Frequency Leakage Research Articles

Analysis and Control of Critical Conduction Mode High-Frequency Single-Phase Transformerless PV Inverter

This article presents a critical conduction mode (CRM) single-phase transformerless full-bridge inverter in a residential photovoltaic system. The CRM full-bridge inverter in bipolar mode features zero-voltage switching capability for the whole line cycle. This enables the inverter to push switching frequency up to hundreds of kHz and achieve high power density with high efficiency. However, CRM operation incurs nonconstant common mode (CM) voltage during the resonant period, causing high frequency leakage current. To minimize the leakage current, a new switching modulation strategy is proposed introducing triangular current mode (TCM) near the ac voltage zero crossing. The switching modulation scheme alleviates the CM voltage by shortening the resonant period and consequently reduces the leakage current. Then, discontinuous conduction mode is inserted between the CRM and TCM operation regions to improve light load efficiency. In this article, the basic operation principle of the CRM full-bridge inverter, impacts of CRM operation on the leakage current, and details of the proposed switching modulation method are discussed. Experimental results with a 2.4-kW prototype built with GaN devices validate its performance.

Frequency-hiding order-preserving encryption with small client storage

The range query on encrypted databases is usually implemented using the order-preserving encryption (OPE) technique which preserves the order of plaintexts. Since the frequency leakage of plaintexts makes OPE vulnerable to frequency-analyzing attacks, some frequency-hiding order-preserving encryption (FH-OPE) schemes are proposed. However, existing FH-OPE schemes require either the large client storage of size O ( n ) or O (log n ) rounds of interactions for each query, where n is the total number of plaintexts. To this end, we propose a FH-OPE scheme that achieves the small client storage without additional client-server interactions. In detail, our scheme achieves O ( N ) client storage and 1 interaction per query, where N is the number of distinct plaintexts and N ≤ n . Especially, our scheme has a remarkable performance when N ≪ n . Moreover, we design a new coding tree for producing the order-preserving encoding which indicates the order of each ciphertext in the database. The coding strategy of our coding tree ensures that encodings update in the low frequency when inserting new ciphertexts. Experimental results show that the single round interaction and low-frequency encoding updates make our scheme more efficient than previous FH-OPE schemes.

CNN ‐based deep learning technique for improved H7 TLI with grid‐connected photovoltaic systems

In this article, a three-phase transformerless inverter (TLI) for a solar photovoltaic (PV) system connected to a high-power grid are proposed, which has advantages of better performance and lower cost. The primary concern about the TLI is fluctuations in the common-mode voltage, which impacts switching frequency leakage current and grid interface system. An improved H7 common-mode voltage (CMV) clamped TLI with discontinuous pulse width modulation (DPWM) is designed using a conventional neural network (CNN)-based deep learning approach. In this, a completely minimized leakage current is obtained to avoid CMV transients. The proposed PV-connected improved H7-TLI provides low-loss DC-side decoupling, which further reduces leakage current and isolation of the PV system during off-grid. In addition, the effects of several factors on CNN deep learning performance are explored, including training data size, image resolution, and network configuration. The proposed technique has the potential to be used in a test instrument for intelligent signal analysis or used in an artificial intelligence system. Switching loss is analyzed using proposed and existing H7 inverters under different load conditions. To verify the theoretical explanation, existing H7 inverters is analyzed by MATLAB/Simulink, and the outcomes are tested experimentally. The total harmonic distortion (THD) analysis of proposed and existing topology is analyzed and compared. The THD values of the existing and proposed topology are 3.74% and 3.23%, respectively.

