The charge equalization for the battery power source with battery power modules (BPMs) in series is presented in the thesis. The bidirectional power converters in BPMs are able to serve as chargers with buck conversion during the charging stage. Even though connected in series, all modules can substantially be operated individually, retaining the advantages of independent operation, such as flexible control, easy protection, simple maintenance, and favorable battery power management. Investigation results indicate that automatic charge equalization is possible for the discontinuous conduction mode (DCM) operation. On the other hand, charge equalization can be achieved much faster by individually regulating the charging currents at the continuous conduction mode (CCM). According to the analyzed results, an equalization strategy is proposed to solve the charge imbalance problem by scheduling the individual battery current. Experiments are carried out to demonstrate the effectiveness of charge equalization.

Charge equalization is a major issue in the service of batteries since they are frequently connected in series to obtain higher output voltage levels for most applications. With series connection, imbalance may happen to the operating batteries during either charging or discharging periods. The imbalance among batteries concerns the operating efficiency and the battery lifetime. The main object of this dissertation is to solve the problem of charge inequality. The importance of charge equalization is first addressed. The problem is demonstrated by experiments of charging/discharging processes. Then, the techniques of battery charging and charge equalization are reviewed. To improve charge equalization, a dynamic balance charging scheme is developed on the basis of buck-boost conversion. The balance charging scheme can be realized by two configurations, that is, ¡§forward allotting¡¨ or ¡§backward allotting¡¨ configurations. The circuits are composed of several duplicated subcircuits and operated by digital control kernel, therefore, they are easy to be applied on battery sets with different numbers of batteries. By dynamically re-allocating the energy drawing from satiated batteries and allotted to hungry ones, the series-connected batteries can reach balance state more efficiently. The balance charging circuits can be employed during off-line or even discharging. However, on observing that the output voltage will vary in a big range when the battery set is discharged, the charge equalization can be integrated with voltage regulation on the output. Evolve from this idea, a balance discharging circuit¡@topology based on multi-winding transformer is proposed. The experiments in this dissertation are carried out on lead-acid batteries, therefore, the reactions and characteristics of lead-acid batteries are discussed. However, the proposed circuits are not restricted to be applied on lead-acid batteries only. Experimental results confirm the theoretical analyses and manifest the effectiveness of the designed circuits.

Due to the differences in batteries of a series-connected battery bank, the restored capacity in each battery may not be the same when being charged. In order to extend battery cycle life, the charger for the battery bank must have the capability of charging equalization. This thesis proposes a non-dissipative balance charging circuit based on buck-boost topology for a series-connected battery bank. Each battery in a battery bank is associated with a buck-boost converter. This topology can efficiently alleviate the unbalance of charge among batteries by taking off the charge from the affluently charged batteries and then allotting to those insufficient ones. To accomplish this complicated and accurate control, a digital signal processor (DSP) with sensors and interface circuits is adopted. It monitors the variations of battery voltages, activates the associated buck-boost converter, and adjusts the duty ratio of the converter to regulate the energy to be released. In virtue of the adoption of digital control kernel, the control circuit can be simple and the control flexibility can be favored. A battery bank with four series connected lead-acid batteries is used for illustrating the operating behavior and describing the operation modes of the balance charging circuit. The results of experiments convincingly advocate the applicability of the proposed approach.

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