Study on the characteristics of boost converter in hybrid fuel cell city bus

In a hybrid power system where a fuel cell engine and a group of Ni-H batteries are connected together by a bi-directional DC-DC converter, the boosting characteristics of the converter are studied. On the base of analyzing the U-I characteristic of the fuel cell engine, two kinds of characteristics of boost converter, linear and non-linear, are proposed. By establishing the mathematical models between voltage and current, also power and voltage, the output power of the hybrid system under each characteristic is studied, showing that with the non-linear U-I characteristic, the output power of boosting DC-DC converter adaptively follows the voltage of the fuel cell engine, obtaining stable power process. The non-linear characteristic has been validated by experiments and a hybrid power system with it has been applied in the fuel cell city bus developed by Tsinghua University