Abstract
Energy storage systems are widely used in various fields such as renewable energy generation, hybrid electric vehicle, power grid, etc. However, the difference in characteristics among energy storage cells is one of the bottlenecks faced by large-scale application of energy storage systems, and the voltage imbalance among cells will gradually increase due to nonuniform characteristics. To solve this problem, this paper proposed a transformer-less voltage equalizer based on multi-stacked type converters for series-connected energy storage cells. Only two switches controlled by same driving signals are required and all cell voltages become uniform automatically without current sensor, voltage sensor and closed-loop control. Compared with the conventional single-switch voltage equalizer, the proposed equalizer not only inherits the current limit characteristic of conventional equalizer in discontinuous conduction mode operation but also obtains higher equalization speed and reduced current ripple. Operation principles and characteristics analysis of proposed equalizer are introduced, and the experimental verification are carried out to verify the effectiveness and superiority of proposed equalizer.
Highlights
The energy storage systems are widely used in various fields such as renewable energy generation, hybrid electric vehicle, power grid, etc [1], [2]
Due to the characteristic differences in capacity, internal impedance and self-discharged rate, the voltages of cells connected in series are usually different in practical applications [3], [4], and the voltage imbalance issue may reduce the effective capacity of energy storage system
The multi-stacked SEPIC converter (MSSC) based on single ended primary inductor converters (SEPIC) converters is consists of an input capacitor Cin1, an input inductor Lin1, a switch Q1, a capacitor C1a, an inductor L1a and a diode D1a, and it is extended by stacking capacitors Cia, inductors Lia and diodes Dia (i = 1, 2, 3, ..., n) paralleled with the cells Bi (i = 1, 2, 3, ..., n), respectively
Summary
The energy storage systems are widely used in various fields such as renewable energy generation, hybrid electric vehicle, power grid, etc [1], [2]. The nondissipative equalizers with energy transfer paths are actively studied due to their higher efficiency and better equalization performance They are divided into several categories: switched-capacitor [7]-[15], switched-inductor [16]-[19], multiwinding transformer [20]-[22], switch selection [23]-[25], voltage multiplier [26]-[28] and multi-stacked type [29], [30]. To further reduce the volume of transformer and number of windings and increase equalization speed, literature [22] proposed an equalizer based on coupled half-bridge converters with the halved secondary winding count. The Equalizer designers can be freed from cumbersome transformer design and extend to n cells by implementing inductors, capacitors and diodes with appropriate rated values
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