JP2005020919A - Controller for electric motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for an electric motor which can suppress a surge voltage during the PAM control without causing the increase of a switching loss of the PWM control when the electric motor is controlled by using the PAM control and the PWM control together. <P>SOLUTION: The controller 11 executes the PAM control during high torque driving of the electric motor M and the PWM control during low torque driving. The controller 11 is provided with an inverter part 13, which converts a DC voltage outputted from a step-up chopper circuit 12 to an AC voltage, and a switching means which delays a switching speed of switching elements SW1-SW6 at the inverter part 13 during the high torque driving of the electric motor M compared with during the low torque driving. Two resistors R1, R2 are connected in series to a gate of each switching element SW1-SW6. And at the same time, a switch S is connected in parallel to one resistor R1. The switching speed of the switching elements SW1-SW6 is changed by turning on/off the switch S. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motor control device, and more particularly to a motor control device that performs PAM control during high torque driving and performs PWM control during low torque driving.
[0002]
[Prior art]
Conventionally, in an inverter device that drives a motor at a variable speed, the motor is generally driven by a rectangular wave that is energized at 120 degrees, and the control is performed by adjusting the voltage by a PWM method (pulse width modulation method) or in the inverter device. This is implemented by adjusting the output voltage of a converter device that supplies a DC power supply.
[0003]
Further, two controls are performed such that the motor is controlled by PAM control (pulse amplitude modulation control) in the high speed (high torque) region, and the motor is controlled by PWM control (pulse width modulation control) in the low speed (low torque) region. An electric motor control device for switching modes has been proposed (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 63-224698 (2, 3 tributes, FIG. 1)
[0005]
[Problems to be solved by the invention]
However, when the switching element of the inverter device is turned off, a surge voltage is generated in the element current path. There is no problem because the input voltage is low when the motor is at low torque, but when the torque is high, the surge voltage is superimposed on the boosted input voltage, so the maximum rating of the switching element needs to be increased. Moreover, in order to suppress the surge voltage, it is necessary to suppress the switching speed. However, if the switching speed is suppressed, the switching loss increases.
[0006]
The present invention has been made in order to solve the above-described problems. The object of the present invention is to control the motor by using both the PAM control and the PWM control, and at the time of the PAM control without increasing the switching loss of the PWM control. An object of the present invention is to provide an electric motor control device capable of suppressing a surge voltage.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is a motor control device that performs PAM control when the motor is driven at high torque and performs PWM control when the motor is driven at low torque. And a converter unit capable of outputting a DC voltage by changing the voltage, an inverter unit for converting the DC voltage to an AC voltage and outputting the AC voltage, and a switching speed of the switching element of the inverter unit when the motor is driven at a high torque. Switching means for making the operation slower than during low torque driving.
[0008]
In the present invention, the motor is driven by PWM control during low torque driving, and the motor is driven by PAM control during high torque driving. In the PAM control to which a high voltage is applied, the switching speed of the switching element of the inverter unit is slower than that at the time of low torque driving, so that the surge voltage can be suppressed as compared with the case where the switching speed is the same as that at the time of PWM control. Therefore, the rating of the switching element can be reduced.
[0009]
According to a second aspect of the present invention, in the first aspect of the invention, when the electric motor is driven at a high torque, the switching frequency of the switching element is lowered than when the electric motor is driven at a low torque. Accordingly, in the present invention, the number of times of switching per unit time is reduced, so that the amount of heat generated by the switching element per unit time is reduced.
[0010]
According to a third aspect of the present invention, in the first or second aspect of the invention, a plurality of resistors are connected in series to the control terminal of the switching element, and some of the plurality of resistors are connected. A switch is connected in parallel with the resistor. The switching speed of the switching element is changed by turning on and off the switch. That is, the switching speed increases when the switch is on, and the switching speed decreases when the switch is off. Therefore, in the present invention, the occurrence of surge voltage can be suppressed by delaying the switching speed of the switching element of the inverter unit with a simple structure.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment in which the present invention is embodied in drive control of an electric motor of an electric vehicle will be described with reference to FIG. FIG. 1 is a circuit diagram of a motor control device 11.
[0012]
As shown in FIG. 1, the motor control device 11 includes a step-up chopper circuit 12 as a converter unit, an inverter unit 13, a control circuit 14, a drive circuit 15, and switching means described later. The step-up chopper circuit 12 is connected to a power source (DC power source in this embodiment) 16.
