Second-order Harmonic Component Research Articles

Synthetic aperture imaging of contact acoustic nonlinearity to visualize the closing interfaces using tone-burst ultrasonic waves

Abstract Contact acoustic nonlinearity (CAN) effect was visualized by synthetic aperture focusing technique (SAFT) via a signal-processing method for acoustic nonlinearity imaging. The proposed signal-processing technique, named Synthetic Aperture Imaging of Acoustic Nonlinearity (SAIAN), allows the SAFT to visualize CAN that is difficult to be visualized by linear ultrasonic imaging. Using the SAIAN algorithm, the fundamental and second-order harmonic frequency components are extracted from the tone-burst wave signal and then these component signals are transformed into pulse-like signals. From the pulse-like signals, the CAN parameter signals can be obtained in the form of pulses, which allows CAN to be visualized by SAFT. In order to verify the effectiveness of the SAIAN, the nonlinear ultrasonic measurements using tone-burst waves were conducted to visualize closing interfaces. As a result, CAN effect appeared at partially closed part of a contacting interface in the images of the CAN signals converted by the SAIAN; on the contrary, the CAN feature was not shown in linear ultrasonic images based on the fundamental frequency component. These results support that the SAIAN is a useful signal processing for acoustic nonlinearity visualization that improves the probability of detection of closing interfaces and the accuracy in crack sizing.

Influence of switch angles on second‐order current harmonic and resonance in switched reluctance motors

This study investigates the origin of resonance in switched reluctance motor (SRM). It has been found that the second-order harmonic component of phase current is one of the major origins, which may cause resonance when its frequency multiplied by three caused by three phases coincides with natural frequency. It has also been demonstrated that there is a natural-frequency-centred band, saying that as long as the excitation frequency or its harmonics locates in the band, resonance will be excited. Accordingly, influence of critical parameters such as turn-on and turn-off angles on second-order current harmonic and corresponding vibration caused by resonance have been fully studied. Based on the study, optimal switch angles can be used to reduce second-order current harmonic, and thus to reduce vibration and noise caused by resonance. Both simulation and experimental results show that resonance can be effectively reduced by selection of optimal switch angles.

Optical Single Sideband Modulator Without Second-Order Sidebands

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

Single-Phase Boost Inverter-Based Electric Vehicle Charger With Integrated Vehicle to Grid Reactive Power Compensation

Vehicle to grid (V2G) reactive power compensation using electric vehicle (EV) onboard chargers helps to ensure grid power quality by achieving unity power factor operation. However, the use of EVs for V2G reactive power compensation increases the second-order harmonic ripple current component at the DC-side of the charger. For single-phase, single-stage EV chargers, the ripple current component has to be supplied by the EV battery, unless a ripple compensation method is employed. Additionally, continuous usage of EV chargers for reactive power compensation, when the EV battery is not charging from the grid, exposes the EV battery to these undesirable ripple current components for a longer period and discharges the battery due to power conversion losses. This paper presents a way to provide V2G reactive power compensation through a boost inverter-based single stage EV charger and a DC-side capacitor without adversely affecting the EV battery. The operation of the boost inverter-based EV charger with second-order harmonic and switching frequency ripple current reduction, the dynamic behavior of the system, the transition between different operating modes, the DC-side capacitor voltage control above a minimum allowed voltage, and the DC-side capacitor sizing are extensively analyzed. The performance of the proposed system is verified using an experimental prototype, and presented results demonstrate the ability of the system to provide V2G reactive power compensation both with and without the EV battery.

Nonlinear and viscous effects on the hydrodynamic performance of a fixed OWC wave energy converter

The hydrodynamic performance of a fixed Oscillating Water Column (OWC) device is experimentally and numerically investigated. Based on the time-domain higher-order boundary element method (HOBEM), by introducing an artificial viscosity term in the dynamic free surface boundary condition, a fully nonlinear numerical wave model is used to simulate the hydrodynamic performance of an OWC device. A set of comprehensive experiments for regular waves is carried out to validate the numerical results as well as to investigate the nonlinear effects on the hydrodynamic performance of OWC. The mechanism of the nonlinear phenomenon is investigated based on the analysis of the experimental and numerical results. The influence of the wave nonlinearity and the viscosity on the hydrodynamic efficiency is quantified by comparing the linear and nonlinear numerical results. It was found that the hydrodynamic efficiency increases with the nonlinearity and viscosity when the incident wave amplitude is small. When the incident wave amplitude is large, the hydrodynamic efficiency is reduced by the weakened transmission of the second-order harmonic wave component due to the strong wave nonlinearity. However, when the wave amplitude is between these two regimes, the wave is weakly nonlinear, the efficiency decreases with the wave amplitude due to the combined effect of the nonlinearity and viscosity.

