JPH07108110B2 - Inverter control device for motor drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction motor driven by an inverter device, particularly a voltage source PWM inverter device, even if slip changes due to fluctuations in load torque of the induction motor. The present invention relates to a technique for always keeping the rotation speed accurately and constant with respect to a set value, and a technique for improving the responsiveness of an inverter device for such speed control.

[Conventional technology]

FIG. 5 is a control block diagram of a conventional motor driving inverter device, and FIG. 6 is an operation waveform diagram of the frequency measuring instrument shown in FIG.

In these figures, the AC power from the AC power supply 2 is converted into DC by the rectifier 3, and this DC is input to the transistor inverter 5 composed of transistors via the smoothing capacitor 4. The transistor inverter 5 converts the input direct current into an alternating current having a desired voltage and frequency and outputs the alternating current to the induction motor 6, so that the induction motor 6 can be operated at an arbitrary speed. The control for causing the transistor inverter 5 to output an alternating current of a desired voltage and frequency is performed as follows.

When the speed at which the induction motor 6 is to be operated is set by the speed setting unit 11, a set speed signal in anticipation of slippage of the induction motor 6 is output from the acceleration / deceleration calculator 12 and given to the frequency command unit 13 to provide the set speed signal. It is converted into the corresponding command frequency signal. In parallel with this, the set speed signal is also given to the function generator 14, and a command voltage signal having a predetermined functional relationship with the command frequency signal is output.

The pulse width modulation circuit 15 inputs the command frequency signal from the frequency command unit 13 and the command voltage signal from the function generator 14,
A pulse train signal obtained by pulse width modulating these with a carrier wave of high frequency is output. This pulse train signal is supplied to the bases of the respective transistors forming the transistor inverter 5 via the base drive circuit 16 and these transistors are sequentially controlled to be turned on and off, so that a desired voltage and frequency can be obtained from the transistor inverter 5. Alternating current is output.

A rotary encoder 7 is directly connected to an induction motor 6 driven by a transistor inverter 5, and an output pulse of the rotary encoder 7 is input to a frequency measuring device 17 and taken out as a detection speed signal of the induction motor 6. The detected speed signal is compared with the set speed signal from the speed setter 11, and the speed set signal output from the acceleration / deceleration calculator 12 is adjusted so that the difference becomes zero. Thus, even if the load torque of the induction motor 6 changes and the slip changes, the rotation speed is adjusted so as to always maintain the set value. Even if the set value from the speed setter 11 changes abruptly, the acceleration / deceleration calculator 12 outputs a set speed signal that changes gently, and the speed of the induction motor 6 is the transistor inverter 5 The output voltage of the transistor inverter 5 is gradually changed in accordance with the output of 1 to suppress overcurrent of the transistor inverter 5.

The operation of the frequency measuring device 17 will be described with reference to FIG. The rotary encoder 7 is designed to output A-phase and B-phase signals whose phase angles are shifted by 90 degrees.
The edge portion of the phase is used to output the quadruple frequency by a known means as shown. The frequency corresponding to the rotation speed of the induction conductor 6 is measured by measuring the pulse having the quadruple frequency for a desired constant time (Tsec). The rotation direction can also be detected by utilizing the fact that the phase angles of the A phase and the B phase are shifted by 90 degrees.

[Problems to be solved by the invention]

The adjustment range of the frequency of the alternating current output by the inverter device is from 1: 100 to 1: 1000 for a wide range. According to the above-mentioned conventional technique, the number of output pulses per one rotation of the rotary encoder has a limit in terms of mechanical accuracy, and even if the frequency is multiplied by 4 as in the conventional example, the low frequency range of the inverter device is reduced. Then, the output pulse within a fixed time Tsec becomes extremely small, and the output pulse is counted as an integer in the measurement, so that an error occurs in the measured value. As a countermeasure, Tsec may be lengthened at least in the low frequency range, but as a result, there is a problem that the response of the measurement control system is deteriorated.

An object of the present invention is to solve the above-mentioned problems, to maintain a wide frequency range output by an inverter device, and to improve the accuracy and responsiveness of a speed control system in a low frequency range. Even if there is a change in the load torque of the induction motor, the target rotation speed is accurately kept constant in a wide speed range.

[Means for solving problems]

In the configuration of the present invention, the set speed signal sent from the speed setter via the acceleration / deceleration calculator is converted into the command frequency signal by the frequency command unit to drive the transistor inverter, and the rotation speed directly connected to the induction motor. Cycle detection means for measuring the width of the output pulse output by the meter with a reference clock to detect a detection speed signal corresponding to the rotation speed of the induction motor, and comparing the detected speed signal and the set speed signal with the former A comparison unit that adds a negative fixed value when it is large and a positive fixed minute value when the latter is large and outputs it as a new correction speed signal by itself is output. The command speed signal obtained by adding the corrected speed signal to the set speed signal and adding at the summing point is input to the frequency command unit to output the command frequency signal.

[Action]

In FIG. 1 and FIG. 3, a cycle detecting means 25 comprising a pulse width counter 22, a reference clock 23 and a frequency calculator 24.
Not only when the rotational speed meter such as the rotary encoder 7 rotates at high speed, but also when the output pulse of the rotary encoder 7 is lower than several tens of pulses per unit time of detection, that is, even when the speed is in a lower frequency range. Good accuracy and responsiveness. The detected speed signal fd output by the cycle detection means 25 is compared with the set speed signal ft output by the acceleration / deceleration calculator 26 in the comparison unit 27. This comparison unit calculates a positive minute value Δf (eg 0.01 Hz) if fd <ft, and a negative minute positive value Δf if fd> ft.
Is added to the correction speed signal fc of the memory incorporated in the comparison unit to output a new correction speed signal fc. This fc is a summing point
At 28, a new minutely corrected command speed signal fi is obtained by adding to ft, and this is repeated. Thus, the rotation speed of the induction motor 6 maintains the set value in a wide speed range with good responsiveness even if the load tokdle varies.

