Phase-locked Loop Technique Research Articles

Magnetic force microscopy: High quality-factor two-pass mode.

Magnetic force microscopy (MFM) is a well-established technique in scanning probe microscopy that allows for the imaging of magnetic samples with a spatial resolution of tens of nm and stray fields down to the mT range. The spatial resolution and field sensitivity can be significantly improved by measuring in vacuum conditions. This improvement originates from the higher quality-factor (Q-factor) of the cantilever's oscillation in vacuum compared to ambient conditions. However, while high Q-factors are desirable as they directly enhance the magnetic measurement signal, they pose a challenge when performing standard MFM two-pass (lift) mode measurements. At high Q-factors, amplitude-based topography measurements become impossible, and the MFM phase response behaves non-linearly. Here, we present a modified two-pass mode implementation in a vacuum atomic force microscope that addresses these issues. By controlling the Q-factor in the first pass and using a phase-locked loop technique in the second pass, high Q-factor measurements in vacuum are enabled. Measuring the cantilever's frequency shift instead of the phase shift eliminates the issue of emerging nonlinearities. The improvements in MFM signal-to-noise ratio are demonstrated using a nano-patterned magnetic sample. The elimination of non-linear responses is highlighted through measurements performed on a well-characterized multilayer reference sample. Finally, we discuss a technique that avoids topography-induced artifacts by following the average sample slope. The newly developed, sensitive, and distortion-free high quality-factor two-pass mode has the potential to be widely implemented in commercial setups, facilitating high-resolution MFM measurements and advancing studies of modern magnetic materials.

Dual Second Order Generalized Integrator – Phase Locked Loop technique applied to a distorted grid-connected solar energy based on a Z-Source Inverter

In this paper, a Dual Second Order Generalized Integrator_Phase Locked Loop (DSOGI_PLL) technique applied to the Photovoltaic (PV) system supplying a Z-Source five-level Inverter (ZSI) is presented. The ZSI assures the increasing voltage of the PV system and provides the desired output DC at the input of the five-level Neutral Point Clamped Inverter (5L_NPCI), without any control which reduces the complexity of the overall system, this is due to the impedance network in its structure. We use Z-Source in order to eliminate the controlled DC bus as well as the use of the DC-DC Boost converter as an intermediary. A DSOGI technique is employed to control and optimize the energy quality, especially in distorted grid conditions and allows one to obtain a very low value of Total Harmonic Distortion (THD) which means lower peak currents, and higher efficiency. Low THD is an essential feature in power systems that international standards such as IEC 61000-3-2, and IEEE-519 set limits on the harmonic currents of various classes of power equipment connected to a distorted three-phase grid. Compared to the classic structure of inverters, the NPC five-level inverter presents a very high performance.

Performance analysis of the FB-PLL applied to real time monitoring of deep sleep brainwaves

Repose is indispensable for the human body, one of its main functions being to replenish energy. During sleep, the body's important restorative activities are performed by the organism, which is a basic human need. With awareness of the dimension that sleep represents and the need to improve its quality, the importance of monitoring in real time becomes evident. Based on this, the fast fourier transform is a technique capable of obtaining characteristics of a signal, such as its frequency, as well as being able to be applied to sleep waves. However, to have a good use, a considerable number of sample experimental cycles is necessary, which demands a certain computational effort. In this sense, this work we sought to apply the Phase-Locked Loop technique. Thus, a Fourier-based synchronization algorithm is proposed to track low-frequency brain waves during sleep. It is also worth noting that this method is capable of performing the estimates in just one cycle. Therefore, the objective is to obtain the estimated curve referring to the frequency and an efficient synchronization algorithm that is able to track deep sleep in real time.

