Seventh Harmonics Research Articles

Rotor magnet demagnetisation diagnosis in asymmetrical six‐phase surface‐mounted AC PMSM drives

Multiphase permanent-magnet synchronous machines (PMSMs) are receiving more and more interest in safety-critical modern industries owing to their higher reliability when compared with conventional three-phase PMSMs. Rotor magnets are critical components, which, in case of fault, directly affect the performance of the PMSMs. Thus, monitoring the rotor magnets status is essential to ensure both high level of efficiency and service continuity. The present study focuses on the investigation of a new approach for the detection of rotor magnet demagnetisation in a vector-controlled asymmetrical six-phase surface-mounted AC PMSM. The main contribution of the proposed technique is the assessment of a rotor demagnetisation fault index derived from the fifth and seventh harmonics of the stator voltage space vector evaluated in the α 5–β 5-plane, and already available in the control system platform. The performance of the proposed approach is evaluated using finite element analysis and numerical simulations, both validated by experimental tests.

Torque enhancement of dual three‐phase PMSM by harmonic injection

The torque enhancement of the dual three-phase permanent magnet synchronous machine (DT-PMSM) drive system by full exploitation of flux-linkage and current harmonics is comparatively studied in this study. The torque capability of DT-PMSM is previously evaluated with strategies of harmonics utilisation, i.e. strategy 1 of third harmonic utilisation and strategy 2 of fifth and seventh harmonic utilisation, which can extend the torque capability by 18.2 and 9.0%, respectively. However, the full exploitation of harmonics including third, fifth, and seventh harmonics in the dual three-phase system is not addressed. In this study, the strategy 3 of third, fifth, and seventh harmonic utilisation is also included. Its corresponding harmonic current control is proposed and the average torque and harmonic torque are analysed in detail. Based on a test rig with existing prototype DT-PMSM, the torque with strategy 3 is increased up to 26.5%, which is superior to the previous strategies.

Optimal Overlap-Time Distribution of Space Vector Modulation for Current-Source Rectifier

This article proposes an improved space vector modulation (SVM) for the current-source rectifier (CSR). Due to the overlap time during commutations of power switches, the pulsewidth-modulation (PWM) currents of CSR may suffer from a number of low-order (mainly fifth and seventh) harmonics, which seriously degrade the harmonic performance of currents and voltages on the grid side. Especially, the overlap-time effect becomes an important issue when the increased switching frequency is applied to CSR. To mitigate these low-order harmonics of the PWM converter currents resulted from the overlap-time effect, the relationship between the overlap time and the low-order harmonics in PWM currents and grid currents are analyzed at first. Then, the design process of the LC filter and the proposed SVM with optimal overlap-time distribution is presented in details. Finally, experimental results are conducted on a low power laboratory prototype to verify the effectiveness of the proposed method.

Power quality improvement of solar power plants in grid connected system using novel Resilient Direct Unbalanced Control (RDUC) technique

Distributed Generation systems (DGs) using solar power is one of the new trends in power generation. These distributed generating units are integrated to form a micro grid to serve the loads among the locality, which is in connection with the utility grid for power transmission. The elimination of the harmonics in the grid and the usage of solar energy resources in the power electronics applications become famous worldwide. In this work, a Resilient Direct Unbalanced Control (RDUC) algorithm is used to improve the performance of the controller by achieving optimal numerical parameters for photovoltaic power generation - Unified Power Quality Conditioner (PV-UPQC). Then the voltage sag, swell and elimination of current harmonics are used to study the effects of proposed RDUC algorithm for photovoltaic feed UPQC system. According to the evaluations, the proposed unified power quality conditioner eliminates both the supply current distortion caused by a non-linear load and the load voltage distortion introduced after adding fifth and seventh harmonics to the Alternating Current (AC) mains voltage. To validate the simulation results of Resilient Direct Unbalanced Control scheme, tests are performed under various operating conditions. Test results show the satisfactory behavior under steady state, and dynamic conditions such as load unbalance, insolation variation, voltage sag and swell. Finally, Total Harmonic Distortions (THDs) of proposed optimization-based grid current and grid voltages found within limits of the IEEE standard.

