Second-order Generalized Integrator Phase-locked Loop Research Articles

Application and practice of portable bi-directional DC-AC energy storage converter based on second order generalized integrator phase-locked loop and HERIC circuit

In various industries, including the production of new energy and electric vehicles, portable bidirectional converters are crucial for enhancing power supply reliability. In recent years, these converters have become increasingly normal in daily life. Bidirectional converters have not been as popular or have not been used as much due to issues with phase tracking on grids connected to leakage current in the converter system. The essential features and principles of the portable bidirectional energy storage converter proposed in this paper, which is based on a second-order generalized integrator phase-locked loop, are theoretically investigated. Formulas are also generated using small signals to address this issue. PLECS simulation software was used for parameter design and algorithm simulation to test the effectiveness of the phase-locked loop under various operating situations. Therefore, a set of appropriate phase-locked structure models for this circuit was developed. An experimental verification platform was constructed to confirm the accuracy of the design parameters: the front stage uses the H-bridge; the backstage, which uses the front stage, adopts the H-bridge; and the rear stage adopts the topology platform of the HERIC topology + LCL filter circuit. The test data indicates that, the addition of the HERIC topology and soft switching resulted in a 94 % reduction in leakage current and a 1.6 % improvement in efficiency. Analysis and comparison results of the test data confirmed the consistency between the experimental effect and the design parameters, achieving the expected effect and proving the accuracy of the topology and mathematical model. The design methodology and design parameters of this thesis are useful and instructive for similar or related research.

An improved derivative‐based phase‐locked loop for single‐phase grid synchronization under abnormal grid conditions

SummaryGenerating a quadrature signal in a single‐phase system using a second‐order generalized integrator (SOGI) requires accurate frequency information. The standard SOGI phase‐locked loop (PLL) includes frequency feedback to the SOGI. However, during grid abnormalities such as voltage sag/swell and phase angle jumps, the SOGI‐PLL faces frequency disturbances that propagate to the phase detector (PD) and affects the quadrature signal generator (QSG). Furthermore, the SOGI‐PLL having two loops dependent on each other creates loop coupling phenomena; either a change in phase or frequency affects each other. SOGI‐PLL is tuning sensitive, as the SOGI block has a gain that needs to be adjusted, increases the complexity, and affects the performance of the system. There is a trade‐off between SOGI gain and PLL parameters that needs to be considered for adequate parameter design to provide accurate grid synchronization while maintaining the stability of the system. To attain better performance, researchers have proposed derivative‐based PLL (DPLL). The conventional DPLL faces challenges to noise and harmonics amplification. This paper presents an improved DPLL for single‐phase grid synchronization under adverse grid conditions. The improved derivative‐based PLL (IDPLL) comprises two improved derivative‐based quadrature signal generator (IDQSG) blocks to extract the phase‐error information for accurately estimating phase and frequency. The detailed mathematical modeling and bode plot for the IDQSG and IDPLL are presented. The proposed IDQSG eliminates the requirement of gain tuning, hence reducing complexity. Moreover, there is no interdependent loop in the IDPLL, which significantly improves the dynamic performance. A hardware setup is developed to evaluate the performance of the system in real‐time. The experimental results are obtained using an field programmable gate array (FPGA)‐based controller.

Mechanistic comparison between Phase-Locked loop and reactive power-based synchronization for the grid connected converters under a weak grid

For grid-connected converters (GCC), the synchronization unit (SU) is indispensable for the vector current control (VCC). Usually, the phase-locked loop (PLL) is employed as SU. However, PLL could introduce negative resistance contributing to potential instability issues. Thus, the second-order generalized integrator PLL (SOGI-PLL) and the reactive power-based synchronization method (RPS) are proposed to enhance the stability. Nevertheless, the intrinsic reason why RPS enhances stability is not clear. Therefore, a detailed comparative analysis among PLL, SOGI-PLL, and RPS is presented in this paper to reveal the mechanism of this stability enhancement. Firstly, an admittance model is derived to analyze the differences between these three synchronization methods. However, it is not intuitive enough to explain the detailed mechanism. Then, a SISO model containing the current controller, physical circuit, and synchronization unit is developed, which is established on the relationship between power and angle. According to this SISO model, it is revealed that the presence of the gain spike introduced by PLL and SOGI-PLL leads to instability. RPS avoids these issues due to its introducing current information for phase margin enhancement and its lower-order structure. Finally, the validity of the mathematical analysis and derived models are verified by experimental results.

