Grid-connected Converters Research Articles

Magnetic Integrated Multi-Trap Filters Using Mutual Inductance to Mitigate Current Harmonics in Grid-Connected Power Electronics Converters

Magnetic Integrated Multi-Trap Filters Using Mutual Inductance to Mitigate Current Harmonics in Grid-Connected Power Electronics Converters

A method for determining stability range of grid‐side converter parameters of PMSG based on negative feedback modelling of phase‐locked loop and outer control loop

AbstractDirect‐drive wind farms are integrated into power grid through power electronic devices, extensively utilizing voltage source converters (VSCs) for grid connection, which has precipitated frequent stability challenges within the grid integration systems of wind farms; it is imperative to properly tune the VSC parameters consequently. In grid‐connected VSC system, the interaction between phase‐locked loop (PLL) and outer control loop (OCL) has a significant impact on system stability. Therefore, it is essential to account for the interactions when establishing the stability boundaries for VSC parameters. This article proposes a new method to determine the parameter stability range in grid‐side converter of direct‐drive permanent magnet synchronous generator (PMSG), based on the interactions between PLL and OCL. This method simplifies the modelling process and improves the accuracy of stability range calculations compared to traditional methods. The system is modelled as a negative feedback system with PLL as the forward path and OCL as the feedback path. Both paths include grid dynamics. This modelling approach not only captures the interaction between PLL and OCL, but is also straightforward and clear. Using the Bode diagram, stability mechanism of the system considering interaction between PLL and OCL is studied. The VSC parameter stability criterion of the system is analysed based on the open‐loop frequency characteristics of the system. Then an analytical description of the stability range for parameters is provided. Simulation results confirm the effectiveness of our proposed method.

Design-Oriented Transient Stability Analysis of Grid-Connected Converters: A Comparative Study of Analysis Methods

Design-Oriented Transient Stability Analysis of Grid-Connected Converters: A Comparative Study of Analysis Methods

A Multifunctional Arc Suppression Device Based on Hybrid Grid-Connected Converters

A Multifunctional Arc Suppression Device Based on Hybrid Grid-Connected Converters

Convolutional Neural Network for the Classification of the Control Mode of Grid-Connected Power Converters

With the integration of power converters into the power grid, it becomes crucial for the Transmission System Operator (TSO) to ascertain whether they are operating in Grid Forming or Grid Following modes. Due to intellectual properties, classification can only be performed based on non-intrusive measurements and models, such as admittance at the PCC. This classification poses a challenge as the TSO lacks precise knowledge of the actual control structures and algorithms. This paper introduces a novel classification algorithm based on Convolutional Neural Networks (CNN), capable of detecting patterns in sequential data. The proposed CNN utilizes a new architecture to separate admittances along the d and q axes, and a decision layer allows to determine the correct converter mode. The performance of the proposed CNN model was assessed through two tests and compared to the traditional feedforward model. The proposed CNN architecture demonstrates significant classification capabilities, as it is able to identify the control mode of the converter even when its control structure is not part of the training dataset.

Model Order Reduction and Stability Enhancement Control for AC/DC Converters Through State Feedback Method

In the DC distribution networks, DC bus voltage is maintained by the grid-connected converter; the controllability and reliability of the grid-connected converter significantly affect the bus voltage characteristic. To address the problem of limited stability and frequent oscillations, this paper proposes a state feedback control method for the AC/DC converter. Conventional AC/DC converter adopts the voltage-current double-closed-loop control structure with the proportional-integral (PI) controllers, which is the equivalent of the typical type II control system, but the typical type II control system cannot fully settle the stability and immunity problems. In contrast, the state feedback control strategy not only achieves the control objectives of the traditional double-closed-loop control but also reduces the AC/DC converter system model to a typical Type I system, which improves stability and thus enhances the oscillation suppression capability of the bus voltage. By selecting multiple state variables and designing the converter pole configuration range, the proposed single-loop state feedback control method manages to optimize both the dynamic and steady-state performances of the grid-connected AC/DC converter. Finally, the effectiveness of the proposed single-loop state feedback control strategy is verified through MATLAB (2018b)/Simulink software simulation and experiments on a DC distribution network platform.

