Optimization of Centralized Equalization Systems Based on an Integrated Cascade Bidirectional DC–DC Converter

Abstract

This paper presents a novel integrated cascade bidirectional dc-dc converter for optimizing a centralized charge equalization system. Through the integrated cascade structure, the polarity switches and the bidirectional dc-dc converter in the traditional centralized system are integrated, and the cells with different voltage polarities are equalized by controlling the operating state of the converter. Compared with the conventional methods, the number of active switches is significantly reduced, leading to a more compact size and a higher reliability. Moreover, with a phase-shifted PWM modulation strategy, the peak value of the transformer current is reduced and the soft-switching operation is realized, thus greatly reducing the transformer and switching losses. Finally, the experimental results on 13 series-connected battery cells show that the proposed scheme exhibits the excellent performance in terms of equalizing efficiency and speed. The performance improvement of the proposed equalizer is further validated by a systematic comparison with the conventional centralized equalization methods.

A bidirectional converter with integrated voltage equalizer for series‐connected supercapacitors

“…Based on ( 5) and (3.3) and considering (10), (11), and ( 21), the optimized values of T 1 and T 2 can be obtained by minimizing I RMS in (20). Figure 8A shows the calculation results.…”

“…According to (10) and (11), in the three cases of V o ¼ 10 V, V o ¼ 15 V, and V o ¼ 20 V, the conditions for realizing ZVS operation are (23), (24), and (25), respectively.…”

“…However, the obvious disadvantage of using a converter as the EU is that a converter is required between every two adjacent cells connected in series, which leads to an increase in the complexity, cost, and size of the system. Using selective switching technology can greatly reduce the number of components but increase the complexity of the control algorithm 9–11 …”

“…In the table, the evaluation results of size, cost, and complexity of the EU are only for the equalization circuit and do not include the charging circuit. The relevant evaluation methods can be found in Liu et al 5 and Qi et al 11 The evaluation of the efficiency is based on reports in the references. The integrated architecture proposed in this paper significantly reduces the components and size of the system, which will be analyzed in detail in Section 5.2.…”

“…Using selective switching technology can greatly reduce the number of components but increase the complexity of the control algorithm. [9][10][11] Since each active switch requires a gate driver IC and its related passive components and auxiliary power supplies, the complexity of the system is proportional to the number of active switches. Equalization methods based on multiple transformers [12][13][14] can reduce the number of active switches.…”