Sensorless control of permanent magnet motors operating at low switching frequency for climate control systems

This paper presents a sensorless vector control of variable speed permanent magnet synchronous motor (PMSM) drives at low switching frequency in space cooling and air-conditioning applications - also referred as climate control systems (CCS). Permanent magnet motors are favored in these applications for their high efficiency of operation. In the same aspect, reducing switching frequency of the inverter driving them minimizes the losses in semiconductor devices. To keep the motor harmonic losses in check, at these switching frequencies, a programmed pulse width modulation scheme is advantageous. The resulting currents are devoid of significant low ordered sidebands. Closed loop sensorless operation in coordination with such PWM scheme, especially for permanent magnet motor drives, is hard to find in literature and is taken for study. The sensorless control strategy uses a linear state observer to estimate the PMSM back-EMF, and a tracking controller to estimate the rotor speed and position. Using simulation results, this paper elaborates on the various operating modes for starting the machine and transition of PWM patterns during acceleration. Detailed design rules for observer and tracking controller are verified through time-domain simulations on a three phase 250W PMSM motor drive. The dynamic performance of the controller is adequate in CCS applications. The results validate both the design methodology and the expected performance attained by the proposed control strategy.