JP2638767B2 - Control method of air conditioner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an air conditioner, and more particularly, to a means for improving a power factor of the air conditioner and reducing a harmonic current.

[0002]

2. Description of the Related Art An air conditioner is provided with an inverter device for controlling a compressor motor by an inverter and a control circuit for controlling the inverter device. FIG. 4 shows an example of this, in which the inverter device converts the AC from the input AC power supply 21 to DC,
A converter circuit 25 includes a reactor 23, a capacitor 24, and the like, and an inverter circuit 27 that converts a DC input from the converter circuit 25 into an AC through inverter control and outputs the AC to a compressor motor 26. In addition, the control circuit side is mainly used by a microcomputer 28 to detect an input current.An input current detection circuit 29 is used for determining a power supply frequency, detecting an input current, and transmitting / receiving timing between an indoor unit and an outdoor unit. The microcomputer 28 includes an input current detection circuit 29, a zero cross detection circuit, and a drive circuit 31 for controlling an inverter circuit 27.
Based on the input signal obtained from 30 etc., the input current is
The drive circuit 31 is controlled so as not to exceed the current capacity of 21. FIG. 5B shows an example of the output of the input current detection circuit 29 input to the microcomputer 28.
A / D conversion is performed inside the microcomputer 28 at the zero-cross timing indicated by a circle to detect an input current. Timer data for generating a PWM waveform is stored in a storage unit inside the microcomputer 28, and a PWM waveform signal is output to the drive circuit 31 by using a timer inside the microcomputer 28, and the inverter circuit Controlling 27.

[0003]

However, since the above converter circuit is of the capacitor input type,
The input current becomes a distorted wave flowing in a pulse shape as shown in FIG. For this reason, there is a problem that the input power factor decreases and the harmonic current increases. Therefore, an object of the present invention is to provide a control method of an air conditioner in which an input power factor is improved and a harmonic current is reduced.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and is an air conditioner having an inverter device, which comprises an input AC power supply, at least a reactor constituting a closed circuit, and a switching element. The switching control of the switching element is performed so that the input current becomes substantially a sine wave having substantially the same phase as the input voltage, and the input current and the instantaneous value of the input current are detected. If the instantaneous value is greater than the first reference value, the on-time of the duty cycle of the switching signal for controlling the switching element corresponding to the instantaneous value is reduced, and the instantaneous value of the detected input current becomes equal to the instantaneous value. A switching signal for controlling the switching of the switching element corresponding to the instantaneous value when the value is smaller than a second reference value. Of decided to control so as to increase the on time of the duty cycle.

[0005]

According to the above control method, when switching control is performed on a switching element provided in a converter circuit (AC / DC conversion means) so that an input current and an input voltage become substantially sine waves having substantially the same phase, An input current and an instantaneous value of the input current are detected. If the instantaneous value of the detected input current is larger than a first reference value of the instantaneous value, a switching signal of the switching element corresponding to the instantaneous value is controlled. When the on-time of the duty cycle is reduced, and the instantaneous value of the detected input current is smaller than a second reference value of the instantaneous value, the duty cycle of the duty cycle of the switching signal for controlling the switching element corresponding to the instantaneous value is reduced. Since the control is made to increase the on-time, the input current waveform should be approximately sinusoidal with almost the same phase as the input voltage. It can be.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the air conditioner has a converter circuit 2 for converting an input AC power supply 1 into a DC.
And an inverter circuit 3 to which a direct current from the converter circuit 2 is supplied, and a power supply provided in the converter circuit 2 to improve the input power factor and reduce harmonics (reactor (choke coil) ) 4 and a switching element (IGBT) 5, an input current control circuit including a reverse blocking diode 6, a compressor motor 7 driven by the inverter circuit 3, and an input current sensor (CT) 8. An input current instantaneous value detection circuit 9 for detecting an instantaneous value of a current, and a zero cross detection circuit for detecting an AC zero cross.
10 and a drive circuit 11 for driving the switching element 5
And a drive circuit 12 for driving the inverter circuit 3 and a microcomputer (hereinafter referred to as a microcomputer) 13 for controlling the drive circuit 12.

[0007] In addition to the reactor 4 and the switching element 5, the converter circuit 2 includes a rectifier circuit 2a for rectifying AC to DC and a capacitor 2b for smoothing DC. The microcomputer 13 generates a PWM waveform corresponding to a desired number of rotations of the compressor motor 7, controls the compressor motor 7 by the inverter based on the PWM waveform, and obtains an input signal obtained from the input current instantaneous value detection circuit 9. The overcurrent protection function is activated based on the calculated input current, and the inverter circuit 3 is controlled so that the rotation speed of the compressor motor 7 is reduced when an overcurrent occurs.

The air conditioner has a zero-crossing detection circuit 10 for detecting an input AC zero-crossing point for discriminating an input frequency and interrupt processing as described above.
Incorporates an A / D converter, a timer, a storage unit, and the like. The present invention utilizes these components to detect the instantaneous value of the input current of the converter circuit 2 and the input current value. When the instantaneous value is larger than the first reference value of the instantaneous value, the on-time of the duty cycle of the switching signal for controlling the switching element corresponding to the instantaneous value is reduced, and the instantaneous value of the detected input current is reduced. When the instantaneous value is smaller than the second reference value, the switching element 5 is controlled so as to increase the on-time of the duty cycle of the switching signal for controlling the switching element corresponding to the instantaneous value.

