JP2017046527A - Power control method and power control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power control method and a power control device capable of improving the accuracy of rotation control of a motor.SOLUTION: A power control method of comparing magnitudes of a duty command value and a carrier wave with each other and generating a PWM signal used for control of a motor depending on the comparison result, includes: a current measurement step of measuring a current supplied to the motor, at a measurement timing when the magnitude of the carrier wave becomes the maximum or the minimum; a command value calculation step of calculating the duty command value calculated at the command value calculation step depending on the current measured by the current measurement step, and a request torque of the motor; a determination step of determining a magnitude relation between the calculated duty command value and the carrier wave at the time point when the duty command value is calculated; and a carrier frequency change step of lowering a frequency of the carrier wave depending on the determination result at the determination step.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a power control method and a power control apparatus.

  A pulse width modulation (PWM) power control method is known as one of power control methods for converting DC power into AC power and applying it to a three-phase AC motor.

  In a general PWM power control method, a current supplied to a motor is sequentially measured, and a duty command value is obtained according to the measured current and a required torque of the motor. Then, the magnitudes of the duty command value and the carrier wave are compared, and a PWM signal is generated based on the comparison result. By operating on / off of the switching element of the inverter using the PWM signal, the pulse width of the voltage applied to the motor is controlled, and desired electric power is supplied to the motor.

  Here, the current supplied to the motor at the timing when the magnitude of the carrier wave is the maximum or minimum, which is the midpoint of the ON section or OFF section of the switching element, so that the noise included in the measurement current is minimized. Is measured. Since the carrier wave changes between when the current is measured and when the duty command value is calculated, depending on the size of the calculated duty command value, the duty command value is already calculated when the calculation of the duty command value is completed. The timing at which the magnitudes of the value and the carrier wave are equal may have passed. In such a case, the timing for operating the switching element is delayed from the original timing.

  As a countermeasure, in Patent Document 1, when the calculated duty command value exceeds the magnitude of the carrier wave at the time when the calculation of the duty command value is completed, the switching element is turned on and turned off. A technique for delaying both timings is disclosed.

JP 2009-100599 A

  In the technique disclosed in Patent Document 1, the pulse width of the voltage applied to the motor is ensured by delaying the timing at which the switching element is turned on and off. However, the timing at which the carrier wave, which is the current measurement timing, becomes the maximum or minimum, does not correspond to the midpoint of the ON section or the OFF section of the switching element. For this reason, the influence of noise included in the measured current cannot be sufficiently suppressed, and there has been a problem that the accuracy of motor rotation control is reduced.

  This invention is made paying attention to such a subject, and it aims at providing the electric power control apparatus which can raise the precision of rotation control of a motor, and an electric power control apparatus.

  One aspect of the control method of the power control apparatus of the present invention is a power control method that compares the magnitudes of the duty command value and the carrier wave and generates a PWM signal used for motor control according to the comparison result. In accordance with the current measurement step for measuring the current supplied to the motor, the current measured by the current measurement step, and the required torque of the motor at the measurement timing at which the magnitude of the carrier wave is maximum or minimum, A command value calculating step for calculating the duty command value calculated in the command value calculating step, a determination step for determining a magnitude relationship between the calculated duty command value and the carrier wave at the time when the duty command value is calculated; And a carrier frequency changing step for changing the frequency of the carrier wave to a low level according to the determination result of the determining step.

  According to one aspect of the present invention, in the carrier frequency changing step, the frequency of the carrier wave is changed to be low according to the determination result in the determining step. Thereby, it is suppressed that the calculated duty command value exceeds the magnitude of the carrier wave at the time when the calculation of the duty command value is completed. Therefore, it is possible to suppress the occurrence of deviation in the interval between the switching element operation timing based on the PWM signal based on the duty command value and the current measurement timing based on the carrier wave.

  By suppressing the occurrence of a gap between the switching element operation timing and the current measurement timing in this way, the current supplied to the motor is measured in the vicinity of the midpoint of the ON section or OFF section of the switching element. become. For this reason, harmonic noise in the measurement current used for controlling the motor is suppressed, so that the accuracy of motor rotation control can be improved.

FIG. 1 is a schematic configuration diagram of a power supply system of the present invention. FIG. 2 is a diagram illustrating an example of a duty command value and a carrier wave that are compared by the PWM signal generation unit. FIG. 3 is a diagram illustrating another example of the duty command value and the carrier wave compared in the PWM signal generation unit. FIG. 4A is a comparison diagram of carrier waves having different frequencies. FIG. 4B is a comparison diagram of carrier waves having different frequencies. FIG. 5 is a block diagram showing the operation of the motor controller.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a power supply system according to an embodiment of the present invention.

