Methods for controlling inverters, electric drive systems, vehicles, and controllable switches of inverters, and corresponding computer program products.

Abstract

The inverter comprises input terminals (IT+, IT-), output terminals (OT), controllable switches (Q, Q') connected to the input terminals (IT+, IT-) and the output terminal (OT), and a control device (116) configured to control the controllable switches (Q, Q') so that the controllable switches (Q, Q') convert a DC voltage (E) at the input terminals (IT+, IT-) into an AC voltage at the output terminal (OT) intended to drive an electric motor (108), the control device (116) controlling the inverter (110) according to a first switching frequency and a temperature (T J , T C and a control device (116) configured to control the controllable switches (Q, O') according to a second switching frequency in response to the controllable switches (Q, O') and the control device (116) configured to determine the second switching frequency in response to an operating point of the electric motor (108).

Description

[Technical Field]

[0001] The present invention relates to an inverter, and an electric drive system and vehicle equipped with such an inverter. The present invention also relates to a method for controlling a controllable switch of an inverter and a corresponding computer program product. The present invention is intended, in particular, for use in automobile vehicles. [Background technology]

[0002] An inverter is used, for example, to generate AC voltage from a DC voltage supplied by a battery. Typically, an inverter includes a DC link capacitor to smooth the DC voltage.

[0003] During inverter operation, inverter components may generate heat, potentially mitigating the inverter's reliable operation. [Overview of the project] [Problems that the invention aims to solve]

[0004] The objective of the present invention is to prevent overheating of at least one of the elements of the inverter. [Means for solving the problem]

[0005] The objective of the present invention is, It is an inverter, Input terminals, Output terminals, A controllable switch connected to the input and output terminals, The object of the present invention can be solved by an inverter comprising a control device configured to control a controllable switch so as to convert a DC voltage at an input terminal to an AC voltage at an output terminal intended to drive an electric motor, wherein the control device is configured to control the controllable switch according to a first switching frequency and according to a second switching frequency depending on the temperature of the inverter elements, and the control device is configured to determine the second switching frequency according to the operating point of the motor.

[0006] By reducing the switching frequency from a first switching frequency to a second switching frequency, it may be possible to control the temperature of the inverter elements. Furthermore, this change in switching frequency may result in more or less acceptable drawbacks depending on the motor's operating point. The present invention makes it possible to set the second switching frequency according to the motor's operating point, and as a result, the second switching frequency may result in a good temperature reduction while still resulting in acceptable drawbacks. For example, the second switching frequency may be reduced relative to the first switching frequency. This reduction may lead to an increase in AC current ripple in the motor phase, which in turn may lead to an increase in motor losses and NVH load. Motor losses and NVH load are more acceptable at low motor speeds than at high motor speeds. The present invention makes it possible to have a high switching frequency reduction at low motor speeds to meet acceptable levels of motor losses and NVH load, and a low switching frequency reduction at high motor speeds where motor losses and NVH load are more important.

[0007] The relevant temperature may be measured, for example, using a suitable temperature sensor. Alternatively, the temperature may be estimated.

[0008] Optionally, the element is one of the controllable switches. This is advantageous because the temperature of the controllable switch depends on the switching frequency. Thus, according to this embodiment, the control device may be configured for the controllable switch according to a first switching frequency and according to a second switching frequency depending on the temperature of at least one of the controllable switches of the inverter, and the control device is configured to determine the second switching frequency according to the operating point of the motor.

[0009] In particular, all the temperatures of the controllable switches may be used.

[0010] The controllable switch may be a transistor, for example, an IGBT.

[0011] Also, optionally, the temperature may be the junction temperature of at least one of the transistors. This is advantageous because the junction temperature is important for the control of the transistor controllable switch to avoid damage or destruction of the transistor controllable switch.

[0012] Also, optionally, the element is a DC link capacitor connected to the input terminals. This is advantageous because the temperature of the DC link capacitor depends on the switching frequency.

[0013] Also, optionally, the operating point of the motor is the modulation index of the motor. This is advantageous because the AC current ripple depends on the modulation index.

[0014] Also, optionally, the operating point of the motor is the rotational speed of the motor. This is advantageous because the AC current ripple depends on the motor speed. Furthermore, the motor speed may usually be used to determine the command for the controllable switch, and as a result, it may be easily available.

[0015] Alternatively, optionally, the control device is further configured to shift from a first switching frequency to a second switching frequency regardless of the rotational speed of the motor. Thus, there may be no need to reduce the torque of the motor at high motor speeds in order to control the temperature of the inverter elements.

[0016] The present invention also relates to an electric drive device comprising an inverter according to the present invention and an electric motor driven by the inverter.

[0017] The present invention also relates to a vehicle comprising a wheel and an electric drive device according to the present invention for driving at least one of the wheels at least indirectly.

