Low cost soft switching DC-DC converter with autotransformer for photovoltaic hydrogen systems

In optimized photovoltaic-supplied hydrogen production systems, quite different levels of DC-voltages have to be linked via DC-DC power converters. For coupling of photovoltaics and electrolysis, a new step down DC-DC power converter has been developed, which uses an IGBT and an autotransformer together with a high frequency, zero-voltage switching concept to reduce losses. The concept allows conventional PWM control, high utilization of components and low components count. Through the soft switching concept, which uses the autotransformers leakage inductance, electromagnetic interferences are low. The circulating reactive energy is low, as well as the rating of the auxiliary switch. For fuel cell operation, a new step-up power converter has been developed, which also uses an autotransformer but operates (due to the low input voltage) with a MOSFET and a regenerative voltage clamp. This power converter is now operating in the solar hydrogen plant in the Research Center Julich (Germany). Circuit analysis and measurement results of both power converters are presented. Efficiencies reach very high values of more than 94%