JPS602880B2 - AC motor control method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling an AC motor.

When performing variable distance operation of an AC motor with a voltage type inverter, generally V/F (inverter output voltage/frequency)
Perform constant control.

Currently, automatic voltage control is being developed that combines a microcomputer and an analog circuit (conventional automatic voltage control circuit) to perform stable V/F constant control even when the AC input voltage (receiving voltage) of a voltage source inverter drops. A circuit can be considered.

A problem with automatic voltage control circuits is the phenomenon in which the output voltage of the voltage source inverter transiently rises when the receiving voltage drops and when the voltage is switched off.

When the receiving voltage drops, the output voltage (DC voltage) of the forward converter also drops, so in order to control the inverter output voltage to be constant, the deviation signal between the voltage setting value and the detected value of the inverter output pressure is amplified. The output of the integrating voltage amplifier that supplies V to the pulse width control circuit for controlling the inverter increases, and the input (voltage coefficient) of the pulse width control circuit increases. The function of this voltage amplifier enables constant voltage control during a power outage (power receiving voltage drop). However, when the received voltage returns to a normal value, the voltage coefficient is larger than the normal value, so a phenomenon occurs in which the output voltage jumps transiently. The present invention solves these problems and provides constant voltage control for the AC motor when the AC input voltage to the voltage source inverter drops, and prevents the inverter output voltage from transiently rising to an overvoltage level when the power is restored. The purpose of this paper is to provide a method for controlling an AC motor according to the following, and will be explained below using examples.

FIG. 1 shows an embodiment of the control method for an AC motor according to the present invention. The electrolytic capacitor 3 connected in parallel between the two is an inverter to which the output of the converter 1 is normally supplied, and here the switching element of the inverter 3 is constituted by a transistor.

Further, 4 is an AC motor (synchronous motor or induction motor) to which the output of the inverter 3 is supplied, 5 is a transformer for detecting the output voltage of the inverter 3, and 6 is a DC motor that rectifies the output of the transformer 5. A rectifier 7 takes out the voltage Vda, and a transformer 7 detects the receiving voltage (three-phase AC input voltage) on the input side of the forward converter 1.The output of the transformer 7 is rectified by the rectifier 8 and sent to the input/output port (1' 9 (referred to as the 0 boat). 10 is the central processing unit of the microcomputer (C
11 is a memory built into the microcomputer, 12 is a digital-to-analog converter (referred to as a D/A converter), and 13 is a voltage obtained by converting the voltage set based on the CPUIO command. Voltage setting value VS
A matching circuit that matches the output voltage detection value Vdct and the output voltage detection value Vdct to extract a deviation signal, 14 is an integral voltage amplifier equipped with an output voltage suppression function (limiter function), and this crab pressure amplifier 14a, A variable resistor 14b and a capacitor 1 are connected in parallel between both ends of the voltage amplifier 4a.
It consists of a series body 4c and a contact (b contact) 14d connected in parallel with this series body.

15 is the cushion setting voltage value +Vc and the cushion circuit 1
The output of this matching circuit 15 is supplied to a cushion circuit 16.

This cushion circuit i6' sends an output having the time t vs. voltage V characteristic shown in the block to the limiter circuit 17 based on the input signal. 18 is a capacitor connected in parallel between the input and output terminals of the cushion circuit 16 ~ 1
g' is connected in parallel with capacitor 8 - contact (b
``Relay contacts 1 and 19' are B contacts of the same relay.

The output voltage suppression value of the voltage amplifier 14a is determined by the limiter circuit 17.
is determined based on the output of 2 Kawama integrating amplifier 1
4 is an analog-to-digital converter (referred to as an A/D converter) for converting the output from analog to digital; 28 is a switching circuit that performs switching by software processing that depends on the CPU; The output (voltage coefficient) of the A-node converter 28 is stored in all the computer memories based on the commands from the CPUIO of the microcomputer, and is also stored in memory 1 based on the commands from the CPUIQ of the microcomputer. The voltage coefficient is taken out and supplied to the pulse width control circuit 22.
The output (voltage coefficient) of the converter 2 is connected to the pulse width control circuit 22.
Switching can be performed freely by software processing depending on the CPU amount W so that the power can be supplied to the CPU.

Reference numeral 22 denotes a pulse width control circuit, and the pulse width control circuit 22 has a built-in ROM (read only memory) in which triangular wave and sine wave data are stored.

A frequency setting signal is supplied to this pulse width control circuit 22 based on a command from the CPUIO.This frequency setting signal can also be used to change the sampling time of the address in the ROM, and also to adjust the input fin pressure. The amplitude of the triangular wave or sine wave can also be changed using the coefficient.The pulse width control circuit 22 compares the intersection points of the triangular wave and the sine wave using a comparator, and when the sine wave is larger than the triangular wave, it is determined that the signal corresponds to the gate-on signal. A logic "1" is sent out, and when the sine wave is smaller than a triangular wave, a logic "0" corresponding to a gate off signal is sent out.These logic "1" or "0" control signals are sent from the pulse width control circuit 22. The signals are sent to the gate circuit of the inverter 3, and the gate circuit controls the pulse width of the inverter 3 based on these control signals. 23 and 24 are wire disconnectors.

