GB2123624A - Power supply system for compressor of air conditioner - Google Patents

Abstract

A power supply system for driving a compressor 17 of an air conditioner has a smoothing circuit 16 connected between a three-phase bridge rectifier 20 and an inverter 30. The smoothing circuit 16, which may comprise a capacitor as shown, is capable of removing ripple to ensure normal operation of the inverter 30 even when a single-phase voltage is applied. Thus, the air conditioner is operable on either a single-phase or three-phase voltage and the standardization of various parts and equipment is facilitated. <IMAGE>

Description

SPECIFICATION Power supply system for compressor of air conditioner Background of the invention The present invention relates to a power supply system for a compressor of an air conditioner and, more particularly, to a power supply system for a compressor with a light load, e.g., of less than 1.8 KW.

Some of the commercially available air conditioners are designed to operate on singlephase voltage, e.g., 200 V and others on threephase voltage. Therefore, the users have to select a suitable air conditioner depending.upon a power supply available and the charges for the electricity. Depending on whether the particular air conditioner is intended for a single-phase or three-phase voltage, the conventional air conditioners have different power supply systems for energizing an electric motor for driving a compressor. As a result, the standardization of various parts and equipment has been difficult.

Besides, forecast of demand had to be made separately on each of the two types, one for single-phase and the other for three-phase.

Summary of the invention The present invention was made to overcome the above and other problems encountering the conventional air conditioners and has for its object to provide a power supply system for a compressor of an air conditioner which can operate on either a single-phase voltage or a three-phase voltage.

To the above and other ends, the present invention provides a power supply system for a compressor of an air conditioner comprising a three-phase bridge rectifier, an inverter for converting the output from the three-phase bridge rectifer to AC power which is supplied to an electric motor for driving the compressor, and a smoothing circuit connected between the threephase bridge rectifier and the inverter and capable of removing ripple to such an extent that normal operation of the inverter is ensured when a singlephase voltage of substantially the same magnitude is applied to two or three input terminals of the three-phase bridge rectifier.

Brief description of the drawings Fig. 1 is a circuit diagram, partially in block diagram, of a power supply system for energizing a motor of an air conditioner in accordance with the present invention Fig. 2 is a circuit diagram of a three-phase bridge rectifier; Figs. 3A and 38 are diagrams showing the output of the rectifier 20; and Fig. 4 is a circuit diagram of an inverter.

Detailed description of the embodiment Fig. 1 shows a power supply system for a motor driving a air conditioner in accordance with the present invention. The air conditioner comprises an interior unit 100 that is positioned in the room or space for which the air conditioning is made and an exterior unit 200 that is positioned outside the room or space. The interior unit 100 comprises an operation switch circuit 10 consisting of switches 2 and 3, a room thermostat 4 which is adapted to respond to room temperature, a selection switch 5 for selecting the cooling or heating operation and a fan motor 6. The series-connected circuit consisting of the switch 2 and the fan motor 6 is connected between power supply lines P, and P2 which in turn are connected to a single-phase 100-V plug 1.The series-connected circuit consisting of the switch 3 and the thermostat 4 is inserted in the power supply line P2. One terminal of the selection switch 5 is connected to the junction between the switches 3 and 4.

The exterior unit 200 comprises devices which operate on a single-phase 100-V power supply which is also the power supply for the interior unit 100, and devices which are operable on either a three-phase or single-phase 200-V power supply.

The devices operating on single-phase 100 V include a four port valve 11 for switching a refrigerant cycle, a fan motor 12, a relay 13 and a power transformer 14. One terminal of the fourport valve 11 is connected to the other terminal of the selection switch 5 while the other terminal of the valve 11 is connected to the power supply line P. The fan motor 12, the relay 13 and the primary of the power transformer 14 are connected between the power supply lines P, and P2.

The devices operable on either three-phase or single-phase, 200 V comprises a three-phase 200-V magnet switch 1 5 which is controlled by the relay 13, three-phase bridge rectifier 20 for rectifying the three-phase AC voltage supplied through the magnet switch 15, a capacitor 1 6 for smoothing the output from the bridge rectifer 20, an inverter 30 for converting the thus obtained smoothed DC voltage into AC voltage and an electric motor 1 7 for driving a compressor whose rotational speed is controlled by the output from the inverter 30.

The secondary of the power transformer 14 is connected to an inverter control circuit 40 which delivers ON-OFF control signals to individual elements making up the inverter 30.

Fig. 2 shows in detail the three-phase bridge rectifier 20 consisting of diodes 21 through 26 inter-connected to form the arms of the bridge.

Fig. 4 shows in detail the construction of the inverter 30 in which diodes 41 through 46 are connected in reverse-parallel with transistors 31 through 36, which are interconnected to form arms of the bridge.

The operation of the air conditioner in accordance with the present invention will be described with reference to Fig. 3. The interior unit 100 is connected to a singie-phase 100-V power supply while the exterior unit 200, to a three-phase or single-phase 200-V power supply.

