The tandem inverter: Combining the advantages of voltage-source and current-source inverters

A combination of a current-source primary inverter and a voltage-source secondary inverter is proposed as the so-called tandem inverter. The primary inverter operates in the square-wave mode handling most of the converted power, while its output harmonic currents are compensated by the much smaller secondary inverter. As a result, the tandem inverter, to be used for control of ac motors, combines the best features of current-source and voltage-source inverters. In particular, in comparison with an equivalent voltage-source inverter, switching losses are greatly reduced, current-control dynamics is improved, and EMI effects on the power system are alleviated. Operating principles of the tandem inverter are described, and results of computer simulations and experiments with a laboratory model are presented.