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This paper proposes a new multifunctional control technique for a grid-connected hybrid distributed generation system composed of a photovoltaic system and a wind power system based on a voltage source converter (VSC). Indeed, aside from the generation and the injection of energy into the grid, the proposed system deals with power quality issues caused by harmonics generated by non-linear loads in order to keep the source current uncontaminated. The VSC serves to first ensure that the power generated from the hybrid renewable energy source is fed to the utility grid and acts as a shunt active power filter in case an abnormal increase in the THD of the source current above the standard permissible values is detected due to the non-linear load connection. The two sources of the hybrid system are connected to a common DC bus to simplify the control and reduce the cost of the system, and a maximum power point tracking controller is used for both sources. The major advantage of this novel proposed multifunctional control technique is its ability to inject harvested power into the grid while simultaneously ensuring the compensation of the harmonics and reactive power. The proposed multifunctional control technique is validated through an extensive simulation analysis using MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

The synchronous generators (SGs) supplying non-linear loads have harmonically distorted terminal voltages. Hence, these distorted terminal voltages adversely affect the performance parameters of the supplied loads such as the power factor, current distortion, losses, and efficiency. To mitigate the harmonic voltages and currents, passive and active filters are generally employed. However, passive filters cause resonance problems, while active filters can cause high costs. On the other hand, in several recent studies to reduce the SG's terminal voltage harmonic distortion, which depends on the constructional design under the no-loading condition, the conventional DC excitation current has been modulated with AC harmonic components. These field current modulation methods have high computational complexity, and require extra hardware for their implementation. In the present paper, firstly, for the reduction of the terminal voltage harmonic distortion of the SG under non-linear loading conditions, the validity of the field current modulation technique is investigated. The numerical results show that by using the field current modulation method, under rated loading conditions, the total harmonic distortion of the terminal voltage can be reduced from 18% to 11%. Secondly, to provide a computational efficient and low-cost tool for optimal field current modulation, which minimizes the terminal voltage harmonic distortion, an Artificial Neural Network (ANN)-based model is proposed. Finally, with the integration of ANSYS Maxwell, ANSYS Simplorer, and MATLAB/Simulink software, the implementation of the developed model is demonstrated for the construction of the optimally modulated field current. [ABSTRACT FROM AUTHOR]

This article proposes a decoupled control scheme for the modular multilevel converter (MMC) to reduce the total harmonic distortion (THD) and eliminate one specific harmonic. First, to realize the decoupled control between the ac and dc paths of the MMC, an improved nearest level control (INLC) method is proposed. It applies the round function to generate the ac output voltage levels, instead of the arm output voltage levels. Thus, a staircase wave is generated by the INLC method. Then, by adding an additional pulse to each quarter of the staircase wave, one specific harmonic can be eliminated without optimizing each conduction angle. Furthermore, a decoupled circulating current fuzzy control method is proposed to suppress the second-order harmonic and balance the arm energy. By this decoupled control structure, the output voltage and the circulating current can be controlled independently. Taking the fifth-order harmonic as an example, simulation and experimental results validate that the proposed scheme can simultaneously realize THD reduction and one specific harmonic elimination in the MMC output voltage. [ABSTRACT FROM AUTHOR]

The interphase reactor (IPR) is one of the most important components of the passive harmonic reduction circuit (HRC), and the optimum turns ratio design of the IPR is of great significance to ensure the effect of the passive HRC. In combination with the pulse number multiplication methods, the configuration of the multipulse rectifiers (MPRs) with single/dual/triple-passive HRCs are constructed, respectively. The general optimum turns ratio design method for the IPRs is proposed, which contains most of the realizable combinations of the HRCs. The relationship between the turns ratio of the IPR and the phase number of the bridge rectifier in the main circuit is established, the influence of the turns ratio selection on the power quality of the MPRs is presented. In addition, this article takes N equal to five as an example to verify the effectiveness of the proposed general optimum turns ratio design method of IPR. The power quality of the MPRs with different HRCs or phase number are compared. All the research can provide a useful guideline and theoretical foundation for the MPR selection and the HRC design under the specific occasions. [ABSTRACT FROM AUTHOR]

Steel production worldwide continues to grow and, consequently, also the energy consumption of the steel sector. With the applications of the electric arc furnace route in the steelmaking process, the concern with aspects of power quality and overload of the transmission grid lines increases. This work presents the zero harmonic distortion (ZHD) converter static synchronous compensator (STATCOM), which makes it possible to increase the displacement power factor of an electric arc furnace (EAF) application from 0.88 to 0.98 with total demand distortion in the grid around 1.44% with the ZHD prototype operation, this being accomplished without using high-order sinusoidal filters and with consolidated components in the industry. [ABSTRACT FROM AUTHOR]

With the increased usage of power electronics at the source and load ends of modern power systems, power quality issues like harmonic control and total harmonic distortion (THD) minimization are being given considerable attention. Selective harmonic elimination and mitigation (SHE and SHM) are well-known effective techniques to control the low-order harmonics in the voltage and current waveforms generated by DC–AC converters, which otherwise pollute the grid waveforms and lead to undesired losses. As these methods also result in lower switching losses, they are mostly beneficial for high-power applications like medium-voltage electric drives and grid-connected systems. This work presents an over-the-decade overview of the enhancements in the SHE and SHM pulse width modulation (PWM) techniques of two-level and multilevel DC–AC converters, discussing various problem formulations and the solving methods of the resulting transcendental expressions. The exclusive use of metaheuristic techniques, neural networks, and predictive control structures in expression solving and controller architecture are discussed. The current and future research directions are presented with a focus on optimization, digitalization, real-time implementation, and low-power application avenues. • The manuscript emphasizes the heightened focus on harmonic controls. • SHE and SHM as effective techniques for controlling low-order harmonics. • SHE and SHM techniques reduce switching losses alongside harmonic control. • Highlighting advancements in pulse width modulation techniques. • Showcases the metaheuristic techniques, NNs, and MPC for designing controller architectures. [ABSTRACT FROM AUTHOR]

