Power quality and stability analysis of large‐scale grid‐connected photovoltaic system considering non‐linear effects

Abstract

This study proposes to incorporate the non-linear factors, such as dead time and phase-locked loop (PLL), into the impedance model of large-scale grid-connected photovoltaic (PV) system and investigates their influence on the system power quality and stability considering the variation of PV capacity. The fundamental component of dead-time voltage can influence the inverter output impedance. The harmonics also have a vital effect on system power quality, especially when the inverter output admittance matches with the grid admittance. The increase of PV capacity can lower the influence of dead time on system phase margin, but may cause serious magnification of certain dead-time harmonics. PLL can make the system asymmetric and brings about the frequency coupling effect. The complex vectors and the transfer function matrix are used to convert the model of PLL from dq-to αβ-axis. The generalised Nyquist stability criterion is utilised to analyse the system stability. The variations of controller parameters in PLL can make the system oscillate. The increase of PV capacity may intensify this effect. Even the stable controller parameters are adopted, large PV capacity can trigger the system oscillation. Finally, the correctness of the theory is verified by simulation analysis and experiment.

A Novel Command-Filtered Adaptive Backstepping Control Strategy with Prescribed Performance for Photovoltaic Grid-Connected Systems

“…There exist many investigations on the stabilization of the PV grid-connected system by researchers around the world [7][8][9][10][11]. From the point of view of the model of the PV grid-connected system, the Reference [7] studies the influence of nonlinearities like dead time and the phase-locked loop with regard to power quality and stability via the generalized Nyquist stability criterion, and verifies the theory with a simulation and experiment. In [8], a feedback linearization technique was introduced for the partial linearization of the three-phase PV grid-connected system, which promotes the design process of the controller, and the zero dynamic stability of the system was acquired under the designed controller, which helps transport the grid power.…”

Stability problems of PV inverter in weak grid: a review

“…T s is the switching period and T on is the ideal conducting time of switches. The average of the inverter output voltage in one switch period is expressed as [30]…”

“…By (9), (10), and (11), the PLL effect can be modelled into the inverter output admittance Y pv [30]. Note that different from the traditional inverter impedance, this is an impedance matrix because of the introduction of conjugation form.…”

“…A new active damping feedback in [39] improves the critical frequency to 0.45 of sampling frequency but more works still can be done to improve the critical frequency furtherly to enlarge the design range of LCL resonant frequency. In addition, the PLL model in phase domain [40,41], dq frame [42][43][44], and αβ frame [30,45] are proposed and the frequency coupling effect have been revealed in recent years. The main concept used in these papers is to incorporate a linearised model of the PLL into the system impedance model.…”

A Novel Control Strategy for Grid-Connected Inverter Based on Iterative Calculation of Structural Parameters

“…With the rapid developing of distributed photovoltaic generation, grid-connected inverters are widely used [1,2], and the control strategies of grid-connected inverters are very important in the renewable energy development. There are three basic control strategies for grid-connected inverter: (1) classical grid-current control strategy, (2) droop or damping control strategy [3], and (3) some other intelligent control strategies.…”