Electric Vehicle Induction Motor System Efficiency Optimization Control Study

At present, massive induction motor (IM) drive systems are applied in the industry and agriculture, and they consume more than 60% of the total energy generated. Generally, the IM is highly efficient when operated under the rated conditions. But with the rated conditions changing, the efficiency is greatly reduced. So it is important to improve the efficiency of electric drives, mainly for two reasons: energy saving and environment protecting.Considering the performances of medium (and sub-medium) power IM drive systems applied in electrical vehicle (EV) and the output characteristics of SVPWM inverter, this paper proposes two methods to realize the efficiency optimization control, which are the optimization of the fundamental magnetic flux and the optimization of SVPWM. The former can balance the motor core loss and copper loss induced by the fundamental voltage. The latter can make the inverter reduce the harmonic voltage output, consequently reducing the motor core loss and copper loss induced by the harmonic voltages.This paper mainly includes the following parts:The iron loss of IM, which is usually ignored in MATLAB/Simulink mathematical model, is very important for efficiency optimization control, precise vector control and other related simulation studies of IM. Based on mathematical analyses, this paper presents a new induction motor model in the a-p stationary frame, including iron loss. In order to insure the stability of simulation, such model doesn't use the differential unit. All parameters of this model can be obtained by conventional locked-rotor and no-load tests. The model has satisfied precision, as well as reliable and practicable characteristics.This paper summarizes the main efficiency optimization control strategies appearing recently years, and proposes a new fuzzy logic based hybrid on-lion minimum input power search control strategy (FLSC), which makes full use of the results of loss model control (LMC) and search control (SC). Unlike the other fuzzy methods that need simulation calculation to get the coefficients of the scaling factors, the gains derivative method of this strategy can make on-line calculation with simple and effective. Meanwhile, for the first time, this paper presents the systematic design methods of new fuzzy sets and Membership Functions (MFs), which can make the control system converge fast with avoiding the oscillation around the optimum flux. The simulation results confirm the validity and usefulness of the proposed techniques.This paper comprehensively investigates the relationship between the Carrier Based PWM (CBPWM) and Space Vector PWM (SVPWM). With making full use of the CBPWM research results, this paper presents a new distribution method for zero vector acting time, which can yields different SVPWM modulators with lower inverter-harmonic-voltage output. Furthermore, the conventional overmodulation techniques for SVPWM inverters need store lots of date in the controller beforehand, which makes a hugememory while the control resolution is not perfect. Based on amplitude control of the reference voltage vector and the vertex voltage vectors, this paper presents a novel digital overmodulation control strategy for SVPWM inverters, which can manage the transition from the linear control range to six-step operation smoothly. With avoiding the necessity of the stored data implementation, this strategy is simple and very suitable for practical digital implementation. The mathematic analyses show that the output fundamental voltage amplitude is linear proportional to the modulation index. In addition, this paper analyses the harmonic components, and the total harmonic distortion (THD) of the output voltage is compared with that of other strategy too. Both math analyses and simulation results, verify that this strategy is very useful for the induction motor with the linear fundamental voltage output gain, low THD and simple application.The experiments of the FLSC efficiency optimization strategy, implementing on TMS320F2407A DSP based 1.8kW/5.4kW IM drive experimental system, verify that this strategy is very fast and highly precise, and can be applied for any steady state of IMs. The SVPWM overmodulation experiments on 100kW/160kW IM applied in Electrical Vehicle drive demonstrate that this simple and effective algorithm, without any hardware requirements, is compatible with the normal algorithm practicing in the linear modulation range. Otherwise, the experimental results indicate that such overmodulation algorithm is very fit for the SVPWM voltage inverter control, especially fit for the source voltage changing frequently or battery-fed inverter system, such as electrical vehicle.