Novel Comprehensive Control Framework for Incorporating VSCs to Smart Power Grids Using Bidirectional Synchronous-VSC

Abstract

This paper presents a new control strategy for voltage-source converters (VSCs) in the frequency-angle domain which enables dc-link voltage regulation via frequency and load angle adjustment. A major advantage of the proposed controller is emulating the behavior of synchronous machines (SMs) with proper regulation of dc-link voltage which eases integration of VSCs interfacing distributed and renewable generation units into ac systems in the presence of conventional SMs. A cascaded frequency, angle and virtual torque control topology is developed to emulate the mechanical behavior of an SM which offers synchronization power to eliminate the need for a phase-locked-loop after initial converter synchronization, and damping power dynamics to damp power oscillations; and presents frequency dynamics similar to SMs, thus it introduces some inertia to the grid. The controller presents high stability margin and fast dc-link voltage regulation, whereas it can provide frequency support in the ac-side during contingencies. Frequency and voltage amplitude are adjusted by two separate loops. Two different variants are proposed for dc-link voltage control; namely direct dc-link voltage control and indirect dc-link voltage control via a dc-link voltage controller. Small-signal dynamics, analysis, and design process are presented. Both simulation and experimental results are provided to validate the controller effectiveness.