  The power supply system 100 shown in FIG. 1 is assumed to be mounted on an electric vehicle. According to this system, electric power is supplied from the battery 101 to the motor 104 via the relay 102 and the inverter 103.

  The battery 101 is a secondary battery and outputs DC power.

  The relay 102 controls driving or stopping of the entire power supply system 100.

  The inverter 103 includes a plurality of switching elements (insulated gate bipolar transistors IGBT) Tr1 to Tr6 and rectifying elements (diodes) D1 to D6. The rectifying elements D1 to D6 are provided in parallel with the switching elements Tr1 to Tr6, respectively, and are provided so that a current flows in a direction opposite to the rectifying direction of the switching elements Tr1 to Tr6. Two switching elements are connected in series, and two switching elements connected in series and one of the three-phase (UVW) input sections of the motor 104 are connected to each other.

  Specifically, switching elements Tr1 and Tr2, switching elements Tr3 and Tr4, and switching elements Tr5 and Tr6 are connected in series, respectively. The connection point of the switching elements Tr1 and Tr2 and the U-phase input part of the motor 104 are connected, the connection point of the switching elements Tr3 and Tr4 and the V-phase input part of the motor 104 are connected, and the switching element Tr5 and The connection point of Tr6 and the W-phase input part of the motor 104 are connected. The switching elements Tr1 to Tr6 thus provided are operated in accordance with the PWM signal output from the motor controller 111, whereby the pulse width of the voltage applied from the battery 101 to the motor 104 is controlled. In general, such control is referred to as PWM current control.

  Note that if no electric power is applied to the inverter 103, the potential at the input portion of each phase of the motor 104 is zero. Further, the potential difference of the capacitor 105 is Vcap. For this reason, the potential of the voltage applied to the input part of each phase of the motor 104 is assumed to be a value in the range from “−Vcap / 2” to “+ Vcap / 2”.

  The motor 104 is a permanent magnet type three-phase AC motor including a permanent magnet in the rotor, and has an input unit for each of the three phases (UVW phase). The motor 104 is a drive source that drives the drive wheels of the electric vehicle, and the drive wheels of the electric vehicle rotate as the motor 104 rotates.

  The capacitor 105 is disposed between the relay 102 and the inverter 103 and is connected in parallel with the inverter 103. Capacitor 105 smoothes the DC power output from battery 101 to motor 104.

  The current sensor 106 measures the magnitude of each current flowing from the inverter 103 to the input part of each phase of the motor 104. In the present embodiment, three current sensors 106 </ b> U, 106 </ b> V, and 106 </ b> W are provided on the power supply line to the input portion of each phase of the motor 104. The current sensors 106U, 106V, and 106W feed back the measured three-phase AC currents Iu, Iv, and Iw of the respective phases to the motor controller 111, respectively.

  The rotor position sensor 107 is, for example, a resolver or an encoder. The rotor position sensor 107 is provided in the vicinity of the rotor of the motor 104 and measures the phase θ of the rotor of the motor 104. Then, the rotor position sensor 107 outputs a rotor position sensor signal indicating the measured rotor phase θ to the motor controller 111.

  The voltage sensor 108 is provided in parallel with the capacitor 105. When the voltage sensor 108 measures the capacitor voltage Vcap, which is a potential difference between both ends of the capacitor 105, the voltage sensor 108 outputs the capacitor voltage Vcap to the gate drive circuit 109.

  The gate drive circuit 109 operates the switching elements Tr <b> 1 to Tr <b> 6 of the inverter 103 according to the PWM signal input from the motor controller 111. In addition, the gate drive circuit 109 measures the temperature of the switching elements Tr1 to Tr6 and detects whether or not the switching elements Tr1 to Tr6 are operating normally. The gate drive circuit 109 outputs to the motor controller 111 an IGBT signal indicating the temperature measured for the switching elements Tr1 to Tr6 and the detected state. The gate drive circuit 109 outputs a capacitor voltage signal indicating the capacitor voltage Vcap measured by the voltage sensor 108 to the motor controller 111.

When the vehicle controller 110 calculates a torque command value T ^* indicating a required torque that is a torque required for the motor 104, the vehicle controller 110 outputs the calculated torque command value T ^* to the motor controller 111.

