Abstract

Islanding is one important concern for grid connected distributed resources due to personnel and equipment safety. Inverter-resident islanding detection methods (IDMs) employ locally measured parameters to detect islanding. Passive type IDMs only monitor local variables such as voltage and frequency while active IDMs inject disturbances into the supply system and detect islanding based on system responses. Although very effective in systems with a single inverter, it is believed that active frequency drifting IDMs might have their effectiveness reduced in multi-inverter systems. This thesis investigates the islanding detection capabilities of multi-inverter systems. Three possible scenarios with passive-active, different and same type of active IDMs were discussed. Their performance was assessed using the concept of non-detection zones (NDZs) in a quality factor ( Q f ) vs. load resonant frequency ( f 0 ) load parameter space extended to multi-inverter systems. This thesis also proposes the use of a small dedicated reactive power source (STATCOM) as the sole active component in a multi-inverter system. In this way, interactions between inverters with active IDMs are prevented while effective islanding detection capability is provided by the islanding detection enhancer. The simulation and experiment results were presented to validate the theoretical analysis and the effectiveness of the proposed techniques.

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