Patent ID: 12261559

DETAILED DESCRIPTION

For example, in the exemplary operating method, when the drive voltage fluctuates, the rotation speed of the motor is adjusted to a speed lower than a speed when there is no voltage fluctuation, so that it is possible to avoid fluctuation, caused by following the fluctuation of the drive voltage, in the rotation speed of the motor.

However, in the exemplary operating method, while the drive voltage is fluctuating (decreasing), the rotation speed of the motor is maintained at a constant low speed, and after a predetermined period of time has elapsed since the power supply voltage returns to a certain level, the speed is increased linearly to the original speed. As a result, the rotation speed of the motor abruptly changes, and the change may make the occupants of the vehicle feel uncomfortable.

In view of the foregoing difficulties, the present disclosure provides a motor control device capable of suppressing fluctuation in a rotation speed of a motor without causing discomfort to an occupant of a vehicle when a power supply voltage for driving the motor fluctuates.

An exemplary embodiment of the present disclosure provides a motor control device that executes fluctuation suppression control when a power supply voltage for driving a motor supplied from a power supply temporarily decreases and then increases to a normal power supply voltage after recovery. The fluctuation suppression control suppresses fluctuation in a rotation speed of the motor which is caused by following fluctuation in the power supply voltage. The motor control device includes a detection unit and a generation unit. The detection unit is configured to detect that the power supply voltage turns to an increase from a decrease. The generation unit is configured to generate, in response to the detection unit detecting that the power supply voltage turns to the increase, an applied voltage to be applied to the motor using a predetermined function such that an actual motor rotation speed decreased according to the decrease of the power supply voltage approaches a target motor rotation speed and an approach speed for which the actual motor rotation speed approaches the target motor rotation speed gradually increases and then gradually decreases over time. The fluctuation suppression control is executed by applying the applied voltage generated by the generation unit to the motor.

In the exemplary embodiment of the present disclosure, with the motor control device according to the present disclosure, the generation unit generates the motor applied voltage that changes smoothly using the predetermined function. Therefore, a sudden change in the motor rotation speed can be suppressed. The motor applied voltage generated by the generation unit is generated such that the actual motor rotation speed, which has decreased due to the decrease in the power supply voltage, gradually increases in speed of approaching the target motor rotation speed over time. In other words, since the initial speed of approach immediately after the power supply voltage turns to an increase is moderate, the fluctuation in the motor rotation speed can be kept small regardless of the fluctuation of the power supply voltage even if the power supply voltage repeatedly fluctuates. In addition, when the power supply voltage returns to the normal voltage and stabilizes, the actual motor rotation speed can quickly approach the target motor rotation speed since the motor applied voltage is generated such that the approach speed gradually increases over time. Furthermore, the motor applied voltage is generated such that the approach speed is gradually decreased after that, so that the actual motor rotation speed can be moderately approximated to the target motor rotation speed.

First Embodiment

A motor control device according to a first embodiment will be described below with reference to the drawings. When a power supply voltage for driving a three-phase motor supplied from a power supply temporarily decreases and then increases to return to a normal power supply voltage, the motor control device according to the present embodiment suppresses fluctuation in a rotation speed of the three-phase motor by following fluctuation in the power supply voltage. Therefore, the three-phase motor controlled by the motor control device according to the present embodiment can be suitably used as a fan motor for rotating a blower fan of an air conditioner of a vehicle, for example. Even when the power supply voltage supplied from an in-vehicle power supply fluctuates, generation of noise due to change in the air volume of the air-conditioning air blown into the passenger compartment can be suppressed if it is possible to suppress fluctuation in a rotation speed of the fan motor, for example. However, the application of the three-phase motor to be controlled by the motor control device according to this embodiment is not limited to the fan motor. That is, the motor control device according to the present embodiment may control various three-phase motors mounted on a vehicle. Also, a three-phase motor used for applications other than vehicles may be controlled. Also, the motor to be controlled may be a motor other than the three-phase motor.

FIG.1shows a configuration of a motor control device10according to the first embodiment. As shown inFIG.1, the motor control device10includes a deviation calculation unit12, a PI calculation unit14, a motor applied voltage upper limit (VM limit) calculation unit16as an upper limit setting unit, a Duty calculation unit18as a calculation unit, a PWM drive signal generation unit20, an inverter22, a current detection unit24, and the like. A part of the configuration of the motor control device10, for example, the PI calculation unit14, the VM limitcalculation unit16, the Duty calculation unit18, and the like can be configured by a microcomputer having a general configuration including a CPU, a ROM, a RAM, and the like.

