DC Component Research Articles

Fast computational depth segmentation using orthogonal fringe patterns without pattern sequence changing.

The recently proposed omnidirectional depth segmentation method (ODSM) has advantages over traditional depth segmentation in terms of robustness and computational costs. However, this method uses at least six fringe patterns and changes their sequences multiple times to perform depth segmentation, which limits its segmentation speed and increases computational complexity. This paper proposes a fast computational depth segmentation (FCDS) method in which only five patterns are used for object segmentation at different depths into isolated regions without the requirement of pattern sequence changing. Phase singularity points are fully utilized due to their significance as depth segmentation markers to extract segmenting lines used for depth determination. Meanwhile, a modified Fourier transform algorithm (MFTA) is introduced to calculate the wrapped phase sequences, which uses two groups of orthogonal phase-shifting fringe patterns and a DC component pattern (five in total). The segmenting lines along orthogonal directions can be extracted with the FCDS method without changing the fringe sequences, which not only solves the problem of phase insensitivity but reduces the calculation costs. Besides, the problem of mis-segmentation is solved with an optimization algorithm for depth segmenting lines and successfully segments objects with abrupt depth changes. The simulation results demonstrate the effectiveness and precision of the proposed method. The experimental results prove the success of the proposed method for segmenting objects of similar color with a segmentation speed that is up to a 120% increase relative to previous methods.

Online Estimation of Per-Phase Stator Resistance Based on DC-Signal Injection for Condition Monitoring in Multiphase Drives

Multiphase drives with high reliability are receiving increasing attention by the research community in safety-critical applications. Condition monitoring is an effective way to improve drive reliability, because it can detect the development of faults and offer the possibility of predictive maintenance. Among the different condition monitoring methods, online estimation of stator resistance is a promising technique for its ability to detect high-resistance connections, overheating of stator windings and other defects. In this article, an online estimation method of stator resistance based on dc-signal injection is proposed for multiphase drives. The dc currents are injected in the subspace with the smallest main inductance to minimize the induced torque ripple. Phase voltages are measured and the dc components are extracted to calculate the resistance in all the phases. Compared with existing methods, the proposed method can estimate the per-phase stator resistance with higher accuracy and higher robustness, which provides additional benefits in condition monitoring applications. In addition, the proposed method is derived in a general way, which makes it applicable to most kinds multiphase drive systems. Experimental results on a nine-phase induction machine and a five-phase induction machine validate the high accuracy, high robustness, and high generality of the proposed technique.

An Adaptive Method for DC Current Reduction in Totem Pole Power Factor Correction Converters

Enabled by improved wideband gap semiconductor devices, the bridgeless totem pole power factor correction (PFC) converter is becoming an increasingly popular topology for front end ac input of high power battery chargers and telecom power supplies, achieving high efficiency as well as low electromagnetic interference. Unlike the conventional boost PFC, in a totem pole structure, different circuits are used for shaping the current in positive and negative half cycles. As a result, sensing inconsistencies may result in a significant dc component in the input current. In field applications, accumulation of dc currents from multiple PFC rectifier based loads can potentially lead to saturation of distribution transformers. This article proposes a low-cost method for adaptive detection and reduction of the dc input current based on time domain analysis of the dc link voltage. The effectiveness of the method in compensating manufacturing tolerances is experimentally validated on a 390 V, 1450 W interleaved totem pole PFC converter, and dc current reduction of up to 99.6% is achieved.

Centroid Moment Tensor of the 2019 MW 5.7 Changning Earthquake Refined Using 3D Green’s Functions Considering Surface Topography

TheMW5.7 Changning earthquake occurred in southern Sichuan basin on 17 June 2019 and was the largest event ever recorded in this region. There are still some arguments existing about the causes of the earthquake and its possible links with water injections. Many studies on this earthquake have been performed, but the event depths obtained among them are significantly different and the source mechanisms also exhibit variations. In this study, we design an inversion scheme and use 3D Green’s functions considering the rugged topography of this region to determine the event location and moment tensor of the Changning earthquake based on waveform fittings. The 3D model can reduce the uncertainty due to the approximation of 1D model and better constrain the solutions. The latitude and the longitude of event location are 28.34°N and 104.82°E respectively and the depth is 3.14 km. The nodal plane solutions are strike 295°/dip 88°/rake 14° and strike 204°/dip 76°/rake 178°. The percentages of DC, CLVD and ISO components are 10, −83, and −7%, respectively. The good waveform fittings at 17 broadband stations indicate the reliability of the source mechanism in this study.