Doppler characteristics of electromagnetic echoes from sinusoidal water waves illuminated by plane wave/Gaussian beam

The Doppler spectra of the scattering fields from sinusoidal water waves illuminated by a plane wave or Gaussian beam are numerically simulated with the method of moment (MoM). When the sinusoidal water surface is illuminated by a plane EM wave, the numerical results show that the Doppler spectrum of the scattering field is distorted seriously due to the frequency leakage. For this case, not only the resonance spectral peaks corresponding to the phase velocity of the water wave but also other equally spaced harmonic peaks appear on the spectrum curve. However, when the sinusoidal water surface is illuminated by a Gaussian beam with appropriate beam width, the harmonic peaks can be effectively suppressed. To better explain this phenomenon, the theoretical model for the spectrum of the scattering field from a sinusoidal water wave is derived based on the first-order small slope approximation theory (SSA-I). And this theoretical model proposed by us could give a reasonable explanation for the above phenomenon.

Three-Point Synchrophasor Estimator With Better Off-Nominal Frequency Leakage Reduction

Synchronous phasor measurements have long been an important tool in power flow modelling and network state estimation as well as in many other tasks that support power grid observability. Classic phasor estimation algorithms are often preferred over complex alternatives. They are based on a variant of the Discrete Fourier Transform (DFT) while relying on a sampling frequency locked to the system nominal frequency. The spectral leakage caused by the small off-nominal frequency excursions in such settings introduces errors that are handled by the estimation algorithms to a different extent. Well-known three-point averaging filter (3P) is a low-cost spectral leakage reduction technique in one of the simplest estimators based on a single-bin DFT. However, it only partially removes the oscillating components. When an independent standard-based frequency tracking is available, the errors can be further compensated with minimal cost. We propose a frequency-corrected three-point estimator (F3P) to eliminate the induced spurious spectrum progressively with the increasing sampling rate while building on the analytical expression of the remaining error. We show performance benefits of the F3P under finite sampling rates when compared to the baseline 3P and to the classical Interpolated DFT (IPDFT) in static conditions. The F3P removes most of the leakage without the need of data resampling. In less ideal conditions with additive 50-dB noise, up to a 10-fold reduction of the 3P error is achieved. The error ratio of the reference IPDFT over the F3P is approximately 1.4 under the same conditions and largely independent of the frequency excursion. The presented simulation results prove the algorithm's superior performance in most of the steady-state tests defined by the relevant Standard, whereas the dynamic performance can be brought to an acceptable level by the use of a single-cycle observation window, with the response times comparable to those of the IPDFT.

Accuracy analysis of GNSS-IR snow depth inversion algorithms

In recent years, with the continuous development of Global Navigation Satellite System (GNSS), it has been applied not only to navigation and positioning, but also to Earth surface environment monitoring. At present, when performing GNSS-IR (GNSS Interferometric Reflectometry) snow depth inversion, Lomb-Scargle Periodogram (LSP) spectrum analysis is mainly used to calculate the vertical height from the antenna phase center to the reflection surface. However, it has the problem of low identification of power spectrum analysis, which may lead to frequency leakage. Therefore, Fast Fourier Transform (FFT) spectrum analysis and Nonlinear Least Square Fitting (NLSF) are introduced to calculate the vertical height in this paper. The GNSS-IR snow depth inversion experiment is carried out by using the observation data of P351 station in PBO (Plate Boundary Observatory) network of the United States from 2013 to 2016. Three algorithms are used to invert the snow depth and compared with the actual snow depth provided by the station 490 in the SNOTEL network. The observations data of L1 and L2 bands are respectively used to find the optimal combination between different algorithms further to improve the accuracy of GNSS-IR snow depth inversion. For L1 band, different snow depths correspond to different optimal algorithms. When the snow depth is less than 0.8 m, the inversion accuracy of NLSF algorithm is the highest. When the snow depth is greater than 0.8 m, the inversion accuracy of FFT algorithm is higher. Therefore, according to the different snow depth, a combined algorithm of NLSF + FFT is proposed for GNSS-IR snow depth inversion. Compared with the traditional LSP algorithm, the inversion accuracy of the combined algorithm is improved by 10%. For L2 band data, the results show that the accuracy of snow depth inversion of various algorithms do not change with the variations of snow depth. Among the three single algorithms, the inversion accuracy of FFT algorithm is better than that of LSP and NLSF algorithms.