[0013]
The step-up chopper circuit 12 includes a reactor 12a, a MOS transistor 12b, a diode 12c, and a capacitor 12d. The gate of the MOS transistor 12b is connected to the drive circuit 15. On / off of the MOS transistor 12b is controlled by the drive circuit 15, and the boost chopper circuit 12 functions to boost the DC voltage input from the power supply 16.
[0014]
The inverter unit 13 includes six switching elements SW1 to SW6 made of MOSFETs and six diodes D1 to D6. Two switching elements SW1 and SW2 are connected in series, and diodes D1 and D2 are connected in parallel to the switching elements SW1 and SW2, respectively. A junction point between both switching elements SW1 and SW2 is connected to a U-phase terminal of the electric motor M. Two switching elements SW3 and SW4 are connected in series, and diodes D3 and D4 are connected in parallel to the switching elements SW3 and SW4, respectively. A junction point between the switching elements SW3 and SW4 is connected to a V-phase terminal of the electric motor M. Further, two switching elements SW5 and SW6 are connected in series, and diodes D5 and D6 are connected in parallel to the switching elements SW5 and SW6, respectively. A junction point between the switching elements SW5 and SW6 is connected to a W-phase terminal of the electric motor M. Each of the diodes D1 to D6 has a cathode connected to the drains of the switching elements SW1 to SW6 and an anode connected to the sources of the switching elements SW1 to SW6.
[0015]
Gates as control terminals of the switching elements SW <b> 1 to SW <b> 6 are connected to the drive circuit 15. The drive circuit 15 is connected to the control circuit 14, and the inverter circuit 13 controls the switching elements SW1 to SW6 to be turned on / off based on a control signal from the control circuit 14, whereby the inverter unit 13 generates a DC voltage at an appropriate frequency. Is converted into a three-phase alternating current and output to the motor M.
[0016]
The control circuit 14 includes a CPU and a memory (both not shown), and various control programs necessary for driving the electric motor M are stored in the memory. The control program has two control modes: a low torque drive mode for controlling the electric motor in a low speed (low torque) region and a high torque drive mode for controlling the electric motor in a high speed (high torque) region. Then, the two control modes are switched according to the load state of the electric motor M. In the low torque drive mode, the motor M is controlled by PWM control (pulse width modulation control). In the high torque drive mode, the motor is controlled by PAM control (pulse amplitude modulation control). During PAM control, the boost chopper circuit 12 boosts the input voltage to the inverter unit 13 from during PWM control. During PWM control, the DC voltage of the power supply 16 is supplied to the inverter unit 13 without being boosted.
[0017]
Each of the switching elements SW1 to SW6 has a plurality of (two in this embodiment) resistors R1 and R2 connected in series to the gate, and a part (one in this embodiment) of the resistor R1 is connected to a switch S (relay). Are connected in parallel.
[0018]
The control circuit 14 compares the value of the rotational speed command value 17 from a vehicle main control device (not shown) with the control switching threshold value stored in the memory, and the rotational speed command value 17 is less than or equal to the control switching threshold value. A comparator 18 that outputs an H (high) signal that turns on the switch S is sometimes provided as a program. That is, each switch S is connected to the output terminal of the comparator 18 in an equivalent circuit. The control switching threshold varies depending on voltage characteristics required when the electric motor M is driven, and is determined, for example, by performing a test in advance. The resistors R1 and R2, the switch S, and the comparator 18 constitute a switching unit that slows the switching speed of the switching elements SW1 to SW6 of the inverter unit 13 when the motor M is driven at high torque than when the motor M is driven at low torque.
[0019]
Next, the operation of the control device 11 configured as described above will be described.
The control circuit 14 receives a rotational speed command signal output from a main controller (not shown), and outputs a command signal for controlling driving of the electric motor M at a predetermined rotational speed to the drive circuit 15 based on the command signal. .
[0020]
In this embodiment, when the torque required to drive the electric motor M is equal to or higher than a predetermined torque, and in the case where the rotational speed command value 17 is equal to or higher than the control switching threshold, the electric motor M is in the high torque drive mode, that is, PAM. Controlled by control. Further, when the torque is less than the predetermined torque, in this embodiment, when the rotation speed command value 17 is less than the control switching threshold, the electric motor M is controlled in the low torque drive mode, that is, PWM control. Then, an AC voltage corresponding to the rotation speed is supplied to the electric motor M.
[0021]
In the PWM control, boosting is not performed by the boosting chopper circuit 12, and a DC voltage is supplied to the inverter unit 13 while keeping the voltage of the power supply 16. Then, the switching elements SW1 to SW6 are PWM-controlled, and an alternating current having a frequency corresponding to the rotation speed to be controlled is output from the inverter unit 13. In order to rotate the electric motor M accurately at a low speed, it is necessary to increase the carrier frequency (switching frequency). However, if the frequency is increased too much, the switching loss per unit time increases. Are set to have a high frequency.
