JPH09163784A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce current leakage for restraining electric shock in an inverter which drives an d.c. motor. SOLUTION: This inverter is operated with a plurality of ON duties combined within one turn of an d.c. motor 4, and is capable of being controlled so that the average of a plurality of ON duties may be a desired ON duty value. This inverter is also provided with a duty operating device 12 which makes classification into a plurality of types of duty ratios so that the average may be equal to the desired duty value without ON duty ratios being used within a range of 40% to 60%, thus it is possible to reduce current leakage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system capable of reducing leakage current in an inverter device having a DC motor of a compressor used as a load in a refrigeration cycle device such as a refrigerator.

[0002]

2. Description of the Related Art A typical example of a conventional method of controlling an inverter device for driving a DC motor is shown. FIG. 6 shows an inverter circuit, and FIG. 7 shows ON-OFF waveforms of the semiconductor switch.

In FIG. 6, reference numeral 1 is an AC power source. Reference numeral 2 is a voltage doubler rectifier circuit that converts the AC voltage of the AC power supply 1 into a DC voltage.

Reference numeral 3 denotes an inverter circuit in which semiconductor switches (transistors) 3a to 3f are three-phase bridge-connected, and diodes are connected in parallel and in opposite directions to each transistor.

Reference numeral 4 denotes a DC motor, which is an inverter circuit 3
Driven by the output of. Reference numeral 5 denotes a position detection circuit that generates a position detection signal of the DC motor 4, and detects the position from the counter electromotive voltage of the DC motor 4.

Reference numeral 6 is a commutation circuit for producing commutation pulses for commutating the semiconductor switches 3a to 3f of the inverter circuit 3 from the output of the position detection circuit 5.

Reference numeral 7 is a rotation speed command means, which outputs a rotation speed command signal for the DC motor 4. Reference numeral 8 denotes a rotation speed detecting means, which detects the rotation speed by counting the position detection signal of the position detection circuit 5 for a certain period or measuring the pulse interval of the position detection signal.

Reference numeral 9 denotes a comparator, which compares the target rotation speed of the rotation speed command means 8 and the actual rotation speed detected by the rotation speed detection means 9 so that they match each other, and increases or decreases the duty value. Is output.

Reference numeral 10 denotes a duty control means, which sets an ON duty ratio from the output of the comparator and outputs a chopping signal.

A drive circuit 11 combines the commutation pulse from the commutation circuit and the chopping signal output from the duty control means to turn on / off the semiconductor switches 3a to 3f of the inverter circuit 3.

In FIG. 1, Tu + means the U-phase semiconductor switch of the upper arm, and Tu- means the U-phase semiconductor switch of the lower arm. The same applies to Tv +, Tv-, and the like. In the waveform of the switching pattern shown in FIG. 2, the HI level is the semiconductor switch ON.

As shown in FIG. 2, the lower arms (3d to 3f) are
Switch), 120 degree energization control, upper arm (3a-3
c switch) is a uniform width PWM for normal 120 degree energization control
Control (ON duty 0 to 100%).

[0013]

When a DC motor is driven by an inverter device, a high frequency current component leaks to the shell via stray capacitance formed between the winding of the DC motor and the motor shell. Is called leakage current.

In this inverter device, there is no problem with the leakage current if the shell is grounded. The leakage current characteristic is shown in FIG. 8. According to this characteristic, the duty ratio is 5%.
When it is 0%, the leakage current value becomes maximum.

Therefore, in the vicinity of the duty of 50%, the margin for designing the leakage current was not obtained so much.

The method for reducing the leakage current is to reduce the stray capacitance between the armature winding and the shell of the electric motor. Therefore, there has been a proposal to reduce the leakage current by reducing the number of windings of the electric motor and the amount of copper.

However, as the efficiency of the electric motor decreases,
From the driving aspect of the electric motor, it cannot be said that this is a suitable improvement method.

The present invention eliminates the above-mentioned drawbacks of the prior art, and provides an inverter device capable of relatively easily reducing the leakage current of the inverter device.

[0019]

In order to achieve this object, an inverter device of the present invention comprises an inverter circuit in which a plurality of semiconductor switches and diodes are bridge-connected,
It is composed of a DC motor operated by an inverter circuit and a duty control means for controlling the ON duty of the semiconductor switch to control the rotation speed of the DC motor.

Further, a plurality of O's can be formed within one revolution of the DC motor.
Operates in combination with N duty.

