JPH0568375A - Control method for air-conditioner - Google Patents

Abstract

PURPOSE:To improve input power factor of an air-conditioner, to suppress higher harmonics, and to eliminate abnormal increase of output voltage from an AC/DC converting circuit under light load. CONSTITUTION:An AC/DC converting circuit 2 for converting an AC power supply into DC power is provided, at least, with a reactor 4 and a switching element 5 constituting a closed circuit together with the power supply wherein the switching element 5 is controlled so that the input current and input voltage will be substantially sinusoidal and in-phase. Under light load(when the input current is low), switching control is stopped when the waveform of input current passes through a zero-cross point and approaches the peak thereof and the switching control is resumed when the waveform of input current reaches the peak. Existing zero-cross detecting circuit 10 and input current sensor 8 of air-conditioner are utilized, respectively, for detecting the zero-cross point and the AC input current, necessary for the control, and the internal timer of a control microcomputor 13 is also utilized in the control.

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 a power supply circuit of an air conditioner.

[0002]

2. Description of the Related Art In an air conditioner, an AC power source is converted into a direct current, the direct current is supplied to an inverter section, and a microcomputer generates a PWM waveform for controlling the inverter of the compressor. The inverter unit is controlled in accordance with the above. By the way, a power supply circuit for converting an AC power supply into a direct current is generally of a capacitor input type, but such a power supply circuit has a poor input power factor because the input current becomes a distorted wave, and the harmonic current Occur. Therefore, in order to improve this input power factor and reduce harmonics, for example, as shown in FIG.
The DC conversion circuit 21, that is, between the AC power supply 22 and the inverter unit 23, an input current control circuit by a reactor 24 and a switching element 25 that form a closed circuit with the power supply is provided, and the switching element 25 is turned on at high speed. It is turned off so that the input current waveform becomes a substantially sine wave.

[0003]

However, in the case of the power supply circuit controlled by the above-mentioned control method, if the load is appropriate, the output voltage will also be an appropriate value, as shown in FIG. However, as shown in FIG. 7B, there is a drawback that the output voltage is abnormally increased when the load becomes light and the input current decreases. Therefore, conventionally, an overvoltage detection circuit 26 as shown in the circuit of FIG. 3 is provided to activate the protection function when an overvoltage is detected, but this alone stabilizes the DC voltage to the inverter section. However, there is a problem in that the power source for other control circuits generated from the output DC voltage cannot be stabilized and the rating of the components used cannot be lowered. Therefore, in the present invention, an air conditioner control that solves these problems, improves the input power factor, reduces the harmonics, and suppresses an abnormal increase in the output voltage during light load, at low cost. It is intended to provide a way.

[0004]

The present invention has been made to solve the above problems, and an inverter section for converting an AC power supply into a DC by an AC / DC converting means and controlling a compressor by an inverter. In the air conditioner configured to supply the AC / DC converting means, at least a reactor and a switching element that form a closed circuit with the AC power supply are provided in the AC / DC converting means, and the input current is substantially a sine wave having substantially the same phase as the input voltage. Therefore, the switching element is controlled so that the switching control is intermittently performed at a light load.

[0005]

In the control method described above, the switching element provided in the AC / DC converting means is switching-controlled so that the input current and the input voltage are substantially sinusoidal in phase, so that the input power factor is improved. , The harmonic current is reduced. Further, when the input current becomes small, that is, when the load becomes small, the switching control is intermittently performed, so that the current flowing through the switching element becomes small. Therefore, it is possible to stabilize the output voltage of the AC / DC converting means against changes in the load. Moreover, the detection of the AC input current necessary for performing the above control and the detection of the zero-crossing point are performed by the input current sensor of the overcurrent protection means existing in the air conditioner, and the input AC for the input frequency discrimination and interrupt processing. The zero-cross detection means can be shared.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the air conditioner, as shown in FIG.
An AC / DC conversion circuit 2 for converting the AC power supply 1 into DC,
The inverter unit 3 to which the direct current from the AC / DC conversion circuit 2 is supplied, and a power supply and a closed circuit provided in the AC / DC conversion circuit 2 for improving the input power factor and reducing harmonics are configured. An input current control circuit including a reactor (choke coil) 4 and a switching element (IGBT) 5,
A reverse blocking diode 6, a compressor motor 7 driven by the inverter unit 3, an input current sensor (CT) 8 for detecting an input current, an input current conversion circuit 9 for obtaining the detected input current, and its AC. Zero-cross detection circuit 10 for detecting the zero-cross of the input current control circuit, a drive circuit 11 for driving the switching element 5 constituting the input current control circuit, a drive circuit 12 for driving the inverter unit 3, and the detected input current is below a predetermined value. And a control device (microcomputer) 13 for setting the drive pulse output to the drive circuit 11 of the switching element 5 to the LOW level only near the peak of the AC half cycle and stopping the switching control of the switching element 5 only for that part. Has been.