Non-linear Min protein interactions generate harmonics that signal mid-cell division in Escherichia coli.

The Min protein system creates a dynamic spatial pattern in Escherichia coli cells where the proteins MinD and MinE oscillate from pole to pole. MinD positions MinC, an inhibitor of FtsZ ring formation, contributing to the mid-cell localization of cell division. In this paper, Fourier analysis is used to decompose experimental and model MinD spatial distributions into time-dependent harmonic components. In both experiment and model, the second harmonic component is responsible for producing a mid-cell minimum in MinD concentration. The features of this harmonic are robust in both experiment and model. Fourier analysis reveals a close correspondence between the time-dependent behaviour of the harmonic components in the experimental data and model. Given this, each molecular species in the model was analysed individually. This analysis revealed that membrane-bound MinD dimer shows the mid-cell minimum with the highest contrast when averaged over time, carrying the strongest signal for positioning the cell division ring. This concurs with previous data showing that the MinD dimer binds to MinC inhibiting FtsZ ring formation. These results show that non-linear interactions of Min proteins are essential for producing the mid-cell positioning signal via the generation of second-order harmonic components in the time-dependent spatial protein distribution.

Relative measurement of the acoustic nonlinearity parameter using laser detection of an ultrasonic wave

The relative acoustic nonlinearity parameter β' is defined by the amplitudes of the fundamental and second-order harmonic components in the detected ultrasonic wave signal, in which a piezoelectric transducer is conventionally used for detection. Although it is not identical to the absolute parameter β defined by the displacement amplitudes, β' has been widely used for the relative comparison between the same materials since its ratio is identical to that of the absolute parameter when the detected signal amplitude is proportional to the displacement amplitude. However, β cannot be replaced by β' for the comparison between different materials due to the difference of respective acoustic impedance. This study aims to show that a laser detection method using a photorefractive interferometer can be used for the relative comparison of acoustic nonlinearity between different materials because its output is independent of the acoustic impedance. To demonstrate, two similar materials, Al6061-T6 and Al2024-T4, and one different material, copper, were tested. Experimental results showed that the ratio β 2024 / β 6061 , measured via the proposed method and the conventional piezoelectric detection method, were in good agreement with the references. However, in the case of β Cu / β 6061 , only the proposed method showed good agreement with the references.

압전형 수신 기법을 이용한 초음파 절대변위진폭 측정

음향 비선형 파라미터는 입사시킨 기본주파수 성분의 변위 진폭 크기와 재료의 비선형성에 의하여 발생된 2차 고조파 성분의 변위 진폭 크기의 비로 정의된다. 본 연구에서는, 압전소자 방식을 이용한 초음파 절대변위진폭 측정의 타당성을 확인하고자, 이 기법을 통해 초음파가 입사된 SUS316 시편의 절대변위진폭을 측정하였다. 또한 비교를 위해, 레이저를 통한 패브리패럿 방식의 간섭계를 이용하여 동일 시편에 대한 절대변위진폭을 측정하였다. 두 가지 기법을 통한 실험 결과는 서로 잘 일치하는 경향을 보였으며, 특히 압전형 수신 기법의 경우 기존의 레이저 변위측정기법에 비하여 반복 측정의 안정성이 우수한 것으로 나타났다. 이 결과로부터 압전형 수신 기법은 기존 레이저 측정 기법에 비하여 과정이 복잡하지만, 미세변위를 더 안정적으로 측정할 수 있어 음향 비선형 파라미터의 측정에 유리할 것으로 기대된다. A nonlinear ultrasonic parameter is defined by the ratio of displacement amplitude of the fundamental frequency component to that of the second-order harmonic frequency component. In this study, the ultrasonic displacement amplitude of an SUS316 specimen was measured via a piezo-electric-based method to identify the validity of piezo-electric detection method. For comparison, the ultrasonic displacement was also determined via a laser-based Fabry-Pérot interferometer. The experimental results for both measurements were in good agreement. Additionally, the stability of the repeated test results from the piezo-electric method exceeded that of the laser-interferometric method. This result indicated that the piezo-electric detection method can be utilized to measure a nonlinear ultrasonic parameter due to its excellent stability although it involves a complicated process.