The double-phase-shift filtering method, which is based on the traditional pure-phase-shift filtering method, is a novel approach to harmonic elimination that can be applied to more complicated signals such as white noise and slip-sweep. Nonetheless, any type of phase-shift filtering method necessitates a relationship between the frequency of fundamental sweep and time, which may cost necessitate an enormous amount of human and physical resources to achieve inaccurate results with low efficiency. This paper combines deep learning with harmonic elimination to produce a double-phase-shift filtering method based on AR2U-Net, a type of U-Net with attention gates structure and recurrent residual blocks for improving accuracy and function while simplifying computational complexity. The input of the AR2U-Net structure in this paper is seismic data of slip-sweep signals in vibroseis, and the output is signal frequency variation with the time of the fundamental waves, which are required to eliminate the harmonic waves and adjacent signals using a double-phase-shift method to obtain the fundamental sweep. The training sets and test sets are formed by forward models, and a Log-Cosh loss function is used to monitor the process, during which the results of AR2U-Net and traditional U-Net are compared to demonstrate the eminent function of AR2U-Net. Following that, the outcomes' Log-Cosh loss functions and accuracy are also compared to validate the conclusion. AR2U-Net, when applied to raw data and combined with the double-phase-shift method, tends to polish the filtering effects and is worth promoting. [ABSTRACT FROM AUTHOR]

When suffering the grid voltage distortion, the phase-locked loop (PLL) should equip with the fast response filter to precisely extract the fundamental voltage information for proper grid integration. To shorten the time delay induced by filters, this article proposes a new three-sample filter (TSF) to fast eliminate the harmonics of sampled grid voltage. Theoretically, it can filter out arbitrary individual harmonic with short time delay which could be as small as only two sampling periods. Moreover, TSF can reject a group of harmonics simultaneously within the specifically set time interval. The implementation issues of TSF as in-loop filter or prefilter for both three- and single-phase applications are demonstrated in synchronous reference frame PLL (SRF-PLL) SRF-PLL. Simulation and experimental results verified its advanced performance. [ABSTRACT FROM AUTHOR]

Integrated low capacity renewable energy sources with storage technologies are called micro grids. These sources can operate independently or by being connected to main grid. This paper deals with Proportional Integral (PI)/Artificial Neural Network (ANN)-based control algorithm for voltage frequency regulation in an isolated micro grid with its hardware implementation. Isolated micro grid is formed by using three SEIGs driven small hydro turbine feeding three-phase four-wire consumer load. The battery storage system is connected parallel to the DC link of the converter to facilitate the instantaneous power balance under dynamic condition and to maintain the reliability of the system. The system with PI/ANN controllers is tested under load variations and when a micro source suddenly gets disconnected due to a fault. The conventional PI controller has shown limitations to load variations and source resynchronization. The ANN-based controller on the other hand has less settling time and also improves the dynamic response of the micro grid as per IEEE 1547 standards. Micro grid is modeled with MATLAB Sim power tool and simulation results are produced considering nonlinear load. Simulated results are validated with a laboratory prototype using dPACE 1104. [ABSTRACT FROM AUTHOR]

Modulation using a higher sided polygonal space vector structure (SVS) is an elegant method to increase the linear modulation range and to eliminate the undesired lower order harmonics from motor phase voltage. This article presents the generation of a dense 15-concentric 30-sided multilevel SVS using a single dc-link for an open end induction motor (OEIM) drive. The proposed scheme eliminates lower order harmonics till 25th order from motor phase voltage throughout the modulation range. The $dv/dt$ stress in the phase voltage applied to the motor will also be highly reduced owing to the multilevel structure. The pulsewidth modulation scheme employed utilizes the denseness of SVS and avoids iterative searches to find the triangle, which encompasses the tip of reference voltage vector, which are typical in multilevel polygonal SVS. The topology consists of an active dc-link fed three-level primary inverter and a capacitor fed five-level secondary inverter connected to either end of an OEIM. The primary inverter acts as the active power supplier for the drive and the secondary inverter filters out the undesirable lower order harmonics from motor phase voltage. The proposed scheme is experientially validated and the results are included in this article. [ABSTRACT FROM AUTHOR]

Decaying DC (DDC) current due to impact loads causes detrimental consequences in weak grids. In this paper, the active power filter (APF) is enhanced to simultaneously compensate for the undesired harmonics, negative sequence components and the DDC component in the event of a transient. To this end, first, a novel DDC component detection method is mathematically deduced for single-phase transient current, followed by its extension to the three-phase system. With respect to existing techniques, the proposed method has a significantly reduced detection time from 1 grid cycle to approximately 0.5 grid cycle. By further exploiting the transient signal properties in dq-frame, the three-phase fundamental-frequency current in positive sequence can be separated. Finally, the enhanced APF control scheme is developed based on the proposed detection algorithm. Experiments verified the effectiveness and advancement of the proposed technique. [ABSTRACT FROM AUTHOR]

Renewable energy sources are installed into both distribution and transmission grids more and more with the introduction of smart grid concept. Hence, efficient usage of cascaded H-bridge multilevel inverters (MLIs) for power control applications becomes vital for sustainable electricity. Conventionally, selective harmonic elimination equations need to be solved for obtaining optimum switching angles of MLIs. The objective of this study is to obtain switching angles for MLIs to minimize total harmonic distortion. This study contributes to the solution of this problem by utilizing two recently developed intelligent optimization algorithms: multi-verse optimization algorithm and salp swarm algorithm. Moreover, well-known particle swarm optimization is utilized for MLI optimization problem. Seven-level, 11-level and 15-level MLIs are used to minimize total harmonic distortions. Simulation results with different modulation indexes for seven-, 11- and 15-level MLIs are calculated and compared in terms of the accuracy and solution quality. Numerical calculations are verified by using MATLAB/Simulink-based models. [ABSTRACT FROM AUTHOR]

