Experimental Investigation of the Hierarchical Control in DC Microgrids Using a Real-time Simulator

Summary

This article presents a DC microgrid with hierarchical control implemented in a simulator, OPAL RT-Lab. It details the circuit modeling, primary and secondary control strategies, and experimental validation. The results demonstrate effective control performance, highlighting the importance of a robust experimental platform for microgrid research and development.

Abstract

The rise of renewable energy sources has underscored the significance of microgrids, particularly DC variants, which are well-suited for integrating photovoltaic panels, battery storage systems, and other DC load solutions. This paper presents the development and experimentation of a DC microgrid with hierarchical control implemented in OPAL RT-Lab, a simulator. The microgrid includes distributed energy resources (DERs) interconnected via power converters, a DC bus, and DC loads. The primary control employs a droop control mechanism and double-loop Proportional-Integral (PI) control to regulate voltage and current, ensuring stable operation and proportional power sharing. The secondary control utilizes a consensus-based strategy to coordinate DERs to restore the bus voltage and ensure accurate power sharing, enhancing system reliability and efficiency. The experimental setup detailed in this paper includes circuit modeling, hardware implementation, and control strategies. The hardware platform's circuitry and controller parameters are specified, and the results can be observed through oscilloscope measurements. Two sets of experiments demonstrating the secondary control response with and without delay are conducted to validate the effectiveness of the control strategy. The outcomes confirm the successful implementation of hierarchical control in the microgrid. This study underscores the significance of a comprehensive experimental platform for advancing microgrid technology, providing valuable insights for future research and development.

Introduction

With the rapid development of renewable energy sources, microgrids have gained significant attention globally¹. They enable the integration of distributed energy resources (DERs), such as solar photovoltaics (PV), along with energy storage systems (ESSs), into the grid, thereby supporting the transition to sustainable and renewable energy. As a critical component in the integration of renewable energy, DC microgrids have garnered considerable attention due to their compatibility with the inherent DC nature of PV systems, batteries, and other DERs. The DC operation reduces the need for multiple energy conversions, which can improve overall syste....

Protocol

In this section, we outline the methods used for developing and experimenting with a DC microgrid that incorporates hierarchical control shown in Figure 1, implemented in OPAL RT-Lab (hereafter referred to as "simulator"). The protocol is divided into three main sections: Physical Setup and Circuit Modeling, Control Strategy Implementation, and Simulator Experimental Setup. It is noted that this protocol does not cover the tertiary control strategy, which involves higher-level optimization and interaction with the main power grid, is beyond the scope of our current experimental setup, and is left for future work.

Discussion

Figure 10 shows the current and voltage responses of the microgrid system under secondary control without communication delays. Before time t₁, the system is regulated solely by droop-based primary control, where it is evident that the voltage cannot stabilize at the nominal value of 48 V, and the current distribution is relatively imprecise. Upon activating the secondary control at time t₁, the voltage quickly recovers to around 48 V at t

Materials

Name	Company	Catalog Number	Comments
Programmable DC  power supply	ITECH	IT-M7700	DC Power Supply
Real-time simulator	OPAL RT-Lab	OP5707XG-16	Real-time controller
Oscilloscope	Tektronix	MSO58 5-BW-500	Oscilloscope
			Electrical components such as cables and resistors