JPH0197198A - Control device for motor drive inverter - Google Patents

Abstract

PURPOSE:To maintain a setting speed accurately at all times regardless of variation of load torque of an induction motor, by switching speed detection method corresponding to high speed and low speed thereby improving accuracy and response in speed control system. CONSTITUTION:Under high speed, output pulse from a rotary encoder 7 is fed to a four time frequency direction judging circuit 22 and counted through a pulse number counter 23. Under low speed, output pulse from the rotary encoder 7 is fed to a clear latch signal circuit 26 and the number of reference clocks 4 between the output pulses is counted through a pulse width counter 27 so as to measure the speed. A switch 31 is switched corresponding to high speed and low speed to produce a speed feedback signal fd.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses an inverter device, especially voltage-type PWM.
Regarding the technology to keep the rotational speed of an induction motor driven by an inverter device accurately and constant to a set value even if the slip changes due to fluctuations in the load torque, the inverter device is used for such speed control. This relates to technology that improves responsiveness.

[Conventional technology]

FIG. 3 is a control block diagram of a conventional motor drive inverter device, and FIG. 4 is an operating waveform diagram of the frequency measuring device shown in FIG. 3.

In these figures, AC power from an AC power source 2 is converted into DC by a rectifier 3, and this DC is input via a smoothing capacitor 4 to a transistor inverter 5 made up of transistors.

This transistor inverter 5 converts the input DC into AC of a desired voltage and frequency and outputs it to the induction motor 6, so that the induction motor 6 can be operated at any speed. Control for outputting alternating current of a desired voltage and frequency from the transistor inverter 5 is performed as follows.

When the speed at which the induction motor 6 should be operated is set with the speed setter 11, a set speed signal that takes into account the slip of the induction motor 6 is outputted from the acceleration/deceleration calculator 12 and given to the frequency command section 13, which converts the set speed signal into the set speed signal. It is converted into a corresponding command frequency signal. In parallel, this set speed signal is also applied to a function generator 14, which outputs a command voltage signal having a predetermined functional relationship with the command frequency signal.

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, and outputs a pulse train signal obtained by pulse width modulating these using a high frequency carrier wave. do. By supplying this pulse train signal to the base of each transistor constituting the transistor inverter 5 via the base drive circuit 16 and sequentially controlling these transistors on and off, the transistor inverter 5 outputs a desired voltage and frequency. AC is output.

A rotary encoder 7 is directly connected to an induction motor 6 driven by a transistor inverter 5, and its output pulses are input to a frequency measuring device 17 and taken out as a detected speed signal of the induction motor m6. This detected speed signal is compared with the set speed signal from the aforementioned speed setter 11, and the speed set signal outputted from the acceleration/deceleration calculator 12 is adjusted so that the difference becomes zero. In this way, even if the load torque of the induction motor 6 fluctuates and the slip changes, the rotational speed is always adjusted to maintain the set value.

Note that even if the set value from the speed setting device 11 changes suddenly,
The acceleration/deceleration calculator 12 outputs a set speed signal that changes slowly, and the speed of the induction motor 6 changes slowly following the output of the transistor inverter 5, so that the transistor inverter 5 is overloaded. It is designed to prevent it from becoming a current.

The operation of the frequency measuring device 17 will be explained with reference to FIG.

The rotary encoder 7 has a phase angle A shifted by 90 degrees.
Phase and B phase signals are output, and the edge portions of the A and B phases are used to output a quadrupled frequency as shown in the figure by known means. The frequency corresponding to the rotational speed of the induction motor 6 is measured by measuring the quadrupled frequency pulse for a desired fixed time (Tsec). Further, the direction of rotation can also be detected by utilizing the fact that the phase angles of the A phase and B phase are shifted by 90 degrees.

[Problem that the invention seeks to solve]

The adjustment range of the frequency of the AC power output by the inverter device is wider than 1:100 and 1:10.
Some even reach 00. In the conventional technology described above, there is a limit to the number of output pulses per rotation of the rotary encoder due to mechanical accuracy, and even if the frequency is multiplied by 4 times as in the conventional example, the low frequency range of the inverter device is limited. In this case, the number of output pulses within a certain period of time Tsec becomes extremely small, and since the output pulses are counted as an integer during measurement, an error occurs in the measured value. As a countermeasure, Tsec may be increased at least in the low frequency range, but this results in a problem that the responsiveness of the measurement control system decreases.