Compared with the conventional three‐phase motors, the dual three‐phase permanent magnet synchronous motors (PMSMs) have many advantages and have been widely used in various drive fields. However, one major disadvantage of these machines is that they are easy to generate large stator current harmonics, which makes it difficult to have an excellent performance in the drive field. To solve this problem, this study introduces a current harmonic elimination method based on a spatial analytical model of flux linkage. The study reconstructed the analytical model of flux linkage from finite element analysis. The analytical model can describe the spatial harmonics of flux linkage by considering the rotor position information. Based on the model, an active feedforward controller was proposed to eliminate current harmonics by actively injecting the corresponding voltage harmonics, the voltage harmonics are calculated by the model of flux linkage. The performance of the proposed method in eliminating current harmonics is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This study presents the design and analysis of an adaptive second-order generalised integrator (SOGI) technique for controlling voltage source inverter in a three-phase three-wire distribution system. The function of the proposed shunt active power filter involves compensation of reactive power for power factor correction, harmonic elimination, load balancing, voltage regulation under non-linear load condition. In this study, an effective approach for load compensation is proposed by designing an adaptive SOGI trained using Levenberg–Marquardt technique and compared with conventional techniques which ensure smooth operation under normal and distorted grid condition. An experimental setup is developed and its performance is analysed during different loading conditions. The experimental results are in line with the expected simulation results. Experimental and simulation results are verified and analysed using Bode plot. [ABSTRACT FROM AUTHOR]

Chatter that occurs between a cutting tool and a workpiece greatly reduces the surface quality and production efficiency. Therefore, it is of great importance to predict and avoid chatter so as to guarantee the stability of the manufacturing process. To realise the accurate prediction of the stability boundary of machine tools, operational modal analysis (OMA) is increasingly receiving attention due to its adequate consideration of variations in working conditions in the industrial environment. However, because of the influence of harmonic components in the response signals, the accuracy in identifying the modal parameters is seriously compromised. In this paper, an adaptive complex Morlet filter (ACMF) is presented to remove the harmonic components by adaptively adjusting the centre frequency and bandwidth according to the local character of the ambient environment in a specific frequency range and filtering out harmonic components that are not strict integer multiples of the fundamental frequency owing to non-rigid periodic motion of the machine tool spindle. In order to show the effectiveness of the proposed method, milling experiments are carried out and experimental modal analysis (EMA) is utilised to make comparisons with the proposed method. Moreover, comparisons between the ACMF and two other typical filtering methods are made. The results indicate that the proposed method performs well in modal parameter recognition for machine tools. [ABSTRACT FROM AUTHOR]

In this article, an adaptive normalized least mean fourth (NLMF) control scheme is employed to generate the anti-harmonic currents of photovoltaic (PV) integrated with grid system for harmonic elimination and power factor (PF) correction (PFC). In addition, a fuzzy tuned PID-based adaptive dc voltage regulator is integrated in the proposed scheme to regulate the reference voltage of the dc bus. The proposed FPID-based NLMF control scheme attains the features of power quality (PQ) related issues elimination such as PFC and harmonics elimination with an extraction of photovoltaic (PV) generated maximum power through the grid interfacing converter (VSC) at a unity PF. Moreover, the PV system’s feed-forward (FF) component is included in the control strategy to enrich the aggressive behavior of the system. The NLMF current controller is employed to measure the three-phase calculated currents by extracting the fundamental weight constituents of the load currents for harmonic mitigation in the presence of point of common coupling (PCC). The proposed control topology is developed on MATLAB/SIMULINK software platform under different load and grid transient conditions. A dSPACE based real-time laboratory platform is developed to justify the proposed scheme under different conditions such as steady-state, load dynamic, removed and unbalanced, grid voltage distorted, unbalanced, swell and sag conditions. The presented control scenario’s results are obtained satisfactory and the grid current’s THD are in the IEEE-519 regular limits. [ABSTRACT FROM AUTHOR]

Summary: This article presents a modified whale optimization (MWO) for harmonic mitigation in a three‐phase 11‐level hybrid cascaded multilevel inverter (HC‐MLI). The proposed MWO has improved rate of convergence as compared with conventional whale optimization (WO). This is achieved by improving the exploration‐exploitation feature of the conventional WO. Selective harmonic elimination–pulse width modulation technique is applied through MWO for generating the optimal switching angles of the HC‐MLI so as to eliminate the lower‐order harmonics such as 5th, 7th, 11th, and 13th from the output voltage. In the proposed MWO optimized HC‐MLI, capacitor voltage balance is made possible even at higher modulation indices using the available redundant switching states of HC‐MLI. The proposed work is useful where the HC‐MLI has to work at the low switching frequency and the conversion efficiency is of prime importance such as medium‐ and high‐power motor drives, static synchronous compensators, and active power filters. The performance of the proposed work is validated through simulation and experimentation on a 1.5‐kW prototype. The results obtained show that the MWO algorithm is more efficient and accurate than other reported algorithms such as genetic algorithm, particle swarm optimization, and WO in terms of performance, harmonic mitigation, and rate of convergence. [ABSTRACT FROM AUTHOR]

Active power filters are conventionally utilized to compensate steady-state harmonic currents and reactive power in the utility, yet their capabilities are usually limited if the elimination of undesirable effects associated with decaying dc components during transients is the target, especially under the weak grid condition. In this letter, active cancellation of the typical first-order decaying dc-mode transients is explored. To this end, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal. Furthermore, fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ – $q$ frame and subsequent calculations. Hardware-in-the-loop experiment results verified the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

