JP5354270B2 - Motor control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor control device capable of satisfactorily determining the step-out of an AC motor based on a drive current of the AC motor. <P>SOLUTION: The motor control device includes a basic wave frequency calculating section 10 for calculating the frequency of a basic wave component of a drive current to be supplied to the AC motor 12 from an inverter circuit 5 interposed between the AC motor 12 and a DC power supply to convert an output of the DC power supply into a three-phase AC based on the number of rotations of the AC motor 12, a band-pass filter 7 having a set frequency band for filtering according to the frequency of the basic wave component and filtering the drive current, an integrating section 8 for sectionally integrating the drive current after passing through the band-pass filter 7 over a predetermined period, and a decision unit 9 for determining whether the AC motor 12 is in a step-out state based on results of integration. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a motor control device that drives an AC motor by converting a DC power source into AC.

  A method is known in which the current flowing in the three-phase stator coil of an AC motor, for example, a three-phase synchronous motor, is detected and fed back to control the rotation of the motor. In this control, it is necessary to synchronize the rotational position of the rotor of the three-phase synchronous motor having a permanent magnet with the rotating magnetic field generated by the stator coil. However, when a sudden rotational fluctuation occurs, there is a case where this synchronization is lost, so-called “step-out” occurs. When the step-out occurs, the current of the stator coil is unbalanced, and an overcurrent may flow through the stator coil, which may damage the motor. Therefore, measures such as detecting such step-out early and stopping the motor or restoring synchronization are required. Japanese Patent Laid-Open No. 11-75389 (Patent Document 1) discloses a technique for determining a step-out by comparing a peak value of a current measurement value with a predetermined set value, and self-recovering the synchronization timing (commutation timing). Is disclosed.

JP-A-11-75389 (80th to 82nd paragraphs, etc.)

  In some cases, noise such as switching noise of an inverter that converts a DC power source into AC is superimposed on the current flowing through the stator coil of the motor. For this reason, the peak value of the current measurement value is affected by this noise, and there is a possibility that step-out cannot be accurately determined. Therefore, there is a demand for a motor control device that can suppress the influence of such noise and accurately determine step-out.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a motor control device that can satisfactorily determine the step-out of an AC motor based on the drive current of the AC motor.

The characteristic configuration of the motor control device according to the present invention for achieving the above object is as follows:
A current value acquisition unit for acquiring a detection result of a drive current supplied to the AC motor from an inverter circuit interposed between the AC motor and a DC power source and converting the output of the DC power source into a three-phase AC;
A fundamental frequency calculator that calculates the frequency of the fundamental component of the drive current based on the rotational speed of the AC motor;
A frequency band that is passed according to the frequency of the fundamental component is set, and a bandpass filter that filters the drive current;
An integration unit that integrates the drive current after passing through the bandpass filter over one period of the fundamental wave component ;
And a determination unit that determines whether or not the AC motor is in a step-out state based on the integration result.

According to this characteristic configuration, the noise component contained in the drive current, which is an alternating current flowing in the stator coil of the alternating current motor, is removed by the bandpass filter, and only the fundamental wave component is extracted. Then, the drive current which is substantially only the fundamental wave component is subjected to interval integration over one period of the fundamental wave component, and it is determined whether or not the AC motor is in a step-out state based on the integration result. Therefore, unlike the prior art, the peak value of the drive current is affected by switching noise or the like in the inverter circuit, and the accuracy of the step-out determination is not impaired. That is, according to this feature configuration, it is possible to provide a motor control device that can satisfactorily determine the step-out of the AC motor based on the drive current of the AC motor.

