Investigations on Sensor/Sensorless control of PMSM drive for grid connected and standalone applications

Abstract

The goal of present work is to study, develop and analyze the sensor/sensorless control of Permanent Magnet Synchronous Motor (PMSM) drive for grid connected and standalone applications. The research work carried out in this thesis is mainly divided into three parts. Firstly, to find simple and effective algorithm to estimate the rotor speed and position of the PMSM drive. The second part mainly focus on developing a controller for sensor based PMSM drive. The main moto of presenting the proposed estimation scheme and controller separately is to show the efficacy of the PMSM drive by validating their performance individually. Finally, the third part is to develop a standalone PV fed PMSM drive for rural areas. This thesis proposes two speed/position estimation algorithms based on MRAS method for sensorless PMSM drive. In literature, initially proposed MRAS technique is based on stator current to compute the speed and position information of PMSM drive. Following this, many other functional candidates such as stator flux, reactive power are reported with varying system performance. So far, all these functional parameters have a physical understanding (stator flux) or a practical existence (such as current, power etc.). Stator flux based MRAS has unsatisfactory performance in the low speed regions. Thereby, going beyond such selection, a new Flux-Torque based MRAS is proposed and satisfactory performance is reported with stability in low speed operation. FluxTorque is combination of physical and practical existence. The proposed speed estimator is formulated using stator flux and electromagnetic torque based MRAS. It performs better during transient conditions and reduces steady state error for wide rotor speed variations including low speed regions. The stability of the proposed estimator is verified through small signal model and the machine parameter sensitivity is also analyzed. The performance of the proposed estimator is validated for variation in the low speed regions including standstill condition. Flux-Torque based MRAS is stable in the low speed region but this scheme requires information of actual and estimated stator flux and electromagnetic torque to estimate speed and position. In order to reduce mathematical complexity and to avoid computation of stator flux, the simple and robust electromagnetic torque based MRAS speed/position estimator is proposed. The proposed estimator is formed usinginstantaneous and estimated electromagnetic torque. Using small signal modelling, the stability and sensitivity analysis are performed. Results show that, the estimator is stable over a wide speed region (including low speed regions) and exhibits robustness against uncertainties in machine parameters. Simulation and experimental results demonstrate the efficacy of the proposed scheme under different test conditions viz. over a wide adjustable speed range which include different low speed regions and standstill at different load conditions with uncertainty in machine parameters. Further this thesis proposes a simple cascaded Pseudo Derivative Feedback and Feed Forward (PDF plus PDFF) controller for permanent magnet synchronous motor drive. The PI plus PI controller and proposed PDF plus PDFF controller are designed and their stability is analyzed using extended root locus technique, and further influence of damping coefficient is discussed in detail. The proposed control scheme significantly improves dynamic response viz. reduces 50 % of overshoot in stator current, eliminates overshoot in speed and has two times faster settling time of the overall system compared to cascaded PI plus PI controller during wide variation in speed with load disturbance. Simulation and experimental results demonstrate the efficacy of the proposed scheme under different test conditions viz. over the wide adjustable speed range which includes different low speed regions and standstill i.e. 0 to 157 rad/s at different load conditions. Finally, this thesis proposes a standalone PV fed PMSM drive for water pumping. The proposed system aims at reducing the switching losses and overall cost by using reduced switch inverter. The proposed system comprises of a PMSM drive, fed by PV source through an inverter employing reduced number of switches. The inverter uses only four switches whereas the conventional VSI utilizes six switches. Field oriented control scheme is employed to control the PMSM drive. Perturb and Observe (P&O) MPPT technique is used to generate a speed reference to PMSM drive. Simulation and experimental results demonstrate the efficacy of the proposed scheme. All aforementioned simulation studies are carried out through MATLAB/ Simulink and it is also experimentally verified through laboratory prototype consists of FPGA controller based PMSM drive.