Design of converter configurations and control structures for hybrid energy storage interfaced renewable microgrid (PhD)

Abstract

The intensive demand for hybridization of energy storage devices and renewable power sources such as PV/wind, battery/supercapacitors ,necessitate significant research on interfacing converters configurations, control structures, and power sharing schemes. Appreciable research has been done and reported in the literature regarding the interfacing configurations and control structures. The interfacing configurations reported consists a dedicated converter for each source, leads to complexity in the control structure, lower utilization, higher cost, and less efficiency. Hence, several multi-input converter configurations that can address the above-mentioned issues are reported in literature. However, these are not capable of interfacing hybrid energy storage. The control structure reported consists a multiple numbers of PI controllers which makes designing/tuning of all the controllers complicated. Moreover, hybrid energy storage nonlinearity can not be handled. Therefore, are search urgency in developing a novel multisource converter configurations and non-linear control structures is spotted. Hence, this work concerns, the electrical design of efficient converter configurations and effective control structure for the synergy of PV, wind, battery, and supercapacitor. Anent the design of interfacing converter configurations, a novel isolated and non isolated multi-source DC-DC converter configurations for the synergy of PV, Wind, battery, and supercapacitor is proposed and validated experimentally. The comprehensive design, modeling, and analysis of the proposed configurations are carried out. Make use of the proposed DC-DC converter configurations, a grid-interactive microgrid system consisting of Photovoltaic(PV),wind, and Hybrid Energy Storage (HES) is developed. The controller is designed along with a power-sharing scheme to operate the system under various operating modes such as (i) Grid-connected and Islanded modes, (ii) state of charge of battery less than or greater than specified limits, (iii) Operating renewable sources (PV and wind) at maximum power point and charging/discharging of energy storage based on power availability. Focusing on the control structure, a conventional PI-based control structure is designed and implemented for a stand-alone DC renewable microgrid. It is observed that conventional PI-based linear controllers are designed around a single operating point. However, due to self-discharge or frequent discharge during operation, supercapacitor voltage can reach the lowest value which adversely affects controller performance, even makes the system unstable. Therefore, a robust non-linear controller (Interconnection Damping Assessment-Passivity Based Controller),is implemented as an outer loop controller to regulate DC-link and supercapacitor voltages. A Finite Control Set-Model Predictive Control is implemented as inner current controllers. In addition, the sizing of the HES unit and lifetime analysis on the battery is performed. The key contributions of this research are: (1) The proposed converter configuration has: (i) Low component count, (ii) Inherent voltage boosting, (iii) Inherent voltage regulation of supercapacitor and inherent power-sharing among battery and supercapacitor(iv) Simple control structure with a reduced number of sensors and(v) Galvanic isolation and high voltage gain capability. (2) The proposed control structure combining IDA-PBC and FCS-MPC tackles system non-linearity and the requirement of extra controller for supercapacitor voltage regulation with a conventional PI-based control structure was circumvented.