Enhanced Phase-locked Loop Research Articles

Adaptive complex coefficient‐filtered extended states observer type three‐phase enhanced phase‐locked loop

AbstractThis paper proposes an adaptive complex coefficient filtered (CCF) full order extended state observer (ESO) type three phase enhanced phase locked loop (EPLL), which is employed in matrix reactance frequency converter (MRFC) for rotating vectors measurement estimation. EPLL phase detector was analysed first to track not only the rad frequency and transient phase, but also the amplitude of the rotating vectors. Full order ESO can filter out more high frequency disturbance, so it can track frequency and phase more accurately than proportion and integration algorithm. CCF modules were analysed in theory to attenuate the disturbance within two times of the EPLL's cut‐off frequency. The whole adaptive CCF‐ESO‐EPLL design, including stability and parameter tuning were then interpreted. The proposed CCF‐ESO‐EPLL adapts the estimated frequency with CCF to attenuate the MRFC switching non‐linear disturbance as well as unknown disturbance by the full order ESO. The MRFC topology necessary measured vectors, as well as the input side reactive power adjustment capacity, were discussed. The theoretical conclusion has been verified on a MRFC prototype. The proposed CCF‐ESO‐EPLL has less parameter tuning, less computation resource requirement, better steady and dynamic performance, and outstanding disturbance robustness.

Green energy solution for grid integrated solar PV system for water storage towers

In India, water storage towers are present almost everywhere, especially across small towns to rural areas. The storage tanks either utilize diesel powered or utility grid fed induction motor (IM) water pumps. The large spaces available with water storage towers can be utilized to plant solar PV panel for large storage towers water pumping operation, hence, making a switch from diesel or grid run storage towers to solar operated storage towers. This paper presents a robust control of grid integrated solar PV-based water pump system with efficient and smooth transition between standalone and grid interfaced modes. A smart DC link voltage control is presented for distributed generation system (DGS), which provides full control on DC link voltage for both modes of operation at all dynamic load conditions. An enhanced phase-locked loop (EPLL) control is utilized for grid source converter (GSC) in grid control operation, making it flexible to different grid scenarios and power quality. It works for harmonics suppression, load balancing and grid side converter control. An enhanced phase-locked loop (EPLL) is implemented for synchronization control algorithm, which provides an accurate estimation of voltage angle even during frequency ramps and exhibiting superior performance particularly in terms of robustness against DC offsets. The primary requirement for smooth operation of grid-tied solar PV system is effective power management between different sources. The issues of power management and power quality, are discussed in this work, and solutions are presented. The implemented control algorithms are tested successfully for dynamic solar insolation, varying load conditions, unbalance in load, sudden grid outage condition. The system appropriateness is validated by experimental results.

Performance enhancement of UPQC based on optimized GBSSA hybrid fuzzy controller with EPLL

In this research, UPQC (Unified Power Quality Conditioner) with optimized hybrid fuzzy controller based GBSSA (Gaussian Barebone Salp Swarm Algorithm) with EPLL (Enhanced Phase Locked Loop) have been proposed for power quality enhancement in power distribution networks. Using the proposed method, the difficulties in major of the power distribution system networks can be solved, related to power quality issues. GBSSA has been employed in this research, to improve solution accuracy and optimization efficiency. Given that, it is permissible to add some extra time cost to acquire a better solution, based on the Non-Free Lunch (NFL) theory, and that the time consumption of function evaluation is rather large, when addressing actual optimization problems, the extra time consumption can be overlooked to some extent. The EPLL control method improves the standard PLL, by reducing its fundamental flaw, which is the occurrence of main frequency errors, as well as double frequency errors. It controls the DC-bus voltage of unified power quality conditioners, during supply voltage and load voltage turbulences. The proposed UPQC control technique has been found to be resilient, to a variety of source and load perturbations, including unbalanced, transient distorted supply, voltage sag, unbalanced load and voltage swell. The proposed optimized GBSSA hybrid fuzzy controller with EPLL has been proven to be more effective in reducing the THD (Total Harmonic Distortion) to 3.22%. Moreover, comparative analysis with a conventional TSF-PLL has been performed with that of Takagi-Sugeno fuzzy controller and implemented using MATLAB (MATrix Laboratory).