A Highly Reliable Single-Phase AC to Three-Phase AC Converter With a Small Link Capacitor

Single-phase ac to three-phase ac converters are needed in numerous applications, including motor drives used for residential applications. These converters, however, suffer from an inherent problem of mismatch between instantaneous input and output powers. Specifically, the instantaneous input power has a dc component along with an alternating component with double-line frequency, while the three-phase instantaneous output power is only dc. Conventional single-phase ac to three-phase ac converters use large electrolytic capacitors to handle this mismatch of power. However, these electrolytic capacitors may have high failure rates, which contribute to reduced lifetime of the converters. Moreover, these capacitors can be bulky and heavy. This article introduces a new single-phase ac to three-phase ac converter that uses a small film capacitor instead of large electrolytic capacitors. Despite using a small film capacitor, the double-line frequency harmonic does not appear at the input or output currents/voltages. The principles of the operation of the proposed topology are presented in this article, and its performance is evaluated through both simulations and experiments.

A Single-Shot 3D Measuring Method Based on Quadrature Phase-Shifting Color Composite Grating Projection

A single-shot three-dimensional measuring method based on quadrature phase-shifting color composite grating projection is proposed. Firstly, three quadrature phase-shifting sinusoidal gratings are encoded in red (R), green (G), and blue (B) channels respectively, composed single- frame color composite grating. This color composite grating is projecting obliquely on the object by DLP. After that, the color camera which is placed in a specific location is used to capture the corresponding color deformed pattern and send it to the PC. Then, by color separation, the color deformed pattern is demodulated as the corresponding three-frame monochromatic deformed patterns with a shifted quadrature phase. Due to the existences of sensitivity differences and color crosstalk among the tricolor channels, we propose a gray imbalance correction method based on the DC component’s consistency approximation. By the established 3D reconstruction physical model, the measurement of 3D shape can be achieved. Many experimental results for static and moving objects prove the proposed method’s feasibility and practicability. Owing to the single-shot feature of the proposed method, it has a good application prospect in real-time and high-speed 3D measurement.

The instantaneous dynamic resistance voltage of DC-carrying REBCO tapes to AC magnetic field

When a REBCO tape carrying DC transport current is exposed to a perpendicular AC magnetic field with amplitude above certain value, flux could be triggered to traversing the superconducting tape. During the process, a biased DC response voltage, called the dynamic resistance voltage will be induced. In the paper, the calculation on the time-dependent dynamic resistance voltage was carried out by the H-formulation model implemented in the finite-element method (FEM) software package COMSOL Multiphysics. Fourier analysis on the waveform of dynamic resistance voltage was utilized to figure out the main components of the response voltage. The DC component, second harmonic component and ratio of the two components can reflect how the instantaneous dynamic resistance responds to the applied AC magnetic field and the DC transport current. The findings in the paper can be used to monitor the state of DC-carrying REBCO tapes subject to an AC magnetic field.

WITHDRAWN: Circulating current harmonics suppression with fuzzy controller in modular multi-level inverter

Abstract This paper describes the MMCs useful for HV high power AC to DC conversion. The MMCs with increased number of sub module levels provide quasi sine processing with less THD on the AC side. Modular multilevel converters (MMCs) have become prominent among emerging topologies of medium& higher voltage applications in the near future. However, one of the demerit of MMCs is the occurrence of circulating nature of flow of electrons, which has a dc portion with ac harmonics of even-order less frequency signals. If not eliminated or reduced, This harmonics allow the arm currents to increase the loss of power and have a higher effect on solid state portions of the current. This paper executes a novel rotating current scheme based on fuzzy logic to track the dc component and limit low-frequency harmonics. The fuzzy system modelling methodologies and stabilising parameter analysis are brought together. The feasibility of the scheme proposed was carried out by simulation.

