Research On Equalization With Compound Structure Applied In Power Supply Of EV

With the advantages of high unit power, fast charge, long cycle life and high-reliability, EV using ultra capacitors as main power became one of the important research orientations. Tens of ultra capacitor groups or hundreds of ultra capacitor monomers were series connected to achieve output voltage needed. To avoid over-charge and over-discharge caused by the deformity of the parameters, equalization system is necessary.High efficiency, rapidity and simple structure are the main most important objectives of equalization system which influence mutually. Based on the existed achievements, A compound structure equalization system which combined the advantages of centralized and decentralized means of equalization is raised to achieve the equalization of series connected ultra capacitors with huge number. The topology of this structure and the influence of difference groupings on efficiency, rapidity and structure are researched, several ways of grouping and topologies were also given.Number of equalizers and layers in the system are almost determined by the circuit of bottom equalizer. In this thesis, a 4-output fly-back equalizing circuit with coaxial winding transformer was chose for the good of the grouping, the efficiency and structure, detailed analysis on this circuit is given, control circuit and coaxial winding transformers'working principles and designing course are expatiated. The upper equalizer switch output voltage to the low voltage unit in the low layer and charge it until its voltage become the same with the highest one. By several cycles, the voltage of the units in the lower layer comes to the same level. The topology of upper equalizer was chose to be half-bridge, IC SG3525 was chose as controlling chip, constant current output and constant voltage output were achieved by the feedback of output voltage and output current.At last, experiment with bottom equalizer and upper equalizer was carried out, waveforms were acquired. 4 2Ah Li-ion batteries were used as the experimental subject to simulate the working process of ultra capacitors. Li-ion batteries'voltage-time curves were acquired and record in the same intervals. Experiment results show that equalizing unit with coaxial winding transformer and upper equalizing unit have ideal results in equalizing course, designed principles were verified. The circuit with simple structure, reliable working state and low cost was of value in practical application.