Operation method and operation device of motor driver for driving motor

An operation method and an operation device of a motor driver for driving a motor are provided. The operation method includes: establishing a hysteresis control method; and adjusting a switch frequency of a power module for operating the motor by using the hysteresis control method according to a change of rotation speed of the motor and a current switch frequency.

TECHNICAL FIELD

The disclosure relates in general to an operation method and an operation device, and more particularly to an operation method and an operation device of a motor driver for driving a motor.

BACKGROUND

With the rapid growth of the electric vehicle market, the motor driver for driving a motor (e.g., an inverter) is also developing towards high density and high efficiency. The motor driver with high density and high efficiency represents having high power output. Failure to effectively dissipate heat, or failure to respond to heat generation in time, can easily cause failure or damage of the driving system, and even increase the chance of danger.

Therefore, it is desired to provide a protection method for the motor driver which provides the maximum performance of the driving system under the demand of high density and high efficiency, in addition to preventing the destruction due to high temperature of the driving system.

SUMMARY

The disclosure is directed to an operation method and an operation device of a motor driver for driving a motor to solve the aforementioned problems.

According to one embodiment, an operation method of a motor driver for driving a motor is provided. The operation method includes: establishing a hysteresis control method; and adjusting a switch frequency of a power module for operating the motor by using the hysteresis control method according to a change of rotation speed of the motor and a current switch frequency.

According to another embodiment, an operation device of a motor driver for driving a motor is provided. The operation device includes a control unit configured for adjusting a switch frequency of a power module for operating the motor by a hysteresis control method according to a change of rotation speed of the motor and a current switch frequency.

The above and other embodiments of this disclosure will become better understood with regard to the following detailed description. The following description is made with reference to the accompanying drawings.

DETAILED DESCRIPTION

In the past, the thermal protection mechanism of automotive drive system was activated by detecting the temperature of the thermal resistor disposed on the power transistor once the temperature exceeded a predetermined value. However, due to the placement of the thermal resistor, the temperature measured by the thermal resistor is to detect the substrate temperature (which is lower) rather than the junction temperature of the power transistor (which is higher); in addition, the difference between the substrate temperature and the junction temperature increases as the load becomes heavier, resulting in a situation where the actual junction temperature has exceeded the load of the power transistor, but the thermal protection mechanism has not yet been activated.

Through the thermal protection mechanism provided by the disclosure, a hysteresis control method is developed by evaluating the junction temperature, so as to ensure that the motor driver operates in a safe and secure manner, and further to maximize the performance of the driving system.

Each embodiment of the disclosure will be described in detail below and illustrated with drawings. In addition to these detailed descriptions, the disclosure may be broadly implemented in other embodiments, and any easy substitution, modification, or equivalent variation of the described embodiments is included in the scope of the disclosure and is covered by the scope of the claims thereafter. In the description of the specification, many specific details and examples of embodiments are provided to provide the reader with a more complete understanding of the disclosure; however, these specific details and examples of embodiments should not be considered as limitations of the disclosure. In addition, well known steps or components are not described in detail to avoid unnecessary limitations of the disclosure.

In addition, the terms such as “equal to”, “touch” and “reach” mentioned herein should be understood as including the value of the number itself; and terms such as “greater than”, “above”, “less than” and “below” should be understood as not including the value of the number itself.

Referring toFIG. 1, a simplified functional block diagram of a driving system1according to one embodiment of the disclosure is shown. The driving system1includes an operation device100, a power supply200, a motor driver300and a motor400. The power supply200may be supplied with power by battery. The motor driver300may be coupled to the operation device100, the power supply200and the motor400. The motor driver300may include a plurality of power modules310, and each power module310may include a plurality of power components, such as switching elements and diodes. The switching elements may be, but not limited to, insulated gate bipolar transistors (IGBTs), silicon carbide (SiC) transistors, gallium nitride (GaN) transistors, etc. In the present embodiment, the motor driver300with high power may be provided with three power modules310connected in parallel. As shown inFIG. 7A, the three power modules310represent three phases U, V, and W. Each phase is composed of three single sub-phases310a, and one single sub-phase310aincludes two switching elements.FIG. 7Bis a circuit diagram of one power module310ofFIG. 7A. However, in practice, the number of power modules310may depend on the required wattage of power. For example, if the required output power is low, one power module310may be used, and each of the single sub-phases310aof this power module310represents U, V and W phases respectively. The operation device100may switch the power module310to determine the rotation speed, position and torque of the motor400, so that the motor400drives the movement of the mechanical carrier (such as wheels).

