Commutation Compensation Strategy for Brushless DC Motor Based on Terminal Voltage Reconstruction

Abstract

In the sensorless brushless DC (BLDC) motor control system, the commutation signal is the key to measure the system performance. To improve the commutation accuracy, a commutation compensation strategy based on terminal voltage reconstruction is proposed. By analyzing the commutation process, the integral of ideal terminal voltage is adopted to determine the commutation error. Then considering the voltage clamping of the freewheel diode, the actual terminal voltage is analyzed in different periods. In the non-commutation period, a PWM cycle is divided into three regions, and the corresponding duration can be calculated by floating phase current, and then the equality of actual and ideal terminal voltage integrals is revealed. In the commutation period, the instantaneous value of back-electromotive force (back-EMF) at commutation point is used to construct the ideal terminal voltage and the commutation time is determined by the edge detection. In this way, the integral of terminal voltage can be calculated precisely. Then the error index is introduced and the relationship between the commutation error and the error index is presented. To eliminate the commutation error, the PI controller is adopted which outputs the compensation angle. The proposed strategy avoids the phase shift errors and the accumulation of integral errors, moreover the feasibility and effectiveness are verified by simulations and experiments under different conditions. In addition, the strategy can also be used to correct the installation error of Hall sensor.