The motor controller 111 outputs a pulse width modulation (PWM) signal to each of the switching elements Tr <b> 1 to Tr <b> 6 of the inverter 103 in order to control the pulse width of the voltage applied to the motor 104. Specifically, the motor controller 111 outputs the three-phase alternating currents Iu, Iv, Iw output from the current sensor 106, the rotor phase θ output from the rotor position sensor 107, and the vehicle controller 110. A voltage command value is calculated based on the torque command value T ^* . Next, the motor controller 111 calculates a duty command value using the voltage command value and the capacitor voltage Vcap output from the voltage sensor 108. Next, the motor controller 111 compares the duty command value with the carrier wave, and generates a PWM signal according to the comparison result. Next, the motor controller 111 outputs the generated PWM signal to the gate drive circuit 109. The gate drive circuit 109 operates the switching elements Tr1 to Tr6 of the inverter 103 based on each input PWM signal. By doing so, the pulse width of the voltage applied to the motor 104 is controlled, and the motor 104 can generate a torque of the torque command value T ^* .

  In the power supply system 100, it is assumed that a power control apparatus is configured by configurations other than the battery 101 and the motor 104, that is, the inverter 103, the current sensor 106, the motor controller 111, and the like.

  Here, the relationship between the duty command value and the carrier wave compared in the motor controller 111 will be described.

FIG. 2 is a diagram illustrating an example of a duty command value and a carrier wave. In this figure, only the duty command value Du ^* used to control the input to the u phase of the motor 104 will be described, and the duty command value Dv ^* used to control the input to the v phase and w phase of the motor 104 will be described. Description of Dw ^* is omitted.

In this figure, time is shown on the horizontal axis and the duty ratio is shown on the vertical axis. Further, a carrier wave standardized so that the maximum value is 1 (100%) and the minimum value is 0 (0%) is shown. Further, the duty command value Du ^* calculated by the motor controller 111 is indicated by a bold line. The duty command value Du ^* is a value in the range from 0 to 1, similarly to the magnitude of the carrier wave.

Further, the motor controller 111 compares the duty command value Du ^* with the carrier wave, and when the duty command value Du ^* is equal to or greater than the carrier wave, the PWM signal that turns the switching element Tr off. Is generated. On the other hand, when the duty command value Du ^* is smaller than the carrier wave, the motor controller 111 generates a PWM signal that turns on the switching element Tr. By doing in this way, the ratio of the area where the switching element Tr occupies in the carrier wave period becomes equal to the duty command value Du ^* .

The current sensor 106 measures the supply current to the motor 104 at the timing (time Ta) when the carrier wave becomes maximum. For example, when the current sensor 106 measures the current flowing through the motor 104 at the time Ta, the motor controller 111 completes the calculation of the duty command value Du ^* at the time Tb, which is the elapsed time from the time Ta by the calculation time Δt.

The calculated duty command value Du ^* is smaller than the magnitude of the carrier wave when the calculation of the duty command value Du ^* is completed (time Tb). In such a case, the duty command value Du ^* and the carrier wave have the same magnitude at the time Ton after the time (time Tb) after the calculation time Δt has elapsed from the measurement timing (time Ta), and PWM. The switching element Tr is turned ON by the signal. Therefore, at the time when the calculation of the duty command value Du ^* is completed (time Tb), the motor controller 111 calculates the duty command value Du ^* and the carrier wave because the calculated duty command value Du ^* is smaller than the carrier wave. Can be compared appropriately.

  Here, the reason why the current sensor 106 measures the three-phase alternating currents Iu, Iv, and Iw at the timing when the carrier wave becomes maximum (time Ta) is as follows.

Switching element Tr is turned ON in Ton carrier wave is a timing below the duty command value Du ^*, the switching element Tr is turned OFF at Toff carrier wave is a timing exceeds the duty command value Du ^*. Due to such operation of the switching element Tr, harmonic current may be included in the current flowing from the battery 101 to the motor 104.

  In the PWM power control method, the switching element Tr is operated at an extremely short interval. Therefore, if the operation timing of the switching element Tr is averaged, the timing at which the carrier wave becomes maximum (time Ta) may be regarded as having the most time difference from the timings Ton and Toff at which the switching element Tr is operated. it can. Therefore, the current sensor 106 measures the three-phase alternating currents Iu, Iv, and Iw at the timing when the carrier wave becomes maximum, thereby reducing harmonic noise included in the three-phase alternating currents Iu, Iv, and Iw. it can. Thereby, the precision of the rotation control of the motor 104 can be improved.