FIG. 2is a simplified functional block diagram of the operation device100of the motor driver300according to one embodiment of the disclosure.FIG. 3is a flowchart of an operation method S100of the motor driver300according to one embodiment of the disclosure.

Referring toFIGS. 1, 2 and 3, the operation device100may include a model building unit110, a loss calculation unit120, a temperature calculation unit130, and a control unit140for adjusting a switch frequency. The model building unit110, the loss calculation unit120, the temperature calculation unit130and the control unit140may be implemented by a hardware circuit or software, for example, by an integrated circuit or a processing unit.

First, in step S120, a hysteresis control method may be established in the control unit140(which will be described in detail inFIGS. 5 and 6). Next, according to step S140, the control unit140may adjust the switch frequency of the power module310for operating the motor400by using the hysteresis control method according to the change of rotation speed of the motor400and the current switch frequency for operating the motor400(which will be described inFIG. 4). The adjustment for the switch frequency of the power module310described herein includes increasing and lowering the frequency, and represents a change in the ON/OFF switch frequency of the power module310, but does not affect the rotation speed or torque of the motor400, which in turn affects the energy of the motor400to drive the movement of the mechanical carrier.

FIG. 4illustrates a hysteresis control method according to one embodiment of the disclosure, which may be established in the control unit140as a control instruction by means of table building. ReferringFIGS. 1, 2 and 4, the control unit140of the operation device100may adjust the switch frequency, for example, by lowering or increasing the switch frequency in a stepwise fashion, or by maintaining the current switch frequency, in accordance with the current switch frequency as the rotation speed of the motor400changes.

For example, in a condition that the current switch frequency (i.e. the switch current at present) is the frequency value f1(12.5 kHz), when the rotation speed N of the motor400drops from the speed value N1of 500 rpm and reaches the speed value N2of 400 rpm, the switch frequency fsw may be adjusted down in a stepwise fashion from the frequency value f1of 12.5 kHz to the frequency value f2of 6.25 kHz accordingly, so as to prevent from failure of the power module310or even a chance of danger caused by the temperature of the power module310greater than its tolerable temperature when the power module310operates the motor400at the speed value N2of 400 rpm with the frequency value f1of 12.5 kHz. However, in a condition that the current switch frequency is the frequency value f1(12.5 kHz), when the rotation speed of the motor400drops from the speed value N1(500 rpm) and then rises up right before reaching the speed value N2(400 rpm), the switch frequency fsw is still maintained at the frequency value f1(12.5 kHz).

In brief, in a condition that the current switch frequency is the frequency value f1(12.5 kHz), the switch frequency is maintained at the frequency value f1(12.5 kHz) when the rotation speed N of the motor400changes in the range of N>400 rpm.

Similarly, in a condition that the current switch frequency is the frequency value f2(6.25 kHz), when the rotation speed N of the motor400drops from the speed value N2of 400 rpm and reaches the speed value N4of 200 rpm, the switch frequency fsw may be adjusted down in a stepwise fashion from the frequency value f2of 6.25 kHz to the frequency value f3of 3.125 kHz accordingly, so that the temperature of the power module310does not exceed its tolerable temperature. However, in a condition that the current switch frequency is the frequency value f2(6.25 kHz), when the rotation speed of the motor400drops from the speed value N2(400 rpm) and then rises up right before reaching the speed value N4(200 rpm), for example, rises up to 300 rpm or to 400 rpm, the switch frequency fsw is still maintained at the frequency value f2(6.25 kHz). When the rotation speed of the motor400is greater than the speed value N2(400 rpm) and has not yet reached the speed value N1(500 rpm), the switch frequency fsw is also maintained at the frequency value f2(6.25 kHz); until the rotation speed of the motor400reaches the speed value N1(500 rpm), the switch frequency fsw may be adjusted up in a stepwise fashion from the frequency value f2of 6.25 kHz to the frequency value f1of 12.5 kHz accordingly instead of remaining at the frequency value f2of 6.25 kHz, so as to maximize the performance of driving system1and to reduce high voltage ripple caused by low frequency operation.

In brief, in a condition that the current switch frequency is the frequency value f2(6.25 kHz), the switch frequency is maintained at the frequency value f2(6.25 kHz) when the rotation speed N of the motor400changes in the range of 200 rpm<N<500 rpm.

