Simple Active Short Circuit Strategy for Air Conditioning Systems

A simple active-short-circuit (ASC) method is proposed for air conditioning systems. Inverters with a single shun-tresistor connected to dc-link are not able to measure the motor currents during the ASC operation. So, it is impossible to estimate motor speed using typical sensorless algorithms. Consequently, it is challenging to use ASC safely for a low-cost inverter. In this paper, open-circuit and ASC are sequentially applied to stop the motor. The motor speed is estimated using a mechanical motor dynamics during the open-circuit operation. When the estimated speed is equal to the preset target speed, the ASC operation is started. It can produce sufficient brake torque and reduce the magnitude of the short-current. The effectiveness of the proposed method is validated by experimental results using a calorimeter chamber.