The deviation calculation unit12calculates a deviation between a target motor rotation speed ω* transmitted from a host control device (not shown) and an actual motor rotation speed ω. The calculated deviation is transmitted to the PI calculation unit14. The PI calculation unit14calculates, as a motor applied voltage, a control amount according to the deviation between the target motor rotation speed ω* and the actual motor rotation speed ω by proportional integral control (PI control). By applying this motor applied voltage to a coil of each phase of a three-phase motor through PWM control, the actual motor rotation speed ω can be approximated to the target motor rotation speed ω*. Note that the control method for calculating the control amount (motor applied voltage) according to the deviation between the target motor rotation speed ω* and the actual motor rotation speed ω is not limited to PI control, and other control methods (for example, PID control, PD control, or the like) may be used.

The VM limitcalculation unit16calculates a motor applied voltage upper limit VM limitset as the upper limit voltage to the motor applied voltage calculated by the PI calculation unit14. As shown inFIG.2, the VM limitcalculation unit16calculates a voltage equivalent to the power supply voltage VDCas the motor applied voltage upper limit VM limitunless the power supply voltage VDCfluctuates (recovery occurs to the original power supply voltage VDCfrom a temporary drop). For this reason, as shown inFIG.1, the VM limitcalculation unit16is able to take in the power supply voltage VDC, and detect its voltage value. Alternatively, the VM limitcalculation unit16may not set the motor applied voltage upper limit VM limitwhen the power supply voltage VDCdoes not fluctuate.

However, when an electrical or electronic device that consumes a large amount of power is activated, such as when an electric power steering is used under a heavy load, the power supply voltage VDCsupplied from the vehicle battery may temporarily drop. When such fluctuation in the power supply voltage VDCoccur, the VM limitcalculation unit16, as shown inFIG.2, calculates the motor applied voltage upper limit VM limitthat changes so as to approximate the voltage value after recovery from a voltage value at time t3to a voltage value at time t4. At time t3, the dropped power supply voltage VDCturns to an increase. From time t3to time t4, the motor applied voltage upper limit VM limitis calculated such that an initial increasing speed is moderate, the increasing speed gradually increases, and then the increasing speed gradually decreases.

The motor applied voltage upper limit VM limitthat changes in this way may be calculated using, for example, a first-order lag transfer function in which the cutoff frequency is a secondary time variable that increases more than the proportional relationship over time. For example, the motor applied voltage upper limit VM limitmay be expressed by the following Formula 1 using the first-order lag transfer function.
VM limit(n)=VM limit(n-1)+2πFT(VDC−VM limit(n-1))  (Formula 1)

In Formula 1, F represents a cutoff frequency and T represents a sampling period. Also, VM limit(n−1) represents a previous value of the motor applied voltage upper limit, and VM limit(n) represents a present value of the motor applied voltage upper limit.

In the present embodiment, the cutoff frequency F in Formula 1 is calculated as a secondary time variable as shown in Formula 2 below.
F=F0+F0C2(Formula 2)

In Formula 2, F0represents a cutoff frequency initial value, and C represents a cutoff frequency counter. The cutoff frequency counter C starts a counting operation in response to the detection in which the dropped power supply voltage VDCturns to an increase. By squaring the count value of the cutoff frequency counter C and multiplying it by the cutoff frequency initial value F0, the cutoff frequency F calculated by Formula 2 changes so as to increase rapidly over time as shown inFIG.3.

In this way, the motor applied voltage upper limit VM limitis calculated using the first-order lag transfer function in which the cutoff frequency F is set as the secondary time variable. In this configuration, the motor applied voltage upper limit VM limitsmoothly changes along an S-shaped curve as shown inFIG.3by synthesizing a change caused by the first-order lag transfer function and a change caused by the cut-off frequency. That is, the motor applied voltage upper limit VM limitis smoothly changed over time such that the initial increasing speed is moderate, the increasing speed gradually increases, and then the increasing speed gradually decreases. The initial increasing speed is moderate. Thus, for example, as shown inFIG.4, if the voltage repeats increasing and decreasing in a case where the dropped power supply voltage VDCreturns to the normal power supply voltage, the fluctuation of the motor applied voltage upper limit VM limitcan be kept small. Therefore, by applying the voltage corresponding to the motor applied voltage upper limit VM limitto the coil of each phase of the three-phase motor, even if the power supply voltage VDCrepeatedly fluctuates, the fluctuation in the motor rotation speed ω can be kept small.