Mother wavelet selection method for voltage sag characterization and detection

Wavelet-based techniques are strongly recommended as a good alternative for the fast detection and characterization of voltage sags. However, the accuracy and effectiveness of these techniques greatly depend on selecting an appropriate mother wavelet. Therefore, in this work, a wavelet correlation-based technique has been developed to select the most appropriate mother wavelet for the characterization and detection of voltage sag. The efficacy and accuracy of the proposed method are tested with twenty different mother wavelets on various voltage sag signals, namely, recorded industrial, multi-stage, and synthetic signals under different conditions of unbalanced. It is shown that the mother wavelet having the highest similarity with a voltage sag provides the best results for its characterization and detection. Further, the various performance parameters of voltage sags, namely magnitude, duration, sag initiation, recovery, are evaluated with the proposed method and results are compared with Independent Component Analysis (ICA), hybrid wavelet, dq-transformation, Enhanced Phase Locked Loop (EPLL), Fast Fourier Transform (FFT) methods showing that the performance of the proposed method is better than other existing methods for sag detection. In addition, the proposed method can also be used for estimating the magnitude of voltage sags.

Grid interface of solar PV transformer-less inverters using enhanced phase locked loop

The era of Renewable Energy sources has overtaken the usage of conventional energy sources like coal, fossil fuels etc. This paper presents grid interface of single phase transformerless inverter system using enhanced phase locked loop. To connect solar PV with grid it is required to estimate phase angle, voltage amplitude and phase angle measurement of grid and the output of inverter. It is required to track exact utility voltage vector for reliable control of power to the grid. This paper compares the frequency measurement and phase angle and voltage amplitude using simple phase locked loop system along with enhanced phase locked loop so that the enhanced phase locked loop (EPLL) is proved to be giving superior performance over simple phase locked loop. The simulation of both the techniques are pursued and the results are compared.

Enhanced control method for voltage regulation of DSTATCOM based SEIG

Self-excited induction generator (SEIG)-based wind energy conversion systems (WECS) are very popular for feeding stand-alone loads in remote areas where there is no grid. SEIG needs adjustable reactive power to regulate terminal voltage and frequency. Usually, a combination of a distributed static compensator (DSTATCOM) and a fixed capacitor bank is used to meet this reactive power demand. DSTATCOM is the most suitable option for power quality compensation. The performance of DSTATCOM depends on its control algorithm that generates the proper switching signals for voltage source inverter (VSI). Many control algorithms have been proposed for DSTATCOM in the literature. Among them, the most frequently used algorithms are synchronous reference frame (SRF), instantaneous reactive power (IRP), and current synchronous detection (CSD) algorithms. An effective control algorithm must accurately estimate the amplitude of the terminal voltage without being affected by harmonics, DC-offset, and frequency variation. For this purpose, an enhanced phase locked loop (EPLL)-based CSD control algorithm is proposed to estimate the amplitudes of individual phase voltages, and to filter SEIG voltages in case of harmonics, DC offset, and frequency variation. The proposed algorithm has been tested under linear and nonlinear load conditions. The obtained results clearly demonstrate the effectiveness of the proposed EPLL-based CSD control algorithm.

An Optimized Enhanced Phase Locked Loop Controller for a Hybrid System

The use of renewable energy sources is the need of the hour, but the highly intermittent nature of the wind and solar energies demands an efficient controller be connected with the system. This paper proposes an adept control algorithm for an isolated system connected with renewable energy sources. The system under consideration is a hybrid power system with a wind power harnessing unit associated with a solar energy module. A controller that works with enhanced phase locked loop (EPLL) algorithm is provided to maintain the quality of power at the load side and ensure that the source current is not affected during the load fluctuations. EPLL is very simple, precise, stable, and highly efficient in maintaining power quality. The double-frequency error which is the drawback of standard phase locked loop is eliminated in EPLL. Optimization techniques are used here to tune the values of the PI controller gains in the controlling algorithm. Tuning of the controller is an important process, as the gains of the controllers decide the quality of the output. The system is designed using MATLAB/SIMULINK. Codes are written in MATLAB for the optimization. Out of the three different optimization techniques applied, the salp swarm algorithm is found to give the most suitable gain values for the proposed system. Solar power generation is made more efficient by implementing maximum power point tracking. Perturb and observe is the method adopted for MPPT.