Nonlinear MPPT techniques to control hybrid power systems

In recent years, grid-connected multifunctional photovoltaic (PV) systems have proven to be highly efficient. This system integrates PV panels with a DC–DC boost converter (DC–DC–BC) and the electrical distribution grid (DEG). Linking the PV to the AC-DEG is accomplished through a three-level multifunctional voltage source inverter (MVSI). The DC–DC–BC component in this study is engineered to perform maximum power point tracking (MPPT) irrespective of normal or abnormal conditions. The conventional MPPT technique poses several challenges and constraints on system usage. Hence, the suggestion is to adopt synergetic control (SC) and sliding mode control (SMC) to enhance the MPPT technique's performance within the proposed system framework. Moreover, predictive direct power control is applied to the MVSI-based shunt active power filter, utilizing a phase-locked loop technique to achieve multiple objectives: minimizing energy fluctuations, injecting active power, correcting power factors, compensating reactive power, and mitigating harmonic currents. To implement the proposed system, the MATLAB is used for this purpose, with several tests used to study the behavior of the controls proposed in this work. Numerical results indicate significant reductions in active and reactive power fluctuations, with estimated rates of 38.46% and 15.30%, respectively, compared to traditional strategies. Moreover, the total harmonic distortion (THD) of the source current after filtering is reduced by 31.88% under solar irradiation of G = 1000 Wm2. Before filtering, the THD of current experiences a reduction estimated at 97.65%. These findings underscore the superior performance of the proposed control technique across all evaluated aspects.

Impact of PLL and non-PLL vector current control techniques on grid connected inverter

In the micro-grids, all the Distributed Power Generation Systems (DPGS) and loads are interconnected across the Point of Common Coupling (PCC). The stability and harmonics of the grid connected inverters are significantly impacted by uncertainties in the renewable energy sources based DPGS. The performance of these grid connected inverters across the PCC depends on the Phase-Locked Loop (PLL) used to track the grid angle and power control structures used to control the power fed to grid. These power control structures can be either PLL based or PLL less systems. The PLL based Vector Current Control Direct Quadrature (VCC DQ) control and PLL less Non-PLL Vector Control (NPVC) techniques are compared along with their controller design and bode plots. Also, the small signal models of grid connected inverter with PLL are presented from which the converter impedance is derived to show the effect of PLL on the system using bode plots. The impact of the PLL based and PLL less control techniques on the grid connected inverter are presented with analytical equations along with simulation and hardware results. A 6 kW grid connected inverter simulation model and 150 W hardware prototype is developed using TI F28379D processor to compare the performance of both with and without PLL control techniques.

Study on frequency stability control strategies for microgrid based on hybrid renewable energy

The dynamic nature of renewable energy sources, such as wind and photovoltaic power generation, significantly impacts the frequency stability of microgrid systems due to their pronounced intermittency, inherent randomness, and limited output support. Despite ongoing research, a comprehensive understanding of control measures to enhance microgrid frequency stability remains lacking. This paper addresses this gap by summarizing domestic and global advancements in control strategies for microgrid frequency stability. Specifically, it examines the operating states of microgrids and associated frequency stability issues and expounds various methods for maintaining frequency stability. The paper proposes innovative control measures to enhance frequency stability, including improvements in master-slave control, droop control, phase-locked loop, and virtual synchronous generator (VSG) techniques, particularly during transitions between islanded and grid-connected modes. The findings demonstrate the effectiveness of these enhanced control strategies in maintaining frequency stability, and the paper concludes by suggesting future research directions in this field.

Synergetic control for three-level voltage source inverter-based shunt active power filter to improve power quality

The present paper proposes a synergetic control (SC) with Phase-Locked Loop (PLL) technique for a three-phase three-levels neutral point clamped-voltage source inverter-based shunt active power filter (SAPF). This one is devoted to compensating for nonlinear load harmonics and reactive power to improve power quality in distribution power systems. SC strategy is known as a robust control with good performances in transient and steady-state performance. Furthermore, it does not require solving the state equations, nor knowing the poles of the system. The DC voltage, as well as the active filter currents, are controlled using SC strategies. The efficiency of the suggested strategy has been verified through simulation tests using Matlab/Simulink software, where the simulation results are analyzed for two scenarios: a diode bridge rectifier with RL load and RC load. The active power filter demonstrated outstanding performance in reducing harmonics, maintaining a dynamic response, and tracking DC voltage for both RL and RC loads, as revealed by the simulation results. By comparing the suggested control with the traditional control, we found that the former outperforms the latter in all aspects. This sheds light on the effectiveness of the suggested control.