In the above description, an example has been explained in which the motor applied voltage upper limit VM limitis calculated using the first-order lag transfer function in which the cutoff frequency F is set as the secondary time variable. However, the motor applied voltage upper limit VM limitmay be calculated using another function. For example, in order to calculate the motor applied voltage upper limit VM limit, a first-order lag transfer function with the cutoff frequency F as a third-order time variable may be used. Furthermore, the motor applied voltage upper limit VM limitthat changes in an S-shape may be calculated using an exponential function or a sigmoid function. In any case, by calculating the motor applied voltage upper limit VM limitusing a predetermined function, the VM limitcalculation unit16calculates the motor applied voltage upper limit VM limitthat changes smoothly in an S-shape.

The VM limitcalculation unit16transmits the calculated motor applied voltage upper limit VM limitto the Duty calculation unit18from time t3to t4. At time t3, it is detected that the dropped power supply voltage VDCturns to an increase. At time t4, the calculated motor applied voltage upper limit VM limitapproximates the power supply voltage VDC(or the actual motor rotation speed ω is approximated to the target motor rotation speed ω*). For other periods, the VM limitcalculation unit16transmits the motor applied voltage calculated by the PI calculation unit14to the Duty calculation unit18. Alternatively, when the motor applied voltage calculated by the PI calculation unit14is greater than the motor applied voltage upper limit VM limit, the VM limitcalculation unit16may transmit the motor applied voltage upper limit VM limitto the Duty calculation unit18, and when the motor applied voltage calculated by the PI calculation unit14is equal to or smaller than the motor applied voltage upper limit VM limit, the VM limitcalculation unit16may transmit the motor applied voltage calculated by the PI calculation unit14to the Duty calculation unit18.

The Duty calculation unit18calculates the PWM duty based on the motor applied voltage or the motor applied voltage upper limit VM limittransmitted from the VM limitcalculation unit16, and the power supply voltage VDC. For example, the Duty calculation unit18may calculate the PWM duty corresponding to the ratio of the magnitude of the motor applied voltage or the motor applied voltage upper limit VM limitto the magnitude of the power supply voltage VDC. Therefore, for example, when the VM limitcalculation unit16transmits the motor applied voltage upper limit VM limitto the Duty calculation unit18, the Duty calculation unit18calculates the PWM duty in order to apply an applied voltage corresponding to the motor applied voltage upper limit VM limitto the coil of each phase of the three-phase motor30. The PWM duty calculated by the Duty calculation unit18is transmitted to the PWM drive signal generation unit20.

The PWM drive signal generation unit20generates a PWM drive signal having a pulse width corresponding to the PWM duty calculated by the duty calculator18, and outputs the PWM drive signal to the inverter22. The inverter22converts DC power from an in-vehicle battery (not shown), which is a DC power supply, into AC power, and supplies the AC power to the three-phase motor30. The inverter22has three-phase legs connected in parallel between the positive and negative terminals of the vehicle battery. The leg of each phase includes multiple switching elements (for example, IGBTs, MOSFETs, or the like) connected in series. The switching elements provided in the leg of each phase of the inverter22are PWM-controlled according to the PWM drive signal generated by the PWM drive signal generation unit20, thereby converting the DC power supplied from the in-vehicle battery into AC power, and being supplied to the three-phase motor30. At this time, the motor applied voltage calculated by the PI calculation unit14or the voltage corresponding to the motor applied voltage upper limit VM limitcalculated by the VM limitcalculation unit16is applied to the coil of each phase of the three-phase motor30.

