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Use of the medium amplitude space vector set by a fault-tolerant asymmetric bridge for direct torque control of induction motors

Abstract:

When an Asymmetric Converter Bridge is used to drive a polyphase motor, each motor winding is independently connected to one converter's leg central point, increasing the system tolerance to commutation faults. In the three-phase case, this converter structure allows for the definition of three different sets composed by six non-zero voltage space vectors, as opposed to the single set of six non-zero voltage space vectors available in the standard converter. These sets differ in magnitude, and can be classified as "small set", "medium set" and "big set". The "small set" of space vectors in the asymmetric bridge is equivalent to the single set of space vectors in the symmetric bridge. The present work analyzes in detail the proposed system behaviour when the "medium set" of space vectors is used to implement direct torque control in an induction motor. Simulated and experimental results prove this system advantages and disadvantages when compared with the conventional one.