Frequency Variation Range Research Articles

Analysis of a Resonant Converter with Wide Input Voltage

A DC-DC converter with a 16:1 (Vin,max = 16Vin,min) wide input voltage operation is presented for auxiliary power supplies on solar power conversion circuits or railway vehicles. The solar cell output voltage is associated with the solar intensity (day or night) and geographical location. Thus, the wide input voltage capability of DC converters is required for photovoltaic power conversion. For low power supplies on railway vehicles, the nominal input voltages are 24 V~110 V for the electric door system, motor drive, solid state lighting systems and braking systems. The presented converter uses buck/boost and resonant circuits to achieve the wide input voltage range operation from 18 V to 288 V. If Vin stays on a low input voltage range (18 V~72 V), the buck/boost circuit is operated at a voltage boost characteristic. On the other hand, the buck/boost circuit is operated at a voltage buck characteristic when the input voltage climbs to a high voltage range (72 V~288 V). Thus, the buck/boost circuit can output a constant voltage. Then, the resonant circuit in the second stage is worked at a constant input voltage case so that the frequency variation range is reduced. Finally, to investigate the performance and effectiveness of the studied circuit, experiments with a 500 W prototype were conducted to investigate the performance of the studied circuit.

Method of estimation of frequency variation relying on estimation of shift of spectral peaks

Problem of estimation of variated frequency of components of polyharmonic signals has been arose. Three-dimensional time-frequency representation of signals is usually used to resolve this problem. But simple and reliable method of instantaneous frequency tracking is needed. Frequency tracking method based on estimation of shifts of peaks of spectrogram has been proposed in this paper. It is assumed that shift of spectral peaks of components of signal is proportional to variation of fundamental frequency. Logarithmic scaling of time-frequency representation is used to make spectral peaks equidistant. Temporal dependence of shift of spectral maximums is obtained using correlation of windowed spectrum at the first frame and spectrum of signal in the current window. Then obtained track is translated in linear scale. Proposed method does not estimate values of instantaneous frequency or central frequency of signal component but estimates its variation. Advantage of the method is that it can estimate frequency track even if range of frequency variation and its central value are known roughly or unknown at all. Multiple components do not interfere to estimate fundamental frequency variation. Reduction of bandwidth is recommended to increase accuracy of frequency track estimation, but analysis of time-frequency representation containing a few components is also possible. Dependency of performance of analysis of synthetic signals using the method on various signal to noise ratios under different conditions was estimated. Applicability of the method for vibrational diagnosing of rotary equipment was checked out using spectral interference method.

High Power Factor CRM Boost PFC Converter With Optimum Switching Frequency Variation Range Control Based on Variable Inductor

Critical conduction-mode boost power factor correction converter with constant <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -time control is widely used in low-to-medium power applications. However, the range of the switching frequency varies with different input voltages and load conditions. In this letter, a theoretical all-fixed switching frequency method based on the continuous variable inductance control is proposed first. Considering that the existing variable inductor technology is difficult to achieve a wide variation range, a switching frequency optimization compromise based on the segment variable inductance (SVI) control is put forward. Ensuring unit power factor, the proposed method significantly reduces the switching frequency variation range, which facilitates the electromagnetic interference filter design. A prototype with SVI control has been built and tested in the lab to demonstrate the validity of the proposed method.

Current Ripple Prediction and DPWM Based Variable Switching Frequency Control for Full ZVS Range Two Parallel Interleaved Three-Phase Inverters

In this article, an improved variable switching frequency zero-voltage switching (ZVS) control strategy is proposed for two parallel interleaved three-phase inverters. Discontinuous pulsewidth modulation is adopted and full-range ZVS can be achieved at any load or modulation ratio. The critical switching frequency can be easily calculated in a digital controller based on current ripple prediction instead of current zero-crossing detection. No additional high-frequency sensor or auxiliary circuit is needed. Compared with the continuous pulsewidth modulation, the switching frequency variation range is narrower and the frequency calculation equation is simplified. In addition, lower peak current ripple leads to lower current stress. Owing to the high switching frequency and the low inductance, the size and the cost of the inverter can be significantly reduced. A 6.6-kW experimental prototype with SiC MOSFETs interfacing 400-V dc with three-phase 110-V ac grid is developed to verify the effectiveness of the proposed control strategy.