For example, when the input current is 5 A, when the switching control is performed with the switching signal shown in FIG. 2A, the input current waveform becomes as shown in FIG. 2B.
The output of the input current instantaneous value detection circuit 9 at this time is as shown by a solid line in FIG. The output of the input current instantaneous value detection circuit 9 is input to the microcomputer 13 and A / D converted inside the microcomputer 13 at timings t0 to t10 to detect instantaneous values I0 to I10. The input current is the instantaneous value I0
To I10. The detection of the input current is not limited to the above-described method, and may be performed by providing a conventional input current detection circuit 29 as shown in FIG. The broken lines in FIG. 2C show the first reference value and the second reference value of the instantaneous value of the detected input current.

The first reference value and the second reference value of the instantaneous value of the detected input current vary depending on the magnitude of the input current as shown in FIG. 3, and are obtained by calculation from the detected input current. As another method, data of a first reference value and a second reference value corresponding to an input current are stored in advance in a storage unit inside the microcomputer 13 and read out from the storage unit in accordance with a detected input current. You may ask for it. Since the input current changes due to the rotation speed and load fluctuation of the compressor motor 7 and the influence of the power supply impedance of the power supply to be used, the detected instantaneous values I0 to I as shown in FIG.
10 is calculated based on the first reference value obtained from the detected input current and the second reference value.
To the reference value. Then, when the instantaneous value is larger than the first reference value, that is, the instantaneous value I in FIG.
With respect to 6, I7, the on-time D6, D7 of the duty cycle of the switching signal for controlling the switching of the corresponding switching element 5 is reduced.

When the instantaneous value is smaller than the second reference value, that is, for the instantaneous values I2 and I3 shown in FIG. 2C, the duty of the switching signal for controlling the switching of the switching element 5 corresponding thereto. The cycle ON times D2 and D3 are increased. Other instantaneous values are equal to or less than the first reference value and equal to or greater than the second reference value.
Not going to change. FIG. 2D shows a switching signal when the above control is performed, and FIG. 2F shows an output of the input current instantaneous value detection circuit 9 at that time. As can be seen from FIG. 2F, the instantaneous values I0 to I10 are equal to or less than the first reference value and equal to or greater than the second reference value, and the input current waveform is shown in FIG. Thus, the sine wave has substantially the same phase as the input voltage. In this embodiment, the input current is set to 5 A. However, the input current is not particularly limited to this value.
An instantaneous value and an input current of the input current are detected, and a first reference value and a second reference value are obtained as shown in FIG. 3 in accordance with the input current, and the instantaneous value, the first and second reference values, By increasing and decreasing the ON time of the switching signal by comparing
Regardless of the magnitude of the input current, the input current can be made substantially sinusoidal with substantially the same phase as the input voltage.

[0012]

As described above, if the air conditioner is controlled by the control method described above, the existing parts of the air conditioner are generally used to the maximum extent, the increase in the number of parts is suppressed, and the cost is reduced. The input current can be reliably made almost sinusoidal with almost the same phase as the input voltage without being affected by load fluctuations or the power supply impedance of the power supply used while suppressing the rise, improving the power factor and increasing the harmonic current. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a main part circuit block diagram of an air conditioner showing one embodiment of the present invention.

FIG. 2 is a schematic waveform diagram for explaining one embodiment of the present invention.

FIG. 3 is a schematic waveform diagram for explaining one embodiment of the present invention.

FIG. 4 is a main part circuit block diagram of an air conditioner showing a conventional example.

FIG. 5 is a schematic waveform diagram when switching control is performed by a conventional control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input AC power supply 2 Converter circuit (AC / DC conversion circuit) 3 Inverter circuit 4 Reactor (choke coil) 5 Switching element (IGBT) 7 Compressor motor 8 Input current sensor (CT) 9 Input current instantaneous value detection circuit 10 Zero cross detection Circuit 11 Drive circuit 12 Drive circuit 13 Microcomputer

Claims (2)

(57) [Claims] 1. An air conditioner having an inverter device,
An input AC power supply and at least a reactor constituting a closed circuit and a switching element, wherein the switching control of the switching element is performed so that the input current becomes a substantially sine wave having substantially the same phase as the input voltage, and an input current and an input current And when the instantaneous value of the detected input current is greater than a first reference value of the instantaneous value, the on-time of the duty cycle of a switching signal for controlling the switching of the switching element corresponding to the instantaneous value If the instantaneous value of the detected input current is smaller than a second reference value of the instantaneous value, the on-time of the duty cycle of the switching signal for controlling the switching of the switching element corresponding to the instantaneous value is increased. A method for controlling an air conditioner, comprising: 2. The control method for an air conditioner according to claim 1, wherein the first reference value and the second reference value are obtained from the input current.