JP4784290B2 - Motor drive device - Google Patents

Description

  The present invention relates to a motor drive device capable of stable drive control.

  Usually, in a vehicle such as an electric vehicle (EV) or a hybrid vehicle (HV), the driving force by electric energy is converted from DC power supplied from a high-voltage battery to three-phase AC power by an inverter. This is obtained by rotating a three-phase AC motor. Further, when the vehicle is decelerated, the battery is stored with regenerative energy obtained by the regenerative power generation of the three-phase AC motor, so that the vehicle travels without wasting energy.

  In such a hybrid vehicle or electric vehicle, an alternating current flows through each switching element of the inverter when the traveling motor rotates normally. However, when the rotor of the motor is locked due to derailment or the like, or when it enters a very low speed state, a large direct current flows through a specific switching element, and the heat loss of that element Will increase rapidly.

  As a means for preventing such an inverter overload when the motor is locked or at an ultra-low speed, for example, Patent Document 1 discloses that each switching element of the inverter is turned on / off in accordance with the sufficiently low rotational speed of the motor. A technique for reducing the carrier frequency of a PWM (Pulse Width Modulation) signal for controlling OFF is disclosed.

Specifically, according to the motor control device described in Patent Document 1, when it is determined that the motor is locked based on the motor rotation speed, the carrier frequency of the PWM signal is decreased from the frequency during normal operation to a lower frequency. Is done. As the carrier frequency decreases, the switching frequency of the switching element of the inverter decreases, so that the switching loss is reduced in each of the switching elements. As a result, even if the motor is locked, it is possible to suppress sudden heat generation in each switching element of the inverter.
JP-A-9-70195 JP 2000-134990 A

  Further, in the motor control device described above, if it is determined that the motor is not locked in response to the detected value of the motor speed exceeding the predetermined value again, it is determined that there is no need to protect the inverter. Thus, the carrier frequency is returned to the original frequency during normal operation.

  However, when the rotational speed of the motor sharply increases, such as when the driving wheel slips from a state locked by an external force, the switching of the carrier frequency based on the detected value of the rotational speed is used for motor drive control. It can lead to bankruptcy.

  This is because in motor drive control, there is generally a relationship that there is an upper limit rotation speed that can ensure the stability of control for a PWM signal of a certain carrier frequency between the carrier frequency and the motor rotation speed. Due to that. In other words, when the motor speed is less than or equal to a predetermined value, control stability is ensured even at a carrier frequency lower than that during normal operation. If it is greatly exceeded, control may fail.

  In order to avoid such a control failure, it is necessary to increase the upper limit rotational speed at which control stability is ensured by immediately increasing the carrier frequency following the steep fluctuation of the rotational speed. However, since the motor control device described above is configured to switch the carrier frequency based on the detected value of the rotational speed of the motor, it cannot cope with a sharp fluctuation in the rotational speed. Therefore, it is difficult to ensure the stability of motor drive control.

  Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to provide a motor drive device capable of stable drive control of a motor.

  According to the present invention, a motor drive device uses a power source, a drive circuit that performs power conversion between the power source and the motor by switching operations of the plurality of switching elements, and a plurality of signals using a signal having a predetermined carrier frequency. And a control device that performs switching control of the switching element. The control device includes a motor rotation number detection unit that detects the rotation number of the motor, and a frequency setting unit that sets a carrier frequency based on a detection value of the rotation number and an increase rate of the rotation number detection value.

  According to the motor drive device described above, since the carrier frequency is set based not only on the detected value of the motor rotation speed but also on the rate of increase, stable motor control can be maintained even with steep rotation speed fluctuations.

  Preferably, the frequency setting unit sets the carrier frequency to a relatively high first frequency when the rate of increase exceeds a predetermined value.

  According to the motor driving apparatus described above, when a steep rotation speed fluctuation is predicted from the rate of increase in the motor rotation speed, the carrier frequency is immediately set to a high frequency, so that control failure of the motor can be prevented in advance. .

  Preferably, the frequency setting unit has a second frequency lower than the first frequency when the rate of increase is equal to or lower than a predetermined value and the rotation speed detection value is lower than a predetermined threshold value. Set to.

  According to the motor driving device described above, the carrier frequency is reduced in response to the determination that the motor rotation speed is stably below the predetermined threshold value, so that the driving circuit does not cause motor control failure. Thermal protection can be achieved.

  Preferably, the motor rotation speed detection unit detects the rotation speed at every predetermined control timing. The frequency setting unit includes a change rate calculation unit that calculates the change rate of the rotation speed detection value between control timings, and a frequency switching unit that changes the carrier frequency based on the calculated change rate. The frequency switching unit sets the carrier frequency to the first carrier frequency in response to the calculated change rate exceeding a predetermined value.

  According to the motor drive device described above, it is possible to predict a steep rotation speed variation based on the rate of change of the motor rotation speed between control timings. Therefore, stable motor control can be maintained regardless of fluctuations in the rotational speed.

  Preferably, the control device has a predetermined control cycle corresponding to a period required to complete the setting of the carrier frequency. The motor rotation speed detection unit detects the rotation speed at each control timing defined by the control cycle. The frequency setting unit is configured to calculate the rate of change of the rotation speed detection value between adjacent control timings, and based on the calculated rate of change and the rotation speed detection value at the current control timing, A motor rotational speed estimation unit that calculates an estimated value of the rotational speed that can be detected at the timing, and a frequency switching unit that switches the carrier frequency at the next control timing based on the rotational speed estimated value. The frequency switching unit sets the carrier frequency to the first carrier frequency at the next control timing in response to the estimated rotation speed being equal to or greater than a predetermined threshold value.