Design and optimization of 3‐kW inductive power transfer charging system with compact asymmetric loosely coupled transformer for special applications

SummaryInductive power transfer (IPT) technology has become popular in wireless charging applications. Compared with the traditional 3‐kW wireless charging application, the diameter for the primary coil and the secondary coil in this special design are required to be smaller than 260 and 110 mm, respectively. In order to achieve this target, an approach to design and optimize the loosely coupled transformer (LCT) is proposed to match the strict geometry limitation, while achieving the high conversion efficiency. Different from the traditional design method, the low resonant current and voltage stress are considered as the input of the design flowchart, especially the LCT. Thus, the overall conversion efficiency can be improved. Based on series–series (S–S) compensation topology, the parameter range of the LCT is determined by analyzing transformer‐based equivalent model. To achieve the desired coil size, an asymmetric LCT with single‐layer primary coil and three‐layer secondary coil is designed and optimized by the proposed approach. Furthermore, the closed‐loop controller with narrow frequency variation range is design to realize constant current (CC) charge and constant voltage (CV) charge. A 3‐kW IPT charging prototype is built to demonstrate the validity of the proposed method. Experimental results show that the peak efficiency from input to battery load is 95.69% at 3‐kW output power in the transition point from CC mode to CV mode.

GaN-Based Megahertz Single-Phase Inverter With a Hybrid TCM Control Method for High Efficiency and High-Power Density

Compared with traditional frequency limitation method DCM and QCFTCM for TCM-based inverter, this article proposes a hybrid TCM method, which can achieve both full range ZVS and frequency variation limitation. An accurate resonant transition model is established and the switching frequency variation range can be obtained for TCM. The hybrid control can be implemented according to the variation ratio γ. In order to determine the optimal γ, an offline optimization algorithm based on loss estimation is proposed. Therefore, an accurate analytical loss model for GaN HEMTs considering the nonlinear junction capacitance is given for TCM and hybrid TCM. The loss model shows that the total losses of hybrid TCM inverter are reduced compared with TCM. Moreover, an interleaved GaN-based megahertz single-phase inverter with digital control is demonstrated with 120 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density. The aforementioned benefits are experimentally verified in the optimal hybrid TCM. With this hybrid control, the measured peak efficiency is 98%. Compared with pure TCM mode, there is a 70% reduction in the switching frequency and the related efficiency is 0.8% higher at light loads. Higher power density (135 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) can be achieved in hybrid TCM through further increasing the switching frequency compared with pure TCM.

A 0.35 μm CMOS mixed controlled crystal oscillator with low phase noise and wide tuning range

This paper presents a high-performance mixed controlled crystal oscillator. The digital-controlled part is based on a Pierce topology with switched-capacitor bank. Wide tuning range and high linearity are simultaneously achieved by combining discrete capacitors and a continuous voltage tuning varactor. The pull ability is around 99 ppm output frequency variation range. For noise reduction, the supply voltage of the mixed controlled crystal oscillator is regulated at 2.5 V by using on-chip low-drop regulators. The measured phase noise is −145 dBc/Hz at 1 kHz offset frequency by using a 40 MHz fundamental AT–cut crystal. The chip area is 3.6 mm2 for a 0.35 μm standard CMOS process with 3.3 V supply voltage and the power dissipation is 7 mW.

Memristor BJT pair based low complex circuits for portable electronics

Circuits consisting of both memristor and bipolar junction transistor (BJT) were found to be extremely beneficial as the current driven by the transistor enhanced the memristive performances. In this work, memristor-BJT pair was considered and its electronic characteristics were investigated. The pair demonstrated the features of tunable current regulator with reduced circuit complexity. Importantly, the duo exhibited stable characteristics for a large range of frequency variations. Interestingly, the ameliorated linearity was obtained in the memristance-time characteristics. Most importantly, variable negative resistance (VNR) was achieved by modulating the current through the couple. This property was employed in solving linear equations that possess negative slope. In addition, VNR was utilized to implement a low circuit complexity based pulse signal generator with tunable amplitude and on duration. The abovementioned results were obtained through simulation and fabrication routes. The ideas proposed in this work pave the way for futuristic highly reliable oscillators and logic control circuits with reduced on-chip area for portable electronic systems.

