JPH04271299A - Control method for air-conditioner - Google Patents

Abstract

PURPOSE:To improve the power factor of input power to an air-conditioner, to suppress higher harmonics, and to stabilize the output voltage of an AC/DC converter circuit against variation of load. CONSTITUTION:In order to improve the power factor of input power to an air-conditioner and to suppress higher harmonics, at least a reactor and a switch element constituting a closed circuit together with a power supply are provided in an AC/DC converter circuit and the switch element is subjected to ON/OFF control. ON interval of the switch element is modified, based on a current detected through an input current sensor employed in an existing overcurrent protective means of the air-conditioner, so that the ON interval is longer for higher detection current (AC input current) or heavier load of the air-conditioner. In other words, current flowing through the switching element is increased to increase current supply to the load thus stabilizing the output voltage of the AC/DC converter circuit and improving the power factor of input power.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an air conditioner that creates a comfortable indoor environment, and more specifically, the present invention relates to an air conditioner that controls input current,
The present invention relates to an air conditioner control method that improves power factor and reduces harmonics.

0002

[Conventional example] Conventionally, in this type of air conditioner, AC power is converted to DC, this DC is supplied to an inverter, and a microcomputer generates a PWM waveform for inverter control of the compressor. , the inverter section is controlled according to this PWM waveform. In addition, in order to improve the input power factor of the air conditioner and reduce harmonics, an AC/DC conversion circuit, that is, a reactor and switching elements that form a closed circuit with the power supply are installed between the AC power supply and the inverter. An input current control circuit (active filter) is provided, and the switching element is controlled to turn on and off at high speed, so that the input current waveform becomes a substantially sine wave. As a method of controlling the air conditioner, for example, the method disclosed in Japanese Patent Application No. 2-1 filed by the applicant is as follows.
There is No. 28655.

Furthermore, in order to increase the input power factor of the air conditioner and to stabilize the output voltage of the AC/DC converter circuit, it has been proposed to change the on-time of the switching element according to the load of the air conditioner. It has become. Therefore, as shown in FIG. 4, for example, an air conditioner includes an output current detection resistor 1 that detects the DC output current, an amplifier 2 and an average value circuit 3 that obtain the average value of this detected current, and The magnitude of the load on the harmonizer is detected using the average value.

0004

[Problems to be Solved by the Invention] However, the above air conditioner control method requires a circuit for detecting direct current and obtaining the average value of this detected current.
There was a problem in that the cost increased accordingly. In addition, the detected current is transferred to an amplifier 2 using the power supply of the logic circuit.
and average value circuit 3, and its output is processed by a logic circuit, so it is common to insulate the power circuit and the logic circuit. However, there were also problems in terms of reliability and safety.

[0005] This invention was made in view of the above problems, and its purpose is to increase the input power factor and to make it possible to use an existing circuit as a circuit for stabilizing the output voltage of an AC/DC conversion circuit. An object of the present invention is to provide a method for controlling an air conditioner, which can be performed at low cost, and can improve reliability and safety.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention converts an alternating current power source into direct current when controlling a compressor using an inverter, and converts the direct current into an inverter for controlling the compressor using an inverter. In addition to improving the input power factor of the air conditioner supplied to the
In order to reduce harmonics, the AC/DC conversion means that converts the AC power into DC is provided with at least a reactor and a switching element that form a closed circuit with the power supply, and the switching element is turned on and off, and the air conditioning The gist is that the ON time of the switching element is changed in accordance with the AC input current detected by the current sensor used in the overcurrent protection means of the machine.

[0007]

[Effect] Since the above method is used, when the AC input current of the air conditioner increases, that is, when the load increases, the on time of the switching element becomes longer, and more current flows through the switching element. current, and more current is supplied to the load. Also, when the AC input current becomes smaller, that is, when the load becomes smaller,
The on-time of the switching element is shortened, and the current flowing through the switching element is reduced. Therefore, the output voltage of the AC/DC conversion circuit can be stabilized against load fluctuations, and the input power factor can be further increased. Since a current sensor is used, there is no need to add a new circuit, and the cost can be reduced.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be explained based on FIGS. 1 to 3. In Figure 1, this air conditioner includes:
an AC/DC conversion circuit 7 that converts the AC power supply 6 to DC;
In order to improve the input power factor and reduce harmonics, the AC/DC conversion circuit 7 is provided between the AC power supply 6 and the inverter unit 8 to which the DC power is supplied, and the AC/DC conversion circuit 7 is connected to the power supply. An input current control circuit (active filter) consisting of a reactor (choke coil) 9 and switching elements (IGBT) 10, 11, etc. that constitute the circuit, a compressor motor 12 driven by the inverter section 8, and an AC input current an input current sensor (CT) 13 that detects the detected current, a conversion circuit 14 that converts the detected current into a voltage, and switching elements 10 and 11 that constitute the active filter.
a driver circuit 15 that drives the inverter section 8, a driver circuit 16 that drives the inverter section 8, and the switching element 1.
A control device (microcomputer) 17 is provided that controls the on/off state of the switching elements 10 and 11 and changes the on time of the switching elements 10 and 11 according to the detected input current.

[0009] In addition to the reactor 9 and switching elements 10 and 11, the AC/DC conversion circuit 7 includes a rectifier circuit 7a for voltage-doubling rectification of AC into DC, and a capacitor 7b for smoothing this DC. ing. Further, the control device 17 generates a PWM waveform according to the target rotation speed of the compressor motor 12, performs inverter control of the compressor motor 12 using this PWM waveform, and controls the compressor motor 12 based on the input current detected by the input current sensor 13. For example, when an overcurrent occurs, the inverter section 8 is controlled to reduce the rotational speed of the compressor motor 12.