Equivalent characteristic impedance based hybrid-HVDC transmission line fault location

Aiming at the transmission line fault in Hybrid-HVDC system, this paper divides the fault evolution process into different stages according to the difference of transition resistance at the fault point and the conduction state change of power electronic devices, emphatically analyzes the conversion conditions between different stages, and proposes an adaptive criterion for judging the moment when the fault evolves into AC feed-in stage. Based on the characteristic component of electrical quantities at AC feed-in stage, this paper defines the equivalent characteristic impedance at any point of transmission line, derives the functional relationship between the fault distance and the equivalent characteristic impedance at inverter side DC bus, and locates the fault point according to this relationship. In order to extract the characteristic component of electrical quantities, a characteristic component extraction algorithm is studied, it can effectively eliminate the influence of constant DC component and decaying aperiodic component. This paper builds the Hybrid-HVDC system simulation model and carries out simulation experiments on PSCAD/EMTDC, and compares the proposed fault location principle with the existing methods. The simulation results verify the effectiveness of the adaptive criterion for judging the AC feed-in stage starting moment and the proposed fault location principle.

Adaptive leakage cancelation method in frequency modulated continuous wave radar for foreign object debris detection

Frequency modulated continuous wave (FMCW) radar is widely used for foreign object debris (FOD) detection. A major defect of FMCW radar is that the unpreventable phase noise of the transmitter will bring leakage signal to the receiver, leading to a severe degradation of detection sensitivity for FOD. In this work, we first analyzed the radar output signal and explored the time-domain characteristics of the leakage signal. Based on this, we proposed a novel adaptive leakage cancelation method that can eliminate the leakage signal in the intermediate frequency domain. The proposed method only needs digital signal processing without additional hardware. Furthermore, this method can track the change of leakage signal adaptively to keep radar's high detection accuracy all the time. An experiment that using a 76 GHz FMCW radar has been carried out to verify the effectiveness of our method. The results showed that the leakage signal calculated by this method has a 99% correlation coefficient with the actual leakage signal. The system noise floor is significantly decreased after the cancelation, and the suppression of DC component which caused by leakage is more than 60 dB, all of those showed that our method achieves almost perfect cancelation of the leakage.

Operation and design analysis of an interleaved high step‐up DC–DC converter with improved harnessing of magnetic energy

SummaryIn this paper, a new interleaved DC–DC converter based on a coupled and a single input inductor is proposed. The suggested high step‐up converter utilizes various inductive and capacitive methods to transfer magnetic energy more efficiently. The output voltage is regulated with the switches' duty cycle and the coupled inductor (CI) turns ratio, which provide a wide output voltage range. Interleaving improves the converter reliability, employs both the first and third areas of CI's B‐H plane, cancels DC component of the CI, and reduces the input current ripple of the proposed converter with twice switching frequency. Utilization of two output ports for voltage stress and ripple reduction in each port, recycling the stored energy of inductances in both forward and flyback mechanisms, alleviation of switch voltage spikes, operation without circulating current, high power density, independency of switch voltage stress to the CI turns ratio, and continuous input current can be mentioned as other features. In this paper, continuous and discontinuous conduction modes' steady‐state analytics, power loss calculations, and design procedure of the proposed converter are followed with comprehensive comparisons to evaluate the capabilities. Eventually, experimental results are presented to validate theoretical calculations.

Merenje komponenti električne snage po standardu IEEE 1459-2010

In this paper, the design and implementation of a novel recursive method for the power measurement ac-cording to the IEEE Standard 1459-2010 have been described. The most important parts are adaptive band and low-pass FIR filters that extract fundamental and dc components, respectively. In addition, by using oversampling techniques and decimation filters, coefficient sensitivity problems of the large-order FIR comb cascade structure are overridden and the parameter estimation accuracy is improved. The symmetrical components are estimated through a transformation matrix of adaptive phase shifters. The effectiveness of the proposed techniques is demonstrated by simulation results.

