JPH04121092A - Induction motor controller - Google Patents

Abstract

PURPOSE:To obtain a controller which can perform current control through a simple structure with low cost by providing a current command value operating means, means for detecting envelop waveform of the peak value of DC bus current, and a voltage controller for controlling the voltage to be applied on a motor based on the difference between a command value and a detection value. CONSTITUTION:A DC bus current is detected by a current detector 8 and peak held by a peak-hold circuit 18 in order to detect an envelop waveform. The waveform is fed to a differential amplifier 20 where it is differentiated from a DC bus current command value iDC and fed to a current controller 21. The current controller 21 operates a voltage command value according to the control side which is then fed to a PWM signal generator 22. The PWM signal generator determines a voltage to be applied on an induction motor based on the voltage command value and a rotary angle in a rotary coordinates and provides a PWM drive signal to a power transistor module 4. The power transistor module 4 is turned ON/OFF according to a signal fed from the PWM signal generator and applies a voltage on an induction motor 5 thus driving the motor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device for an induction motor, and more particularly to a control device for driving an electric motor while controlling current in order to control the speed or generated torque of the motor. .

[Prior art] Fig. 5 shows a control device for an induction motor described in 1, for example, rAC servo motor and microcomputer system (supervised by Takashi Kenshiro, Sogo Denshi Publishing Co., Ltd.), in which (1) is a power supply, ( 2) is a rectifier, (3) is a smoothing capacitor that smoothes the rectified power supply voltage, and (4) is a power transistor module consisting of 6 power transistors and 6 freewheeling diodes.
(5) is an induction motor.

(6) is a pulse generator that outputs pulses proportional to the rotation speed of the motor, and (7) is an F/V converter (7al,
Speed controller (7bl, V/F converter [7c), OR circuit (7d), counter (7e), adder (7f),
A/D converter [7gl, data ROM (7h) or 71), D/A converter (7ml, multiplication type D/A
This is a current command calculation means consisting of a converter (7n) to 7p). (8a) or 8c) is a current detector that detects the current of each phase of U-V-W, and (9) is a hysteresis comparator (9) that calculates the difference between current command value 11 and detected value i.
a) or 9c).

Voltage control means for controlling the output voltage includes drive circuits (9d) to 9f) for controlling the switching state of the power transistor module (4) according to the outputs of the hysteresis comparators (9a) to 9c).

Detects the bus current of the inverter's smoothing circuit.

A technique for controlling the output by comparing it with a reference value is shown in Fig. 6, for example, in JP-A-1-231666, and Fig. 6 shows an inverter device having a protection function for switch ink elements.
) is a power supply, (2) is a rectifier, and (3) is a smoothing capacitor that smoothes the rectified power supply voltage.

(4) is a power transistor module consisting of six power transistors and six freewheeling diodes; (5)
is an induction motor. (8) is a current detector, f401
is a current detection circuit that amplifies and processes the detected value of the detector (8), (41) is a control circuit that controls the entire inverter, and (42) is a power transistor module (
4) is a gate circuit that drives. Further, the current detection circuit (40) includes an abnormality detection means (81) that generates an abnormality signal when the current value detected here exceeds a predetermined upper limit value.

Next, the operation will be explained. What is the method by which the first conventional control device shown in FIG. 5 controls torque?

It is based on vector control of an induction motor, and its principle is well known in various documents, so a detailed explanation will be omitted and only the operation of this configuration will be explained here.

Induction motor (4) generated by pulse generator (5)
A pulse proportional to the rotational speed (hereinafter referred to as a rotational speed detection signal) is converted into a voltage by an F/V converter (7a). The converted rotation speed signal is.

The difference from the speed command signal is taken and the speed controller (7b) generates a torque current command. This signal is sent to the V/F converter (
7c), the OR circuit (7d) adds it to the rotation speed detection signal, and the counter (7e) counts the rotation angle data θ. bawl.

The output of the speed controller (7b) is converted into digital data by the A/D converter (7g), phase data is obtained via the ROM (7h), and added to the rotation angle data by the adder (7f). − phase θ1 of the current is obtained. A
The /D-converted output of the speed controller (7b) becomes a current amplitude signal via another data ROMf7i) and a D/A converter (7m). The negative current phase θ1 is ROM
(7j) or 71) becomes digital data, and by multiplying it by the current amplitude signal in a 9-multiplying D/A converter (7n) or 7p), the current command 1u for each phase of U, ■, and W, lv + 1w”.

On the other hand, by the current detector (8a) or 8c).

The current of each phase of U, ■, and W is detected, and the voltage control means (9)
controls the output voltage according to the difference between these detected values and the current command value.

That is, the hysteresis comparator (9a) to 9c) compares the current command value, and outputs a logic "1" if the command value is large, and a logic "0" if the detected value is large. The level for determining magnitude has hysteresis depending on the previous logical output state.