Implementation of Phasor Measurement Unit Based on Phase-Locked Loop Techniques: A Comprehensive Review

The dynamic monitoring, control, and protection of modern power systems in real time require time-stamped electrical measurements to accurately estimate the bus voltage phasors using the state estimation function under normal and abnormal conditions. These measurements can be acquired by time-synchronized devices, known as phasor measurement units (PMUs). PMUs can measure bus voltage and branch current phasors of a three-phase network, as well as the frequency and the rate of change of frequency (ROCOF), with high speed, accuracy and time stamping provided by global positioning system (GPS) at the coordinated universal time (UTC). Various phasor estimation algorithms have been proposed in the literature, while most of them are concentrated in the discrete Fourier transform (DFT) algorithm, where an integer number of samples multiple of the nominal frequency is required for the computations. In cases where the frequency of the power grid deviates from its nominal value, the raw application of the DFT approach can lead to large errors during phasor estimation. Another approach of the phasor estimation is based on the phase-locked loop (PLL) techniques, widely used in grid tie inverters. PLL techniques can track dynamically (continuous time) the estimated frequency to the time-variant frequency of the power grid. A brief introduction to the basic concepts of the synchrophasor definition is provided, while the main DFT methods for synchrophasor estimation according to recent literature are mentioned. PLL-based PMU techniques are reviewed for both steady-state and dynamic conditions according to IEEE standards. In conclusion, the performance of PLL-based PMU algorithms presented in this literature review is discussed.

Short-pulse frequency stabilization of a MW-class ECRH gyrotron at W7-X for CTS diagnostic

At the Wendelstein 7-X stellarator, a 174 GHz Collective Thomson Scattering (CTS) diagnostic will be implemented. One of the 140 GHz Electron Cyclotron Resonance Heating (ECRH) gyrotrons will be operated at around 174 GHz in a higher cavity mode, using it as source for the CTS mm-wave probing beam. To prevent any damage to the CTS receiver, a notch filter cuts out the high-power gyrotron signal at the entrance of the receiver. The bandwidth of the gyrotron signal determines the notch filter bandwidth. First proof-of-principle experiments on frequency stabilization were conducted on W7-X ECRH gyrotrons employing Phase-Locked Loop techniques. The gyrotron output frequency was controlled with the accelerating voltage, which is applied between the anode and cathode of the gyrotron diode-type Magnetron Injection Gun. Frequency stabilization experiments with 10 ms pulses were conducted at the gyrotron nominal frequency of 140 GHz as well as at 174 GHz. It is concluded that the gyrotron frequency could be stabilized for at least 3 ms at 140 GHz and 8 ms at 174 GHz. In the frequency spectrum, a clear main peak of the gyrotron frequency at 140 GHz with a full -15 dB linewidth of below 500 Hz was achieved.

Synchronized time lens based temporal magnifier assisted by the phase lock loop.

We propose a synchronized time lens based temporal magnifier for the characterization of an ultrafast pulse, which is assisted by the phase lock loop (PLL) to actively lock the repetition rates of the pump laser and signal laser. A feedback control system combining a proportional-integral (PI) circuit and a piezoelectric transducer (PZT) inside the signal laser cavity is used to synchronize the repetition rates between the pump and signal lights. Benefitting from the PLL technique, the temporal position of the signal pulse remains as the numerical aperture of the time lens system, and therefore it has a high short-time stability for pulse measurement. This synchronized time lens based temporal magnifier can record single-shot pulses within continuous round trips. By engineering the dispersion of the pump, signal, and idler lights, we demonstrate a 200× magnification of the signal pulse. Our technique offers a simple synchronized method in a time lens system for ultrafast temporal characterization, which provides new insights into the observation of the fiber laser dynamics.

