Optimal Voltage and Current Control of an HVDC System to Improve Real-Time Frequency Regulation

TL;DR

This paper introduces an optimal control strategy for HVDC systems that enhances real-time grid frequency regulation by regulating DC-link voltage and current, integrating advanced control methods and dynamic modeling.

Contribution

A novel control approach combining LQG and feedback loops for HVDC systems to improve grid frequency regulation and mitigate control conflicts.

Findings

Enhanced GFR performance in simulations

Effective coordination between HVDC and generators

Robustness under various control parameter settings

Abstract

High-voltage direct-current (HVDC) systems for constant or intermittent power delivery have recently been developed further to support grid frequency regulation (GFR). This paper proposes a new control strategy for a line-commutated converter-based (LCC) HVDC system, wherein the DC-link voltage and current are optimally regulated to improve real-time GFR in both rectifier- and inverter-side AC networks. A dynamic model of an LCC HVDC system is developed using the DC voltage and current as input variables, and is integrated with feedback loops for inertia emulation and droop control. A linear quadratic Gaussian (LQG) controller is also designed for optimal secondary frequency control, while mitigating conflict between the droop controllers of the HVDC converters. An eigenvalue analysis is then conducted, focusing on the effects of model parameters and controller gains on the proposed strategy. Simulation case studies are also performed using the Jeju-Haenam HVDC system as a test bed. The results of the case study confirm that the proposed strategy enables the HVDC system to improve GFR, in coordination with generators in both-side grids, by exploiting the fast dynamics of HVDC converters. The proposed strategy is also effective under various conditions for the LQG weighting coefficients, inertia emulation, and droop control.