H-∞ loopshaping controller design of micro-source inverters

Abstract

Abstract — The range of electric parameters of Distributed Power Generation Systems (DPGSs) is wide and uncertain. The main objective of this paper is to propose H ∞ controller design for the grid-forming problem using structured uncertainties to improve the performance of the system facing parametric uncertainties, and to obtain fast transient response with minimum overshoot, precise current control with zero steady-state error, and low distortion and current ripple. The procedure is verified by simulation to demonstrate the performance of the proposed strategy for the nominal case and perturbed parameters cases. Keywords— Distributed power generation system (DPGS); robust control; uncertainty system; H ∞ control; power quality. I. I NTRODUCTION The introduction of micro grid via power electronic technology improves the performance of Distributed Power Generation Systems (DPGSs) and facilitates the use of renewable energy resources. Inverters are used to interface the DPGSs to the utility grid as they match the characteristics of the DPGSs and the requirements of the grid connections. DGPSs must have dynamic properties needed to provide security of supply, voltage quality and stability of supply in the short-term and long-term to ensure the proper operation of power systems and have a good power quality, mainly based on total harmonic distortion (THD) [1]. The control system of a DPGS must provide the different possible operating modes: grid forming, grid supporting and grid feeding. The control of a DPGS is mainly designed in accordance with the electrical grid conditions at the Point of Common Coupling (PCC). The purpose of the controllers is to achieve satisfactory performance in terms of steady state error requirements for utility connected converters and to improve disturbance rejection properties by rejecting utility voltage harmonics. The general structure having different input power sources (photovoltaic, fuel cell, wind turbine, etc.) is depicted in Fig. 1. The main task of the input controller is to extract the maximum power from the renewable energy sources and to protect the input side converter while the grid side controller must manage the active and reactive power which is transferred from renewable energy systems to the grid. The power quality assessment is mainly based on total harmonic distortion (THD) in voltages and currents. Many control schemes have been proposed for the control of DGPSs. The PI control scheme in the synchronously rotating dq reference frame is commonly used and can work well with balanced systems, but it cannot cope with unbalanced disturbance currents, which are common in micro grids [2].