Direct Power Control for Three-Level Multifunctional Voltage Source Inverter of PV Systems Using a Simplified Super-Twisting Algorithm

This study proposes a simplified super-twisting algorithm (SSTA) control strategy for improving the power quality of grid-connected photovoltaic (PV) power systems. Some quality issues are considered in this study including the power factor, reducing the total harmonic distortion (THD) of current, compensating the reactive power, and injecting at the same time the energy supplied by the PV system into the grid considering non-linear load. This improvement is achieved by two topologies; controlling both the boost DC–DC converter and the DC–AC inverter that links the PV system to the grid. The DC–DC converter is controlled using proportional-integral (PI) and SSTA to maximize the power generated from the PV panel regardless of its normal and abnormal conditions, while the DC–AC inverter is employed to direct power control strategy with modified space vector modulation using the phase-locked loop (PLL) technique of a three-level neutral-point-clamped (NPC) inverter based on the proposed strategies (PI and SSTA). In addition, a shunt active power filter (SAPF) is used to connect the PV system to the AC grid and feed a non-linear load. To validate the simulation results presented in this paper using Matlab software, a comparative study between the PI controller and the SSTA is presented. The results show the effectiveness and moderation of the suggested SSTA technique in terms of feasibility, tracking performance, less power ripple, dynamic response, THD value, overshoot, steady-state error, and robustness under varying irradiation, temperature, and non-linear conditions.

A New Control for Improving the Power Quality Generated by a Three-Level T-Type Inverter

A new controller based on a fractional-order synergetic controller (FOSC) is proposed for a three-level T-type inverter using a shunt active power filter (SAPF). The SAPF is designed to compensate for the reactive power and eliminate the current harmonics caused by non-linear loads, in cases of distorted or unbalanced source voltages. The proposed FOSC technique with the designed parameters and defined macro-variable is a robust control technique that operates well in both transient and steady-state scenarios, ensuring fast convergence and closed-loop system stability. The FOSC technique utilizes a phase-locked loop (PLL) technique on a self-tuning filter (STF) to enhance the SAPF’s ability to compensate current harmonics and reactive power in all situations involving non-linear loads and source voltage variations according to IEEE Std. 519. The proposed control was implemented and verified using Matlab software, where the obtained results were compared with the results of the conventional control based on proportional-integral (PI) controllers in different operating conditions. The results indicate that the proposed FOSC technique outperformed the traditional control in terms of DC voltage tracking and the minimization of the total harmonic distortion of the current.

A mode switching based transient ride‐through phase‐locked loop

AbstractIn the case of grid voltage quality problems, the traditional phase‐locked loop (PLL) is hard to detect the accurate grid frequency and phase during the transient response, which will be detrimental to the transient synchronous stability of grid‐connected inverters. This paper proposes a mode switching based transient ride‐through PLL (TRT‐PLL), aiming to improve the transient phase‐locking performance through detection technique and mode switching. The TRT‐PLL incorporates a hybrid filter (HF), a dual‐speed detection module, and a state switch into the traditional synchronous reference frame PLL (SRF‐PLL) structure. The theoretical analysis and paradigm design of TRT‐PLL is presented in detail. Digital simulations and physical experiments are carried out for the comparisons with other existed PLL techniques. The results demonstrate that the satisfied transient performance of the TRT‐PLL has significant advantages, especially in the event of phase jumps.

