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Examines the use of distributed, monolithic travelling-wave amplifiers. Guidance on reducing amplifier noise by rendering dipole-domain-generated noise contributed by the individual field effect transistor (FET); Use of insulated gate FET to permit higher gate breakdown voltage operation in the accumulation mode; Reduction of even harmonics and the improvement of efficiency.

This paper elucidates the working of shunt active filters in dynamically varying grid conditions. The accuracy of harmonics eliminated is based on the harmonic extraction technique and the switching techniques used. The harmonics of the electrical system are computed and based on the various harmonics produced; the shunt active filter has to supply a compensating current in opposition at the point of common coupling. Space Vector Pulse Width modulation (SVPWM) is an effective switching technique used but its performance is not satisfactory in the over-modulation regions. In this paper, optimised switching technique using a neural network for SVPWM is used which has lesser computation time and computes the gating pulses effectively in the over-modulation regions. Shunt active filter mitigates the impact of harmonics even in the over-modulation regions. The hardware is implemented using FPGA Spartan 6 controller, which utilises fewer hardware resources. The optimised switching topology results with improved harmonic reduction even in the over-modulation regions with unbalanced loading conditions is presented in this paper. [ABSTRACT FROM AUTHOR]

In recent wireless communications, spectrally flexible transmissions such as carrier aggregation and cognitive radio pose severe challenges for the high-efficient radio-frequency power amplifier (PA) design. The non-linear characteristics of PAs may yield substantial unwanted emissions that can violate the emission limits, thus interfere with other communication systems within the frequency vicinity. Furthermore, in frequency-division duplexing systems, if the unwanted emissions happen to fall into the intended receiver band, it may cause severe receiver desensitisation. In this paper, we present a novel digital predistortion (DPD) technique based on a frequency selective architecture, which is aimed at reducing the unwanted harmonic emissions at any pre-specified frequency and linearising the fundamental signal at the same time. The method can simplify the predistortion structure compared with the whole spurious suppression DPD method and thus reduce the computational complexity of the predistortion process. Furthermore, the identification of the DPD coefficients is based on a breeding particle swarm optimisation algorithm, which can enhance the calculation flexibility as well accelerate the convergence speed compared with traditional gradient methods. Both simulation and measurement results demonstrate sufficient spur suppression at the target frequency. [ABSTRACT FROM AUTHOR]

Online detuning state detection and the subsequent detuned element identification of a passive filter bank is of great concern in regard to achieving condition-based maintenance of an HVDC transmission system. In this paper, a novel method that can rapidly detect the online detuning state of filter banks with arbitrary structures of an HVDC system and accurately identify the detuning element is proposed. The method is based on the calculated amplitude change rates (ACRs) of several deliberately selected harmonic components of the measured real-time current in each branch of the filter. The principle and the implementation of the proposed method are presented, and the relationship between the ACR of the harmonic current and the detuning degree of an individual element is deduced theoretically. Based on the above works, the criteria for identifying the detuning state of the filter bank, the detuned element in the series and parallel part of the filter, and the detuning degree of the element are given. Diverse simulation results, such as applications on a single- and a double-tuned DC filter bank, sensitivity analysis and performance comparison, are provided to show the correctness and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a synchronous reference frame (SRF) method based on a modified phase lock loop (PLL) circuit is developed for a three-phase four-wire shunt hybrid active power filter (APF). Its performance is analysed under unbalanced grid conditions. The dominant lower order harmonics as well as reactive power can be compensated by the passive elements, whereas the active part mitigates the remaining distortions and improves the power quality. As different control methods show contradictory performance, fuzzy logic controller is considered here for DC-link voltage regulation of the inverter. Extensive simulations of the proposed technique are carried out in a MATLAB-SIMULINK environment. A laboratory prototype has been built on dSPACE1104 platform to verify the feasibility of the suggested SHAPF controller. The simulation and experimental results validate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

This paper presents a self-powered inductor-based converter which harvests thermoelectric energy and boosts extremely low voltage to a typical voltage level for supplying body sensor nodes. Electromagnetic interference (EMI) of the converter is reduced by spreading spectrum of fundamental frequency and harmonics via pseudo-random modulation, which is obtained via combining the linear feedback shift register and digitally controlled oscillator. Besides, the methods, namely extracting energy near MPP and reducing the power dissipation, are employed to improve the power efficiency. The presented inductor-based converter is designed and verified in CSMC CMOS 0.18-µm 1P6M process. The results reveal that it achieves the high efficiency and EMI reduction at the same time. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis, design, and experimental results of a new integrated electronic ballast based on the half-bridge boost rectifier followed by the half-bridge series resonant parallel loaded inverter. The electronic ballast features a high power factor and low harmonics input current. The involved converters share the power switches, reducing costs significantly. The input stage of the ballast works in discontinuous inductor current mode with constant duty cycle and variable switching frequency. It is important to maintain this operating condition in order to get a high power factor. Integrating the power stages results in higher complexity in the control design because a close relationship still exists between the power stages. Within the paper, the operating characteristic is established in order to obtain a design method for the ballast. The obtained method is used to design a laboratory prototype for a 26-watt fluorescent lamp. Some experimental results are included. [ABSTRACT FROM AUTHOR]

