JP4705839B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device that can drive an electric motor by switching between PWM drive control and rectangular wave drive control.

  Conventionally, when controlling an AC motor, PWM drive control that allows easy torque control and fine control has been widely used. However, the PWM control has limited use of the voltage of the DC power supply. For this reason, it is not suitable for driving in a high rotation and high torque region. On the other hand, the rectangular wave drive control can apply the maximum voltage of the DC power supply to the electric motor. Further, in the high rotation region, the efficiency is improved as compared with the PWM control that suppresses the voltage of the AC motor by the field weakening control. In addition, the operating range of the AC motor can be expanded.

  By the way, when the AC motor is operated, when PWM drive control or rectangular wave drive control is selected and used, torque fluctuation occurs due to the difference in voltage applied to the motor when switching between the two controls. Patent Documents 1 and 2 are known as techniques for suppressing this torque fluctuation.

Patent Document 1 discloses a motor control device that can reduce torque fluctuations by performing offset adjustment on the current flowing through the AC motor when switching between the PWM drive control and the rectangular wave drive control. In Patent Document 2, when switching between PWM driving and rectangular wave driving control, an intermediate region between PWM driving and rectangular wave driving can be provided, and the torque fluctuation can be reduced by continuously changing the phase and voltage. A motor controller is shown.
Japanese Patent Laid-Open No. 2004-23920 JP-A-11-285288

The motor control device disclosed in Patent Document 1 has a difference between a voltage applied to the AC motor at the time of PWM drive control and a voltage applied to the AC motor at the time of the rectangular wave drive control, and the PWM drive generated by the difference between the applied voltages. An offset at the time of switching between control and rectangular wave drive control is detected, and the inverter is controlled so as to cancel this offset. However, the difference in applied voltage generated at the time of control switching causes a sudden change in current, which causes a sudden change in the torque generated by the AC motor.
When switching from PWM drive control to rectangular wave drive control, the motor control device disclosed in Patent Document 2 performs PWM processing based on a modified sine wave signal having an intermediate phase and amplitude with respect to the voltage waveform before and after the switching, thereby converting the control signal. Assuming that the square wave is a sine wave having an infinite or sufficiently large amplitude, the voltage waveform before switching and the voltage waveform after switching are converted into two sine waves having different phases and amplitudes. I have control. At this time, the rectangular wave drive control is performed using a carrier wave having a constant period, as in the PWM drive control. However, since the phases of the PWM drive control and the rectangular wave drive control are different, a phase delay occurs in the high rotation region in the rectangular wave drive control. In order to prevent this phase lag from occurring, it is necessary to generate a rectangular pulse voltage in accordance with the cycle of the AC motor rotation speed.

  The present invention has been made in view of these problems, and provides a power converter that can prevent a voltage applied to an AC motor from being changed abruptly and prevent torque fluctuations of the AC motor. It is in.

  In order to solve the above problems, the present invention employs the following means.

These include: an inverter that intermittently converts DC power from a DC power source and converts it into AC power and supplies the AC motor; a means for detecting the rotational position of the AC motor; and a means for detecting a current supplied to the motor. And a control circuit that performs on / off control of the switching element that constitutes the inverter based on a command value given from the outside, and the control circuit intermittently switches each half-wave of AC power to a plurality of switching elements. Switching means for switching between PWM drive control for generating a rectangular wave and rectangular wave drive control for generating a single rectangular wave by intermittently switching each half wave of AC power in half-wave units. From PWM drive control to rectangular wave drive When switching to control, the multiplication result of the moving angular velocity (ω1) of the current voltage vector phase (θv1) and the period (Ts) of PWM drive control is used as the current voltage vector. The value added to the phase (θv1) is used as the voltage vector phase (θs1) at the next rectangular wave drive calculation task, and the difference between the current voltage amplitude and the voltage amplitude at the rectangular wave is divided into n equal parts. By using the value added to the amplitude as the amplitude at the next voltage command, the voltage amplitude command value in the rectangular wave drive control is increased in stages for each calculation task performed for each carrier cycle.

  Since this invention is provided with the above structure, it can prevent changing the voltage applied to an alternating current motor rapidly, and can prevent the torque fluctuation of an alternating current motor.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a power conversion device according to the present embodiment. As shown in the figure, the control circuit 2 calculates a voltage to be applied to the AC motor, generates a command signal for on / off control of a switching element (power module) constituting the inverter 7, and uses the generated command signal as a power module drive circuit. Send to 3. The power module drive circuit 3 drives the inverter 7 based on the received command signal to rotationally drive the AC motor 5.

  The three-phase AC current supplied to the AC motor is detected by a current detector and fed back to the control circuit 2. In the figure, 8 is a DC power source for the inverter 7, 6 is a resolver for detecting the rotor position of the AC motor, and 9 is an input command signal from an external controller.