Solar, Wind and Their Hybridization Integration for Multi-Machine Power System Oscillation Controllers Optimization: A Review

Massive growth in global electrical energy demand has necessitated a genuine exploration and integration of solar and wind energy into the electrical power mix. This incorporation goes a long way in improving the cumulative generated power capacity of the power system. However, wind and solar photovoltaic (PV) are intermittent in nature, making the provisioning of a good maximum power tracking (MPPT) scheme necessary. Furthermore, the integration is characterized by synchronization challenges and introduces various modes of power system oscillations as it is converter-driven. This greatly affects the overall stability of the integrated power mix. Consequently, various technological models have been designed to address these challenges ranging from MPPT schemes, phase-lock loop (PLL), virtual synchronous generator (VSG), power system stabilizers (PSS), flexible AC transmission system (FACTS), coordinated control and artificial intelligence (AI). In this work, a multi-machine power system model is reviewed for integration stability studies. Various technical solutions associated with the integration are also reviewed. MPPT, PLL, VSG, PSS, FACTS, coordinated control, and various optimization technique schemes used for damping controller design are discussed.

A Robust Control for Solar and SyRG Based Hydro Generation Microgrid With Grid Synchronization

The control of a microgrid is quite challenging thus this work implements a robust and fast control technique based on an enhanced second-order generalized integrator with a modified frequency locked loop (ESOGI-MFLL) for switching operation between an islanded and the grid-connected mode. For phase angle estimation, a circular limited cycle oscillator frequency locked loop with an inner loop filter (CLO-FLL-WIF) is implemented instead of a conventional phase-locked loop technique to provide better synchronization performance for polluted grid voltages. This microgrid is combing a solar photovoltaic (PV) generation, a synchronous reluctance generator for pico-hydro generation, and the battery, which works in both standalone and grid-connected modes while feeding local loads uninterruptedly. The output power conversion of a PV array is influenced by irradiation of the solar PV array; therefore, a maximum power point tracking namely an incremental conductance method is used. The implemented control techniques are used for fundamental extraction of load components of voltage and currents for assessment of reference currents with their respective phases of synchronization while maintaining the required IEEE power quality standard-519. In addition, the comparative results validate the faster response of ESOGI-MFLL control algorithm to the existing control algorithm. Simulated and test results of a microgrid for islanded, switching mode, and grid-connected mode demonstrate its performance under load unbalance and generation perturbation.

Leveraging half-cycle orthogonal signal generation approach for PLL-less tracking of single-phase grid parameters

This article presents a fast and accurate single-phase grid voltage parameter tracking scheme under distorted grid voltage conditions. The input stage of the proposed scheme consists of a half-cycle moving-window discrete Fourier transform (HC-MWDFT) based pre-filter, whose design guidelines are discussed in the viewpoint of its stability and orthogonal signal generation. Combining a positive feed-forward comb filter and a fractional complex resonator helps to attenuate odd-order harmonics and allows fast extraction of fundamental components. Unlike the phase-locked loop (PLL) techniques, the grid frequency is indirectly estimated using a simple open-loop frequency detector. The proposed method is free from tedious controller tuning aspects and can avoid external phase/frequency feedback loops. The amplitude and phase information are adaptive to the grid frequency by employing a simple linear regression-based error correction technique. The overall efficacy of the proposed algorithm is assessed using numerical and experimental methods.

Current harmonic reduction for grid-connected photovoltaic system (PV) based on improved control of three-phase seven-level PUC inverter

In this article, we have improved the control for three-phase of packed U-Cell seven-level inverter, the latter considered as a new multilevel converter topology and has the advantage of very high energy efficiency, and the number of components reduced but has disadvantages related to the harmonics injected into the grid causing switching states if the number of levels increased. In this paper, an improved control based on the sinusoidal control (SPWM), and space vector control (SVPWM) has been proposed for the seven-level packed PUC-Cell inverter. The Proportional resonant (PR) controllers are implemented to adjust the grid currents in the synchronous DQ frame and to maintain synchronism between the inverter and the grid, a Phase-locked loop technique (PLL) can be used. This control is composed of two regulation loops the first allows for regulation of the active and reactive currents delivered to the grid and the second regulates the DC voltage. The evaluation of our results obtained is based on the value of the total harmonic distortion obtained (THD ≪ 5 % of the international standard). This control strategy eliminates current harmonics, improves the quality of power delivered into the grid from the photovoltaic system. An analysis and comparison between this seven-level PUC-cell inverter structure, and the conventional seven-level cascade inverter structure is done, and the simulation results in Matlab/Simulink demonstrate the effectiveness and feasibility of the proposed control method.

