Frequency Ramp Research Articles

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.

Hybrid Feedforward Single-Phase Phase-Locked Loop for Accurate Measurement Offset Rejection and Frequency–Ramp Tracking

Hybrid Feedforward Single-Phase Phase-Locked Loop for Accurate Measurement Offset Rejection and Frequency–Ramp Tracking

A Low-Cost Test Platform for Performance Analysis of Phasor Measurement Units

In this paper, a customizable low-cost voltage waveform generator based on a real-time desktop PC and embedded data acquisition card synchronized with Coordinated Universal Time (UTC) is presented. A software approach to phase-locked loop synchronization with an external Global Positioning System (GPS) pulse signal is utilized to achieve a time uncertainty of ±1μs. This avoids expensive hardware modules for synchronization and timing purposes, which are commonly presented in literature. Besides the application for controlling the test platform, our own phasor data concentrator (PDC) application is running concurrently on the host PC. The latter is used for collecting and comparing the syncrophasor data from the test platform against the syncrophasor data measured by phasor measurement units (PMUs) under the test. The paper describes all procedures for generating reference test signals. Numerous case studies were performed, and experimental results for steady-state compliance as well as frequency ramp and phase modulation tests for dynamic compliance are presented in detail. All tests confirm that customizable test platform meets the requirements of IEEE/IEC standards. Compared to other calibrators, the cost as well as the specifications and point-by-point concept of data processing makes the described test platform suitable for performance analysis of PMU algorithms implemented on various development boards.

Single-Phase SOGI-PLLs for Fast and Accurate Frequency Ramp Tracking

Single-Phase SOGI-PLLs for Fast and Accurate Frequency Ramp Tracking

Study on Resonance Phenomenon Caused by Voltage Fluctuation of Power Supply in JT-60SA EF Coil

For the large research Tokamak JT-60SA, evaluating the withstand voltage between conductors is one of the most critical factors for the coil design. The power supply feeding the coil injects a wide spectrum of frequency components. The transient response and resonance phenomena induce a non-uniform voltage distribution in the coil. The transiently concentrated voltage can cause the insulation breakdown between conductors, and JT-60SA may not be able to operate safely. This study conducted an impulse test to evaluate the withstand voltage between adjacent conductors for an equilibrium field (EF) coil. The actual power supply voltage for the EF coil was measured to investigate the ramp rate (dv/dt) and frequency spectrum. In addition, based on the results of a resonance test of the EF dummy coil, a circuit simulation model for the EF coil was developed to evaluate the effect of the transient response and resonance phenomenon on the voltage in the coil. The results of this study provide fundamental data that can be used to ensure that the EF coil does not cause insulation breakdown.

A Robust Forward Compensated Type-2 PLL Without DC Phase Error During Frequency Ramp for Embedded Magnetic Encoder

To achieve high performance vector control of permanent magnet synchronous machine (PMSM), high precision rotor angle is essential. Compared to traditionally used angle feedback device, e.g., encoder and resolver, the embedded magnetic encoder (EME) achieves high precision angle estimation without extra space occupation by installing several linear Hall sensors into PMSM cavity to monitor the flux leakage and rotor angle. The conventional synchronous reference frame (SRF) phase-locked loop (PLL) can extract phase and frequency from three or two Hall signals simultaneously. Although the type-2 SRF-PLL shows good robust performance against parameter variation, phase error emerges when input frequency changes. More specifically, a DC phase error appears in type-2 SRF-PLL during speed ramp stage due to insufficient order. Increase of the loop order removes the DC phase error but leads to instability risk. In this paper, a novel forward compensation (FC) module is attached on type-2 SRF-PLL to achieve phase error-free when frequency changes, where the instability risk is avoided. The effectiveness of proposed FC module is analytically and experimentally proved, where the phase error elimination, noise immunity and dynamic response are evaluated.

