JPS6264272A - Controller for pwm inverter - Google Patents

Abstract

PURPOSE:To hold an AC output voltage constant irrespective of the variation in an input voltage by controlling the frequency and the pulse width of an inverter by a reference frequency and a corrected voltage reference signal. CONSTITUTION:An input DC voltage V is detected by a voltage detector 11, amplified by an amplifier 6e, a reference voltage (v) generated from a V/F characteristic generator 2 is then divided by a divider 12, amplified by an amplifier 6e, a voltage reference signal is calculated, and input to D/A converters 5a, 5b. A reference frequency is also input from a microprocessor 4 to the converters 5a, 5b. The outputs of the converters 5a, 5b are applied through amplifiers 6a-6c to comparators 9a-9c. The comparators 9a-9c output drive signals for turning ON or OFF switching elements of phases of an inverter.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a control device for a PUM (Pulse Width Modulation) inverter using a DC power supply, and particularly to a control device for a PUM (pulse width modulation) inverter using a DC power supply, and in particular a constant V/F (ratio of output voltage to output frequency) control. This invention relates to a correction circuit for DC power supply voltage fluctuations.

[Technical background of the invention and its problems]

An example of a conventional internal S inverter that controls V/F at a constant level is shown in FIG.

In FIG. 4, the output command signal set by the output command setting device 1 is input to the V/F characteristic generator 2, and its output is V
It is converted into a pulse train of frequency reference f* via the F converter 3, inputted to the clock of the microprocessor 4, and processed internally to produce a sine wave reference pulse fU for the U phase and W phase,
f is output, and multiplier type OA converters 5a, 5 respectively.
b.

On the other hand, the voltage reference signal v* from the V/F characteristic generator 2 (as shown in FIG. After being converted into an analog value, it is further passed through an amplifier 6a.

6c and become U-phase and W-phase sine wave control signals Sυ and Sυ, respectively.

The sine wave control signal SU+SW is further connected to a resistor 7a,
V-phase sine wave control signal S via 7b and amplifier 6b.
It is converted into ν and compared with the triangular carrier wave T generated by the oscillator 8 by the respective comparators 9a, 9b, and 9c, and outputs a drive signal that turns on and off each switching element of the U phase, ■ phase, and W phase of the inverter. and this results in 3
You are getting a phase sine wave inverter output.

Figure 7 shows the signal waveforms of each part mentioned above, (A) - is 1
Kyo, (B) is fu, (C) is Ty SLJw sv, (
D) shows a U-phase drive signal, and (E) shows a V-phase drive signal.

In the circuit shown in Figure 4 above, there is a one-to-one correspondence between the frequency reference f* and the drive signal, so the inverter output voltage is proportional to the main circuit input DC voltage V, and therefore when the input DC voltage V increases, the V/F ratio increases. When the ratio increases and the value of (2) decreases, a problem arises in that the V/F ratio decreases, which is particularly a problem when used to drive an AC motor.

In order to prevent the inverter output voltage from being affected by input voltage fluctuations, the output voltage is rectified by a rectifier 10 as shown in FIG. 5, and the deviation is compared with the voltage reference V by a deviation detector 13 as a feedback signal. There is a method of adding it to the voltage reference V, amplifying it with an amplifier 6d, and using it as an actual voltage reference signal, but such feedback control has the problem of causing instability of the output voltage when input voltage fluctuations are large. .

Another way to prevent input voltage effects is to set the input voltage V to -
There is a method of passing the voltage through a chopper circuit to convert it into a constant DC voltage and using this as the input DC voltage, but in this case, the entire device becomes large, which poses problems in terms of size and cost.

[Purpose of the invention]

An object of the present invention is to provide a control device for a V/F-controlled PlIM inverter that maintains an AC output voltage constant regardless of input voltage fluctuations.

[Summary of the invention]

The present invention provides a control device for a DC voltage input PWM inverter that performs constant V/F control in accordance with a set reference frequency. It is equipped with a voltage correction circuit that divides by the ratio to obtain an actual voltage reference signal, and uses the above reference frequency and the corrected voltage reference signal to control the frequency and pulse width of the inverter, thereby adjusting to fluctuations in the DC input voltage. This allows the V/F ratio to be kept constant regardless of the situation.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

Compared to the conventional circuit shown in FIG. 4, FIG. 1 is provided with a voltage correction circuit that corrects the voltage reference signal - according to the main circuit input DC voltage V, and other aspects are the same as the conventional circuit shown in FIG. 4.

That is, the input DC voltage V is detected by the voltage detector 11,
After being amplified by the amplifier 6e, the reference voltage V generated by the V/F characteristic generator 2 is divided by the divider 12, and then the reference voltage V generated by the V/F characteristic generator 2 is divided by the divider 12.
d and finally as a voltage reference signal.

(2) is calculated and input to the DA converters 5a and 5b. Here■
.

is the standard value of the input DC voltage V (that is, the input DC voltage where V can be used as is as -).

FIG. 2 shows the relationship between V and V* when V>Vo.

When the voltage reference signal V* is corrected according to the human-powered DC voltage V in this way, when the input DC voltage V is higher than the standard value v0, the voltage reference signal V tree decreases in inverse proportion to it, and each sine wave control signal Sυ ? SV* The peak value of SV also becomes smaller, and the on-period of the drive signal of each phase becomes smaller in inverse proportion to the input DC voltage V. Eventually, the output voltage of the inverter becomes proportional to the frequency reference fx regardless of fluctuations in the input DC voltage V. V/F constant control is performed stably.

FIG. 3 shows another embodiment of the present invention. In this case, the output voltage of the inverter is fed back through the rectifier 10, the deviation from the voltage reference V is detected by the deviation detection @ 13, and the output voltage of the divider 12 is output. This suppresses fluctuations in the inverter output voltage due to factors other than DC input voltage fluctuations, thereby making it possible to obtain a more stable output voltage.

〔Effect of the invention〕

As explained above, according to the present invention, by simply adding a simple correction circuit that corrects the voltage reference signal corresponding to the same frequency reference according to fluctuations in the DC input voltage and changes the pulse width in the PWH, the DC input voltage can be changed. V regardless of voltage fluctuations
A rational Pli1M inverter control device that can maintain the /F ratio constant can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the operation of the voltage reference correction circuit in FIG. 1,
FIG. 3 is a block diagram showing another embodiment of the present invention, FIGS. 4 and 5 are block diagrams each showing an example of a conventional control device, and FIG. 6 is a frequency reference signal and voltage reference in FIG. 4. A characteristic diagram showing the relationship with the signal, and FIG. 7 is a waveform diagram of each part in PvM control. 1 Output command setter 2 V/F characteristic generator 3 VF converter 4 Microprocessor 5a, 5b Multiplying type DA converter 68-6e Amplifier 8 Oscillator 9a, 9b, 9c Comparator 10 Rectifier 11 Voltage detector 12 Divider 13 Deviation Detector (8733) Agent Patent Attorney Yoshiaki Inomata (and 1 other person) Section 2, Figure 3, Figure 6, Section 7

Claims (1)

[Claims] In a control device for a DC voltage input PWM inverter that performs constant V/F control in accordance with a set reference frequency, the voltage reference proportional to the reference frequency is divided by the ratio of the actual DC input voltage and the standard DC input voltage. 1. A control device for a PWM inverter, comprising a voltage correction circuit that uses the reference frequency as an actual voltage reference signal, and controls the frequency and pulse width of an inverter using the reference frequency and the corrected voltage reference signal.