  According to the motor drive device described above, steep fluctuations in the rotational speed can be predicted by obtaining an estimated value of the rotational speed at the time when the setting of the carrier frequency is completed. Therefore, stable motor control can be maintained regardless of fluctuations in the rotational speed.

  Preferably, the motor rotation number detection unit detects the rotation number at each control timing defined by a predetermined control cycle. The frequency setting unit sets the carrier frequency to the first carrier frequency at the next control timing in response to the rotation detection value at the current control timing being greater than or equal to a predetermined threshold value.

  According to the motor drive device described above, since the steep rotation speed fluctuation is determined directly from the rotation speed detection value, the carrier can be generated in a shorter control cycle without calculating the rotation speed change rate or the estimated value. The frequency can be switched.

  According to the present invention, since the carrier frequency is set not only based on the detected value of the motor rotation speed but also based on the rate of increase, stable motor control can be maintained even with a steep rotation speed fluctuation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is a schematic block diagram of a motor drive device according to an embodiment of the present invention.
Referring to FIG. 1, motor drive device 100 includes battery B, voltage sensors 10 and 13, current sensor 24, capacitor C 2, boost converter 12, inverter 14, resolver 30, and control device 40. Is provided.

  AC motor M1 is a drive motor for generating torque for driving drive wheels of a hybrid vehicle or an electric vehicle. Further, AC motor M1 is a motor that has a function of a generator driven by an engine and operates as an electric motor for the engine and can start the engine, for example.

  Boost converter 12 includes a reactor L1, NPN transistors Q1, Q2, and diodes D1, D2.

  Reactor L1 has one end connected to the power supply line of battery B, and the other end connected to an intermediate point between NPN transistor Q1 and NPN transistor Q2, that is, between the emitter of NPN transistor Q1 and the collector of NPN transistor Q2. .

  NPN transistors Q1 and Q2 are connected in series between the power supply line and the earth line. The collector of NPN transistor Q1 is connected to the power supply line, and the emitter of NPN transistor Q2 is connected to the ground line. In addition, diodes D1 and D2 that allow current to flow from the emitter side to the collector side are arranged between the collector and emitter of the NPN transistors Q1 and Q2, respectively.

  Inverter 14 includes U-phase arm 15, V-phase arm 16, and W-phase arm 17. U-phase arm 15, V-phase arm 16 and W-phase arm 17 are provided in parallel between the power supply line and the earth line.

  U-phase arm 15 includes NPN transistors Q3 and Q4 connected in series. V-phase arm 16 includes NPN transistors Q5 and Q6 connected in series. W-phase arm 17 includes NPN transistors Q7 and Q8 connected in series. Further, diodes D3 to D8 that flow current from the emitter side to the collector side are connected between the collectors and emitters of the NPN transistors Q3 to Q8, respectively.

  An intermediate point of each phase arm is connected to each phase end of each phase coil of AC motor M1. In other words, AC motor M1 is a three-phase permanent magnet motor, and is configured such that one end of three coils of U, V, and W phases is commonly connected to the midpoint. The other end of the U-phase coil is at the midpoint of NPN transistors Q3 and Q4, the other end of the V-phase coil is at the midpoint of NPN transistors Q5 and Q6, and the other end of the W-phase coil is at the midpoint of NPN transistors Q7 and Q8. Each is connected.

  Switching elements included in boost converter 12 and inverter 14 are not limited to NPN transistors Q1 to Q8, but may be constituted by other power elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs.

  The battery B is a secondary battery such as nickel metal hydride or lithium ion. Voltage sensor 10 detects voltage Vb output from battery B, and outputs detected voltage Vb to control device 40.

  Boost converter 12 boosts the DC voltage supplied from battery B and supplies the boosted voltage to capacitor C2. More specifically, when boost converter 12 receives signal PWMC from control device 40, boost converter 12 boosts a DC voltage according to the period during which NPN transistor Q2 is turned on by signal PWMC, and supplies the boosted voltage to capacitor C2.

  Further, when boost converter 12 receives signal PWMC from control device 40, boost converter 12 steps down the DC voltage supplied from inverter 14 via capacitor C 2 and supplies the voltage to battery B.

  Capacitor C <b> 2 smoothes the DC voltage output from boost converter 12, and supplies the smoothed DC voltage to inverter 14.

  The voltage sensor 13 detects the voltage Vm across the capacitor C2 (that is, corresponds to the input voltage of the inverter 14. The same applies hereinafter), and outputs the detected voltage Vm to the control device 40.

  When the DC voltage is supplied from the capacitor C2, the inverter 14 converts the DC voltage into an AC voltage based on the signal PWMI from the control device 40 and drives the AC motor M1. Thereby, AC motor M1 is driven to generate the required torque specified by torque command value TR.

  Further, the inverter 14 converts the AC voltage generated by the AC motor M1 into a DC voltage based on the signal PWMI from the control device 40 during regenerative braking of the hybrid vehicle or the electric vehicle on which the motor driving device 100 is mounted, The DC voltage thus supplied is supplied to the boost converter 12 via the capacitor C2.