Amplitude-Phase Detection for Power Converters Tied to Unbalanced Grids with Large X/R Ratios

Amplitude-phase information of the voltage/current phasor, which is the prerequisite for grid-tied converter control and protection, can change almost instantaneously in low-voltage distribution systems with small X/R ratios. However, the equivalent impedances of high-voltage power systems are usually inductive (with large X/R ratios), and the power flow of pertinent grids generates decaying dc (DDC) components with large amplitude and long duration during large disturbances. Therefore, the X/R ratios and DDC components must be fully considered in amplitude-phase detection to achieve effective converter control and protection. To this end, the main components present in the transient voltage/current of a high-voltage power system after unbalanced disturbance are first analyzed, and the general transient model is obtained by synthesizing multimode DDC components. Then, by resorting to waveform characteristics of different components, an amplitude-phase detection algorithm is proposed based on the multicomponent parallel-detection structure. Compared to existing techniques, the detection time is reduced to half grid cycle. Finally, an iterative variable-interval integral algorithm is developed, improving the antinoise ability of detection algorithm and overcoming the computational burden issue. This enables the direct integration of algorithm into the converter's embedded processor. Experiment results verified the effectiveness and superiority of the proposed technique.

Mathematical Morphology-Based Artificial Technique for Renewable Power Application

This paper suggests a combined novel control strategy for DFIG based wind power systems (WPS) under both nonlinear and unbalanced load conditions. The combined control approach is designed by coordinating the machine side converter (MSC) and the load side converter (LSC) control approaches. The proposed MSC control approach is designed by using a model predictive control (MPC) approach to generate appropriate real and reactive power. The MSC controller selects an appropriate rotor voltage vector by using a minimized optimization cost function for the converter operation. It shows its superiority by eliminating the requirement of transformation, switching table, and the PWM techniques. The proposed MSC reduces the cost, complexity, and computational burden of the WPS. On the other hand, the LSC control approach is designed by using a mathematical morphological technique (MMT) for appropriate DC component extraction. Due to the appropriate DC-component extraction, the WPS can compensate the harmonics during both steady and dynamic states. Further, the LSC controller also provides active power filter operation even under the shutdown of WPS condition. To verify the applicability of coordinated control operation, the WPS-based microgrid system is tested under various test conditions. The proposed WPS is designed by using a MATLAB/Simulink software.

Analysis on Circulating Current and Split Capacitor Voltage Balance for Modular Multilevel Converter Based Three-phase Four-wire Split Capacitor DSTATCOM

We propose a modular multilevel converter (MMC) based three-phase four-wire (3P4W) split capacitor distribution static synchronous compensator (DSTATCOM), aiming at compensating unbalanced and reactive load currents. Due to the zero-sequence current compensation, the circulating current characteristics of 3P4W MMC-DSTATCOM are different from conventional MMCs. Moreover, the distinct working principle of MMC would affect the features of split capacitor voltage. The decoupled positive-, negative- and zero-sequence second-order and DC components of the circulating current are deduced explicitly. Two proportional-integral controllers with dual dq transformation are employed to suppress the positive- and negative-sequence components of second-order circulating current, while quasi proportional-resonance controller is designed to eliminate the zero-sequence component. Besides, the phenomenon of the unbalanced split capacitor voltages is revealed, and fast-tracking balancing method by controlling zero-sequence current flowing through the split capacitors is provided. Digital simulation results verify the accuracy of the analysis and the feasibility of the suppression methods.

A Novel Sub-Cycle-Based Method for Estimation of Decaying DC Component and Fundamental Phasor

Accurate estimation of the fundamental phasors of voltage or current is a challenge to power system engineers. It becomes even more challenging when the decaying dc component (DDC) is present in the signal. This article proposes a sub-cycle-based algorithm for reducing the effect of DDC for accurate estimation of the phasor of fault current signal in the presence of odd harmonics and multiple DDCs. In the proposed algorithm, the equality property of the sinusoidal signal samples around its peak is utilized to estimate DDC with only four samples and the window length requirement of half-cycle plus two samples. A novel noise removal methodology is also proposed. The fundamental phasor is calculated by taking the difference of the half-cycle discrete Fourier transform (HCDFT) of fault current and HCDFT of DDC. Simulations are performed to show the effectiveness of the proposed method, and it is compared with few previous estimation algorithms. Tests with the system-generated signals show the efficacy and accuracy of the proposed sub-cycle-based method.