  In FIG. 2, the case where the current measurement timing by the current sensor 106 is the timing at which the carrier wave becomes maximum has been described, but the present invention is not limited to this. Even if the current sensor 106 measures the current at the timing when the carrier wave becomes maximum or minimum, the noise of the three-phase alternating currents Iu, Iv, and Iw can be similarly reduced. Since the switching element Tr is operated in synchronization with the current measurement timing, if the operation timing of the switching element Tr is averaged, the operation timing of the switching element Tr is the timing at which the carrier wave is maximized and the timing at which it is minimized. Can be regarded as the midpoint of Therefore, the timing at which the carrier wave is maximized or minimized is farthest in time from the averaged operation timing of the switching element Tr. Therefore, noise caused by the operation of the switching element Tr included in the measurement current can be suppressed by the current sensor 106 measuring the current at the timing when the carrier wave becomes maximum or minimum.

  FIG. 3 is a diagram illustrating another example of the duty command value and the carrier wave that are compared by the motor controller 111.

  The case where the current sensor 106 measures the current at the times Ta1 and Ta2 when the carrier wave is maximum or minimum will be described with reference to FIG. Further, the carrier waves before the time Tb1 and Tb2 after the calculation time Δt from the time Ta1 and Ta2 which are current measurement timings are indicated by dotted lines.

  First, the case where the current is measured at the timing when the carrier wave becomes maximum (time Ta1) will be considered.

The motor controller 111 can compare the duty command value Du1 ^* and the carrier wave after time Tb1 after the calculation time Δt has elapsed. At time Tb1, since the calculated duty command value Du1 ^* is greater than the carrier wave, motor controller 111 generates a PWM signal that turns on switching element Tr. However, originally, the timing of the switching element Tr is turned ON by the duty command value Du1 ^* should be time Tc1 that is the duty command value Du1 ^* and the carrier wave becomes equal size.

Thus, when duty command value Du1 ^* is larger than the carrier wave at time Tb1, switching element Tr is operated at time Tb1, which is different from the original time Tc1, and therefore to motor 104. The accuracy of the control of the applied power is reduced.

  Next, consider the case where the current is measured at the timing (time Ta2) at which the carrier wave is minimized.

In such a case, the motor controller 111 can compare the duty command value Du2 ^* and the carrier wave after the time Tb2 after the calculation time Δt has elapsed from the time Ta2. When the duty command value Du2 ^* is smaller than the carrier wave at time Tb2, the switching element Tr is operated at a timing different from the original timing, so the accuracy of controlling the power applied to the motor 104 is reduced. End up.

  Here, the deviation amount ΔDc from the median value (1/2 (50%)) of the carrier wave at time Tb1 is the deviation amount Δt from the median value (1/2 (50%)) of the carrier wave at time Tb2. equal. Therefore, such a deviation amount ΔDc can be expressed by the following equation using the calculation time Δt and the frequency f of the carrier wave.

Therefore, when the duty command value Du1 ^* is smaller than “0.5 + ΔDc”, the switching element Tr is determined by the control timing of the switching element Tr based on the PWM signal obtained by the motor controller 111 and the duty command value Du1 ^* . There is no deviation from the operation timing. When the duty command value Du2 ^* is larger than “0.5−ΔDc”, the switching element Tr is controlled based on the control timing of the switching element Tr based on the PWM signal obtained by the motor controller 111 and the duty command value Du2 ^* . There is no deviation from the timing at which Tr is operated.

Therefore, if the duty command value Du ^* is in the range from “0.5−ΔDc” to “0.5 + ΔDc”, the control timing of the switching element Tr by the PWM signal obtained by the motor controller 111 and the original duty command There is no deviation from the timing when the switching element Tr is turned ON by the value Du ^* . Therefore, if 2ΔDc, which is the size of this range, is defined as the upper limit modulation rate M ^* , the upper limit modulation rate M ^* can be expressed by the following equation.

As described above, if the duty command value Du ^* is a value within the range of “0.5−ΔDc” to “0.5 + ΔDc”, the switching element Tr based on the PWM signal obtained by the motor controller 111 is used. There is no deviation between the control timing and the timing when the switching element Tr is originally controlled by the duty command value Du ^* . Therefore, the range of the duty command value Du ^* where no deviation occurs can be expressed by the following equation using the upper limit modulation factor M ^* .

