AbstractA solar home system (SHS), containing three independent parts, namely a load voltage dc–dc converter, an energy storage device (ESD) charger, and an ESD equalizer, will become bulky and costly. Thus, based on Cuk converter, an integrated charging equalizing converter (ICEC) is proposed. The ICEC can achieve load voltage converting, battery/supercapacitor (SC) charging, and equalizing simultaneously. The idea of the ICEC is using a voltage multiplier (VM) to replace the capacitor in Cuk convertor, and then reusing the VM as a charging equalizer. When the Cuk converter is operating, the voltage ripple generated on the VM, which can be regarded as an ac voltage source, is utilized to drive the VM. Therefore, compared with the traditional methods, the charging and equalizing can be achieved without extra switches and magnetic elements. A prototype for four SCs is built to verify the feasibility of the proposed method. And the system efficiency is 87%, corresponding to the input power 5.6 W, the load output power 3.54 W, and the charging balance power 1.33 W. Moreover, a quantitative comparison shows the proposed method can reduce the system size and cost effectively.

Abstract This thesis proposes a charging equalizer for hybrid energy storage systems, incorporating the Zeta converter, voltage multiplier, and multi‐winding transformer. The objective is efficient charging and equalization for battery and supercapacitor strings. The Zeta converter serves to charge the battery string, while the transformer with multi‐winding shares the inductor of Zeta converter as the primary side, facilitating battery string balancing through the utilization of current ripple in the inductor. Additionally, the voltage ripple generated by the Zeta converter is utilized to drive the voltage multiplier, enabling the charging and equalization of the supercapacitor string. The system's operation halts upon reaching the predefined threshold voltage for the supercapacitor strings. The proposed circuit transforms into a Zeta converter by employing a single‐pole double‐throw switch, facilitating the charging of the battery strings. Experimental validation uses four series‐connected supercapacitors and four series‐connected batteries, demonstrating successful equalization and charging for both energy storage components.

This article presents a double-layer-integrated charging equalizer based on magnetic coupling to address battery module imbalances. The proposed architecture consists of a main transformer and parallel transformers. The main transformer ensures the overall module balance, while the parallel transformers achieve individual cell balancing. The system eliminates the need for additional magnetic components and operates independently. The experimental results on a nine-cell (three modules) setup demonstrate its reduced voltage variation during charging mode, with an efficiency of 90.1% at 35-W output. The proposed solution offers an effective and practical approach to address battery module imbalances in a concise manner.

Applying the recycled power battery to automatic guided vehicles can greatly reduce system cost and prolong the life cycle of the battery. However, the consistency of recycled power batteries is poor, and the imbalance of battery voltage will occur during the charging or discharging process. Therefore, a double-switch single-transformer integrated equalizer is proposed to balance automatic guided vehicles in both charging and discharging operations. The equalizer's multiwinding transformer shares the dc–dc converter's inductor, and the secondary side generates current by utilizing the current ripple on the primary windings. The battery string is balanced by the multiwinding transformer, without extra switches, when the circuit works in charging and discharging mode. A prototype for four battery cells is built to verify the proposed equalizer and its dynamic balance conditions, and a comparison with existing equalizers is presented. The results show that the system in both modes can realize the automatic balance without affecting the function of the dc–dc converter. The proposed circuit requires fewer components than the existing bidirectional integrated equalizer.

In a high-voltage energy storage system (HV-ESS), the voltage equalizer faces two challenges: 1) improving the extensibility and 2) reducing the number of switches. Therefore, an integrated voltage equalizer based on parallel transformers is proposed, which uses one mosfet to balance the HV-ESS. All the bottom-layer transformers (BLT) are paralleled, and the input voltages of BLTs are identical. Moreover, the top-layer transformer (TLT) drives parallel-BLTs, directly transforming balanced energy to each battery cell. Whatever the number of the BLT, the TLT uses one secondary winding to drive. Thus, the proposed voltage equalizer is highly scalable. The experimental results show that the proposed circuit effectively balances nine series-connected battery cells. It provides a highly scalable integrated voltage equalizer for the HV-ESS.

Using a multi-winding transformer to drive voltage multipliers (VM) for balancing ultra-capacitors (UC) string can improve the scalability of the equalizer. However, each winding of the multi-winding transformer differs in the ratio of turns, leakage inductance, and bypass resistance, resulting in an imbalance between UC modules. Therefore, a modular equalization system based on double-layer voltage multipliers for series-connected ultra-capacitors string is proposed, which uses VMs to balance the UC cells and modules, respectively. The converter’s energy transfer inductor acts as the voltage equalizer’s driver. An experimental charging test for two UC modules was performed. Cell and module voltages gradually became consistent.

A single-magnetic bidirectional integrated equalizer using the multi-winding transformer and voltage multiplier for the hybrid energy storage system is proposed. The multi-winding transformer and voltage multiplier, driven by the current ripple of the inductor in the bidirectional buck-boost converter, are used for the battery string and supercapacitor string voltage balance, respectively. Compared to the previous balance circuits, for the schedule of the proposed equalizer, only one winding and one diode are used for each battery. Meanwhile, one capacitor and two diodes are used for each supercapacitor, simplifying the balance circuit. This method has the advantages of low cost, suitable for cells with different voltage levels, multiplexed converter switches, and extremely simple structure. It does not have any active switch for the voltage balancing function. A prototype for four supercapacitor cells and four batteries is set up. The results show that the proposed circuit balances the HESS when the DC-DC converter works, which verifies the theoretical analysis.

