The air conditioning compressors for vehicles are mainly driven by IPMSMs (Interior Permanent Magnet Synchronous Motors) considering the speed range, efficiency, and durability of the motor. Among the many types of compressors, the scroll type is often adopted to reduce system size and noise. However, friction and collision due to refrigerant load causes unwanted noise and vibration that adversely affect the compressor and creates a considerably audible noise especially in electric vehicles.
In this paper, a simple control method was proposed to suppress vibration and noise generated during the IF start-up of an electric compressor. In addition, a method to reconstruct the undetectable current in a three-phase VSI (Voltage Source Inverter) using a three-shunt resistor is proposed.
The IPMSM is controlled sensorlessly using a back emf observer in the normal speed range. An IF open loop starting method is used to speed up from standstill. During IF start-up, the speed fluctuations due to the fluid load causes mechanical vibration and noise. In addition, a three-phase VSI with the three-shunt resistor has a region in which two currents cannot be detected when the output voltage of the inverter is high, which adversely affects sensorless control.
In this paper, initial rotor position estimation method to reduce mechanical vibration and noise, and a simple torque compensation method through speed comparison are proposed. In addition, the torque can be variably reduced through angle comparison and the switch from open loop to sensorless control is presented.
The proposed method uses initial rotor position estimation rather than the conventional rotor alignment method. In addition, the command torque slope increases according to the open-loop speed command. This slope changes according to the hysteresis error between the open-loop speed command and the estimated speed. During the transition from open-loop to the close-loop sensorless control, the command torque slope for angle synchronization is adjusted by the error between the estimated angle and the reference angle. Variable current reduces the collisions of the compressor scroll in the stop, start and transition sections. As a result, mechanical vibration and noise can be reduced. Finally, to reconstruct the undetectable phase current, the time delay between voltage and current was used. When two phase currents are not detected, the first phase current is estimated using the stored voltage ratio and current ratio. Then, the remaining undetectable current is reconstructed using the estimated and detected currents.
The proposed starting method was validated through experiments with an 11kW IPMSM driven HVAC (Heating, Ventilation & Air conditioning) compressor. Experimental results show that vibration and noise from standstill to the normal speed range can be reduced using the proposed method. Furthermore, the undetectable current can be reconstructed using the proposed reconstruction algorithm when the output voltage of the inverter is high.