Anti-islanding modeling of grid-tied inverters

For grid-tied inverters, islanding occurs when the grid is disconnected but the inverters are still energizing the local loads. When the inverter output active and reactive power match the local loads, the inverter output voltage and frequency will keep the same values as before. Islanding poses a hazard to maintenance workers and equipment. To detect islanding, a disturbance signal is usually added to the reference of the inverter output real power or reactive power with positive feedback manner. If the inverter output voltage or inverter output frequency is driven outside of the normal range, islanding is detected and the inverter will be de-energized. A parallel RLC load is widely used to verify effectiveness of anti-islanding detection. In this paper, transfer functions of anti-islanding loop gain are derived. These transfer functions are used to design anti-islanding control loop. Time domain simulation results are also included.