Modeling of a Chain Link Statcom in EMTP-RV

Abstract

This paper describes an alternative circuit arrangement to form a static synchronous compensator (STATCOM), by connecting a number of gate turn off (GTO) thyristor converter 'chain links' in series per phase on the AC side of the system. Each GTO converter forms one 'link' of a 1-phase bridge voltage-sourced converter (VSC) and is referred to as a 'chain link converter'. In the proposed scheme, each GTO is switched 'ON' and 'OFF' once per cycle of the fundamental frequency by using a sinusoidal pulse width modulation (SPWM) technique. This SPWM technique uses two triangular carrier bands - one positive and one negative - per link, and has a carrier frequency of twice the fundamental frequency and one modulating signal for all the links. A 1-phase, 3-link STATCOM is modelled in EMTP-RV and evaluated. The 1-phase version is suitable for analysis purposes at this stage to gain insight into the operational behavior of this special type of STATCOM. A 3-phase version of this topology will be implemented next. The proposed STATCOM is connected at the end point of a radial transmission line to stabilize the voltage by compensating the reactive power at the point of connection. The performance of this STATCOM is analysed by using open loop control under both steady state and transient operating conditions. An open loop control is employed here as a preliminary step towards the subsequent controller design by evaluating the behavior of the STATCOM for different values of control inputs under different operating conditions. The details of the model along with the results of the preliminary simulation tests in EMTP-RV are presented here