A method to estimate the absolute ultrasonic nonlinearity parameter from relative measurements

The ultrasonic nonlinearity parameter (β) is determined from the particle displacement amplitudes of the fundamental and second-order harmonic components in an ultrasonic wave propagated through a material. This parameter is generally referred to as the absolute parameter. However, measuring the second harmonic component is especially difficult because its amplitude is usually much smaller than those of signals in typical ultrasonic measurements. For this reason, most studies use the relative parameter determined using the measured electric signal amplitudes of the fundamental and second harmonic ultrasonic waves. However, in many occasions, the absolute parameter is needed for a quantitative assessment of material degradation. This study proposes a method to estimate the absolute parameter from a measured relative parameter along with a proportionality constant between normalized absolute and relative parameters. This method is based on the observed fact that the ratio of between normalized relative and absolute parameters is identical after compensating proportionality constant. The method was experimentally validated for Al6061-T6 alloy specimens heat-treated for different aging times. The parameter determined through the proposed method were compared with the absolute parameters which were measured separately. The results show that these two parameters were close to each other within the measurement errors.

An Input Current Feedback Method to Mitigate the DC-Side Low-Frequency Ripple Current in a Single-Phase Boost Inverter

A boost DC/AC converter is popular in AC line-integrated energy storage systems (ESSs) based on low-voltage DC sources such as battery, fuel cell, or supercapacitor. The direct DC/AC power conversion in the boost inverter introduces a second-order harmonic ripple current at the DC side of the boost converter, which leads to internal heating of the energy storage devices and degradation of their lifetime. In this paper, a novel current feedback method is proposed to mitigate the second-order harmonic current component at the DC side. The proposed method is able to significantly reduce the second-order harmonic component in the DC-side current of the boost inverter without increasing other harmonic components. Performance of the proposed method is validated on a single-phase grid-connected DC/AC boost inverter-based battery ESS experimental prototype.

Operating Region of Modular Multilevel Converter for HVDC With Controlled Second-Order Harmonic Circulating Current: Elaborating P-Q Capability

The operating region of the modular multilevel converter (MMC) is limited by the maximum-allowable voltage ripple of cells, which is associated with the arm energy variation. Injecting the controlled second-order harmonic component into the circulating current can reduce energy variation of the arm and, thus, extend the operating region of MMC. Care must be taken, however, that the second-order circulating current affects the arm current, and inappropriately injected harmonic current may cause an undesirable arm current polarity change. Therefore, this paper first investigates and proposes the maximum-allowable second-order circulating current for extending the operating region reliably and efficiently. The active and reactive power capability of MMC is further elaborated and illustrated in line with the maximum excess energy capability for two cases, running with: 1) the original operating region and 2) the extended operating region. Finally, the $P$ - $Q$ diagrams for contingent operating conditions with faulty or disabled submodules are presented. Understanding the unique shape and change of $P$ - $Q$ capability with credible submodule failure contingency should be crucial for planning MMC-HVDC lines, and determining the energy requirements and the level of redundancy in submodules properly in order to achieve the envisioned benefits of the new HVDC. The efficacy and accuracy of the research findings are validated for the MMC-HVDC system using PSCAD/EMTDC.

Modified controls for doubly fed induction generator under unbalanced voltage for torque stability controller

This paper presents both the previously and newly modified Stator Flux Oriented Control (SFOC) with Pulse Width Modulation (PWM) and Hysteresis Current Controller (HCC) structures for Doubly Fed Induction Generator (DFIG) in wind turbines to improve responses of active power, reactive power and generator's torque during the grid voltage unbalance. In the proposed SFOC-based scheme, which emphasizes on improvement of generator's torque performance, PI controllers with Fuzzy logic, Notch filters and the Torque Stability Controller (TSC) are utilized. The other control techniques use single or multiple applications of PI controller with anti-windup, hybrid PI-Fuzzy controller with anti-windup and Notch filter to eliminate the second-order harmonic components. The designed system consists of a wound rotor induction generator and power-electronics converters at both rotor and grid sides. The modifications are applied to the rotor side converter (RSC). Simulations in Matlab/Simulink illustrate the enhanced stability of torque, active and reactive powers delivered by DFIG in both the SFOC-based and HCC-based schemes. Moreover, comparisons in simulation results, obtained separately from all the presented control structures, are provided to evaluate the effectiveness of the newly proposed scheme.