This article proposes a modified grey wolf optimization (MGWO) which has improved rate of convergence and avoids local optima stagnation. This is achieved by improving the exploration–exploitation balance in conventional grey wolf optimization (GWO). Moreover, the use of weighted-distance strategy allows quick identification of the global optima in the proposed MGWO. This optimization is then applied for the control of a three-phase, 11-level hybrid cascaded multilevel inverter (HC-MLI). Selective harmonic elimination pulsewidth modulation technique is implemented through MGWO which generates optimal switching angles for the HC-MLI so as to eliminate lower order harmonics such as 5th, 7th, 11th, and 13th from the output voltage. In MGWO optimized HC-MLI, balancing of capacitor voltage is made possible at higher modulation index by making use of the available redundant switching states. The performance of the proposed work is validated through simulation and experimentation on a 1.5 kW prototype. The results obtained through simulation show that the MGWO algorithm is more efficient and accurate than other reported algorithms such as GWO, genetic algorithm, and particle swarm optimization in terms of performance, harmonic reduction, and convergence rate. [ABSTRACT FROM AUTHOR]

This paper proposes a novel polygonal voltage space vector structure (SVS) having 30 sides, for a star-connected induction motor drive. The SVS eliminates the presence of harmonics up to 25th order from motor phase voltage throughout the entire modulation range, providing a torque profile devoid of lower order pulsations. Linear modulation is extended till 99.63% of base speed without exceeding the motor phase voltage rating. Topology consists of a dc-link fed primary inverter and two equal low voltage modular capacitor fed secondary inverters. Here the harmonics generated by the primary inverter is canceled by the secondary inverter which acts as a switched capacitive filter. Detailed description of the SVS generation and timing calculations are provided in this paper. Effectiveness of the proposed scheme is validated using experimental results, inverter loss calculations, and harmonic analysis. [ABSTRACT FROM AUTHOR]

This paper proposes an optimized synchronous PWM method for harmonic elimination in a quasi square wave inverter. The synchronized PWM method enables online harmonic computation and PWM pulse generation in a multitasking digital controller to eliminate lower order harmonics. The multitasking digital controller reduces the look-up table requirement and helps in realizing efficient implementation to eliminate dominant harmonics. This method offers a simple scalable solution for combined fifth and seventh harmonic elimination using two low-cost eight-bit PIC microcontrollers (PIC18F4550, PIC18F452). Experimental results are demonstrated for a single-phase three-level inverter. The proposed method achieves 90% reduction of fifth and seventh harmonic components from a quasi square wave inverter output. [ABSTRACT FROM AUTHOR]

Highlights • The very effective strategy to reject unwanted negative and harmonic components. • No unreal disturbance in the estimated frequency for phase angle jumps. • A wide variability (trade-off between attenuation of unwanted components and speed). • Setting the values of all parameters for the strategy is easy and already well elaborated. • The DSC 2 element for rejection even harmonics (with time delay T /2) can be omitted. Abstract A technique has been developed that incorporates the advantages of the cascaded delayed signal cancellation and dual second order generalized integrator schemes, the first one being used now as a pre-filter for the second element. A reconstructor block is applied as well to prevent unreal changes in the estimated frequency in case of phase angle jumps of the grid voltage. Experimental results are evaluated in terms of quality of the positive voltage sequence, frequency and phase angle identification for the grid voltage disturbed by harmonic and negative sequence components as well as for amplitude, frequency, and phase angle jumps in the voltage. [ABSTRACT FROM AUTHOR]

A 12-pulse converter has been commonly used for a large-scale power generating system. The arrangement of a delta–delta (Δ–Δ) and a delta–wye (Δ–Y) phase-shift transformer pair in series with the voltage source eliminates undesirable harmonics from nonlinear loads. Recently, a novel front-end for a multi-generator power system was proposed, which utilizes a single Y–Δ transformer to shunt between the two 30° phase-shifted generator outputs and results in the comparable harmonic elimination performance to the conventional 12-pulse rectifier. The shunt-type Y–Δ transformer front-end achieves more than 75% transformer size reduction, making it extremely attractive to large-scale industrial and shipboard applications. However, the exact 30° phase shift between the two rotating generators can drift in a practical system, especially under dynamic conditions. The harmonic performance under the non-ideal 30° phase-shift condition can deteriorate with the Y–Δ shunt-type front-end. To understand the impact of non-ideal phase-shifted generator sources, this paper derives the mathematical models through the use of an equivalent circuit, a square-wave analysis, and the phasor representation to show the harmonic cancellation principle and verifies the results with the computer simulation. [ABSTRACT FROM AUTHOR]

Highlights • Extreme learning machine is proposed for SHE in single phase inverters. • The proposed method is fast when compared with neural network. • Simulations results were verified with the experimental results. Abstract In this study, a new system for the elimination of selected harmonics in single phase inverters is proposed. Extreme learning machine is used for the selected harmonic elimination system. The nonlinear equation set representing the inverter output voltage for the specific values of the modulation index is solved off line using Newton-Raphson method. The corresponding switching angles are obtained. The extreme learning machine is trained and tested with these modulation index and switching angles. Modulation index is used as an input to the extreme learning machine and switching signals are generated. A conventional carrier-modulator comparison process is used to produce switching instants in real time. The signals are applied to a single phase inverter feeding single phase load. Simulations are made using Matlab/Simulink and verified by experimental results. It was shown that the selected harmonics are eliminated from the load current and voltage for any given modulation index. [ABSTRACT FROM AUTHOR]