Automatic Detection of Amplitude-Distorted Samples from Clipped Seismic Waveforms

AbstractSeismic waveforms are essential for seismology but are clipped when their actual amplitudes are too high to be faithfully recorded by seismometers. The clipping effects are popular for both big earthquakes and small earthquakes within a short epicentral distance. Here, we illustrate potential risks of direct usage of clipped waveforms by examining the frequency leakage and show the failure of bandpass filtering for different clipping levels; then we summarize two characteristics of clipped records: (1) The temporal gradient is unusually large around the clipped segment compared with the unclipped portions, and (2) the clipped samples cluster into one segment or several if many samples are involved. Next, we propose three criteria for distinguishing clipped samples from the perfect samples based on these two characteristics. Finally, we design a numerical algorithm for automatic detection of clipped samples using constraints on the gradient, amplitude, and gradient-varying range. Numerical experiments show the excellent performance of our algorithm on automatically detecting the clipped samples. Our algorithm seamlessly integrates all necessary constraints for both flat-top type and back-to-zero type and thus can correctly recognize these two types simultaneously; in addition, it is basically data driven and thus can work well without considering seismometer configuration and instrument type, which would be helpful for real-time detection of clipped records without interruption from human operations. As a robust and swift tool of automatic detection on amplitude-clipped samples, our algorithm could identify most typical clipped records and reduce potential risks due to using unrecognizable clipped waveforms; furthermore, it would be helpful for fast detection and possible restoration of clipped waveforms in the presence of huge volumes of data.

Stability analysis and control optimisation based on particle swarm algorithm of modular multilevel matrix converter in fractional frequency transmission system

Modular multilevel matrix converter (M3C) is a competitive option in the fractional frequency transmission system (FFTS) application. Focusing on stability and power quality issues, this study firstly proposes a new mathematical model and control strategy. Different from the previous research, this control scheme is based on the frequency decoupling model of double dq coordinate transformation and the control of the sub-converter, which implements the frequency decoupling control and solves the frequency leakage problem. Subsequently, a complete state-space model and small-signal model of M3C are built for analysing small disturbance stability. On this basis, the optimisation of M3C in FFTS is studied, and an optimisation method based on particle swarm algorithm is proposed. This method can directly design the adaptive objective function according to the optimisation requirements of system control performance to simultaneously optimise all controller parameters of the system. After optimisation, the stability and dynamic performance of the system have been significantly improved. Finally, the effectiveness of the proposed control and optimisation is verified by the simulation results in MATLAB/ Simulink.

Subspace-Based Blood Power Spectral Capon Combined with Wiener Postfilter to Provide a High-Quality Velocity Waveform with Low Mathematical Complexity

In Doppler analysis, the power spectral density (PSD), which accounts for the axial velocity distribution of the blood scatterers, is estimated. The conventional spectral estimator is Welch's method, which suffers from frequency leakage at small observation window length. The performance of adaptive techniques such as blood power Capon (BPC) has been promising at the cost of higher computation complexity. Reducing the computational complexity while retaining the benefits of BPC would be necessary for real-time implementation. The purpose of the work described here was to investigate whether it is possible to decrease the computation load in BPC and still obtain acceptable results. The computation complexity in BPC is owing primarily to the matrix inversion required for computing the PSD estimate. We here propose the subspace blood power Capon technique, which employs a data covariance matrix with reduced number of rows in estimation of the weight vector. In maximum velocity estimation in the spectra, the signal noise slope intersection envelop estimator that makes use of the integrated power spectrum is employed. The evaluations are made based on both simulated and in vivo data. The results indicate that it is possible to reduce the order of complexity to almost 12.25% at the cost of 2.31% and 2.24% increases in the relative standard deviation and relative bias of the estimates. Moreover, the Wiener post-filter as a post-weighting factor, which will be multiplied by the final weight vector of the spectral estimator, estimates the power of the desired signal and the power of the interference plus noise to improve the contrast. The proposed estimator has exhibited a promising performance at beam-to-flow angles of 45°, 60° and 75°. Furthermore, the robust performance of the proposed estimator against variation in the flow rate is also documented.