The current detection unit24detects a current based on an induced voltage generated in the coil of each phase by switching the coil to be energized in the three-phase motor30. Thus, the actual rotational speed ω of the three-phase motor30can be calculated by detecting the current based on the induced voltage generated in the coil of each phase. The actual rotation speed ω of the three-phase motor30may be calculated in the current detection unit24, or may be calculated in a configuration, which is separate from the current detection unit24, based on the detected current. Alternatively, a position sensor that detects the rotational position of the three-phase motor30may be used to detect the actual rotational speed ω of the three-phase motor30.

Next, an example of processing contents of fluctuation suppression control will be described with reference to the flowchart ofFIG.5. In the fluctuation suppression control, when a power supply voltage VDCtemporarily decreases and then increases to return to a normal power supply voltage VDC, the motor control device10according to the present embodiment suppresses fluctuation, caused by following the fluctuation in the power supply voltage VDC, in the rotation speed of the three-phase motor30.

In step S100, the motor rotation speed is PI-controlled according to the target motor rotation speed ω*. As a result, the actual rotation speed ω of the three-phase motor30is controlled so as to follow the target motor rotation speed ω*. With such control, for example, as shown inFIG.2, even if a temporary drop in the power supply voltage VDCstarts at time t1, the actual motor rotation speed ω is maintained at the target motor rotation speed ω* until time t2.

Here, from time t1to time t2inFIG.2, the PWM duty is increased in order to maintain the actual motor rotation speed ω at the target motor rotation speed ω* regardless of the decrease in the power supply voltage VDC. However, at time t2, the PWM duty reaches 100% and cannot be increased any further. Therefore, after time t2, the actual motor rotation speed ω cannot be maintained at the target motor rotation speed ω* by the PI control, and the actual motor rotation speed ω will also decreases as the power supply voltage VDCdecreases.

At time t3inFIG.2, when the decreased power supply voltage VDCturns to an increase, the PWM duty decreases from 100% to a value less than 100%. In step S110of the flowchart ofFIG.5, after the power supply voltage VDCtemporarily drops and the PWM duty becomes 100%, it is determined that the PWM duty drops from 100% to a value less than 100% (for example, 98%). That is, in step S110, it is determined that the decreased power supply voltage VDCturned to an increase based on the change in the PWM duty. Alternatively, whether or not the power supply voltage VDCturns to an increase may be determined directly from the change in the power supply voltage VDC. When the determination result in step S110is “Yes”, the process proceeds to step S120. On the other hand, when the determination result in step S110is “No”, the process returns to step S100.

In step S120, immediately following the increase in the power supply voltage VDC, the rotation speed of the three-phase motor30rapidly increases. As a result, the fluctuation suppression control that suppresses the fluctuation in the rotation speed of the three-phase motor30according to the fluctuation in the power supply voltage VDC. Specifically, in step S120, the cutoff frequency counter C starts counting.

In step S130, it is determined whether or not the motor applied voltage upper limit VM limitcalculated in the fluctuation suppression control has become equal to or higher than the power supply voltage VDCrestored to the original voltage value. When the determination result in step S130is “Yes”, the process proceeds to step S170since it is no longer necessary to continue the fluctuation suppression control. On the other hand, when the determination result in step S130is “No”, the process proceeds to step S140in order to continue execution of the fluctuation suppression control. In step S130, additionally or alternatively, it may be determined that the actual motor rotation speed ω is equal to or greater than the target motor rotation speed ω*.

In step S140, the motor applied voltage upper limit VM limitis calculated by using the predetermined function from the voltage value at time t3at which the dropped power supply voltage VDCturns to an increase to the voltage value of the power supply voltage VDCafter recovery such that the initial increasing speed is moderate, the increasing speed gradually increases, the increasing speed gradually decreases, and then the motor applied voltage upper limit VM limitapproximates to the voltage value after recovery at time t4. Note that the motor applied voltage calculation process in step S140is repeatedly executed until it is determined, in step S130, that the motor applied voltage upper limit VM limitis equal to or higher than the power supply voltage VDC. In each motor applied voltage calculation process in step S140, which is repeated as described above, a different motor applied voltage upper limit VM limitis calculated since the count value of the cutoff frequency counter C, the power supply voltage VDC, and the previous value of the motor applied voltage upper limit VM limitchange each time the process is executed. Thus, the motor applied voltage upper limit VM limitis changed along an S-shaped curve.