〔Example〕

FIG. 1 is a control block diagram of an inverter device for driving a motor according to the present invention, FIG. 2 is a circuit diagram of the cycle detecting means shown in FIG. 1, and FIG. 3 is an operation waveform diagram thereof. FIG. 4 is a flow chart in the comparing section of FIG.

In these figures, those denoted by the same reference numerals as those in FIG. 5 have the same functions. That is, the transistor inverter 5 which drives the induction motor 6 by converting the direct current obtained by the alternating current power source 2, the rectifier 3 and the smoothing capacitor 4 into the alternating current of the desired frequency is composed of the frequency command unit 13, the function generator 14 and the pulse width modulation. It is driven through the circuit 15 and the base drive circuit 16. Then, the transistor inverter 5 outputs the AC power based on the command frequency signal output from the frequency command unit 13.

Now, the rotary encoder 7 is directly connected to the induction motor 6 so that output pulses are output as signals from the A phase whose phase angle is deviated by 90 degrees and are taken into the inverter device via the respective insulation circuits 21. Has become.
The output pulse is detected by the cycle detecting means 25 including the pulse width counter 22, the reference clock 23 and the frequency calculator 24, and the detected speed signal fd corresponding to the actual rotation speed of the induction motor 6 is detected and output. The details of the pulse width counter 22 are as shown in FIG. 2, and the operation waveforms thereof are as shown in FIG. That is, the output pulse of the rotary encoder 7 input through the insulating circuit 21 is shaped by the Schmitt trigger inverter 251, and is input to the JK FF 252. Here, the output pulse indicated by A in FIG. 3 is toggled to output H and L pulses B for each cycle of the output pulse A as shown in B in FIG. The AND gate 253 takes the logical product of the 3 MHz clock pulse output from the reference clock 23 and outputs the pulse C in FIG. The J-K FFs 256 and 257 and the gates 258 and 259 are reset circuits that reset the counter 254 to which the pulse C is input, and the calculated value is input to the frequency calculator 24 via the latch circuit 255. Considering the number of poles of the induction motor,
Detected speed signal corresponding to rotation speed by converting period to frequency
fd is obtained. Next, returning to FIG. 1 again, description will be made.

When the speed setter 11 sets the set value of the rotational speed at which the induction motor 6 should operate, the acceleration / deceleration calculator 26 outputs the set speed signal ft corresponding to the set value without anticipating the slip, and the target value becomes When it changes abruptly, it outputs so as to gradually approach the set speed signal ft. This signal ft and the detected speed signal fd output from the above-mentioned cycle detection means 25 are input to the comparison unit 32. The comparison unit 32
When fd <ft, a small positive value Δf (for example, 0.01Hz) is set to fd>
At the time of ft, the negative Δf is added to the correction speed signal fc of the previous value of the memory built in the comparison unit and output as a new correction speed signal fc. This is as shown in FIG. This corrected speed signal fc is added to ft at the addition point 28 to obtain a new commanded speed signal fi. In addition, the above
fc corresponds to the slip of the induction motor. This new signal
fi is input to the frequency command unit 13 and the function generator 14 described above to generate a new command frequency signal Fi. That is, ft and
By comparing the magnitudes of fd, fi, that is, Fi, is finely adjusted by a constant value Δf, and is repeatedly controlled at high speed in the direction in which the difference is reduced.

〔The invention's effect〕

According to the present invention, a rotation speed meter such as a rotary encoder is directly connected to an induction motor driven by an inverter device, and when the rotation speed is detected by its output pulse and fed back to a control circuit of the inverter device, the rotation speed is measured by a cycle detection means. By doing so, there is an effect that the detection of the rotation speed and the response speed of the control system become faster. Therefore, there is an effect that the set speed is always maintained accurately even if the load torque of the induction motor changes.

[Brief description of drawings]

FIG. 1 is a control block diagram of an inverter device for driving a motor according to the present invention, FIG. 2 is a circuit diagram of the cycle detecting means shown in FIG. 1, and FIG. 3 is an operation waveform diagram thereof. FIG. 4 is a flow chart in the comparison part of FIG. 1, FIG. 5 is a control block diagram of a conventional motor drive inverter device, and FIG. 6 is an operation waveform of the frequency measuring instrument shown in FIG. It is a figure. 2 ... AC power supply, 3 ... Rectifier, 4 ... Smoothing capacitor, 5 ... Transistor inverter, 6 ... Induction motor, 7 ... Rotary encoder, 22 ... Pulse width counter, 23 ... Reference clock, 24 ... … Frequency calculator, 25…
… Cycle detection means, 26 …… Acceleration / deceleration calculator, 27 …… Comparison section, 28 …… Addition point.

Claims (1)

[Claims] 1. A tachometer directly connected to an induction motor in a method for driving a transistor inverter by converting a set speed signal sent from a speed setter via an acceleration / deceleration calculator into a command frequency signal in a frequency command section. Cycle detection means for detecting the detection speed signal corresponding to the rotation speed of the induction motor by measuring the width of the output pulse output by the reference clock,
The detected speed signal and the set speed signal are compared, and when the former is large, a negative small value is added, and when the latter is large, a fixed fixed minute value is added to the correction speed signal of the built-in memory to make a new correction With a comparison unit that outputs as a speed signal,
A motor drive characterized in that a command speed signal obtained by adding the corrected speed signal output from the comparison unit to the set speed signal and adding at a combining point is input to the frequency command unit to output the command frequency signal. Inverter control device.