Birth of an inverter air conditioner


Earlier the coefficient of performance (COP) of the heat pump system was not necessarily high, the early heat pump system used groundwater, a heat storage tank, and an auxiliary heater. Moreover, since the temperature adjustment was performed during the on/off operation of the compressor, energy loss at that time was also a major issue. To solve these problems, it was necessary to consider the application of an inverter device capable of continuously controlling the capacity of the compressor. The motor, which is the power source of the compressor, has the property that the rotation speed increases when the frequency of the power supply is increased and decreases when the frequency is decreased. If this frequency can be used to change the frequency, it would be possible to control the capacity of the compressor freely, but since the converter device at that time was large in size and weight and also they were expensive; it did not happen immediately. There were many problems to be solved in order to apply it to air conditioners.


Few heat pump air conditioners manufacturer development department began with commercial air conditioners, which have relatively few restrictions. A "sine wave approximate pulse width modulation method" was developed in which a high-power transistor that can switch up to 2kW of power was used in the inverter system, and this was controlled by a microcomputer. The size of the first inverter device has been reduced to one-sixth of its size. The world's first commercial inverter air conditioner equipped with this inverter device was introduced to the market in October 1980.


Following the commercial inverter air conditioner, few manufacturers immediately started developing a household inverter air conditioner. In the development for home use, various problems remained that cannot be solved only by the technology developed for business use. One of those problems was a demand for cost reduction and miniaturization over commercial use. Moreover, the problem of compressors controlled at various speeds remained unsolved. When the number of rotations of the compressor was increased, the lubricating oil in the mechanism part excessively flowed out, and on the contrary, when the number of rotations was decreased, poor lubrication occurred. Moreover, as the number of rotations of the rotor increased, the degree of valve collision became severe, and the discharge valve broke, the vanes were worn, and abnormal noise occurred.


To solve this problem, technology for high-power transistors, microcomputers, and software was necessary, and the air conditioner manufacturers proceeded with its development by consolidating the technologies of air conditioner. A double voltage rectification method is newly adopted to convert a 100 V AC home air conditioner to 200 V AC (240 V later) and supply it to the compressor. For downsizing, a circuit connecting the compressor and the inverter device is connected to the computer.


A giant transistor to control was developed. As a result, the compressor that had been operating at either 50Hz or 60Hz can now be continuously changed from 30Hz to 90Hz, depending on the load, and the rotational speed of the compressor can also be changed. The developed inverter device has been significantly reduced in volume compared to the previously developed commercial type, and it has become possible to place it on top of the compressor, which was previously impossible. In addition, other problems related to the refrigeration cycle were resolved by September 1981, and the world's first home-use inverter air conditioner got developed. The developed air conditioner was released in 1982.


Few other air conditioner manufacturers also developed inverter air conditioners one after another, and the market expanded rapidly.

After that, the demand for energy saving of air conditioners increased more and more, and inverter air conditioners continued to evolve. In 1997 was the first air conditioner in the world to employ the PAM control method (pulse voltage amplitude waveform control method). Until then, most inverter air conditioners used an AC motor and were controlled under a specified voltage, but in PAM control, a DC motor was used and the voltage could be adjusted was raised from 90% to 99%. This method has improved energy-saving performance all at once, and since it has made it possible to significantly increase the rotation speed of the compressor motor, it can quickly cool or heat, further accelerating its spread.


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