  Note that regenerative braking here refers to braking with regenerative power generation when the driver operating the hybrid vehicle or electric vehicle performs footbrake operation, or while not operating the footbrake, Including decelerating (or stopping acceleration) the vehicle while regenerating power.

  Current sensor 24 detects motor currents Iv and Iw flowing through AC motor M <b> 1, and outputs the detected motor currents Iv and Iw to control device 40. In FIG. 1, only two current sensors 24 are shown. This is because, when AC motor M1 is a three-phase motor, if motor currents Iv and Iw flowing in two phases are detected, motor current Iu flowing in the remaining phases is calculated based on the detected motor currents Iv and Iw. Because it can. Therefore, when the motor currents Iu, Iv, and Iw flowing in the three phases are detected independently, three current sensors 24 may be provided.

  The resolver 30 is attached to the rotation shaft of the AC motor M1, detects the rotation angle θ of the rotor of the AC motor M1, and outputs it to the control device 40.

  Control device 40 receives torque command value TR from an externally provided ECU (Electric Control Unit), receives output voltage Vm from voltage sensor 13, receives DC voltage Vb from voltage sensor 10, and receives motor current from current sensor 24. Iv and Iw are received and the rotation angle θ is received from the resolver 30. Based on output voltage Vm, torque command value TR, motor currents Iv, Iw, and rotation angle θ, control device 40 uses inverters 14 to drive NPN transistors Q3-Q8 when inverter 14 drives AC motor M1 by a method described later. A signal PWMI for switching control is generated, and the generated signal PWMI is output to the inverter 14.

  When the inverter 14 drives the AC motor M1, the control device 40 uses the DC voltage Vb, the output voltage Vm, the torque command value TR, and the motor rotational speed MRN to perform an NPN transistor Q1 of the boost converter 12 by a method described later. , Q2 for switching control is generated, and the generated signal PWMC is output to the boost converter 12.

  Further, the control device 40 is configured to generate an alternating current generated by the alternating current motor M1 based on the output voltage Vm, the torque command value TR, and the motor currents Iv and Iw at the time of regenerative braking of the hybrid vehicle or the electric vehicle on which the motor driving device 100 is mounted. A signal PWMI for converting the voltage into a DC voltage is generated, and the generated signal PWMI is output to inverter 14. In this case, the NPN transistors Q3 to Q8 of the inverter 14 are switching-controlled by the signal PWMI. Thereby, the inverter 14 converts the AC voltage generated by the AC motor M1 into a DC voltage and supplies it to the boost converter 12.

  Further, at the time of regenerative braking, control device 40 generates signal PWMC for stepping down the DC voltage supplied from inverter 14 based on DC voltage Vb, output voltage Vm, torque command value TR, and motor rotation speed MRN. The generated signal PWMC is output to the boost converter 12. As a result, the AC voltage generated by AC motor M1 is converted to a DC voltage, stepped down, and supplied to battery B.

FIG. 2 is a functional block diagram of the control device 40 in FIG.
Referring to FIG. 2, control device 40 includes an inverter control circuit 401 and a converter control circuit 402.

  Based on torque command value TR, motor currents Iv, Iw, output voltage Vm, and rotation angle θ, inverter control circuit 401 turns on / off NPN transistors Q3-Q8 of inverter 14 by a method described later when AC motor M1 is driven. A signal PWMI for turning off is generated, and the generated signal PWMI is output to the inverter 14.

  Further, the inverter control circuit 401 is based on the torque command value TR, the motor currents Iv and Iw, the output voltage Vm, and the rotation angle θ at the time of regenerative braking of the hybrid vehicle or electric vehicle on which the motor driving device 100 is mounted. A signal PWMI for converting the AC voltage generated by M1 into a DC voltage is generated and output to inverter 14.

  Converter control circuit 402 is a signal for turning on / off NPN transistors Q1, Q2 of boost converter 12 when AC motor M1 is driven based on torque command value TR, DC voltage Vb, output voltage Vm, and rotation angle θ. PWMC is generated, and the generated signal PWMC is output to boost converter 12.

  In addition, the converter control circuit 402 receives a signal from the inverter 14 based on the torque command value TR, the DC voltage Vb, the output voltage Vm, and the rotation angle θ at the time of regenerative braking of the hybrid vehicle or electric vehicle on which the motor driving device 100 is mounted. A signal PWMC for stepping down the DC voltage is generated, and the generated signal PWMC is output to boost converter 12.

  As described above, the boost converter 12 can also step down the voltage by the signal PWMC for stepping down the DC voltage, and thus has the function of a bidirectional converter.

FIG. 3 is a functional block diagram of the inverter control circuit 401 in FIG.
Referring to FIG. 3, inverter control circuit 401 includes current command converter 410, subtracters 412 and 414, PI controllers 416 and 418, two-phase / three-phase converter 420, and PWM (Pulse Width Modulation). ) Generation unit 422, three-phase / two-phase conversion unit 424, and carrier frequency setting unit 426.

  The three-phase / two-phase converter 424 receives the motor currents Iv, Iw from the two current sensors 24, 24. The three-phase / 2-phase converter 424 receives the motor current Iu based on the motor currents Iv, Iw. = -Iv-Iw is calculated.

  Further, the three-phase / two-phase converter 424 performs three-phase to two-phase conversion on the motor currents Iu, Iv, and Iw using the rotation angle θ from the resolver 30. That is, the three-phase / two-phase conversion unit 424 uses the three-phase motor currents Iu, Iv, Iw flowing in the respective phases of the three-phase coil of the AC motor M1 as currents flowing in the d-axis and the q-axis using the rotation angle θ. Convert to values Id and Iq. Then, the three-phase / two-phase converter 424 outputs the calculated current value Id to the subtractor 412 and outputs the calculated current value Iq to the subtractor 414.

