Commutation failure, which is a very frequent dynamic event in HVDC inverters, can deteriorate the availability of HVDC links and thus affect the performance of the power system. Most commutation failures are caused by voltage reduction due to ac system faults. In this paper, efforts are made to lower the effect of commutation failure on the power system, and the remedy is implemented in a fuzzy controller. In order to achieve control flexibility, the output of the fuzzy controller is made appropriate by setting a self-adjusting proportional factor. The validity and effectiveness of the fuzzy controller is verified by simulation which shows that the fuzzy controller can decrease commutation failure frequency induced by ac system faults.

Active Disturbance Rejection Control (ADRC) is an effective solver for object with large inertia, strong coupling or hardly modeling. However, how to tune and optimize the parameters of this control system, especially of ESO, is the key problem which block its aboard appliance. Now the tuning methods mainly includes manual tuning with experience, simple model and genetic algorithm. The performance of the parameters of ESO shows in the errors of some state variables. And so it is a multi-objective optimal problems. In these scheme, the aim function is constructed from these errors with some weight values through linear or no-linear function. Then the multi-objective problem becomes one objective problem. In such scheme, how to get weight values is very important. So it is hard to get the global optimal solutions. In fact, we can optimize these parameters with multi-objective solutions. NSGA-II is a very good choice in these multi-objective solutions. This article optimized the parameters of ESO with NSGA-II. There are some faults in NSGA-II, such as more calculation and more calculation time. So this article developed this algorithm. These showed good performance in emulation.

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