A novel system impedance measurement for power system analysis and improvement in power quality
This thesis presents an investigation of on-line supply impedance measurement. Network impedance values are invaluable for power system modelling and simulation. Without knowledge of a network structure and the impedances that make up that structure it is impossible to simulate or predict harmonic propagation within a plant. If the impedance structure for a plant is known then it may be possible to alleviate voltage distortion problems by simply redistributing sensitive loads to points of low harmonic distortion. Alternatively distorting loads may be repositioned thus removing the need for additional filters or compensation equipment. The supply impedance, in particular, is of interest. At a simple level it is important for wiring, fuse and circuit breaker calculations. It is also important when designing filters for power factor correction or harmonic attenuation. Two novel on-line impedance measurement techniques are presented. Both techniques apply a small disturbance to a power network, using measurements of the subsequent transients it is possible to identify the system impedance at the point of measurement. These techniques are implemented both in simulation and experimentally. Excellent identification was possible for linear impedance networks. The performance of the techniques was also investigated in the presence of various non-linear loads. Limitations to both approaches are identified. An active shunt filter was designed and constructed for this work. Experimental impedance measurement was undertaken using this hardware. It was therefore possible to demonstrate the possibility of impedance measurement using an existing active shunt filter and during its normal operation. Finally experimental measurement data was used to demonstrate the operation of the active shunt filter using reference currents determined from supply voltage and supply impedance.