[0018] The present invention also relates to a method for controlling a controllable switch of an inverter, the controllable switch being connected to the input and output terminals of the inverter and controlling the controllable switch to convert a DC voltage at the input terminal into an AC voltage at the output terminal intended to drive an electric motor, the control device being configured to determine a second switching frequency according to the operating point of the motor according to a first switching frequency and according to the temperature of the elements of the inverter and according to a second switching frequency.

[0019] The present invention also relates to a computer program product comprising instructions that cause a computer to execute the method according to the present invention when the program is executed by the computer.

[0020] The present invention will be described more specifically with reference to the accompanying drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic diagram showing an embodiment of a vehicle provided with an inverter according to the present invention. [Figure 2] It is an example of an embodiment of the inverter of FIG. 1. [Figure 3]This graph shows the decrease in switching frequency as a function of the motor's modulation index. [Figure 4] This graph shows the decrease in switching frequency as a function of motor speed. [Modes for carrying out the invention]

[0022] Next, with reference to Figure 1, the vehicle 100 according to the present invention will be described. In the example described, the vehicle 100 is an automobile.

[0023] The vehicle 100 comprises wheels 102 and an electric drive unit 104 configured to drive at least one of the wheels 102 at least indirectly. The vehicle 100 further comprises a DC voltage source 106, such as a battery, for supplying power to the electric drive unit 104. The DC voltage source 106 is configured to supply a DC voltage E.

[0024] The electric drive unit 104 includes an electric motor 108 and an inverter 110 configured to drive the motor 108, for example, by supplying power. For example, the motor 108 is a rotary asynchronous electric motor comprising a stator and a rotor configured to rotate around the rotation axis relative to the stator at a rotational speed w.

[0025] A stator is provided with stator phases. In the example described, motor 108 is a three-phase electric motor with three stator phases.

[0026] The inverter 110 is intended to drive the motor 108 so that a phase current flows through each of the stator phases, thereby generating a rotating magnetic field that rotates around the rotating shaft.

[0027] The inverter 110 has input terminals IT+ and IT- connected to a DC voltage source 106 such that a DC voltage E is present at the input terminals IT+ and IT-. More precisely, the input terminals IT+ and IT- include a positive input terminal IT+ connected to the positive terminal of the DC voltage source 106, and a negative input terminal IT- connected to the negative terminal of the DC voltage source 106 and the electrical ground GND.

[0028] The inverter 110 further includes an output terminal OT connected to the motor 108. An AC voltage is intended to be present at the output terminal OT to supply power to the electric motor 108. The AC voltage may be single-phase or multi-phase. In the described example, where the motor 108 is a three-phase electric motor, the AC voltage is a three-phase AC voltage.

[0029] The inverter 110 further comprises controllable switches Q, Q', called main switches, connected to input terminals IT+, IT- and output terminal OT. The main switches Q, Q' may be semiconductor switches, for example, comprising transistors.

[0030] Each main switch Q, Q' comprises, for example, one of the following: a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), and a silicon carbide MOSFET (SiC MOSFET).

[0031] In the example described, the inverter 110 has switch legs 114 associated with each stator phase of the motor 108. 1-3 Each switch leg 114 1-3 It comprises a high-side (HS) main switch Q' connected to the positive input terminal IT+ and a low-side (LS) main switch Q connected to the negative input terminal IT-. The HS main switch Q' and the LS main switch Q are connected to each other at a midpoint connected to the output terminal OT connected to the relevant stator phase of the motor 108.

[0032] Each switch leg 114 1-3It is intended to be controlled to rectify between two configurations. In the first configuration, called the high-side (HS) configuration, the HS main switch Q' is closed (on) and the LS main switch Q is open (off), resulting in essentially a DC voltage E being applied to the relevant stator phases. In the second configuration, called the low-side (LS) configuration, the HS main switch Q' is open (off) and the LS main switch Q is closed (on), resulting in essentially a 0 voltage being applied to the relevant stator phases.

[0033] The inverter 110 further comprises a control device 116 configured to control the main switches Q, Q' so that the main switches Q, Q' convert a DC voltage E to an AC voltage. In the example described, the control device 116 is configured to rectify each switch leg 114 between the two configurations described above.

[0034] The inverter 110 further includes a DC link capacitor 118 connected to the input terminals IT+ and IT-. The DC link capacitor 118 is configured to smooth the DC voltage E (e.g., limit voltage overshoot).

[0035] The electric drive unit 104 controls the main switch Q, Q', AC voltage, and DC voltage, and the junction temperature T of at least one of these. J The system may further include temperature sensors 120, 122, and 124 for measuring each of these quantities. Alternatively, one or more of these quantities can be estimated instead of measured. In particular, the junction temperatures of all main switches Q, Q' may be measured or estimated. It is also possible that only the junction temperature of one of the main switches Q, Q' is measured or estimated.

