Self- Commissioning of Sensorless AC Motor Drives
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For higher energy efficiency and greater motion control flexibility, inverters are used to drive electric motors. High-performance operation of motor drives requires complicated control algorithms and corresponding motor parameter information. Nonetheless, the users may not have the required skills or tools to obtain accurate motor data for high-performance control. Therefore, it is necessary for commercial motor drives to have highly accurate self-commissioning capability. The motor drive parameters obtained by self-commissioning are essential to design the current and speed controllers; high-frequency signal injection based sensorless control, observer-based sensorless control, and energy efficiency improvement schemes such as maximum torque per ampere (MTPA) control. Yet, established self-commissioning methods are not mature enough to provide self-sufficient, robust, and complete solution and also to fully cover newly emerging motor types such as interior permanent-magnet synchronous motors. In order to improve them, the dissertation focuses on a comprehensive study on the end-to-end selfcommissioning of general-purpose industrial sensorless ac motor drives. The dissertation targets full coverage of all motor drive parameters in a self-sufficient way through step-by-step estimation of the relevant parameters. The proposed parameter estimation methods are applicable to all AC motor types whenever the motor nature allows so. First of all, a novel method for spatial inductance map identification is proposed to estimate relevant inductance values which is used to tune the current controller. This method uses open loop voltage injection with automatic selection of injection amplitude and frequency and does not need rotor position information. After current-loop auto-tuning, a precise and robust method for initial rotor position is presented for synchronous motors. Later, estimation methods for stator resistance and saturated inductances are provided for all AC motors. Also, the nature of induction motor introduces unique difficulties in the standstill estimation of magnetizing inductance and rotor resistance. Existing traditional methods of low-frequency current injection and flux integration are not successful enough to provide robust results that can be replicated in many different motorinverter pairs. A simple novel method that makes use of the redundancy of resistive drops during dc-magnetization of the motor is presented to solve to these difficulties. Upon finishing stationary tests, rotational test is required for the estimation of mechanical parameters. Inertia estimation and consequent speed-loop auto-tuning has some challenges such as automatic test torque selection satisfying most of the practical conditions with varying mechanical inertia and loads, creating controlled speed oscillations, and robust signal detection during the test. This dissertation proposes novel solutions to these. Overall, this dissertation proposes an end-to-end, self-sufficient, and robust solution for self-commissioning of sensorless industrial AC drives.