Here, in the motor controller 111, the duty command values Du ^* , Dv ^* , and Dw ^* are expressed as follows using the three-phase AC voltage command values Vu ^* , Vv ^* , and Vw ^* and the capacitor voltage Vcap of the capacitor 105: It can be shown as:

  Using equation (4), equation (3) can be expressed as follows:

Therefore, the motor controller 111 determines whether the three-phase AC voltage command values Vu ^* , Vv ^* , and Vw ^* satisfy the expression (5), thereby controlling the control timing of the switching element Tr by the motor controller 111, It can be determined whether or not there is a deviation from the original timing when the switching element Tr is turned on by the duty command value Du1 ^* .

Here, when the electric vehicle equipped with the motor 104 is accelerating, the required torque T ^* of the motor 104 continues to be higher than usual. For this reason, there is a possibility that a state where a PWM signal that can control the switching element Tr at an original timing according to the duty command value D ^* cannot be generated continues.

Therefore, the frequency of the carrier wave is set so that there is no deviation between the control timing of the switching element Tr based on the PWM signal obtained by the motor controller 111 and the original timing at which the switching element Tr is operated by the duty command value D ^*. Can be considered. In the following, a method for suppressing the occurrence of deviation in switching timing by changing the frequency of the carrier wave will be described.

  FIG. 4A is a diagram illustrating carrier waves having two different types of frequencies. Here, it is assumed that the current sensor 106 measures the current at the timing (time Ta) at which the carrier wave becomes maximum.

  In this figure, a first carrier wave having a frequency f is indicated by a dotted line, and a second carrier wave having a frequency lower than the first carrier wave is f ′ (f ′ <f). Is shown as a solid line. Note that the period of the second carrier wave is longer than the period of the first carrier wave having a high frequency.

As described above, the magnitude of the carrier wave when the calculation time Δt has elapsed from the time Ta, which is the measurement timing, is “0.5 + M ^* / 2”. This value can be expressed as follows using equation (2).

Therefore, when the frequency f of the carrier wave is lowered, the magnitude of the carrier wave is increased when the calculation time Δt has elapsed from the measurement timing. Note that the magnitude of the carrier wave when the calculation time Δt has elapsed from the measurement timing is an upper limit value of the magnitude of the duty command value D ^* that can be appropriately compared with the carrier wave when generating the PWM signal. Therefore, the upper limit value of the duty command value D ^* can be increased by lowering the frequency of the carrier wave.

Further, in order to generate the PWM signal appropriately, the duty command value D ^* needs to be equal to or less than the magnitude of the carrier wave at the time when the calculation time Δt has elapsed from the measurement timing. There is.

  By transforming this equation (7), the following equation can be obtained.

  Therefore, in order to generate the PWM signal appropriately, the frequency f of the carrier wave needs to satisfy the equation (8). Here, the higher the frequency f of the carrier wave, the finer the control cycle of the switching element Tr by the PWM signal. Therefore, in order to improve the accuracy of the rotation control of the motor 104, it is preferable that the frequency f is high. Therefore, it is preferable to set the frequency f of the carrier wave to the value of the following equation so as to be the maximum within the range satisfying the equation (8).

The calculation time Δt in equation (9) is a fixed value. For this reason, the frequency f of the carrier wave obtained using Equation (9) is a value corresponding to the calculated duty command value D ^* . Therefore, when the current sensor 106 measures the current at the timing when the carrier wave becomes maximum, the changed carrier frequency is set lower as the duty command value D ^* increases.

  In FIG. 4, the current sensor 106 has been described with reference to the example in which the current is measured at the timing when the carrier wave becomes maximum. However, the present invention is not limited to this. For example, as a modification, the current sensor 106 may measure the current at a timing at which the carrier wave is minimized.

  FIG. 4B is a diagram illustrating carrier waves of two different types of frequencies, similar to FIG. 4A. Note that the current sensor 106 measures the current at the timing (time Ta) at which the carrier wave is minimized.

Here, the magnitude of the carrier wave when the calculation time Δt has elapsed from the time Ta, which is the measurement timing, is “0.5−M ^* / 2”. This value can be expressed as follows using equation (2).

Therefore, in order to appropriately generate the PWM signal, the duty command value D ^* is not less than the magnitude of the carrier wave at the time when the calculation time Δt has elapsed from the measurement timing, and it is necessary to satisfy the following equation.

  By transforming this equation (11), the following equation can be obtained.

  As described above, the carrier wave frequency is preferably higher. Therefore, it is preferable to set the frequency f of the carrier wave to the value of the following equation so as to become the maximum within the range satisfying the equation (12).