In step S150, the PWM duty for applying an applied voltage corresponding to the motor applied voltage upper limit VM limitto the coil of each phase of the three-phase motor30is calculated. The calculated PWM duty is output to the PWM drive signal generation unit20in step S160.

In step S170, the fluctuation suppression control is terminated. At this timing, the count operation of the cutoff frequency counter C is stopped. Then, in step S180, the count value of the cutoff frequency counter C is cleared. After that, the processing shown in the flowchart ofFIG.5is terminated.

As described above, the motor control device10according to the present embodiment calculates the motor applied voltage upper limit VM limitthat changes smoothly, using a predetermined function, from the voltage value at time t3at which the dropped power supply voltage VDCturns to an increase to the voltage value of the power supply voltage VDCafter recovery. Then, an applied voltage corresponding to the calculated motor applied voltage upper limit VM limitis applied to the coil of each phase of the three-phase motor30. Therefore, a sudden change in the actual motor rotation speed ω can be suppressed.

The motor applied voltage upper limit VM limitis generated such that the actual motor rotation speed ω, which has decreased due to the decrease in the power supply voltage VDC, gradually increases in speed of approaching the target motor rotation speed ω* over time. In other words, since the initial speed of approach immediately after the power supply voltage VDCturns to an increase is moderate, the fluctuation in the actual motor rotation speed ω can be kept small regardless of the fluctuation of the power supply voltage VDCeven if the power supply voltage VDCrepeatedly fluctuates.

Further, when the power supply voltage VDCreturns to a normal voltage value and stabilizes, the motor applied voltage upper limit VM limitis set such that the actual motor rotation speed ω gradually increases in speed of approaching the target motor rotation speed ω* over time. Therefore, the actual motor rotation speed ω can be quickly brought closer to the target motor rotation speed ω*. Furthermore, after that, the motor applied voltage upper limit VM limitis generated such that the approach speed is gradually decreased, so that the actual motor rotation speed ω can be moderately approximated to the target motor rotation speed ω*.

Second Embodiment

A motor control device according to a second embodiment of the present disclosure will be described below with reference to the drawings. The motor control device10according to the first embodiment described above suppresses the fluctuation of the actual motor rotation speed ω by setting the motor applied voltage upper limit VM limitthat is the upper limit for the motor applied voltage when the decreased power supply voltage VDCrises.

On the other hand, a motor control device110according to the second embodiment suppresses the fluctuation of the actual motor rotation speed ω, when the decreased power supply voltage VDCrises, by setting a transient target motor rotation speed ntrgtthat changes from the actual motor rotation speed ω when the power supply voltage VDCturns to an increase to the target motor rotation speed ω* such that an increasing speed of the motor rotation speed ω gradually increases, and then the increasing speed gradually decreases. The motor control device according to the second embodiment will be described below, focusing on differences from the motor control device10according to the first embodiment.

As shown inFIG.6, the motor control device110according to the present embodiment includes a transient target motor rotation speed (ntrgt) calculation unit116as a transient target setting unit instead of the VM limitcalculation unit16of the motor control device10according to the first embodiment.

As long as the power supply voltage VDCdoes not fluctuate (that is, a recover does not occur from a temporary drop to the original power supply voltage VDC), the ntrgtcalculation unit116sets, as the transient target motor rotation speed ntrgt, a rotation speed equal to the target motor rotation speed ω* as shown by a dash-dot line inFIG.7. Alternatively, when the actual motor rotation speed ω begins to decrease at time t2inFIG.7even though the PWM duty is 100%, the ntrgtcalculation unit116may set the transient target motor rotation speed ntrgtso as to follow the decrease in the actual motor rotation speed ω. Further, the ntrgtcalculation unit116may not set the transient target motor rotation speed ntrgtuntil the power supply voltage VDCtemporarily decreases and then the decreased power supply voltage VDCturns to an increase.

The power supply voltage VDCmay fluctuate such as temporarily decreasing and then returning to the original power supply voltage VDC. In this case, as shown inFIG.7, the ntrgtcalculation unit116calculates the transient target motor rotation speed ntrgtusing the predetermined function from an actual motor rotation speed ω at time t3at which the dropped power supply voltage VDCturns to an increase to the target motor rotation speed ω* such that the initial increasing speed is moderate, the increasing speed gradually increases, the increasing speed gradually decreases, and then the motor rotation speed ω approximates to the target motor rotation speed ω* at time t4.