Heteromagnetic Swinging Inductor and Its Application for Power Factor Correction Converters

A variable inductor concept based on a magnetic structure consisting of composite of magnetic materials is introduced to meet the designed inductance function of current. A design of the inductor, termed heteromagnetic swinging inductor (HMSI), was fabricated using a toroid core with a gap that was filled by a custom-developed low-permeability magnetic powder + polymer material. Having the gap filled with the magnetic material allowed for greater flexibility in L–I design with added benefit of low fringe field. The analytical model of HMSI was derived and verified by simulation. And the step-by-step design of arbitrary L–I curve HMSI was posted. We applied this swinging inductor to a critical conduction mode boost power factor correction converter to reduce its switching frequency variation range. First, the required L–I curve of the HMSI needed for narrow range of switching frequency was calculated. Then, the HMSI core structure consisting of two magnetic materials was designed. Finally, a prototype of the HMSI was fabricated and tested. Experimental result showed that for a 110-Vrms input, the converter with the HMSI had a switching frequency variation factor, defined as Δ f / f min, six times less than that of the converter using a linear inductor.

Top Coating Anti-Erosion Performance Analysis in Wind Turbine Blades Depending on Relative Acoustic Impedance. Part 1: Modelling Approach

Top coating are usually moulded, painted or sprayed onto the wind blade Leading-Edge surface to prevent rain erosion due to transverse repeated droplet impacts. Wear fatigue failure analysis based on Springer model has been widely referenced and validated to quantitatively predict damage initiation. The model requires liquid, coating and substrate speed of sound measurements as constant input parameters to define analytically the shockwave progression due to their relative vibro-acoustic properties. The modelling assumes a pure elastic material behavior during the impact event. Recent coating technologies applied to prevent erosion are based on viscoelastic materials and develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. In order to analyze the erosion performance by using Springer model, appropriate impedance characterization for such viscoelastic materials is then required and represents the main objective of this work to avoid lack of accuracy. In the first part of this research, it is proposed a modelling methodology that allows one to evaluate the frequency dependent strain-stress behavior of the multilayer coating system under single droplet impingement. The computational tool ponders the operational conditions (impact velocity, droplet size, layer thickness, etc.) with the appropriate variable working frequency range for the speed of sound measurements. The second part of this research defines in a complementary paper, the ultrasonic testing characterization of different viscoelastic coatings and the methodology validation. The modelling framework is then used to identify suitable coating and substrate combinations due to their acoustic matching optimization and to analyze the anti-erosion performance of the coating protection system.

Quasi-Fixed Switching Frequency Control of CRM Boost PFC Converter Based on Variable Inductor in Wide Input Voltage Range

With traditional constant on-time control, the switching frequency variation range of critical conduction mode boost power factor correction converter is large during a half line cycle, not to mention the wide range of input voltage's rms value. For this issue, this article puts forward a quasi-fixed switching frequency control, which combines the variable on-time and variable inductor technology together. Furthermore, a lower output voltage ripple and a higher efficiency are obtained. In spite of the power factor decrease, the input current harmonics still satisfy the IEC61000-3-2 Class D limits. The detailed theoretical analysis and experimental results are presented in this article.

Adaptive Hysteresis Current Based ZVS Modulation and Voltage Gain Compensation for High-Frequency Three-Phase Converters

This article proposed a systematic approach for the control of three-phase bidirectional zero-voltage switching (ZVS) converters. Combining the adaptive hysteresis-band current control and turn- on delay modifications, ZVS conditions are realized in full line-cycle in all loading conditions like active power, reactive power, light load, and heavy load. The soft-switching resonant period is carefully analyzed, and the current band is designed accordingly, which minimized the additional conduction loss. Meanwhile, a zero-sequence voltage injection control is included in the approach, which compensates the voltage gain by 15% and narrows down the switching frequency variation range. The hardware design approach is also provided including the LCL filter design and a low-cost high-bandwidth high-accuracy current sensor design. A highly integrated 5-kW silicon carbide implemented three-phase ZVS converter prototype with printed circuit board integrated inductors and customized current sensors is designed. All the control is implemented in a single microcontroller unit, which achieves a high electromagnetic compatibility. The designed prototype achieves a total power density of 5.5 kW/L and a peak efficiency of 98.5%. All the analysis and the proposed control approach are experimentally verified on the designed prototype.

