Dynamic Strategy for Effective Current Reduction in Brushless DC Synchronous Motors Fault Tolerant Operation

This work presents a flexible strategy for RMS current reduction of healthy phases for brushless DC synchronous motors (BLDC) operating in phase opening failure, avoiding motor degradation without reducing its performance and allowing safe shutdown when a phase failure is detected. After the diagnosis of an open-phase failure, a corrective action divided into three steps is proposed. First, the traditional Six-Step operating mode with 120° electric degrees is changed to a new operating mode that uses the two healthy phases at 180° electric degrees to reduce torque loss due to phase failure. Second, a trapezoidal shape (with adjustable angles according to the RMS current level) is imposed as a current reference for the controller to reduce the current level and, consequently, improve the efficiency of the motor. Third, the passband of the speed control loop is reduced to minimize the influence of speed oscillations in controller failure. The experimental results presented show that the mode of operation with the proposed dynamic current reduction strategy allows an approximate reduction of up to 27% in the effective current and up to 41% in the motor temperature variation, compared to the usual failure mode of operation of the BLDC motor without the proposed strategy. The dynamics of change in the trapezium angle allowed a weighting between the current level and the oscillation of the speed, preventing the motor in phase failure from having a high-speed variation.