Abstract
This paper proposes an extended model based predictive flux control (MPFC) with modified disturbance observer speed loop for induction motors. The main advantages of the proposed method are the improvement of load estimation, the suppression of current overshoot at step changes in reference speed and the removal of weighting factor in the newly formulated cost function. Weighting factor is removed by using extended reference transformation which translates reference torque, generated by the speed controller, into equivalent stator flux vector eliminating the challenging task of gain tuning at different points of operation. Then, the load torque is considered as an unknown disturbance and the accuracy of load estimation during speed jumps is improved by using a reduced order PI observer (ROPIO) with low-pass filter (LPF) for improved integration. The observer is combined with disturbance rejection based control to design a composite speed controller replacing conventional PI loop. The effectiveness of the proposed method is validated on a two-level three-phase inverter fed induction motor drive using dSpace DS1104 controller board. The dynamic response of the proposed method is compared to previously proposed disturbance observer based controller (DOBC) for predictive torque control method. The load estimation error of the proposed method at speed jumps is reduced by 66% while current surges are also suppressed effectively.
Highlights
Model based predictive torque control (MPTC) is an emerging type of MPC for AC motor drives and recently it has received a tremendous attention by the research communities [1]
This paper proposes a modified MPTC without weighting factor and reduced order PI observer (ROPIO) based disturbance observer based controller (DOBC) considering the reference speed jumps
SIMULATION RESULTS selected simulation results are presented to validate the performance of modified ROPIO (M-ROPIO) used with model based predictive flux control (MPFC)
Summary
Model based predictive torque control (MPTC) is an emerging type of MPC for AC motor drives and recently it has received a tremendous attention by the research communities [1]. Other methods for recovering nominal performance of the outer speed loop include integral sliding mode control (I-SMC) [17], PID control [18] and feedback linearization [19] These methods suffer from various problems such as chattering in I-SMC, difficulty in practical implementation of D part in PID and complexity of the techniques as compared to the simple PI solutions for disturbance rejections such as reduced order PI observer. It is proven in [21] that ROPIO is designed for disturbance rejection, it is inherently robust to parameter variations, explicitly limiting the disturbances to load torque changes only In all these DOBC-MPTC formulations, it is assumed that reference speed is differentiable at all times, ignoring the sudden speed jumps where derivative term becomes infinite.
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