Three-phase H-bridge frequency inverter is usually composed of an uncontrolled rectifier bridge and three pieces of H-bridges. It is difficult to solve the current analytical expression of DC support capacitor due to the non-linear feature of rectifier bridge and harmonic influence of H-bridge inverter.However

correct current analytical expression is of great importance for the design of capacitor. In this paper

the correct analytical expression of harmonic spectrum and its effective value of DC support capacitive current of three H-bridge frequency inverter are deduced on the basis of analysis of single phase H-bridge and

at the same time

the capacitance selection of the support capacitor is discussed. It is proved by the simulation and experiment that the design issue of the DC support capacitor can be solved effectively by the proposed method and excellent actual result is obtained in the practice.