Similarly, in a condition that the current switch frequency is the frequency value f3(3.125 kHz), when the rotation speed N of the motor400drops from the speed value N4of 200 rpm to the speed value NO of 50 rpm or even to 0 rpm, the switch frequency fsw is still maintained at the frequency value f3(3.125 kHz). That is, when the rotation speed N of the motor400drops to a speed value NO, which is close to the blocked rotor state (i.e., a state where the rotor of the motor400is stationary), the temperature of the power module310does not exceed the tolerable temperature even if the motor400is operated at a frequency value f3of 3.125 kHz. However, in a condition that the current switch frequency is the frequency value f3(3.125 kHz), when the rotation speed of the motor400drops from the speed value N4(200 rpm) and then rises up right before a rest, for example, rises up to 200 rpm, the switch frequency fsw is still maintained at the frequency value f3(3.125 kHz). When the rotation speed of the motor400is greater than the speed value N4(200 rpm) and has not yet reached the speed value N3(300 rpm), the switch frequency fsw is also maintained at the frequency value f3(3.125 kHz); until the rotation speed of the motor400reaches the speed value N3(300 rpm), the switch frequency fsw may be adjusted up in a stepwise fashion from the frequency value f3of 3.125 kHz to the frequency value f2of 6.25 kHz accordingly instead of remaining at the frequency value f3of 3.125 kHz, so as to maximize the performance of driving system1and to reduce high voltage ripple caused by low frequency operation.

In brief, in a condition that the current switch frequency is the frequency value f3(3.125 kHz), the switch frequency is maintained at the frequency value f3(3.125 kHz) when the rotation speed N of the motor400changes in the range of 0<N<300 rpm.

Thus, the hysteresis control method described herein may include at least one hysteresis loop, as described above. As shown in the embodiment inFIG. 4, the hysteresis control method may include two hysteresis loops L1and L2. In the hysteresis loops L1and L2, the switch frequency fsw of the power module310at a certain rotation speed N of the motor400may be determined according to the speed up or down state of the rotation speed N of the motor400and the current switch frequency. For example, in the hysteresis loop1, in a condition that the rotation speed is 250 rpm (at the frequency value f2), when the rotation speed N of the motor400is in a speed down state and the rotation speed N reaches the speed value N4(200 rpm), the switch frequency fsw is adjusted from f2(6.25 kHz) down to f3(3.125 kHz). In the hysteresis loop L1, in a condition that the rotation speed is 250 rpm (at the frequency value f2), when the rotation speed N of the motor400is in a speed up state and the rotation speed N reaches the speed value N3(300 rpm), the switch frequency fsw is still maintained at the frequency value f2without jumping.

Similarly, in the hysteresis loop1, in a condition that the rotation speed is 250 rpm (at the frequency value f3), when the rotation speed N of the motor400is in a speed up state and the rotation speed N reaches the speed value N3(300 rpm), the switch frequency fsw is adjusted from f3(3.125 kHz) up to f2(6.25 kHz). In the hysteresis loop1, in a condition that the rotation speed is 250 rpm (at the frequency value f3), when the rotation speed N of the motor400is in a speed down state and the rotation speed N reaches the speed value N4(200 rpm), the switch frequency fsw is still maintained at the frequency value f3without jumping.

In the hysteresis loop L2, in a condition that the rotation speed is 450 rpm (at the frequency value f2), when the rotation speed N of the motor400is in a speed up state and the rotation speed N reaches the speed value N1(500 rpm), the switch frequency fsw is adjusted from f2(6.25 kHz) up to f1(12.5 kHz). In the hysteresis loop L2, in a condition that the rotation speed is 450 rpm (at the frequency value f2), when the rotation speed N of the motor400is in a speed down state and the rotation speed N reaches the speed value N2(400 rpm), the switch frequency fsw is still maintained at the frequency value f2without jumping.

In the hysteresis loop L2, in a condition that the rotation speed is 450 rpm (at the frequency value f1), when the rotation speed N of the motor400is in a speed down state and the rotation speed N reaches the speed value N2(400 rpm), the switch frequency fsw is adjusted from f1(12.5 kHz) down to f2(6.25 kHz). In the hysteresis loop12, in a condition that the rotation speed is 450 rpm (at the frequency value f1), when the rotation speed N of the motor400is in a speed up state and the rotation speed N reaches the speed value N1(500 rpm), the switch frequency fsw is still maintained at the frequency value f1without jumping.

FIG. 5illustrates one implement of the step S120A of establishing the hysteresis control method, especially the step S120A of establishing at least one hysteresis loop of establishing the hysteresis control method. Referring toFIGS. 1, 2 and 5, first, in step S121, the loss calculation unit120obtains a loss information of the power module310when operating the motor400at a rotation speed with a predetermined frequency. Specifically, the loss calculation unit120may calculate the loss information of the power module310when operating the motor400at this rotation speed with the predetermined frequency based on a loading information of the motor400.

