JPH01283086A - Current control amplifier for inverter - Google Patents

Abstract

PURPOSE:To cope with control of any specification merely by altering the program by a method wherein a soft starter is formed by a program. CONSTITUTION:The output of a carrier voltage generator 215 is connected to one input terminal of a multiplication type D/A converter 221, and a CPU 1 is connected to the other input terminal. The output terminal of the converter 221 is connected to the non-inversion input terminal of a comparator 217 through a resistor 216, and any signals of U, V, W phases of sine waves is input to the other inversion input terminal through a resistor 219. The output of the comparator 217 is supplied to a power converter through a terminal 220. Data for maximizing the output value of an analog signal is applied from the CPU 1 to the converter 221. A soft start can be performed by gradually reducing the data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current control amplifier for an inverter, and more particularly to a current control amplifier for an inverter that eliminates hardware adjustment elements.

[Conventional technology]

Conventionally, induction motors (hereinafter referred to as IM) have been widely used as constant-speed motors under a constant frequency power source, taking advantage of their robustness and low-speed characteristics, but the above-mentioned IM requires rapid acceleration and deceleration. It was not used as a servo motor.

However, in recent years, a vector control method has been developed as a means for variable speed control of IM.

Here, an example of an IM acceleration/speed control means using a vector control method will be explained with reference to FIG.

In FIG. 4, the 200s are members related to vector control.

That is, 201: speed control amplifier, 202: divider, ZO
a: Constant setter, 204: Coordinate converter.

205: Multiplier, 206: Converter, 207: Current control amplifier, 20B: Power converter, 209: Induction motor (IM
), 210: Adder, 211A: Speed detector, 212:
Differentiator, 213, 214, 215. 216: Constant setter, 217: Divider, 218; Vector oscillator, 219:
It consists of a multiplier.

Then, when various control/state signals are input to CPU10I, this CPU101 outputs data such that the rate multiplier 104 outputs a pulse train according to the speed command value in the input signal, and the rate multiplier 104 The output pulse of the flip-flop circuit 10
6, the waveform is shaped by the gate 11 from the synchronization circuit 107.
1,112, 113, 114 to the droop counter 115.

On the other hand, the speed detector 211A indicates the IM at that time.
rotation is detected and fed back to the synchronization direction discrimination circuit 133.

The output of this discrimination circuit 133 is
to determine the direction of rotation of the motor.

Further, the output of this discrimination circuit 133 is transmitted to the F/V converter 134.
This output is input to the vector control section.

Further, the output of this F/V converter 134 is transmitted to the absolute value circuit 13.
5. The signal is supplied to the vector control unit via an A/D converter 132 and a secondary magnetic flux generator 136.

By the way, when focusing on the current control amplifier 207 in the inverter having the vector control section configured as described above, the following problem occurs.

One unit constituting this current control amplifier 207 can be configured as shown in FIG. 5, for example.

When a triangular wave is generated from the carrier voltage generating section 215, the waveform at point A becomes a triangular wave as shown in FIG.

This triangular wave is input to the non-inverting input terminal of the comparator 217 via the resistor 216. In addition, any of the U, V, and W phases, which are sine waves, is input to the terminal 218, and the resistor 21
9 to the inverting input terminal of the comparator 217. The output of this comparator 217 is then output from a terminal 220 as a rectangular wave for PWM control.

However, in a circuit like the one shown in Figure 5, the feedback system is not stable when the power is turned on, so a phase (U, V, or W) may occur in which the 0-point output remains on. , the situation is as shown in FIG. 6 (in such a state, an overcurrent occurs).

That is, in FIG. 6, both the U phase and W phase are permanently turned on.

In order to prevent such a situation from occurring, a soft start circuit as shown in FIG. 7 has conventionally been used.

That is, the output of the carrier voltage generation circuit 215 is a multiplication type D/
The power supply 222 is input to one terminal of the A converter 221, the power supply 222 is input to the other terminal of the converter 221 via a resistor 223, and the connection point between the resistor 223 and the D/A converter 221 is A parallel circuit of a capacitor 225 and a resistor 226 is connected to the terminal 224 via an inverter 227.

