Study and development of anti-islanding control for synchronous machine-based distributed generators, November 2001 - March 2004

Original publisher: Golden, Colo. : National Renewable Energy Laboratory, [2006] OCLC Number: (OCoLC)216884352 Subject: Interconnected electric utility systems -- Equipment and supplies. Excerpt: ... Based on equations ( 2.1 ) - ( 2.13 ), an equivalent circuit of the synchronous machine can be developed as shown in the Figure 2. L��R L r q fd a l +-+ R i L fd d 1d i i u L 1d fd d ad E R fd 1d-( a ) d-axis equivalent circuit��r d R L a l-+ + L 1q i q u L q i aq 1q R 1q-( b ) q-axis equivalent circuit Figure 2: Synchronous generator d-and q-axis equivalent circuits 2.2 Excitation System Model and Reactive Power Regulation Most generators are equipped with an AVR. These devices maintain the terminal voltage of the generator at a specified value by modulating the field voltage and hence the field current to supply the required reactive power to the load. However, as a distributed generation, the voltage regulation is prohibited by IEEE 1547, unless special agreements are made. A common operation mode for DG is reactive power ( or power factor ) regulation. The exciter systems widely used for synchronous machines are commonly subdivided into the four different categories. More detailed aspects of modeling an excitation system for simulation studies can be found in [ 14 ]. For simplicity of analysis in the time frame involved, the excitation system here is represented as a tuned PI controller with a necessary lag circuit. The parameters of the circuit model are approximated from the aggregate response of terminal voltage of a generator. Figure 3 shows the model of the excitation system used for the machine simulation. A feedback PI controller is cascaded with the exciter to regulate the reactive power of the machine. Therefore, when the grid is connected, the reactive power output of the machine will follow the desired reference value. The parameters of the PI controller are given in the Appendix of this report. 8