The automatic voltage controller AVR (analog processing part) includes transformers 5 and 7, rectifiers 6 and 8, and matching circuits 13 and 15.
and integrating voltage amplifier 14, cushion circuit 16, Mitsuta circuit 17, capacitor 18, IJ relay contact 19, and A/
It consists of a D converter 20 and the like. The operation of such a configuration will be explained using FIG. 2.

Now, when the inverter device operation command is input, relay contact 1
4d, 19 are turned off.

At startup, a cushion setting signal is applied to the matching circuit 15, the cushion circuit 16 is operated by the output of the matching circuit 15, and the output of the cushion circuit 16 shown in the block is input to the limiter circuit 17.
The output voltage suppression value of the limiter-equipped pressure amplifier 14a is continuously changed based on the output. On the other hand, the detected value Vdd of the output voltage of the inverse converter 3 is coupled to the matching circuit 13, and the input voltage (receiving voltage) to the forward converter 1 is connected to the rectifier 8.
The detection voltage obtained by rectification is sent to the 1/0 port 9, and the output corresponding to the input from the 1/0 port 9 is sent to the CPU.
It is sent to IO and used as data for determining power outage and power restoration.

Based on a command from the CPUIO, a set voltage Vs corresponding to the output frequency supplied via the D/A converter 12 (so that the V/F is constant) is supplied to the matching circuit 13. This matching circuit 13 supplies a deviation signal between the voltage setting value Vs and the voltage detection value Vdet to the integrating voltage amplifier 14. The output of the integrating voltage amplifier 14 is a voltage coefficient that matches the set voltage VS and the detected voltage Vdet, and is converted by the A/D converter 20 and supplied to the pulse width control circuit 22. In this case, the output of the integrating voltage amplifier 14 is determined based on the output voltage suppression value on the output side of the voltage amplifier 14a. After a certain period of time after starting, voltage amplifier 1
The output voltage suppression value of 4a is fixed to a constant value. The pulse width control circuit 22 inputs the input voltage coefficient from the automatic voltage control device AVR and the frequency setting signal supplied based on the CPUIO command, and based on this input, pulse width control is applied to the gate circuit of the inverter 3. A signal is sent out, and the gate of the inverter 3 is controlled based on the output of this gate circuit. At time t, the received voltage begins to drop as shown in FIG. 2a.

In this case, when the voltage of the received power drops, the voltage setting value Vs is constant, so conventionally, the integrating voltage amplifier 14 automatically increases the voltage coefficient so that the output voltage of the inverter 3 matches the voltage setting value Vs. work. Therefore, the voltage coefficient becomes a larger value than the normal value, and therefore, if the operation is continued with that voltage coefficient when the power is restored, an output overvoltage phenomenon occurs. Therefore, in the present invention, when the received power voltage drops, the CPUIO detects that the received power voltage has become 90% of the normal level, and the voltage coefficient at time t2, that is, the output of the A/D converter 20, is stored in the memory. 11 (Fig. 2 b, c)
reference).

The voltage coefficient value at this time is considered to be the voltage coefficient when the power supply is normal. Then, as shown in FIG. 2a, the output voltage of the integral voltage amplifier 14 is automatically controlled by the output obtained via the A/D converter 20 until the received power voltage decreases and the output voltage or torque of the load motor is secured. By doing so, and increasing the voltage coefficient, output voltage constant (V/F constant) control is executed (see Fig. 2 b and d). When the received voltage returns to 70% at time t3 as shown in FIG. The value previously stored in the memory 11 when the received power voltage drops by 90% is supplied to the pulse width control circuit 22 via the switching circuit 21 in response to a command from the CPUIO (see FIGS. 2b and 2c).
Therefore, from time etc., the pulse width control circuit 22 has A/○.
In place of the voltage coefficient which is the output of the converter 20, the received voltage 9
At the time of 0% drop, the voltage coefficient stored in the memory 11 is supplied (see Figure 2b). Pulse width control circuit 22
supplies a desired pulse width control signal to the gate circuit of the inverter 3 based on these voltage coefficients and frequency setting signals, and gate-controls the inverter 3 by the output of this gate circuit. In this way, the memory 11 of the microcomputer
Conventionally, by using the voltage coefficient stored in the voltage coefficient, the jump in the voltage coefficient is reduced and the output overvoltage of the voltage type inverter is prevented. On the other hand, at time t3, relay contacts 14d and 19 are turned on, so that integral voltage amplifier 14
The input and output terminal voltage of the cushion circuit 16 becomes zero due to discharge. Eventually, when power restoration is confirmed at time t4, the contacts 14d and 19 of the integrating voltage amplifier 4 and the cushion circuit 16 are turned off. Therefore, by turning off the contacts 14d and 19, the integral voltage amplification device 4 and the cushion circuit 1 are turned off.
6 is released, the output voltage of the cushion circuit 16 rises over time. This output is supplied to the limiter circuit 17, and based on the output of the limiter circuit 17, the limit value of the voltage amplifier 14a is set. is gradually raised from 0 based on the output of the cushion circuit 16 as indicated by the dotted line A in FIG.
The output rises in accordance with the limiter value. Then, the time t when the voltage coefficient based on the output of the voltage amplifier 14a matches the voltage coefficient set from the CPU 10 at the time of power restoration.
At step 5, the software is processed by CPUIQ to switch to the automatic voltage controller AVR side and return to normal operation (see Figure 2 d).

