Circulating current control for carrier-based discontinuous modulation in inverters with parallel legs

This paper presents a discrete time controller for the circulating current of three-phase voltage fed converters with two magnetically coupled legs that uses carried-based discontinuous modulation. The discontinuous modulation produces multilevel equivalent PWM line-to-line output voltages with reduced harmonic distortion and equally distributes the commutations between the switches. A state machine is used to reduce the number of commutations. Using this state machine a non-linear controller is proposed to keep the circulating current close to zero. Moreover, it is important to mention that the implementation of the proposed modulation and controller are straightforward, requiring neither a complex hardware nor a high development effort. Furthermore, simulation and experimental results are presented to demonstrate the good performance of the proposed method.