Low-Order Passivity-Based Robust Current Control Design for Grid-Tied VSCs

Abstract

This paper presents a systematic robust current control design approach for three-phase voltage-source converters. Robustness is guaranteed by combining intrinsic passive properties of the impedance uncertainty at the point of common coupling together with stability results from Passivity-based Control theory. This approach ensures stability against typical uncertainty sources at mid and high-frequencies, such as cable resonances or other converters interaction, with significant less conservative performances than the obtained with traditional Robust Control theory. The approach uses multi-objective controller synthesis formulation that allows to logically combine robustness requirements with performance objectives avoiding heuristic iteration over the control structure and parameters. The controller synthesis is performed by means of a non-smooth H∞ optimization technique that tunes all free parameters of a vector-based controller function, which constraints its structure. This results in a synthesized controller with lower order than those obtained with convex optimization definitions of the H∞ control problem. The design methodology is validated in time and frequency domain by means of theoretical analysis and experimental results with three usual grid filters: L, LCL and LLCL.

Stability Improvement of Parallel-Connected Inverters Under Very Weak Distorted Grid Using Observer-Based Incremental Control Scheme

“…In [7], the mutual interactions of parallel inverter system tied with L-type and LC-type grid impedances are modeled and analyzed by presenting the nodal admittance matrix concept in the stationary frame. In [8]- [10], the concept of passivity theory is adopted to mitigate the interaction between parallel inverters, in which the full passivity region can be achieved by the presented design guidelines. Another study in [11] establishes the multi-input multioutput matrix for the multi-inverter system.…”