EPLL Control Technique Optimum Controller Gains to Control Voltage and Frequency in Standalone Wind Energy Conversion System

This study describes how to regulate the frequency and terminal voltage of a freestanding wind energy conversion system using an Enhanced Phase Locked Loop (EPLL)-based strategy to supply power to varied loads regardless of wind speed. In a standalone wind turbine energy conversion system, the EPLL control scheme extracts the reference source currents (SWECS). The control algorithm employs two proportional-integral (PI) controllers to create the active and reactive power components of the consumers' load currents, estimate reference source currents, and connect the zigzag transformer to PCC with VSC for neutral current compensation. To obtain optimal PI controller gains and most-suited settings to apply to SWECS, optimization approaches are used. The control algorithm is the most significant aspect of the system, and the speed with which it calculates, evaluates, and guesstimates determines the generation of source currents based on the algorithm's ideal controller PI gains. By properly estimating source currents, the EPLL control method improves dynamics and power quality issues, and the optimization technique is employed to acquire the gains of PI controllers. The proposed system employs the EPLL algorithm on a three-phase, four-wire system with changing loads to achieve ideal total harmonic distortion of source currents and voltages on the PCC, as defined by IEEE-519 standards. A battery energy storage device coupled to the VSC dc link keeps the load's necessary power constant. If the generator output exceeds the consumer demand, the excess power is delivered to BESS for temporary storage. When consumer demand exceeds generated power, a BESS delivers deficit power to the load, which adjusts and the frequency under various load conditions. The suggested system simulated results were tested with 3-phase 4-wire for harmonics reduction, load balancing, neutral wire current compensation, frequency and voltage control using MATLAB / Simulink.

More-Stable EPLL

The enhanced phase-locked loop (EPLL) is one of the most famous PLLs in single-phase applications and a versatile tool for different signal processing applications, especially for the grid synchronization of power converters. Recently, it has been proved that the EPLL has a quite narrow stable zone (compared to its unstable zone) in the positive parameter space from a small-signal point of view. This zone will be even more narrow if maintaining a minimum stability margin is required. This article aims to modify the EPLL structure to improve its stability margin, and at the same time, make it unconditionally stable in the positive parameter space from a small-signal point of view.

Fuzzy Logic Based Synchronization Method for Solar Powered High Frequency On-Board Grid

This paper proposes a method for synchronizing a grid inverter with the voltage of an on-board high-frequency power grid. The described synchronization method belongs to the adaptive methods, which use fuzzy logic in the process of estimating the fundamental component of the voltage. The synchronization system has been tuned to achieve the primary goal of achieving synchronization in the shortest possible time. This is to allow for the efficient energy fed from photovoltaic sources into the on-board grid at 400 Hz. The proposed method was implemented in the field programmable gate array (FPGA) based power converter controller and static and dynamic tests for harmonic, interharmonic and subharmonic voltage disturbances were performed. Dynamic tests for phase jump, frequency jump and sag of the on-board voltage were also performed. To evaluate the effectiveness of synchronization with high-frequency voltage, the grid current control system in the grid tied inverter was elaborated. Proper current waveforms at the perturbed voltage were recorded while identifying the effectiveness of power ripple suppression. The results obtained were compared with the enhanced phase locked loop (EPLL) synchronization method. Satisfactory test results confirmed the suitability of the proposed method in systems coupling the photovoltaic source to the on-board high-frequency power grid.

Enhanced PLL (EPLL) Synchronization and HBCC Controlling of Grid-Interactive (PV-SOFC) Hybrid Generating System

Objective: In a grid-interactive (PV-SOFC) generation system, the inverter is the main constituent. Further, the quality of the injected signal in utility depends upon inverter control and synchronization. Thus, the main objective of thispaper is to control the single-phase inverter for a hybrid DC generation system and obtain synchronization between the grid signal and hybrid renewable energy source (RES) inverted output signal. Methods/Statistical analysis: This paper suggests software modeling of the grid-interactive hybrid photovoltaic array (PV) and solid oxide fuel cell (SOFC) power generation system to supply continue load demand. The enhanced phase locked loop (EPLL), and hysteresis band current controller (HBCC) utilize to control single-phase inverter for hybrid generation system. The main benefit of EPLL configuration beyond traditional PLL’s is to compose and keep up phase change zero between input and output of voltage controlled oscillator (VCO). So, the EPLL tracks thephase angle and amplitude of the signal. The incremental conductance based MPPT technique is implemented in the proposed architecture to enhance the system’s efficiency by maximizing extracted power from the PV configuration. In addition, the synchronization between the grid signal and hybrid RES inverted output signal is obtained with EPLL. The simulation results with system design parameters are carried out in MATLAB 2015. Findings: The efficacy of the proposed synchronization circuit of EPLL is confirmed through the compensation of twice time-frequency error, which is introduced in traditional PLL. Further, from the simulation results, it is observed that smooth frequency is obtained with the proposed EPLL. Moreover, the performance index parameter (%THD) of current in the presence of EPLL and HBCC is smaller than the traditional PLL. Novelty: This paper introduces a hybrid EPLL and HBCC approach to control the single-phase inverter for a hybrid PV-SOFC generation system. Keywords: Photovoltaic array (PV); incremental conductance based maximum power point tracking (INC-MPPT); synchronization; solid oxide fuel cell (SOFC); hysteresis band current controller; enhanced phase locked loop (EPLL); grid

