[Paper Review] Grid-Forming and Spatially Distributed Control Design of Dynamic Virtual Power Plants

Verena Häberle, Ali Tayyebi+3 more|arXiv (Cornell University)|Feb 4, 2022

Smart Grid Energy Management4 citations

TL;DR

This paper proposes a novel grid-forming control design for dynamic virtual power plants (DVPPs) using adaptive divide-and-conquer strategies with dynamic participation factors to aggregate heterogeneous distributed energy resources (DERs) for fast frequency and voltage control. The method ensures stable, grid-forming operation under weak grid conditions and enables hybrid DVPPs with both grid-forming and grid-following DERs, verified via IEEE nine-bus system simulations with superior transient performance and robustness to parameter variations.

ABSTRACT

We present a novel grid-forming control design approach for dynamic virtual power plants (DVPP). We consider a group of heterogeneous grid-forming distributed energy resources (DER) which collectively provide desired dynamic ancillary services, such as fast frequency and voltage control. To achieve that, we study the nontrivial aggregation of grid-forming DERs to establish the DVPP, and employ an adaptive divide-and-conquer strategy that disaggregates the desired control specifications of the aggregate DVPP via adaptive dynamic participation factors to obtain local desired behaviors of each DER. We then design local controllers at the DER level to realize these local desired behaviors. In the process, physical and engineered limits of each DER are taken into account. We extend the proposed approach to make it also compatible with grid-following DER controls, thereby establishing the concept of so-called hybrid DVPPs. Furthermore, we generalize the DVPP design to spatially dispersed DER locations in power grids with different voltage levels and R/X ratios. Finally, the DVPP control performance is verified via numerical case studies in the IEEE nine-bus transmission grid with an interconnected medium voltage distribution grid.

Motivation & Objective

• To address the challenge of providing fast, reliable dynamic ancillary services in future power systems dominated by non-synchronous DERs.
• To overcome limitations of grid-following DVPPs, such as dependency on stiff grids, poor black-start capability, and instability under weak grid conditions.
• To design a grid-forming DVPP control framework that enables stable, coordinated operation of heterogeneous DERs while respecting individual device constraints.
• To extend the approach to hybrid DVPPs combining grid-forming and grid-following DERs for greater flexibility and grid-code compliance.
• To validate the control design in spatially distributed, multi-voltage-level power systems under realistic dynamic conditions.

Proposed method

• Uses an adaptive divide-and-conquer strategy with time-varying dynamic participation factors to disaggregate aggregate DVPP control specifications into local DER-level behaviors.
• Designs local grid-forming controllers at each DER using LPV H∞ state-feedback control to achieve desired local dynamics while respecting physical and operational limits.
• Integrates both grid-forming and grid-following DERs into a hybrid DVPP framework by extending the control design to accommodate different control signal causalities.
• Applies a linear parameter-varying (LPV) H∞ control synthesis to handle parameter variations such as changing power capacity, ensuring robustness across operating conditions.
• Employs a linearized converter model for controller design and validates performance on the full nonlinear system in electromagnetic transients (EMT) simulations.
• Validates the approach in a multi-voltage-level test system combining a 24-bus IEEE nine-bus transmission grid with a medium-voltage distribution grid.

Experimental results

Research questions

• RQ1 How can a group of heterogeneous grid-forming DERs be aggregated to collectively provide fast frequency and voltage control without relying on a stiff grid?
• RQ2 What control strategy enables stable, coordinated operation of grid-forming DERs while respecting individual device constraints and dynamic limits?
• RQ3 How can the control design be extended to include both grid-forming and grid-following DERs in a hybrid DVPP configuration?
• RQ4 What performance advantages does the proposed LPV H∞ controller offer over conventional PI-based controllers in terms of tracking accuracy and disturbance rejection?
• RQ5 How does the proposed DVPP control perform under spatially dispersed DER configurations with varying R/X ratios and voltage levels?

Key findings

• The proposed grid-forming DVPP design enables stable, autonomous frequency and voltage support without dependency on a stiff grid, supporting black-start capability and operation in weak grid conditions.
• The adaptive dynamic participation factor strategy successfully disaggregates aggregate control specifications into feasible, device-specific local behaviors that respect individual DER limits.
• The LPV H∞ controller outperforms conventional PI-based controllers in reactive power matching accuracy and high-frequency disturbance rejection, especially under parameter variations such as changing capacity.
• Numerical case studies in the IEEE nine-bus system with an interconnected MV distribution grid confirm the DVPP’s ability to provide fast, coordinated dynamic ancillary services across multiple voltage levels and R/X ratios.
• The hybrid DVPP framework successfully integrates grid-forming and grid-following DERs, enabling flexible and robust operation under diverse grid conditions.
• The control design demonstrates robustness to time-varying parameters, with the LPV H∞ controller maintaining performance without re-tuning, unlike conventional controllers requiring gain re-tuning.