This article presents the application of the harmony search (HS) optimization algorithm for harmonic elimination in a new topology of multilevel inverters with a reduced number of electronic switching elements. The main objective of the harmonic elimination strategy is eliminating undesired low rank harmonics in order to improve the quality of the output waveform. The harmonic elimination strategy is achieved by solving a system of nonlinear equations. In this paper, HS optimization is applied using artificial neural networks (ANNs) on a new 21-level inverter topology. The algorithm is based on the music improvisation process. MATLAB programming software was used to develop a HS optimization program for harmonic elimination. The main reason for using selective harmonic elimination based on ANNs in this study is to control the proposed multilevel inverter in real-time. In order to assess the performance of the proposed optimization method, it was compared to particle swarm optimization and the genetic algorithm. A small-scale laboratory of the proposed 21-level inverter is built to validate the simulation results and to prove the efficiency of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper presents a novel multilevel radio frequency (RF) pulsewidth modulation (PWM) method for all-digital transmitters (ADTx) that actively eliminates the selected harmonics of RF-PWM. Compared with existing multilevel RF-PWM techniques, this method uses several adaptive thresholds and controls the pulsewidth of the corresponding subpulses to make the selected harmonics cancel each other out and keep the fundamental frequency component proportional to input envelope. For the third-harmonic elimination, the corresponding five-level RF-PWM scheme presented in this paper shows that it can significantly relax the filtering requirements and improve the wideband performance of the ADTx. The proposed scheme is verified by extensive simulations and offline measurements. The simulations show good potential for high-frequency operation up to gigahertz ADTx. The measured results show that the third-harmonic suppression of the proposed scheme has increased with the decreasing of the time resolution for digital implementations. For a 3.80-dB peak-to-average power ratio (PAPR) QPSK signal and a 6.04-dB PAPR 16QAM signal at 200-MHz carrier, the proposed scheme can achieve above −51- and −48-dBc third-harmonic suppression, respectively, when the time resolution is 50 ps and relative time resolution is 1%, and improves above 30 dBc to the existing schemes. [ABSTRACT FROM AUTHOR]

This study focuses on introducing a criteria for conducting harmonic excitation signal elimination as well as investigating its effectiveness towards achieving complete isolation of harmonic disturbance in performing EMA under operational condition. By modulating the ratio between harmonic excitation and impact knocking frequencies, it was revealed that the harmonic signal was efficiently attenuated with sufficient number of averaging blocks. The results highlighted close agreement between simulation and experimental approaches with maximum deviation of 2 %, under specific design criteria. It was determined that a non-periodic triggering frequency significantly affect the elimination performance in terms of trend and amplitude reduction. This work underlines the importance of controlling the triggering frequency to yield the desired design criteria for achieving rapid and highly efficient elimination of harmonic excitation signal. The results have proven that the proposed technique can be further adapted to isolate the harmonic in conventional EMA conducted under operational condition. [ABSTRACT FROM AUTHOR]

Wind energy is one of the developed forms of renewable energy which has seen a rapid increase in its demand by the utilities. The Doubly Fed Induction Generator (DFIG) based variable-speed wind turbine with pitch control scheme is the most popular wind power generator in the wind power industry. In this generator, a stator is directly connected to the grid, whereas rotor is connected to the grid via back-to-back power electronics converters. Due to this nonlinear devices connected to the grid, quality of power deteriorates. It draws a significant amount of harmonic currents. This leads to the generation of voltage harmonics in the grid due to the impedance of the transmission lines. A number of publications report related to the improvement of power quality, specifically, the harmonic elimination techniques for a wind energy conversion system. A critical assessment is required for making a choice on an exact harmonic elimination technique for a specific case. That is why an exhaustive review of all those techniques is very relevant. Only a countable number of attempts have been made in this regard. This paper emphasizes on various available harmonic mitigation techniques. This ensures the safeguarding of grid connected doubly fed induction generators from the harmful effects of harmonics. Thus, it helps in maintaining standards related to power quality. [ABSTRACT FROM AUTHOR]

Conventional voltage-source inverters used for induction motor drives generate a hexagonal space vector structure. In the overmodulation range, the hexagonal space vector structure generates low-order harmonics in the phase voltage resulting in low-order torque ripple in the motor. Inverter topologies with an octadecagonal (18 sided) space vector structure eliminate fifth-, seventh-, eleventh-, and thirteenth-order harmonics from the phase voltage, and hence, the dominant sixth- and twelfth-order torque ripple generation is eliminated. Octadecagonal space vector structures proposed in the past require multiple dc sources, which makes four-quadrant operation of the drive system difficult and costly. In this paper, the formation of a multilevel nine-concentric octadecagonal space vector structure using a single dc source is proposed. Detailed experimental results, using open-loop $V/f$ control and rotor field-oriented control, are presented to validate the effectiveness of the proposed drive scheme. [ABSTRACT FROM PUBLISHER]

In this letter, the five-level packed U-cell (PUC5) inverter is reconfigured with two identical dc links operating as an active power filter (APF). Generally, the peak voltage of an APF should be greater than the ac voltage at the point-of-common coupling (PCC) to ensure the boost operation of the converter in order to inject harmonic current into the system effectively; therefore, full compensation can be obtained. The proposed modified PUC5 (MPUC5) converter has two equally regulated separated dc links, which can operate at no load condition useful for APF application. Those divided dc terminals amplitudes are added at the input of the MPUC5 converter to generate a boosted voltage that is higher than the PCC voltage. Consequently, the reduced dc-links voltages are achieved since they do not individually need to be higher than the PCC voltage due to the mentioned fact that their summation has to be higher than PCC voltage. The voltage balancing unit is integrated into the modulation technique to be decoupled from the APF controller. The proposed APF is practically tested to validate its good dynamic performance in harmonic elimination, ac-side power factor correction, reactive power compensation, and power quality improvement. [ABSTRACT FROM AUTHOR]

