r. ghazi

One of the significant concerns in the MTDC systems is that voltage source converters (VSCs) do not hit their limits in the post-contingency conditions. Converters outage, DC line disconnection, and changeable output power of wind farms are the most common threats in these systems. Therefore, their destructive impact on neighboring AC systems should be minimized as much as possible. The fixed droop control is a better choice than others to deal with this, although it also has some limitations. Accordingly, a novel centralized droop-based control strategy considering N-1 contingency is proposed in this paper. It prevents converters from exceeding their limits while causes optimal power sharing and minimum DC link voltage deviation immediately, without secondary control layer. It also utilizes maximum wind power without curtailment. These properties improve the performance of the MTDC system in post-contingency conditions. The effectiveness of the proposed control method is validated by simulation of a 4-terminal VSC-MTDC system in MATLAB/Simulink R2016a.

Nowadays the demand for photovoltaic (PV) systems has greatly increased due to their various advantages. In many applications for the purposes of reducing losses, increasing the efficiency and having the lower size and weight the transformer has been removed from the grid connected PV systems. In such situations, due to the absence of the galvanic isolation, the common mode voltage becomes unstable leading to flow of leakage current through the parasitic capacitor. The leakage current increases losses, deteriorates the quality of injected currents, causes the electromagnetic interference and finally presents personal safety problems. Therefore, it should be reduced to statutory limits which is defined by the VDE0126-1-1 standard. In the present paper attemps have been made to do so, using the single-vecror and double-vector model predictive control (MPCs) systems. In this approach, without using any extra hardware not only the leakage current is reduced, but the switching frequency and the THD index are also simultaneously minimized. The simulation results confirm the superior performance of the proposed method over other valuable methods.