Stability improvement of a single machine system by E-STATCOM

Abstract

Power systems are normally expected to deliver electric energy to the customers at rated voltages and frequency. This steady operation is, however, affected by necessary or accidental perturbations in the system. If the change is critical or large, the system can end up in unstable oscillations or instability. This happens because of real and reactive power imbalances in the event of contingencies. This work proposes to improve the system performance using STATCOM (Static Synchronous Compensator) interfaced through an energy storage device (E-STATCOM). The storage device considered in this article is a supercapacitor. The STATCOM draws or supplies reactive power to the system while the supercapacitor caters for real power need. The STATCOM-supercapacitor control has been tested on a single machine infinite bus configuration. The STATCOM supercapacitor combination is connected at the middle of the transmission line, which is the weakest point in the system. Necessary dynamic relations for the single machine system with STATCOM and supercapacitor have been derived. The performance of the system has been evaluated by simulating the system on MATLAB comparing the E-STATCOM and no control scenarios. Disturbance like torque pulse and three-phase short circuits are considered. In addition to the supercapacitor current control, auxiliary signals in the STATCOM modulation index and voltage phase angle loops have been introduced. From a number of simulation studies it is observed that the STATCOM supercapacitor control is very effective in controlling the oscillations in the system.