[0022]
In the PAM control, boosting is performed by the boosting chopper circuit 12, and the voltage of the power supply 16 is boosted to a predetermined voltage corresponding to the load of the electric motor M, and then supplied to the inverter unit 13. Then, each of the switching elements SW1 to SW6 is switched at a predetermined frequency. At this time, in order to suppress switching loss, the switching frequency is changed to be lower than that during low torque driving.
[0023]
On the other hand, the comparator 18 compares the rotational speed command value 17 with the control switching threshold value. When the rotational speed command value 17 is less than the control switching threshold value, the comparator 18 sends a signal for turning on each switch S. Is output. When each switch S is turned on, the gate resistance becomes smaller than when the switch S is in the off state, and the switching speed is increased, so that the switching loss is suppressed.
[0024]
Further, the comparator 18 compares the rotational speed command value 17 with the control switching threshold value. When the rotational speed command value 17 is equal to or larger than the control switching threshold value, the comparator 18 sends a signal for turning off each switch S. Is output. When each switch S is turned off, the gate resistance becomes larger than when the switch S is in the on state, and the switching speed becomes slow. Accordingly, the rise and fall of the voltage are delayed and the surge voltage is suppressed.
[0025]
The present embodiment has the following effects.
(1) At the time of high torque driving, the electric motor M is driven by PAM control, and the switching speed of the switching elements SW1 to SW6 of the inverter unit 13 is slower than that at the time of low torque driving, so that surge voltage can be suppressed. Therefore, the rating of the switching elements SW1 to SW6 can be reduced.
[0026]
(2) When driving at high torque, the switching frequency of the switching elements SW1 to SW6 is lowered compared to driving at low torque, so the number of switchings per unit time is reduced and the amount of heat generated by the switching elements SW1 to SW6 per unit time is reduced. it can.
[0027]
(3) Two resistors R1 and R2 are connected in series to the gates of the switching elements SW1 to SW6, and a switch S is connected in parallel to one resistor R1. Thus, the switching speed of the switching elements SW1 to SW6 is changed. That is, since the gate resistance of the switching elements SW1 to SW6 can be switched by turning on and off the switch S, the switching speed of the switching elements SW1 to SW6 of the inverter unit 13 is delayed by a simple structure to generate a surge voltage. Can be suppressed.
[0028]
(4) Since the comparator 18 that outputs an on / off signal to the switch S constituting the switching means is configured in software by the CPU control program, it is easy to change the control switching threshold according to the driving conditions. is there.
[0029]
(5) At the time of low torque driving, the switching speed of the switching elements SW1 to SW6 of the inverter unit 13 does not become slow, so that switching loss can be suppressed. (Second embodiment)
Next, a second embodiment will be described with reference to FIG. The first embodiment is that the comparator 20 is provided as a circuit (dedicated circuit) separate from the control circuit 14 instead of incorporating the comparator 18 constituting the switching means into the control circuit 14 by software. This is very different from the embodiment. The same parts as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0030]
As shown in FIG. 2, two resistors R <b> 3 and R <b> 4 are connected in series with the inverter unit 13 on the output side of the boost chopper circuit 12. The connection point of the resistors R3 and R4 is connected to the inverting input terminal of the comparator 20. An input voltage threshold value to the inverter unit 13 is input to the non-inverting input terminal of the comparator 20 as a control switching threshold value. That is, the comparator 20 compares the voltage corresponding to the input voltage to the inverter unit 13 detected by the two resistors R3 and R4 with the input voltage threshold value, and outputs an ON / OFF signal of the switch S.
[0031]
When the voltage corresponding to the input voltage of the inverter unit 13 is less than the input voltage threshold, the comparator 20 outputs a signal for turning on each switch S. When the voltage corresponding to the input voltage of the inverter unit 13 is equal to or higher than the input voltage threshold, the comparator 20 outputs a signal for turning off each switch S. The gate resistance changes corresponding to the on and off states of each switch S, and the same operations and effects as in the first embodiment are exhibited.
[0032]
Therefore, according to the second embodiment, in addition to the same effects as (1) to (3) and (5) of the first embodiment, the following effects are obtained.
(6) The comparator 20 is provided as a separate circuit from the control circuit 14. Therefore, the switching speed of the switching elements SW1 to SW6 of the inverter unit 13 can be switched without imposing a load on the CPU of the control circuit 14.