Conductivity power of zero sequence for asymmetrical non-sinusoidal modes of three-phase electrical network with grounded neutral wire

The paper analyzes the work of a three-phase network with grounded neutral wire with nonlinear asymmetric consumers based on the theory of instantaneous power. In non-symmetric, non-sinusoidal modes of three-phase electric networks with grounded neutral wire, instantaneous reactive power contains three components. The regime’s imbalance is characterized by instantaneous active and reactive conditional capacities of zero sequence qb and qa. Conditional powers of the zero sequence qb and qa contain components that are due to asymmetry and non-sinusoidal mode character, which are characterized by a constant qb and qa an alternating component respectively. Since the positive, negative and zero sequence of voltage and current in the asymmetric non-sinusoidal mode are defined as the sum of the symmetric components, respectively, of the positive sequence of the first and seventh harmonics, the negative sequence of the first and fifth harmonics, the zero sequence of the first and third harmonics, the presence of the first harmonic of current and the voltage of the zero sequence forms the constant component and the second harmonic of capacities qb and qa, and the presence of the third harmonic of current and voltage forms mainly the second and fourth harmonics of these capacities. It is expedient to divide instantaneous conditional power qb and qa into instantaneous conditional capacities , which are determined by the product of instantaneous positive and negative sequential stresses on the zero sequence current, and the instantaneous conditional capacities that are determined by the product of instantaneous currents of the positive and negative sequences on the voltage of the zero sequence. The analytical expressions for the determination of the permanent components in the integral and complex forms of recording for the conditional capacities that characterize the imbalance of the current regime and the zero sequence voltage that can be used in the process of symmetry and compensation of higher harmonics have been obtained

SIMPLIFIED MODELS OF ELECTRIC DRIVES WITH FREQENCY CONTROL IN STUDIES OF POWER QUALITY

. The article presents two simplified models of AC drive with adjustable speed with voltageinverter and voltage generation using pulse width modulation-physical and mathematical, designed to assess the degree of total harmonic distortion of the line current. The physical one is an input rectifier inverter turned on to the network in series with a mains choke. A resistor is connected to the DC bus-simulating the load of an asynchronous motor. A similar scheme implemented in the SIMULINK software in the form of a mathematical simplified model was investigated. The aim of the study was to determine the possibility of using simplified models to assess the relationship between the total levels of harmonic distortion and the relative harmonics of the current consumed from the network, from the magnitude of the inverter load. The obtained simulation results are compared with the models and results of a physical model with a frequency Converter and an asynchronous motor. The visualization of functional dependencies between the fifth, seventh and eleventh harmonics, respectively, total harmonic distortions and network current consumption is shown. As a criterion for assessing the similarity of the simulation results, the hypothesis of equality of the average statistical samples was proposed and nonparametric comparison methods were used. The presented graphs illustrate the obvious similarity of the results obtained on the physical and simulation models with the data of the field experiment, which was confirmed by statistical studies. This is most clearly shown in the diagrams of type "boxplot", from which it follows that the median physical model with asynchronousmotor is guaranteed to be in the range of ±0.5 standard deviations from the mean of the sampling model in MATLAB. A preliminary conclusion is made about the adequacy of models based on comparison of experimental data.

Sliding Mode Control With Grid Voltage Modulated DPC for Voltage Source Inverters Under Distorted Grid Voltage

The grid voltage modulated direct power control (GVM-DPC) for grid-connected voltage source inverters has been introduced so that it can overcome the poor steady-state performance of the DPC. However, it was designed for a nondistorted grid voltage. In this paper, the GVM-DPC is modified to overcome a distorted grid voltage (e.g., fifth and seventh harmonics). First, a band pass filter is applied to extract the fundamental component of the voltage so as to build a model for the implementation of the GVM-DPC method. Next, a sliding mode control (SMC) is designed to handlethe terms of the harmonic in order to minimize the total harmonic distortion (THD) of the output currents. Simulations and experimental results are presented to verify the effectiveness of the proposed SMC with GVM-DPC control strategy. It is shown that although the performance of real and reactive powers are sacrificed, the THD of the current is significantly reduced.

Reduction and Elimination of Harmonics using Power Active Harmonic Filter

The Three Phase 4 wire Harmonic Filter is used to mitigate harmonics which is caused by expanding utilization of present day control electronic system and mechanical assembly drives, uninterruptible power supplies, SMPS and so on. These are responsible of producing nonlinear current and accordingly stack in the system with Harmonics. The capacitance of the power capacitor frames a dangerous circuit related to the sustaining transformer. Experience demonstrates that the selffull recurrence of this circuit is commonly somewhere in the range of 250 and 500 Hz, for example in the locale of the fifth and seventh Harmonics. Loads requiring consonant separating incorporate 6-pulse drives (AC/DC), UPS, recurrence converters. Active harmonic filters diminish your THD levels to inside IEEE/CEA limits. These channels are IGBT-based power converters. This channel infuses negative of the consonant current bringing about for all intents and purposes no symphonious bending. Phase balancing and power factor correction is also achieved. The simulation output and experimental results are found to be satisfaction because our goal is subject in mitigation of harmonics and power quality improvement.

