| Phase: |
Theme |
| Theme: | Grids and Storage (T06) |
| Status: | Active |
| Start Date: | 2023-04-01 |
| End Date: | 2026-06-30 |
| Principal Investigator |
| Shu, Zhan |
Project Overview
The national grid is shifting from centralized AC to distributed DC power generation and distribution with an increasing number of multiple-operational and variable sources and loads. The converters catering to these various terminations interact through the local or main grid. Such interaction may have an adverse impact on stability and performance. Traditional methods based on standalone converter models fail to address these issues satisfactorily, and this calls for new tools and approaches.
This project aims to develop stability analysis and control design approaches for interacted converter systems in emerging smart grids that are majorly DC. The key idea is to treat variable characteristics of terminations as discrete events or variables and capture the interactions through a connection graph model. In so doing, the entire system can be analyzed and designed under the framework of hybrid distributed systems.
Outputs
| Title |
Category |
Date |
Authors |
| Distributed control of DC microgrids: A relaxed upper bound for constant power loadsMotivated by the increasing interest in DC microgrids, we study the distributed secondary control problem of DC microgrids which aims to simultaneously guarantee load current sharing and DC bus voltage restoration. In particular, we analyze in-depth the effects of nonlinear constant power loads (CPLs), and successfully establish an upper bound for CPLs to guarantee the stability of DC microgrids. This established bound is less conservative than existing counterparts, allowing the connected power of CPLs to be much larger than that of linear resistive loads. Moreover, this bound explicitly reveals the connections between CPLs and droop gains, i.e., the upper bound of CPLs can be increased by decreasing droop gains, and vice versa. Three case studies are provided to verify the established results. University of Alberta | Publication | 2025-03-25 | "Lantao Xing", Shu, Z., "Jingya Fang", "Changyun Wen", "Chenghui Zhang" |
| Distributed Secondary Control for DC Microgrids with Near-Infinite Constant Power Load AccommodationIn DC microgrids, constant power loads (CPLs) inherently exhibit negative impedance characteristics, which are widely believed to degrade system stability as their penetration level increases. Consequently, extensive research has aimed to establish safe upper bounds for CPL penetration. However, these upper bounds are typically derived as sufficient conditions, making them overly conservative. Moreover, when multiple DC sources are connected in parallel to a common DC bus, the simultaneous need for current sharing and DC bus voltage regulation further complicates system control. To address these challenges, this paper proposes a novel distributed secondary control method based on the dynamic averaging of virtual voltage drops (VVDs). The proposed method offers two key advantages: 1) It ensures both precise current sharing and voltage regulation in single-bus DC microgrids, even in the presence of mixed ZIP loads, i.e., constant impedance loads (Z), constant current loads (I), and constant power loads (P). 2) Unlike existing approaches that impose conservative limits on CPL penetration, the proposed method theoretically demonstrates that the safe upper bound for CPLs can be arbitrarily large, enabling the DC microgrid to accommodate an almost infinite number of CPLs without compromising stability. Both Simulation and experiment studies are conducted to validate the effectiveness of the proposed method. University of Alberta | Publication | 2026-06-02 | "Zhiyong Liu", "Lantao Xing", "Jingyang Fang", Shu, Z., "Hongye Su" |