Design of Enhanced PLL for Single-Phase Grid Connected Transformerless Inverters

Abstract: Renewable energy sources integrated withconventional sources fed grid to meet the ongoing electricalenergy demands. This paper presents design of EnhancedPhase locked loop (EPLL) for single phase grid connectedtransformer less inverter. The knowledge of phase angle,frequency, voltage magnitude is under consideration tointegrate the solar PV to single-phase grid. It is required totrack exact utility voltage vector for reliable control of powerto the grid. The paper also presents Simulink modeling,analysis of Enhanced PLL and compares its performance withbasic phase locked loop (PLL) used.Index Terms: Enhanced phase locked loop (EPLL),Transformerless inverter, single phase grid connected,

Operation and Control of a Grid-Connected Asymmetrical Cascaded Multilevel Inverter

This article presented a new structure for the grid-connected multilevel inverters (MLIs) circuit with the ability of the cascaded connection. The proposed inverter is capable of transformerless connection of distributed generation resources to the network. The control system manages the power injection to the grid by minimizing the output current harmonics as well as exchanging reactive power with the grid. The self-balancing state of the capacitors' voltage is occurred only with the switching technique without any measurement sensors. An enhanced phase-locked loop (EPLL) and a proportional resonant (PR) controller are employed for the proposed asymmetric MLI. An important feature of the proposed inverter is the ability of stable performance and fast dynamics of the control system to the changes of the reference values. Simulation and experimental results are presented in order to validate the performance accuracy of the proposed MLI.

Single-Phase Enhanced Phase-Locked Loops Based on Multiple Delayed Signal Cancellation Filters for Micro-Grid Applications

The grid voltage information such as the phase-angle, the frequency, and the amplitude is crucial for the design of synchronization and control of power converters in the micro-grid. The conventional approach to estimate the grid voltage information is accomplished by phase-locked loop (PLL) techniques. Among various existing PLL techniques, filter-based PLLs can provide more accurate estimations even under adverse grid conditions. In this paper, a new single-phase filtering technique based on multiple delayed signal cancellation (MDSC) is proposed for extracting both in-phase and quadrature components of the selected harmonic order of the single-phase grid voltage signal. This MDSC technique can be realized in both the direct-form and the recursive-form. In comparison with existing single-phase cascaded delayed signal cancellation (CDSC) techniques, this MDSC technique utilizes less memory for the extraction of grid voltage fundamental frequency component. The proposed MDSC filter can be applied as a pre-filter to the enhanced PLL (EPLL) for the prompt and accurate estimations of the grid voltage information under adverse grid conditions. Both frequency adaptive and non-adaptive MDSC-based EPLL schemes are proposed in this paper. To validate the effectiveness of the proposed methods, experiments are conducted on the MDSC-based EPLLs and compared with the CDSC-EPLL under various grid voltage disturbances.

Dynamic Performance Enhancement of Single-Phase and Two-Phase Enhanced Phase-Locked Loops by Using In-Loop Multiple Delayed Signal Cancellation Filters

The estimation of phase-angle, frequency, and amplitude are vital for the control of grid-connected power electronic systems in both single-phase and three-phase systems. The single-phase enhanced phase-locked loop (1P-EPLL) and two-phase enhanced phase-locked loop (2P-EPLL) techniques can be used to estimate single-phase and three-phase grid voltage quantities, respectively. However, under the presence of harmonics, unbalance, and dc offsets, the estimated quantities by these enhanced phase-locked loops (EPLLs) may contain periodic ripples. These periodic ripples are eliminated by using multiple delayed signal cancellation (MDSC) filters in the phase-angle estimation loop and amplitude estimation loop of these EPLLs. To improve the dynamic responses of MDSC-based EPLLs, proportional-integral (PI) controller is replaced with a proportional-integral-derivative (PID) controller. The design guidelines for choosing the control parameters are provided. The MDSC filters in the EPLLs are realized both in direct-form and recursive-form structures. The proposed EPLLs are verified experimentally by using real-time system and compared with recent advanced EPLLs.