A Diagnostic Method of Simultaneous Open-Switch Faults in Inverter-Fed Linear Induction Motor Drive for Reliability Enhancement

To enhance the reliability in an inverter-fed linear induction motor (LIM) drive under simultaneous open-switch faults, practical online basis fault detection and localization schemes are presented. The open-switch faults in the inverter incur overcurrent stress to other electric components, resulting in a severe secondary fault in the entire system. As compared with the conventional schemes that the fault detection and faulty switch identification rely on the averaging or current error from the reference value, the proposed algorithms are achieved through signal processing schemes such as harmonic analysis, averaging, and waveform analysis by using only the measured current information. In addition, the proposed scheme classifies the open-switch faults as four faulty groups according to their unique fault signature, which enables the proposed scheme to identify faulty switches effectively. Since the fault detection is accomplished by using the relative magnitude of the second-order harmonic component in phase currents, the influence on steady-state error or dc offset of current is significantly reduced. Once the fault is detected, the operating mode is changed to identify the faulty group which the fault belongs to. By identifying the faulty group, the faulty switches can be found in a much more straightforward way. The entire LIM drive system is implemented using DSP TMS320F28335 to verify the feasibility of the proposed fault detection and faulty switch identification schemes. Without requiring any additional hardware or measuring apparatus, the proposed diagnostic algorithm can effectively detect a fault even under simultaneous open-switch faults by online basis.

Fault Diagnosis in a Permanent Magnet Synchronous Generator based Variable Speed Grid-connected Wind Power Conversion

Switch open fault characteristics and simple diagnosis scheme in a permanent magnet synchronous generator (PMSG) based variable-speed grid-connected wind power conversion are presented. In the back-to-back converter, the failure in switching devices may occur either in a machine side converter (MSC) or in a grid side converter (GSC), which decreases the generator output power and degrades the stability in wind power generation system. To detect such a fault, a monitoring scheme for the second-order harmonic components in the qaxis current is proposed, where the harmonic values are simultaneously observed in the MSC as well as in the GSC to monitor abnormal operation of system. To determine the harmonic values irrespective of operating conditions, the normalized currents are employed for the harmonic calculation. To verify the effectiveness of the proposed fault diagnosis scheme, the comparative simulation results are presented. As a result, an on-line simple diagnosis scheme which monitors the condition of generation system can be realized without requiring any additional hardware equipment.

Improved Control of DFIG during Grid Voltage Distortion for Reduction of Current Harmonic Using PI-Fuzzy

This paper presents a new vector Hysteresis Current Control (HCC), which is applied on a three-phase three-level Voltage Source Inverter (VSI) and eliminate rotor currents harmonics using PI-Fuzzy controller (PI-F). The proposed control technique is used to control the active and reactive power of wind turbines by means of controlling the rotor currents of the Doubly Fed Induction Generator (DFIG) during grid voltage distortion for reduction of current harmonic using PI-F. These control techniques use single or multiple applications of hybrid PI-F with anti-windup and Notch filter to eliminate the second-order harmonic components and negative sequence components. In the newly proposed SFOC-based scheme, PI controllers with Fuzzy, Notch filters and the Sequence Component Controller (SCC) are utilized. The designed system consists of an induction generator with slip ring and power-electronics converters at both rotor and grid sides. The modifications are applied to the Rotor Side Converter (RSC). Simulations in Matlab/Simulink illustrate the enhanced stability of torque, active and reactive powers delivered by DFIG in both the PWM controller (PWM) and HCC schemes. Moreover, comparisons in simulation results, obtained separately from all the presented control structures, are provided to evaluate the effectiveness of the newly proposed scheme.