FIG. 6illustrates a loading information of the motor400according to one embodiment of the disclosure, which is also the result of a lookup table being created. As shown inFIG. 6, the loading information records the current values (Ampere) for operating the motor400at different rotation speeds (N) and torques (T), with the speed range from 0 to 2900 rpm for the horizontal axis and the torque range from 0 to 3000 Nm for the vertical axis, representing the rotation speed and torque curve characteristic of the motor400under different current commands. For example, at the rotation speed of 50 rpm and the torque of 1200 Nm, the current value is 30 amps. Therefore, different motor types may correspond to different loading information, and the loading information of each motor may record rotation speed and torque curve, which may be obtained by manually building current command, or by model-based calibration using simulation software (e.g. finite element analysis software).

In step S121ofFIG. 5, the loss information may include conduction loss and switching loss. The conduction loss may include the conduction loss Pcond,IGBTof the switching element (e.g., IGBT) and the conduction loss Pcond,DIODEof the diode. The switching loss may include the switching loss Psw,IGBTof IGBT and the switching loss Psw,DIODEof the diode. The conduction loss Pcond,IGBTand the switching loss Psw,IGBTof IGBT and the conduction loss Pcond,DIODEand the switching loss Psw,DIODEof the diode may be expressed by the following equations (Eq. 1) to (Eq. 4) respectively:

fswis the predetermined frequency of the power module310; T0is the work period; VCEis the voltage between the collector and emitter of the switching element; ICis the collector current of the switching element; Miis the modulation index; φ is cos−1(pf), wherein pf is the power factor; Eonis the open-state loss of the switching element; Eoffis the closed-state loss of the switching element; VFis the forward voltage of the diode; IDis the forward current of the diode; ERRis the reverse recovery loss; Inomis the rated current; Vnomis the rated voltage; VDCis the DC voltage source.

Herein, the loss information Psumin step S121is the sum of (Eq. 1) to (Eq. 4) above, that is, Psum=Pcond,IGBT+Psw,IGBT+Pcond,DIODE+Psw,DIODE. According to the loading information inFIG. 6, if the current operating point of the motor400(i.e., the current value at a certain rotation speed and torque) is known, the loss information Psumof power module310may be obtained according to (Eq. 1) to (Eq. 4). For example, as shown inFIG. 6, the rated torque of the motor400in this example is 1200N*m. When operated at 50 rpm, the motor400is close to a blocked rotor state. When the current command at rotation speed of 50 rpm and torque of 1200N*m is input and the motor400is operated with a predetermined frequency fsw, the current and voltage flowing through the switching element and diode may be brought into the above (Eq. 1) to (Eq. 4) to obtain the loss information Psumof the power module310operating the motor400in a blocked rotor state (rotation speed of 50 rpm and torque of 1200N*m) with this predetermined frequency fsw.

Referring toFIGS. 1, 2 and 5, after the loss information Psumis obtained, in step S122, the temperature calculation unit130establishes a thermal model of the power module310according to a three-dimensional model M1of the power module310and the loss information. In this step, the three-dimensional model M1of the power module310may be obtained from the model building unit110. The three-dimensional model M1of the power module310is shown inFIG. 7Aand is constructed, for example, by computer-aided design (CAD) software, containing the contours of various parts of the power module310at various viewing angles. The temperature calculation unit130may receive the three-dimensional model M1of the power module310, the physical parameters of the power module310(e.g., material properties such as thermal conductivity), and the loss information of the power module310obtained in step S121as the input, and uses finite element analysis software (e.g., ANSYS) and sets boundary conditions for thermal simulation to obtain the thermal model of the power module310. The temperature calculation model may show the temperature distribution of the various parts of the power module310after thermal simulation, so a simulation temperature may be obtained according to the thermal model, wherein the simulation temperature is the temperature of the power module310when operating the motor400at the rotation speed in step S121with the predetermined frequency in step S121, and the simulation temperature represents the junction temperature of the power module310.

Next, in step S123, the value of the predetermined frequency is determined according to the simulation temperature and the tolerable temperature of the power module310in a manner that the simulation temperature is below the tolerable temperature. If the simulation temperature is below the tolerable temperature, the predetermined frequency is utilized as the switch frequency of the power module310to operate the motor400at this rotation speed. However, if the simulation temperature exceeds the tolerable temperature, the predetermined frequency value is reduced until the simulation temperature is below the tolerable temperature.

