Investigation of the Influence of Direct and Indirect Current Control Methods on the Dynamic Properties of a State Space Speed Control

Abstract

In highly dynamic drive systems, state space speed control methods can be used to dampen mechanical oscillations. While a complete state space control allows arbitrary speed control loop dynamics, in reality, these are limited by the underlying current control and its ability to implement the required torque in the electric machine. If a state space speed control is used, the current control method must be able to implement the torque demanded from the speed control. In this paper, two potential current control methods for such a speed control loop are examined. A simulation of the drive system disturbance reaction shows which current control method is better suited for use in the state space speed control. While the hysteresis control, by definition, guarantees a maximum deviation from the current set-point and therefore achieves good control performance, the performance of the field-oriented control depends on the tuning of the controller parameters. Depending on the drive systems resonant frequency, the total time constant used in the controller tuning equations must not exceed a certain limit, otherwise the speed control performance degrades. If a current control is to be implemented for a given drive system, a comparison of the resonant frequency and the total time constant, achievable in this drive system, can reveal if the field-oriented control offers sufficient dynamics in the current control loop.