Research on mechanism and evolution features of frequency split phenomenon of tire acoustic cavity resonance

The acoustic cavity resonance inside the tire–wheel assembly is known to contribute to audible noise in the passenger compartment of vehicles. To obtain control methods of tire acoustic cavity resonance, its characteristics and producing mechanism need to be clarified first. In this article, the finite element model of a tire coupled with acoustic medium in the tire cavity is constructed. The Euler method is introduced to study the modal characteristics of tire cavity under the influence of tire inflation pressure, load, and tire rotation velocity. Frequency splitting phenomena under four separate conditions (stationary tire without load, stationary tire with load, rotating tire without load, and rotating tire with load) are simulated and analyzed. The slope change of the resonance frequency as a function of rotation speed is found to be close to the reciprocal of tire radius which can be explained by a model of wave propagation in a ring-shaped channel with moving media inside the ring. The obtained function of the slope change can help determine the frequency variation range under different vehicle velocity, structure load, and tire inflation pressure, which can then help to control the cavity resonance energy and provide a more comfortable driving experience.

Rheological and Electrical Study of a Composite Material Based on an Epoxy Polymer Containing Cyclotriphosphazene.

In this work, we have studied, formulated, prepared, and characterized the rheological and electrical behavior of a composite material based on an epoxy resin Diglycidyl Ether of Bisphenol A (DGEBA) reinforced with hexaglycidyl cyclotriphosphazene (HGCP). The epoxy system was cured with 4,4’-methylene dianiline (MDA). DGEBA-HGCP-MDA epoxy composite materials with reinforced HGCP which varied from 5% to 10% by weight were prepared by mixing in the molten state. The morphology was evaluated by SEM. The rheological behavior was studied using small deformation rheology. The electrical characterization was carried out with a frequency variation range from 1 Hz to 100 KHz at room temperature. These measurements revealed that the rheological and electrical behaviors strongly depend on the quantity of HGCP in the DGEBA matrix. The linear viscoelastic properties study reveals that the modulus of elasticity G’ is dependent on the amount of HGCP present in the epoxy resin DGEBA. The capacitance-frequency measurements suggest a distribution of localized states in the band gap of the blends.

Research on Frequency Control of Islanded Microgrid with Multiple Distributed Power Sources

At present, some achievements have been made in the research on the energy management of microgrid operation. However, the research is mainly on the operation of grid-connected microgrid, while the research on the energy management of islanded microgrid is still relatively few. Frequency is one of the characteristics that affects the reliability and power quality of the microgrid. The essence of controlling frequency stability is to maintain source-load balance and redistribution of active power. Therefore, this paper proposes a frequency control strategy based on dynamically cutting machine to reduce load by analyzing the use priority of different distributed power supply and the division of load importance degree, and combining the influence degree of different frequency variation range on microgrid. To coordinate and control distributed power supply, energy storage device, and load in different frequency change areas, this paper proposes different control strategies. The seed strategies of the control strategy are discussed one by one. Experimental results show that the frequency control strategy can significantly improve the frequency stability of the power supply system and reduce the operating cost of islanded microgrid.

Optimal Switching Frequency Variation Range Control for Critical Conduction Mode Boost Power Factor Correction Converter

Critical conduction mode boost power factor (PF) correction converter is widely used in low-to-medium power applications for its advantages of high PF, zero-current turn-on of the switch, and no reverse recovery in diode. Nevertheless, the switching frequency varies continually with the input voltage phase angle with traditional constant on-time control. This makes the electromagnetic interference (EMI) spectra display great differences and complicates the design of EMI filter. An optimal switching frequency variation range control strategy is proposed in this article. The optimal harmonics amounts for the lowest switching frequency variation range without and with a limited PF are both figured out. In addition, a lower output voltage ripple is obtained. A prototype has been built and tested in the lab to demonstrate the validity of the theoretical analysis.