[0036] Next, an example of the control device 116 will be described with reference to Figure 2. In the following description, only the features of the control device 116 that are useful for understanding the present invention will be described.

[0037] The control device 116 is configured to determine commands for the switch leg 114 from, for example, a torque target t* determined by operating an accelerator pedal or a speed controller of the vehicle. 1-3 It includes a command determination module 202 configured to determine commands for 1-3 . These commands are intended to switch the switch leg 114 1-3 between the HS configuration and the LS configuration of the switch leg 114. 1-3 The commands are, for example, pulse width modulation (PWM) commands. Also, for example, the commands are determined according to space vector modulation.

[0038] The command determination module 202 is configured to determine commands according to the received switching frequency.

[0039] As described below, this switching frequency is selectively the nominal switching frequency F and, according to the temperature of the elements of the inverter 110, is the switching frequency F for derating. D The switching frequency F for derating is preferably lower than the nominal switching frequency F. D

[0040] The switching frequency F for derating is used, for example, according to the junction temperature T D or according to the capacitor temperature T. For example, the switching frequency F for derating J is used when the junction temperature T C exceeds a predetermined threshold value T D or when the capacitor temperature T J exceeds a predetermined threshold value T J,thd The switching frequency F for derating is generally dynamically determined according to the operating point of the motor 108. C C,thd D For this purpose, the control device 116 may first include an operating point determination module 204. D

[0041]

[0042] In the first embodiment, the operating point is the modulation index M of the motor 108, and therefore the operating point determination module 204 determines, for example, the DC voltage E and the phase voltage V 1-3 The system is configured to determine the modulation index M from at least one of the following: For example, the modulation index M is defined as M = V / E, where V is the phase voltage V 1-3 This is the peak-to-peak amplitude of one of the fundamental waves.

[0043] Next, the control device 116 sets the operating point, i.e., the derating switching frequency F as a function of the modulation index M in the described embodiment. D The system may further include a derating switching frequency determination module 206 configured to determine the derating switching frequency F. Preferably, the derating switching frequency F D This is determined dynamically, i.e., updated as the modulation index M changes. For example, the switching frequency F for derating. D is, F D According to the formula =Ff, it is equal to the nominal switching frequency F minus the switching frequency drop f, which is a function of the modulation index M.

[0044] Next, the control device 116 determines the joint temperature T J and capacitor temperature T c The comparison module 208 may further include a comparison module 208 configured to compare both temperatures T with their respective thresholds. J , T c When the temperature T falls below the respective threshold, the nominal switching frequency F is provided to the command determination module 202, and the temperature T J , T c When at least one of the following exceeds its associated threshold, the derating switching frequency F D It is further configured to provide this to the command determination module 202.

[0045] Figure 3 illustrates an example of the relationship between the switching frequency reduction f and the duty cycle DC, which directly corresponds to the modulation index M. For example, the duty cycle DC is given by DC = √3 × M.

[0046] As shown in the diagram, in the low modulation index M range (from 0 to approximately 0.18 in the diagram), the derating switching frequency f is constant (approximately 5.5 kHz in the diagram). Then, in the intermediate modulation index M range (from approximately 0.18 to approximately 0.6 in the diagram), the derating switching frequency f increases proportionally to the modulation index M. Then, in the high modulation index M range (from 0.6 to approximately 1), the derating switching frequency f becomes constant again (approximately 8 kHz in the diagram).

[0047] Because the derating switching frequency FD depends on the operating point, the second switching frequency F is independent of the motor speed w, especially at high motor speeds w. D It is possible to transition to this.

[0048] More precisely, the switching frequency is changed from the nominal switching frequency F to the derating switching frequency F. D By reducing the frequency, overheating of the controllable switches Q, Q', and / or DC link capacitor 118 is prevented. However, this reduction increases the AC current ripple in the stator phase, resulting in increased motor noise, vibration, and harshness (NVH) load. These drawbacks are not as extreme at low rotor speeds w as at high rotor speeds w. Therefore, the switching frequency F is used for derating. D This is why a modulation index M is preferable. Thus, at high motor speeds w, a lower switching frequency can be used because it is more acceptable and results in better temperature control. As a result, there is no need to reduce the phase AC current (and therefore the motor torque).

[0049] In another embodiment, the operating point determination module 204 is absent, and the derating switching frequency determination module 206 determines the derating switching frequency F according to the measured or estimated motor speed w. D It is configured to determine this. In fact, at a constant DC voltage E, the modulation index M increases as the motor speed w increases, so it is possible to use the motor speed w instead of the modulation index M.

[0050] An example of the relationship between the switching frequency reduction f and the motor speed w is shown in Figure 4.

