upper and lower bridge arms of the same half bridge of the hybrid power device from being directly connected, the MOS power device remains in the off state, and the freewheeling diode realizes current freewheeling; after entering the freewheeling stage, the hybrid power device inverter output is completely disconnected, the MOS power device is turned on at zero voltage, and the freewheeling diode performs current freewheeling together; at the end of the freewheeling stage, in order to prevent the upper and lower bridge arms of the same half bridge of the hybrid power device from being directly connected, the MOS power device is first turned off at zero voltage, and the hybrid power device then performs inverter output, and the freewheeling diode realizes current freewheeling in the process. In this way, the rationality and reliability of the freewheeling process of the MOS power device and the freewheeling diode are guaranteed.

[0056] Furthermore, in some embodiments, the use specifications of the freewheeling diode are determined according to the maximum operating current of the drive motor and the maximum conduction current of the MOS power device. From the analysis of the freewheeling process, when entering and ending the freewheeling, the freewheeling diode bears the entire current of the motor for a short time. Therefore, the short-term overcurrent capacity of the freewheeling diode must be greater than the maximum allowable operating current of the drive motor. According to the maximum conduction current of the MOS power device, the maximum conduction voltage drop can be obtained by referring to the relationship curve between the conduction current and the conduction voltage drop parameter of the MOS power device. According to the maximum conduction voltage drop of the MOS power device, the maximum conduction current of the freewheeling diode is determined, and the sum of the maximum conduction currents of the two is greater than or equal to the maximum output current of the hybrid power device, thereby determining the use specifications of the diode. In this way, by selecting appropriate specifications of the freewheeling diode, the circuit stability is ensured.

[0057] Considering that in a hybrid power device, a MOS power device is involved in both forward current output and reverse current freewheeling, under high current conditions, there is a risk of overheating of the MOS power device. Therefore, in some embodiments, the electric drive system also includes a current acquisition module and a junction temperature estimation module; the current acquisition module is arranged between the inverter unit and the drive motor, and is used to collect the current value of the three-phase current of the drive motor, and transmit the current value to the control unit; the junction temperature estimation module is used to estimate the real-time junction temperature value of the Si-IGBT power device, the MOS power device and the freewheeling diode and feed it back to the control unit. That is to say, a current acquisition module is arranged between the inverter unit and the drive motor, and the current acquisition module is a device for collecting the current value of the three-phase current of the drive motor, and its working principle is mainly realized by a current sensor. After collecting the current value, the current acquisition module transmits it to the control unit; at the same time, a junction temperature estimation module is arranged, which can estimate the real-time junction temperature value of the Si-IGBT power device, the MOS power device and the freewheeling diode and feed it back to the control unit by an estimation method based on a thermal equivalent circuit model or other methods. In this way, by monitoring the junction temperature and current of the MOS power device, the control unit can promptly detect potential over-temperature risks and take corresponding measures to intervene, thereby avoiding damage to the MOS power device due to overheating.

[0058] Furthermore, in some embodiments, the control unit is also used for: when the real-time junction temperature value of the MOS power device is less than the maximum junction temperature limit of the MOS power device, if the Si-IGBT power device and the MOS power device are in the off state, controlling the MOS power device and the freewheeling diode to jointly perform current freewheeling; when the real-time junction temperature value of the MOS power device is greater than the maximum junction temperature limit of the MOS power device, if the current value collected by the current acquisition module is greater than or equal to the maximum conduction current of the freewheeling diode, and the Si-IGBT power device and the MOS power device are in the off state, controlling the MOS power device and the freewheeling diode to jointly perform current freewheeling; if the current value collected by the current acquisition module is less than the maximum conduction current of the freewheeling diode, controlling the MOS power device to be turned off, and controlling the freewheeling diode to perform current freewheeling.

[0059] That is to say, the control unit can adopt the following freewheeling control method to avoid overheating of the MOS power device: set the maximum on-state current I of the freewheeling diode Fm The maximum junction temperature limit T0 of the MOS power device is obtained, and the reverse freewheeling current I is obtained, that is, the current value collected by the current acquisition module, and the real-time junction temperature value T of the MOS power device estimated by the junction temperature estimation module. mos , when T mos When T0 is less than, if the hybrid device of the forward inverter output is in the off state, the MOS power device is controlled to be turned on and the freewheeling diode is used to conduct the current. mos >T0, if I≥I Fm , and the hybrid device with forward inverter output is in the off state, the MOS power device is controlled to be turned on and to conduct the current together with the freewheeling diode. If I Fm , the MOS power device is controlled to be turned off, and the freewheeling diode is used to continue the current alone. In this way, the risk of overheating of the MOS power device is effectively reduced.