In this case, after time t5, the output voltage value of the integrating voltage amplifier 14 operates so that the voltage setting Vs and the output voltage ydet match. Then, it almost coincides with the voltage coefficient (output voltage of the integrating voltage amplifier 14) before the power outage occurred, and
Returns to normal operation (see Figure 2b).Using the above-described present invention provides the following various effects: {1}
By combining control by a computer (microcomputer) and an analog control circuit, the advantages of the conventional analog circuit (automatic voltage control circuit) can be utilized.

(21) Constant output voltage control when the receiving voltage drops can be smoothly performed using a voltage amplifier with an integral limiter while maintaining normal operation.

Glue When the AC input voltage drops to a first predetermined pressure due to the computer (microcomputer) being exhausted, it is possible to store the voltage coefficient, which is the output of the automatic voltage control device, in the memory of the computer. When the AC input voltage returns to the third predetermined voltage value, the voltage amplifier with the integral type limiter is controlled and turned off, and the voltage coefficient output from the automatic voltage control device is replaced with the voltage coefficient output from the computer memory mentioned above. Since I decided to use the voltage coefficient stored in
It is possible to suppress transient output overvoltage when power is restored.

[4' Adding a cushion circuit to the automatic voltage control device
Based on the output of this cushion circuit, the limiter value of the pressure amplifier with an integral type limiter is raised from zero, making it easy to return to the automatic voltage control system after power is restored. Processing becomes very easy.

'51 By combining software and hardware, voltage constant control from power outage (receiving voltage drop) to power restoration can be executed stably and smoothly, and overvoltage can be prevented when power is restored.

1 is a block diagram showing an embodiment of the control method for an AC motor according to the present invention, and FIGS. 2a to 2d are explanatory diagrams of the operation of FIG. Daily converter, 2 is an electrolytic capacitor, 3
is an inverter, 6 and 8 are rectifiers, 9 is a 1/0 boat, 10
is the CPU, 11 is the memory, 12 is the ○A converter, 13
, 15 is a matching circuit ~ i4 is a voltage amplifier with an integral limiter, military 4d, 19 is a relay contact, 16 is a cushion circuit, 11 is a limiter circuit, 20 is an A/D converter "21
2 shows a switching circuit, and 22 shows a pulse width control circuit.

Figure 1 Figure 2

Claims (1)

[Claims] 1. A deviation signal obtained by matching the output voltage of the inverter with a voltage setting value based on the output frequency of the voltage source inverter and having a constant ratio of voltage and frequency is supplied to a voltage amplifier with an integral type limiter. The voltage coefficient of the automatic voltage control device obtained by analog-to-digital conversion of the output of the voltage amplifier with limiter is supplied to the pulse width control circuit, and the set frequency and voltage coefficient inputted by the pulse width control circuit are used to control the inverter. In the method for controlling an AC motor, the AC input voltage is input to a computer, and the pulse width control circuit includes a built-in memory. , the frequency setting signal and voltage coefficient from the computer are input, and the data stored in the built-in memory is used to send out the pulse width control signal of the inverter, so that the AC input voltage is set to a first predetermined value. storing the voltage coefficient of the automatic voltage control device at that time in the memory of the computer when the voltage drops;
Further, from the time when the AC input voltage drops to a second predetermined voltage until it returns to a third predetermined voltage, control by the automatic voltage control device is performed by the voltage amplifier with an integral type limiter, so that the AC input voltage is When the power is restored to a third predetermined voltage value, the voltage amplifier with an integral type limiter is controlled and cut off, and the voltage coefficient stored in the memory of the computer is used instead of the voltage coefficient from the automatic voltage control device. After reconfirming power recovery, the voltage amplifier with an integral type limiter is controlled and disconnected, and the limiter value of the voltage amplifier with an integral type limiter is set from zero based on the output of the compression circuit. When the output of the integrating amplifier matches the voltage coefficient stored in the memory, the output of the automatic voltage control device is again supplied to the pulse width control circuit to restore normal operation of the inverter. A method for controlling an AC motor, characterized in that the AC motor is reset.