JPS63302796A - Frequency changer - Google Patents

Abstract

PURPOSE:To improve operating efficiency, to prevent overexcitation and to reduce noise, by fluctuating the voltage applied in correspondence with the fluctuation of a load coupled to an AC motor. CONSTITUTION:A current sensor 16 detects the input current, i.e. the phase current, of an AC motor 5. Its output waveform is digitized with an A/D conversion circuit 18 through a current detection circuit 17, taken into a microcomputer 10 and compared with phase current data 10a. The microcomputer 10 produces a PWM wave in accordance with a frequency command 19 and an output voltage setting 10b. The voltage value applied in the same frequency is thereby varied and in accordance with the fluctuation of a load the applied voltage is fluctuated.

Description

[Detailed description of the invention] [Industrial application field]

This invention, for example, AC! The present invention relates to a frequency variable device used for variable speed control of a motive force.

[Conventional technology]

FIG. 4 is a block diagram showing the form of a conventional frequency variable device disclosed in, for example, Japanese Unexamined Patent Publication No. 60-229696, and FIG. 5 is a voltage versus frequency characteristic (hereinafter referred to as , called v/F pattern)
FIG. In FIG. 5, direct current is obtained from a commercial AC power supply 1 via a rectifier circuit 2 and a smoothing port Ri3, and this direct current is converted into alternating current by, for example, a transistor type inverter 4, and the alternating current output powers an alternating current ffi motor 5. Driven. A mechanical load (not shown) is connected to the AC type IJ machine 5. As a control device for the impark 4, a microcomputer 10 (hereinafter referred to as a microcomputer) and a control circuit N511 are provided. The microcomputer 10 receives a frequency signal inputted by an input means (not shown), that is, a signal representing the output frequency F2 of the impark 4 necessary to bring the AC motor 5 to a desired rotational speed, and converts it into the inverter output frequency up to the immediately preceding frequency signal. The frequency is increased by comparing it with the signal representing F (, F2>
It determines whether to perform downward control (when F2<F+) or to perform downward control (when F2<F+), and sends out the judgment result as a direction judgment signal R, and also divides frequencies F and F2 into appropriate steps and represents it. A signal, that is, a frequency signal Q, is sequentially sent to the control circuit 11 at an appropriate timing, that is, in terms of time. The control circuit 11 includes a changeover switch 14 that selectively takes out the outputs of the voltage setting device 12 for increasing control, the voltage setting device 13 for decreasing control, and the outputs of both type pressure setting devices 12 and 13, and A waveform shaping circuit 15 is provided for supplying a control signal to the inverter 4 to control it to a predetermined frequency and a predetermined voltage according to the signal and the frequency signal Q described above. The changeover switch 14 is the microcomputer 1
Climb control (F2>Fl
), the switch is made to the voltage setting device 12 side, and the downward control (F
2 <F l ), the voltage setting device is switched to 136W. The voltage setting device 12 has a V/F characteristic U when the frequency increases as shown in FIG.
A voltage V corresponding to the input frequency from the microcomputer 10 according to P. Similarly, the voltage setter 13 outputs a signal representing the voltage voow corresponding to the input frequency in accordance with the V/F characteristic DOWN when the frequency decreases. According to the device shown in FIG. 5 configured as described above, the output of the inverter 4 is controlled by I11 according to the V/F characteristic according to the UP characteristic shown in FIG. 4 when the frequency increases, and according to the DOWN characteristic shown in the same figure when the frequency decreases. Controlled according to V/F characteristics. Therefore, by considering load characteristics, power supply fluctuations, etc., and providing appropriate UP and DOWN characteristics according to the frequency control direction, motor breakdown can be prevented regardless of load characteristics or power supply fluctuations. . Therefore, is it caused by breakdown of the electric motor? There is no possibility that the first-stream protection circuit will operate (this means that higher-quality operation can continue).

Problems to be Solved by the Invention] Therefore, the problem with the prior art is that 2N class V/F data is stored in the memory, and when the frequency increases and decreases, the V/F data is
Although the F data is used differently, the V/F characteristics cannot be changed in response to changes in the mechanical load connected to the AC wh machine. Therefore, when the mechanical load is light, overexcitation occurs and the input current of the AC M motor (hereinafter referred to as phase current) increases, and when the load is heavy, the phase current increases due to insufficient applied voltage. However, there was a problem in that the operating efficiency of the AC motor decreased. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a device that can increase or decrease the applied voltage in response to an increase or decrease in the load connected to an AC motor. [Means for solving the problem] The frequency variable device according to the present invention includes means for detecting the phase current of an AC motor and reading the value of the phase current into a microcomputer;
From means that can vary the applied voltage value at the same frequency,
The AC motor is driven with the applied voltage that minimizes the phase current.

