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Statcom-based Transient-frequency Regulation in a Transmission System

Fig. 1. FQ current controller for STATCOM
With the increasing usage of renewable energy sources throughout the world, transient regulation is becoming a growing research area. Using a 200 MVA synchronous generator in a simple generator-STATCOM-load configuration, transient regulation with a 100 MVA STATCOM reduces grid frequency perturbations.

Simulink is used as a simulation environment, having a 200 MVA synchronous generator connected to a 60 Hz simple transmission system through a 210 MVA, 13.8 kV⁄230 kV transformer. A 5 MW load is also connected directly to the synchronous generator to roughly approximate generation losses. The transformer is then connected to a lossless transmission line. Connected in parallel to the generator is a 100 MVA STATCOM. The transmission line then connects the generation and STATCOM side to a 50 MW, 50 MVar load.

Additionally, a governor is included to control and regulate the frequency of the generator. For the STATCOM, a DG controller is created and simulated, seeking to provide both constant point-of-common-coupling (PCC) output voltage control and constant grid frequency control. A phase-locked loop (PLL) is simulated with a 5 Hz bandwidth to obtain grid frequency information. The frequency controller has a bandwidth of 200 Hz to increase transient regulation speed. In addition, the STATCOM is also simulated with a controller designed to maintain constant grid frequency and to provide constant output power to the grid. These two STATCOM control schemes are simulated in the simple system, with the load having a step between +5% and -5%, and are then compared to the results of the system simulated with just the governor-controlled generator.

STATCOM-based transient frequency regulation is shown to improve frequency perturbations in a simple system simulation. Frequency takes less time with either STATCOM controller turned on than with just the generator regulating the frequency. Furthermore, overshoot and undershoot of frequency from 60 Hz is decreased with the STATCOM controller. These results provide preliminary optimism that STATCOMs can be used as an effective frequency controller, thus contributing to the stability of renewable power generation.