This paper considers the linearisation of an asymmetrical two-way Doherty amplifier by the method that uses the second harmonics and fourth-order non-linear signals for linearisation. These even-order signals for linearisation are extracted at the output of the peaking amplifier, adjusted in amplitude and phase and injected at the input and output of the carrier amplifier transistor in the Doherty configuration. The effect of linearisation has been experimentally confirmed on a fabricated asymmetrical Doherty amplifier with the additional circuit for linearisation. The suppression of the third-order intermodulation products has been carried out for two-tone test, 64QAM and WCDMA digitally modulated signals in a range of signal power. [ABSTRACT FROM AUTHOR]

Multiple pulse width modulated (MPWM) AC choppers are gaining popularity over phase controlled circuits mainly due to the minimization of harmonics and the improvement in the input power factor. In this paper a direct digitally controlled MPWM AC Chopper using power transistors is described. A 120° chopping period is used for the main transistors in the three-phase power circuit to allow the circuit to accommodate loads of any power factor angle. Single-phase sensing is used to generate all control signals necessary for three-phase power control. The experimental results obtained with a three-phase prototype circuit are presented. The circuit described is expected to find extensive use in microprocessor based MPWM AC power controllers and AC line regulators. [ABSTRACT FROM AUTHOR]

Harmonic suppressed active antenna integrated with power amplifier yields improved efficiency, higher output power and reduced harmonic radiation from transmitter front end. This paper presents different harmonic suppression techniques of active antenna integrated with power amplifier. This paper also proposes and demonstrates novel PBG engineered structures to suppress higher order harmonics of integrated active antenna. [ABSTRACT FROM AUTHOR]

Various attempts have been made for the selective reduction of harmonies in the output of AC/AC converters. However, when some harmonics are reduced other harmonic amplitudes increase. Thus, to reduce the harmful effects of these harmonics on other equipment operating on the same line, it may be necessary to use filters. A suitable type of filter depending on the line inductance for such cases is suggested in this paper. Experimental results are also presented. [ABSTRACT FROM AUTHOR]

In order to obtain an analytical solution of the step-recovery diode as a harmonic multiplier, various models of the diode have been used by several authors without sufficient explanation. This paper examines and compares the properties of these models by taking as a reference Kotzebue's experimentally verified model. An improvement of the 'resistive' model is also put forward. [ABSTRACT FROM AUTHOR]

In a permanent magnet synchronous motor (PMSM) control system, usually, the phase voltage instruction is limited independently to prevent a three-phase pulse width modulation (PWM) wave from overflowing. This method decreases the efficiency of the bus voltage and causes voltage vector direction errors. To solve these problems, we propose a harmonic injection sinusoidal pulse-width modulation (SPWM). This method uses harmonic injected sinusoidal PWM to improve the utilisation ratio of the bus voltage, and consequently improve system performance. In this paper, we analyse the problem in terms of potential difference. The simulation results show that the proposed method can increase the utilisation ratio of the bus voltage up to 15.4%, and the voltage vector mode obtained with the proposed algorithm is larger than that obtained with the conventional one. The method with harmonic injection consequently improves current response, without affecting voltage vector accuracy. The experiment results validate the proposed method. [ABSTRACT FROM PUBLISHER]

This paper presents an all-digital concept for sinusoidal pulse-width modulation (SPWM) generation that uses modern arithmetic algorithms to impose a sinusoidal variation of the switching pulses that control the power transistors of a single-phase inverter, thus improving the linear characteristics of the inverter output signal. The developed modulation strategy is given a mathematical description, which can then be modelled and synthesised on field programmable gate arrays (FPGAs). The only existing harmonics present within the spectrum of the final signal are the multiple of the switching frequency. The order of these harmonics is so high (switching frequency related with output frequency sidebands), that a filter can easily be designed to reject these frequencies. The ability to accurately control the output characteristics of the inverter within 1% and also maintain less than 1% harmonic distortion, demonstrates the feasibility of the digital synthesiser. [ABSTRACT FROM AUTHOR]

