Braking Torque Control Strategy for Brushless DC Motor With a Noninductive Hybrid Energy Storage Topology

This article first presents a simple hybrid energy storage system (ESS) that consists of a battery, a supercapacitor and two mosfets, without additional inductors and other power devices. Then, according to the operation characteristics of the brushless DC motor, the energy transmission of this storage system is discussed when the motor operates in constant speed mode, acceleration mode, and braking deceleration mode, respectively. In the braking operation mode, four types of switching vectors are further designed based on the ESS. By analyzing the influence of different switching vectors on the two objectives of braking torque control and braking energy regeneration, the priority grade of each vector is determined from these two perspectives. On this base, the switching vector selection mechanism based on average grade ranking is constructed. The proposed strategy gives consideration to both smooth braking torque control and effective braking energy regeneration by adopting unified switching vectors during the whole braking process, without needing to switch control strategies according to the speed range. The feasibility of the presented method is validated by the experimental results.