In addition, the determination unit of the motor control device of the present invention causes the AC motor to be out of step when an integration result for one period of the fundamental component of the three-phase driving current exceeds a predetermined set value. It is preferable to determine that the

When the AC motor rotates in synchronization, the three-phase drive current is in an equilibrium state, and the sum total at the moment is ideally zero. For this reason, the result of interval integration for one period of the fundamental wave component of the drive current is ideally equal in three phases. The same applies when integrating over a plurality of periods. The reason why they are ideally equal is that in an actual AC motor, a noise component and an offset component may be included, and they are not always equal. However, when the three phases are in an equilibrium state, almost the same integration result is obtained. Therefore, if the difference between the integration results of the driving currents of the three phases is within a setting range defined by a predetermined setting value, It can be determined that synchronization is obtained. As described above, noise tolerance can be improved by integrating one period of the fundamental wave component of the drive current that has passed through the band-pass filter. Furthermore, since the three-phase balance is accurately determined, the determination unit can satisfactorily determine whether or not the AC motor is in a step-out state.

A block diagram schematically showing a configuration example of a motor control system for driving an AC motor Block diagram schematically showing a configuration example of a motor control device

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram schematically showing the configuration of a motor control system that drives an AC motor. A motor control system that drives a motor 12 that is an AC motor includes an inverter circuit 5 that is interposed between the motor 12 and a DC power supply 20 and converts the output of the DC power supply 20 into a three-phase AC. . The inverter circuit 5 includes a plurality of switching elements. It is preferable to apply an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET) to the switching element. Here, the case where IGBT is used as a switching element is illustrated.

  The inverter circuit 5 is configured by a three-phase bridge circuit. Two IGBTs are connected in series between the input plus side 21 and the input minus side 22 of the inverter circuit 5, and this series circuit is connected in parallel in three lines. That is, a bridge circuit in which a set of series circuits corresponds to each of the stator coils u-phase, v-phase, and w-phase of the motor 12 is configured. In FIG. 1, IGBTs Q5, Q1, and Q3 are upper-stage switching elements corresponding to the u-phase, v-phase, and w-phase, respectively. The IGBTs Q6, Q2, and Q4 are lower-stage switching elements corresponding to the u-phase, the v-phase, and the w-phase, respectively. Note that flywheel diodes (regenerative diodes) are connected in parallel to the IGBTs Q1 to Q6, respectively. The flywheel diodes are connected in parallel such that the cathode terminal is connected to the collector terminal of the IGBT and the anode terminal is connected to the emitter terminal of the IGBT.

  The collectors of IGBTs Q1, Q3, Q5 on the upper side of each phase are connected to the input plus side 21 of the inverter circuit 5, and the emitters are connected to the collectors of IGBTs Q2, Q4, Q6 on the lower side of each phase. Further, the emitters of the IGBTs Q2, Q4, Q6 on the lower side of each phase are connected to the input minus side 22 (ground) of the inverter circuit 5. The intermediate points (IGBT connection points) of the series circuit by the IGBTs (Q5, Q6), (Q3, Q4), (Q1, Q2) of each phase to be paired are the u-phase, v-phase, and w-phase of the motor 12, respectively. It is connected to the stator coils 12u, 12v, 12w, respectively.

  The gates of the IGBTs Q1 to Q6 are connected to an ECU 50 as a control unit via a driver circuit 51, and are individually controlled for switching. The ECU 50 is configured with a logic circuit such as a microcomputer as a core. The ECU 50 corresponds to the motor control device of the present invention. The drive signal input to the gate of the IGBT or MOSFET that switches the high voltage requires a voltage higher than the voltage of a general logic circuit, and therefore is input to the inverter circuit 5 via the driver circuit 51.

  The ECU 50 supplies the motor 12 with a three-phase AC drive current by performing PWM control on the IGBTs Q <b> 1 to Q <b> 6 based on the target torque and the rotational speed for the motor 12. Thereby, the motor 12 powers according to the rotation speed and the target torque. The motor 12 functions as a generator, and the regeneration when the inverter circuit 5 receives power from the motor 12 side is the same as during powering. ECU50 converts IGBTQQ1-Q6 into direct current | flow by carrying out PWM control based on the target torque with respect to the motor 12, and rotation speed. It is also possible to simply rectify using flywheel diodes connected in parallel to the IGBTs Q1 to Q6.