Accurate Frequency Estimation by Using Three-Point Interpolated Discrete Fourier Transform Based on Rectangular Window

Windowed interpolated discrete Fourier transform (DFT) has been well-studied to deal with the spectral leakage and picket fence effects in frequency estimation. When the number of acquired sine-wave cycles is small, the long-range spectral leakage of the negative frequency is the main cause of low accuracy. In this article, a novel frequency estimator using three-point interpolated DFT based on rectangular window is proposed. The spectral superposition of positive and negative frequencies is adopted in the proposed interpolation algorithm to remove both short- and long-range spectral leakage. The influence of white noise on frequency estimation can be reduced because the adopted rectangular window has the narrowest mainlobe width or the smallest equivalent noise bandwidth among all windows. Simulation and experimental results confirm that the proposed method outperforms existing windowed interpolated DFT algorithms.

Modeling and Control of Modular Multilevel AC/AC Converter in Y Configuration for Fractional Frequency Transmission System

The modular multilevel AC/AC converter topology in Y configuration, which is called Y‐MMC, suitable for fractional frequency transmission system is proposed in this paper. Y‐MMC can directly connect two three‐phase AC systems of different frequencies and voltage amplitudes with only six equivalent branches, and it has satisfying performance in power quality and characteristics. Y‐MMC enjoys a simple and symmetrical structure with no circulating current problem. The detailed topology and operating principle of Y‐MMC are addressed in this paper. The frequency‐decoupled mathematical model of the Y‐MMC system is deduced. Corresponding control scheme is thoroughly designed, including the inner loop current control, the outer loop control, the individual‐balancing control, and frequency leakage suppression control. The paper also lays emphasis on the optimization of reactive power distribution between the main branches and the assistant branches of Y‐MMC. The validity of the Y‐MMC topology and the effectiveness of the proposed control scheme are verified by the simulation results in MATLAB/Simulink. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

EM Scattering From a Simple Water Surface Composed of Two Time-Varying Sinusoidal Waves

Some novel phenomena, which cannot be well explained by the traditional Bragg scattering theory, have been observed through the electromagnetic (EM) scattering from a water surface composed of two sinusoidal waves. According to the traditional Bragg scattering theory, the scattering intensity from water surface is only proportional to the spectral density of the Bragg resonant waves. However, the scattering field numerically simulated by the method of moment (MoM) method reveals that the resonant scattering field would also be affected by the amplitude of the non-resonant wave. In some special cases, despite the existence of the Bragg resonant waves, the Bragg resonant scattering field disappears when the amplitude of the non-resonant water wave is equal to some specific values. From the numerical results, another noticeable phenomenon is found that the Doppler spectrum of the scattering field is distorted seriously due to the frequency leakage. When the water surface with finite length is illuminated by a plane EM wave, not only the resonance spectral peaks corresponding to the phase velocity of the water wave but also other harmonic peaks appear on the spectrum curve. However, if a Gaussian beam is used instead of the plane EM wave, the harmonic peaks can be effectively suppressed. To better understand the phenomena, the theoretical model of the scattering field from the simple water surface is derived in the framework of the first-order small slope approximation method. And the empirical formulas for selecting the Gaussian beam width and water surface length are also proposed.