Impedance-Based Stability Analysis of Grid-Connected Inverters under the Unbalanced Grid Condition

As a common interface circuit for renewable energy integrated into the power grid, the inverter is prone to work under a three-phase unbalanced weak grid. In this paper, the instability of grid-connected inverters under the unbalanced grid condition is investigated. First, a dual second-order generalized integrator phase-locked loop (DSOGI-PLL)-based inverter under balanced and unbalanced conditions is modeled. A fourth-order impedance model is established to describe its impedance characteristics under the unbalanced grid condition. To analyze this multi-input multi-output system, a simplified stability analysis method based on the generalized Nyquist stability criterion and matrix theory is proposed. Then, the influences of circuit and control parameters on the stability of the grid-connected inverter system under the unbalanced grid condition are investigated. Finally, the accuracy of the derived frequency-coupled impedance model is verified via simulations, and the effectiveness of the proposed simplified stability analysis method on the system stability analysis is verified via both simulations and hardware experiments.

Control for Power Quality Improvement of Solar Photovoltaic-Distributed Static Synchronous Compensator Interfaced with Weak Grid Using Multi-Variable Filter Dual Second-Order Generalized Integrator Phase-Locked Loop

This study proposes a control method for transferring power generated by a solar photovoltaic system. The control algorithm, called MVF-DSOGI-PLL or Multi-Variable Filter Dual Second-Order Generalized Integrator Phase-Locked Loop), accurately estimates symmetrical components, phase angle, and positive sequence voltages of the Common Point of Interface (CPI) in distorted grid conditions. The approach creates a compensatory current to reduce PQ difficulties by extracting the size of the basic current load undergoing operation employing the SOGI method. These systems can operate in either modes of PV-DSTATCOM or DSTATCOM, depending on solar insolation’s availability. The simulation models of the grid-interfaced SPV systems are developed in Matlab/Simulink to evaluate the performances of the suggested control method. The results of simulation demonstrate that the suggested control systems efficiently transfers the power generated by PV arrays to a grid while performing tasks like load balancing, power factor correction (PFC), and harmonics reduction. Furthermore, the MVF-DSOGI-PLL-based control algorithm successfully mitigates PQ issues in distribution networks with weak grids, ensuring that PQ levels remain between a limited set by the IEEE-519 standard. A laboratory prototype of the proposed system is implemented to assess its steady states and dynamic efficient under fluctuating solar insolation, and load imbalance distortions.

FFDSOGI-PLL-based DSTATCOM for Power Quality Enhancement

This paper proposes a control technique based on a frequency-fixed dual second-order generalized integrator phase-locked loop (FFDSOGI-PLL) for a Distribution Static Compensator (DSTATCOM). The goal is to mitigate power-quality (PQ) issues in a three-phase distribution network with a weak grid. The phase angle, symmetrical components, and positive sequence of supply voltages were estimated using the FFDSOGI-PLL even in a polluted grid environment. The active component magnitude of the fundamental load current was extracted using SOGI, which also reduces the PQ issues by generating compensating current. The effectiveness of the proposed FFDSOGI-PLL-based DSTATCOM was verified for functions like load balancing, power factor correction (PFC), harmonics reduction, etc. This was done in MATLAB/SIMULINK under steadystate and dynamic conditions. The simulation results show that the FFDSOGI-PLL-based control algorithm has faster convergence and quick dynamic response. Hence, the DSTATCOM performance is satisfactory for mitigating PQ issues with the FFDSOGI-PLL-based control technique.

Simulation Research on Phase Locking Technology Based on Modified DSOGI-PLL

Abstract For complex working conditions in power grid, it is easy to produce a large number of harmonics, and the double second-order generalized integrator phase-locked loop (DSOGI-PLL) cannot effectively suppress low-order harmonics, a new DSOGI-PLL based on modified sequential cascaded harmonic cancellation module is proposed in this paper. By designing a harmonic cancellation module that eliminates specific frequency harmonics, different frequency harmonic cancellation modules are cascaded in order from small to large to eliminate low frequency harmonics near the basic frequency. By building the simulation model, the comparison analysis verifies that the modified DSOGI-PLL has higher accuracy in tracking the frequency and phase of the voltage signal, and is more suitable for the power grid.

Analysis of modified plug-in electric vehicle charger controller with grid support functionalities.