This article presents the application of the harmony search (HS) optimization algorithm for selective harmonic elimination PWM (SHEPWM) in a new topology of multilevel inverters with reduced number of electronic switching elements. The main objective of the harmonic elimination strategy is eliminating undesired low-rank harmonics in order to improve the quality of the output waveform. The harmonic elimination strategy is achieved by solving a system of nonlinear equations. In this paper harmony search optimization is applied using artificial neural networks (ANNs) on a new 21-level inverter topology. The algorithm is based on a music improvisation process. MATLAB programming software is used to develop a harmony search optimization program for harmonic elimination. A small-scale laboratory of the proposed 21-level inverter is built to validate the simulation results and to prove the efficiency of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In this paper, an electronic phase-shifting strategy has been optimized for a multiparallel configuration of line-commutated rectifiers with a common dc-bus voltage used in motor drive application. This feature makes the performance of the system independent of the load profile and maximizes its harmonic reduction ability. In order to further reduce the generated low-order harmonics, a dc-link current modulation scheme and its phase-shift values of multidrive systems have been optimized. Analysis, simulations, and experiments have been carried out to verify the proposed method. [ABSTRACT FROM PUBLISHER]

This paper describes an intensive analysis of a harmonic identification algorithm in non-ideal voltages source systems. The dq-axis Fourier with a positive sequence voltage detector (DQFP) is a novel harmonic identification algorithm for active power filters. A compensating current control system based on repetitive control is presented. A design and stability analysis of the proposed current control are also given. The aim of the paper is to achieve a robustness of the harmonic identification in a distorted and unbalanced voltage source. The proposed ideas are supported by a hardware in the loop technique based on a eZdspTM F28335 and the Simulink program. The obtained results are presented to demonstrate the performance of the harmonic identification and the control strategy for the active power filter in non-ideal systems. [ABSTRACT FROM AUTHOR]

This paper focuses on implementation of differential equation of the single-phase source-load system based control algorithm for three-phase distribution static compensator (DSTATCOM) in a power distribution system with a stiff source. The DSTATCOM has been adopted to alleviate the power quality issues such as load unbalancing, reactive power, and current harmonics, which are caused by solid-state equipment and devices. The proposed control algorithm is employed for extraction of fundamental active and reactive current components of polluted load currents, which are used for estimation of reference source currents. The control algorithm carries out computations by using a sliding sampling window that has a width of half of the fundamental cycle. The primary advantages of this control algorithm are immune to noise, not influenced from DC component that may exist in load current, and being less affected from frequency deviations. A prototype of voltage source converter (VSC)-based DSTATCOM is developed using a field programmable gate array (FPGA) processor to validate the proposed control algorithm and its performance is analyzed under steady-state and dynamic conditions. Experimental results demonstrate satisfactory performance of the DSTATCOM with the proposed control algorithm under linear and non-linear loads. [ABSTRACT FROM AUTHOR]

Wide bandgap semiconductor switches have been increasingly utilized to improve the power density and efficiency of power converters, as such devices are able to operate at very high frequencies, e.g., up to 100 MHz, with reduced power losses. However, such a high-frequency operation may impose a challenge to the digital control system, and the system clock frequency should be up to 100 GHz in high-precision applications, which is difficult to realize in low-cost microprocessors. Instead of using extremely high-frequency clocks, preprocessing-based solutions that utilize digital pulse-width-modulated (DPWM) dither techniques can also enhance the DPWM resolution with moderate frequency clocks. Unfortunately, this is usually achieved at the expense of introducing low-frequency harmonics, which may complicate system controller and output filter design. In this paper, an optimal dither technique is proposed to enhance the resolution of DPWM power converters. The concepts of positive dither and negative dither are first proposed in this paper. Furthermore, vector-diagram-based analysis indicates that with proper utilization of positive dithers and negative dithers and carefully selected dither sequences, the lowest order harmonic introduced by the conventional dither technique can be completely eliminated when the dither period is multiples of six switching periods. In other cases, the proposed optimal dither technique can produce minimized lowest order harmonic. Finally, experimental results obtained from a Gallium Nitride (GaN) devices-based synchronous buck converter validate the feasibility of the proposed dither technique. [ABSTRACT FROM PUBLISHER]

In conventional HVDC systems where the harmonic filters and shunt capacitors are installed at the ac grid side, the converter transformers inevitably suffer the detrimental impacts caused by harmonic penetration. In this paper, combined with an inductive filtering method, a parallel delta-connected filtering-winding scheme for 12-pulse converter transformer units is proposed to reduce the harmonic currents flowing through the transformers and, thus, to attenuate the harmonic effects on them. This paper describes the presented transformer configuration in terms of the wiring scheme of the 12-pulse converter transformer unit and corresponding flowing paths of different harmonic currents with the orders of 3,6n\pm 1\left(\mathrmn=1,3,5,\ldots \right), 11 and 13 in the filtering winding circuit. Then, the mechanism of the proposed scheme on harmonic suppression to the converter transformers is explained theoretically. In an attempt to validate the theoretical analysis, simulations based on PSCAD/EMTDC and experiments in a laboratory prototype system are performed to evaluate the harmonic eliminating performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

Elimination of harmonics by the use of power filters is required for power quality improvement; provides a wide area for the researchers to develop efficient power filters with improved control platforms. This paper motivates the implementation of the embedded control platform for better control of the power filters for faster elimination of harmonics. Although many embedded processors fascinates the implementation of the control techniques but finding the feasible platform is a great task. Software implementations are feasible for most of the power electronics converters but the hardware design with required digital hardware is a challenging task. The present paper deals with the development of the control technique for the Hybrid Active Power Filter with Xilinx System Generator Platform. The virtual FPGA (Field Programmable Gate Array) platform provided by the Xilinx System Generator has the ability to generate better switching signals for the control of the power filter to generate compensating signal for elimination of harmonics to maintain the power quality in the distribution lines. Experimental results obtained by the setup developed in the Power System Laboratory presents the effectiveness of the Embedded Platform. Various source voltage conditions also simulated and performance is verified for the developed Hybrid Active Power Filter. [ABSTRACT FROM AUTHOR]