Therefore, when the current sensor 106 measures the current at the timing at which the carrier wave is minimized, the carrier frequency after the change becomes lower as the duty command value D ^* becomes smaller.

  As another modification, the current sensor 106 may measure the current at the timing when the carrier wave becomes maximum and minimum.

First, consider the case where the current sensor 106 measures current at the timing at which the carrier wave is minimized. In such a case, when the calculated duty command value is smaller than the duty command value when the calculation time Δt has elapsed from the current measurement timing, the PWM signal generation unit 505 performs the duty command value Du ^* and the carrier wave. Cannot be properly compared. Therefore, the frequency of the carrier wave is changed using Expression (9).

Next, consider the case where the current sensor 106 measures current at the timing at which the carrier wave is minimized. In such a case, when the calculated duty command value is larger than the duty command value when the calculation time Δt has elapsed from the current measurement timing, the PWM signal generation unit 505 determines that the duty command value Du ^* is The carrier wave cannot be properly compared. Therefore, the frequency of the carrier wave is changed using Expression (12).

  Next, the configuration of the motor controller 111 in FIG. 1 will be described with reference to FIG.

  FIG. 5 is a block diagram showing the configuration of the motor controller 111.

The current command value calculation unit 501 generates a d-axis current command value Id ^* and a q-axis current command value Iq based on the torque command value T ^* calculated by the vehicle controller 110 in FIG. 1 and the rotational speed ω of the motor 104. ^* Is calculated.

  The rotation speed ω of the motor 104 is obtained as follows.

  The phase calculator 506 calculates the rotor phase θ based on the rotor position sensor signal output from the rotor position sensor 107 in FIG.

  The rotational speed calculation unit 507 calculates the rotational speed (electrical angular speed) ω by differentiating the rotor phase θ calculated by the phase calculation unit 506.

The current control unit 502 includes measured values of the d-axis current command value Id ^* and the q-axis current command value Iq ^* output from the current command value calculation unit 501 and the current flowing from the phase conversion unit 508 to the motor 104. A d-axis current Id and a q-axis current Iq are input. The current control unit 502 calculates the d-axis voltage command value Vd ^* and the q-axis voltage command value Vq ^* based on these input values. Specifically, the current control unit 502 obtains the d-axis voltage command value Vd ^* so that there is no deviation between the d-axis current command value Id ^* and the d-axis current Id. Further, the current control unit 502 obtains the q-axis voltage command value Vq ^* so that there is no deviation between the q-axis current command value Iq ^* and the q-axis current Iq.

  The phase conversion unit 508 is based on the three-phase alternating currents Iu, Iv, Iw measured by the current sensors 106U, 106V, 106W in FIG. 1 and the rotor phase θ calculated by the phase calculation unit 506. , D-axis current Id and q-axis current Iq are calculated.

  Note that the timing at which the current sensor 106 measures the magnitude of the carrier wave is synchronized with the timing at which the d-axis current Id and the q-axis current Iq output from the phase converter 508 change. For example, when the current sensor 106 measures the current flowing to the motor 104 at the timing when the magnitude of the carrier wave becomes maximum, the phase conversion unit 508 is synchronized with the timing when the magnitude of the carrier wave becomes maximum. The d-axis current Id and the q-axis current Iq output from the above change.

The phase conversion unit 503 uses the d-axis voltage command value Vd ^* and the q-axis voltage command value Vq ^* and the phase θ of the rotor of the motor 104 output from the phase calculation unit 506, and uses a three-phase AC voltage command value. Vu ^* , Vv ^* , and Vw ^* are obtained.

As described above, the potential supplied to the input portion of each phase of the motor 104 is in the range from “−Vcap / 2” to “+ Vcap / 2”. Therefore, the three-phase AC voltage command values Vu ^* , Vv ^* , and Vw ^* are in the range from “−Vcap / 2” to “+ Vcap / 2”.

The duty converter 504 uses the above equation (4) based on the three-phase AC voltage command values Vu ^* , Vv ^* , Vw ^* and the capacitor voltage Vcap of the capacitor 105 in FIG. ^* , Dv ^* , and Dw ^* are generated and output to the PWM signal generation unit 505.

Further, the duty converter 504 determines whether or not all of the three-phase AC voltage command values Vu ^* , Vv ^* , and Vw ^* satisfy the above formula (5). As described above, it is possible to determine whether or not it is necessary to change the frequency f of the carrier wave according to the determination result.