Power quality issues, which are mainly due to power electronic devices that are invariably used not only in domestic sector but also industries, still persist despite various mitigation strategies. The slow but steady invasion of Electric vehicles or Plug-in Electric Vehicles (PEVs) in recent years, in the automobile sector, adds woes to the power quality issues further. Majority of the charging systems presently available for charging PEVs are unidirectional and so supports Grid to Vehicle (G2V) mode only as the bidirectional integration of those vehicles into the grid is still a big challenge. However, Vehicle to Grid (V2G) support mode also deserves an equal importance as the PEV charger with V2G mode of operation is capable of supporting grid functionalities also, on need basis, which largely depends on the power circuit topology and controller topology it uses. Hence, in this work an improved controller topology has been designed and developed to alleviate the burdens on the grid. Support for active power demand, voltage swell and sag mitigation, in addition to catering its prime objective of charging the batteries are focused. A Second Order Generalized Integrator Phase Locked Loop (SOGI-PLL) based controller has been developed and implemented in the proposed work to improve the transient response, apart from controlling the steady-state oscillations of the grid to which it is connected to. A single phase non-isolated bidirectional PEV charger with proposed control topology has been simulated in MATLAB-Simulink for vehicle support and grid support mode of operations. The simulation proves the satisfactory operation of the proposed charger in the four quarters of active power and reactive power (PQ) plane, thus complies the design objectives of bidirectional power flow. The results obtained from the simulation show improved performance in terms of DC link voltage overshoot, steady-state oscillations, overall efficiency, voltage and current Total Harmonic Distortions (THD)

Enhanced Frequency Adaptive Demodulation Technique for Grid-Connected Converters

This article presents an enhanced frequency adaptive demodulation technique for grid-synchronization of grid-connected converters in variable frequency condition. Demodulation works by generating demodulated voltages which contain undesired double frequency components. As a result, high-order low-pass filters with high cutoff frequency are required to eliminate the undesired components. This reduces the dynamic performance. Frequency adaptive demodulation technique enhances the dynamic performance by rejecting the double frequency components as opposed to filtering, however, at the cost of additional computational complexity. This article overcomes this problem by using double demodulation without recreating the double frequency component for rejection purposes. This reduces the computational complexity significantly. Suitability of the proposed method is verified through numerical simulation and experimental study. Comparative study with existing frequency adaptive demodulation and second-order generalized integrator phase-locked loop techniques demonstrate the validity and performance improvement by the proposed technique.

Modeling and frequency characteristic analysis of DSOGI-PLL in dq reference frame

Dual second-order generalized integrator phase-locked loop (DSOGI-PLL) is widely used in grid-connected system for grid synchronization because of its simple implementation and good filtering capability. However, the frequency characteristics of DSOGI-PLL affect the impedance modeling of the system, which in turn affect the impedance-based stability analysis. In order to improve the accuracy of system modeling, in this paper, the equivalent transfer function of positive-sequence calculator (PSC) block constructed in αβ reference frame in DSOGI-PLL is presented in dq reference frame, where the relationship between DSOGI-PLL and traditional synchronous reference frame PLL (SRF-PLL) small-signal model is investigated. Then, based on the established model, DSOGI-PLL and SRF-PLL are compared from the tracking characteristics and robustness characteristics. It is further demonstrated that DSOGI-PLL is able to improve the robustness performance of PLL while maintaining the same tracking performance as SRF-PLL. Finally, simulation results are presented to validate the established model and frequency characteristic analysis.

A Type-3 Modified SOGI-PLL With Grid Disturbance Rejection Capability for Single-Phase Grid-Tied Converters

This article presents a type-3 second-order generalized integrator phase-locked loop (SOGI-PLL) algorithm for single-phase system. Disturbances, such as dc offset and harmonics, are present in the practical grid voltages, due to occurrence of faults, sensors, and analog-to-digital converters. The type-3 SOGI-PLL exhibits fast dynamic performance with gain and phase-lead compensation. However, the general type-3 SOGI-PLL introduces fundamental frequency oscillations in the estimated quantities at the output, when grid voltage contains disturbances. The incorporation of filters for suppression of frequency oscillations, due to dc offset, reduces the bandwidth of PLL, which affects the dynamic response of PLL by introducing phase delay. Thus, a modified notch-filter SOGI (MNF-SOGI) based type-3 SOGI-PLL is proposed with frequency adaptive control to eliminate the phase error, without affecting the dynamic performance. A detailed analysis is presented on the effect of dc offset and scaling error. To enhance dynamic response, filtering, and stability designed guideline based on settling time is also discussed. The proposed type-3 MNF-SOGI-PLL has better grid parameter estimation and fast response with inherent dc offset rejection capability. The effectiveness of the proposed type-3 MNF-SOGI-PLL is evaluated under various grid disturbance conditions and experimentally verified.