Design of hybrid‐frequency current source based on multiresonance network

In order to overcome the low efficiency and poor resolution of single‐frequency transmitters for electromagnetic sounding and wireless power transfer (WPT), a well‐organized multifrequency resonant network is proposed to generate a synthetized current with two or more frequencies. The complete design and realization of the hybrid‐frequency current source is presented. The characteristic equation method is applied to extract the resonance frequencies from the given network. On the other hand, the nonlinear equation system about the passive elements is built and solved by the trust–region algorithm based on the expected frequencies. The multifrequency sinusoidal pulse width modulation method is first proposed to create the barcode driving signals for a full‐bridge inverter. The asynchronous modulation is recommended to reduce the harmonic components beyond the resonance frequencies, and the modulation ratios for the driving signals are adjusted at any resonance frequency so that the energy can be distributed evenly at different resonance points. The simulation results prove that almost all energy is concentrated at the resonance frequencies, and the frequency leakage is hardly seen. The resonant network and its control method is very useful to create a hybrid‐frequency current source for high‐efficiency and high‐resolution electromagnetic sounding and WPT. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Time-frequency characteristics estimation of underwater moving objects using memory-dependent derivative method

The line-spectra changes of the radiated noise of underwater moving object is observed as the form of narrow-band time varying signal due to the Doppler effect. The modulation law of the time varying signal contains a large number of feature information of moving targets, which can be used for detection and classification. The goal of time-frequency analysis is to extract subtle changes the function relationship of frequency over time. In this research, a memory-dependent derivative methodology is proposed to deal with accurate time–frequency representation of time varying signals under strong background noise. Memory-dependent derivative is a convolution of a common derivative by the time-varying signals with a dynamic weighted function in the past period time. Considering the stated methodology, it is derived that the discrete data from previous times to estimate signal value at current time and reduce the effects of the noise. Using the Fourier transformation with different scales and delays transformation as the kernel function, the energy concentrated time-frequency curve is obtained with higher resolution and without frequency leakage. The simulated results demonstrate that given method is immune to background noise and estimate the main frequencies with high accuracy, specially the rapid change of the modulated frequency.

Low PAPR Filter Bank Single Carrier for 5G mMTC

Asynchronous transmission for 5G massive machine type communication (mMTC) reduces power consumption and provides longer battery life of mMTC devices compared to synchronous transmission because of less signaling interaction between the base station and mMTC devices. To reduce frequency leakage from other user devices, several waveforms based on modification on orthogonal frequency division multiple (OFDM) with low out-of-band (OOB) emission property has been proposed in 5G new radio. However, those waveforms are typically of high peak to average power ratio (PAPR) and it has been shown for those waveforms there is OOB emission regrowth for mMTC devices caused by nonlinear power amplify (PA). We propose a low PAPR filter bank single carrier frequency division multiple access (SC-FDMA) waveform, called LP-FBSC, which helps to resist OOB emission regrowth caused by nonlinear PA. Two filters are applied in one stream to achieve low PAPR and low OOB emission performance, where one filter is poly phase network (PPN) structure in time domain for low OOB emission purpose, and the other is applied at frequency domain with element-wise multiplication for low PAPR purpose. In addition, the proposed method introduces multiple streams for purpose of even further reduced PAPR, where the modulated data and filter coefficients of the other streams are determined from those of first stream. For Pi/2-BPSK and Pi/4-QPSK modulation, the PAPR for LP-FBSC can be as low as 2.6 dB and 4.2 dB while low OOB emission property being maintained.

Fluctuation Signal Analysis of Hydraulic Turbine Based on Hilbert-Huang Transform and Median Filter

As a new time-frequency analysis technique, Hilbert-Huang Transform (HHT) behaves differently in signal decomposition and analysis method, but it is weak in noise resistance, even low noise may disturb the HHT result greatly. The paper launches an investigation on the application of HHT for fluctuation signal analysis of turbine draft tube. The analytic framework for HHT is introduced, median filter is adopted to reduce the frequency leakage of certain signal component. The experiment data from the turbine of hydropower station is analyzed by the method. The results shows that the proposed method can reveal time-frequency features of the signal effectively.

