Research On Several Key Technologies Of Low Cost Induction Motor Drive Control System

In this thesis,a low cost induction motor drive system is analyzed and studied in detail.In order to reduce the cost,the typical sampling methods are compared and the three-resistor sampling topology is selected for further research.In the traditional three-resistor based current sampling scheme,the sampled currents will become inaccurate when the duration of zero voltage vectors of an inverter is too short.To overcome this problem,a novel three-resistor sampling method is proposed by establishing a predictive current model of an induction motor on the synchronous rotating frame for the demonstration purpose in this paper.The principle of this method is validated by simulation and experiments.The results verify that the existing problems can be solved effectively and the motor can perform well with higher modulation index under the new scheme.In addition,the efficiency optimization method of the motor is studied and analyzed based on the three-resistor sampling system.The motor loss function expressed with rotor speed and electromagnetic torque is deduced from the mathematical equivalent model of an induction motor including iron loss.To minimize the motor loss,the efficiency optimization method is presented and the optimum rotor flux is calculated and set on-line to make sure that the motor is running with the highest efficiency.The methods studied in this thesis are proposed strictly from the theoretical analysis and performed in Matlab/Simulink environment and experiment platform.The results verify that the proposed three-resistor sampling strategy and the efficiency optimization method can save the cost of the drive system and improve the efficiency of an induction motor.The studied technologies in this paper can provide the theoretical and technical support for practical applications,and have great significance for the low cost induction motor drives.