When the logic "1" is output, the drive circuit (9d) to 9f) turns on the element of the upper arm of the power transistor module and operates to increase the current value. If logic "0" is output, the lower arm element is turned on and operates to reduce the current value. In this way, the output voltage is controlled so that the detected value matches the command value. This comparison and control of the switch ink state is performed for each phase u"v"w.

Further, the operation of the second conventional example shown in FIG. 6 will be explained. In FIG. 1, when the load is excessive or the load motor is short-circuited for some reason, an excessive current flows through the DC bus.

This current is detected by a current detector (8), and an abnormality detection means (81) determines whether the detected current value exceeds a predetermined upper limit, and if it does not, generates an abnormality signal. Based on this abnormal signal, the gate circuit (42)
The voltage supplied to the power transistor module (4) is lowered or made zero to cut off the power transistor module (4) and protect it from destruction. .

[Problem to be solved by the invention] Since the conventional induction motor control device is configured as described above, three sets of control circuits such as a current detector and a hysteresis comparator are used to control the current of each phase. The configuration is complicated and expensive.

Further, in the second conventional example, the purpose is only to protect switching elements such as power transistors, and control of the current value itself is not considered.

This invention was made to solve the above-mentioned problems, and it is possible to perform current control for controlling the torque of an induction motor with a simple structure and at low cost while protecting switching elements such as power transistors. The purpose is to obtain a control device.

[Means for Solving the Problems] An induction motor control device according to the present invention includes a current command value calculating means, a DC bus current peak value envelope waveform detecting means, and a current command value calculating means, a DC bus current peak value envelope waveform detecting means, and a control device according to the difference between the command value and the detected value. This device consists of a voltage control device that controls the power applied to the motor.

[Operation 1] The control device for an induction motor according to the present invention calculates a command value of an envelope waveform of a peak value of a DC bus current from a rotation speed detected or estimated by a means for detecting or estimating the rotation speed of an induction motor.

The envelope waveform of the detected peak value of the DC bus current is made to match the command value according to the difference between the detected value detected by the means for detecting the envelope waveform of the peak value of the DC bus current and the command value. (Since the output voltage applied to the motor is controlled, current control and even torque control can be performed with only one current detector, improving control responsiveness of speed or generated torque, and comparators for three phases can also be used.) Since this is not necessary, it is possible to simplify the single circuit configuration and reduce costs.

In addition, if the detected DC bus current exceeds a predetermined maximum current value, the voltage output to the motor is controlled to be cut off, so the switching element can be protected even if an accident such as a load short circuit occurs.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In the figure, (1) to (5) are the same as the conventional one.

(6) is a tacho generator that outputs a voltage proportional to the rotation speed of the induction motor (5), and (7) inputs the rotation speed command value ωm8 given from the outside and the rotation speed signal from the tacho generator (6). A first difference is calculated by using a current command value calculation means that calculates an envelope waveform command value of the peak value of the DC bus current to calculate the difference between the 1 rotation speed command value ωm1 and the rotation speed detection value detected by the tacho generator (6). a dynamic amplifier (lO), a speed detector (11) that inputs the signal from this first differential amplifier and calculates a torque command value, and a first function generator (12) that calculates a slip frequency from the torque command value. and an adder (14) that adds the calculated value of the first function generator and the detected value of the tacho generator (6) to obtain a primary frequency.

An integrator (15) that integrates the primary frequency of the adder to obtain the rotation angle of the coordinate system, and a variable torque command value calculated by a second function generator (13) based on the rotation angle of this integrator. and a multiplier (16) that multiplies the torque command value calculated by the speed detector (11).

(19) is a DC bus current peak value envelope waveform detection means, which includes a current detector (8) which is a sensor for detecting the DC bus current, an operational amplifier f31) that receives input, and an output terminal of the operational amplifier (31). The peak hold circuit (1) is composed of a diode (321) connected to the capacitor (33) connected between the cathode of the diode (32) and GND, and a resistor (34) connected in parallel with the capacitor (33).
8) Consists of.

(20) is a second differential amplifier which calculates and outputs the difference between the command values of the current command value calculation means (7) and the peak value envelope waveform detection means (19).

(23) is a comparator that compares the output of the peak value envelope waveform detection means (19) with the maximum current value preset by resistor [24] and resistor 2 (25).

A cutoff signal is being output.

(9) is a current controller (21) and a PWM signal generator (22).
A voltage control device consisting of
The output of the differential amplifier (20) is input to the PWM signal generation fan, and the output of the comparator (23) and the integrator (15) of the current command value calculation means (7) are input.

Next, the operation will be explained. As the induction machine (5) rotates, the tachogenerator (6) outputs a voltage proportional to the zero rotation speed of the induction machine (5), which is hereinafter referred to as a rotation speed detection signal.

The rotation speed detection signal is obtained by calculating the difference between it and the rotation speed command value given externally by a differential amplifier (flO), and then using a speed detector (ill).
is input. The speed detector (11) calculates a torque command value based on the difference between the one rotation j detection signal and the rotation speed command value. The function generator (12) calculates the slip frequency from this torque command value, and adds it to the rotation speed detection signal in the adder (14), thereby obtaining the -th layer wave number.