[0060] ​In addition, in some embodiments, the maximum junction temperature limit of the MOS power device mentioned above can be determined based on the difference between the maximum allowable operating temperature of the MOS power device and the junction temperature rise value; the junction temperature rise value is estimated based on the forward output loss and reverse output loss of the MOS power device when the forward output current of the hybrid power device is maximum. In other words, the determination of the maximum junction temperature limit of the MOS power device needs to be considered in combination with the forward output loss (including switching loss, conduction loss) and reverse freewheeling loss (mainly conduction loss) of the MOS power device. When the forward output current of the hybrid device is maximum, the forward output loss and reverse freewheeling loss of the MOS tube are maximum. Therefore, based on the forward output loss and reverse freewheeling loss of the MOS power device when the forward output current of the hybrid device is maximum, the junction temperature rise value ΔT of the MOS power device is estimated, combined with the maximum allowable operating temperature T of the MOS power device obtained by using the manual. jmax , the maximum junction temperature limit of the MOS power device can be calculated as T0 = T jmax -ΔT. In this way, the maximum junction temperature limit of the MOS power device is accurately calculated, which lays a good foundation for avoiding overheating of the MOS power device.

[0061] Optionally, the junction temperature rise value mentioned above may be the product of a power loss value calculated by a power loss model when the forward output current of the hybrid power device is maximum and a heat dissipation thermal resistance parameter; the power loss model is expressed as the following formula:

[0062]

[0063] Among them, P m is the power loss value; I n , U n and E sw (I n , U n ) are respectively the test current, test voltage and test loss value of the MOS power device; f is the frequency of the MOS power device; U DC is the power supply voltage; I m K is the forward current amplitude of the hybrid power device; m is the correction coefficient; T is the current cycle of the drive motor; u r 、u F are respectively the initial voltage drops of the MOS power device in forward conduction and reverse conduction; r r 、r F are respectively the internal resistance of the forward conduction and reverse conduction of the MOS power device; i r (t), i r(t) are the forward current and reverse current of the MOS power device respectively; D is the switching duty cycle of the MOS power device.

[0064] That is to say, when determining the maximum junction temperature limit of the MOS power device, the maximum current of the hybrid device forward output can be obtained through product design requirements, and the switching loss curve and the on-state voltage drop curve can be obtained through the hybrid device manual and test data, such as the data of the double pulse test, and the loss power model shown in the above formula can be established. In this way, when the hybrid device outputs the maximum current forward, the loss power P of the MOS power device can be calculated through the loss power model. m , combined with the heat dissipation thermal resistance parameter R obtained from the user manual thJF , the junction temperature rise of the MOS power device can be estimated by ΔT = P m *R thJF In this way, the junction temperature rise value of the MOS power device can be calculated accurately and quickly.

[0065] In addition, when the control unit requires a forward inverter output, the control unit first turns off the MOS power device and then performs a forward inverter output to prevent the upper and lower bridge arms of the hybrid device from being directly connected, causing a power short circuit.

[0066] The embodiment of the present application provides an electric drive system, wherein the input end of the inverter unit of the electric drive system is connected to the power supply unit, and the output end is connected to the drive motor. The inverter unit includes three single-phase inverters, each of which includes two hybrid power devices, each of which is composed of a Si-IGBT power device, a MOS power device based on a target semiconductor material, and a freewheeling diode in parallel, wherein the Si-IGBT power device and the MOS power device jointly realize the forward inverter output of the electric drive system, and the MOS power device and the freewheeling diode jointly realize the current freewheeling of the electric drive system, and the control unit controls the inverter unit to enter a forward inverter output state or a reverse freewheeling state through a drive module. In this way, the MOS power device based on the target semiconductor material is reused to replace part of the freewheeling diode for freewheeling, which can reduce the use specifications of the freewheeling diode, thereby reducing the cost and volume of the power module.

[0067] like Figure 3 As shown, Figure 3 : is a flow chart of a control method of an electric drive system provided in an embodiment of the present application. The electric drive system is the electric drive system in any of the foregoing embodiments. The control method is applied to a control unit and includes:

[0068] In step 301, a target signal of the electric drive system and a demand of an external system are obtained; the target signal includes the current value of the three-phase current of the drive motor, and the real-time junction temperature value of the Si-IGBT power device, the MOS power device and the freewheeling diode;

[0069] In step 302, according to the target signal and the requirements of the external system, the inverter unit is controlled to enter a forward inverter output state or a reverse freewheeling state through the driving module.