Due to the electrical isolation, fewer switches, and easy control, the transformer-based integrated equalizer is promising in commercial applications. However, few balance energy transmission channels limit the transformer-based integrated equalizer applied to the long battery string. Therefore, a integrated voltage equalizer with a modularized architecture (MEA-TE) is proposed. The proposed equalizer increases the energy transmission channels, which realizes the balance for the long battery string. The modularized equalizer consists of three parts: the dcdc converter, the converter-to-module transformer (CMT), and the module-to-cell transformers (MCT). The MOSFET in the dc-dc converter drives the CMT, and the CMT drives all the MCTs to balance each cell. The proposed MEA-TE equalizer only uses one MOSFET to balance the large battery pack. The MEA-TE platform for eight battery cells is established. The results demonstrate that the MEA-TE equalizer can realize the balance of the large battery pack.

In the hybrid energy storage system (HESS), the voltages between the battery cell and the supercapacitor cell are different, increasing the circuit and control complexity of the balance system. Therefore, a bidirectional integrated equalizer based on the Sepic–Zeta converter is proposed for the HESS, which realizes both battery string and supercapacitor string balance during the energy exchange. The inductors in the Sepic–Zeta converter are used as the primary side of the balanced multiwinding transformer. The Sepic–Zeta converter generates the current ripples to drive the multiwinding transformer. The secondary side generates currents to balance the HESS, and hence, the equalizer itself is essentially switchless. Therefore, the proposed circuit can reduce the complexity of the HESS. Experimental and comparative results show that the proposed equalizer achieves the balance of the HESS.

Due to the complexity of driving conditions and the increase of the driving range of electric two-wheelers and three-wheelers vehicles, the power battery string is in a long-period unbalanced discharge state, which affects the power output and even causes certain safety risks. A compact-size multi-winding transformer-based discharge equalizer is proposed to solve these problems and minimize the impact on the system volume by sharing the primary inductor with a boost discharger. When the boost converter is powering a load, the multi-winding transformer equalizer is driven by utilizing the square wave voltage generated on the inductor in the boost converter and produces multiple identical voltage levels to achieve voltage balance. Thus, the automatic balance can be achieved with only one winding and one diode for each module. An experimental prototype containing four batteries was established to verify the feasibility of the proposed method. Moreover, a quantitative comparison shows the proposed method obtain a more compact-size equalizer because of no need for a separate transformer, compared with the traditional equalization method based on the transformer.

The traditional pure switched-capacitor equalizer suffers from a large inrush current and low balance speed. An automatic parallel resonant switched-capacitor equalizer (PReSCE) for series-connected battery strings is proposed, which utilizes resonant switched-capacitor to eliminate the inrush current. The parallel ReSC converters not only minimizes output impedance at the low switching frequency, but delivers the excess energy to the low-voltage battery directly from the high-voltage battery in one cycle. Both of the two functions increase the balance speed. All of the switches are controlled by a pair of complementary pulsewidth modulation signals at a fixed operational frequency. Both simulation and experiment are used to verify the theoretical analysis and system feasibility of the proposed circuit. The results show that the PReSCE circuit eliminates the inrush current and increases the balance speed three times than the parallel pure switched-capacitor equalizer.

The hybrid energy storage system (HESS) uses the retired power battery can prolong the battery life cycle and lower the system’s cost. A series-parallel resonance switched-capacitor equalizer for the HESS is proposed in this paper, which uses series-parallel resonance switched-capacitor to realize the balance. In addition, the use of series-parallel resonance circuits can realize the conversion of different voltage levels, and energy can flow through the HESS via equalizer. Therefore, the entire HESS only needs one equalization circuit to achieve system equalization. Moreover, a prototype consisting of a ternary-lithium battery pack, a polymer-lithium battery pack and a supercapacitor pack is built.

The traditional balance circuit is employed to balance the retired battery string. It will occupy some space for the extra switches, inductors, or/and capacitors of the energy storage system. This letter is trying to share the inductor of the dc-dc converter with the balance system by utilizing the current ripple on the inductor of the multiwinding transformer. The balance circuit does not require additional switches and control logic. The results of dynamic charging conditions show that the circuit is appropriate for balancing the battery string, and the system efficiency with the proposed approach reaches 94.1% at rated 28-W input power. The balance system only increases one diode and one inductor for each cell, which reduces the cost by 60% and 66% separately compared with the traditional resistance equalizer and transformer-based equalizer.

The traditional pure switched-capacitor equaliser brings the large inrush current and low energy density. This study proposes a series of resonant switched-capacitor (ReSC) voltage equaliser, which realises energy transferred directly from source cells to target cells by the series ReSC converter. The ReSC converter eliminates the inrush current and improves the capacitors’ energy density to increase the balancing speed. Meanwhile, all the switches are controlled by a pair of complementary PWM signals at a fixed operational frequency without voltage monitors. Both simulation and experiment are used to verify the system feasibility and theoretical analysis of the proposed circuit. In the same experimental condition, the proposed series resonant circuit reduces the inrush current. It improves the energy density of capacitors three times compared with the pure series switched-capacitor equaliser.