Operating principles for hidden-link convertor drive

In contrast to the DC-link frequency convertor drive which is now being produced by many drive manufacturers very little attention has been paid to its counterpart, the hidden-link convertor drive. This apparent lack of interest is surprising, as the convertor has some perational advantages when compared with the DC-link frequency convertor and other drives, especially at high powers and where full four-quadrant capability is required. The single operating mode of the power convertor is described at starting, low and high speed. Commutation occurs naturally, and two types of commutation process can be identified. The hidden-link convertor dates from the 1930s and has previously been described as a brushless or commutatorless motor when supplying a synchronous machine.