In this paper, a novel rectifier transformer that has a round-shaped structure is investigated. The transformer can convert three-phase power into 12-phase, which supplies to a rectifier composed by four bridges for producing dc voltage with 24-pulse. With such transformers, rectifier performance can be improved in both input and output waveforms. The principle of harmonics elimination is explained and some critical problems may be encountered in design are discussed. The experiments on the prototype are carried out for performance assessments regarding characteristics, such as ripple factor, total harmonic distortion, efficiency, etc. The results demonstrated the effectiveness of the novel transformer in harmonics mitigation. [ABSTRACT FROM AUTHOR]

This paper presents a technique for reducing the input current ripple on multiphase power converters that provide multiple heterogeneous power supply rails, such as those present in portable electronics and computers. Through asymmetric interleaving of individual phases, the input current ripple can be reduced compared to conventional interleaving. The technique is derived based on an analytic description of the relevant current waveforms. Practical requirements of a digital control implementation of the proposed technique are analyzed, and its possible performance improvement is quantified through simulations and experimental results. With the proposed technique, close to a 3x reduction in input current ripple, compared to conventional methods, is demonstrated using an experimental prototype comprising a microcontroller that controls a multiphase 180 nm CMOS power management IC. [ABSTRACT FROM AUTHOR]

This paper presents a method for generating a multilevel dodecagonal voltage space vector structure using a single dc source for induction motor drives. Multilevel dodecagonal structure combines the advantages of both multilevel and dodecagonal structures, and hence, generates low dv/dt phase voltage along with the elimination of fifth- and seventh-order harmonics over the entire modulation range. This eliminates low-order harmonic currents and prevents the generation of sixth-order torque ripple in the motor. The topology used requires only one dc source making four-quadrant operation of the drive system simpler compared to previously proposed multilevel topologies generating dodecagonal space vector structures. The topology used consists of a three-level flying capacitor (FC) inverter cascaded with a capacitor fed H-bridge. The FC inverter operates at a lower switching frequency and the low-order harmonics are eliminated by the switching action of the cascaded H-bridge inverter. The capacitors in the cascaded H-bridge modules are maintained at a substantially smaller voltage compared to the dc-link voltage and are inherently balanced during the pulsewidth modulation operation. This results in low switching loss, in the FC inverter as well as in the cascaded H-bridge inverter. Experimental results are included to validate the operation of the topology and modulation scheme presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a new active method for power factor correction (PFC) is presented and applied to a single-stage AC/DC flyback converter to reduce the total harmonic distortion of the input current, achieve better power factor compensation, and improve converter reliability. The proposed circuit consists of a low-power portable dual-purpose inverter that can work in 2 main modes. In the normal mode of converter operation, the PFC circuit operates as an active harmonic filter compensator. In the second mode, which occurs in converter outage conditions, the inverter behaves as a sinusoidal backup voltage power supply for the converter by using a backup battery and the SPWM control method. In this technique, the main switch of the converter operates in borderline conduction mode, but the RMS input current as well as peak and ripple currents are reduced significantly. Simulation analysis and experimental results are presented. [ABSTRACT FROM AUTHOR]

The present paper proposes a novel method to eliminate harmonics in a solar powered CHMLI (cascaded H-bridge multilevel inverter). The problem uses Newton Raphson and PSO (Particle Swarm Optimization) based SHE (Selective Harmonic Elimination) techniques for solving the non-linear transcendental equations and to obtain the optimal switching angles. The optimized switching angles obtained offline are utilized to minimize the THD (Total Harmonic Distortion). The major concern in the harmonic-elimination problem in the non-equal dc sources system is the solution of the nonlinear transcendental equations. However, the proposed method can solve this problem in a simpler manner, by just converting non-equal dc sources into equal dc source using the ANFIS (Adaptive Neuro Fuzzy Inference System)/Constant Voltage Maximum Power Point Tracker algorithm for the Photo-voltaic system. The performance are evaluated using simulation results for PV fed 11-level cascade H-bridge inverter with induction motor drive. The simulation results are validated using an experimental model of CHMLI with Xilinx Spartan ® -3A DSP FPGA based controller. [ABSTRACT FROM AUTHOR]

Rapid and accurate phase synchronization is critical for the reliable control of grid-tied inverters. However, the commonly used software phase-locked loop methods do not always satisfy the need for high-speed and accurate phase synchronization under severe grid imbalance conditions. To address this problem, this study develops a novel open-loop phase locking scheme based on a synchronous reference frame. The proposed scheme is characterized by remarkable response speed, high accuracy, and easy implementation. It comprises three functional cascaded blocks: fast orthogonal signal generation block, fast fundamental-frequency positive sequence component construction block, and fast phase calculation block. The developed virtual orthogonal signal generation method in the first block, which is characterized by noise immunity and high accuracy, can effectively avoid approximation errors and noise amplification in a wide range of sampling frequencies. In the second block, which is the foundation for achieving fast phase synchronization within 3 ms, the fundamental-frequency positive sequence components of unsymmetrical grid voltages can be achieved with the developed orthogonal signal construction strategy and the symmetrical component method. The real-time grid phase can be consequently obtained in the third block, which is free from self-tuning closed-loop control and thus improves the dynamic performance of the proposed scheme. The proposed scheme is adaptive to severe unsymmetrical grid voltages with sudden changes in magnitude, phase, and/or frequency. Moreover, this scheme is able to eliminate phase errors induced by harmonics and random noise. The validity and utility of the proposed scheme are verified by the experimental results. [ABSTRACT FROM AUTHOR]

