Three-Stage/-Phase Voltage/Current DC-link AC-AC Converter with Synergetic Control

Abstract:
Next-generation regenerative Variable Speed Drive (VSD) systems tend to utilize SiC MOSFETs to achieve high efficiency (η) and power density (ρ) by increasing the switching frequency. Passive components can accordingly be downsized. In particular, there is a trend towards Integrated Motor Drives (IMDs), where the complete VSD system is placed in the machine housing. Thus, a more compact design is realized. Since power electronics and machines coexist, thermal aspects are important, and reducing losses eases this task, but this is typically counteracted by higher switching frequency. This work introduces a three-stage AC-AC converter concept that, even though it increases the number of semiconductors by two, enables increased frequency by employing a synergetic control strategy. The heat sink volume is reduced, and fewer magnetic components are utilized. Thus, high power density is achieved. A 2-level Voltage Source Rectifier (VSR) is connected at the grid port, ensuring sinusoidal grid currents, while a Current Source Inverter (CSI) feeds the machine with sinusoidal voltages. A buck-type DC-DC converter acts as an interface between the rectifier and the inverter stage, facilitating the synergetic operation among all stages. A etarho−Pareto performance space for a 13 kW system design is presented, exploring the performance limits of this new concept. A comparison with the conventional approach of a Voltage source Back-to-Back Converter (V-BBC) shows that the proposed concept is advantageous regarding efficiency and power density. Finally, a practical realization featuring η = 98.80 % and ρ = 7.68 kW/dm3 is discussed.