The primary frequency is integrated by an integrator (15) and becomes the rotation angle of a one-rotation barrel system. Based on this rotation angle, the Kansha generator (1
3) calculates the variation of the torque command value.

By multiplying this and the torque command value by a multiplier (16), a direct current command value iDe'' is obtained.

On the other hand, the DC bus current is detected by a current detector (8),
A peak hold circuit (18) holds the peak, and the envelope waveform is detected.

The difference between this waveform and the DC bus current command value i be is calculated by the differential amplifier (20) and input to the current controller (21).The current controller (21) calculates the voltage command value according to the control side. is calculated and given to the PWM signal generator (22).

The PWM signal generator determines the voltage to be applied to the induction machine from the voltage command value and the rotation angle of the rotation coordinate.

A PWM modulated drive signal is provided to the power transistor module (4). The power transistor module (4) turns on and off according to the signal given from the PWM signal generator, applies voltage to the induction machine (5), and drives the motor.

When the peak-held current value is larger than the predetermined maximum current value, the comparator (23) generates a cutoff signal, and the PWM signal generator (22) generates a cutoff signal based on the cutoff signal, and the PWM signal generator (22) outputs the power transistor module (4).
) are all turned off to prevent the current from increasing further and destroying the device.

Here, looking at the relationship between the envelope waveform of the peak value of the motor current and the DC A-line current, if the motor does not have a neutral point, the motor current of each phase satisfies the relationship + lu" lv + iw = O. That is, the sum of phase currents including polarity is zero, and the sum of positive polarity currents and the sum of negative polarity currents are equal.

As shown in Figure 3, when the phase current is not circulating through the diode of the power transistor (4), the bus current flows through either phase of the upper arm of the power transistor (4), and the bus current flows through the positive terminal of the motor. The negative phase current passes through the motor windings, becomes the negative phase current of the remaining phases, and returns to the negative side of the 8 wires through the lower arm of the power transistor (4).

Therefore, at this time, the sum of the positive polarity and negative polarity of the motor phase currents becomes the bus current, and since voltage is applied, the current has an increasing waveform, and the peak value occurs during this period. . When the phase current is circulating, the current flows only between the motor and the power transistor and is not reflected in the q-line current, but since no voltage is applied, the current has a decreasing waveform and the peak value is It does not affect. Therefore, since the peak value of the a-line current represents the sum of positive or negative polarity currents among the phase currents, the phase currents can be controlled by controlling this. Here, if the voltage is controlled symmetrically in three phases, each voltage waveform will be as follows. If the load is symmetrical.

Since the current waveform delayed by the power factor angle α is as follows, if the voltage is controlled symmetrically when controlling the a-line current, the bus current will be distributed symmetrically to each phase. The bus current command value is 1. For example, in the fb1 formula, 0≦0 (=ω・−α
)≦-π, the sum of positive polarity currents is I all = Bsin (θ+-π), as can be seen from Figure 4, and the amplitude B is a function of the torque command value 7 The phase is a function of θ, so , θ is obtained by multiplying the output of the speed controller (11) which is the output torque command value of the function generator (13) using human power.

[Effects of the Invention] As described above, the induction motor control device according to the present invention includes a current command value calculation means for calculating the command value of the DC bus current from the rotation speed, and detects the envelope waveform of the peak value of the DC bus current. and a means for controlling an output voltage applied to the motor according to the difference between the command value and the detected value, and a means for controlling the output voltage to match the detected direct current bus current with the command value. II to control the voltage and to cut off the voltage output to the motor if the detected DC bus current exceeds a predetermined maximum current value.
I (In general, it is possible to obtain a control device that can perform current control for controlling the torque of an induction motor with a simple configuration and at low cost while protecting switching elements such as power transistors.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a control device for an induction motor according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of the peak hold circuit shown in FIG. 1, and FIG. FIG. 4 is a diagram showing the relationship between the peak values; FIG. 4 is a diagram showing the relationship between the motor voltage/current waveform and the envelope waveform of the peak value of the phase current; FIG. 5 is a block diagram showing a conventional induction motor control device. FIG. 6 shows another conventional inverter device having a switching element protection function. (7) is a current command value calculation means, (9) is a voltage control device,
(191 is DC bus current peak value envelope waveform detection means. In Figure 1, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] By controlling the switching of a switching element with a three-phase full bridge configuration connected to a DC power source, a three-phase induction motor without a neutral point can be operated with its speed or generated torque as a command value. In a control device that drives while controlling to match, a current command value calculation means for calculating an envelope waveform command value of a peak value of a DC bus current, and a DC bus current for detecting an envelope waveform of a peak value of a DC bus current. peak envelope waveform detection means, and a voltage control device that controls output power applied to the motor according to the difference between the command value of the current command value calculation means and the detected value of the DC bus current peak value envelope waveform detection means. A control device for an induction motor.