Zero Current Switching Switched-Capacitors Balancing Circuit for Energy Storage Cell Equalization and Its Associated Hybrid Circuit with Classical Buck-Boost

Abstract

To overcome the problem of switching loss during the balancing process, a novel cell balancing circuit is proposed with the integration of a zero current switching technique. Moreover, the balancing circuit proposed can change between a classical buck-boost pattern and a resonant switched-capacitor pattern with flexible control to cater to the balancing requirements under different driving scenarios. The results of the simulation of field experiments demonstrate successful balancing, various balancing speed, and low energy loss. The proposed balancing circuit proves to be effective for a wide range of application and is the first attempt to integrate a dual balancing function in a single balancing circuit for cells.Energies 2019, 12, 2726 2 of 15 However, those methods are not flexible enough for changing scenarios. Furthermore, as a hard switching operation is adopted in a large number of cell balancing circuits [21][22][23], electromagnetic interference (EMI) and high switching energy loss will appear. On the other hand, the service life of energy sources will also be affected by a current spike in hard switching circuits. In this paper, a novel balancing circuit is proposed to realize zero-current switching (ZCS) similar to quasi-resonant [24,25] during the switched-capacitor mode and has been proven to further reduce energy loss [24][25][26][27][28][29].Different states of EVs, such as the drive state, brake state, and park state, may have different requirements on the output power, balancing speed, and balancing loss. Many existing papers [22,23] do not take the real driving state into account and make a fixed cell balancing strategy, which decreases the overall balancing efficiency [30][31][32][33]. They are based on switched-capacitor techniques [34,35]. Some papers have realized the difference in energy management at different driving states and proposed specific energy controllers respectively. The energy saving controller for electric mining trucks is introduced in Reference [36], as it runs in high-frequency start-up processes. A predictive energy controller based on preceding vehicle movement management is designed in Reference [37] for lined up EVs on the road. A real-time energy controller for EVs in a charge-depletion mode is discussed in References [38][39][40] for adaptive energy consumption minimization.In this paper, a novel and multi-functional balancing circuit is proposed with a ZCS technique to improve energy saving during the balancing process. The multi-functional circuit can easily change between a buck-boost pattern and switched-capacitor pattern with flexible switching frequency and duty ratios, i.e., the circuit can adapt to changing driving states. Figure 1 demonstrates six different operating modes with different cell balancing requirements for the corresponding driving states. Moreover, voltage sensors can be installed at each cell in order to collect the voltage signals for an intelligent control box. In the real-time feedback control, switching frequency and duty ratios are adjus...

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