Sensorless Control Strategy for BLDC Motors Based on a Type-3 Phase Locked Loop

Abstract

This paper presents the design procedure of a high-performance sensorless control strategy for the widely used brushless DC (BLDC) motors. Generally, conventional sensorless techniques are based on detecting the zero-crossing instants (ZCP) of the back electromotives forces (back-EMFs) of the three phases. These methods, although widely adopted and marketed on an industrial level, involve many limitations such as filtering delays, difficulty to operate at low speeds and immunity against Electromagnetic Interferences (EMI). In this paper, the main objective is to develop a sensorless control technique integrally independent from the zero-crossing points of the back-EMFs. In the proposed method, a zero-delay adaptive filter was used to extract the fundamental and the quadrature components of the line-to-line voltage of the motor. Then, the Synchronous Reference Frame Phase Locked Loop (SRF-PLL) is used to estimate the electrical angle of phase-to-phase back-EMF along with the rotor speed. The conventional SRF-PLL was implemented using a second-order loop filter (type-3 PLL) in order to improve synchronization performances and for better rejection of voltage spikes induced in motor phases during commutations. The benefits of the control technique are brought to light through simulation results. An experimental prototype was designed to confirm the validity of the proposed method.