[For production]

By reading into a microcomputer the phase current values obtained when the voltage applied to the AC motor is varied while the frequency of the AC motor is stable, the applied voltage that minimizes the phase current in the present invention is obtained.

[Embodiments of the invention]

An embodiment of this invention will be described below. FIG. 1 is a diagram showing the overall configuration of the present invention, and FIG. 2 is a flowchart showing the operation for determining the applied voltage that minimizes the phase current of the AC M motor 5 in the present invention. In FIG. 1, direct current is obtained from a commercial AC power supply 1 via a rectifier circuit 2 and a smoothing circuit 3, and this direct current is supplied to an inverter 4.
The current is converted into alternating current, and the alternating current motor 5 is driven. A mechanical load (not shown) having load torque fluctuation is connected to the AC motor 5. A microcomputer 10 and a waveform shaping circuit 15 are provided as control devices for the inverter 4. Further, a current sensor 16 is provided to detect the input current, that is, the phase current, of the AC motor 5, and its output waveform is transmitted to the A/D converter circuit 18 via the RI current/output circuit 17.
The phase current data is digitized, taken into the microcomputer 10, and compared with phase current data 10a. Microcomputer 10 has frequency command 19
PWM wave acid generation 10c according to output voltage setting 10b
. Next, the microcomputer 10 determines the output voltage from the phase current data.
The operation will be explained using a flowchart. In FIG. 2, in [Al, the AC motor 5 is driven at a frequency F1 voltage vout. If the frequency is stable, increase the output voltage Vout to VMAX (B1(vMAX
is the maximum voltage that can be driven at frequency F). When the output voltage changes, the phase current value is read by the means and stored in the memory. The output voltage Vout is lowered by a certain value ΔV, and then the phase current values are read and sequentially stored in the memory. After that, repeat the output voltage Vout
When the reading of the phase ri current value when VHIN (VM IN is the minimum drivable output voltage at frequency F) is completed, the process proceeds to EC). Here, the minimum value of the read phase current data is determined 10a, and the output voltage Vout at that time is set as the new output voltage setting (Dl. Also, the new output voltage is set.

After [D], after a certain period of 'ruff has passed, read the phase current (El, and if the phase current value change exceeds a certain value of 61, return to Bl,
Reset the output voltage that minimizes the phase current. T, if a longer time T2 has elapsed (Fl also resets the output voltage in the same way. Figure 3 shows how to determine the applied voltage that minimizes the phase current of the AC motor in another embodiment of this invention. This is a flowchart 1 diagram showing the operation. In Figure 3, IAI drives an AC motor at frequency F and lightning voltage out. If the frequency is stable,
Output voltage Vout, a voltage Vout that is higher by a certain value ΔV than Vout + Δ” A voltage V that is lower than pVOut by ΔV
110Vou drives the AC motor 5 with 3Ti voltage of out-ΔV, reads the phase current at that time and stores it in the memory.
The current value when driven by t ΔV'''C is I 10, Vou
If it is I 6 at time t, and ■- at Vout-ΔV, then I+. Compare Io and I- (in Cl, when ■. is small, Vo
1F which outputs ut). Also, when 10 is the minimum [0],
Return to IB+ with Vout + ΔV as new Vout. And the new Vout, Vout +ΔV, vout−
Compare again the phase current values when driven with three voltages of ΔV. [
Cl. (When it does not apply to Dl, set Vout-ΔV to Vou
Return to (B) as t. In this way, the output voltage Vout at which the Igft current is minimum is determined. Also, after setting a new output voltage [Fl], after a certain period of time T, H, read the phase current (G), and if the change in phase current exceeds a certain value of 61, return to 1B], and the phase current is the minimum. Reset the output voltage. T, when a longer time T2 has elapsed (Hl also resets the output voltage in the same way. [Effects of the Invention] As described above, in this invention, the voltage applied in response to the increase or decrease in the load connected to the AC motor Since the configuration is such that the voltage can be increased or decreased, the operating efficiency of the AC motor can be improved, overexcitation can be prevented, and noise can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the overall configuration of this invention. Figure 2 is the first
Flowchart 1 and Figure 3 represent the operation of determining the applied voltage that minimizes the phase current of the AC motor in the embodiment shown in the figure.
The figure is a flowchart showing the operation of determining the applied voltage in the second embodiment, and FIG. 4 is a diagram showing the configuration of the conventional example.
Figure 5 shows the conventional example of a:/verter, 5...
0...Microcomputer, 15...Waveform shaping circuit, 16...
Current sensor, 17 ・Current detection circuit, 18...A/,
D conversion circuit, 19...frequency command. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent: Masuo Ohatsu (2 others, Figure 2, Figure 3)

Claims (1)

[Claims] A frequency variable device characterized by comprising means for detecting the phase current of the AC motor and reading it into a microcomputer, means for varying the applied voltage at the same frequency, and means for finding the application where the phase current of the AC motor is the minimum. Device.