An Improved Dual-Loop Feedforward Control Method for the Enhancing Stability of Grid-Connected PV and Energy Storage System Under Weak Grids

Abstract

Although the stability of the grid-connected photovoltaics (PV) and energy storage systems under weak grids has been widely researched, the classical improvement methods focus more on suppressing the harmonics introduced by the phase-locked loop (PLL). Furthermore, the current distortion caused by the DC voltage loop is difficult to be eliminated. In this study, based on the hybrid energy storage system of battery-supercapacitor, a dual-loop compensation method is proposed. First, the small-signal model and output impedance matrix are built in d-q axis. Second, for different disturbance loops, a DC voltage loop disturbance compensation method based on power feedforward is proposed to suppress the harmonics caused by the DC voltage controller (DVC). In addition, a voltage feedforward PLL disturbance compensation method is proposed, which can reduce the PLL perturbations and revise the output impedance to improve system stability. Finally, the output impedance frequency characteristic analysis and the hardware-in-the-loop (HIL) simulation results show that the proposed control method can effectively improve the stability of the system under weak grids.

Modeling and stability analysis of interaction between converters in AC-DC distribution systems

“…The literature (Xue et al, 2020) analyzed the degree of influence of each parameter on the DC port impedance under different control modes. The literature (Li et al, 2022) used small signal analysis and impedance method to analyze the influence of PLL and voltage loop controller on the stability of the system in gridconnected inverter, and proposed a voltage feedforward PLL interference compensation method and an adaptive bandwidth frequency low-pass filter (LPF) to improve the system stability.…”

Virtual inertia analysis of photovoltaic energy storage systems based on reduced-order model

“…With the rapid growth of photovoltaic power generation systems (Chang et al, 2017;Hatziargyriou et al, 2020), DC-based photovoltaic energy storage systems have attracted widespread attention . Both photovoltaics and energy storage need to be connected to the DC bus through power electronic converters (Li et al, 2022;Seane et al, 2022;Li et al, 2023). It's worth noting that power electronic converters are the main reason for the low inertia of the photovoltaic energy storage system (PVESS).…”