Accurate Identification of Frequency-Coupling Admittance for Grid-Connected Converters Under all Operating Conditions

Accurate Identification of Frequency-Coupling Admittance for Grid-Connected Converters Under all Operating Conditions

Innovative adaptive virtual impedance for resonance frequency mitigation in grid-connected converters

Microgrid architectures are typically composed of multiple parallel grid-connected inverters, interconnected via LCL filters to comply with grid code requirements while offering low cost and superior dynamic performance compared to L filters. However, the use of LCL filters in microgrids introduces two types of resonance: extrinsic resonance related to each LCL filter and intrinsic resonance resulting from the coupling effects of multiple parallel LCL filters. These resonances can lead to small oscillations, degrading power quality, or large oscillations, compromising microgrid reliability and stability, especially with variations and poor design of LCL filter parameters. Thus, early detection and correction of these oscillations are essential for resilient microgrid operation. This paper proposes a residual-based adaptive virtual impedance technique to effectively detect and mitigate unwanted resonance frequencies. Unlike previous approaches that primarily focus on static impedance adjustments or non-adaptive methods with slow detection of the undesired resonance frequencies, the proposed method diverges by emphasizing the dual functionality of the virtual impedance. It operates in two steps: first, a residual algorithm swiftly identifies undesired oscillations, producing higher values during instability and low values under normal conditions. Second, an adaptive virtual impedance is introduced to restore stability, with its components continuously computed until the residual value falls below the threshold for normal operation. Unlike previous approaches that often focus solely on harmonic sharing or stability without addressing the rapid detection of oscillations, the proposed technique integrates both detection and mitigation, providing a robust solution for enhancing microgrid stability and reliability in the presence of resonances. A comprehensive case study, including simulations, real-time simulations, and experimental tests, is conducted to validate the technique's effectiveness and superior performance.

Oscillation Mechanism and Suppression of Variable-Speed Pumped Storage Unit with Full-Size Converter Based on the Measured Single-Input and Single-Output Impedances

As the penetration rate of clean energy gradually increases, the demand for flexible regulation resources in the power grid is increasing accordingly. The variable-speed pumped storage unit with a full-size converter (FSC-VSPSU) can provide fast and flexible regulation resources for the power grid, which assists in the stable operation of the clean-energy-dominated power systems. Thus, its application is gradually becoming widespread. FSC-VSPSU relies on the power electronic converter for grid connection. When the impedance mismatch between FSC-VSPSU and the power grid occurs, the grid-connected system will experience oscillations, which seriously threatens its safe and stable operation. Aiming at this, this article firstly relies on the SISO impedance measurement and an equivalent impedance analysis to obtain the stability analysis criterion. Furthermore, applying the impedance matching analysis with the Bode diagram, the influence rules of the parameters of the grid-connected FSC-VSPSU on oscillation are obtained. In addition, with the summarized oscillation analysis results, this study delves into an exploration of pertinent strategies for oscillation suppression. Finally, a grid-connected FSC-VSPSU simulation model is built in MATLAB/SIMULINK, and the simulation results verify the correctness of the oscillation analysis results and the effectiveness of the proposed oscillation suppression strategy.

Generalized Envelope-Based Modeling of Single-Phase Grid-Connected Power Converters

Generalized Envelope-Based Modeling of Single-Phase Grid-Connected Power Converters

Comparison of the Impacts of Background Distortion with Even and Odd Orders in the Supraharmonic Range on Grid-Connected Converters

In this paper, a comparison of the emissions of grid-connected converters under grid distortion in the supraharmonic range is performed. The investigated supraharmonic grid distortion is divided into two types, namely odd-integer and even-integer multiples of the grid frequency. It is found that the first distortion type does not affect the emissions of the grid-connected converters, while the second distortion is responsible for the 2N-harmonic emissions that appear in the frequency spectra of the grid-connected converters, which, in turn, interact with the supraharmonic primary emissions of these converters, resulting in additional supraharmonic emissions. To explain this behavior, a mathematical analysis is provided for two types of grid-connected converters with an inverter interface and with a diode bridge rectifier interface. Simulations and experimental studies are performed to verify the main findings of the mathematical analysis.

