Analysis of Harmonic Resonance Characteristics in Grid-Connected LCL Virtual Synchronous Generator

Abstract

The virtual synchronous generator (VSG), which emulates the essential behavior of the conventional synchronous generator, has attracted great attention. This paper proposes to analyze the harmonic resonance characteristics in VSG using the state-space model. The analysis is based on a full-order state-space small-signal model that fully considers the dynamic of the inner loops and the VSG-based outer power control loop. Participation analysis is used to point out the contributions of different states to the eigenvalues. Moreover, eigenvalue locus and singular value decomposition (SVD) are applied together to evaluate the impact of the inner loop parameters on the harmonic resonance characteristics around the LCL filter resonance frequency. The analysis indicates that the harmonic resonance instability is mainly caused by decreasing the proportional gains of the current loop and the voltage loop. Finally, extensive numerical simulation and experimental results are given to verify the validity of the theoretical analysis. Both the simulation and experimental results indicate that the voltage of the common coupling point is unstable after decreasing the proportional gains of the current and voltage controllers. As Kpc decreases from 5 to 0.4 or Kpv decreases from 0.6 to 0.2, the harmonic distortion factor (HDF) around the LCL filter resonance frequency increases. Furthermore, the consistency of simulation results, experimental results, and the theoretical analysis results is validated.

Analysis of Grid-Connected Stability of VSG-Controlled PV Plant Integrated with Energy Storage System and Optimization of Control Parameters

“…To improve the stability and stability margin of the PV generation and ES system, Milano et al [9] and Jiang et al [13] employed the root locus method to analyze the impact of control parameter variations on system stability. However, root locus-based parameter optimization methods often exhibit subjectivity and lack well-defined, scientifically quantifiable design criteria.…”

“…[12] suggested that when a single VSG is connected to the grid, if the line resistance and reactance are of similar magnitudes, active and reactive power become coupled, leading to oscillations. Jiang et al [13] used a state-space model to analyze the influence of inner loop proportional gain, integral coefficient, and virtual inductance parameters on harmonic oscillation characteristics. Xu et al [14,15] improved dynamic characteristics by adding a differential loop in the VSG power loop but introduced high-frequency interference, affecting calculation accuracy.…”

Review on Virtual Inertia Control Topologies for Improving Frequency Stability of Microgrid

“…While all VSG strategies control active and reactive power, each has its control frame. Furthermore, different VSG control strategies have been introduced to enable the inverter to emulate the properties of an SG [41,52]. As a result, every VSG implementation entails an approximately direct mathematical model of an SG [4].…”

“…Furthermore, to approximate the electromagnetic properties of SG for VSG, the SG's stator equation is usually simulated without considering the electromagnetic relationship between rotor and stator, and this can be expressed as [52]:…”

“…And the reactive power simulates the SG's voltage regulation and determines the modular signal's amplitude. The VSG active power mathematical equation, comprising a simple VSG governor, is as follows [52]:…”