Rapid Online Identification of Non-Linear Current-Controller Bandwidth in STATCOM Application

Abstract

Control bandwidth plays an important role in the operation of a static synchronous compensator (STATCOM). The bandwidth not only defines how fast the controller reacts to the changes in the power requirements, but it is also an important factor determining the linear operating region of the controller. As the system parameters often varies over time, online measurement of the bandwidth is most desired. Recent studies have presented broadband methods such as the pseudo-random binary sequence (PRBS) and Fourier techniques which can be applied to measure the controller bandwidth. In the method, a PRBS perturbation is added to the controller reference current, the resulting output current is measured, and Fourier methods are applied to compute the control-to-output frequency response. The PRBS usually produces the frequency response rapidly and accurately, but the method often requires a relatively high perturbation amplitude which can easily violate the normal system operation. This paper proposes the use of a discrete-interval binary sequence (DIBS) for this application to minimize the injection. The DIBS is a binary sequence that has been computer-optimized to maximize the energy at specified harmonic frequencies without increasing the signal amplitude in the time-domain. Experimental results based on a three-phase STATCOM at different grid inductances are presented to demonstrate the effectiveness of the proposed method.