A DC-link voltage balancing strategy based on controllable neutral current injected for T-type three-level active power filter

By the way of establishment of mathematical model for three-phase four-wire T-type three-level Active Power Filter (APF), the relation of DC-link voltage difference, the neutral current and the duty-ratio of each bridge arms are revealed. Consequently, a control strategy of DC-link voltage balancing is proposed with the controllable neutral current injection, which is easier to be realized and more accurate compared with conventional ones. To deal with the unbalanced load operation, a separated-phase control strategy is also proposed. Results of simulation verify that by using the proposed control strategy the capacitors voltage difference can be suppressed well, while the compensation effect of APF is almost not affected compared with the popular ones and it is suitable for unbalanced load condition.