  Current command conversion unit 410 converts torque command value TR from the external ECU into current commands Id * and Iq * for outputting the requested torque specified by torque command value TR, and the converted current command Id *. , Iq * are output to the subtracters 412 and 414, respectively.

  Subtractor 412 receives current command Id * from current command conversion unit 410 and receives current value Id from three-phase / two-phase conversion unit 424. Then, the subtractor 412 calculates a deviation (= Id * −Id) between the current command Id * and the current value Id, and outputs the calculated deviation to the PI control unit 416. Subtractor 414 receives current command Iq * from current command converter 410 and receives current value Iq from three-phase / 2-phase converter 424. Then, the subtractor 414 calculates a deviation (= Iq * −Iq) between the current command Iq * and the current value Iq, and outputs the calculated deviation to the PI control unit 418.

  PI control units 416 and 418 calculate voltage manipulated variables Vd and Vq for motor current adjustment using PI (proportional / integral) gains for deviations Id * −Id and Iq * −Iq, respectively, The voltage manipulated variables Vd and Vq are output to the two-phase / three-phase converter 420.

  The two-phase / three-phase conversion unit 420 performs two-phase three-phase conversion on the voltage operation amounts Vd and Vq from the PI control units 416 and 418 using the rotation angle θ from the resolver 30. That is, the two-phase / three-phase converter 420 applies the voltage operation amounts Vd and Vq applied to the d-axis and the q-axis to the voltage operation amounts Vu and Vv applied to the three-phase coil of the AC motor M1 using the rotation angle θ. , Vw. Then, the two-phase / three-phase converter 420 outputs the voltage manipulated variables Vu, Vv, and Vw to the PWM generator 422.

  The PWM generator 422 generates a signal PWMI based on the voltage manipulated variables Vu, Vv, Vw and the voltage Vm from the voltage sensor 13 and outputs the generated signal PWMI to the inverter 14.

  As described above, inverter control circuit 401 converts the required torque of AC motor M1 (corresponding to torque command value TR) into current commands Id * and Iq * of the d-axis component and q-axis component of AC motor M1. So-called current control is employed in which feedback is performed by PI control so that the actual current values Id and Iq coincide with these current commands.

  Here, in PWM control known as motor current control, a signal PWMI for turning on / off the NPN transistors Q3 to Q8 of the inverter 14 is obtained from a triangular wave signal which is a carrier wave signal and a two-phase / 3-phase converter 420. The received voltage operation amounts Vu, Vv, and Vw are compared and generated based on the comparison result. The NPN transistors Q3 to Q8 are controlled to be turned on / off based on the carrier frequency fc of the generated signal PWMI. That is, the switching frequency of NPN transistors Q3 to Q8 is equal to the carrier frequency fc of signal PWMI. Therefore, reducing the carrier frequency fc leads to a reduction in the switching frequency, which in turn reduces the switching loss of the NPN transistors Q3 to Q8. This is effective in reducing heat generation in the NPN transistors Q3 to Q8.

  Therefore, in the motor drive device according to the embodiment of the present invention, when the rotational speed of AC motor M1 decreases and AC motor M1 is determined to be locked by an external force, as in the conventional motor drive device described above. By reducing the carrier frequency fc of the signal PWMI, the NPN transistors Q3 to Q8 of the inverter 14 are protected.

  Specifically, the carrier frequency setting unit 426 in FIG. 3 sets one of the two types of carrier frequencies fc according to the motor rotation speed. One of the two types of carrier frequencies fc is a carrier frequency during normal operation (hereinafter also referred to as a normal frequency) fc_H, and the other is a carrier frequency for inverter protection (hereinafter also referred to as a protection frequency) fc_L. The normal frequency fc_H is set to a frequency (for example, 10 kHz) at which the efficiency of AC motor M1 and inverter 14 (= (shaft output of AC motor M1) / (input from battery B to inverter 14)) is good. On the other hand, the inverter protection frequency fc_L is lower than the normal frequency fc_H and is set to, for example, 1.25 kHz.

  The carrier frequency setting unit 426 locks the AC motor M1 when the rotational speed of the motor is below a predetermined value R_lim (corresponding to the region RG1 in the figure) in the output characteristics of the AC motor M1 shown in FIG. The carrier frequency fc is set by switching from the normal frequency fc_H to the inverter protection frequency fc_L. Thereby, the switching loss in NPN transistors Q3-Q8 is reduced, and thermal destruction is prevented.

  Eventually, when the motor rotational speed becomes equal to or higher than the predetermined value R_lim again and it is determined that AC motor M1 has come out of the locked state, carrier frequency setting unit 426 changes carrier frequency fc from inverter protection frequency fc_L to the original normal frequency fc_H. Switch and set.

  At this time, depending on the driving state of the vehicle, the drive wheel may slip from a state locked by an external force. In AC motor M <b> 1, the motor rotation speed rapidly changes from a rotation speed lower than predetermined value R_lim to a rotation speed that greatly exceeds predetermined value R_lim.