  The arithmetic unit 1 built in the control circuit 2 is configured to generate a voltage command with a current (id) in the magnetic flux direction (d-axis) and a current (iq) in the direction orthogonal to the d-axis (q-axis). To be able to generate Further, the voltage command after the calculation is converted into a PWM (pulse width modulation) signal, and the inverter 7 is driven via the power module drive circuit 3. Note that the arithmetic device 1 uses a carrier wave comparison type PWM generator, and generates a PWM by comparing the carrier wave with the target voltage generated by the arithmetic device.

  Further, the rectangular wave drive control outputs one pulse for each half cycle of the AC motor. For this reason, the amplitude of the output voltage from the inverter 7 is fixed. The output of the AC motor is controlled by changing the phase of the output voltage.

  FIG. 2 is a diagram for explaining a voltage vector phase and a phase interval of the AC motor. The arithmetic device 1 divides the voltage vector applied to the AC motor into six patterns of vectors (1) to (6). The arithmetic unit calculates the phase θv of the voltage vector necessary for generating the required torque, and the phase interval (1) (330 to 30 °), (2) shown in FIG. ) (30-90 °), (3) (90-150 °), (4) (150-210 °), (5) (210-270 °), (6) (270-330 °) .

FIG. 3 is a diagram for explaining the inverter output during the rectangular wave drive control. In FIG.
(A) shows the count value (voltage phase θv) of the counter of the arithmetic unit, (b) shows the phase sections (1) to (6) shown in FIG. 2, and (c) shows the voltage command calculation task (calculation of calculation). (D) shows a carrier wave generated based on the voltage phase θv, (e) shows a U-phase pulse generated based on the carrier wave, and (f) shows a carrier wave generated based on the carrier wave. A generated V-phase pulse (g) indicates a W-phase pulse generated based on the carrier wave.

  For example, as shown in FIG. 3, when the voltage vector phase θv is in the section (3) (90 to 150 °), the arithmetic unit 1 sets the voltage pulse patterns of the U, V, and W phases to Off, On, and Off, respectively. Set. As described above, in rectangular wave driving, it is determined in which phase section the phase of the voltage vector currently exists, and control is performed so as to output a voltage vector corresponding to the existing phase section.

  Here, the period of each phase section is about 1/6 period of the electrical rotation period of the AC motor. In the rectangular wave driving algorithm, the time of each phase interval is used as a PWM carrier wave. Therefore, while the PWM carrier wave period is a specific fixed frequency during PWM drive control, the rectangular wave carrier wave period is changed according to the electrical angular rotation period of the AC motor in the rectangular wave drive, and is about 1/6 of the AC motor period. Let it be a period. The voltage command is updated for each trough of the carrier wave.

  FIG. 4 is a diagram illustrating a drive region of the power conversion device. In AC motor drive control using a power converter, efficiency differs between PWM drive control and rectangular wave drive control. In FIG. 4, the horizontal axis is the rotational speed, and the vertical axis is the torque. The motor can be used in an area surrounded by a solid line. In the high rotation / high torque region 14 surrounded by the dotted line, the counter electromotive voltage of the motor becomes high, and it is necessary to cope with this.

  Here, in the rectangular wave driving, a maximum voltage can be applied in the high rotation / high torque region 14. For this reason, the efficiency is improved as compared with PWM drive control in which field weakening control or the like is performed.

  On the other hand, in the rectangular wave drive control, since the maximum voltage is applied, the efficiency is lowered compared with the PWM control in a high rotation / low torque range. Further, in the rectangular wave drive control, an overcurrent may flow because the switching frequency is low. Therefore, it is desirable to perform the rectangular wave drive control only in the high rotation / high torque region.

  Assuming that an AC motor is installed in an electric vehicle, it is conceivable that the torque command from the electric vehicle control device reciprocates near the switching point between the rectangular wave drive control and the PMW drive control. In such a case, in order to prevent frequent switching, it is desirable to provide hysteresis 15 for switching between the two controls as shown in FIG.

  FIG. 6 is a diagram showing a change in carrier frequency and timing of a calculation task when switching between PWM drive control and rectangular wave drive control, and a switching pulse 23 generated when switching from PWM drive control to rectangular wave drive control. .

  In FIG. 6, before the time t0 is the PWM control region, and is switched to the rectangular wave control region at the time t0. In the rectangular wave drive control, a calculation task is activated for each valley point of the carrier wave, and the voltage pattern calculated by this task is output at the valley point of the next carrier wave. The set voltage pattern has a voltage phase and a voltage amplitude as will be described later.