The present invention solves the above problems, maintains a wide range of frequencies output by the inverter device, and improves the accuracy and responsiveness of the speed control system in the low frequency range. The purpose of this invention is to maintain the target rotational speed accurately and constant over a wide speed range even if there are fluctuations in the load torque of the induction motor.

[Means for solving problems]

This invention converts a set speed signal sent from a speed setter via an acceleration/deceleration calculator into a command frequency signal in a frequency command section to drive a transistor inverter, in which a tachometer is directly connected to an electric motor. frequency detection means for measuring the number of output pulses output by the tachometer over a desired fixed period of time to detect a detected speed signal corresponding to the rotational speed of the motor; and measuring the width of the output pulse using a reference clock to detect the detected speed. A cycle detection means for detecting a speed signal, a changeover switch for selecting one of the detected speed signals outputted by both of the detection means, and an acceleration/deceleration calculation unit for the detected speed signal and the inverter device sent by the changeover switch. and a proportional/integral adjustment section that adjusts the set speed signal according to the deviation from the set speed signal outputted by the controller as a command speed signal, and adjusts the command speed signal output by the proportional/integral adjuster to the frequency command. The command frequency signal is input to the section and outputs the command frequency signal.

[Effect]

In FIG. 1, the frequency detection means 25 consisting of the quadruple frequency/direction discrimination circuit 22, the pulse number counter 23 and the converter 24 is used when the tachometer such as the rotary encoder 7 is at high speed, that is, in the high frequency range of the inverter device. When speed detection accuracy and responsiveness are good. On the other hand, clear latch signal circuit 26, pulse width counter 27 and converter 2
The period detection means 29 consisting of 8 has good speed detection accuracy and responsiveness when the output pulses of the rotary encoder 7 are at a lower speed of several tens of pulses or less per unit time of detection, that is, in a lower frequency range. The detection speed signal fd outputted by both the detection means 25 and 29 is switched to the changeover switch 3 according to the frequency.
1 is selected, and the deviation value from the set speed signal ft of the acceleration/deceleration calculator 32 at the addition point 33 is determined. In accordance with this deviation value, it is adjusted by receiving a proportional operation and an integral operation in a proportional/integral adjustment section 34, and is added to the above-mentioned ft at a summing point 35 to obtain a new command speed signal fi. In this way, the rotational speed of the induction electric motor m6 maintains the set value with good responsiveness in a wide speed range even if the load torque fluctuates.

〔Example〕

FIG. 1 is a control block diagram of the inverter device for driving a motor according to the present invention, and FIG. 2 is an operation waveform diagram of the frequency detection means and period detection means shown in FIG. 1.

In these figures, the same reference numerals as in FIG. 3 have the same functions. That is, the transistor inverter 5 converts the DC obtained by the AC power supply 2, the rectifier 3, and the smoothing capacitor 4 into AC of a desired frequency to drive the induction motor 6. It is driven via a circuit 15 and a base drive circuit 16. Then, the transistor inverter 5 outputs AC power based on the command frequency signal output by the frequency command section 13.

Now, a rotary encoder 7 is directly connected to the induction motor 6, and outputs output pulses as signals from the A phase and B phase, which have a phase angle shifted by 90 degrees, and is input to the inverter device via the respective insulation circuits 21. It is now possible to The quadruple frequency/direction discrimination circuit 22 processes the edge portions of the A phase and B phase as shown in the upper part of FIG. 2 and outputs a quadruple frequency signal as in FIG. The rotation direction is determined by detecting the phase angle of the B phase.

The quadrupled frequency signal is counted for a fixed time Tsec by a pulse number counter 23 consisting of an up/down counter, and converted into a frequency by a converter 24 and converted into a detected speed signal fd. In this way, the frequency detection means 25 consisting of the quadrupled frequency/direction discrimination circuit 22, the pulse number counter 23, and the converter 24 detects and outputs the detected speed signal fd corresponding to the rotational speed of the induction motor m6 via the rotary encoder 7. .