  Further, the ECU 50 performs feedback control based on the rotation speed and the motor current. As shown in FIG. 1, a current sensor that functions as a current detection unit 13 is provided to measure the drive current supplied to the u-phase, v-phase, and w-phase stator coils 12 u, 12 v, and 12 w of the motor 2. It has been. The detected value by the current sensor is received by the ECU 50 and used for feedback control. In this example, a configuration is shown in which the currents of all three phases are measured, but since the three phases are in an equilibrium state and the sum of instantaneous current values is zero, only the currents of the two phases are measured and the ECU 50 The remaining one-phase current may be obtained by calculation.

  Further, the motor 12 is provided with a rotation detection sensor such as a resolver as the rotation detection unit 11, and detects the rotation angle (mechanical angle) of the rotor of the motor 12. The rotation detection sensor functions as the rotation detection unit 11 alone or in cooperation with the ECU 50. The rotation detection sensor is set according to the number of poles (the number of pole pairs) of the rotor, and can convert the rotation angle of the rotor into an electrical angle θ and output a signal corresponding to the electrical angle θ. The ECU 50 calculates the rotational speed (angular velocity ω) of the motor 12 and the control timing of the IGBTs Q1 to Q6 of the inverter circuit 5 based on the rotational angle and the electrical angle θ.

  FIG. 2 is a block diagram schematically showing the configuration of the ECU 50 as the motor control device. In FIG. 2, the components other than the ECU 50 in the motor control system are simply simplified as appropriate. As described above, the ECU 50 is configured with a logic circuit such as a microcomputer as a core. Therefore, each function part of ECU50 does not need to be comprised independently, respectively, and it is sufficient if each function is implement | achieved by cooperation with a program and common hardware. As shown in FIG. 2, the ECU 50 includes a target current setting unit 1, a PI control unit 2, a 2-phase / 3-phase conversion unit 3, a PWM control unit 4, a 3-phase / 2-phase conversion unit 6, a band A pass filter 7, an integration unit 8, a determination unit 9, and a rotation state calculation unit 10 are included.

  As a method of controlling an AC motor, a control method called vector control (field oriented control: FOC) is known. In the vector control, a motor current flowing through the stator coils of the three phases of the AC motor is represented by a vector of a d axis that is a direction of a magnetic field generated by a permanent magnet disposed on the rotor and a q axis that is orthogonal to the d axis. Performs feedback control by converting coordinates to components. This vector control is also adopted in this example.

  The target current setting unit 1 is a functional unit that sets a target current for driving the motor 12. The target current setting unit 1 receives a target torque required for the motor 12 from a control unit different from the ECU 50, for example, an ECU that controls the entire vehicle, and changes the rotational state such as the target torque and the rotational speed of the motor 12 to the target current. Based on this, the target current value is calculated. The rotation state of the motor 12 is detected by the rotation angle detector 11 as described above. The target current value is calculated as a two-phase current of a d-axis current and a q-axis current.

  The PI control unit 2 is a functional unit that performs current control for determining a drive current for driving the motor 12 and determines a drive voltage based on the determined current. The PI control unit 2 is based on the target current set by the target current setting unit 1 and the motor current (drive current) detected by the current detection unit 13 and fed back via the three-phase / two-phase conversion unit 6. Current control is performed to determine the drive current. As the current control method, proportional control (P control) or proportional-integral control (PI control) is generally used. In this example, the case where the proportional-integral control method is used is illustrated, but it is of course possible to use the proportional control method. The motor current is detected by the current detector 13 as described above, and these are actually currents flowing through the three-phase stator coils 12v to 12W. On the other hand, the PI control unit 2 performs current control on the two-phase current of the d-axis current and the q-axis current in the vector space. Therefore, the three-phase current detected by the current detection unit 13 is converted into a two-phase current in the three-phase / two-phase conversion unit 6 and transmitted to the PI control unit 2. The PI control unit 2 calculates by substituting the determined value of the drive current into the voltage equation, and determines the d-axis voltage and the q-axis voltage, which are two-phase drive voltages.

