High current, low voltage modular power converter for lead acid battery charging

The submarine lead acid batteries require high current (~8 kA) and low voltage (~10 V) battery chargers because of their high capacities. The need to install the power converters in small place is the driving force for reduced volume and high efficiency. Moreover, the high power lead acid batteries require very low voltage and current ripples and a very high level of performance from the power converters, particularly in terms of DC stability and dynamic response. To meet these requirements full bridge phase shifted, hard switching PWM technique is used in this application. By allowing zero voltage transition of phase shifted switching power modules, the power density of the system is considerably increased. This paper describes this quasi resonant (8 A, 10 V) power converter intended as a stable high current source for series connected 4 lead acid battery cells. The converter is made with a modular concept with 8 current sources (1 kA, 10 V) in parallel. Also 45deg phase shift is added between these 8 modules to reduce the output voltage and current ripple.