Muscle velocity recovery cycles in myopathy

ObjectiveTo understand the pathophysiology of myopathies by using muscle velocity recovery cycles (MVRC) and frequency ramp (RAMP) methodologies. Methods42 patients with quantitative electromyography (qEMG) and biopsy or genetic verified myopathy and 42 healthy controls were examined with qEMG, MVRC and RAMP, all recorded from the anterior tibial muscle. ResultsThere were significant differences in the motor unit potential (MUP) duration, the early and late supernormalities of the MVRC and the RAMP latencies in myopathy patients compared to controls (p < 0.05 apart from muscle relatively refractory period (MRRP)). When dividing into subgroups, the above-mentioned changes in MVRC and RAMP parameters were increased for the patients with non-inflammatory myopathy, while there were no significant changes in the group of patients with inflammatory myopathy. ConclusionsThe MVRC and RAMP parameters can discriminate between healthy controls and myopathy patients, more significantly for non-inflammatory myopathy. MVRC differences with normal MRRP in myopathy differs from other conditions with membrane depolarisation. SignificanceMVCR and RAMP may have a potential in understanding disease pathophysiology in myopathies. The pathogenesis in non-inflammatory myopathy does not seem to be caused by a depolarisation of the resting membrane potential but rather by the change in sodium channels of the muscle membrane.

EFFECT OF SLUB PARAMETERS ON YARN UNEVENNESS, HAIRINESS AND STRENGHT PROPERTIES OF SLUB YARNS

In this study yarn unevenness, diameter variation, hairiness and strength properties of slub yarns with various slub structures were investigated. The yarns (Ne20) in different slub thickness (1.2, 1.4, 1.6 and 1.8), slub length (1 – 3, 5 – 7 and 10 – 12 cm.), slub frequency (0.5, 3 and 6 pcs/m) and slub ramp length (1, 2 and 4 cm.) were produced from PET fibers. The multipopulation slub yarn which have two-slub length was also spun. The measurements of the yarns were made on the Fancy Yarn Profile of the Uster Tester 5 and the Uster Tensojet devices. The values of the test result were analyzed and evaluated statically. The slub parameters were found significant effect on the unevenness and strength properties of the yarns. As the slub thickness, slub length and frequency increased, the yarn unevenness, hairiness increased and the yarn strength decreased. Ramp length was found statistically significant for yarn breaking strength and elongation.

Inherent phase-based real inertia power response of STATCOM with supercapacitor during high RoCoF events in AC grid

This paper describes the Inherent Phase-Based Real Inertia Power response of a STATCOM with DC side supercapacitor during high RoCoF events in the AC network. In this paper, a case study of the SVC PLUS FS® is considered, followed by simulation results for frequency ramps with different RoCoF and significant short-circuit ratio reduction. The grid-forming Virtual Synchronous Machine control concept is extended with a virtual active power control loop, ensuring the stability of the system during high RoCoF events (up to 6 Hz/s). Eventually, the proposed solution provides the flexibility of the inertia time constant of the Virtual Synchronous Machine without compromising the control stability.

Review of Discrete Fourier Transform During Dynamic Phasor Estimation and the Design of Synchrophasor Units

In a large and complex interconnected power system, the measurement of synchronized bus voltage and line current plays a vital role in the monitoring and precise control of various sophisticated electrical equipment for secure and reliable operation. Phasor measurement units (PMUs) are incorporated into a wide area of the power system to extract the different signals of synchronized phasors. In this paper, the capacity of the PMU phasor estimation algorithm is explored based on discrete Fourier transform (DFT) under different sampling frequency rates during various dynamic scenarios in accordance with the IEEE C37.118.1a-2014 standard. Furthermore, the performance of the DFT algorithm varies according to the phase angle and dynamic parameters such as frequency, frequency ramp rates, modulation frequency, harmonic levels, step change, decaying dc, and noise levels. The simulation results reveal that accuracy of the phasor estimation algorithm based on DFT can be achieved at high sampling frequency rates. Furthermore, the results of DFT-based phasor estimation are compared with Shank’s estimation method (SEM) and the least-squares estimation method (LEM). The presented method is best suited to PMU algorithms development based on DFT for better visualization of the smart electric grid.