[0070] The implementation process of each step in the above method is specifically described in detail in the implementation process of the role and function of each module in the above system, which will not be repeated here.

[0071] In order to explain the solution of this application in more detail, a specific embodiment is introduced below:

[0072] This embodiment provides a solution for realizing current freewheeling by using SiC-MOS and freewheeling diodes. The overall architecture of this solution is as follows: Figure 4 As shown, it is in Figure 1 On the basis of the electric drive system shown in FIG. 1 , a current acquisition module 17 and a junction temperature estimation module 18 are added, a DC bus capacitor 19 is connected in parallel to the power supply unit 11, and the serial numbers of the remaining modules are the same as before. Figure 4 The hybrid power device 16 is not shown. Figure 5 As shown, it is composed of a Si-IGBT power device 161, a SiC-MOS power device 162 and a freewheeling diode 163 in parallel. The Si-IGBT power device 161 is composed of multiple Si-IGBT wafer chips in parallel; the SiC-MOS power device 162 is composed of multiple SiC-MOS wafer chips in parallel, and together with the Si-IGBT power device 161, it realizes the forward inverter output of the electric drive system, and together with the freewheeling diode, it realizes the current freewheeling of the system; the freewheeling diode 163 is composed of multiple fast recovery diode wafer chips in parallel.

[0073] The scheme of this embodiment reuses SiC-MOS to replace part of the freewheeling diodes for freewheeling, thereby reducing the usage specifications of the freewheeling diodes, thereby reducing the cost and volume of the module; this scheme utilizes the characteristics of SiC-MOS's reduced on-state voltage during small current freewheeling and the reduced on-state voltage of the freewheeling diode during large current freewheeling, and reduces the reverse freewheeling loss of the hybrid module during joint freewheeling, thereby improving system efficiency.

[0074] This embodiment also proposes Figure 6 The freewheeling control method shown comprises:

[0075] S601, set the maximum conduction current of the freewheeling diode to I Fm ;

[0076] S602, setting the maximum junction temperature limit T0 of the SiC-MOS power device;

[0077] S603, obtaining a reverse freewheeling current I through a current acquisition module;

[0078] S604, obtaining the real-time junction temperature value T of the SiC-MOS power device through the junction temperature estimation module mos ;

[0079] S605, determine the real-time junction temperature value T mos Is it less than the maximum junction temperature limit T0? If yes, execute S608; otherwise, execute S606;

[0080] S606: Determine whether the reverse freewheeling current I is greater than the maximum conduction current of the freewheeling diode I Fm If yes, execute S608, otherwise execute S607;

[0081] S607, control the SiC-MOS power device to turn off, and return to S603;

[0082] Specifically, at this time, the electric drive system is freewheeling by the freewheeling diode alone, and the diode freewheeling current flows to Figure 7 As shown;

[0083] S608, determining whether the driving bridge arm state is off, if yes, executing S609, otherwise executing S607;

[0084] S609, controlling the SiC-MOS power device to turn on and perform current follow-up;

[0085] Specifically, at this time, the electric drive system is freewheeling by the SiC-MOS power device and the freewheeling diode. The diode and the MOS tube freewheeling flow direction is as follows: Figure 8 As shown;

[0086] S610, determining whether the driving bridge arm state needs to be turned on, if yes, executing S611, otherwise executing S609;

[0087] S611, control the SiC-MOS power device to turn off;

[0088] S612, determine whether the SiC-MOS power device is in the off state, if yes, execute S613, otherwise return to S611;

[0089] S613, control the driving bridge arm to be turned on, and return to S603.

[0090] Through the above-mentioned freewheeling control method, the risk of overheating of the SiC-MOS power device can be effectively reduced while using SiC-MOS and the freewheeling diode to jointly realize current freewheeling.

[0091] Some embodiments of the present application also provide a vehicle, which includes the electric drive system involved in any of the aforementioned embodiments.

