Adaptive Non-Linear Deadbeat Current Control of STATCOM Based on Online Controller-Bandwidth Measurement

Static synchronous compensators (STATCOMs) are now used extensively in grid-connected applications to regulate the voltage at the connection point with a power grid. A key parameter defining the stability and operating efficiency of a STATCOM is the device's controller-bandwidth. As the system parameters affecting the bandwidth vary with grid conditions, online analysis followed by an adaptive control is required to keep the controller-bandwidth within required values. Previous studies have applied wideband techniques based on pseudo-random binary-sequence (PRBS) injection, which can be used to obtain the controller bandwidth in real time. This approach involves adding the PRBS perturbation on top of the controller reference signal, measuring the system output current, and using Fourier techniques to determine the specific frequency response characterizing the controller bandwidth. The PRBS most often provides the desired frequency response accurately, but also typically requires a large signal amplitude that might interrupt regular system performance. This article proposes applying a discrete interval binary sequence (DIBS) for minimizing the perturbation amplitude in this type of application. The DIBS is based on an optimization algorithm that maximizes the signal energy at specific frequencies without affecting the signal's amplitude in the time-domain. The obtained controller-bandwidth is then applied by an adaptive non-linear deadbeat current-controller to provide a desired system operation for the STATCOM application under varying operating conditions. Experimental results using a threephase STATCOM with varying grid conditions are used to show the efficiency of the proposed methods.