Characterization of the Frequency Ramp Nonlinearity Impact on the Range Estimation Accuracy and Resolution in LFMCW Radars

The ranging accuracy and range resolution in linear-frequency-modulated continuous-wave (LFMCW) radars are vulnerable to the nonlinearity of the transmitted frequency ramp. The frequency ramp nonlinearity (FRN) leads to the degradation of accuracy in range estimation and deteriorates the range resolution in LFMCW radars, which becomes even worse as the target range increases. The uncertainty of the type of FRN makes the problem more complicated. This paper proposes a new range-dependent resolution model and a new range-dependent accuracy model based on the theoretical analysis and experimental evaluations, which characterizes the impact of different types of FRN on the range resolution and accuracy in LFMCW radars. The proposed models have established the quantitative relationship between the FRN, the target distance, and the range accuracy and resolution. A nonlinearity index is utilized in the analysis to quantify the extent of FRN. Moreover, a novel design methodology is also proposed which may guide the design of LFMCW radars under the influence of FRN. Four typical types of FRN that are reasonable in practical LFMCW radars are taken into consideration in both simulations and experiments to validate the proposed theory and methodology.

PF-FEDG: An open-source data generator for frequency disturbance event detection with deep-learning reference classifiers

Accurate and fast classification of FDEs is crucial to power systems situation awareness and stability control. However, various database used in recent studies makes it hard to directly compare different classification methods. To relieve the lack of a standardized database that can be used as a benchmark, this work proposes an open-source package which generates frequency events based on PowerFactory named PF-FEDG. PF-FEDG can produce various labeled FDEs with random parameters such as generator trips, load disconnections, line outages, frequency ramp ups, frequency ramp downs, and frequency oscillations. Furthermore, the package includes three reference FDEs classifiers based on deep learning techniques. These models are tested on the IEEE 39-bus system and IEEE 118-bus system and achieve high performance. The package generating capability and the reference classifiers can be used by the community as benchmarks for comparison and development of new algorithms for FDEs detection. The code of PF-FEDG is available on GitLab.

Hybrid Model-Based BESS Sizing and Control for Wind Energy Ramp Rate Control

This paper presents a hybrid model constituting dynamic smoothing technique and particle swarm optimization techniques to optimally size and control battery energy storage systems for wind energy ramp rate control and power system frequency performance enhancement. In today’s modern power system, a high-proportion renewable energy grid is inevitable. This high-proportion renewable energy grid is a power system with abundant integration of renewable energy resources under the presence of energy storage tools. Energy storage tools are integrated into such power systems to balance the fluctuation and intermittence of renewable energy sources. One of the requirements in a high-proportion renewable energy grid is the fractional power balance between generation and load. One of the requirements set by power system regulators is the generation variation between two time points. A power producer is mandated to satisfy the ramp rate requirement set by the grid owner. This paper proposes dynamic smoothing techniques for initial size determination and particle swarm optimization based on optimal sizing and control of battery energy storage systems for ramp rate control and frequency regulation performance of a power system integrated with a large percentage of wind energy systems. Wind energy data taken from Zhangjiakou wind farm in China are used. The results indicate that the battery energy storage system improves the ramp rate characteristics of the wind farm. In addition, the virtual inertia capability of the battery energy storage system enabled the transient and steady-state frequency response of the test power system to improve significantly.

A High-Performance Pll Observer for Sensorless Three-Phase Induction Motor Control

This paper presents an enhanced estimation algorithm based on the PLL (phase-locked loop) approach, which is used to estimate the rotor speed in induction motors (IM) drives. It can be challenging to obtain an accurate estimate during frequency ramps using existing PLL schemes. Thus, the performance of PLL schemes can be degraded during the acceleration and deceleration operations when applied to motor drives. In addition, the performance of conventional PLL scheme estimation is negatively affected by disturbances, for example, DC offsets. One of the novelties of the proposed speed observer (HPPO - High-Performance PLL Observer) is error normalization, which is based on the currents and a mechanism of variable gain based on the reference speed. The reference speed is also used to build an additional feedforward adjustment action. These modifications improve estimator results during load insertions and at low rates. In order to validate the proposed HPPO algorithm, it is implemented experimentally in a laboratory prototype using a 2.2kW IM. The motor is driven by a three-phase pulse width modulation (PWM) power converter, which is controlled by a DSP TMS320F28069. Numerical analysis and experimental results are carried out to validate the proposed scheme's high performance.

