Optimization of PM Brushless DC Motor Drive Speed Controller Using Modification of Ziegler-Nichols Methods Based on Bodé Plots

The most commonly used methods for design of the industrial speed controllers are: experimental, root locus, frequency and optimization methods. The most commonly used experimental methods are Ziegler-Nichols methods: stability margin and step response function. Ziegler-Nichols methods are applied for design of speed controller of PM brushless DC motor drive. Both methods give the controller parameters, which result in relatively high overshoot in response to reference signal. Therefore, optimal speed controller parameters are determined by modification of Ziegler-Nichols methods based on Bode's frequency diagrams. Thereby, controller integral time constant is increased and controller gain is reduced (increased) to achieve faster and better load torque compensation than traditional controller synthesis based on compensation of maximum time constant of drive. Desired overshoot in response to reference change is achieved by adding a first order filter at the drive input. Synthesis results and responses are given in this paper