Analysis of Motor Driving Circuit in EV/HEV with Battery Circuit Model Employed

Abstract

In the EV/HEV motor driving system, one of the most important elements that should be taken into account would be a battery that drives the whole system, because the rest of the circuit elements except battery have been relatively well established in the power electronics area. Because of the high frequency power harmonic noises inherent in the circuit, exact voltage fluctuation analysis of the driving circuit at the design stage has been emphasized quite a lot so far. This paper describes the analysis of motor driving circuit with novel battery model employed: as a result, the fluctuated battery voltage for a given DOD (Depth of Discharge) could be calculated. A filter design procedure that takes into consideration of the battery characteristics is also described for a fixed DOD. The effectiveness of the designed filter was confirmed by simulation, which was performed by using MATLAB, Ansys' Simplorer, and Agilent Technology's ADS (Advanced Design System). EV (Electric Vehicle) or HEV (Hybrid-Electric Vehicle) basically employs power electronic circuit to charge battery as well as to drive a motor, and the high voltage in the circuit, typically in the range of hundreds volts, needs to be chopped to control the driving circuits, and as a result it is inevitable to produce high frequency harmonic voltage/ current components inside. Therefore one of the most important things the HEV motor circuit designer needs to consider is the prediction of the electromagnetic compatibility of the driving circuit at the design stage. This is crucial to avoid unnecessary trial and errors after fabrication of the whole driving circuit only to find that the circuit needs to be revised to satisfy EMC standards such as IEC/CISPR and ISO. Therefore, precise analysis of the motor driving circuit is mandatory in the EV/HEV development process at the design stage. The main elements of power electronic circuit in the HEV are such as a high voltage battery, IGBT (Insulated Gate Bipolar Transistor) inverter to control motor through PWM (Pulse Width Modulation) algorithm, BLDC (Brushless DC) motor, and so on. Since the other elements except the battery have been common in the classical driving circuit simulation, an emphasis is put on the battery circuit modeling, which enables to simulate the driving circuit at various DOD levels. For this purpose, battery circuit model includes not only a simple DC model in time domain, but also complex R-C elements in frequency domain, coming from charge transfer resistance and double layer capacitors in the battery. Since the R and C in the battery model depend on the DOD level of the battery, one needs to take into consideration the frequency-dependent battery impedance as well as the load condition to design the filters in the motor driving circuit. (1)(2) This paper is organized as follows. In the next chapter, battery model which is used in the analysis of motor driving system is introduced. In chapter 3 all the circuit elements, such as battery, inverter, and filters, are integrated to form the whole circuit, and brief filter design procedure is described. Chapter 4 demonstrates the simulated results of the voltage fluctuations and the conducted noise, and the effectiveness of the filter is also shown. Finally, this paper ends with a conclusion and further works in the last section.