A New Norm-Based Current Control Method for Energy-Efficient/Wide-Speed-Range Drive of Salient-Pole Permanent-Magnet Synchronous Motors

This paper proposes a new current control method for energy-efficient and/or wide speed-range drive of salient-pole permanent magnet synchronous motors. The proposed method is distinguished from conventional ones by the following features: 1) the original command is a signed current-norm; 2) the exact d-axis and q-axis current commands that perform energy-efficient and/or wide-speed-range drive are analytically and simply determined from the singed current norm command; 3) for speed control mode, the system turns out to be nonlinear, but its stability can be guaranteed based on Popov´s stability theorem; 4) it can be applied for a mode similar to torque control; 5) current limit operation can be carried out accurately but very simply. Concrete analytical d-axis and q-axis current commands are presented, which satisfy exactly optimum current control strategies such as maximum torque/current strategy, maximum power factor strategy, and voltage limit strategy. A design method for PI speed controller that guarantees system stability is also presented.