  However, as described above, in the method of increasing the carrier frequency fc from the inverter protection frequency fc_L to the normal frequency fc_H in response to the detected value of the motor rotation speed being equal to or greater than the predetermined value R_lim, the motor rotation speed fluctuates rapidly. The carrier frequency fc cannot be followed. Therefore, there arises a problem that drive control of AC motor M1 fails.

FIG. 5 is a schematic diagram for explaining the stability of drive control of AC motor M1.
Referring to FIG. 5A, in PWM control, a voltage manipulated variable with a predetermined frequency (in FIG. 5, only the u-phase voltage manipulated variable Vu1 is illustrated), and a triangular wave signal ec with a prescribed carrier frequency fc And a signal PWMI for turning on / off each of the NPN transistors Q3 to Q8 of the inverter 14 is generated. Note that the frequency of the voltage operation amount Vu1 is proportional to the motor rotation speed of the AC motor M1, and increases as the motor rotation speed increases. Then, based on the generated signal PWMI, each of the NPN transistors Q3 to Q8 of the inverter 14 is subjected to switching control, and a current (which flows through each phase of the AC motor M1 so that the AC motor M1 outputs a commanded torque ( Motor drive current).

At this time, by changing the voltage manipulated variable Vu1 in a sine wave shape as shown in FIG. 5A, a sinusoidal u-phase motor drive current Iu1 whose frequency substantially matches the frequency of the voltage manipulated variable Vu1 is obtained. . In this way, the motor drive current of each phase is controlled, and torque corresponding to the torque command value TR is output from the AC motor M1. Here, referring to FIG. As a result, the case where the voltage manipulated variable Vu1 changes to the voltage manipulated variable Vu2 whose frequency has increased approximately twice will be considered. Note that the carrier frequency fc of the triangular wave signal ec is the same as the carrier frequency in FIG.

  In this case, the motor drive current Iu2 controlled using the signal PWMI obtained by comparing the voltage manipulated variable Vu2 and the triangular wave signal ec has an output waveform greatly fluctuating from the sine wave as shown in FIG. It becomes. Or although illustration is abbreviate | omitted, there exists a possibility that motor drive current Iu2 may remove | deviate from a sine wave, and may become overcurrent. As described above, when the control of the motor drive current Iu2 becomes unstable, the torque output from the AC motor M1 also varies with respect to the torque command value TR. As a result, the drivability of the vehicle is significantly reduced.

  That is, in motor drive control, there is an upper limit rotation speed that can ensure the stability of control for a PWM signal having a certain carrier frequency between the carrier frequency fc and the motor rotation speed. When this upper limit rotational speed is exceeded, control failure occurs. In the motor output characteristics of FIG. 4, the predetermined value R_lim corresponds to the upper limit rotation speed when the carrier frequency fc is set to the inverter protection frequency fc_L. Therefore, in order to maintain the stability of the drive control of AC motor M1, even when the motor rotation speed suddenly rises above a predetermined value R_lim that is the upper limit rotation speed at inverter protection frequency fc_L, the carrier frequency follows this. It is required to increase fc immediately.

  Therefore, the motor driving apparatus according to the present embodiment is characterized in that carrier frequency setting section 426 sets carrier frequency fc in consideration of not only the detected value of motor rotation speed but also the rate of increase in motor rotation speed. The configuration is as follows.

  That is, in the motor output characteristics of FIG. 4, even if the motor rotation speed detected at the present time is below the predetermined value R_lim, if the motor rotation speed increase rate is relatively high, that is, the motor rotation speed is If it is determined that the motor speed rapidly increases, it is predicted that the motor rotation speed is likely to exceed the predetermined value R_lim within a very short period. Therefore, the carrier frequency setting unit 426 is configured to switch the carrier frequency fc from the inverter protection frequency fc_L to the normal frequency fc_H ahead of the current time based on this prediction. According to this, when the motor rotation speed actually exceeds the predetermined value R_lim, the carrier frequency fc is already set to a frequency that ensures control stability during normal operation, so that control failure may occur. Absent. As a result, stable drive control of AC motor M1 is maintained.

  Hereinafter, a specific method for setting the carrier frequency in the motor drive device of the present embodiment will be described.

  FIG. 6 is a schematic diagram for explaining an example of the carrier frequency fc setting method executed by the carrier frequency setting unit 426.

  Referring to FIG. 6, carrier frequency setting unit 426 calculates motor rotation speed R (tn) at each predetermined control timing, and calculates the rate of change between control timings for the calculated motor rotation speed R (tn). calculate. Then, based on the calculated change rate, it is determined whether or not the rate of increase of the motor rotational speed is relatively high, that is, whether or not the motor rotational speed increases sharply.

  Control timings tn-2, tn-1, tn,... Are defined by a predetermined control period T. The control cycle T starts from the current control timing tn and is set to a period required until the setting of the carrier frequency fc of the triangular wave signal ec is actually completed in the PWM generation unit 422.

Specifically, when receiving the rotation angle θ from the resolver 30, the carrier frequency setting unit 426 substitutes the detected value of the rotation angle θ into the following equation for each predetermined control timing tn and sets the motor rotation speed R (tn). Calculate.
R (tn) = {(θn−θn−1) / (tn−tn−1)} · K (1)
Where θn: rotation angle at current control timing tn, θn-1: rotation angle at previous control timing tn-1, R (tn): motor rotation speed at current control timing tn, K: motor rotation from rotation angle Conversion factor to number.