Enhanced Position Sensorless Control Using Bilinear Recursive Least Squares Adaptive Filter for Interior Permanent Magnet Synchronous Motor

In the back electromotive force (EMF)-based sensorless control of interior permanent magnet synchronous motor (IPMSM), the inverter nonlinearity and flux linkage spatial harmonics will possibly give rise to (6k ± 1)th harmonics in the estimated back EMF, especially the fifth and seventh harmonics. Those harmonics will consequently introduce (6k)th harmonic ripples to the estimated rotor position, especially the sixth harmonic component. In order to solve this problem, a bilinear recursive least squares (BRLS) adaptive filter is proposed and integrated into a sliding-mode position observer to suppress the dominant harmonic components in the estimated back EMF and as a result, the accuracy of the estimated rotor position can be greatly improved. A unique feature of the BRLS adaptive filter is its ability to track and suppress the specified harmonic components in different steady state and dynamic operational conditions. The proposed method can compensate for harmonic ripples caused by the inverter nonlinearity and machine spatial harmonics at the same time; this method is also robust to machine parameter variation, and the BRLS algorithm itself is machine parameter independent. The implementation of the proposed BRLS filter in the sensorless control of IPMSM is explained in details in this paper. The enhanced drive performances using the BRLS filter have been thoroughly validated in different steady state and dynamic operational conditions on a 1.5-kW IPMSM sensorless drive.

Control Strategies of Mitigating Dead-time Effect on Power Converters: An Overview

To prevent short-circuits between the upper and lower switches of power converters from over-current protection, the dead time is mandatory in the switching gating signal for voltage source converters. However, this results in many negative effects on system operations, such as output voltage and current distortions (e.g., increased level of fifth and seventh harmonics), zero-current-clamping phenomenon, and output fundamental-frequency voltage reduction. Many solutions have been presented to cope with this problem. First, the dead-time effect is analyzed by taking into account factors such as the zero-clamping phenomenon, voltage drops on diodes and transistors, and the parameters of inverter loads, as well as the parasitic nature of semiconductor switches. Second, the state-of-the-art dead-time compensation algorithms are presented in this paper. Third, the advantages and disadvantages of existing algorithms are discussed, together with the future trends of dead-time compensation algorithms. This article provides a complete scenario of dead-time compensation with control strategies for voltage source converters for researchers to identify suitable solutions based on demand and application.

An Analog LO Harmonic Suppression Technique for SDR Receivers

A low-complexity analog technique to suppress the local oscillator (LO) harmonics in software-defined radios is presented. Accurate mathematical analyses show that an effective attenuation of the LO harmonics is achieved by modulating the transconductance of the low-noise transconductance amplifier (LNTA) with a raised-cosine signal. This modulation is performed through the bias network of a cascode device with a negligible increase in the LNTA noise figure. The proposed technique results in a notch at the third harmonic and at least 36 dB of attenuation at the fifth and the seventh harmonics. Experimental results in 130-nm CMOS and postlayout simulation results in 65-nm CMOS verify the proper functionality of the proposed technique and the accuracy of the proposed analyses.

Speed Regulation System of a Flux-Modulated Permanent-Magnet In-Wheel Motor Based on Sliding Mode Control and Adaptive Notch Filter

This paper presents a new nonlinear algorithm of speed regulation system for a flux-modulated permanent magnet in-wheel (FMPMW) motor. To improve the robustness and static performance of speed regulation system, sliding mode control with a sigmoid function is adopted. Compared with PI controller, the proposed algorithm can improve the robustness and minimize the torque ripple of the system. In addition, an adaptive notch filter is proposed to restrain the fifth and seventh current harmonics, which the static performance of control system can be further improved. Based on a 2-kW FMPMW prototype motor, the simulation and experimental results verify the good robustness and static performance of the proposed algorithm.