This paper presents a multistage pulse-width modulated system for generating three-phase controlled stepped voltage waveforms. A four stage system is discussed. Voltage control is achieved by pulse-width modulation. Harmonics are eliminated by suitable transformer connections. In the four-stage system the eleventh and thirteenth harmonics predominate in its three-phase output voltage waveforms. The advantages of the proposed system are discussed. The results are experimentally verified and compared with the conventional systems. [ABSTRACT FROM AUTHOR]

The performance of an induction motor fed by PWM inverters is mainly determined by the harmonic contents of the output voltage. This paper presents a method of numerically calculating the harmonics in the output voltage waveform. Equal pulse-width modulation and sinusoidal PWM are studied. Analysis has been done for single-phase and three-phase bridge inverters. A systematic procedure is given for computing the harmonics and the results are tabulated. [ABSTRACT FROM AUTHOR]

The paper describes three methods that can be used for controlling the power of resistive loads. One of the methods described here aims at reducing any one unwanted harmonic to a very small value in the case of an a.c./a.c, phase-controlled converter feeding a resistive load. All three methods discussed are compared with the method suggested by Bland (1975) with regard to harmonics, power factor and practical realization of the power circuit. The power circuit and the control circuitry are described. Design criteria for choosing the components in the power circuit are also discussed. [ABSTRACT FROM AUTHOR]

An active power filter is used to eliminate current harmonics produced by nonlinear loads. This paper discusses a fully digital method of controlling a power inverter used to inject the active filter compensating currents into the power system. A digital signal processor performs the harmonic isolation and generates a digital reference current. A hysteresis current controller has been implemented in a field programmable gate array that generates the inverter switching signals using this reference. This reduces the analogue circuitry and enhances the system's immunity to electromagnetic interference. The performance of a small-scale inverter under completely digital control is presented and discussed. [ABSTRACT FROM AUTHOR]

Presents a method of pulsewidth modulation (PWM) for general use with microcomputer-implemented inverter systems. Defined linear relationship between the successive pulsewidths of the PWM pattern; Simple determination of the composition of the PWM pattern; Maintenance of very low harmonic levels at the output of the linear PWM-inverter; Effective generalized approach for drastic minimization of harmonics.

In addition to the focus towards growing demand on electrical energy due to the increase in population, industries, consumer loads, etc., the need for improving the quality of electrical power also needs to be considered. The design and development of solar photovoltaic (PV) inverter with reduced harmonic distortions is proposed. Unlike the conventional solar PV inverters, the proposed inverter provides the advantages of reduced harmonic distortions thereby intend towards the improvement in power quality. This inverter comprises of multiple stages which provides the required 230VRMS, 50 Hz in spite of variations in solar PV due to temperature and irradiance. The reduction of harmonics is governed by applying proper switching sequences required for the inverter switches. The detailed analysis is carried out by employing different switching techniques and observing its performance. With a separate mathematical model for a solar PV, simulations are performed in MATLAB software. To show the advantage of the system proposed, a 3 kWp photovoltaic plant coupled with multilevel inverter is demonstrated in hardware. The novelty resides in the design of a single chip controller which can provide the switching sequence based on the requirement and application. As per the results obtained, the solar-fed multistage inverter improves the quality of power which makes this inverter suitable for both stand-alone and grid-connected systems. [ABSTRACT FROM AUTHOR]

Genetic algorithm (GA)-based harmonic elimination technique is proposed for designing AC chopper. GA is used to calculate optimal firing angles to eliminate lower order harmonics in output voltage. Total harmonic distortion of output voltage is taken for the fitness function used in the GA. Thus, the ratings of the load are not mandatory to be known for calculating the switching angles using proposed technique. For the performance assessment of GA, Newton–Raphson (NR) method is applied in this present work. Simulation results show that the proposed technique is better in terms of less computational complexity and quick convergence. Simulation results were verified by field programmable gate array controller-based prototype. Simulation study and experimental investigations show that the proposed GA method is superior to the conventional methods. [ABSTRACT FROM PUBLISHER]

In the case of undistorted and balanced grid voltages, low ratio shunt active power filters (APFs) can give unity power factors and achieve current harmonic cancellation. However, this is not possible when source voltages are distorted and unbalanced. In this study, the cost-effective hybrid active power filter (HAPF) topology for satisfying the requirements of harmonic current suppression and non-active power compensation for industry is presented. An effective strategy is developed to observe the effect of the placement of power capacitors and LC filters with the shunt APF. A new method for alleviating the negative effects of a nonideal grid voltage is proposed that uses a self-tuning filter algorithm with instantaneous reactive power theory. The real-time control of the studied system was achieved with a field-programmable gate array (FPGA) architecture, which was developed using the OPAL-RT system. The performance result of the proposed HAPF system is tested and presented under nonideal supply voltage conditions. [ABSTRACT FROM AUTHOR]

