Improved Online Optimization-Based Optimal Tracking Control Method for Induction Motor Drives

An online optimization-based optimal tracking control method to control IM drives in the entire speed and torque ranges is proposed in this article. The main feature of the proposed method is considering the nonlinear core saturation effects in generating the optimal reference currents in MTPA, field-weakening, and maximum torque per voltage (MTPV) regions. Constrained optimization problems are formulated and solved using Lagrange multipliers method to derive improved nonlinear MTPA and MTPV optimality conditions. Unlike most of the existing loss minimization methods in the literature, using optimal reference point look-up tables is avoided in the proposed method. Moreover, the effects of stator resistive drops, dc-link voltage variations, and inverter nonlinear voltage drop, which are usually neglected in the literature, are considered in generating optimal reference currents. A new straightforward and well-structured optimal reference point calculation scheme is proposed by dividing the operating plane of IM into four regions. The optimal reference currents in each region are then generated by solving the corresponding optimization problem. The smooth operation and transition of the proposed control method between MTPA and field-weakening regions are verified using simulations. The effectiveness of the proposed method is experimentally validated on a 4.7-kW, 4-pole, three-phase induction motor drive.