If any one of the three-phase AC voltage command values Vu ^* , Vv ^* , Vw ^* does not satisfy Expression (5), the duty converter 504 needs to change the frequency of the carrier wave. The change request C is output to the carrier frequency calculation unit 509.

On the other hand, when all of the three-phase AC voltage command values Vu ^* , Vv ^* , and Vw ^* satisfy Expression (5), the duty conversion unit 504 does not need to change the frequency of the carrier wave, so the change request C Is not output to the carrier frequency calculation unit 509.

The upper limit modulation factor M ^* in equation (5) can be obtained as follows.

The carrier frequency calculation unit 509 receives the duty command values Du ^* , Dv ^* , Dw ^* and the change request C from the duty conversion unit 504.

  If the change request C is not input, the carrier frequency calculation unit 509 outputs a predetermined carrier frequency f to the PWM signal generation unit 505 and the upper limit modulation rate calculation unit 510.

  On the other hand, when the change request C is input, the carrier frequency calculation unit 509 obtains the changed carrier frequency f using Expression (7). Then, the carrier frequency calculation unit 509 outputs the changed carrier frequency f to the PWM signal generation unit 505 and the upper limit modulation rate calculation unit 510.

The carrier frequency calculation unit 509 calculates the carrier frequency f using the largest duty command value among the duty command values Du ^* , Dv ^* , and Dw ^* . For example, when the duty command value Du ^* is the largest among the duty command values Du ^* , Dv ^* , and Dw ^* , the carrier frequency f is calculated using the largest duty command value Du ^* . By doing in this way, the PWM signal which shows the original control timing of the switching element Tr according to those command values can also be obtained for the duty command values Dv ^* and Dw ^* .

The upper limit modulation factor calculation unit 510 calculates the duty command values Du ^* , Dv ^* , and Dw ^* after the current sensors 106U, 106V, and 106W measure the three-phase alternating currents Iu, Iv, and Iw. The calculation time Δt until is stored in advance. The calculation time Δt may include a current measurement time (processing time such as AD conversion) by the current sensors 106U, 106V, and 106W.

Upper limit modulation factor calculation section 510 calculates upper limit modulation ratio M ^* using carrier wave frequency f output from carrier frequency calculation section 509, calculation time Δt, and equation (2).

  The PWM signal generation unit 505 generates a triangular carrier wave based on the carrier frequency f output from the carrier frequency calculation unit 509. Note that the carrier wave generated by the PWM signal generation unit 505 is standardized, and the minimum value is 0 and the maximum value is 1.

Then, the PWM signal generation unit 505 compares the magnitudes of the duty command values Du ^* , Dv ^* , Dw ^* and the carrier wave, and generates a PWM signal according to the comparison result. As shown in FIGS. 4A and 4B, an appropriate PWM signal can be generated by changing the frequency of the carrier wave to a value corresponding to the duty command value D ^* .

  The following effects can be obtained by this embodiment.

  As described above, in the power conversion method of this embodiment, the current sensor 106 executes a current measurement step of measuring the current supplied to the motor at the measurement timing at which the magnitude of the carrier wave is maximized or minimized. Then, the duty conversion unit 504 executes a command value calculation step for calculating a duty command value according to the current measured by the current sensor 106 and the required torque of the motor 104. Further, the duty conversion unit 504 determines whether or not the expression (5) is satisfied, whereby the magnitude relationship between the calculated duty command value and the carrier wave at the time when the duty command value is calculated is determined. A determination step for determining is performed. Then, the carrier frequency calculating unit 509 performs a carrier frequency changing step of changing the frequency of the carrier wave to a low level according to the determination result of the determining step by the duty converter 504.

The magnitude of the carrier wave changes from when the current sensors 106U, 106V, 106W measure the three-phase alternating current until the duty converter 504 completes the calculation of the duty command value (calculation time Δt). For example, as shown in FIG. 3, when the duty command value Du1 ^* calculated using the measured current at time Ta1 exceeds the magnitude of the carrier wave at time Tb1 when the calculation time Δt has elapsed, Before the calculation of the duty command value is completed, the duty command value and the carrier wave have the same magnitude. Therefore, there is a difference between the control timing (time Tb1) of the switching element Tr by the PWM signal generated by the PWM signal generation unit 505 and the original control timing (time Tc1) of the switching element Tr indicated by the duty command value. Therefore, the PWM signal generation unit 505 cannot generate an appropriate PWM signal.

