PWM-controlled series compensation on a radial feed power system

A series compensation scheme is described employing two pulse width modulation (PWM) switched reactor modules in parallel with a capacitor. The two-module PWM-switched reactors provide continuously variable reactance by employing simple duty ratio control. The switching instants of the two reactor modules are controlled to have 180° phase shift, but equal duty ratio, to achieve harmonic cancellation. The complete series compensator provides a wide range of capacitive and inductive compensation. The harmonic distortion produced by this series compensation scheme with multiple-controlled reactors is analysed. An experimental model of the proposed compensator has been constructed and tested; this was inserted in a radial feed transmission line, to reduce the level of fluctuation of the receiving power on a nominal load subjected to another large load switching. For the two-module system, the voltage harmonics have been found to be well below the IEEE 519-1992 recommended limit, with a switching frequency of only 300 Hz. At the same time, the influence of the large load switching can be significantly reduced by the application of this compensator. The simplicity of the scheme and the quality of the results indicates its potential as another useful power quality controller