Performance Analysis of the Alternate Arm Converter for Electric Drive Applications

The Modular Multilevel Converter (MMC) has gained much attention for medium voltage adjustable speed drive applications. However, it requires a large number of switching devices, and to achieve a wide range of speed control, its energy storage requirement is also very high. Owing to lower energy storage requirement and device count, the Alternate Arm Converter (AAC) can be a good alternative to MMC-based drive applications. Hence, the concept of AAC-based induction motor drive is put forward in this paper. The energy requirements of AAC for variable speed operation with different types of load characteristics are thoroughly investigated. In addition, the impact on AAC submodules (SMs) capacitor voltage control co-existing with rotor flux-oriented speed control is analyzed in detail. It is shown that for the high-speed medium voltage drive applications whose operating frequencies are above 36 Hz, the AAC-based drive requires lower energy storage than the MMC-based drive. Finally, the theoretical analysis is verified using a simulation model developed in PSCAD software. A scaled-down laboratory experimental prototype of AAC is also developed and results are presented.