Active Short Circuit Method for Reducing Short-Current in Air Conditioning Systems

A simple active-short-circuit (ASC) method is proposed for air conditioning systems with compressors and voltage source inverters (VSI) using a single current sensor. The open-circuit operation for stopping the motors may cause inverter failure due to high regenerated energy. Thus, the ASC method can be an alternative. However, VSIs with a single shunt-resistor connected to dc-link are not able to measure the motor phase currents during the ASC operation. So, it is impossible to protect inverters and motors against high short-currents during ASC. Consequently, it is challenging to apply ASC safely for a low-cost inverter. In this article, 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 simulations and experimental results using a calorimeter chamber.