Next, a method for controlling an air conditioner according to the present invention will be explained with reference to the explanatory diagrams (current waveform diagram and time chart diagram) of FIG.

First, when controlling the compressor with an inverter, assuming that AC power 6 is input to the air conditioner, the AC power 6 is converted to DC by the AC/DC conversion circuit 7. The switching elements 10 and 11 are turned on and off at predetermined timings so that the input current from the AC power supply 6 has a substantially sinusoidal waveform with substantially the same phase as the input voltage waveform, and the ON time of the switching elements 10 and 11 is as described above. It can be changed according to the current detected by the input current sensor 13 for overcurrent protection.

Here, if the current detected by the input current sensor 13 for overcurrent protection becomes large, the control device 1
At 7, the switching elements 10 and 1 are activated according to the detected current.
The on-time of AC power supply 6 is lengthened (as shown in FIG. 12(a)), and by turning on and off the switching elements 10 and 11, the input current waveform from AC power supply 6 is made into a sine wave as shown in FIG. 4(b). Note that when there is an overcurrent for the air conditioner, an overcurrent protection function that reduces the rotation speed of the compressor motor 12 is activated.

Furthermore, when the current detected by the input current sensor 13 becomes medium, the control device 17 shortens the on time of the switching elements 10 and 11 according to the detected current (as shown in FIG. show). Further, when the detected current is small, the control device 17 further shortens the on time of the switching elements 10 and 11 according to the detected current (as shown in FIG. 2(e)). In this case, as shown in (d) and (f) of the figure, the input current waveform from the AC power source 6 is made into a sine wave by the on/off of the switching elements 10 and 11 depending on the on time.

The on-time of the switching elements 10 and 11 may be determined in advance according to the AC input current and stored in the storage section of the control device 17. Alternatively, the current detected by the input current sensor 13 may be input to the control device 17 at predetermined time intervals, and the on-time corresponding to the detected current may be calculated for each input.

As described above, in order to improve the input power factor of the air conditioner and reduce harmonics, the switching elements 10,
11 on and off, and increases its power factor, alternating current/
In order to stabilize the output voltage of the DC conversion circuit 7, the on-time of the switching elements 10 and 11 is changed depending on the load of the air conditioner. Since the on-time of the switching elements 10 and 11 can be changed using the AC input current detected by the existing input current sensor 13 and conversion circuit 14, the cost can be lower than that of the conventional method. It is possible to improve reliability and safety.

FIG. 3 is a schematic circuit diagram of an air conditioner illustrating a modification of the above embodiment. That is, in the case of the above embodiment, AC 100V (50/60Hz) is used for the AC power supply 6, but in the case of this modified embodiment, the AC power supply 6
AC200V (50/60Hz) is used. In the figure, the same parts as those in FIG. 1 and parts corresponding thereto are denoted by the same reference numerals, and redundant explanation will be omitted.

In the figure, 7c is the 200V of the AC power supply 6.
18 is a switching element (IGBT), and 19 is a diode. Further, the switching element 18 has the same function as the switching elements 10 and 11 of the above embodiment, and the diode 19 is a reverse blocking diode.

In this case, since the switching element 18 is controlled to turn on and off in the same way as the switching elements 10 and 11, the same effects as in the above embodiment can be obtained. Note that since the operation of this modified embodiment is similar to that of the above embodiment, the explanation thereof will be omitted.

[0019]

[Effects of the Invention] As explained above, according to the air conditioner control method of the present invention, in order to improve the input power factor of the air conditioner and reduce harmonics, the AC/DC converter circuit is supplied with power. At least a reactor and a switching element forming a closed circuit are provided, and the switching element is controlled to turn on and off, and the switching element is turned on and off in response to the AC input current detected by the overcurrent protection means of the air conditioner. By controlling the time, it is possible to stabilize the output voltage of the AC/DC converter circuit against fluctuations in the load of the air conditioner, and it is also possible to further increase the input power factor. Since the circuit can be used in common, there is no need to add a new circuit, making it possible to reduce costs and improve reliability and safety.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of an air conditioner to which an air conditioner control method is applied, showing one embodiment of the present invention;

[Fig. 2] An explanatory diagram illustrating a method of controlling the air conditioner shown in Fig. 1.

FIG. 3 is a schematic circuit diagram of an air conditioner showing a modified embodiment of the present invention.

[Figure 4] Schematic partial circuit diagram of a conventional air conditioner

[Explanation of symbols]

6 AC power supply 7 AC/DC conversion circuit 7a Rectifier circuit 7b Capacitor 7c Rectifier circuit 8 Inverter section 9 Reactor (choke coil) 10 Switching element (IGBT) 11 Switching element (IGBT) 12 Compressor motor 13 Input current sensor (CT) 14 Conversion circuit 17 Control device (microcomputer) 18 Switching element (IGBT) 19 Diode

Claims (3)

[Claims] Claim 1. An air conditioner that converts AC power into direct current and supplies the direct current to an inverter section for controlling the compressor with an inverter, when the compressor is controlled by an inverter, the input power of the air conditioner is In order to improve efficiency and reduce harmonics, the AC/DC conversion means for converting the AC power into DC is provided with at least a reactor and a switching element that form a closed circuit with the power supply, and the switching element is turned on and off. A method for controlling an air conditioner, characterized in that the AC input current of the air conditioner is detected, and the ON time of the switching element is changed in accordance with the detected AC input current. 2. The method of controlling an air conditioner according to claim 1, wherein the on-time of the switching element is made longer as the detected AC input current is larger. 3. The method for controlling an air conditioner according to claim 1, wherein the AC input current is detected by a current detection sensor used in overcurrent protection means of the air conditioner.