Time-Domain Simulations of Single-Phase Enhanced PLL for Power Converters under Distorted Grid Conditions

With the developing number of alternate energy sources being connected to the Grid, there is a need for robust Grid synchronization technique that is capable enough despite the grid frequency and phase variations. Single phase Enhanced Phase Locked Loop (EPLL) presented in this paper meets these requirements. A detailed study of the performance of EPLL for disturbances in input grid voltage magnitude, phase and frequency is detailed through mathematical equations. Extensive simulations are carried out in Matlab/Simulink to analyze the phase and frequency tracking by EPLL. Dynamic response is examined carefully in terms of estimation of grid voltage, frequency and phase error.

Adaptive EPLL for improving power quality in three‐phase three‐wire grid‐connected photovoltaic system

A phase-locked loop (PLL) plays an integral part in synchronisation circuits and is immensely used in grid-connected systems, active filters, and uninterrupted power supplies. A number of these circuits based on synchronous reference frame and its modifications, second-order generalised integrator, enhanced PLL (EPLL) have recently been reported in literature. This article proposes an adaptive version of EPLL whose gain adjusts automatically with the variation of error. Adaptive EPLL (A-EPLL) is developed for positive sequence extraction of load current and its performance is tested for active filter operation. A PV system is also connected at the DC link of the shunt active power filter (SAPF) and the developed controller is tested under dynamic load changes. The complete control technique is tested for harmonics reduction, load balancing, and power balance between grid, load, and photovoltaic (PV) source. Detailed experimental results showing a new adaptive PLL for load compensation are illustrated here.

Optimal operation of PV‐DG‐battery based microgrid with power quality conditioner

This study presents an optimal control operation of a photovoltaic-battery based standalone microgrid, feeding non-linear loads. To ensure continuous power supply to the critical loads during low insolation or low battery state of charge, a diesel generator (DG) is used as an auxiliary generator. This cost effective hybrid system with maximum utilisation of the renewable as well as fossil fuel based generators can be employed in hospitals, telecom stations in remote areas. In order to nullify the effect of non-linear loads on the DG, modified enhanced phase-locked loop (EPLL) based power quality conditioner is used. The characteristic equation of conventional EPLL is amplitude dependent, thus, the controller tuning parameters need to be modified if the input signal varies over a large range. The presented controller overcomes this problem making the system more robust in eliminating noise and harmonics and extracting fundamental component of a given signal. This component is drawn from the DG with the help of a voltage source converter, thus, making its current always distortion free. The proposed control scheme is simulated in MATLAB. Furthermore, experimental verification is done on a laboratory prototype of the same. The steady state and dynamic responses of the system validate its satisfactory performance.

An Improved $\alpha\beta$ -EPLL Based on Active Disturbance Rejection Control for Complicated Power Grid Conditions

The enhanced phase-locked loop (EPLL) adds an amplitude estimate to the conventional phase-locked loop (PLL), which solves the problem of double-frequency disturbance in the Phase-Locked Loop mathematical model at steady state. However, there are few researches on disturbance resistance design of EPLL in complicated grid environment. Therefore, periodic disturbances of different frequencies are introduced into frequency estimation and amplitude estimation of EPLL when the grid voltage has DC offset, three-phase unbalance, high-order harmonic disturbance and sub-synchronous oscillation (SSO). This will interfere with the frequency and amplitude estimation performance of the EPLL, and then affect the closed-loop control and frequency tracking of the converter. In order to improve disturbance rejection of the EPLL. Firstly, the mathematical model of the disturbance in the frequency and amplitude loop is deduced and analyzed. Then the active disturbance rejection control (ADRC) is used to improve the EPLL. Through the simulation model of MATLAB/Simulink, the parameters of the ADRC and the ESO are compared and validated. The proposed EPLL based on ADRC is verified experimentally for the tracking performance under the frequency stability or drop in complicated power grid environment.

Modeling and Stability Assessment of Single-Phase Grid Synchronization Techniques: Linear Time-Periodic Versus Linear Time-Invariant Frameworks

The grid synchronization unit, which is often based on a phase-locked loop (PLL) or a frequency-locked loop (FLL), highly affects the power converter performance and stability, particularly under weak grid conditions. It implies that a careful stability assessment of grid synchronization techniques (GSTs) is of vital importance. This task is most often based on obtaining a linear time-invariant (LTI) model for the GST and applying standard stability tests to it. Another option is modeling and dynamics/stability assessment of GSTs in the linear time-periodic (LTP) framework, which has received a little attention. In this letter, the procedure of deriving the LTP model for single-phase GSTs is first demonstrated. The accuracy of the LTP model in predicting the GST dynamic behavior and stability is then evaluated and compared with that of the LTI one. Two well-known single-phase GSTs, i.e., the second-order generalized integrator-based FLL (SOGI-FLL) and enhanced PLL (EPLL), are considered as the case studies.