ac characteristics in ac/dc/dc conversion

The ac characteristics of a double-conversion system are investigated. Using a simple method, the harmonic composition of the alternating currents are determined as a function of the connection type of the ac/dc rectifier and of the parameters characterizing the dc/dc chopper operations. It is shown that the best ac characteristics are only achieved when the chopper modulation frequency is a multiple of the product of the ac/dc convertor pulse number and the inverse of the supply period. Under these conditions, subharmonics and unbalance components are not generated in the ac currents.