In detail, step S121to step S123ofFIG. 5are illustrated with the condition of the motor400operated in a state which is close to the blocked rotor state (50 rpm, 1200N*m) to determine the most appropriate switch frequency for operating the motor400in the blocked rotor state. First, the predetermined frequency is set to 12.5 kHz to operate the motor400at 50 rpm, and the loss information Psumis obtained. Next, the thermal model is established according to the three-dimensional model M1of the power module310(FIG. 7) and the loss information Psum, and the simulation temperature of the power module310operating the motor400at 50 rpm with the predetermined frequency of 12.5 kHz is obtained. The simulation temperature is then compared with the tolerable temperature. If the simulation temperature exceeds the tolerable temperature, the predetermined frequency is lowered, for example, to 6.125 kHz, the above steps are repeated to obtain the loss information Psumof the power module310operating the motor400at 50 rpm with 6.125 kHz, the simulation temperature of the power module310operating the motor400at 50 rpm with the predetermined frequency of 6.125 kHz is obtained, and the simulation temperature is compared with the tolerable temperature again. If the simulation temperature still exceeds the tolerable temperature, the predetermined frequency is further reduced, for example to 3.125 kHz. Finally, the simulation temperature of the power module310operating the motor400at 50 rpm with the predetermined frequency of 3.125 kHz does not exceed the tolerable temperature, and 3.125 kHz may therefore be determined as being the switch frequency for operating the motor400at 50 rpm. In a similar manner, an appropriate switch frequency for each rotation speed range may be obtained, as shown in the hysteresis control method inFIG. 4.

In brief, as may be seen from the embodiment inFIG. 4(hysteresis curve of rotation speed and frequency), operating the motor400with the frequency value f1at any rotation speed greater than the speed value N2(400 rpm), including N1, may ensure that the temperature of the power module310is below its tolerable temperature. Operating the motor400with the frequency value f2at any rotation speed greater than the speed value N4(200 rpm) and below or equal to the speed value N2(400 rpm), including N2and N3, may ensure that the temperature of the power module310is below its tolerable temperature. Operating the motor400with the frequency value f3at any rotation speed below or equal to the speed value N4(200 rpm), or even close to the blocked rotor state, including NO and N4, may ensure that the temperature of the power module310is below its tolerable temperature.

This is because when the rotation speed is gradually reduced, the switching loss of the power module310dominates the main factor causing overheating compared to the conduction loss. Therefore, lowering the switch frequency may effectively reduce the temperature to avoid exceeding the tolerable temperature of the power module310.

Conversely, if the rotation speed increases in a gradual upward trend, the switch frequency may be adjusted up again to achieve the maximum performance of the driving system1. The switch frequency may be adjusted under a condition without damaging the peripheral electrical properties of the power module310, so as to avoid high voltage ripple caused by low frequency operation. Thus, as shown inFIG. 4, when the rotation speed (starting from the frequency value f3) rises to the speed value N3, the switch frequency may be adjusted up from the frequency value f3to the frequency value f2accordingly, instead of continuing to operate with the lower frequency value f3; when the rotation speed (with the frequency value f2) rises further to the speed value N1, the switch frequency may be adjusted up from the frequency value f2to the frequency value f1accordingly, instead of continuing to operate with the lower frequency value f2.

With respect to the frequency values f1, f2and f3mentioned above, the frequency values f1, f2and f3may be determined by the way of simulation according to the aforementioned contents to obtain the simulation temperature corresponding to the junction temperature of the power module310, and whether the simulation temperature exceeds the tolerable temperature is determined. In addition, it is also possible to verify whether the temperature of the thermal resistor obtained from experiment corresponds to the temperature of the thermal resistor obtained from the simulation by means of actual experiment under the same conditions, in order to verify the accuracy of the simulation and ensure that the junction temperature under simulation matches the temperature under actual experiment.

For example, if the motor400is respectively operated with the frequency values f1, f2, and f3(12.5 kHz, 6.25 kHz, and 3.125 kHz) at a rotation speed of 50 rpm and a torque of 1200N*m, the simulation temperature of the thermal resistor (about 58° C., 40° C., and 30° C., respectively) matches the temperature of the thermal resistor under actual experiment (51° C., 36° C., and 29° C., respectively), which shows that the results of simulation and actual experimental correspond to each other, thus verifying that the frequency values f1, f2, and f3through simulation are appropriate.

In summary, the operation method and operation device of the motor driver for driving a motor according to the disclosure may provide a thermal protection mechanism: a hysteresis control method is used to adjust the switch frequency of the power module for operating the motor according to the change of rotation speed of the motor and the current switch frequency. In addition, the hysteresis control method is developed by evaluating the junction temperature, so as to ensure that the motor driver operates in a safe and secure manner, and further to maximize the performance of the driving system.