A 1.1-V Analog Multiplexer With an Adaptive Digital Clamp for CMOS Video Digitizers

We present the design of an integrated multiplexer and a dc clamp for the input analog interface of a high-speed video digitizer in the 1.1-V 65-nm complementary metal-oxide-semiconductor process. The ac-coupled video signal is dc restored using a novel all-digital current-mode charge pump. An eight-input multiplexer is realized with T-switches, each containing two series-connected bootstrapped switches. A T-switch's grounding branch is merged with the pull-down end of the clamping charge pump. An adaptive digital feedback loop encompassing a video analog-to-digital converter (ADC) controls the clamp charge pump. The bootstrapped switches have been adapted to suit the video environment, allowing on-the-fly recharging. The varying on-resistance of the conventional bootstrapped switch is utilized to linearize the multiplexer response by canceling the effect of the nonlinear load capacitance contributed by the clamp transistors. Under worst case conditions, the multiplexer maintains a 62-85-dB spurious-free dynamic range over a range of known input video frequencies, and it reduces the second-order harmonic component upon optimization. The dc clamp provides 12-bit precision over the full range of the video ADC and can set the dc at the target level for at most 194 video lines.

Open Fault Characteristics and Simple Diagnosis Scheme in a Back-to-Back Converter for Wind Power Conversion

Switch open fault characteristics and simple diagnosis scheme in a back-to-back converter are presented for a permanent magnet synchronous generator (PMSG) based variable-speed grid-connected wind power conversion. In the back-to-back converter, the failure in switching devices may occur either in a machine side converter (MSC) or in a grid side converter (GSC), which decreases the generator output power and degrades the stability in wind power generation system. To detect such a fault, the second-order harmonic components of the q-axis current are monitored in the MSC as well as in the GSC. To verify the effectiveness of the proposed scheme, the comparative simulation results are presented.

Second-Order Harmonic Reduction Technique for Photovoltaic Power Conditioning Systems Using a Proportional-Resonant Controller

This paper proposes a second-order harmonic reduction technique using a proportional-resonant (PR) controller for a photovoltaic (PV) power conditioning system (PCS). In a grid-connected single-phase system, inverters create a second-order harmonic at twice the fundamental frequency. A ripple component unsettles the operating points of the PV array and deteriorates the operation of the maximum power point tracking (MPPT) technique. The second-order harmonic component in PV PCS is analyzed using an equivalent circuit of the DC/DC converter and the DC/AC inverter. A new feed-forward compensation technique using a PR controller for ripple reduction is proposed. The proposed algorithm is advantageous in that additional devices are not required and complex calculations are unnecessary. Therefore, this method is cost-effective and simple to implement. The proposed feed-forward compensation technique is verified by simulation and experimental results.

Distortion Modeling of Feedback Two-Stage Amplifier Compensated With Miller Capacitor and Nulling Resistor

Accurate distortion modeling of feedback amplifier with Miller compensation is the main subject of this paper. Inspired by traditional Rosenstark method, a nonlinear signal-flow-based method has been developed. Based on the proposed method, the nonlinear coefficients of each gain stage can be evaluated exactly and the rules of cascading, feedback can be found conveniently. As a result, the second- and third-order harmonic distortion factors are obtained in a simple manner. The application range includes all kinds of Miller compensation strategies with or without feedforward compensation path. The distortion modeling of a two-stage opamp compensated with Miller capacitor and nulling resistor is used to show versatility of the proposed method. In addition, simplified distortion factor expressions, approximate characteristic frequencies of the distortion factors and the value of external configuration resistors for canceling the second-order harmonic components at DC are also derived and can be used to accelerate distortion evaluation of opamp designs. Accuracy of the method was verified by comparing the results between theoretical analysis and transistor level simulation.

Simple Online Fault Detecting Scheme for Short-Circuited Turn in a PMSM Through Current Harmonic Monitoring

To detect a stator winding fault caused by a short-circuited turn in a permanent magnet synchronous motor, a simple online fault detecting scheme is presented. The proposed scheme is based on the monitoring of the second-order harmonic components in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current through harmonic analysis. To verify the effectiveness of the proposed scheme, a test motor which allows an interturn short in the stator winding has been built, and the entire control system has been implemented using the DSP TMS320F28335.