Robust Virtual Inertia Control of a Low Inertia Microgrid Considering Frequency Measurement Effects

Abstract

Virtual inertia emulation could be regarded as an inevitable component of microgrids with renewable energy, enhancing microgrid inertia and damping properties. In applying this control technique, a phase-locked loop (PLL) is necessary to obtain the estimation of the system frequency data. However, the employment of PLL could cause larger frequency oscillation to the microgrid due to its dynamics. This issue would be exacerbated in a low-inertia microgrid driven by high renewable penetration, severely deteriorating the frequency stability. Thus, the effect of PLL with measurement delay is a critical issue in utilizing the virtual inertia control. To overcome such problem, this paper proposes a robust virtual inertia control for a low-inertia microgrid to minimize the undesirable frequency measurement effects, improving the microgrid frequency stability. The robust H ∞ control design using a linear fractional transformation (LFT) technique is used to develop the virtual inertia control loop, considering the dynamics of PLL with measurement delay and the uncertainties of system inertia and damping. The efficacy of the proposed H ∞ control method is compared to the conventional and optimum proportional-integral (PI)based inertia control. The results show that the H ∞ -based robust virtual inertia control is superior to both conventional virtual inertia control and optimum PI-based virtual inertia control against a wide range of microgrid operating conditions, disturbances, and parametric uncertainties.INDEX TERMS Frequency stability, H ∞ control, inertia control, microgrid, renewable energy, virtual synchronous generator.

Frequency and State-of-Charge Restoration Method in a Secondary Control of an Islanded Microgrid without Communication

“…From the perspective of grid-forming DG, all variables on the right-hand side of Equation (6) are known, so the output power of the grid-forming ESS can be calculated by Equation (6). The SOC of the grid-forming ESS can be expressed as [37]:…”

“…During grid-connected mode operation, the microgrid voltage is maintained by the main grid, and in this mode, the main grid manages load changes in the microgrid with little impact on the system frequency, since the main grid has large inertia relative to the microgrid. In contrast, during islanded mode operation, the microgrid has small or zero mass moment of inertia (e.g., a microgrid with only inverter-interfaced units) [3][4][5][6][7]. Due to their weak inertia, islanded microgrids are vulnerable to load changes.…”

Applying Virtual Inertia Control Topology to SMES System for Frequency Stability Improvement of Low-Inertia Microgrids Driven by High Renewables

“…To overcome these new stability threats, one straightforward solution is the development of auxiliary control, usually named virtual inertia control or virtual synchronous generator (VSG), which imitates the behavior of actual synchronous generators without using prime movers or rotating mass, tackling stability issues [1][2][3][4][5][6]. Such control system could be established with an energy storage system (ESS) and inverter.…”

“…The simulation studies were performed under a MATLAB/Simulink ® 2019 environment. To evaluate the efficacy and robustness of the proposed control method, the obtained results were compared with conventional ESS-based virtual inertia control in References [2][3][4][5][6]21].…”

“…The main contributions of this paper over the existing virtual inertia control techniques are as follows: (1) this is the first paper that proposes an explicit model of the SMES system that can capture the key dynamic characteristics of virtual inertia control topology for enhancing inertia emulation capability, improving frequency stability, and resiliency of the microgrid; (2) the dynamic effects of the proposed SMES-based virtual inertia control are analyzed and validated by the time domain simulation, evaluating a new trade-off between inertia response/emulation and short-term ESS power in regard to frequency stability improvement; (3) compared with the conventional ESS-based virtual inertia control in References [2][3][4][5][6]21], the proposed control strategy shows remarkable performance and stability in terms of high energy/power and fast response, resulting in the lowest frequency deviation and transient excursion. Thus, the lower and short-term power from the ESS could be solved, avoiding system instability, cascading outages, and wide-area power blackouts.…”