Realization of Reactive Power Compensation Near the LCC-HVDC Converter Bridges by Means of an Inductive Filtering Method

In this paper, a reactive power (Q) balance strategy is proposed to enhance the stability of the HVDC inverter connected to weak grids. The main circuit topology of a new line-commutated-converter (LCC)-based HVDC system is presented, where a new converter transformer and related fully tuned (FT) branches are included in the converter subsystem for implementing an inductive filtering method. The phasor analysis is used to reveal a special Q-compensation performance of the new LCC-HVDC system. Then, an equivalent impedance representation, which takes the Q-compensation degree at the ac valve side of the converter into consideration, is established by a mathematical modeling. Based on these, the impact of the inductive filtering on the Q-compensation characteristic of the converter is investigated under different HVDC control modes (e.g., constant dc-current and dc-voltage controls at the rectifier and the inverter sides, respectively). Finally, both the transient simulation and experimental results validate the theoretical analysis, and further demonstrate that the proposed Q -balance strategy can compensate reactive power near the converter bridges (the Q-absorber), widen the operating range of the converter, and enhance the stability of the LCC-HVDC connected with weak grids.