F. Filicori, C. Guarino Lo Bianco, A. Tonielli
IEEE Trans. on Ind. Electr., Vol.40, No. 1, pp. 105-115, Feb. 1993.
In Industrial Automation and Robotic applications, Direct-Drive motors represent a suitable solution to friction and backlash problems typical of mechanical reduction gears. Variable Reluctance (VR) motors are well suited for Direct-Drive implementation, but because of the strongly non-linear electromechanical characteristics, these motors are traditionally designed as stepper motors. The main aim of the work described in the paper is the design of a high-performance ripple- free dynamic torque controller for a VR motor, intended for trajectory tracking in robotic applications. An original modelling approach is investigated, in order to simplify the design of the high-performance torque controller. Model structure and parameter estimation techniques are presented. Different approaches to the overall torque controller design problem are also discussed and the solution adopted is illustrated. A cascade controller structure is considered. It consists of a feedforward non-linear torque compensator, cascaded to a non-linear flux or current closed- loop controller. The feedforward compensator is carefully considered and optimization techniques are used for its design. Two optimization criteria are proposed: the first minimizes copper losses while the second minimizes the maximum value of the motor feeding voltage. Although developed for a specific commercial motor, the proposed modelling and optimization strategies can be used for other VR motors with magnetically decoupled phases, both rotating and linear. Laboratory experiments for model validation and preliminary simulation results of the overall torque control system are presented.