Current Ripple Prediction and DPWM-Based Variable Switching Frequency Control for Full ZVS Range Three-Phase Inverter

In this article, a variable switching frequency full zero-voltage switching (ZVS) range bidirectional three-phase voltage-source inverter is proposed. Discontinuous pulsewidth modulation is used so that at any time only two phase legs need to achieve ZVS. The boundary switching frequency can be calculated in a digital controller based on current ripple prediction instead of current zero-crossing detection. No additional high-frequency sensor or auxiliary circuit is needed. The frequency variation range is narrow in a line cycle at any load condition. An LCL filter is used to attenuate the inverter-side high ripple current and improve the grid current quality. Owing to the high switching frequency and the small filter parameters, the power density can be greatly increased. Both the device and the filter losses are reduced, and the efficiency is high. A 3.5 kW simulation and experimental prototype with silicon carbide (SiC) device interfacing 400 V dc with three-phase 110 V ac grid is developed to verify the effectiveness of the proposed control strategy.

Synchronous random switching frequency modulation technique based on the carrier phase shift to reduce the PWM noise

Pulse width modulation (PWM) technique brings harsh acoustic noise in motor drive system. Thus, synchronous random switching frequency modulation (SRSFM) technique based on carrier phase shift for paralleled three-phase voltage source inverters is proposed in this study to eliminate the PWM noise. The proposed SRSFM technique is able to remove the high-frequency PWM noise more effectively than the conventional random switching frequency PWM; it not only completely eliminates the PWM noise nearby odd-order carrier frequency but also reduces PWM vibration noise around even-order carrier frequency depending on the switching frequency variation range. Furthermore, the SRSFM technique is simple to implement and requires no additional hardware. Finally, the effectiveness of the proposed method is verified by detailed experimental results.

Long-Term Frequency Stability Assessment Based on Extended Frequency Response Model

Large frequency deviation degrades the operation performance of the boiler and its auxiliaries. It affects the output of thermal power units. A significant change in power generation leads to a great frequency deviation. An extended frequency response model for long-term frequency stability assessment is constructed to consider the effects of frequency deviations on boiler auxiliaries. The static power-frequency characteristic of the thermal power unit within an extensive frequency variation range is analyzed. It reveals that the active power output of the generating unit is not monotonically increasing with frequency dropping. An inflection point is observed on the static power-frequency characteristic curve when considering boiler auxiliary frequency characteristics. In the range of greater frequency deviation, the output power decreases rapidly with frequency declination, and an unstable equilibrium point (UEP) of frequency stability is identified. A quantitative index is proposed for frequency stability assessment based on UEP. The stability characteristic and the frequency stability quantitative index based on UEP are analyzed. The frequency dynamic behaviors of the extended model are demonstrated to analyze frequency stability characteristics within an extensive frequency variation range by a single machine system and the IEEE 39-bus system with considering boilers and its auxiliaries.

Effect of collisionality on the microinstabilities in the Globus-M spherical tokamak

Simulations of the microtearing instability developing in plasma of the Globus-M spherical tokamak were performed using the GENE gyrokinetic code in the flux-tube linear approximation mode. Under the effect of the instability, the magnetic islands form on the scale of the ion Larmor radius, and the magnetic field fluctuations occur that generate electron heat fluxes. The ion heat fluxes as well as the fluxes associated with the electrostatic fluctuations are negligible. The maximum growth rate of the microtearing instability is reached at a collision frequency within the experimental range of the collision frequency variation, within which the BT × τE ∝ ν*−0.4±0.1 scaling calculations were performed [1]. In similar calculations performed at the MAST tokamak, the growth rate decreases with decreasing collisionality in the entire range of the collision frequency variation, within which the BT × τE ∝ ν*−0.82 scaling calculations were performed [2]. This can explain why the dependences of energy confinement time on the collision frequency obtained for the MAST&NSTX and the Globus-M tokamaks are different.