A dq-axis current control technique for fast transient response in vector controlled drive of permanent magnet synchronous motor

In the vector controlled drive of AC motor, the dq-axis current control plays an important role of determining the overall system performance. Under some circumstances such as limited DC bus voltage, significantly sudden reference/load disturbance, the conventional PI controller would produce the saturated control voltage, causing the sluggish responses even though the integral antiwindup is employed. Also, the undesirable responses could be observed such as high overshoot, long settling time, etc. In this paper, a dq-axis current control technique for fast transient response in the vector controlled drive of permanent magnet synchronous motor is proposed. The Pontryagin´s maximum principle is used to solve for the optimal-time voltage solution in the dq-axis current dynamical equations. Based on this principle, the technique can guarantee the dq-axis current transition from one point to another point with the minimum-time. Since the optimal-time voltages representing in synchronously rotating dq-axis, thus this optimal-time controller can easily replace two PI controllers for the dq-axis current loops in the existing vector controlled drive system without modification of system structure. Both simulation and experiment will be carried out to substantiate the proposed technique. The overall system will be implemented in a 32-bit fixed-point digital signal processor based controller (TMS320F2812 eZdsp board).