Flux Polar Control of AC Motor Drives

Transport electrification is leading to an impressive development of electric drives using permanent magnet synchronous motors (PMSMs) and induction motors (IMs). According to this trend, impressive research efforts to develop torque control schemes characterized by high performance, easy to tune, and able to deal with saturated machines have been made in recent years. Moreover, these control solutions must guarantee a linear torque regulation for the entire speed range, including the deep flux-weakening (FW) operation with maximum torque per volt (MTPV). Currently, the control of the torque is mostly based on vector control schemes using inner current control loops whose references are in many cases provided by multi-dimensional calibrated maps to linear the torque regulation. However, the performance of the current loops depends on the motor inductance, i.e., the machine operating point, thus requiring demanding tuning procedures. Therefore, the goal of the thesis is to develop a unified torque controller for ac motors using inner flux- and load angle- control loops since they are both independent of the machine inductance. Hence, their performance is only limited by the sampling frequency of the digital controller, thus guaranteeing the same torque regulation performance in deep FW with MTPV. Moreover, the torque linearity is guaranteed from zero up to the maximum speed reaching FW with MTPV using a single calibrated load-angle map that allows the maximum torque production under inverter current and voltage constraints. This control technique can be applied either on synchronous motors (PMSMs) and induction motors (IMs) guaranteeing optimal performance in all the speed range. However, the main obstacles to use of this strategy are the creation and usage of the load angle map in the control code. In fact, the load angle map is generated accordingly to the motor flux maps and the control constrains introduced by the optimal exploitation of the machine potential, i.e., the MTPA and MTPV locus besides the inverter current limit. Despite the generation of the load angle control map requests some care, the proposed method can be considered in a way easier than the solution currently used, as the DFVC, DTC, CVC ones, because of the simplicity of the strategy adopted. All the machine characteristics, including the non-linear behaviour due to the saturation of the magnetic material, are reflected in the control map generated. Non-additional care must be used in the tuning process of the control loops as it is requested in the mentioned strategies that are highly affected by the non-linear behaviour of the machine. The simulation results and the experimental ones confirm the robustness of this control technique that gives excellent results both on the control of non-linear synchronous motors and induction ones.