  The two-phase / three-phase conversion unit 3 is configured to cause the two-phase drive voltage of the d-axis voltage and the q-axis voltage calculated by the PI control unit 2 to actually flow the drive current to the three-phase stator coils 12v to 12w. This is a functional unit that converts the driving voltage into a three-phase voltage. The PWM control unit 4 is a functional unit that generates gate drive signals for switching the IGBTs Q1 to Q6 of the inverter circuit 5 so as to generate the three-phase drive voltages determined by the two-phase / three-phase conversion unit 3. is there. The inverter circuit 5 is switching-controlled by the PWM control unit 4, converts the output of the DC power supply 20 into AC, and drives the motor 12.

  In this way, the motor 12 is controlled by detecting the motor current flowing through the three-phase stator coils 12v to 12w of the motor 12 and feeding back this. In this control, it is necessary to synchronize the rotational position of the rotor of the motor 12 having a permanent magnet and the rotating magnetic field generated by the stator coils 12v to 12w. However, when a sudden rotational fluctuation occurs, there is a case where this synchronization is lost, so-called “step-out” occurs. When the step-out occurs, the current balance of the stator coils 12v to 12w may be lost, and an overcurrent may flow through the stator coils 12v to 12w, thereby possibly damaging the motor. Therefore, measures such as detecting such step-out early and stopping the motor or restoring synchronization are required. Therefore, the ECU 50 includes a band-pass filter 7, an integration unit 8, and a determination unit 9 as a synchronization shift (step-out) determination unit.

  The band-pass filter 7 is a functional unit that filters the drive currents of the stator coils 12 u to 12 w detected by the current detection unit 13. The band-pass filter 7 has a characteristic of passing a signal in a frequency band set according to the frequency of the fundamental wave component of the three-phase alternating current that is the drive current of the motor 12. Since the frequency of the fundamental wave component varies depending on the rotation state of the motor 12, the band-pass filter 7 is a target frequency variable filter. The characteristics of the bandpass filter 7 are set according to the frequency of the fundamental wave component calculated by the rotation state calculation unit 10 based on the detection result of the rotation angle detection unit 11. Accordingly, the rotation state calculation unit 10 functions as a fundamental wave frequency calculation unit of the present invention, as will be described later. In this example, the ECU 50 is configured with a microcomputer as a core, and the bandpass filter 7 is a digital filter.

  The fundamental frequency calculation unit (rotation state calculation unit) 10 is a functional unit that calculates the frequency of the fundamental component of the drive current supplied from the inverter circuit 5 to the motor 12 based on the rotational speed of the motor 12. In the present embodiment, the bandpass filter 7 is a digital filter, and a bandpass filter is realized by a filter operation as shown in the following equation (3). The bandpass filter 7 is a variable filter, and a map in the ECU 50 is searched based on the calculation result of the fundamental frequency calculation unit 10 to set parameters for filter calculation. For example, if the rotational speed of the motor 12 is N, the number of pole pairs of the permanent magnet provided in the rotor is Pn, and the resolution of the rotational angle detector 11 (resolver) is X, the frequency W is expressed by the following equation (1). Is required. Then, as shown in the following equation (2), a bandpass map (bandpassMap) is searched based on the obtained frequency W to obtain parameters [a, b].

W = N × Pn × X (1)
[a, b] = bandpassMap (W) (2)

  For example, the bandpass filter 7 is realized by a filter calculation represented by the following formula (3). In Expression (3), i_uf (n), i_vf (n), i_wf (n) indicate three-phase currents after passing through the filter, and i_u (n), i_v (n), i_w (n) indicate the current detector 13. Indicates the current value of the three-phase current detected by n, and n indicates the number of operations of the digital filter (n-th). Parameters [a, b] obtained by searching the bandpass map are coefficients in equation (3) as a [a1, a2] and b [b0, b1, b2].

