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 AC motor control, 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 are improved and EMI effects on the power system are alleviated. The operating principles of the tandem inverter are described and the results of computer simulations and experiments with a laboratory model are presented.