Mechanical-sensorless robust control of permanent-magnet synchronous motor using phase information of harmonic reactive power

This paper proposes a novel control strategy of a permanent-magnet synchronous motor without mechanical sensors. The strategy is based on use of harmonic reactive power and utilizes its relative phase information to estimate the rotor position, i.e., d-axis direction that corresponds to the magnetic poles on the rotor. The harmonic reactive power can be calculated by filtering a specific harmonic voltage vector and a harmonic current vector and is never affected by variation of the winding resistance that may be caused by temperature fluctuation or a skin effect due to the harmonics. Since the harmonic reactive power has a relative phase with respect to a phase reference signal, which is proportional to the estimation error of the rotor position, the estimated position converges to the true value by zeroing the phase shift. To achieve this estimation algorithm, a phase-locked-loop (PLL) technique is employed in the rotor position estimator. In the PLL, the harmonic reactive power is converted to a digital pulse to extract only the relative phase information and to eliminate amplitude information that is relevant to d-axis and q-axis inductance and the rotor speed. Therefore, the proposed estimation technique is almost perfectly robust against every motor parameter and any operating conditions. The paper describes a theoretical aspect of the method and presents several computer simulation and experimental results to show the feasibility of the proposed strategy.