PMSM rotor double-alignment by PI and sliding-mode controllers

In this paper, we introduce two novel closed-loop current control techniques for rotor alignment in a phase axis direction in PMSM drives. This alignment procedure is used both in sensor and sensorless PMSM drives to correctly implement vector control strategies. The two novel closed-loop current control techniques employ PI and sliding-mode controllers. The design formulae, based on the mathematical model of the motor, are derived for all controller parameters. Using closed-loop schemes it is possible to develop the maximum torque during rotor alignment, and reduce alignment error. To avoid large alignment errors, due to static friction torque, when the initial rotor position is close to the chosen phase axis direction we propose a new procedure based on a double-alignment in two consecutive phase axis directions. Experimental results demonstrate that using closed-loop current control together with double-alignment procedure the alignment error is minimized and independent of the initial rotor position.