JPS62296794A - Frequency-variable device - Google Patents

Abstract

PURPOSE:To widen a driving range according to the fluctuation of a load, by making the duty ratio of a PWM variable so that the characteristic of V/F may be variable according to the load fluctuation of an AC motor. CONSTITUTION:An excess current detection circuit 7 detects excess current at the DC power section of a power converter, namely, the output current of a smoothing circuit 3 and supplies its output to a count data output circuit 14. By this method, by a micro-computer 10, the output of a constant A count value T for PWM variation command is delivered from the count data output circuit 14 in a microcomputer 10 to a counter 11 of a PWM control circuit 6. The PWM control circuit 6 is composed of a counter 11, a rectangular wave output circuit 12, and a waveform synthesizing circuit 13 having its output connected to an inverter driving waveform shaping circuit 15.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a frequency variable device used for variable speed control of an AC motor, for example.

[Conventional technology]

FIG. 6 is a characteristic line diagram of voltage versus frequency characteristics (hereinafter referred to as V/F pattern) of AC output in a conventional frequency variable device disclosed in, for example, Japanese Patent Laid-Open No. 60-229696.

The operation of the variable frequency device shown in FIG. 6 will be explained. Direct current is obtained from a commercial AC power supply l via a rectifier circuit 2 and a smoothing circuit 3, and this direct current is converted into alternating current by, for example, a transistor-type inverter 4, and an alternating current motor 5 is driven by the alternating current output. A mechanical load (not shown) is connected to the AC motor 5.

As a control device for the inverter 4, a microcomputer 10 and a control circuit 111 are provided. The microcomputer 10 receives a frequency signal input by an input means (not shown), that is, the output frequency F2 of the inverter 4 necessary to bring the AC motor 5 to a desired rotational speed.
The signal representing the inverter output frequency F just before that
(F2
>F) or downward control (when Fz<Fl), and sends the result of the determination as a direction determination signal R, and divides frequencies F1 to F2 into appropriate steps. A signal representing this, that is, a frequency signal Q, is sequentially sent to the control circuit 111 at appropriate timings, that is, at time intervals.

The control circuit 111 includes a voltage setting device 112 for increasing control;
Voltage setting device 113 for descending control, dual pressure setting device 112,
A changeover switch 114 for selectively taking out the output of 113.
A waveform shaping circuit 115 is provided for supplying a control signal to control the inverter 4 to a predetermined frequency and voltage according to the signal taken out by the changeover switch 114 and the frequency signal Q described above.

The changeover switch 114 is switched to the voltage setting device 112 side for upward control (F2>Fl) according to the direction judgment signal R from the microcomputer 10, and for downward control (FZ>Fl).
<Fl), it is switched to the voltage setting device 113 side.

The voltage setter 112 sets the voltage (2) corresponding to the input frequency from the microcomputer 10 according to the V/F characteristic UP when the frequency increases in FIG. Similarly, the voltage setting device 113 outputs a signal representing the V/F characteristic DO when the frequency decreases.
According to WN, a signal representing the voltage VDo corresponding to the input frequency is output.

According to the variable frequency device shown in FIG. 6 configured as described above, the output of the inverter 4 is controlled according to the V/F characteristic based on the UP characteristic shown in FIG. It is controlled according to the V/F characteristic due to the D OWN characteristic of.

Therefore, by considering load characteristics, power supply fluctuations, etc., and providing appropriate UP and DOWN characteristics according to the frequency control direction, it is possible to prevent motor breakdown regardless of load characteristics or power supply fluctuations. can.

Therefore, the overcurrent protection circuit is not activated due to breakdown of the motor, and higher quality operation can be continued.

[Problem that the invention seeks to solve]

Therefore, the problem with the conventional technology is that two types of V/F characteristic data are stored in the memory in the microcomputer in order to respond to fluctuations in the mechanical load applied to the AC motor, and the control form becomes complicated. Therefore, there is a drawback that the amount of memory used in the microcomputer becomes enormous.