Next, the carrier frequency setting unit 426 substitutes the motor rotational speed R (tn-1) at the previous control timing tn-1 and the motor rotational speed R (tn) at the current control timing tn into the following equation: A rate of change dR (tn) / dt of the motor rotation speed R (tn) between adjacent control timings is calculated. The calculated motor rotation speed change rate dR (tn) / dt corresponds to the slope between adjacent control timings tn−1 and tn in the temporal change in motor rotation speed shown in FIG.
dR (tn) / dt = {R (tn) -R (tn-1)} / (tn-tn-1) (2)
Then, when the calculated motor rotation speed change rate dR (tn) / dt exceeds a predetermined threshold, the carrier frequency setting unit 426 has a relatively high motor rotation speed increase, that is, the motor rotation speed. Is determined to rise rapidly. In FIG. 6, it is predicted that the motor rotation speed exceeds the predetermined value R_lim within a short period from the current control timing tn. Therefore, the carrier frequency setting unit 426 switches and sets the carrier frequency fc from the current inverter protection frequency fc_L to the normal frequency fc_H. The set carrier frequency fc (= fc_H) is output to PWM generation section 422.

  According to this, since the carrier frequency fc is set to the normal frequency fc_H at the timing when the motor rotation speed exceeds the predetermined value R_lim, the control failure of the AC motor M1 as described in FIG. Avoided. As a result, the AC motor M1 can ensure stable control regardless of steep fluctuations in the motor rotation speed.

  FIG. 7 is a flowchart for explaining an example of the carrier frequency fc setting method executed by the carrier frequency setting unit 426.

  Referring to FIG. 7, when the rotation angle θ is input from the resolver 30 (step S01), the carrier frequency setting unit 426 uses the above equation (1) to calculate the motor rotation speed R (tn) at the current control timing tn. ) Is calculated (step S02).

  Subsequently, the carrier frequency setting unit 426 calculates the rate of change dR (tn) / dt of the motor rotation speed between adjacent control timings according to the above equation (2) (step S03). Then, the carrier frequency setting unit 426 determines whether or not the calculated motor rotation speed change rate dR (tn) / dt exceeds a predetermined threshold value R_std (step S04).

  At this time, when it is determined that the motor rotation rate change rate dR (tn) / dt exceeds the threshold value R_std, the carrier frequency setting unit 426 immediately sets the carrier frequency fc to the normal frequency fc_H ( Step S05).

  On the other hand, when it is determined in step S04 that the motor rotation speed change rate dR (tn) / dt is equal to or less than the threshold value R_std, the carrier frequency setting unit 426 further performs the motor rotation speed R ( It is determined whether or not (tn) is lower than a predetermined value R_lim (step S06). When it is determined that the motor rotation speed R (tn) is lower than the predetermined value R_lim, the carrier frequency setting unit 426 determines that the AC motor M1 is in the locked state, and sets the carrier frequency fc to the inverter protection frequency fc_L. (Step S07). On the other hand, when it is determined that the motor rotation speed R (tn) is equal to or greater than the predetermined value R_lim, the carrier frequency setting unit 426 sets the carrier frequency fc to the normal frequency fc_H (step S05).

  The carrier frequency fc set in steps S05 and S07 is output to the PWM generation unit 422. The PWM generation unit 422 generates a signal PWMI having the set carrier frequency fc, and outputs the generated signal PWMI to the NPN transistors Q3 to Q8 of the inverter 14 (step S08).

  As described above, when the motor rotation speed change rate dR (tn) / dt exceeds the predetermined threshold value R_std, the carrier frequency fc is immediately relatively increased regardless of the motor rotation speed R (tn). By setting the normal frequency fc_H, the upper limit rotational speed at which the control stability of the AC motor M1 is ensured can be increased. For this reason, it is possible to cope with steep fluctuations in the motor rotation speed, and to prevent control failure.

  6 and 7, the carrier frequency fc is set based on the rate of change dR (tn) / dt of the motor rotation speed between the adjacent control timings tn−1 and tn. A similar effect can be obtained even when the carrier frequency fc is set based on the rate of change dR (tn) / dt of the motor rotation speed between the control timing (for example, tn-4) and the current control timing tn. .

[Modification 1]
FIG. 8 is a schematic diagram for explaining another example of the carrier frequency fc setting method executed by the carrier frequency setting unit 426.

  Referring to FIG. 8, when carrier frequency setting unit 426 calculates change rate dR (tn) / dt of motor rotation speed between control timings according to the above-described method, the calculated change rate dR (t of motor rotation speed). tn) / dt is used to calculate an estimated value (hereinafter also referred to as an estimated motor rotational speed) R (tn + 1) of the motor rotational speed at the next control timing tn + 1. Then, the carrier frequency setting unit 426 determines whether or not the rate of increase of the motor rotational speed is relatively high based on the calculated estimated motor rotational speed R (tn + 1), that is, whether or not the motor rotational speed increases sharply. Determine whether.

  Specifically, when receiving the rotation angle θ from the resolver 30, the carrier frequency setting unit 426 calculates the motor rotation speed R (tn) at the current control timing tn based on the rotation angle θ. Then, the rate of change dR (tn) / dt of the motor rotational speed between adjacent control timings is calculated based on the calculated motor rotational speed R (tn). These calculations are performed in the same procedure as described in FIG.

