An Improved Current Detecting Method for STATCOM Considering Unbalanced Compensation

Background: Static Synchronous Compensator plays an essential role in governing the reactive power and harmonics of power systems. The accuracy and real-time performance of reactive power and harmonic detection are necessary to ensure balancing compensation effectiveness. The traditional dq current detection method can only extract positive sequence components in the positive sequence rotational reference frame and extract negative sequence components in the negative sequence rotational reference frame. Objective: This paper aims to give a practical and straightforward current detection solution to enhance the compensator performance and simplify the control system by extracting the positive sequence, negative sequence, and harmonics in the positive sequence rotational reference frame. Methods: Firstly, a grid-connected four-quadrant converter with an Inductance-Capacitance- Inductance (LCL) filter balancing compensation topology is constructed. Then an improved current detection algorithm is proposed to extract the positive sequence, negative sequence, and harmonics in the positive rotational reference frame separately. Finally, the Direct Current (DC) side voltage design method is discussed to avoid the overmodulation effects. Results: Matlab simulation and a prototype 500kVA Static Synchronous Compensator (STATCOM) experiment are implemented to demonstrate the proposed method. Conclusion: The proposed strategy can effectively improve the compensation accuracy, and the system structure is simplified while the stability and reliability of the whole system are ensured.