Finite Control Set Model Predictive Control for Grid-Connected Parallel Power Converters With Guaranteed Optimality

Finite Control Set Model Predictive Control for Grid-Connected Parallel Power Converters With Guaranteed Optimality

Current-Oriented Phase-Locked Loop Method for Robust Control of Grid-Connected Converter in Extremely Weak Grid

Current-Oriented Phase-Locked Loop Method for Robust Control of Grid-Connected Converter in Extremely Weak Grid

Self-Excitation Startup Strategy of Cascaded H-Bridge Grid-Connected Converter Based on Dynamic Virtual Impedance

Self-Excitation Startup Strategy of Cascaded H-Bridge Grid-Connected Converter Based on Dynamic Virtual Impedance

Evaluation of power system instability probability considering output randomness of grid-connected converter

Abstract In recent years, there has been a notable increase in the installed capacity of new energy sources. Nevertheless, the random nature of the output power of G-CCs may potentially result in power system instability. This paper presents a closed-loop interconnection model comprising a G-CC as a feedback subsystem and a VSC-HVDC system as a feedforward subsystem. The instability condition of the closed-loop system is derived from the open-loop mode resonance theory. Subsequently, a mathematical model is developed to represent the random output of the G-CC. This approach allows the probability of open-loop mode resonant instability of the power system to be evaluated, as well as the risk of sub-synchronous resonant instability caused by the output randomness of the G-CC. Finally, validation is performed by building a simulation example system and a time-domain simulation system in MATLAB.

Impedance modeling and quantitative stability analysis of grid-connected voltage source converters under complex unbalanced conditions

The stability issues caused by voltage source converters (VSCs), which are commonly used in renewable energy systems, are investigated in this paper. Much literature has investigated the impedance models and quantitative stability analysis for converters under the weak and unbalanced grid. However, on the one hand, harmonic-transfer-function (HTF)-based modeling methods are complex, and the established infinite-order models may suffer from unreasonable truncation. On the other hand, these existing impedance models without considering all unbalance factors are inaccurate. Both of these may bring wrong stability analysis results. Therefore, this paper proposes a simple impedance extension method and considers all unbalance factors to derive the impedance model of the converter. However, due to the established higher-order impedance model, the traditional impedance-ratio based stability analysis method is not applicable to multi-input multi-output (MIMO) systems. The commonly used eigenvalue-based GNC and diagonalization-based methods applicable to MIMO systems are cumbersome and not suitable for quantitative analysis. Therefore, in this paper, a quantitative analysis tool of system stability based on the phase-frequency characteristics of determinants is developed. Then, stability regions in the multi-parameter space are obtained. Finally, the established impedance model and the quantitative analysis results are validated via both simulations and hardware experiments.© 2017 Elsevier Inc. All rights reserved.

Small-Signal Stability Analysis and Optimization of Grid-Forming Permanent-Magnet Synchronous-Generator Wind Turbines

Due to the ability to improve the low-inertia characteristics of power systems and offer reliable voltage and frequency support, grid-forming permanent-magnet synchronous-generator wind turbines (PMSG-WTs) based on virtual synchronous-generator (VSG) technology are emerging se the direction for future developments. Previous studies on the small-signal stability of grid-forming PMSG-WTs that connect to the grid usually simplify them into grid-connected grid-side converters (GSC), potentially leading to errors in stability analyses. Therefore, this paper considers the machine-side converter (MSC) control and establishes impedance models for grid-forming PMSG-WTs. Based on the sensitivity calculation of controller parameters using symmetric difference computation based on zero-order optimization, the impact of the internal controller on outside impedance characteristics is quantitatively analyzed. Additionally, an optimization method to enhance the stability of a hybrid wind farm by adjusting the ratio of grid-forming and grid-following wind turbines is proposed.

A New Grid-Connected Asymmetrical Multilevel Converter for PV Application

A New Grid-Connected Asymmetrical Multilevel Converter for PV Application

Low-Complexity and Less-Conservativeness Ostrowski Stability Criterion for Parallel Fractional Grid-Connected Converters Under Unbalanced Grid

Low-Complexity and Less-Conservativeness Ostrowski Stability Criterion for Parallel Fractional Grid-Connected Converters Under Unbalanced Grid

Analytical Switching Modelling Method of Grid-Connected Converters for Transient Stability Analysis

Analytical Switching Modelling Method of Grid-Connected Converters for Transient Stability Analysis