This study presents a novel online, accurate and simple model-based maximum torque per ampere (MTPA) strategy for input-output feedback linearisation control of induction motor (IM) drives. Despite conventional MTPA control principles which are under the assumption of iron loss neglecting, the proposed strategy takes iron loss effect into account. This study highlights the iron loss influence on MTPA scheme. Firstly, the cross-coupling effects in the IM model and torque non-linearity due to the iron loss in torque-speed characteristics of the IM are discussed. The criterion for the MTPA scheme is then introduced and investigated by gradient approach so that when the gradient vectors of the torque and stator current magnitude are parallel, the MTPA strategy is satisfied. Finally, to confirm the validity of the proposed control scheme, experiments are carried out.

Among the conventional loss minimisation algorithms (LMAs), the model-based approaches have the advantages of fast response and high accuracy. Here, a novel online model-based power losses minimisation approach is presented for indirect field-oriented control (IFOC) of induction motor (IM) drives. The proposed method is introduced as maximum torque per power losses (MTPPL) in which the power losses for a given torque are minimised. The results demonstrate that the proposed approach preserves the LMA merits, while the criterion for the MTPPL scheme is achieved. The mentioned criterion is investigated by a gradient approach so that while the gradient vectors of the torque and power losses are parallel, the MTPPL strategy is realised. The closed-loop IFOC of the MTPPL approach is implemented in real time for a laboratory 2.2 kW threephase IM drive. The experimental results show the capability and validity of the proposed control scheme. Nomenclature V, I, ψ voltage, current, flux vectors T e electromagnetic torque R winding resistance R i iron loss resistance L l leakage inductance L m coupling inductance between stator and rotor p pole pair number of stator ω r electrical rotor speed ω angular speed of rotor flux ω slip = ω − ω r slip speed

To accomplish benefits such as high accuracy and fast response, the model-based loss minimisation algorithms (LMAs) are introduced in the literature, as one of the main available techniques for minimising power losses in electrical motors. They are appropriate for dynamic applications, which necessitate very fast update of the control variable. This study proposes a novel real-time LMA based on super-twisting sliding mode controller (SMC) for induction motor (IM) drives, while keeping a good dynamic response. In this regard, a loss minimisation criterion for the efficiency optimisation is proposed and scrutinised. It is shown analytically that LMA will be realised if the nonlinear controller forces this criterion to zero. Moreover, a supertwisting SMC integrated with the iron loss is proposed which directly regulates both the power loss-minimising criterion and the electromagnetic torque by choosing those as control outputs. The stability of the super-twisting SMC is also verified through the Lyapunov's stability principle. The complete closed-loop control of the proposed LMA-based IM drive is successfully implemented in real-time using a digital signal processor board TMS320F28335 for a laboratory 3-phase IM drive of 2.2 kW. The performance and functionality of the proposed scheme are assessed through experimental results.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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