This article presents a novel control strategy for a 1-ϕ 2-level grid-tie photovoltaic (PV) inverter to enhance the power quality (PQ) of a PV distributed generation (PVDG) system. The objective is to obtain the maximum benefits from the grid-tie PV inverter by introducing current harmonics as well as reactive power compensation schemes in its control strategy, thereby controlling the PV inverter to achieve multiple functions in the PVDG system such as: (1) active power flow control between the PV inverter and the grid, (2) reactive power compensation, and (3) grid current harmonics compensation. A PQ enhancement controller (PQEC) has been designed to achieve the aforementioned objectives. The issue of underutilisation of the PV inverter in nighttime has also been addressed in this article and for the optimal use of the system; the PV inverter is used as a shunt active power filter in nighttime. A prototype model of the proposed system is developed in the laboratory, to validate the effectiveness of the control scheme, and is tested with the help of the dSPACE DS1104 platform. [ABSTRACT FROM AUTHOR]

In this article, two new highly linear tunable transconductor circuits are proposed. The transconductors employ only six MOS transistors operated in saturation region. The second transconductor is derived from the first one with a slight modification. Transconductance of both transconductors can be tuned by a control voltage. Both of the transconductors do not need any additional bias voltages and currents. Another important feature of the transconductors is their high input and output impedances for cascadability with other circuits. Besides, total harmonic distortions are less than 1.5% for both transconductors. A positive lossless grounded inductor simulator with a grounded capacitor is given as an application example of the transconductors. Simulation and experimental test results are included to show effectiveness of the proposed circuits. [ABSTRACT FROM AUTHOR]

For improving the alteration performance of multilevel inverter, selective harmonics elimination methods play a significant role. In this document, an incorporated method is suggested for removing the harmonics of multilevel inverter with uneven DC sources. The suggested incorporated method is the mixture of fuzzy logic intelligent system and particle swarm optimisation (PSO) algorithm. For generating the training information set in terms of switching angle, Fuzzy is one of the synthetic intelligent methods which apply harmonic voltage and harmonic distortion. PSO is one of the swarm intelligence-based optimisation algorithms which is employed for choosing optimal switching angle from the training data set. The suggested hybrid method is executed in MATLAB/Simulink platform. At dissimilar unequal input voltage levels, the performance of the suggested method is checked by cascade H-bridge multilevel inverter. The production of the suggested method is compared with the theoretical effects. [ABSTRACT FROM AUTHOR]

This article presents a simple mathematical model for the output-voltage/input-voltage characteristics of the carbon nanotube field-effect transistor (CNTFET)-based and the single-electron tunnelling transistor (SET)-based inverting amplifiers. The model, basically a Fourier-series, yields closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output voltage resulting from a multisinusoidal input voltage. The special case of a two-tone equal-amplitude input signal is considered in detail. The results show that the harmonic and intermodulation performance of the CNTFET-based and SET-based inverting amplifiers is strongly dependent on the values of the bias voltage and the amplitudes of the input tones. Moreover, the results show that for the CNTFET-based inverting amplifier, either the relative second-order or the relative third-order intermodulation component is dominant, while for the SET-based inverting amplifier, the relative third-order intermodulation is always dominant. The results also show that all the harmonics and intermodulation products may exhibit minima at different values of the input bias voltages and tone amplitudes. [ABSTRACT FROM AUTHOR]

In this article a novel controllable reactor based on regulating the transformer's primary equivalent impedance by controlling its secondary voltage source inverter load is proposed. When the secondary current of a transformer is forced to be proportional to and in inverse phase with its primary current, the primary side of the transformer exhibits a linear adjustable reactance with respect to the proportion coefficient. The voltage source pulse width modulation (PWM) inverter connected to the secondary side of the transformer provides the required secondary current. In order to realise a large-capacity reactor, a transformer with multiple secondary windings is used to reduce the capacity requirement of each PWM inverter. A large-capacity (800 kVA) prototype is fabricated. The experimental results verify the characteristics of the novel controllable reactor - linear reactance tuning, few harmonics and fast response. [ABSTRACT FROM AUTHOR]

Large signal analysis of a wideband non-linear amplifier excited by a multisinusoidal signal is presented. The special cases of two equal-amplitude sinusoids and their injected harmonics, sum- and difference-frequency components are considered in detail and the results are compared, whenever possible, with previously published simulation and experimental results. [ABSTRACT FROM AUTHOR]

