A Transformer-Less Voltage Equalizer for Energy Storage Cells Based on Double-Tiered Multi-Stacked Converters

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.