GNLMP Control for Solar PV-Battery Based Microgrid With Ms-EPLL Synchronization

Solar photovoltaic (SPV)-based microgrid systems have established themselves as the novel clean and green solution to climate change. Thus, research is oriented toward a viable and universal solution to renewable energy based power generation. Though much progress is made in this frontier, there are still specific problems in the conventional control approach. Set-point controllers, an easy choice for control architecture, fail to satisfy the intermittent natured SPV source, compelling to look for a dynamic gain tuning technique to overcome stability margin issues. In this article, a graph signal processing least mean <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> th (GNLMP) adaptive current control method is introduced, which is computationally fast, robust, and improves the power quality (PQ) of the injected utility current. A microgrid, by definition, must possess the facility to work in an islanded mode to supply local commodities whenever there is a utility outage or utility faults and resynchronizes to the utility when the grid codes are in match according to the IEEE-519 std. Synchronization is demonstrated here using a more stable enhanced phase-locked loop (Ms-EPLL) technique, a modified version of EPLL. The PLL technique is more stable than EPLL by adding nonlinear term in each of phase and amplitude line. The GNLMP current control and Ms-EPLL synchronization technique are verified for acceptable steady-state and dynamic behavior via tests performed on an experimental setup. Seamless transfer synchronization and meeting PQ as the IEEE-519 std., i.e., total harmonic distortion <5%, are the significant outcome of this article.

PI-based PLL and 24-sector control of a 3P-3L-NPC inverter for grid-tied PV system synchronization

This article addresses one of the most serious issues in electricity: frequency and voltage anomalies. Actually, because renewable energy production is intermittent, the frequency and voltage of electricity produced are unstable and dependent on weather conditions. This issue causes industrial processes to fail, affecting the quality of the electrical supply and having a massive economic impact. Power electronics inverters are designed to compensate for system fluctuations in solar power generation. However, measurement noise in the grid voltage desynchronizes the inverter and network signals. The authors propose using a phase-locked loop technique based on inverter period control and a network voltage observer to achieve such synchronization of grid-connected photovoltaic (PV) systems. In this work, the grid integration of the PV system is carried out through a three-phase three-level neutral point clamped inverter due to better current quality with fewer harmonics and lower stress voltage of the inverter's components when compared to two-level voltage source inverters. The method is successfully applied in a simulated case study and experimental results validate it.

Phase locked-loop with decaying DC transient removal for three-phase grids

Frequency and phase of the power grid, which are critical for reliable control and protection of grid-tied devices, are generally detected by the closed-loop phase locked-loop (PLL). In highly inductive high-voltage transmission systems, decaying DC (DDC) components with large amplitude can be easily introduced by load disturbances and/or grid abnormalities, leading to severe performance degradation of the PLL during the transient. Focusing on this issue, in this paper, modifications to the conventional synchronous reference frame (SRF)-PLL have been made to address the short-term disturbances including the DDC component, and the system operation is divided into the normal state and the DDC-transient state. The SRF-PLL is only adopted for the normal state where the DDC component is negligible. In the presence of a significant DDC component, as well as disturbances including negative-/zero-sequence components and harmonics, the weak effectiveness of the conventional SRF-PLL is proved, and an efficient DDC component extraction method, with a detection time of 0.5 grid cycle, is introduced for the three-phase system. The real-time amplitude and phase of the positive-sequence component can be efficiently extracted via the proposed scheme, by exploiting the transient signal properties in the dq-frame and assuming a constant grid frequency during the short transient. Finally, a proper design of switching logic has been proposed to allow for the fast and precise transition between the normal and the DDC-transient state, thereby ensuring high steady-state accuracy as well as short-term DDC transient immunity. Hardware-in-the-loop based experiments have been used to verify the effectiveness of the proposed PLL technique.