A Battery Equalizing Circuit Based on Multi-winding Transformer

Since industrialization, the development of productivity has brought serious pollution. Since the new century, human beings attach more importance to clean energy. To mitigate the instability, energy storage components, such as batteries or ultracapacitors, are widely used in clean energy systems. Due to the present level of science and technology, energy storage devices are often used in series to meet the voltage requirements for specific applications. Nevertheless, voltage differences caused by individual characteristic differences will affect the performance of batteries. Hence, there is necessity to equalize energy storage components. What’s more, in the traditional voltage sharing circuit, with the decrease of battery voltage difference, the equalizing current will also become smaller. In some cases, that current may even be small enough to affect the normal operation of the circuit. To overcome this problem, this paper introduces a voltage equalizing circuit which can achieve a big current even when voltage difference is very close to zero. The structure of this circuit is based on half-bridge converter and multiport transformer. The formation principle of transformer secondary side voltage is analyzed in detail. According to this, transformer ratio n is redesigned to gain a proper equalizing current. A simple equalization control method is introduced. At last, the theory is verified by simulation and a 20-cell voltage sharing experiment.