A novel method of insulation parameters measurement based on hybrid flexible arc suppression device in distribution networks

As one kind of active arc suppression devices, the hybrid flexible arc suppression device (HFASD) with current-based arc suppression method can eliminate the ground-fault current during the single-line-to-ground (SLG) fault. One of the most important aspects for current-based arc suppression method is the insulation parameters measurement. The reference current of current-based arc suppression method is calculated by the insulation parameters, including the ground capacitance and ground leakage conductance. For the sake of obtaining high-precision reference current of current-based arc suppression method, the insulation parameters should be measured accurately. However, the most of existing methods of insulation parameters measurement should increase the additional device cost and measure inaccurately. In this paper, HFASD based on second-order generalized integrator phase-locked loop (SOGI-PLL) algorithm and twice injection current method is proposed to measure the insulation parameters under the normal condition of distribution networks. The simulation and experimental results verify the effectiveness of the proposed method under different influence factors.

An Enhanced Frequency-Adaptive Single-Phase Grid Synchronization Technique

Second-order generalized integrator phase-locked loop (SOGIPLL) relies on the frequency feedback from the PLL estimation. The frequency is used to generate the equivalent in-phase and in-quadrature signals of the single-phase grid voltage. The phase-angle-coupled frequency feedback makes the SOGIPLL structure vulnerable to various grid voltage transients such as voltage sag, phase-angle jumps (PAJs), and frequency variations. This article proposes a PLL independent frequency estimation technique. It estimates the frequency using the simplified teager energy operation on the normalized in-phase voltage component output of the SOGI. The phase-angle is estimated using the third-order polynomial approximated arctangent function on the in-phase and in-quadrature outputs of the proposed frequency-adaptive SOGI. The grid synchronization technique presented in this work avoids the use of any trigonometric operations and PLL gain tuning issues. Additionally, the impact of steady-state grid disturbances, namely, harmonics and dc offset on the proposed synchronization technique is investigated. Finally, its performance robustness is compared with other techniques during both grid transients and steady-state disturbances using both simulation analysis and experimental validation.

DSOGI-PLL With In-Loop Filter Based Solar Grid Interfaced System for Alleviating Power Quality Problems

This article deals with a dual second-order generalized integrator phase-locked loop (DSOGI-PLL) with in-loop filter-based control approach for a single-stage, three-phase three-wire solar-grid-interfaced system under abnormal grid voltage conditions, unbalanced load conditions, and varying solar insolation levels. The DSOGI with in-loop filter algorithm with enhanced filtering capability, employed for both voltages and currents, helps to attenuate the harmonics, eliminates dc offset, and estimates the sequence components. This algorithm elicits the fundamental component of highly nonlinear load current required for calculating the reference magnitude of the grid currents. Even during unbalanced load conditions, these fundamental components of currents are free from the dc offset and dominant harmonics of double frequency. In order to maintain the sinusoidal and balanced grid currents, the positive sequence voltages are estimated to get the accurate unit templates during the unbalanced and abnormal grid voltages conditions. Moreover, these positive sequence voltages are used by PLL to compute the phase required for the magnitude and the angle calculation of the currents and voltages. The dc-link voltage is maintained at maximum power point by an incremental conductance based technique. This system is simulated in MATLAB/Simulink environment. Test results on a developed laboratory prototype are observed in accordance with the standard of the IEEE-519.

Linear Kalman Filter-Based Grid Synchronization Technique: An Alternative Implementation

Grid synchronization techniques play a significant role in integrating renewable energy sources to the electric power grid. In this context, estimating the phase and frequency of the grid voltage signal is an interesting problem. Out of various techniques available in the literature, linear Kalman filter (LKF) is one of the most popular one. In this article, we propose an alternative implementation of the LKF for grid synchronization application. The proposed implementation uses a linear parametric model of the grid voltage signal including dc offset. It does not involve any quadrature signal generation, rather it works by estimating the phase angle. This helps to estimate the unknown grid frequency directly from the phase angle. This clearly differentiates the proposed alternative implementation with respect to the existing implementations. Performance improvement by the proposed technique is verified extensively through comparative numerical simulation and experimental studies. Comparative results demonstrate the suitability of the proposed technique with respect to other state-of-the-art techniques namely second-order generalized integrator phase-locked loop and enhanced phase-locked loop.

A Three-Sample-Based PLL-Less Hysteresis Current Control and Stability Analysis of a Single-Phase Active Distribution System

This article proposes a computationally simple strategy by using a three-sample-based technique for a grid-connected inverter in a single-phase active distribution system. The proposed control is to improve the performance during varying grid conditions such as voltage sag, swell, and frequency swing. A comparative analysis between the proposed controller and the conventional second-order generalized integrator phase-locked loop (PLL) based controller for dynamic grid conditions in weak-grid scenario has been presented. Additionally, a frequency domain analysis via describing function method is used to model the dynamics of nonlinear hysteresis current controller to analyze the closed-loop stability of the system. Further validation of the proposed control algorithm is simulated in MATLAB/SIMULINK environment for various scenarios. To establish the effectiveness of the proposed approach in real time, the proposed control strategy is tested in a 1 kVA based experimental setup.