In synchros and resolvers, brushes, and slip-rings produce a lot of noise in the output signal. Compared to encoders, the application of such position sensors in precision control systems is restricted because of their low accuracy. In this paper, a novel scheme of a brushless synchro is introduced. In this scheme, the primary and secondary windings are mounted on the stator, and the stator magnetic flux passes a certain path in the rotor with inducing voltage in the secondary winding. In this paper, a software method based on simple look-up table is used to enhance accuracy and reliability of the output signal of the proposed synchro. The operation principle of the brushless synchro is clearly described in the paper using a finite element method (FEM). The number of turns for the stator coils is calculated by a method based on desired harmonic elimination to have a sinusoidal magneto motive force. Some prototypes have been fabricated, and two experiments have been implemented in order to verify the theoretical concepts and to evaluate the accuracy of the fabricated synchros. Results show the proposed brushless synchro has high accuracy. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a new inverter topology is proposed for generating a multilevel dodecagonal voltage space vector structure for open-end winding induction motor (IM) using a single dc source. Dodecagonal voltage space vector structure eliminates fifth- and seventh-order harmonic voltages from phase voltage output and hence eliminates the fifth- and seventh-order harmonic currents through the motor leading to removal of the dominant sixth-order torque ripple generation in the motor over the entire modulation range. Multilevel space vector structure generates output voltage with better THD and low dv/dt. In the proposed topology, two three-level inverters drive an open-end winding IM, one inverter from each side. DC-link of primary inverter is from a dc source which delivers the entire active power, whereas the secondary inverter dc-link is maintained by a capacitor, which is self balanced during the inverter operation. The PWM scheme implemented ensures low switching frequency for primary inverter. Secondary inverter operates at a small dc-link voltage. Hence, switching losses are small for both primary and secondary inverters. Experimental results show the elimination of fifth- and seventh-order harmonic voltages over the entire modulation range, validating effectiveness of the proposed multilevel inverter scheme. [ABSTRACT FROM PUBLISHER]

This article proposes a novel adaptive fuzzy controller for shunt active power filters. The main fuzzy controller operated with the auxiliary fuzzy controller is called the adaptive fuzzy controller. This controller can perfectly control the compensating currents for any harmonic loads in the system. A new approach to design the auxiliary fuzzy controller without the engineering experiences is presented; moreover, the synchronous detection with Fourier method for harmonic detection is also proposed. A proportional and integral controller is used for the DC bus voltage control of shunt active power filter. The eZdspTMf28335 board (Spectrum Digital Incorporated, Stafford, Texas, USA) is the main processor in the system. The experimental results of harmonic elimination can confirm good performance of the adaptive fuzzy controller designed by the new approach operated with the synchronous detection with Fourier method. Furthermore,the average value for the percent of total harmonic distortion of the source currents after compensation is satisfied under IEEE Standard 519-1992 [1]. [ABSTRACT FROM AUTHOR]

Microgrids (MGs) are small scale energy unit networks that can offer an adequate energy supply to cover local demand by incorporating renewable energy and storage technologies. The system capacity is generally between several kW to several MW. They work in terms of low voltage (LV) level or medium voltage (MV) level. They can also be connected/disconnected from main grid whenever it is necessary. This paper presents a comparison of two soft computing (SC) techniques fuzzy logic (FL)/artificial neural network (ANN) over a conventional proportional integral (PI)-based voltage frequency controllers used for improving the performance of MG under islanding mode. Microgrid is formed by using three 7.5kW, four pole, 50Hz, self-excited induction generators (SEIGs) driven by small hydro turbine feeding three-phase four-wire consumer load. The proposed topology functions excellently in maintaining phase angle, voltage and frequency (VF) regulation of the micro sources (MSs) in islanded mode as well as in resynchronization when one of the MSs is turned off due to fault or unavailability of resources. The conventional PI controller is replaced by a controller based on SC techniques, as it has disadvantages like explicit description of mathematical model, affected by variations in consumer loads and sources, thus the proposed SC techniques enhance the performance of VF controller. A comparative analysis of PI/FL/ANN controller is also carried out to highlight the superiority of AI controller. The performance of controller with proposed configuration is verified for balanced/unbalanced non-linear load. Microgrid and control schemes are simulated in MATLAB Sim Power Systems environment. [ABSTRACT FROM AUTHOR]

This paper presents the application of well known recursive least square (RLS) harmonic estimation technique and its elimination with improved current control technique based shunt active power filter (SAPF) in a distorted power network. The estimation of amplitude and phase angle of fundamental and harmonics is performed using RLS algorithm, known for their simplicity of computation, accuracy and good convergence properties. The estimates are updated recursively as samples of the harmonic signals are received. In order to eliminate harmonics produced by the nonlinear load connected in the distribution network, a three-phase SAPF with modified current control technique is employed. In this paper, based on the analysis and modeling of SAPF with closed-loop control, a feed forward compensation path of load current and a new pulse width modulation (PWM) control scheme is proposed to improve the dynamic performance of the SAPF. In this case the amplitude and phase angle of the converter AC voltage should be adjusted using PWM, thus producing either leading or lagging reactive power. Harmonic contented in the signal is estimated at the point of common coupling (PCC) with and without SAPF. The comparative results of amplitude and phase angle of fundamental and selected harmonics are determined considering installation of SAPF in the distribution network. The system is studied using MATLAB environment to justify the effectiveness of proposed control technique in comparison to the other techniques discussed in the recent literature. [ABSTRACT FROM AUTHOR]