Ultracapacitor character analysis and its application in unified power quality conditioner as energy storage system

This dissertation focuses on the Ultracapacitor (UCAP) character analysis and its application in Unified Power Quality Conditioner (UPQC) as an Energy Storage System (ESS) for improved UPQC performance. It includes three parts as described below.;The first part is Paper I. The UCAP is a popular choice for the ESS because of its distinct characters. In the application UCAP's transient behavior need to be studied for design purpose. Usually these transient characters are not shown in the product data sheet. In this paper UCAP frequency analysis is performed, and based on the test data the equivalent model of the UCAP is built. The fitting result shows that using multi-level ladder circuit can perfectly fit the UCAP transient characters.;The second part is Paper II. A UPQC is to compensate both source voltage sag and load current imperfections in power distribution system. With the UCAP based Energy Storage System, the UPQC has an optimized power flow between UPQC and system during the transit state, also the UPQC's serial and shunt part has an improved performance with UCAP. The impact of UCAP model on its control and simulation is analyzed. From the analysis, UCAP based Energy Storage System can well fulfill the requirement of UPQC to provide high active power during transit time and improve the UPQC overall performance.;The third part is Paper III. Conventionally the PI control method is applied in UPQC, including DVR and APF part. With ESS the Hinfinity control method is applied in UPQC. This paper shows that the two methods have their own advantages and disadvantages. In the practical application the control method can be chosen by considering the different transit states.