DC-link capacitor voltage balancing strategy for three-level four-leg DSTATCOM-SMES system

One of the most challenges of using diode clamped multilevel inverters is the DC-link capacitor voltages unbalance problem. This paper present a new approach for balancing the intermediate DC-link capacitor voltage of three-level four-leg DSTATCOM-SMES system. The DSTATCOM-SMES is connected to a four-wire distribution system feeding a non-unity power factor unbalanced load. The control system is designed in synchronous reference frame based on symmetrical components theory to guarantee a full compensation of positive-negative- and zero-sequence of currents components in case of unbalancing conditions. The proposed balancing strategy is carried out using an appropriate balancing control loop combined with the main control system of bidirectional chopper and without a need to an additional circuit. The DSTATCOM-SMES can operate either for unity power-factor correction mode or for voltage regulation mode. The validity and effectiveness of the proposed control system for both operation modes is highlighted by computer simulations under balanced and unbalanced conditions.