On the other hand, the clear latch signal circuit 26 detects the rising edge of the A-phase output pulse from the isolation circuit 21, and as shown in the lower part of FIG. are output alternately. The latch signal and the clear signal are input to the pulse width counter 27 together with the clock pulse of the reference clock 30, where the period of the output pulse is measured by counting the clock pulse of one width of the output pulse, and the period of the output pulse is measured. Here too, it is converted into a detected speed signal fd. Thus clear launch signal circuit 26, pulse width counter 27 and converter 28
The period detecting means 29 consisting of also detects and outputs a detected speed signal fd corresponding to the rotational speed.

When the set value of the rotational speed at which the induction motor 6 should be operated is set using the speed setter 11, the acceleration/deceleration calculator 32 generates a set speed signal f corresponding to the set value without expecting slip.
t, and when the target value changes rapidly, the output speed gradually approaches the set speed signal ft.

On the other hand, the aforementioned frequency detection means 25 and period detection means 29
The respective detected speed signals fd outputted from are automatically selected by the changeover switch 31, the former detected speed signal fd in the high frequency range and the latter detected speed signal fd in the low frequency range, and one of the detected speed signals fd is subtracted. It is added as a value (-) to the set speed signal ft at a summing point 33. That is, the deviation value between ft and fd is calculated. Proportional/integral adjustment section 3
Reference numeral 4 denotes an adjusting section that exhibits a known proportional operation and an integral operation, and operates so that the output is proportional to the input and also proportional to the time integral of the input. The deviation value at the summing point 33 is adjusted as described above by the proportional/integral adjustment section 34, and is added to the set speed signal ft at the next summing point 35 to obtain a new command speed signal rt. This new signal fi is input to the frequency command section 13 and function generator 14 described above to generate a new command frequency signal Fi. That is, f
fi, that is, Fi, is adjusted according to the deviation between t and fd, and the operation is performed in the direction of reducing the deviation.

〔Effect of the invention〕

This invention directly connects a rotation speed meter such as a rotary encoder to an induction motor driven by an inverter device, and detects the rotation speed using its output pulse and feeds it back to the control circuit of the inverter device. Pulses are measured, and at low speeds where the output pulse is less than a few tens of pulses per unit time of speed detection, the rotation speed is measured by the period detection means, so the rotation speed detection and the response speed of the control system are faster. There is an effect.

Therefore, even if there are fluctuations in the load torque of the induction motor, the set speed can be maintained accurately at all times.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of the inverter device for driving an electric motor according to the present invention, FIG. 2 is an operation waveform diagram of the frequency detection means and period detection means shown in FIG. 1, and FIG. 3 is a diagram of the conventional technique. FIG. 4 is a control block diagram of an inverter device for driving a motor according to the present invention, and FIG. 4 is an operation waveform diagram of the frequency measuring device shown in FIG. 3. 2... AC power supply, 3... Rectifier, 4... Smoothing capacitor, 5... Transistor inverter, 6... Induction motor, 7... Rotary encoder, 25...
Frequency detection means, 29... Period detection means, 31...
Changeover switch, 32... Acceleration/deceleration calculator, 33.35
...Addition point, 34...Proportional/integral adjustment section.

Claims (1)

[Claims] 1) In a device that drives a transistor inverter by converting a set speed signal sent from a speed setting device via an acceleration/deceleration calculator into a command frequency signal in a frequency command section, a tachometer is directly connected to the electric motor, and this rotation frequency detection means for measuring the number of output pulses output by the speedometer for a desired fixed period of time to detect a detected speed signal corresponding to the rotational speed of the motor; A period detection means for detecting a signal, a changeover switch for selecting one of the detected speed signals outputted by both of the detection means, and an acceleration/deceleration calculator of the inverter device and the detected speed signal sent by the changeover switch. A proportional/integral adjustment section that adjusts the set speed signal according to the deviation from the set speed signal to be output as a command speed signal is provided, and the command speed signal outputted by the proportional/integral adjustment section is adjusted to the frequency command section. 1. A control device for an inverter for driving a motor, characterized in that the control device inputs the command frequency signal to output the command frequency signal.