Dynamical Characterization of STATCOM Application: Applying Computer-Optimized Orthogonal Perturbations

Static synchronous compensators (STATCOMs) have become important devices in grid-connected applications to provide reactive power support and improve power quality. Studies have shown that STATCOMs can be efficiently analyzed and adaptively controlled based on a certain set of frequency responses. As most STATCOMs are complex and strongly time varying in their operation, realtime methods applying wideband identification techniques have become popular in obtaining these transfer functions. In the methods, an external voltage or current perturbation is added, for example, to the controller reference, and Fourier techniques are applied to the measured current and voltage responses to extract the spectral information. The challenge in a STATCOM application is that the variables are often coupled, and typically the system is very sensitive to external signals thus limiting the available methods to measure the frequency responses. This paper proposes computer-optimized orthogonal perturbations to measure the desired frequency responses for a STATCOM application. Due to orthogonality, the perturbations make it possible to simultaneously measure several coupled frequency responses. In addition, the perturbation spectrum can be optimized so that the energy is maximized at user- defined frequencies without increasing the signal time-domain amplitude. Therefore, the perturbations are well suited to STATCOM applications. Experimental measurements are presented to demonstrate the effectiveness of the proposed method.