JP6942416B2 - Power supply voltage monitoring device for inverter control of motor - Google Patents

Description

The present invention relates to a power supply voltage monitoring device that monitors fluctuations in the power supply voltage when an external commercial power supply is used as the power supply for inverter control of the motor.

Inverter control is known as a method for controlling the rotation speed of an induction motor. In this inverter control, when the motor is rotated at a predetermined rotation speed, it is necessary to constantly monitor the voltage of the external commercial power source, which is the power source, and correct the inverter control in response to the fluctuation of the voltage of the commercial power source. Therefore, in the device for controlling the inverter of such a motor, a voltage detection circuit for monitoring the voltage of the power supply is provided (see, for example, Patent Document 1).

As a method of detecting the voltage of the power supply, the voltage of the power supply is 100V or 200V AC, while the signal input to the microcomputer is DC of about 5V, so the AC power from the power supply is stepped down. The voltage of the power supply is detected based on the stepped-down power on the secondary side of the step-down transformer (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2015-188996 (0023, FIG. 4) JP 2011-128973 (Claim 1, FIG. 1)

In the above-mentioned conventional one, a step-down transformer is used to detect the voltage of the power supply, but the step-down transformer has a problem that the unit price is relatively high and the price of the entire device is high. Further, the step-down transformer is often larger than other electronic components, and therefore, there is a possibility that it may be an adverse effect when the entire device is miniaturized.

Therefore, in view of the above problems, it is an object of the present invention to provide a power supply voltage monitoring device for inverter control of a motor capable of monitoring the voltage of the power supply without using a step-down transformer.

Supply voltage monitoring device in the inverter control of the motor according to the present invention in order to solve the above-mentioned problems, which monitors the variation of the external commercial power supply voltage supplying AC power to the inverter control unit for controlling the rotational speed of the motor, In the power supply voltage monitoring device that feeds back to the inverter control unit to rotate the motor at a predetermined rotation speed in response to the fluctuation of the voltage of the commercial power supply, it is lower than the minimum voltage expected as the fluctuation range of the voltage of the commercial power supply. A pulse generation unit is provided in which the voltage is set to a threshold value and a pulse of a time width in which the voltage of the AC power supplied from the commercial power supply continues to be higher than this threshold value is provided, and this pulse is used in the feedback control unit. It is characterized in that the motor is rotated at the predetermined rotation speed by inputting to a microcomputer.

According to the above configuration, since a pulse having a width corresponding to the voltage of the power supply is generated, the voltage of the power supply can be detected from the width of the pulse.

By inputting the pulse generated by the pulse generation unit to the microcomputer via the photocoupler, the high voltage power supply side and the low voltage microcomputer side can be electrically isolated.

As is clear from the above description, since the present invention generates a pulse corresponding to the voltage, it is not necessary to use a step-down transformer for monitoring the voltage of the power supply.

The figure which shows the structure of one Embodiment of this invention. Diagram showing the relationship between the voltage of the power supply and the generated pulse width

With reference to FIG. 1, reference numeral 1 denotes an external commercial power source, which supplies 100 volt AC power in the present embodiment. After rectifying the 100 volt AC power, the voltage dividing resistors 11 and 12 generate a detected voltage and input it to the negative terminal of the comparator 2. On the other hand, the comparison voltage generated from the reference power supply 3 of 15 volts is input to the positive terminal of the comparator 2. With this configuration, the LED 41 emits light when the detected voltage is higher than the comparative voltage.

The LED 41 is integrated with the phototransistor 42 to form a photocoupler. When the LED 41 is emitting light, the phototransistor 42 is turned on, and a pulse signal having the same pulse width as the time when the phototransistor 42 is turned on is generated based on the 5-volt input power supply 5 and input to the microcomputer 6. Will be done.

Therefore, a pulse signal having a pulse width proportional to the voltage of the commercial power supply 1 is input to the microcomputer 6.

A more specific description will be given with reference to FIG. Taking the case where the output waveform of the commercial power supply 1 is the standard waveform AC1 (effective value 100 volts, maximum value 141 volts) and the waveform AC2 at the time of low voltage in the state where the voltage drops, as an example, it is higher than the maximum value of AC2. A low voltage is set as the threshold L, and the comparison voltage input to the positive terminal of the comparator 2 is set so as to correspond to this threshold L. Then, if the waveform is AC1, the LED 41 emits light for t1 time every cycle of the AC frequency of the power supply. On the other hand, when the voltage drops to the waveform AC2, the light emission time of the LED 41 is shortened to t2. That is, when the voltage of the commercial power supply 1 decreases, the light emitting time of the LED 41 becomes short, and although not shown, when the voltage rises, the light emitting time of the LED 41 becomes long.

Since a pulse signal having a pulse width corresponding to the light emission time of the LED 41 is input to the microcomputer 6, the microcomputer 6 can detect the voltage of the commercial power supply 1 from the input pulse width.

The present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the gist of the present invention.

1 Commercial power supply 2 Comparator 3 Reference power supply 6 Microcomputer 42 Phototransistor L Threshold

Claims (2)

Monitors fluctuations in the voltage of an external commercial power supply that supplies AC power to the inverter control unit that controls the rotation speed of the motor, and rotates the motor at a predetermined rotation speed in response to fluctuations in the voltage of the commercial power supply. In the power supply voltage monitoring device that feeds back to the inverter control unit, a voltage lower than the minimum voltage expected as the fluctuation range of the voltage of the commercial power supply is set as a threshold value, and the voltage of the AC power supplied from the commercial power supply is this threshold value. A pulse generating unit for generating a pulse having a time width in which a higher state continues is provided, and this pulse is input to the microcomputer of the feedback control unit to rotate the motor at the predetermined rotation speed. Power supply voltage monitoring device for inverter control of motors. The power supply voltage monitoring device for inverter control of a motor according to claim 1, wherein the pulse generated by the pulse generation unit is input to the microcomputer via a photocoupler.

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