Further, the carrier frequency setting unit 426 uses the calculated motor rotational speed R (tn) and the motor rotational speed change rate dR (tn) / dt to estimate the motor rotational speed R (tn + 1) at the next control timing tn + 1. ) Is calculated.
R (tn + 1) = dR (tn) / dt × T + R (tn)
= [{R (tn) -R (tn-1)} / T] * T + R (tn)
= 2R (tn) -R (tn-1) (3)
However, T: Control period, that is, (tn−tn−1).

  That is, according to Equation (3), the estimated motor rotation at the next control timing tn + 1 is calculated from the motor rotation number R (tn) at the current control timing tn and the motor rotation number R (tn−1) at the previous control timing. The number R (tn + 1) is obtained.

  Then, the carrier frequency setting unit 426 has a relatively high rate of increase in the motor rotational speed in response to the calculated estimated motor rotational speed R (tn + 1) exceeding the predetermined value R_lim, that is, the motor rotational speed is Judged to rise sharply. In the case of FIG. 8, at the current control timing tn, the motor rotation speed R (tn) is lower than the predetermined value R_lim, which is the upper limit rotation speed at the inverter protection frequency fc_L, and control stability is obtained. At the control timing tn + 1, it is predicted that the motor rotation speed R (tn + 1) exceeds the predetermined value R_lim. Therefore, the carrier frequency setting unit 426 switches and sets the carrier frequency fc from the current inverter protection frequency fc_L to the normal frequency fc_H. The set carrier frequency fc (= fc_H) is output to PWM generation section 422.

  According to this, since the carrier frequency fc is set to the normal frequency fc_H at the next control timing tn + 1, even if the motor rotation speed R (tn + 1) exceeds the predetermined value R_lim as predicted, Control failure of AC motor M1 as described in b) is avoided. As a result, the AC motor M1 can ensure stable control regardless of steep fluctuations in the motor rotation speed.

  FIG. 9 is a flowchart for explaining another example of the carrier frequency fc setting method executed by the carrier frequency setting unit 426. In the flowchart of FIG. 9, steps S03 and S04 in the flowchart of FIG. 7 are changed to steps S030 and S040. Therefore, detailed description of the overlapping steps will not be repeated.

  Referring to FIG. 9, carrier frequency setting unit 426 includes motor rotation speed R (tn) at current control timing tn obtained in step S02 and motor rotation speed R (tn−) at previous control timing tn−1. 1) is substituted into equation (3) to calculate the estimated motor rotation speed R (tn + 1) at the next control timing tn + 1 (step S030).

  Then, the carrier frequency setting unit 426 determines whether or not the estimated motor rotation speed R (tn + 1) is equal to or greater than a predetermined value R_lim (step S040).

  At this time, when it is determined that the estimated motor rotation speed R (tn + 1) is equal to or greater than the predetermined value R_lim, the carrier frequency setting unit 426 immediately sets the carrier frequency fc to the normal frequency fc_H (step S05).

  On the other hand, when it is determined in step S040 that the estimated motor rotational speed R (tn + 1) is lower than the predetermined value R_lim, the carrier frequency setting unit 426 further determines that the motor rotational speed R (tn) at the current control timing is the predetermined value. It is determined whether it is lower than R_lim (step S06). When it is determined that the motor rotation speed R (tn) is lower than the predetermined value R_lim, the carrier frequency setting unit 426 determines that the AC motor M1 is in the locked state, and sets the carrier frequency fc to the inverter protection frequency fc_L. (Step S07). On the other hand, when it is determined that the motor rotation speed R (tn) is equal to or greater than the predetermined value R_lim, the carrier frequency setting unit 426 sets the carrier frequency fc to the normal frequency fc_H (step S05).

  As described above, when the estimated motor rotation speed R (tn + 1) is equal to or greater than the predetermined value R_lim, the control stability of the AC motor M1 is improved by immediately setting the carrier frequency fc to the relatively high normal frequency fc_H. The upper limit number of rotations to be secured can be increased. For this reason, it is possible to cope with steep fluctuations in the motor rotation speed, and to prevent control failure.

[Modification 2]
In the two examples described above, the rate of change dR (tn) / dt of the motor rotation speed or the estimated motor rotation speed R (tn + 1) is calculated, and a steep fluctuation in the motor rotation speed is predicted based on the calculation result. It was. According to this, since the carrier frequency fc is switched from the inverter protection frequency fc_L to the normal frequency fc_H before the motor rotation speed exceeds the predetermined value R_lim, the motor rotation speed exceeds the upper limit rotation speed at the inverter protection frequency fc_L. It is possible to prevent the control failure of the AC motor M1 that may occur due to the above.

  Furthermore, as shown in this modification, it is possible to cope with steep fluctuations in the motor rotation speed by setting the carrier frequency fc directly from the instantaneous value of the motor rotation speed calculated from the rotation angle θ. can do.

  That is, the carrier frequency setting unit 426 according to the present modification immediately changes the carrier frequency fc from the inverter protection frequency fc_L to the normal frequency in response to the motor rotation speed R (tn) at the current control timing tn exceeding the predetermined value R_lim. The configuration is switched to fc_H.

  According to this, the carrier frequency setting unit 426 can shorten the control cycle T required to complete the setting of the carrier frequency fc, as much as the load required for calculation is reduced compared to the above two examples. Become. Therefore, according to the present modified example, the carrier frequency fc can be switched at an earlier timing, although no means for predicting a steep fluctuation in the motor rotation speed is involved in the above two examples. As a result, it is possible to cope with steep fluctuations in the carrier frequency.