As the predetermined function used to calculate the transient target motor rotation speed ntrgt, similarly to the faction in the first embodiment, a first-order lag transfer function in which a cutoff frequency F is set as a secondary time variable, a first-order lag transfer function in which a cutoff frequency F is set as a third-order time variable, an exponential function, a sigmoid function, or the like can be used.

At least from time t3to time t4inFIG.7, the PI calculation unit114calculates, as the motor applied voltage, a control amount according to a deviation between the actual motor rotation speed ω and the transitional target motor rotation speed ntrgt. The Duty calculation unit118calculates a PWM duty corresponding to the ratio of the magnitude of the motor applied voltage calculated by the PI calculation unit114to the magnitude of the power supply voltage VDC. As a result, as shown inFIG.7, during the period from time t3to time t4, regardless of whether the power supply voltage VDCreturns to the original voltage value, the voltage applied to the coil of each phase of the three-phase motor130can be controlled such that the actual motor rotation speed ω changes in an S-shape by following the transient target motor rotation speed ntrgt. As a result, even with the motor control device110according to the present embodiment, it is possible to obtain the same effects as those described in the first embodiment when a power supply voltage VDCtemporarily decreases and then increases to return to a normal power supply voltage VDC.

Next, an example of processing contents of fluctuation suppression control will be described with reference to the flowchart ofFIG.8. In the fluctuation suppression control, when a power supply voltage VDCtemporarily decreases and then increases to return to a normal power supply voltage VDC, the motor control device110according to the present embodiment suppresses fluctuation in the rotation speed of the three-phase motor30by following the fluctuation in the power supply voltage VDC.

Steps S200to S220and steps S270to S280are similar to steps S100to S120and steps S170to S180in the flowchart ofFIG.5, so description thereof will be omitted.

In step S230, it is determined whether or not the transient target motor rotation speed ntrgtcalculated in the variation suppression control matches with the target motor rotation speed ω* transmitted from the host control device. In this determination process, since the actual motor rotation speed ω changes according to the transient target motor rotation speed ntrgt, it may be determined whether or not the actual motor rotation speed ω matches with the target motor rotation speed ω*. When the determination result in step S230is “Yes”, the process proceeds to step S270since it is no longer necessary to continue the fluctuation suppression control. On the other hand, when the determination result in step S230is “No”, the process proceeds to step S240in order to continue execution of the fluctuation suppression control.

In step S240, using the predetermined function, the transient target motor rotation speed ntrgtis calculated so as to change from an actual motor rotation speed w at time t3at which the dropped power supply voltage VDCturns to an increase to the target motor rotation speed ω* such that the initial increasing speed is moderate, the increasing speed gradually increases, the increasing speed gradually decreases, and then the motor rotation speed ω approximates to the target motor rotation speed ω* at time t4. Note that the transient target motor rotation speed ntrgtis repeatedly calculated in step S240until the determination result in step S230becomes “Yes”, which is the same as the calculation of the motor applied voltage upper limit VM limitin the first embodiment.

In step S250, a PWM duty for applying a motor applied voltage corresponding to the deviation between the transient target motor rotation speed ntrgtand the actual motor rotation speed ω to the coil of each phase of the three-phase motor130is calculated. Then, in step S260, the calculated PWM duty is output to the PWM drive signal generation unit120.

There have been described the preferred embodiments of the present disclosure. However, the present disclosure is not limited to the above-mentioned embodiments. However, the disclosure may be otherwise variously modified within the spirit and scope of the disclosure.

For example, the motor control units10,110and methods thereof described in the present disclosure may be implemented by a special purpose computer which is configured with a memory and a processor programmed to execute one or more particular functions embodied in computer programs of the memory. Alternatively, the motor control units10,110and methods thereof according to the present disclosure may be achieved by a dedicated computer provided by constituting a processor with one or more dedicated hardware logic circuits. Alternatively, the motor control units10,110and methods thereof described in the present disclosure may be implemented by one or more special purpose computer, which is configured as a combination of a processor and a memory, which execute computer programs and are programmed to perform one or more functions, and a processor which is configured with one or more hardware logic circuits. The computer program may be stored, as instructions to be executed by a computer, in a tangible non-transitory computer-readable medium.