Dynamic Load Model of PWM-Inverter Air-Conditioner

Abstract

Recently, power demand by air-conditioners is rapidly increasing, and it occupies about 40% of summer peak load. It is guessed that air-conditioners have considerable effects on power system load characteristics. This paper presents a load model for a PWM-inverter air-conditioner. The air-conditioner converts AC into DC, and then inverts DC to three-phase AC. It adjusts thermal output by changing the output frequency of the inverter. The voltage characteritic is basically constant-power. However, if the current reaches a ceiling value, the frequency of the inverter is lowered. The voltage characteristic shifts to constant-current after this. The response to a sudden voltage change consists of a quick electrical oscillation caused by the rectifier, and a slow response due to frequency control of the inverter. The response considerably changes with the operating state. In modeling the air-conditioner, the rectifier is represented in detail, but simple models are used for the inverter and the motor. It is shown that this model accurately simulates the response of the air-conditioner.