Kovbasa S. Development of the theory of sensorless vector control of electromechanical systems with induction motors

In the dissertation developed a new solution of an important scientific and applied problem of creating new methods of sensorless vector control for electromechanical systems with induction motors (IM), which allow to provide the same with the sensored systems level of control performances. The quasi-vector speed control algorithms with improved static and dynamic characteristics are synthesized. Developed algorithms guarantees the asymptotic regulation (tracking) of the rotor speed and the stator flux vector, as well as achieving of the asymptotic stator flux orientation under no-load operation condition. In the loaded state, the system remains locally stable in the stability region, which is defined by the values of the IM parameters. A new concept of sensorless direct field oriented vector control of induction motor is developed. The main concept idea consist in the following: due to the nonlinear controller action, system's errors dynamics is formed as the decomposition of the original electromechanical object structure into three interconnected subsystems, whose stability and robustness properties provide for the composite system properties of the local exponential stability. A new method of sensorless control synthesis for IM is developed. According to the proposed method the nonlinear controllers forms a resulting system's structure in the form of nonlinearly coupled subsystems: speed estimation, mechanical and electromagnetic subsystem with properties of exponential stability under persistancy of excitation conditions. Subsystems stability properties together with hierarchical time-scale dynamic separation guarantees for closed-loop composite system local exponential stability properties. As a result, robust to inverter nonidealities asymptotic speed-flux trajectory tracking together with asymptotic rotor flux orientation and speed-flux estimation is achieved. The speed sensorless vector control algorithm of induction motor with torque per Ampere ratio maximization is developed. Control algorithm is based on the feedback linearization technique and guarantees asymptotic tracking of smooth torque trajectories together with torque per Ampere ratio maximization for constant or slowly varying torque references. A method of the flux reference calculation in the form of a dynamic torque function is developed. Proposed flux reference calculator provide maximization of the torque per Ampere ratio in both constant and variable torque operation conditions. The adaptive observer of induction motor stator currents and rotor fluxes is developed. Proposed observer under persistency of excitation conditions provides asymptotical estimation of constant or slowly varying rotor speed and rotor flux vector components. Using developed adaptive observer and nonlinear separation principle direct field oriented vector control of induction generator is improved and provides local asymptotic flux and DC-link voltage regulation without direct speed measurement. The technology of induction motor control algorithms rapid prototyping is developed. This technology includes: a family of controllers based on 32-bit floating-point digital signal processors; a number of experimental power converters; real-time software implementation of developed control algorithms for digital signal processor based controllers; experimental rigs with induction motors in the power range from 0.75 kW to 50 kW. The created technology of rapid prototyping allow to carry out full-scale experimental investigations of the developed sensorless control structures. Results of experimental investigations confirms high performances of induction motor control in the electromechanical systems with developed sensorless control algorithms. Experimental studies of the inverter nonidealities influence on the induction motor control is performed. An advanced algorithm of inverter dead time compensation has been proposed. It is shown experimentally, that proposed compensation algorithm in the developed speed sensorless control scheme provide speed regulation range extension to the level 1:100. Induction motor parameters identification algorithm is developed and experimentally verified. Industrial prototypes of the traction drives with rated power up to 180 kW for electric vehicles are developed, manufactured end experimentally tested. Keywords: sensorless vector control, induction motor, speed observer, electromechanical system.