[0092] The above description is only an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0093] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0094] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

Claims

1. An electric drive system, characterized in that: It includes a power supply unit, an inverter unit, a drive motor, a control unit and a drive module; wherein: The input end of the inverter unit is connected to the power supply unit, and the output end of the inverter unit is connected to the drive motor; the inverter unit includes three single-phase inverters, each single-phase inverter includes two hybrid power devices, and each hybrid power device is composed of a Si-IGBT power device, a MOS power device based on a target semiconductor material, and a freewheeling diode in parallel; the inverter unit is used to realize the forward inverter output of the electric drive system through the Si-IGBT power device and the MOS power device, and realize the reverse freewheeling of the electric drive system through the MOS power device and the freewheeling diode; The control unit is used to control the inverter unit to enter a forward inverter output state or a reverse freewheeling state through the drive module.

2. The electric drive system according to claim 1, characterized in that: The target semiconductor material includes any one of the following: SiC, GaN.

3. The electric drive system according to claim 1, characterized in that: The control unit is specifically used for: When the electric drive system enters the freewheeling stage, the MOS power device is controlled to remain in an off state, and the freewheeling diode is controlled to perform current freewheeling; After the electric drive system enters the freewheeling stage, controlling the MOS power device and the freewheeling diode to jointly perform current freewheeling; At the end of the freewheeling stage, the MOS power device is controlled to be turned off, and then the Si-IGBT power device and the MOS power device are controlled to perform inverter output together.

4. The electric drive system according to claim 3, characterized in that: The use specification of the freewheeling diode is determined according to the maximum allowable operating current of the drive motor and the maximum conduction current of the MOS power device.

5. The electric drive system according to claim 1, characterized in that: It also includes a current acquisition module and a junction temperature estimation module; the current acquisition module is arranged between the inverter unit and the drive motor, and is used to collect the current value of the three-phase current of the drive motor and transmit the current value to the control unit; The junction temperature estimation module is used to estimate the real-time junction temperature values ​​of the Si-IGBT power device, the MOS power device and the freewheeling diode and feed back the values ​​to the control unit.

6. The electric drive system according to claim 5, characterized in that: The control unit is also used for: When the real-time junction temperature value of the MOS power device is less than the maximum junction temperature limit value of the MOS power device, if the Si-IGBT power device and the MOS power device are in the off state, the MOS power device and the freewheeling diode are controlled to jointly perform current freewheeling; When the real-time junction temperature value of the MOS power device is greater than the maximum junction temperature limit of the MOS power device, if the current value collected by the current acquisition module is greater than or equal to the maximum on-current of the freewheeling diode, and the Si-IGBT power device and the MOS power device are in the off state, the MOS power device and the freewheeling diode are controlled to jointly perform current freewheeling; if the current value collected by the current acquisition module is less than the maximum on-current of the freewheeling diode, the MOS power device is controlled to be turned off, and the freewheeling diode is controlled to perform current freewheeling.

7. The electric drive system according to claim 6, characterized in that: The maximum junction temperature limit of the MOS power device is determined based on the difference between the maximum allowable operating temperature of the MOS power device and the junction temperature rise value; the junction temperature rise value is estimated based on the forward output loss and reverse output loss of the MOS power device when the forward output current of the hybrid power device is maximum.

8. The electric drive system according to claim 7, characterized in that: The junction temperature rise value is the product of the power loss value calculated by the power loss model when the forward output current of the hybrid power device is the maximum and the heat dissipation thermal resistance parameter; the power loss model is expressed as the following formula: Among them, P m is the power loss value; I n , U n and E sw (I n ,U n ) are respectively the test current, test voltage and test loss value of the MOS power device; f is the frequency of the MOS power device; U DC is the power supply voltage; I m K is the forward current amplitude of the hybrid power device; m is the correction coefficient; T is the current cycle of the drive motor; u r 、u F are respectively the initial voltage drops of the MOS power device in forward conduction and reverse conduction; r r 、r F are respectively the internal resistance of the forward conduction and reverse conduction of the MOS power device; i r (t), i r (t) are the forward current and reverse current of the MOS power device respectively; D is the switching duty cycle of the MOS power device.

9. A control method for an electric drive system according to any one of claims 1 to 8, characterized in that: Applied to the control unit, the control method comprises: Obtaining target signals of the electric drive system and requirements of an external system; the target signals include current values ​​of the three-phase currents of the drive motor, and real-time junction temperature values ​​of the Si-IGBT power device, the MOS power device, and the freewheeling diode; According to the target signal and the requirements of the external system, the inverter unit is controlled to enter a forward inverter output state or a reverse freewheeling state through the driving module.

10. A vehicle, characterized in that: The vehicle comprises the electric drive system according to any one of claims 1 to 8.

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