Online Efficiency-Optimization Controlof Induction Motor Drives For EV

It is very necessary to keep the induction motor (IM) with high efficiency during the whole range of base speed, especially for the application of Electric Vehicle (EV). IM is widely used in EV since its simpler construction, small motor size, low maintenance and better reliability. But in the conventional vector-controlled method, the flux is generally set to rated value, which greatly decreases the efficiency of IM especially in light-load condition. Online efficiency-optimization control (EOC) of IM drives is proposed and studied in this paper to solve the low-efficiency problem.A 4kW squirrel-cage IM is used to verify our method. The conventional rotor-flux oriented vector control theory is implemented. TMS320LF2407a produced by TI is chosen to be the main control unit. The frame of system and the control circuit are designed. The full digital FOC system is realized.The input power measurement and the flux adjustment are the two key steps in the realization of EOC. In the section of input power measurement, altogether three methods are presented. In the first method, the dc link voltage and current of a space vector PWM voltage-source inverter is thoroughly studied. Based on their characters, different filter techniques are designed and implemented which make the direct product an effective method to obtain the input power. Neglecting the inverter loss, two new techniques to acquire the input power are presented. Through the coordinate transformation, one is founded on d-q coordinate variables which are very convenient for programming, and the other is based on a simplified loss model in which the iron loss is calculated by a two-order polynomial gained from the blocked-rotor test and curve fitting. In the section of flux adjustment, three methods are also presented. They are golden-section searching method, ramp search method, and a hybrid one with a planned evaluation of the optimized flux.The relation between input power of IM control drives and different flux level is studied by simulation using Matlab Simulink. The basic law of the effectiveness of EOC according to different working condition of IM is summarized. The three methods of flux adjustment are also simulated and the ramp method is verified by experiment. The close agreement between the simulation and experimental results confirms the validity and usefulness of our proposed techniques in improving the efficiency of IM drives.