  The integration unit 8 is a functional unit that integrates the drive current after passing through the bandpass filter 7 over a predetermined period as shown in the following equation (4). In Expression (4), i_uin, i_vin, and i_win indicate interval integration results. The integration interval is determined based on the fundamental wave frequency W, and is set to an integral multiple of the fundamental wave period. The shortest case is one period of the fundamental wave, and in this embodiment, it is set to 3-4 periods. In this embodiment, since digital signal processing is performed, interval integration is realized by integrating i_uf, i_vf, and i_wf calculated in an iterative operation corresponding to the integration interval.

  The determination unit 9 is a functional unit that determines whether or not the motor 12 is in a step-out state based on the integration result. This determination is performed based on, for example, the following formula (5). In Expression (5), A is a threshold value, which is a limit value for determining whether or not the three-phase current is in an equilibrium state.

  Expression (5) is a logical expression, and when one of the first, second, and third terms in parentheses is “true”, the determination result Y on the left side is “true”. Indicates logical OR. The first term, the second term, and the third term are “true” when the subtraction results in parentheses are larger than the reference value A, respectively. In other words, when any of the difference between the u-phase current and the v-phase current, the difference between the v-phase current and the w-phase current, or the difference between the w-phase current and the u-phase current exceeds the limit value A. Becomes true. When any one of the first term, the second term, and the third term is “true”, the determination result Y is “true”, and the three-phase current is not in an equilibrium state.

  When the three-phase current is not in an equilibrium state, the determination of the motor 12 is in a step-out state because the motor 12 is out of synchronization, that is, in a step-out state. The determination result is transmitted to, for example, the target current setting unit 1, the value of the target current is set to zero, and the motor 12 is stopped. Further, the determination result may be output to the outside of the ECU 50 as indicated by a broken line in FIG. Then, a controller other than the ECU 50, for example, an ECU that controls the entire vehicle, may stop the motor 12 by setting the torque target required for the motor 12 to zero.

  Note that when the current flowing through the stator coils 12u to 12w is integrated over a section that is an integral multiple of the period of the fundamental frequency, the integration result is ideally zero. Therefore, the threshold value A is preferably set to a value with a margin with respect to zero. Further, from such characteristics, the determination unit 9 determines whether or not the result of the interval integration of each phase is zero (within the reference value B close to zero) without obtaining the difference of the interval integration results of each phase. It may be determined whether or not the motor 12 is in a step-out state. Further, at this time, even if the result of whether or not the result of the interval integration of each phase is within the reference value B is determined based on the result of the interval integration of any single phase without obtaining a logical sum. Good. When the result of the one-phase piecewise integration indicates a disturbance in the current, it can be determined that the synchronization is shifted because the three-phase equilibrium state is broken.

  As described above, according to the present invention, it is possible to provide a motor control device that can satisfactorily determine the step-out of an AC motor based on the drive current of the AC motor.

5: Inverter circuit 7: Band pass filter 8: Integration unit 9: Determination unit 10: Rotation state calculation unit (fundamental frequency calculation unit)
12: AC motor 20: DC power supply

Claims (2)

The frequency of the fundamental wave component of the drive current supplied to the AC motor from an inverter circuit that is interposed between the AC motor and the DC power source and converts the output of the DC power source into three-phase AC is determined by the rotational speed of the AC motor. A fundamental frequency calculation unit that calculates based on
A frequency band that is passed according to the frequency of the fundamental component is set, and a bandpass filter that filters the drive current;
An integration unit that integrates the drive current after passing through the bandpass filter over one period of the fundamental wave component ;
And a determination unit that determines whether or not the AC motor is in a step-out state based on the integration result. The determination unit determines that the AC motor is in a step-out state when an integration result for one period of the fundamental wave component of the three-phase driving current exceeds a predetermined set value. The motor control apparatus described.

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