Single-phase flexible arc suppression device based on BSC-SOGI-PLL method for distribution networks

The single line-to-ground (SLG) fault is a research focus, considering it is amongst the top frequent occurrences of faults in distribution systems. The neutral point treatment is crucial for continuous safe operation of distribution systems. However, the traditional arc suppression coil cannot compensate for the active component in ground current. Therefore, we present a single-phase flexible arc suppression device (SFASD) based on backstepping control and second-order generalized integrator phase-locked loop (BSC-SOGI-PLL) method. The SFASD with a cascaded H-bridge (CHB) topology is connected to the neutral point of distribution systems for eliminating the ground current. The comparisons between the BSC-SOGI-PLL and the BSC method concerning the effect of arc suppression are discussed. The effectiveness of the proposed SFASD based on the BSC-SOGI-PLL components for arc suppression is verified on the scale-down experimental platform.

Gain normalized adaptive observer for three-phase system

This paper proposes the estimation of parameters and symmetrical components of unbalanced grid using adaptive observer framework. Recent adaptive observers proposed in the literature doesn’t employ any gain normalization in their frequency estimation loop. This can be problematic in the presence of large voltage dip. This paper proposes a solution to overcome this limitation using a novel gain normalized - frequency-locked loop (GN-FLL). Technical details of GN-FLL, stability analysis and tuning are provided in this paper. Comparative experimental results with adaptive Luenberger observer, second-order generalized integrator - phase-locked loop (SOGI-PLL) and enhanced PLL (EPLL) are provided to demonstrate the effectiveness the proposed technique in the single-phase case. Comparative experimental results with double SOGI-FLL (DSOGI-FLL) and adaptive notch filter (ANF) are provided to demonstrate the effectiveness the proposed technique in the three-phase case.

Decoupled Power Control With Indepth Analysis of Single-Phase Electric Springs

Electric spring (ES) as a new effective way to solve the power quality issues caused by the uncertainty of wind and photovoltaic (PV) power, has the advantages of small volume, flexible configuration and low cost. Aiming at improving the dynamic responses of the existing power control for ES-2, a new control with in-depth analysis on the decoupling of the active and reactive powers is proposed in this paper. By introducing second order generalized integrator phase locked loop (SOGI-PLL) and fictitious-axis emulator (FAE) into the control algorithm, the virtual orthogonal voltage and current signals were constructed and the mathematic model of ES-2 in the dq axis synchronous rotating reference frame was established. Then, the control system consisting of three closed loops, namely active power loop, current loop and ES voltage loop, is arranged. Among the three loops, a damped proportional resonance (PR) controller is adopted in the ES voltage loop to ensure the accurate control of the output voltage of ES-2. Instead, traditional PI controllers are used for the current and power loops. Finally, the effectiveness of the proposed decoupled power control is validated by both simulation and experimental results.

Robust Normalized Mixed-Norm Adaptive Control Scheme for PQ Improvement at PCC of a Remotely Located Wind–Solar PV-BES Microgrid

The energy poverty in rural areas is due to the intermittent power supply from the existing utility. The proposed remotely located wind–solar photovoltaic array and battery energy storage (BES) supported microgrid, intends to overcome the uncertainty of the renewable power generation by compensating power quality (PQ) disturbances at the point of common coupling (PCC). Robust normalized mixed norm (RNMN) adaptive algorithm filters the load current component to remove the harmonics pertaining due to nonlinear load currents and improves the voltage profile at PCC. It allows the connection of sensitive loads without affecting their life and applicability at PCC. RNMN algorithm provides enhanced convergence rate as well as it reduces the steady-state error effectively. BES controlled by a bidirectional dc–dc converter ensures power supply to the critical loads during scarce generation by renewables resources. Proportional resonant controller provides superior performance over conventional proportional integral controller while dealing with the sinusoidal signals. Rejection of dc offset with effective harmonics elimination is provided by the improved second-order generalized integrator phase-locked loop. The speed regulation of the synchronous generator driven by a wind turbine is achieved by a sensorless field-oriented control technique. The maximum power point of each renewable resource is attained by individual implementation of perturb and observe scheme. The power sustainability is provided to the limited reach microgrid while overcoming the issues of load curtailment and PQ. Test results obtained on a developed prototype demonstrate the applicability of the control algorithms promising solution in controlling the intermittency and fluctuations related complex issues faced by the remotely located microgrid.