An impedance-based method for the detection of over-load and network faults in inverter interfaced distributed generation

An impedance-based method is presented for detecting and differentiating over-load and fault conditions for an inverter-interfaced power generator. When the observed impedance falls below a threshold, current limiting occurs. The impedance-based method, unlike other current limiting strategies, is able to differentiate between an over-load and a network fault. The inverter presented in this paper exports a fixed current for detected over-loads and a higher fixed current for detected faults. An experimental system using a 10 kVA inverter was used to test three cases. The first demonstrates the response of the inverter when the impedance of the load is gradually decreased. The second demonstrates the output of the inverter when a three-phase fault is applied and the third demonstrates the output when a single-phase fault is applied. The impedance-based method is shown to be able to ride-thought the fault and return to normal operation once the fault has been cleared.