The output of the D/A converter 221 is connected to a non-inverting input terminal of a comparator 217 via a resistor 216, and a terminal 218 is connected to an inverting input terminal of the comparator 217 via a resistor 219.

With this configuration, when the power is turned on, the carrier voltage is large due to the time constant circuit consisting of the capacitor 225 and the resistor 226, and as time passes, the carrier voltage is generated exponentially to a steady state, and the voltage decreases. The rise is controlled to prevent the above-mentioned phenomenon of no turning on.

[Problem to be solved by the invention]

However, with the soft start circuit shown in FIG. 7, it is troublesome to adjust the time constant circuit consisting of the capacitor 225 and the resistor 226, and there is also the problem that the components deteriorate over time.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a current control amplifier for an inverter that controls an induction motor at variable speed according to various control signals, and includes a carrier voltage generation section that generates a triangular wave, and a carrier voltage generation section that generates a triangular wave. The output is input to one input terminal, and the output current value is gradually brought closer to the target value at the other input terminal. be.

[Effect]

According to the invention, the soft start Il can be programmed.
1, adjustment can be made by changing the program.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A current control amplifier for an inverter according to the present invention will be explained below based on illustrated embodiments.

FIG. 1 is a block diagram showing a current control amplifier for an inverter according to the present invention, and FIG. 2 is a flowchart of a program used in the current control amplifier for an inverter according to the present invention.

As shown in FIG. 1, the output of the carrier voltage generation circuit 215 is connected to one input terminal of a multiplication type D/A converter 221, and the CPU 1 is connected to the other input terminal. This D
The output terminal of the /A converter 221 is connected to the non-inverting input terminal of the comparator 217 via the resistor 216, and the other inverting input terminal receives a sine wave U, V, or W phase signal via the resistor 219. Enter via. The output of this comparator 217 is then passed through the terminal 220 to the power converter 208 as the output of the current control amplifier 207 shown in FIG.
supplied to

In the state shown in FIG. 1, the control shown in the flowchart in FIG. 2 is performed, and the manner in which the control is performed will be explained using FIG. 3.

The CPU provides the D/A converter 221 with data that maximizes the output amplitude value of the analog signal for t seconds (
Step 1. Step 2). This situation can be seen in the range R in Figure 3.
Shown in 1. Note that in this figure, rNJ means data with which the above-mentioned output amplitude value becomes the maximum.

Next, if seconds have passed, subtract 1 from the above data.
(That is, N-1) and (Step 3), the output waveform at that time has a slightly small amplitude as shown by the range R in FIG.

However, since the target value shown in the figure has not yet been reached (step 4), subtracting 1 further results in rN-2J, and the amplitude becomes even smaller as shown in range R1.

Thereafter, the range R4 is reached in the same manner, and the amplitude at this time reaches the target value. Note that since the range Rs has already reached the target value, there is no need to perform the process of subtracting rlJ.

In this way, the amplitude of the output value is gradually lowered and supplied to the comparator 217, so that the comparator 217 outputs an output that can be soft-started to the power converter 208.
(See Figure 4).

〔effect〕

According to the present invention, it is possible to apply the control to any specification simply by changing the program, so that it is possible to be freed from the troublesome adjustment and component deterioration of conventional electrical components.

[Brief explanation of the drawing]

Fig. 1 is a block configuration diagram showing the main parts of the current control amplifier of the inverter of the present invention, Fig. 2 is a flowchart of the program used for the main parts of the invention, and Fig. 3 is a diagram showing the operating status of the above program. , FIG. 4 is a diagram showing a conventional vector control method for controlling an induction motor, and FIGS. 5 to 7 are diagrams showing the necessity of instantaneous overcurrent prevention. 1...CPU (Built-in instantaneous overcurrent prevention program)
, 215...Carrier voltage generation circuit, 221...Multiplication type D/A converter, 217...Comparator.

Claims (1)

[Claims] 1. In a current control amplifier for an inverter that controls an induction motor at variable speed in accordance with various control signals, a carrier voltage generation section that generates a triangular wave; and an output of the carrier voltage generation section that is connected to one side. and a multiplier type digital/analog converter, the other input terminal of which is inputted with the output of a control unit that controls the output current value so as to gradually approach the target value. Inverter current control amplifier.