Furthermore, there is a tendency to diversify V/F characteristic data in order to perform inverter driving more suitable for the fluctuations in the mechanical load, and as a result, the above-mentioned problem becomes inevitable.

This invention was made to solve these problems, and it reduces the amount of memory used by a microcomputer, changes the V/F characteristics in accordance with mechanical load fluctuations, and more efficiently. Another object of the present invention is to obtain a frequency variable device capable of driving an AC motor with a wide range of motion.

[Means for solving problems]

The frequency variable device according to the present invention is provided with a circuit that can change the PWM duty according to load fluctuations of an AC motor by detecting the current of a DC power supply section of a power converter.

[For production]

In this invention, the PWM duty ratio is controlled by detecting the current value of the DC power supply section of the power converter.
A PWM wave is obtained by inputting a current data value that can change the WM duty into a counter and outputting a rectangular wave at the start and end of the counter.

〔Example〕

Embodiments of the frequency variable device of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of one embodiment, FIG. 2 is a diagram showing the V/F characteristics in this invention, and is a diagram showing changes in the V/F characteristics in this invention, and FIG. 2 is a timing diagram showing the operation of the PWM control circuit. FIG.

Next, the configuration of a first embodiment of the present invention will be explained with reference to FIG. In FIG. 1, the same parts as those in FIG. 6 will be described with the same reference numerals.

In FIG. 1, a frequency command 8 is output to a PWM (pulse width modulation) wave generator 8 and an inverter drive wave forming circuit 15 within the microcomputer IO.

The PWM wave generator 9 is configured to send out a PWM wave as shown in FIG. 3(A) to the counter 11 and the waveform synthesis circuit 13.

Further, data is exchanged between the count data memory 16 of the microcomputer 1o and the count data output circuit I4, and the count data output circuit 14 sends an output to the counter 11.

The PWM control circuit 6 is composed of a counter 11, a rectangular wave output circuit 12, and a waveform synthesis circuit 13, and the output of the waveform synthesis circuit 13 is transmitted to the inverter drive waveform shaping circuit 15.
It is designed to output to .

The output of this inverter drive waveform shaping circuit 15 is sent to the inverter 4.

On the other hand, the power of the commercial AC power supply 1 is rectified by the rectifier circuit 2,
In addition to the inverter 4 as a power converter after being smoothed by the smoothing circuit 3, it is converted into AC power by this inverter 4,
An AC motor 5 is driven by the output of the inverter 4.

Further, the output of the smoothing circuit 3 is detected by the overcurrent detection circuit B7, and the output is applied to the count data output circuit 14.

Next, the operation of this invention will be explained. Direct current is obtained from a commercial AC power supply 1 via a rectifier circuit 2 and a smoothing circuit 3,
This direct current is converted into alternating current by the inverter 4, and the alternating current electric current 8!5 is driven by the alternating current output. A varying mechanical load (not shown) is connected to the AC motor 5.

A microcomputer 10, a PWM control circuit 6, and an inverter drive waveform shaping circuit 15 are provided as a control device for the inverter 4, and an overcurrent detection circuit 7 detects the current value of the DC power supply section, which increases or decreases due to load fluctuations of the AC motor 5. ing.

The microcomputer 10 outputs a frequency command 8 manually entered by an input means (not shown), that is, an output frequency F1 of the inverter 4 necessary to bring the AC motor 5 to a desired rotational speed.

This frequency command 8 is applied to a PWM wave generator 9 and an inverter drive waveform shaping circuit 15. This PWM wave orderer 9
Now, as shown in FIG. 2, the output frequency F is determined from the V/F characteristic data set on the memory in the microcomputer 10
The PWM duty data (ON10N+OFF ratio) corresponding to the output voltage ■1 at , is determined, and a PWM wave is output. Note that at this time, the duty ratio of the PWM wave may be constant or variable.

