A Balance Control Strategy of DC-Link Voltages for Single Phase Cascaded STATCOM Based on d-q Coordinates
Sun Yicha · Power System Technology · 2013
DC-link voltage balance is regarded as the presupposition to ensure the secure and reliable operation of single-phase cascaded STATCOM, and the differences of active power losses among H-bridges are the basic reason leading to unbalanced DC-link voltages. A mathematical model of single-phase cascaded STATCOM in d-q coordinates is established and based on instantaneous power theory the reason causing unbalanced DC-link voltages is analyzed, and a three-loop control strategy composed of feed-forward decoupling current inner loop, average voltage outer loop and balanced voltage outer loop is designed. Comparing with the control strategy in a-b-c rest frame, the proposed control strategy not only achieves the grid-side current control without steady-state error but also is more convenient to realize DC-link voltage balance. The effectiveness of the proposed method is validated by results of simulation and experiments.