Design and analysis of novel optimal harmonic elimination strategy based on MOPSO to obliterate low‐order harmonics of odd‐nary cascaded transformers‐based multilevel inverter

Creating a high‐step staircase sinusoidal voltage taking into account of low number of switches is recognized as a significant challenge ahead of inventors of power electronics. This paper suggests a maiden cascaded transformer‐based multilevel inverter to effectively develop and solve the abovementioned challenge. Hence, via appending the bidirectional switches to the capacitors of submultilevel inverter as well as low‐frequency transformers, the proposed inverter structure can flexibly operate as so‐called “odd‐nary asymmetrical multilevel inverter.” From the perspective of low‐order harmonics produced by all inverter structures, apart from inverter type, it is essential that an effective strategy to be implemented to eliminate these harmonics. Toward this subject, kerf‐style Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) has been scheduled as an optimization problem. Because of nature of multiobjective state of the problem, application of the multiobjective optimization technique is inevitable. Considering significant performance of Multi Objective Particle Swarm Optimization (MOPSO) for solving the nonlinear objectives, the elimination of fifth, seventh, and 11th harmonics is formulated by relevant fitness functions based on MOPSO. Putting it all together, the relevant analytical study accompanying both the simulation and experimental results has transparently verified the performance of the proposed multilevel inverter. Furthermore, elimination of all three designated low‐order harmonics, ie, fifth, seventh, and 11th harmonics using MOPSO‐based kerf‐style SHEPWM strategy has been well confirmed.

Extremely efficient terahertz high-harmonic generation in graphene by hot Dirac fermions

Multiple optical harmonic generation-the multiplication of photon energy as a result of nonlinear interaction between light and matter-is a key technology in modern electronics and optoelectronics, because it allows the conversion of optical or electronic signals into signals with much higher frequency,andthe generation of frequency combs.Owing to the unique electronic band structure of graphene, which features massless Dirac fermions1-3, it has been repeatedly predicted that optical harmonic generation in graphene should be particularly efficient at the technologically important terahertz frequencies4-6. However, these predictionshave yet to be confirmed experimentally under technologically relevant operation conditions. Here we report the generation of terahertz harmonics up to the seventh order in single-layer graphene at room temperature and under ambient conditions, driven by terahertz fields of only tens of kilovolts per centimetre, and with field conversion efficiencies in excess of 10-3, 10-4 and 10-5 for the third, fifth and seventh terahertz harmonics, respectively. These conversion efficienciesare remarkably high, given that the electromagnetic interaction occurs in a single atomic layer. The key to such extremely efficient generation of terahertz highharmonics in graphene is the collective thermal response of its background Dirac electrons to the driving terahertz fields. The terahertz harmonics, generated via hot Dirac fermion dynamics, were observed directly in the time domain as electromagnetic field oscillations at these newlysynthesized higher frequencies. The effective nonlinear optical coefficients of graphene for the third, fifth and seventh harmonics exceed the respective nonlinear coefficients of typical solids by 7-18 orders of magnitude7-9. Our results provide a direct pathway to highly efficient terahertz frequencysynthesis using the present generation of graphene electronics, which operate at much lower fundamental frequencies of only a few hundreds of gigahertz.

EMI Reduction Methods in Wireless Power Transfer System for Drone Electrical Charger Using Tightly Coupled Three-Phase Resonant Magnetic Field

Wireless power transfer (WPT) technology is a promising way for convenient and safe battery charging without any electrical contact, which may cause an unwanted electric spark or deliver dangerous electric current to the users. When transferring power from the source to the battery, strong electromagnetic fields (EMFs) are generated. Moreover, the inverter output contains a wide range of harmonics. Therefore, it is important to reduce the EMFs and electromagnetic interference (EMI) in a WPT system. For the first time, in this paper, we propose a new tightly coupled three-phase resonant magnetic field (TC-TPRMF) charger for a drone operating at 60 kHz, which can completely eliminate the third harmonic and its integer multiples in the output voltage. Furthermore, to reduce the selective EMI, the conduction angle control is proposed for the WPT charging system. Through a series of measurements, we verified that the proposed TC-TPRMF with the conduction angle control can reduce the seventh and 11th harmonics of the Tx current by 6.08 and 11.84 dBμA, respectively. The coil-to-coil power transfer efficiency and total system power transfer efficiency are maintained at 91% and 72%, respectively.