Further, the ON duty ratio is changed from 40% to 6%.
Do not use between 0%. Further, the torque detection means for detecting the load torque during one rotation of the DC motor and the ON duty are controlled so as to be pseudo coincident with the load torque.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is
An inverter circuit in which a plurality of semiconductor switches and diodes are bridge-connected, a DC motor operated by the inverter circuit, and duty control means for controlling the ON duty of the semiconductor switch to control the rotation speed of the DC motor Therefore, the rotation speed can be changed by changing the ON duty ratio.

According to a second aspect of the present invention, the DC motor is operated by combining a plurality of ON duties within one rotation, and an average value of the plurality of ON duties is set to a desired O value.
It can be controlled to have an N duty value.

According to the third aspect of the invention, since the ON duty ratio is controlled so as not to be used between 40% and 60%, the leakage current can be reduced.

According to a fourth aspect of the present invention, a torque detecting means for detecting the load torque during one rotation of the DC motor is provided, and the ON duty can be controlled so as to match the load torque in a pseudo manner. In addition to being able to reduce the load pulsation, it is possible to reduce the vibration of the compressor and the like. (Embodiment 1) Hereinafter, an embodiment of the present invention will be described.
This will be described with reference to FIGS. It should be noted that the same configurations as those of the related art are denoted by the same reference numerals and detailed description thereof will be omitted. FIG. 1 is a first embodiment and is an overall configuration diagram of an inverter device.

In FIG. 1, reference numeral 12 denotes a duty calculator, which divides the duty value obtained by the duty control means 10 into several kinds of duty ratios, equalizes the duty values as an average, and outputs a chopping signal to the drive circuit 11. Is.

FIG. 2 shows an example of the switching waveform of the U-phase upper arm when the duty is 50%. The same applies to the V phase and the W phase. In the figure, a is an example divided into 10% and 90%, and b and c are examples divided into 20%, 30%, 70% and 80%. An example at a duty of 40% is also shown in FIG.

The setting of 0% and 100% is the same as the case of halving the chopping frequency (carrier frequency).

As described above, in the present embodiment, since the ON duty ratio is set between 0% to 40% and 60% to 100% where the leak current is small, the leak current can be reduced and the design margin can be reduced. Can be increased. (Embodiment 2) Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram of an inverter device showing a second embodiment of the present invention. FIG. 5 shows characteristics of load variation and duty ratio during one revolution of the DC motor.

In FIG. 4, 13 is a torque detection circuit for detecting the torque during one revolution of the DC motor from the current busbar. Reference numeral 14 denotes a duty control means, which combines the output of the torque detection circuit 13 and a signal obtained from the difference between the target rotation speed and the actual rotation speed and outputs the combined signal to the duty calculator. The output of the duty control means is shown by a wavy line in FIG. 5, and the output of the duty calculator is shown by a solid line.

In the duty calculator, the output from the duty control means is redistributed in one rotation, and 40% to 60%.
Do not use with the duty ratio of. With the configuration shown in FIG. 5, it is possible to reduce the leakage current and also reduce the vibration due to the load torque fluctuation.

[0033]

As described above, the DC motor control device of the present invention can reduce the leakage current, can increase the design margin for the leakage current, and can reduce the vibration due to the load torque fluctuation.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an inverter device according to a first embodiment of the present invention.

FIG. 2 is a time chart showing a U-phase chopping signal at a duty of 50% according to the first embodiment of the present invention.

FIG. 3 is a time chart showing a chopping signal at a duty of 40% according to the first embodiment of the present invention.

FIG. 4 is an overall configuration diagram of an inverter device according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a relationship between load torque and duty according to the second embodiment of the present invention.

FIG. 6 is an overall configuration diagram of a conventional inverter device.

FIG. 7 is a characteristic diagram showing ON / OFF waveforms of a conventional semiconductor switch.

FIG. 8 is a leakage current characteristic diagram of a conventional inverter device.

[Explanation of symbols]

 3 Inverter Circuit 4 DC Motor 10, 14 Duty Control Means 12 Duty Calculator 13 Torque Detector

Claims (3)

[Claims] 1. An inverter circuit in which a plurality of semiconductor switches and diodes are bridge-connected, a DC motor operated by the inverter circuit, and a duty control for controlling the duty ratio of the semiconductor switch to control the rotation speed of the DC motor. An inverter device comprising: a means, and a duty calculator capable of combining a plurality of types of duty values having different duty ratios within one rotation of the DC motor. 2. The duty calculator has a duty ratio of 40.
The inverter device according to claim 1, wherein the inverter device is divided into a plurality of types of duty ratios so that the average value is equal to a desired duty value without being used in the range of 60% to 60%. 3. The torque detecting means for detecting the load torque during one revolution of the DC motor and the duty calculator control the duty ratio so that the load torque is pseudo coincident with the load torque. The inverter device according to 2.