This paper proposes a method to reduce the DC link capacitor of the ISG (Integrated Starter Generator) inverter for the micro-hybrid system of which ESS (Energy Storage System) is composed of a 12V battery, a 48V super-capacitor and a bidirectional DC-DC converter. Firstly, analysis is performed to calculate the required dc link capacitance according to the allowable ripple voltages and some inverter switching frequencies. And then, a method to reduce the ripple voltage is presented in which increased is the switching frequency, namely decreasing the switching period smaller than the current control period. Thirdly, the other method is presented to compensate the ripple voltage with a bidirectional dc-dc converter which is controlled much faster than the inverter. Finally, several simulations are done to verify the effectiveness of the proposed method. Using the proposed method, the required capacitance can be reduced to about a half of that of the initial design.