A Novel Computational Approach for Harmonic Mitigation in PV Systems with Single-Phase Five-Level CHBMI

In this paper, a novel approach to low order harmonic mitigation in fundamental switching frequency modulation is proposed for high power photovoltaic (PV) applications, without trying to solve the cumbersome non-linear transcendental equations. The proposed method allows for mitigation of the first-five harmonics (third, fifth, seventh, ninth, and eleventh harmonics), to reduce the complexity of the required procedure and to allocate few computational resource in the Field Programmable Gate Array (FPGA) based control board. Therefore, the voltage waveform taken into account is different respect traditional voltage waveform. The same concept, known as “voltage cancelation”, used for single-phase cascaded H-bridge inverters, has been applied at a single-phase five-level cascaded H-bridge multilevel inverter (CHBMI). Through a very basic methodology, the polynomial equations that drive the control angles were detected for a single-phase five-level CHBMI. The acquired polynomial equations were implemented in a digital system to real-time operation. The paper presents the preliminary analysis in simulation environment and its experimental validation.

Selective harmonic elimination in multilevel inverter using hybrid APSO algorithm

This study presents selective harmonic elimination pulse width modulation technique-based hybrid asynchronous PSO-Newton-Raphson (APSO-NR) algorithm for the elimination of undesired harmonics in cascaded H-bridge multilevel inverter. The proposed algorithm is applicable to all levels of MLI having equal and non-equal DC sources. In the proposed method, ring topology-based APSO algorithm is hybrid with NR method. APSO worked as a global search technique and NR is used for the refinement of best solutions. APSO-NR is applied to the seven-level inverter to eliminate fifth and seventh harmonics. In simulations, the performance of the proposed algorithm is compared with genetic algorithm, bee algorithm and particle swarm optimisation. The results proved that the proposed algorithm is efficient, and gives more precise firing angles in less number of iterations with high capability of tackling local optima. For the 48% of modulation index range, APSO-NR minimised the fitness function value lower than (10 -25 ). The proposed algorithm is validated through the experimental implementation of the three-phase seven-level inverter.

Selective Harmonic Elimination With Optimal DC Sources in Multilevel Inverters Using Generalized Pattern Search

This paper presents the computation of optimal dc sources and switching angles using the generalized pattern search (GPS) optimization method for harmonic elimination in a cascaded multilevel inverter. The goal is to solve nonlinear equations for eliminating low-order harmonics and reaching desired fundamental component. For case study, 5- and 7-level inverters are chosen. The 7-level inverter with equal dc sources and 5- and 7-level inverters with an optimal dc source are applied to eliminate fifth and seventh harmonics. To obtain this goal, MATLAB software is used. Considering simulation results, cost, and simpler implementation, 5-level inverter with an optimized dc source is more effective in all modulation indexes in comparison with 7-level inverter. Also, results demonstrate the superiority of GPS over genetic algorithm (GA) in attaining accurate global minima. For better evaluation of optimizing more dc sources and GPS performance in comparison with GA, 7-level inverter with two optimal dc sources is applied to eliminate fifth, seventh, 11th, and 13th harmonics. Finally, to validate the accuracy of the 5-level inverter with an optimal dc source and GPS performance, the experimental results are provided for a 5-level cascaded H-bridge inverter.

Reduction of Total Harmonic Distortion in Cascaded H-Bridge Inverter by Pattern Search Technique

Pattern Search technique can be used to find the solution for the optimization problem. In this paper, pattern search algorithm has been utilized to calculate the switching angles for the cascaded H-bridge inverter with the consideration of minimizing total harmonic distortion. Mathematical equations for the optimization problem were formulated by fourier analysis technique. Lower order harmonics such as third, fifth, seventh, ninth and eleventh order harmonics were taken into account to mitigate the total harmonic distortion of the inverter. Simulations have been carried out for thirteen level, fifteen level and seventeen level cascaded H-bridge inverter using matlab software. Total harmonic distortion of voltage and current for resistive load, resistive-inductive load and motor load were analyzed.

Natural Sampling SVM-Based Common-Mode Voltage Reduction in Medium-Voltage Current Source Rectifier

Conventional space vector modulation (SVM)-based common-mode voltage (CMV) reduction in medium-voltage (MV) current source rectifier (CSR) cannot be used in practice. Conventional SVM contains high-magnitude low-order harmonics, particularly the fifth and seventh harmonics, that are lying closely to the resonance frequency (4.5–5.5 p.u.) of the LC filter of the converter, thus, introducing resonance as the grid-side damping is small. Recently, a natural sampling SVM (NS-SVM) with superior low-order harmonics performance has been proposed for MV CSR. On this basis, a NS-SVM-based CMV reduction method is proposed for MV CSR in this paper. The proposed scheme achieves both good CMV reduction and superior low-order harmonics performance simultaneously. Additionally, effort to lower computational burden on calculating dwell times is made. Experiments are finally provided.