[0033]
The embodiment is not limited to the above, and can be implemented with appropriate modifications as follows, for example.
○ There are two types of drive modes. For example, two or more control switching thresholds are set, the number of resistors connected to the gate and the number of switches connected in parallel to the resistors are increased, and the switching speed operation mode is set to the high torque drive mode, the medium torque drive mode, and the low The number of torque drive modes may be increased to three.
[0034]
The switching elements SW1 to SW6 are not limited to MOSFETs but may be IGBTs or bipolar transistors. In the case of a bipolar transistor, the base is the control terminal.
[0035]
The electric motor M is not limited to an electric vehicle, and may be an electric motor driven by an inverter. For example, an electric motor for a machine tool or an electric motor of a compressor may be used.
In the second embodiment, the signal to be compared by the comparator 20 is not limited to the voltage corresponding to the input voltage of the inverter unit 13 but may be a signal corresponding to the temperature of the switching elements SW1 to SW6, for example. In this case, a sensor for detecting the temperature of the switching elements SW1 to SW6 is provided, and the detection signal is input to the inverting input terminal of the comparator 20, and a predetermined control threshold voltage is input to the non-inverting input terminal. The predetermined control threshold voltage is set based on, for example, a value corresponding to the temperature of SW1 to SW6 during high torque driving obtained in advance by a test.
[0036]
In the second embodiment, the control switching threshold value may be a fixed predetermined voltage or changeable. For example, when the temperature change of the operating environment of the electric motor M is large, the control switching threshold value may be changed depending on the temperature of the environment.
[0037]
○ The switching speed may be decreased only when the switching elements SW1 to SW6 are turned off. For example, the on / off control of the switch S is performed in synchronization with the switching off timing.
[0038]
The boost chopper circuit 12 may be configured to output a predetermined voltage higher than that of the power supply 16 during PWM control.
O Instead of inputting the rotational speed command value 17 to the comparator 18, it is possible to detect the rotational speed of the electric motor M and input the value.
[0039]
The converter unit is not limited to the boost chopper circuit 12 that boosts the voltage of the DC power supply, but may be a conversion device that has both the action of converting the alternating current of the AC power supply into direct current and the boosting action.
[0040]
As switching means for switching the switching speed of each of the switching elements SW1 to SW6, it is possible to supply two power sources with different voltages to the control terminal and change the switching speed by switching the supply source. .
[0041]
The following technical idea (invention) can be understood from the embodiment.
(1) In the invention according to any one of claims 1 to 3, during the high torque driving, the switching speed of the switching element is switched so as to be slow at least when the switching element is turned off. It is done.
[0042]
(2) In the invention according to any one of claims 1 to 3 and the technical idea (1), the control terminal of each switching element can be supplied with two systems of power having different voltages. The switching speed can be changed by switching the supply source.
[0043]
(3) In the invention according to any one of claims 1 to 3 and the technical ideas (1) and (2), an environmental temperature of the electric motor is added as a condition for switching the switching speed. .
[0044]
【The invention's effect】
As described above in detail, according to the first to third aspects of the invention, when the electric motor is controlled by using both the PAM control and the PWM control, the surge voltage does not increase the switching loss of the PWM control. Can be suppressed.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a control device according to a first embodiment. FIG. 2 is a circuit diagram of a control device according to a second embodiment.
DESCRIPTION OF SYMBOLS 11 ... Control apparatus, 12 ... Boost chopper circuit as converter part, 13 ... Inverter part, 16 ... Power supply, 18 ... Comparator which comprises a switching means, 20 ... Similarly comparator, M ... Electric motor, SW1-SW6 ... Switching element , R1, R2... Resistors constituting the switching means, S.

Claims (3)

In the motor control device that performs PAM control when the motor is driven at high torque and performs PWM control when the motor is driven at low torque,
A converter unit that can output a DC voltage by changing a voltage, an inverter unit that converts the DC voltage into an AC voltage, and outputs the AC voltage. When the motor is driven at a high torque, the switching speed of the switching element of the inverter unit is set to a low torque. An electric motor control device comprising switching means for making the operation slower than that during driving. The motor control device according to claim 1, wherein when the electric motor is driven at a high torque, the switching frequency of the switching element is lowered than when the electric motor is driven at a low torque. A plurality of resistors are connected in series to the control terminal of the switching element, and a switch is connected in parallel to some of the plurality of resistors. The motor control device according to claim 1 or 2, wherein the switching speed is changed.

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