HVDC & FACTS

In this paper a novel configuration of unified power flow controller (UPFC) which consists of two shunt converters and a series capacitor is proposed. In this configuration, a series capacitor is used between two shunt converters to inject desired series voltage. As a result, it is possible to control the active and reactive power flow as same as the conventional configuration of UPFC. The main advantage of the proposed
UPFC in comparison with the conventional configuration is injection of a series voltage waveform with a very low total harmonic distortion (THD). Also, using two shunt converters instead of a series and a shunt converters, results in reduction of design efforts and simplification of control, measuring and
protection strategies. An optimal control strategy based on the discrete model of converters is applied to shunt converters. The proposed UPFC is simulated using PSCAD/EMTDC and MATLAB software and simulation results are presented to validate the effectiveness of the novel configuration of UPFC. Also, the experimental results which are obtained from an experimental set-up are presented.

The advent of multi-level Statcom technology with high power density provides the platform for a cost
effective and practical relocatable unit. The RXPE SVG range of Medium Voltage Statcoms is just that
where it is possible to have a transformerless direct connection of a Statcom at voltage levels from 3.3kV up to 35kV. These can be easily containerised into standard units so that relocation is straight-forward using conventional transport options. Other capacities can be optimised using internal dry-type transformers to provide the most appropriate package for the specific requirement.

The applications of this technology for capacity enhancement serves both developed networks such as the UK where there is the need to maximise capacity both due to regulatory requirements as well as way leave restrictions, as well as developing networks where there is the need to stabilise voltage on long feeders with fluctuating loads with poor power-factor and limited capital spend capability.

One particularly case-study for Southern Africa will be shown, where an existing 110kV/33kV substation has reached a maximum transfer capability. Additional reactive power will provide much needed MW transfer capability, however load growth is such that this benefit will only last for 5 years, by which time the second transmission line will have been constructed. Once the transmission line is constructed, then the Statcom will become redundant at that location. The use of a relocatable statcom therefore is of great technical and commercial benefit since it can be rapidly deployed in a temporary configuration until the major reinforcement arrives, then it can be placed on the back of a truck and transported to another site where it can be redeployed in a similar manner.

Reactive power in the right location can provide significant active power benefit if it is coordinated as part of the overall voltage control strategy. The Statcom can also have additional benefits including voltage dip reduction, flicker mitigation and active harmonic filtering.

In this paper a new power circuit topology for FACTS controllers is introduced. This topology is neither series nor parallel FACTS controller. This controller injects an additive compensating voltage between each of two phases of a three phase power line by using a voltage source inverter (VSI). So, it is named as line to line compensator (LLC). Analytical analysis and simulation results by MATLAB/SIMULINK are presented and a test setup is built to verify the operation of proposed FACTC controller.