Enabling renewable power generation and efficient energy use. An anti-islanding method and an active damping method for OCC converters

Power electronics converters are essential for applications of micro-grids, renewable resources integration in power systems, and power conditioning for efficient energy use. In practice, long cable connection between the source and the power converter may affect the system stability when the power converter voltage is regulated. The first part of the thesis addresses the standard compliance issue for connecting renewable to grid on the meter side, i.e. how to detect and handle islanding condition. An active anti-islanding method for three-phase grid-tied inverters was proposed. The method is based on asymmetric injection of the converter currents at a sub-harmonic frequency, which allows accurate detection of the islanding condition with minimum perturbation to the power system. Theoretical analysis have been confirmed by simulation and experimental tests with a 40kW One-Cycle Control grid tied inverter according to the test procedure outlined in the standard IEEE Std. 1547. The experiments have demonstrated that anti-islanding can be achieved with a negligible perturbation to the power system, where an increase in the THD of the current was observed less than 0.1% at full load.;The second part of the thesis investigates the stability in the presence of high source impedance, develops an impedance based design criterion for stability, and proposes an active damping method. Frequency domain analysis was performed to compare the information provided by the classical feedback control approach with those obtained by the ratio between source and input impedance. Based on these new findings, an active damping method was developed and implemented in a 300W One-Cycle Control DC-DC converter that demonstrated excellent system stability under long cable condition. Simulations and experimental results confirmed the theoretical analysis.