Fuzzy logic based DC modulation controllers for improvement of AC-DC system stability

Abstract

With the increase in size and complexity of Power Systems, the problems associated with long distance AC bulk power transmission, like reactive power support, system stability etc have also increased. A search for more efficient mode of transmission has led to the development of DC transmission. An HVDC transmission link is highly controllable and hence its effective use depends on the appropriate utilization of this controllability to ensure desired performance of the power system. In this thesis, investigations are carried out on the improvement of power system stability by employing auxiliary controls for controlling HVDC power flow. AC/DC load flow using eliminated variable method is utilized in the transient stability analysis. Transient stability analysis is carried out on single machine infinite bus system and multi machine system, using different control signals derived from the AC system and employing different types of controllers. The best possible combination of the different control signals, which stabilizes the system, is found out and its effectiveness is verified. Apart from the conventional, fuzzy logic based variable gain controller is also developed to further improve the stability of the power system. A new fuzzy logic based DC modulation controller is also developed for a multi machine system taking the average error and its derivative as inputs. The stability performance of the power system with such fuzzy logic controller is presented.