Research on Quality Control Center in Power Systems for Coming in Practice

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This research project aimed to investigate a Quality Control Center (QCC), the core of a new power distribution system FRIENDS, for coming in practical use. The brief results are as follows :1. Configurations of connection between the high voltage side of QCC and network lines were investigated and the features of them were revealed.2. Transfer switching methods to realize flexible network reconfigurations were investigated. As a result, "Individual Thyristor Control Method" and "Transfer Switching Utilizing UPS" were developed. The latter is not effected by the system voltage magnitudes and phase angles before and after transfer switching.3. In an UPS type interior structure, a compensation method of the unbalanced three phase loads was proposed by controlling three phase voltage magnitudes and phases with PWM controlled converter independently.4. By dividing the load changes into quick and slow elements, a method for sharing and cooperating between PWM convertors and Dispersed Energy Storage Systems (DESS) was developed.5. To improve the value of renewable energy systems as power sources, a control method of DESS for cooperating with them was developed.6. UPQC (Unified Power Quality Controller) type configuration was proposed as one of interior structure of QCC.It can realize high quality power distribution under the voltage fluctuation in high voltage side and cancel the harmonics distortion and unbalances between three phases of loads as UPS type.7. The economical merit of DC power distribution for potential percentage of DC load was investigated. Estimation methods for necessaries of capacities and marginal cost of equipment in QCC were developed.8. Autonomous, decentralized and cooperative operation of QCCs was investigated and it was confirmed that the concept of multi agent would be promising.