  Therefore, the duty conversion unit 504 determines whether or not Expression (5) is satisfied. This determination result is based on whether the duty command value exceeds the carrier wave at the time when the calculation of the duty command value is completed, that is, the PWM signal generation unit 505 does not change the frequency of the carrier wave. Indicates whether or not can be generated. For this reason, if Formula (5) is not satisfied and the carrier wave frequency is not changed, it is determined that the PWM signal generation unit 505 cannot generate an appropriate PWM signal, and the carrier wave frequency is changed to a lower value.

  As shown in FIG. 4A, the lower the carrier wave frequency, the larger the upper limit value of the duty command value that can generate a PWM signal appropriately. Further, as shown in FIG. 4B, the lower the carrier wave frequency is, the smaller the lower limit value of the duty command value that can generate a PWM signal appropriately. Therefore, by reducing the frequency of the carrier wave, the range of the duty command value that can generate an appropriate PWM signal can be increased.

  Therefore, if the PWM signal can be generated appropriately, it is possible to suppress the deviation between the control timing of the switching element Tr by the PWM signal and the original control timing of the switching element Tr indicated by the duty command value. Therefore, the noise included in the three-phase alternating current measured by the current sensor 106 is suppressed by measuring the three-phase alternating current at the timing when the carrier wave becomes maximum or minimum, so that the accuracy of controlling the motor 104 is improved. Can be improved.

Moreover, in the power conversion method of this embodiment, the carrier frequency calculation part 509 changes the frequency of a carrier wave to the value shown by Formula (9) or Formula (13). Expressions (9) and (13) are both upper limit values in the range of the frequency of the carrier wave that can appropriately generate a PWM signal using the calculated duty command value D ^* .

  Therefore, by changing the frequency f of the carrier wave to the value of the equation (9) or the equation (13), the carrier frequency f becomes too low, the control cycle of the switching element Tr becomes longer by the PWM signal, and the motor 104 It can suppress that the precision of rotation control of this worsens.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

DESCRIPTION OF SYMBOLS 100 Power supply system 101 Battery 103 Inverter 104 Motor 105 Capacitor 106 Current sensor 109 Gate drive circuit 111 Motor controller 501 Current command value calculation part 504 Duty conversion part 505 PWM signal generation part 509 Carrier frequency calculation part 510 Upper limit modulation rate calculation part

Claims (5)

A power control method for comparing the magnitudes of a duty command value and a carrier wave and generating a PWM signal used for motor control according to the comparison result,
A current measurement step of measuring a current supplied to the motor at a measurement timing at which the magnitude of the carrier wave is maximum or minimum;
A command value calculating step for calculating a duty command value in accordance with the current measured in the current measuring step and the required torque of the motor;
A determination step of determining a magnitude relationship between the duty command value calculated in the command value calculation step and the carrier wave at the time when the duty command value is calculated;
A frequency changing step of changing the frequency of the carrier wave low according to the determination result of the determining step,
A power control method characterized by the above. The power control method according to claim 1,
In the frequency changing step, when changing the frequency of the carrier wave, the frequency of the carrier wave after the change is obtained according to the duty command value.
A power control method characterized by the above. The power control method according to claim 1 or 2,
In the current measurement step, at a measurement timing at which the magnitude of the carrier wave is maximum, the current supplied to the motor is measured,
In the determination step, it is determined whether the duty command value calculated in the command value calculation step is larger than the carrier wave at the time when the duty command value is calculated,
In the frequency changing step, the carrier wave frequency is changed lower as the duty command value increases.
A power control method characterized by the above. The power control method according to claim 1 or 2,
In the current measurement step, at a measurement timing at which the magnitude of the carrier wave is minimized, the current supplied to the motor is measured,
In the determination step, it is determined whether the duty command value calculated in the command value calculation step is smaller than the carrier wave at the time when the duty command value is calculated,
In the frequency changing step, the carrier wave frequency is changed to be lower as the duty command value is smaller.
A power control method characterized by the above. A power control device that compares the magnitudes of a duty command value and a carrier wave and generates a PWM signal used for motor control according to the comparison result,
A current measuring unit for measuring a current supplied to the motor at a measurement timing at which the magnitude of the carrier wave is maximum or minimum;
A command value calculation unit that calculates a duty command value according to the current measured by the current measurement unit and the required torque of the motor;
A determination unit that determines a magnitude relationship between the duty command value calculated by the command value calculation unit and the carrier wave at the time when the duty command value is calculated;
A frequency changing unit that changes the frequency of the carrier wave low according to the determination result of the determining unit,
The power control apparatus characterized by the above-mentioned.

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