Step detection in power system waveforms for improved RoCoF and frequency estimation

The evaluation of the signal frequency and Rate of Change of Frequency (RoCoF) from voltage or current waveforms is used for critical grid control, monitoring and protection applications. However, when step changes in the amplitude or phase of the signal occur, conventional frequency and RoCoF estimation methods, typically based on phasor models, are highly unreliable and can yield large frequency errors. To address this issue, this paper proposes a technique that uses dictionaries based on common signal dynamic models to identify and track amplitude and/or phase steps in AC signals. Additional signal dynamics including amplitude modulations, frequency ramps and harmonic tones are also characterized. Distinct from a previous iteration of this method developed by the authors, the proposed Step Change Detection (SCD) technique separates the envelope and angle of the signal’s analytic form for independent analysis of these components. For numerical validation the method is applied to synthetically generated signals with challenging combinations of signal dynamics. The technique is shown to greatly improve frequency and RoCoF approximations as compared to state-of-the-art phasor estimation methods.

Sulfur-urushiol copolymer: A material synthesized through inverse vulcanization from renewable resources and its latent application as self-repairable and antimicrobial adhesive

The growing cost of petroleum derivatives and the increasingly stringent environmental regulations have led the adhesive industry to re-seek solutions from natural resources in the past decades. However, most currently available natural adhesives (e.g. polysaccharides) are conflicted with low performances such as weak adhesion and easy microbial degradation, etc. On the other hand, owning self-repairability has become a popular way for a new material to extend its lifetime, to reduce its environmental footprint, and to meet the increasing demands of smart functions. This is also true to adhesive industry with self-repairable adhesive highly desirable.In this work, plant resourced urushiol and industrial waste of elemental sulfur (S) was used to prepare sulfur-urushiol copolymers (IVurux) as a high-strength, self-repairable and antimicrobial adhesive through inverse vulcanization, a facile and green approach free of solvent and catalyst. The polymerization between unsaturated bonds of urushiol and sulfur in forming a reversibly crosslinked network with polysulfide segments has been verified by FTIR and 1H NMR analysis. The adaptable covalent S-S bonds from polysulfide segments endow the copolymer networks with a distinct self-healing property, while the rich catechol groups from urushiol moiety guarantee the material with an outstanding adhesive property.The adaptable covalent networking was well validated by a distinct rubbery plateau in rheological measurements of both temperature ramping test and frequency sweep test. The crosslinking density was revealed to increase with sulfur content, with frequency scaling exponent of G’ in the plateau regime varying from G’∼ω0.27 in IVuru70 (S content 30 wt%) to G’∼ω0 in IVuru50 (S 50 wt%) and IVuru40 (S 60 wt%), while when S >60 wt% few unreacted sulfur presented in the product as indicated from XRD and DSC analysis. Moreover, the self-healing property was well demonstrated in a repeated breaking-healing cycle test with 92.7% recovery obtained after 4 breaking cycles for IVuru50, and the dynamic S-S bond exchange was studied by stress relaxation to be temperature dependent with an activation energy of metathesis ∼100 kJ/mol. Furthermore, the P(sulfur-r-urushiol)s were examined to exhibit a considerable adhesion strength ∼3.0 MPa, about 6 times of a commercial hide glue, with IVuru60 being the best as a balanced contribution between catechol groups and covalent networking for adhesive and cohesive bonding. Meanwhile, a very good self-repairability of the adhesive was demonstrated with heating being the trigger for S-S metathesis. Ultimately, the P(sulfur-r-urushiol) copolymers were found to be hydrophobic with a contact angle ∼ 85° and have an excellent antimicrobial activity against S. aureus and S. cerevisiae with a high inhibition efficiency >80% and >52%, respectively. Such a high-strength, self-repairable and antimicrobial adhesive material foresees promising applications in broad fields in light of its advantages of fabrication simplicity, environmentally friendliness and good durability.