  FIG. 10 is a flowchart for explaining another example of the carrier frequency fc setting method executed by the carrier frequency setting unit 426. In the flowchart of FIG. 10, steps S03, S04, and S06 in the flowchart of FIG. 7 are changed to step S041. Therefore, detailed description of the overlapping steps is omitted.

  Referring to FIG. 10, carrier frequency setting unit 426 determines whether or not motor rotation speed R (tn) at current control timing tn obtained in step S02 is equal to or greater than a predetermined value R_lim (step S041). . At this time, when it is determined that the motor rotation speed R (tn) is equal to or greater than the predetermined value R_lim, the carrier frequency setting unit 426 immediately sets the carrier frequency fc to the normal frequency fc_H (step S05).

  On the other hand, when it is determined in step S041 that the motor rotation speed R (tn) is lower than the predetermined value R_lim, the carrier frequency setting unit 426 determines that the AC motor M1 is in the locked state, and sets the carrier frequency fc to the inverter protection frequency. Set to fc_L (step S07).

  As described above, according to the embodiment of the present invention, not only the detected value of the motor rotation speed but also the configuration in which the carrier frequency is switched according to the increase rate of the motor rotation speed is high. When the value fluctuates sharply and exceeds the upper limit rotation speed at the current carrier frequency, the upper limit rotation speed also follows and increases. Therefore, control failure of the AC motor can be prevented in advance. As a result, the stability of AC motor drive control is ensured.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be applied to a motor drive device mounted on a vehicle.

It is a schematic block diagram of a motor drive device provided with the control apparatus of the secondary battery by embodiment of this invention. It is a functional block diagram of the control apparatus in FIG. It is a functional block diagram of the inverter control circuit in FIG. It is a figure which shows the relationship between the output characteristic of an AC motor, and a carrier frequency. It is a schematic diagram for demonstrating stability of drive control of AC motor M1. It is a schematic diagram for demonstrating an example of the setting method of the carrier frequency fc performed in a carrier frequency setting part. It is a flowchart for demonstrating an example of the setting method of the carrier frequency fc performed in a carrier frequency setting part. It is a schematic diagram for demonstrating the other example of the setting method of the carrier frequency fc performed in a carrier frequency setting part. It is a flowchart for demonstrating the other example of the setting method of the carrier frequency fc performed in a carrier frequency setting part. It is a flowchart for demonstrating the other example of the setting method of the carrier frequency fc performed in a carrier frequency setting part.

Explanation of symbols

  10, 13 Voltage sensor, 12 Boost converter, 14 Inverter, 15 U-phase arm, 16 V-phase arm, 17 W-phase arm, 24 Current sensor, 30 Resolver, 40 Control device, 401 Inverter control circuit, 402 Converter control circuit, 410 Current command conversion unit, 412, 414 subtractor, 416, 418 PI control unit, 420 2-phase / 3-phase conversion unit, 422 PWM generation unit, 424 3-phase / 2-phase conversion unit, 426 carrier frequency setting unit, Q1-Q8 NPN transistor, D1-D8 diode, C1, C2 capacitor, B battery, M1 AC motor.

Claims (6)

Power supply,
A drive circuit for performing power conversion between the power source and the motor by switching operations of a plurality of switching elements;
A control device that performs switching control of each of the plurality of switching elements using a signal having a predetermined carrier frequency,
The controller is
A motor rotation number detection unit for detecting the rotation number of the motor;
A motor drive device, comprising: a frequency setting unit that sets the carrier frequency based on a detection value of the rotation speed and an increase rate of the rotation speed detection value.   The motor driving apparatus according to claim 1, wherein the frequency setting unit sets the carrier frequency to a relatively high first frequency when the rate of increase exceeds a predetermined value.   The frequency setting unit is configured to reduce the carrier frequency to be lower than the first frequency when the rate of increase is equal to or lower than the predetermined value and when the rotation speed detection value is lower than a predetermined threshold value. The motor driving device according to claim 2, wherein the frequency is set to 2. The motor rotation speed detection unit detects the rotation speed at every predetermined control timing,
The frequency setting unit includes:
A change rate calculation unit for calculating a change rate of the rotation speed detection value between the control timings;
A frequency switching unit that changes the carrier frequency based on the calculated rate of change,
The motor driving device according to claim 3, wherein the frequency switching unit sets the carrier frequency to the first carrier frequency in response to the calculated change rate exceeding the predetermined value. The control device has a predetermined control period corresponding to a period required for completing the setting of the carrier frequency,
The motor rotation speed detection unit detects the rotation speed at each control timing defined by the control cycle,
The frequency setting unit includes:
A change rate calculation unit that calculates a change rate of the rotation speed detection value between the adjacent control timings;
A motor rotational speed estimation unit that calculates an estimated value of the rotational speed that can be detected at the next control timing based on the calculated rate of change and the rotational speed detection value at the current control timing;
A frequency switching unit that switches a carrier frequency at the next control timing based on the rotation speed estimated value;
The frequency switching unit sets the carrier frequency to the first carrier frequency at the next control timing in response to the estimated rotational speed value being greater than or equal to the predetermined threshold value. The motor drive device described. The motor rotation speed detection unit detects the rotation speed at each control timing defined by a predetermined control cycle,
The frequency setting unit sets the carrier frequency to the first carrier frequency at the next control timing in response to the rotation detection value at the current control timing being greater than or equal to the predetermined threshold value. The motor drive device according to claim 3.

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