In addition to the reactor 4 and the switching element 5, the AC / DC converting circuit 2 is provided with a rectifying circuit 2a for rectifying AC into DC and a capacitor 2b for smoothing this DC. Further, the control device 13 generates a PWM waveform according to a desired rotation speed of the compressor motor 7, inverter-controls the compressor motor 7 by this PWM waveform, and based on the input current detected by the input current sensor 8. The inverter unit 3 is controlled so that the overcurrent protection function is activated and, for example, when the overcurrent occurs, the rotation speed of the compressor motor 7 is reduced.

The air conditioner has the input current sensor 8 for detecting the input current as described above, the zero-cross detection circuit 10 for detecting the zero-cross point of the input AC for the discrimination of the input frequency and the interrupt processing, and Since the microcomputer of the controller 13 has a built-in timer, these are used in the present invention to control the switching element 5 to be turned on and off based on the switching pattern shown in the lower part of FIG. There is. Such a switching pattern is determined in advance according to the magnitude of the input current detected by the input current sensor 8, and when the zero-cross detection circuit 10 detects the zero-cross point of the input AC, the switching pattern according to the detected input current is set. To be done.

2A and 2B show respective waveforms of an output voltage, an input voltage, an input current, and a drive pulse when the switching element 5 is switching-controlled by the control method of the present invention, The (A) side is an example when the input current detected by the input current sensor 8 is equal to or more than a preset value, and the (B) side is a value where the input current detected by the input current sensor 8 is preset. This is an example of the following case. As can be understood from the figure, when the input current value is a predetermined value or more, the drive circuit 11 is controlled based on the switching pattern shown in the lower part of FIG. 2 (A), and the drive circuit 11 turns on the switching element 5. However, when the input current value is less than a predetermined value, the switching control is stopped when the waveform of the input current approaches the peak as shown in the lower part of FIG. 2B. The switching control is restarted when the waveform of the input current exceeds the peak and approaches the middle side, and this control is executed every half cycle of the input AC. By performing such switching control, the output voltage can be lowered from the position indicated by the broken line to the position indicated by the solid line, so that an abnormal rise in the output voltage at light load can be eliminated.

[0010]

According to the air conditioner control method as described above, it is not necessary to provide an overvoltage detection circuit because an abnormal increase in output voltage at light load is suppressed and a stable output voltage can be obtained. In addition, the ratings of the components used can be lowered, and the power supply for other control circuits of the air conditioner, which is generated from the output current voltage, can be stabilized, and the DC voltage to the inverter section can be stabilized.

[Brief description of drawings]

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

FIG. 2 is a schematic waveform diagram when switching control is performed by the control method of the present invention.

FIG. 3 is a circuit block diagram of a main part of an air conditioner showing a conventional example.

FIG. 4 is a schematic waveform diagram when switching control is performed by a conventional control method.

[Explanation of symbols]

 1 AC power supply 2 AC / DC conversion circuit 2a Rectification circuit 2b Capacitor 3 Inverter section 4 Reactor (choke coil) 5 Switching element (IGBT) 6 Reverse blocking diode 7 Compressor motor 8 Input current sensor (CT) 9 Input current conversion circuit 10 Zero cross detection circuit 11 Drive circuit 12 Drive circuit 13 Controller (microcomputer)

Claims (3)

[Claims] 1. An air conditioner configured to convert AC power into DC by AC / DC conversion means and supply the DC power to an inverter section for controlling the inverter of the compressor.
The AC / DC converting means is provided with at least a reactor and a switching element that form a closed circuit with the AC power source, and 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. A control method for an air conditioner, characterized in that switching control is intermittently performed when the load is light. 2. An input current is detected, a light load is judged based on the input current, and the input current is detected by sharing the input current detecting means of the existing overcurrent protection means of the air conditioner. The method for controlling an air conditioner according to claim 1. 3. The intermittent switching control according to claim 1, wherein when the input current is less than a predetermined value, the switching control is stopped for a predetermined time near the peak of the input voltage waveform during the AC half cycle. Air conditioner control method.