Further, the overcurrent detection circuit 7 detects the overcurrent of the DC power supply section of the power converter, that is, the output current of the smoothing circuit 3, and applies the output to the count data output circuit 14. Thereby, the microcomputer 10 outputs a constant count value T from the count data output circuit 14 to the counter 11 of the PWM control circuit 6 as a PWM change command. The data T is then stored in the count data memory 16.

The waveform in FIG. 3(A) is the waveform output from the PWM wave generator 9.1. It is ON in the -12 section and OFF in the 12-14 section.

The counter 11 detects the fall of the PWM wave signal (waveform shown in FIG. 3 (8)), starts counting, and counts the output data T as the PWM change command from the count data output circuit 4.

The waveform in FIG. 3(B) is a signal that turns ON when the falling edge of the PWM waveform is detected and turns OFF after the counter 11 finishes counting, that is, it is rectangular for the time t3 to L2 corresponding to the output data as the PWM change command. This is a rectangular wave signal output from the wave output circuit 12.

The waveform in FIG. 3(B) is the waveform in FIG. 3(A) (PWM
wave) and is synthesized by the waveform synthesis circuit 13 to form the rectangular waveform shown in FIG. 3(C), that is, 1. -1. ONL the section, 13-1
A waveform is formed in which four sections are turned off.

In this way, 12-1. A waveform with a long ON time, that is, a waveform with a large duty ratio, is input to the inverter drive waveforming circuit 15, and a waveform for driving the inverter 4 is created according to a frequency command from the microcomputer 10.

As described above, the duty ratio of the PWM wave is changed, but when an overcurrent is detected when the count value T is input to the counter 11 and the inverter is driven with the resulting waveform, Then, the previous count value is loaded from the count data memory 16 and new output data T is added and output to the counter 11.

In this way, voltage V2 is set for frequency F as shown in FIG. 2C, and V2-V.

By increasing the output voltage, an overcurrent condition will not occur.

In addition, in the operation of the PWM control circuit 6 in this invention, the rectangular wave and the reference PWM wave are synthesized on the circuit, but the data of the reference PWM wave and the count data value that changes due to current detection are combined in the microcomputer 10. By adding, equivalent pWM variable control becomes possible.

FIG. 4 is a block diagram showing the entire configuration of a second embodiment of the invention. Further, FIG. 5 is a timing diagram showing the operation of the PWM control circuit 6 in FIG. 4.

In FIG. 4, a microcomputer 10, a PWM control circuit 6, and an inverter drive waveform forming circuit 15 are provided as a control device for the inverter 4, and an overcurrent detection circuit detects the current value of the DC power supply section, which increases or decreases due to load fluctuations of the AC motor 5. 7 and an A/D (analog/digital) converter 17 are provided.

Next, the operation shown in FIG. 4 will be explained. The microcomputer 10 outputs a frequency command 8 inputted by an input means (not shown), that is, an output frequency F1 of the inverter 4 necessary to bring the AC motor 5 to a desired rotational speed. Then, the PWM data generation circuit 18 outputs count data T corresponding to the output voltage V at the output frequency F1 from the V/F characteristic data set on the memory in the microcomputer.

The overcurrent detection circuit 7 detects the current value of the DC power supply section of the power converter, and the A/D converter 17 A/D converts the value.

The PWM data generation circuit 18 reads the digitized current data (1) and generates reference current value data (I) corresponding to the frequency (F). When 1, >I, a constant value T is added to the count data T1, and (T, +T) is output to the counter 11, and ■+<r. On the other hand, T,
T is subtracted from , and ('r, -'r) is output to the counter 11.

Then, the output count value ('r+-T, )) is stored in the count data memory 16 (not shown in FIG. 4).

The PWM control circuit 6 includes a trigger pulse generator 19, a counter 11, and a rectangular wave output circuit 12.

The waveform in FIG. 5(A) is the output waveform from the trigger pulse generator 19, and the counter 11 starts counting at the rising edge of the waveform in FIG. 5(8), and receives the input data value from the PWM data generation circuit 18. After counting T, in Figure 5 (
Output the waveform of B).