[0051] As illustrated, in the low motor speed range w (0 to approximately 1000 rpm in the illustrated example), the derating switching frequency f is constant (approximately 5.5 kHz in the illustrated example). Then, in the intermediate motor speed range w (approximately 1000 rpm to approximately 5900 rpm in the illustrated example), the derating switching frequency f increases proportionally to the speed w. Then, in the high motor speed range (approximately 5900 rpm to approximately 7000 rpm in the illustrated example), the derating switching frequency f is again constant (approximately 9 kHz in the illustrated example).

[0052] The control device 116 may include a computer device comprising a data processing unit (such as a microprocessor) and main memory accessible by the processing unit. The computer device may further include a computer program containing instructions for the processing unit in order to perform the functions of the modules described above. This computer program is intended to be loaded into the main memory, for example, so that the processing unit can execute its instructions. Alternatively, all or part of these modules can be implemented in the form of hardware modules, i.e., in the form of microwired electronic circuits, which do not include a computer program.

[0053] It should be noted that the present invention is not limited to the embodiments described above. It will be apparent to those skilled in the art that various modifications can be made to the embodiments described above in light of the teachings just disclosed.

[0054] In the above-mentioned detailed description of the present invention, the terms used should not be construed as limiting the invention to the embodiments presented herein, but rather as encompassing all equivalents within the scope of those skilled in the art by applying that general knowledge to the practice of the teachings just disclosed.

Claims

1. An inverter (110), Input terminals (IT+, IT-) and Output terminal (OT), Controllable switches (Q, Q') connected to the input terminals (IT+, IT-) and the output terminal (OT), A control device (116) is configured to control the controllable switches (Q, Q') so that the controllable switches (Q, Q') convert the DC voltage (E) at the input terminals (IT+, IT-) to an AC voltage at the output terminal (OT) intended to drive an electric motor (108), wherein the control device (116) According to the first switching frequency (F), and The temperature (T) of the elements (Q, 118) of the inverter (110) Ｊ , T Ｃ ) Depending on the second switching frequency (F Ｄ ) According to, configured to control the controllable switches (Q, Q'), the control device (116) determines the second switching frequency (F Ｄ ) according to the operating point of the electric motor (108), and further, regardless of the rotational speed (w) of the electric motor (108), when the temperature (T Ｊ ) of the element (Q) which is a switch exceeds a threshold value (T Ｊ，ｔｈｄ ), and / or when the temperature (T Ｃ ) of the element (118) which is a capacitor exceeds a threshold value (T Ｃ，ｔｈｄ ), it is configured to shift from the first switching frequency (F) to the second switching frequency (F Ｄ ) which is lower than the first switching frequency (F), a control device (116), and is provided with The operating point of the electric motor (108) is the modulation index (M) of the electric motor (108). Inverter (110).

2. The inverter (110) according to claim 1, wherein the element (Q) is one of the controllable switches (Q, Q').

3. The controllable switch (Q, Q') is a transistor, and the temperature (T Ｊ The inverter (110) according to claim 2, wherein ) is the junction temperature of the transistor.

4. The inverter (110) according to claim 1, comprising a DC link capacitor (119) connected to the input terminals (IT+, IT-) and configured to smooth the DC voltage (E), wherein the element is the DC link capacitor (118).

5. An electric drive device (104) comprising an inverter (110) according to any one of claims 1 to 4, and an electric motor (108) driven by the inverter (110).

6. A vehicle (100) comprising wheels (102) and an electric drive device (104) according to claim 5 for driving at least one of the wheels (102) at least indirectly.

7. A method for controlling a controllable switch (Q, Q') of an inverter (110), the controllable switch (Q, Q') being connected to the input terminals (IT+, IT-) and output terminal (OT) of the inverter (110), and the method comprising controlling the controllable switch (Q, Q') to convert a DC voltage (E) at the input terminals (IT+, IT-) to an AC voltage at the output terminal (OT) intended to drive an electric motor (108), The control device (116) According to the first switching frequency (F), and The temperature (T) of the elements (Q, 118) of the inverter (110) Ｊ , T Ｃ ) Depending on the second switching frequency (F Ｄ ) According to, The controllable switches (Q, Q') are controlled, and the second switching frequency (F) is controlled according to the operating point of the electric motor. Ｄ It is configured to determine the temperature (T) of the element (Q), which is a switch, independently of the rotational speed (w) of the electric motor (108). Ｊ ) is the threshold (T Ｊ，ｔｈｄ ) if it exceeds and / or the temperature of the element (118) which is a capacitor (T Ｃ ) is the threshold (T Ｃ，ｔｈｄ If it exceeds the first switching frequency (F), the second switching frequency (F) which is lower than the first switching frequency (F) is lowered. Ｄ ) is configured to transition to, The operating point of the electric motor (108) is the modulation index (M) of the electric motor (108). method.

8. A computer program product that, when executed by a computer, includes instructions causing the computer to perform the method described in claim 7.

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