PMSM servo‐drive control system with a state feedback and a load torque feedforward compensation

The purpose of this paper is to discuss the design and verification of a non‐classical structure of servo‐drive controller with the state feedback and a load torque feedforward compensation.

First a well known nonlinear mathematical model of a PMSM is transformed into a linear form by introducing new variables. The state space new model presented in rotated orthogonal reference frame is decoupled by means of equation in d and q axis. To achieve correct dynamic performance of the servo‐drive system the state feedback with an internal input model and load torque feedforward compensation is proposed. The observed load torque has been used as an input signal for the feedforward compensator. The design of the control system and simulation analysis were performed in Matlab/Simulink. The proposed control algorithm was implemented in a DSP controller (TMS320F2812). The experiments were carried out by using a 0.6 kW PMSM drive system.

It is shown that the proposed compensator can eliminate the effects of load torque changes by steady‐state operation and significantly improve dynamic behaviour during load changing. A novel mathematical formula how calculate an appropriate gain for feedforward compensator is given.

Analysis of possible disturbance compensation shows that full dynamic compensation of disturbance is impossible. Only the compensation of load torque for a steady state is possible. The described control structure operates without state variables limitations so it is not recommended to application where the high dynamic of transient process is required.

The proposed control system can be used in industrial applications where load torque compensation is needed instead the high dynamic performance.

Presented mathematical formula how calculate an appropriate gain for feedforward compensator is a theoretical contribution of the authors. The test results are consistent with the computer simulation test results and validate the correct dynamic performance of the proposed control method.