Implementation of anti-islanding scheme for distributed generation system using over/Under voltage and frequency monitoring technique

Abstract

In this project we have integrated Photovoltaic system with power grid. By interconnecting separate utilities with the high voltage (DG) system, it is possible to pool both generation and demand, not only providing a number of economic and other benefits, including a more efficient bulk transfer of power from generation to demand centers. The interconnected DG system, by linking together all participants across the transmission system, makes it is possible to select the cheapest generation available. Transmission circuits tend to be far more reliable than individual generating units, and enhanced security of supply is achieved because the transmission system is better able to exploit the diversity between individual generation sources and demand. An interconnected DG system enables surplus generation capacity in one area to be used to cover shortfalls elsewhere on the system, resulting in lower requirements for additional installed generation capacity, to provide sufficient generation security for the whole system. Without DG interconnection, each separate system would need to carry its own frequency response to meet demand variations, but with interconnection the net response requirement only needs to match the highest of the individual system requirements to cover for the largest potential loss of power (generation) rather than the sum of them all.

Main idea is to work on Anti-Islanding Scheme in which we calculate voltage, frequency of both sides. If they lie in tolerable range then permission to close command is issued for respective circuit breaker.

High performancePIC18F458 RISC CPU is used for processing the inputs. Sinusoidal signal from load end of system are converted to digital form and after full wave rectification these samples are used for calculation of voltage. To measure frequency input is given to the controller in the form of pulses and then pass it to ADC controller.

Measuring phase angle was quite an interesting task and caused a lot of effort. Time difference between starting of two waves is used to compute phase angle.