The waveform of the output from the trigger pulse generator 19 shown in FIG. 5(A) and the waveform of the output from the counter 11 shown in FIG. 5(B) are input to the rectangular wave output circuit 12. It is configured to turn ON at the rising timing t1 of the waveform and turn OFF at the rising timing t2 of the waveform shown in FIG. 5(B).

That is, the ON time (L2t+) of the rectangular wave output circuit 12 changes as shown in FIG. 5(C) depending on the input data value T from the PWM data generation circuit 1st.

The output from the rectangular wave output circuit 12 is input to an inverter drive waveform shaping circuit 15, and a waveform for driving the inverter 4 is created according to a frequency command from the microcomputer 10.

As described above, the duty ratio of the PWM wave is changed, but when the count value T is input to the counter 11 and the inverter 4 is driven with the resulting waveform, the current value of the power converter When data different from the reference current data is input, the previous count value is subsequently loaded from the memory, a new constant value T is added (or subtracted), and the result is output to the counter 11.

In this way, the current value of the DC power supply section of the power converter can be adjusted to A
The /D converted value becomes equal to the reference current value and is optimized according to load fluctuations.

〔Effect of the invention〕

As explained above, this invention detects the current of the DC power supply section of the power converter and adjusts the PW in accordance with the load fluctuation of the AC motor.
Since the duty ratio of M is changed, the PW
The duty ratio of M can be varied, and the output voltage value at the same frequency of the power converter can be varied, resulting in higher efficiency and a wider operating range in response to load fluctuations, as well as reduced use of microcomputer memory. It is possible to prevent the amount from increasing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the frequency variable device of the present invention, FIG. 2 is a diagram showing changes in voltage/frequency characteristics in the frequency variable device as described above, and FIG. 3 is a diagram of the PWM control circuit in the frequency variable device as described above. FIG. 4 is a block diagram of the second embodiment of the frequency variable device of the present invention, and FIG. 5 is a timing chart for explaining the operation. FIG. 5 is a timing chart for explaining the operation of the PWM control circuit in the frequency variable device of FIG. 4. Figure 6 is a block diagram of a conventional frequency variable device.
FIG. 7 is a diagram showing changes in voltage/frequency characteristics in the frequency variable device of FIG. 6. 1...Commercial AC power supply, 3...Smoothing circuit, 4...Inverter, 5...AC electric stage, 6...PWM control ft
11 circuit, 7... overcurrent detection circuit, 9... PWM wave generator, 10... microcomputer, 11...
Counter, 12... Rectangular wave output circuit, 13... Waveform synthesis circuit, 14... Count data output circuit, 15.
...Inverter drive waveform shaping circuit, 16...Count data memory, 17...A/D converter, 18...P
WM data generation circuit, 19... trigger pulse generator, Note that the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A power converter that outputs AC power of any frequency and any voltage from DC power to drive an AC motor, an overcurrent detection means that detects the current of the DC power supply section of this power converter, and the above-mentioned a first means for determining pulse width modulation duty data corresponding to the output voltage of the power converter at an output frequency necessary for the AC motor to reach a predetermined rotational speed, and outputting a pulse width modulation wave; a second means for determining count data based on the output of the overcurrent detection means; and a rectangular wave obtained from the count value of the count data output from the second means by detecting the pulse width modulated wave and the pulse width modulation. a waveform synthesizing means for changing the duty ratio of the pulse width modulated wave by synthesizing the waves with the pulse width modulated wave, and a circuit for generating a driving waveform for the power converter from the output of the waveform synthesizing circuit in accordance with a frequency command. Variable device. (2) The second means compares the current value of data obtained by converting the analog output of the overcurrent detection means into digital data with a reference current value corresponding to the output frequency of the power converter, outputs count data, and outputs a waveform. The frequency variable device according to claim 1, wherein the synthesizing means synthesizes and outputs a rectangular wave in which the duty ratio of the pulse width modulated wave is changed according to the counted value of the count data using a trigger pulse. .