Models and methods for assessing the value of HVDC and MVDC technologies in modern power grids

Abstract

This report reflects the results of U.S. Department of Energy's (DOE) Grid Modernization project 0074 "Models and methods for assessing the value of HVDC [high-voltage direct current] and MTDC [multiterminal direct current] technologies in modern power grids." The work was done by the Pacific Northwest National Laboratory (PNNL) and Oak Ridge National Laboratory (ORNL) in cooperation with Mid-Continent Independent System Operator (MISO) and Siemens. The main motivation of this study was to show the benefit of using direct current (DC) systems larger than those in existence today as they overlap with the alternating current (AC) systems. Proper use of their flexibility in terms of active/reactive power control and fast response can provide much-needed services to the grid at the same time as moving large blocks of energy to take advantage of cost diversity. Ultimately, the project's success will enable decision-makers and investors to make well-informed decisions regarding this use of DC systems. This project showed the technical feasibility of HVDC macrogrid for frequency control and congestion relief in addition to bulk power transfers. Industryestablished models for commonly used technologies were employed, along with high-fidelity models for recently developed HVDC converter technologies; like the modular multilevel converters (MMCs), and voltage source converters (VSC). New detailed models for General Electric Positive Sequence Load Flow (GE PSLF) and Siemens's Power System Simulator (PSS®E), widely used analysis programs, were for the first time adapted to include at the same time both Western Electricity Coordinating Council (WECC) and Eastern Interconnection (EI), the two largest North American interconnections. The high-fidelity models and their control were developed in detail for MMC system and extended to HVDC systems in point-to-point and in three-node multi-terminal configurations. Using a continental-level mixed AC-DC grid model, an HVDC macrogrid power flow and transient stability models, the results showed that the HVDC macrogrid relieved congestion and mitigated loop flows in AC networks, and provided up to 24% improvement in frequency responses. These are realistic studies, based on the 2025 heavy summer Western Interconnection (WI) planning model and EI multiregional modeling working group (MMWG) 2026 summer peak cases. This work developed high-fidelity models and simulation algorithms to understand the dynamics of MMC systems. The developed models and simulation algorithms are up to 25 times faster than the existing algorithms. Control algorithms for high-fidelity models were designed and tested for point-to-point and multi-terminal configurations. The multi-terminal configuration was tested connecting simplified models of EI, WI, and Electric Reliability Council of Texas (ERCOT). The developed models showed up to 45% improvement in frequency response with the connection of all the three asynchronous interconnections in the United States using fast and advanced DC technologies like the multi-t...

High Penetration Power Electronics Grid: Modeling and Simulation Gap Analysis

“…One of the studies considers the benefits of introducing a higher penetration of solid-state power substations like HVdc systems. An Oak Ridge National Laboratory (ORNL) and Pacific Northwest National Laboratory (PNNL) [28,29] study considered different configurations of HVdc systems based on voltage-source converters (VSCs) and line-commuted converters (LCCs) connecting US interconnections. One configuration is a VSC based multiterminal direct current (MTdc) systems connecting EI, ERCOT, and Western Interconnection (WI) grids.…”

“…Organization/Reference Scenarios and Studies Challenges Identified Outcomes ORNL, PNNL [28,29] Different configurations of HVdc systems based on VSCs and LCCs connecting US interconnections have been researched.…”

“…The typical simulation of duration of components is hundreds of milliseconds to two seconds with a time step on the order of nanoseconds to microseconds. The number of states simulated is on the order of tens of thousands (with a maximum of 50,000 estimated), and the time taken to simulate ranges from 1 min to 10 h [28,29].…”

Hybrid EMT-TS Simulation Strategies to Study High Bandwidth MMC-Based HVdc Systems

“…Modern power grid is experiencing a major evolution from ac to mixed ac-dc transmission systems with decreasing costs and noticeable economic and technical benefits of dc technologies. Some of the technical benefits of dc technologies include the abilities to interconnect several asynchronous grids, to integrate renewable energy generations, to support underground transmission, to increase the power transfer capability over long distances [1], [2], and to supply loads through variable frequency drives (VFDs) [3] - [5]. The dc technologies are also capable of providing ancillary services to enhance the economics and reliability of power systems and optimize the performance of ac grids [2].…”

“…This work has developed high-fidelity dynamic models of modular multilevel converters (MMCs) -based high-voltage direct current (HVdc) system [6]. The deliverables also include the development of high-fidelity models and control algorithms of multi-terminal MMC-HVdc systems connecting Eastern Interconnection (EI), Western Electricity Coordinating Council (WECC), and Electric Reliability Council of Texas (ERCOT) [2], [6]. The developed control strategy for the multi-terminal MMC-HVdc system exhibits up to 51.75% improvement in frequency response with the connection of all the three asynchronous power grids in the United States [7].…”