Electromagnetic Forces and Mechanical Responses of Stator Windings before and after Rotor Interturn Short Circuit in Synchronous Generators

This paper studies the stator winding electromagnetic force behaviors before and after rotor inter-turn short circuit (RISC) in synchronous generator. Different from other studies, this paper not only studies the electromagnetic force characteristics, but also investigates the mechanical responses, the damage regularity, and the countermeasure of the stator winding. Firstly, formulas of electromagnetic force online and end part are obtained. Then, a 3D finite element model of a 3-pair-pole simulation generator is applied to get the electromagnetic force, and the dangerous stator slot is found. Finally, the mechanical response of each end winding is acquired, and especially the directional deformations of nose part are calculated. It shows that the occurrence of RISC will bring in times of rotor rotating frequency components to electromagnetic force, but the DC component and 2p times of rotor rotating frequency components are still the main that will be decreased. Additionally, the winding insulation wear in the same layer is more serious than that in a different layer, nose fatigue fracture begins with the center, and nose insulation wear starts from the top.

Improved 2 + 1 phase-shifting algorithm for suppressing ambient light influence

By constructing two phase-shifted fringe images and a flat image, the 2 + 1 phase-shifting algorithm can reduce the error caused by motion and realize real-time and high-resolution three-dimensional (3-D) measurement. However, the nonlinear gamma of the digital light processing and the ambient light will affect the light-field distribution of the flat image, and extensive experiments have shown that the distribution of the captured flat image is inconsistent with the DC component of the deformed patterns. Therefore, based on the linear calibration model, a more realistic DC component of the deformed patterns is deduced from the captured flat image. The AC components of the deformed patterns can be extracted more genuinely by subtracting the deduced DC component from deformed patterns. So, the influence of ambient light can be suppressed efficiently to improve 3-D measuring accuracy. The experimental results show the feasibility and validity of the proposed method.

Hybrid PWM Methods for Harmonic Reduction in Neutral Point Clamped Three-Level Inverter Drive for Pump Applications

Two hybrid PWM methods are proposed in this paper for a pump drive based on three-level Neutral-Point Clamped (NPC) inverter. The envisaged PWM methods are aimed at reducing output voltage harmonic distortion. While the first PWM method incorporates suitable voltage injection to the carrier signals, the second PWM method incorporates voltage injection to both carrier and the modulating signals for controlling the NPC drive. Detailed harmonic analysis is presented using Double Fourier Integral Approach (DFIA) for both the hybrid PWM methods by separately identifying their basic unit cells, their boundaries that demarcates different regions of inverter drive. Complete analytical expressions for dc, fundamental, carrier and side-band harmonic components present in the output voltage of the NPC drive are presented for both the hybrid PWM methods. The proposed PWM methods are simulated using Matlab/Simulink and are experimentally validated using an induction motor driven pump load, following V/f control. Superiority of the hybrid PWM methods in comparison to the existing PWM methods are demonstrated with vTHD , weighted THD (vWTHD ), iTHD , harmonic loss factor etc., supporting the envisaged PWM methods.

An Analytical Fast Decaying DC Mitigation Method for Digital Relaying Applications

This paper proposes a novel fast and accurate method to mitigate the decaying DC (DDC) component from the fault current signal. At the first stage, it starts to identify the DDC parameters by integrating six sub-cycle samples of current signal considering the symmetry feature of odd harmonics. By receiving the next samples, the estimation of DDC parameters is updated and improved. This procedure continues until the integral of a full cycle current signal is calculated. To improve the accuracy of phasor estimation procedure, in each stage, by subtracting the DDC component from original current signal, the discrete Fourier transform method is applied to estimate the fundamental phasor. Performance of the proposed method for different DDC parameters and fault conditions is verified through various test studies, and its robustness against harmonics, noise, off-nominal frequency, and multiple DDCs conditions is also investigated. Besides, to demonstrate the reliability of proposed method in terms of dependability and security, it is implemented on the phasor estimation block of a distance relay. Three types of data including mathematical, simulated, and real power system signals are used to evaluate the performance of proposed method. Obtained results confirm the desirable performance of proposed method in various operating conditions.