Therefore those elements whose power consumption is relatively small are energized by 100 V while the motor 1 7 whose power consumption is the greatest is energized by threephase or single-phase 200 V.

When both the switches 2 and 3 in the switching circuit 10 are closed and the selection switch 5 is switched to select the desired mode, the fan motor 6 is driven to blow the air and the four-port valve 11 responds to the switched mode of the selection switch 5 so as to establish the appropriate refrigerant cycle. The thermostat 4 is opened or closed depending upon room temperature. When the thermostat 4 is closed, the fan motor 6 is driven to blow the air and simultaneously the relay 13 is activated or energized to cause the magnet switch 1 5 to close.

When the exterior unit 200 is connected to the three-phase 200-V power supply the full-wave rectification is carried out by the diodes 21 through 26 making up the three-phase bridge rectifier 20, whereby the voltage as shown in Fig.

3A is derived. The thus derived voltage is smoothed by the capacitor 16 so that a DC voltage with a very small ripple is supplied to the inverter 30. As shown in fig. 4, the inverter 30 has six transistors 31 through 36 and the inverter control circuit sequentially applies rectangular waveform signals, which have phases differing from each other, to the bases, respectively, of the transistors 31 through 36, whereby a three phase AC voltage is applied to the motor 1 7. Since the inverter 30 and the inverter control circuit 40 are of the conventional type, detailed explanation shall be omitted.

The motor 1 7 causes a refrigerant to circulate, whereby the air conditioning operation is carried out.

When room temperature reaches a predetermined temperature, the thermostat 4 is opened. Then the four-port valve 11 maintains its normal position, but the fan motor 12, the relay 1 3 and the inverter control circuit 40 are deenergized. Simultaneously, the magnet switch 1 5 is opened so that the three-phase bridge rectifier 20 is de-energized. As a result, the exterior unit 200 interrupts its operation. Thereafer, when the thermostat 4 is closed, the above-described airconditioning operation is started again.

In this case, a DC voltage which is derived from the three-phase bridge rectifier 20 and smoothed by the capacitor 1 6 is applied to the inverter 30.

Even when the voltage as shown in Fig. 3A is applied directly to the inverter 30; that is, even when the capacitor 1 6 is eliminated, normal operation of the motor 17 is ensured. Thus the capacitor 1 6 may be eliminated.

Therefore, in the past, the standard air conditioners in which the interior unit 100 is connected to a single-phase 100-V power supply while the exterior unit 200, to a three-phase 200 V power supply, did not have the capacitor 16.

This was to achieve simpler construction.

The reason why the capacitor 1 6 is inserted according to the invention is to enable operation when two of terminals R, S and T are connected to a single-phase 200-V power supply and the three-phase bridge rectifier 20 is used as a singlephase bridge rectifier. In this case the ripple component in the output of the rectifier 20 is larger so that a smoothing capacitor 1 6 is essential to ensure normal operation of the motor 1 7.

More particularly, assume that the terminals R and T are connected to a single-phase 200-V power supply. Then, two sets of diodes shown in Fig. 2 accomplish full-wave rectification so that a full-wave rectified voltage as shown in Fig. 3B is derived across the output terminals of the rectifier 20. The fuli-wave rectified voltage drops to 0 V for every 1 800, so that, if this voltage were supplied as it is, the inverter 30 could not supply a required current to the motor 17, and hence the normal operation would not be carried out.

But, the inserted capacitor 1 6 smoothes the voltage of Fig. 3B, thereby reducing the ripple component and enabling the normal operation of the inverter 30.

If the exterior unit 20 with the capacitor 1 6 is supplied as a standard unit, the air conditioner as shown in Fig. 1 is operable on either single-phase 200-V or three-phase 200-V.

So far, the output from the three-phase bridge rectifier 20 has been described as being smoothed by the capacitor 16, but it is to be understood that instead of the capacitor 1 6, a smoothing circuit including an inductance may be equally used.

So far, the inverter 30 has been described as consisting of transistors, but it is to be understood that a thyristor inverter may alternatively be used.

So far, the air conditioner has been described as comprising one interior unit and one exterior unit, but it is to be understood that the present invention may equally applied to a so-called multi-air conditioner in which a plurality of interior units are connected to a single exterior unit.

As is clear from the above description, when use is made of a power supply system according to the present invention, the air conditioners is operable on either a single phase or three phase power supply. Therefore, the standardization of various parts and equipment can be extended and it is not necessary to make separate forecasts of demands for two types of air conditioners, one operable on a three-phase voltage and the other on a single-phase voltage.

Claims (2)

Claims

1. A power supply system for a compressor of an air conditioner comprising: a three-phase bridge rectifier; an inverter for converting the output from said three-phase bridge rectifier to an AC voltage which is supplied to an electric motor for driving said compressor; and a smoothing circuit connected between said three-phase bridge rectifier and said inverter and capable of removing ripple to ensure normal operation of said inverter when two of three input terminals of said three-phase bridge rectifier are fed with a single phase AC voltage.

2. A system as set forth in Claim 1 wherein said smoothing circuit comprises a capacitor.