A unified control of back-to-back converter

In this paper a novel unified modelling and control procedure for Back-to-Back converters is introduced. The proposed procedure captures in a single state-space model detailed converter dynamics of both LCL filters and DC-capacitor. A linear multivariable approach has been identified as the most suitable control strategy for taking full advantage of the unified model. A state-feedback controller has been designed for controlling both inverter output currents and DC-bus voltage. It has been shown the main advantage of the proposed modelling procedure is in its detailed knowledge of the existing coupling between the AC currents and the DC-capacitor voltage. As a result, the proposed unified controller takes into account the whole system dynamics in order to maintain the DC-bus voltage nearly constant. The proposed control strategy was experimentally validated by using two 15kVA VSCs (Voltage Sourced Converters) in Back-to-Back configuration. The performance of the unified controller was compared with the performance of the conventional strategy based on the cascade control structure. It was experimentally demonstrated the proposed unified control significantly outperforms the conventional control of DC-bus voltage.