Integrated circuit technology characterization and evaluation using automated CAD tool

In this paper an automated CAD tool that can be used in integrated circuit technology characterization is proposed. The proposed methodology fills the gap found in old, as well as, new IC design methodologies. The tool allows the user to perform a rapid and full characterization for different device models available in a process design kit (PDK). A set of pre-defined suite of test-benches are created to cover different aspects of circuit design. A seamless integration of the tool in typical design environments is achieved using SKILL code and OCEAN script. Moreover, the tool can compare different PDK releases or different technologies in terms of DC/AC performance, high frequency operation, leakage, and layout area efficiency. The paper presents the tool structure, interface, and capabilities. Finally, a characterization example is applied to CMOS 130 nm technology; results are shown for different devices characterization: MOSFET, BJT, Diode, Resistor, and Capacitor.

Exploiting Voltage Regulators to Enhance Various Power Attack Countermeasures

The security implications of on-chip voltage regulation on the effectiveness of various voltage/frequency scaling-based countermeasures such as random dynamic voltage and frequency scaling (RDVFS), random dynamic voltage scaling (RDVS), and aggressive voltage and frequency scaling (AVFS) are investigated. The side-channel leakage mechanisms of different on-chip voltage regulator topologies are mathematically analyzed and verified with circuit level simulations. Correlation coefficient between the input data and monitored power consumption of a cryptographic circuit is used as the security metric to compare the impact of different on-chip voltage regulators when implemented with the aforementioned countermeasures. As compared to a cryptographic circuit without countermeasure, the RDVFS technique implemented with an on-chip switched-capacitor voltage converter reduces the correlation coefficient over 80 percent and over 92 percent against differential and leakage power analysis attacks, respectively, through masking the leakage of the clock frequency and supply voltage information in the monitored power profile.

Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor Liquid Annular Seals Utilizing Computational Fluid Dynamics

Circumferentially grooved, annular liquid seals typically exhibit good whirl frequency ratios (WFRs) and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15-step groove-on-rotor annular liquid seal by means of computational fluid dynamics (CFD), in contrast to the previous studies which focused on a groove-on-stator geometry. The seal dimensions and working conditions have been selected based on experiments of Moreland and Childs (2016, “Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics,” M.Sc. thesis, Texas A&M University, College Station, TX). The frequency ratios as high as four have been studied. Implementation of pressure-pressure inlet and outlet conditions make the need for loss coefficients at the entrance and exit of the seal redundant. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of the excitation frequency. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, preswirl ratio (PSR), and rotordynamic coefficients. It was found that PSR will be about 0.3–0.4 at the entrance of the seal in the case of radial injection, and outlet swirl ratio (OSR) always converges to values near 0.5 for current seal and operational conditions. The negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients, and small direct damping coefficients explains the destabilizing nature of these seals. Finally, the influence of surface roughness on leakage, PSR, OSR, and stiffness coefficients is discussed.

IDA‐PB control with integral action of Y‐connected modular multilevel converter for fractional frequency transmission application

Y-connected modular multilevel converter (Y-MMC) is a new topology of direct AC/AC power conversion, with broad application prospects in fractional-frequency transmission system. This study studies the mathematical model of Y-MMC and builds the port-controlled Hamiltonian model. Since vector control scheme can hardly ensure global stability, the interconnection and damping assignment passivity-based control (IDA-PBC) method is applied for controller design of Y-MMC. Three typical IDA-PBC strategies are then proposed, featuring the asymptotical stability of the desired equilibrium. To eliminate steady-state error, integrators are further added to the IDA-PB controller. Different from the previous research, the proposed method enables the decoupling of different-frequency components and the suppression of frequency leakage. Besides, the reactive power distribution coefficients are introduced to characterise the optimisation allocation of reactive power between arms. Finally, the effectiveness and superiority of the proposed control strategy are verified by both the simulation and experiment results.