A 24 GHz Self-Calibrated All-Digital FMCW Synthesizer With 0.01% RMS Frequency Error Under 3.2 GHz Chirp Bandwidth and 320 MHz/µs Chirp Slope

A 24 GHz self-calibrated all-digital frequency-modulated continuous-wave (FMCW) synthesizer is presented in this article. A multi-bank digitally controlled oscillator (DCO) is employed to provide adequate frequency tuning range and high frequency resolution. A full background self-calibration scheme is proposed to linearize the DCO tuning curve for highly linear and fast chirp generation. An overlap compensator based on an adaptive lookup table (LUT) is utilized to eliminate the frequency overlaps between adjacent DCO tuning bands. The compensation words in the LUT are altered by least-mean-square (LMS) algorithm for robust and precise matching. A ramp tracker, which features real-time ramp tracking with zero steady-state phase error, is employed to estimate and stabilize the frequency ramp. Implemented in 40 nm bulk CMOS, the FMCW synthesizer prototype consumes 28 mW with a 0.26 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> core area. The maximum chirp bandwidth is 3.2 GHz, corresponding to 13.33% of the center frequency. Measurement results show that the root-mean-square (RMS) frequency error is reduced by 1/10 with self-calibration after 2 ms convergence time. The maximum chirp slope is up to 320 MHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> with 309 kHz RMS frequency error. The minimum RMS frequency error is 7.35 kHz under 5 MHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> chirp slope, corresponding to 0.0002% of the chirp bandwidth.

A Forward Compensation Method to Eliminate DC Phase Error in SRF-PLL

The Type-II synchronous-reference-frame (SRF) phase locked loop (PLL) fails to precisely keep tracking on phase of input signals when the frequency of input signals is under ramp state, whereas the type-III SRF-PLL addresses the above issue but stability problem arises. In this letter, a forward compensation (FC) module is introduced to the Type-II SRF-PLL to minimize the dc phase error due to the ramp frequency of input signals, named as FCSRF-PLL, which features low computational burden, simple structure, noise immunity, and high robustness. More importantly, the parameter tuning in the proposed method will not cause stability problem. The effectiveness of the proposed FCSRF-PLL is verified through experiments based on dSPACE.

Laser Frequency-Offset Locking at 10-Hz-Level Instability Using Hybrid Electronic Filters

Lasers with well-controlled relative frequencies are indispensable for many applications in science and technology. We present a frequency-offset locking method for lasers based on beat-frequency discrimination utilizing hybrid electronic $LC$ filters. The method is specifically designed for decoupling the tightness of the lock from the broadness of its capture range. The presented demonstration locks two free-running diode lasers at 780 nm with a 5.5-GHz offset. It displays an offset frequency instability below 55 Hz for time scales in excess of 1000 s and a minimum of 12 Hz at 10-s averaging. The performance is complemented with a 190-MHz lock-capture range, a tuning range of up to 1 GHz, and a frequency ramp agility of $200\phantom{\rule{0.2em}{0ex}}\mathrm{kHz}/\ensuremath{\mu}\mathrm{s}$.

A Self-Adapted Two-Point Modulation Type-II Digital PLL for Fast Chirp Rate and Wide Chirp-Bandwidth FMCW Signal Generation

Different from the conventional two-point modulation (TPM) type-II phase-locked loops (PLLs) requiring non-trivial gain calibrations and TPM type-III PLLs with loop stability concern and limited chirp rate, a self-adapting gain mismatch TPM type-II digital PLL is proposed in this article. It directly detects frequency error as its input signal, allowing frequency ramp tracking with zero steady-state frequency error using a type-II PLL. In addition, the maximum trackable slope in the case of the proposed TPM type-II PLL is intrinsically larger than that of the conventional TPM type-III PLL. A polarity navigator is embedded in the digital loop filter to improve the linearity at the chirp turning-around points (TAPs). Fabricated in a 28-nm complementary metal–oxide–semiconductor (CMOS) technology, the proposed PLL consumes 23 mW from a 1-V power supply and occupies 0.31 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measurement results indicate that the proposed PLL can generate a precise triangular chirp with 2.27-GHz bandwidth (BW) and 18.2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> period at 12.5 GHz. To the best knowledge of the authors, this work demonstrates the widest normalized Chirp-bandwidth and the fastest chirp rate simultaneously.