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Summary A traditional charging system is composed of a charger and a separate voltage equalizer. By integrating the voltage equalization circuit into the charger as an equalization charger, the components can be reduced, and the system can be simplified. The equalization charger consists of two functional parts: The front stage generates a PWM voltage wave, and the rear stage generates multiple uniform output voltages. In this paper, a new n‐stage current rectifier (CR) is proposed as the rear stage, which has higher power conversion efficiency than traditional voltage multipliers. The full‐bridge (FB) converter is selected as the front stage and combined with the n‐stage CR to form a phase‐shift (PS) FB converter, which can realize zero voltage switching (ZVS) operation under light load conditions. The basic working principle of the equalization charger is described, and analytical models for converter design are derived. A prototype for three battery modules was built and tested under the condition of initial voltage unbalance. Experimental results show that the proposed equalization charger has good voltage equalization characteristics, and the standard deviation is as low as about 4 mV. Experimental results show that all switches can achieve ZVS under light load conditions.

Energy storage systems include not only a charge/discharge bidirectional converter but also a separate voltage equalizer. This paper proposes a bidirectional converter with an integrated voltage equalizer, which saves a DC-AC converter, thus significantly reducing the size, cost, and complexity of the equalization circuit. In addition, integrating the equalizer into the bidirectional converter also has a positive impact on the realization of ZVS operation. Analytical models have been established that can be used for accurate prediction, optimal design, and effective control of the proposed converter. A control strategy is proposed, which not only enables the cells to be automatically balanced when the cell string is charged/discharged but also enables ZVS operation within a wide range of voltage changes and minimizes the RMS value of the primary current. An experimental prototype of 60 W applied to nine supercapacitors (SCs) in series was built, and the experimental results verified the theoretical analysis and demonstrated the characteristics of the proposed converter.bidirectional converter, supercapacitors (SCs), voltage equalizer, voltage multiplier 1 | INTRODUCTION Supercapacitors (SCs) have been widely used in portable electronic devices, regenerative energy systems, hybrid vehicles, uninterruptible power supplies, and so on, and because of their long service life, they are expected as an alternative to traditional rechargeable batteries. [1][2][3] Since the voltage of a single SC is low, typically 0-3.0 V, multiple SCs need to be connected in series to form a string to provide a higher voltage level. Due to the slight difference in characteristics between cells and the influence of the ambient temperature, the voltage of each cell in the series-connected SC string will gradually become unbalanced.Many methods for cell balancing have been proposed, each with different advantages and disadvantages. The active balance method transfers energy through an external circuit to achieve balance between the cells. According to the energy flow mode, these methods are classified into four types: cell-to-cell, cell-to-string, string-to-cell, and cell(s)-tostring-to-cell(s). 4 Compared with other types of equalizers, string-to-cell equalizers can achieve cell balance through a single power conversion stage. The number of active switches in these equalizers is usually small, and the control method is relatively simple. The low complexity of these equalizers is very attractive, especially suitable for small-and medium-sized energy storage systems.

This paper proposes an integrated equalization charger that integrates the charger, module-level equalizer, and cell-level equalizer into the energy storage system, which greatly simplifies the system. The proposed control strategy can not only improve the equalization charging characteristics of the system, such as fast balancing speed and high efficiency, but also enable all active switches to achieve zero voltage switching (ZVS) operation. The established analytical models and control block diagram facilitate the design and development of the converter. The proposed converter can balance the cells while charging the string. An experimental prototype was developed, and the experimental results verified the theoretical analysis and demonstrated the characteristics of the proposed converter. K E Y W O R D S battery balancing, battery charger, phase-shift switched capacitor converter (PS-SCC), voltage equalizer, zero voltage switching (ZVS)