  As shown in FIG. 6, in the rectangular wave drive control, a calculation task is started for each “valley” of the carrier wave, and the voltage pattern set by this task is output at the next “valley” time of the carrier wave according to the setting of the microcomputer. The The voltage pattern has a voltage phase and a voltage amplitude. The first calculation task (rectangular wave drive calculation task) 17 after control switching divides the difference between the current voltage amplitude and the voltage amplitude at the time of the rectangular wave into n equal parts, adds it to the current voltage amplitude, and the amplitude at the next voltage command. And In the second calculation task 18, the current voltage amplitude and the voltage equally divided by n are added to obtain the voltage vector amplitude at the next voltage command. In the third calculation task 19 to the (n-1) th calculation task, the voltage phase at a phase advanced by one from the current rectangular wave drive control voltage pattern is set.

FIG. 7 is a diagram for explaining the contents of the calculation task. In the first calculation task after switching from PWM drive control to rectangular wave drive control, the task is started at time t1. Next, the moving angular velocity (ω1) of the current voltage vector phase (θv1) is multiplied by the period (Ts) of PWM drive control, and the result (ω1 · Ts) is added to the current voltage vector phase (θv1). The addition result (θv1 + ω1 · Ts) is set as a voltage vector phase (θs1) at the next rectangular wave drive calculation task. Further, the difference between the current voltage amplitude and the voltage amplitude at the time of the rectangular wave is divided into n equal parts, and the result is added to the current voltage amplitude to obtain the amplitude at the next voltage command (step S1).

  In the second calculation task, the task is started at time t2. In the second calculation task, the phase at the time of switching the rectangular wave voltage pattern at a position close to the current phase θs1 is set as the voltage vector phase at the next voltage command. Further, the current voltage amplitude and the voltage divided by n are added to obtain the voltage vector amplitude at the next voltage command (step S2).

  In the calculation task from the third time to the (n-1) th time, a phase advanced by one from the current rectangular wave drive control voltage pattern is set as the voltage phase. Further, a value obtained by adding the current voltage amplitude and the n-divided voltage is set as a voltage vector amplitude at the next voltage command (step S3).

  In the calculation task from the nth time, the voltage command is a voltage command at the time of rectangular wave driving (step Sn). In the above, switching from PWM drive control to rectangular wave drive control has been described. However, switching from rectangular wave drive control to PWM control can be performed in the same manner.

  As described above, according to the present embodiment, the AC motor applied voltage after switching the rectangular wave drive control can be increased stepwise, so that torque fluctuation can be suppressed. In addition, when the power conversion device is applied to an AC motor mounted on an electric vehicle, the movable range of the AC motor can be expanded, and the efficiency or driving ability of the electric vehicle can be increased. In addition, when switching between PWM drive control and rectangular wave drive control in an AC motor of an electric vehicle, a voltage can be gradually applied without causing a phase delay, and therefore torque fluctuations can be prevented. Moreover, the vibration of the vehicle is prevented by preventing the torque fluctuation, and the electric passenger does not feel uncomfortable.

It is a figure explaining the power converter device concerning this embodiment. It is a figure explaining the voltage vector phase and phase area of an AC motor. It is a figure explaining the inverter output at the time of rectangular wave drive control. It is a figure explaining the drive area | region of a power converter device. It is a figure explaining a hysteresis characteristic. It is a figure which shows the change of the carrier frequency at the time of switching of PWM drive control and rectangular wave drive control, and the timing of a calculation task. It is a figure explaining the content of a calculation task.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Arithmetic unit 2 Control circuit 3 Power module drive circuit 4 Three-phase alternating current 5 AC motor 6 Resolver 7 Inverter 8 DC power supply 9 External controller

Claims (2)

An inverter that intermittently converts DC power from a DC power source into AC power and supplies the AC power to the AC motor;
Means for detecting the rotational position of the AC motor and means for detecting the current supplied to the motor, and on / off control of the switching elements constituting the inverter based on these detected values and command values given from the outside Control circuit
The control circuit is configured to generate a plurality of rectangular waves by intermittently switching each half wave of the AC power through the switching element and intermittently splitting each half wave of the AC power in units of half waves to generate a single rectangular wave. Switching means for switching between the rectangular wave drive control to be generated,
When switching from PWM drive control to rectangular wave drive control, the multiplication result of the moving angular velocity (ω1) of the current voltage vector phase (θv1) and the period (Ts) of PWM drive control is added to the current voltage vector phase (θv1). The value is the voltage vector phase (θs1) at the next rectangular wave drive calculation task, and the value obtained by adding the result obtained by dividing the difference between the current voltage amplitude and the voltage amplitude at the rectangular wave into n equal parts is added to the current voltage amplitude next time. A power conversion device characterized in that the voltage amplitude command value in rectangular wave drive control is increased in stages for each calculation task to be performed for each carrier cycle by using the amplitude at the time of voltage command . The power conversion device according to claim 1,
The drive circuit switches from PWM drive control to rectangular wave drive control when the motor is operated at a high rotational speed and high torque.

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