A study on the torque ripple minimization of a voltage source inverter fed selfsynchronous machine is presented. This study is based on a design of a position sensor which allows us to suppress undesirable voltage harmonics and hence to minimize electromagnetic torque ripple. We use the optimized pulse width modulation (PWM) method as a basis for the design of this position sensor. Thus, the obtained inverter control circuit is a very simple design and there is no need for a microprocessor or for specialized PWM integrated circuits for its implementation. The obtained simulation results are compared with practical results for a self-controlled synchronous machine, using the classical control method and the proposed method. [ABSTRACT FROM AUTHOR]

A novel adaptive infinite impulse response (IIR) comb filter structure for the estimation and elimination of harmonic interference signals is presented. Two filter blocks are presented. The first is an adaptive notch filter implemented by a computationally simple but exact gradient-based algorithm. The adaptive notch filter is used to estimate and track the fundamental frequency of the harmonic series. The second block is a tunable IIR comb filter whose parameters are determined based on the estimate of the fundamental frequency. The purpose of both filter blocks is to effectively cancel the harmonic series. The proposed comb filtering is more robust as well as computationally simpler than the comb filtering technique used by Nehorai and Poraz (1986). Error surface analysis is included to indicate that the error surface characteristics for the proposed solution is a significant improvement when compared to the conventional adaptive comb filter approach used by Nehorai and Poraz (1986). Simulation results are included to demonstrate the performance characteristics of the proposed solution. [ABSTRACT FROM AUTHOR]

A further improvement of the method of generating three-phase stepped voltage waveforms is described. The proposed system consists of a three-phase inverter that is transformerless, a triple-frequency single-phase inverter with a transformer, and three power semiconductor switches that link the two inverters. The voltage waveform obtained has a total harmonic distortion of 7.99%, and the predominant harmonics are the 17th and 19th. This method makes possible a reduction in the size and weight of equipment for producing an uninterrupted power supply with reduced harmonic distortion. The theoretical results are verified by an experimental set up using power transistors with a rating of 450 V and 30 A. [ABSTRACT FROM AUTHOR]

A cyclotron resonance maser oscillator, or gyromonotron, has been designed to produce radiation at a 1·25 mm wavelength by its operation at the second harmonic of the electron cyclotron frequency in an applied magnetic field of 45 kG. Based on linear gyrotron theory and electron orbit computer simulations, an output power in the 1 to 10 kW range at an efficiency of or exceeding 10% should be achievable. In initial tests of this tube, more than 50 W of radiation at both the first and second harmonics were observed at various values of applied magnetic field. However, beam interception necessitated modifications in tube construction. The modified tube was an efficient first harmonic radiator, but the second harmonic was suppressed. Further modifications to the tube necessary to obtain the second harmonic radiation are currently under investigation. [ABSTRACT FROM AUTHOR]

A method based on the describing function concept has been used to derive the frequency change in an oscillator due to the presence of harmonies. To check the result obtained, a simple oscillator has been used. The experimental results agree well with the theory. [ABSTRACT FROM AUTHOR]

An improved technique is proposed for stabilizing the output of a variable-frequency RC sine-wave oscillator. Very low harmonic distortion figures and fast amplitude settling are achieved together by sampling the peaks of the output waveform to produce a d.c. voltage having virtually no ripple content. A simplified analysis of the stabilization loop is included, and the effects of non-ideal sampling on distortion are considered. [ABSTRACT FROM AUTHOR]

Linear time-varying analysis of the step recovery diode harmonic generator is investigated to assess its value as a means of obtaining a very general and flexible technique for the evaluation of the circuit properties without recourse to analogue computation procedures. The approach is used to evaluate the effects of diode transition time and conducting resistance, and of source and terminating impedances and bias (conduction time). The effects of idler circuits on efficiency and terminating impedances are readily evaluated and the influence of idler loss characterized in a number of idler combinations for high-order multipliers. The effects of finite output circuit Q are also shown. [ABSTRACT FROM AUTHOR]

Measurements of the second harmonic power radiated by Yig samples under oblique pumping are reported. These indicate the suitability of this operation for high-power operation. Enhancement of doubling is shown to result from an increase in the magnitude of the gyromagnetic constant.
In the usual method of frequency doubling in ferrites the uniform mode is made to execute an elliptical orbit, and the second harmonic power is generated in a direction perpendicular to the plane of the orbit (Ayres et al. 1956). This operation, in which the second harmonic component of magnetization coincides with the direction of the magnetostatic field, may be termed longitudinal doubling. Alternatively, second harmonic components of magnetization are generated in the transverse plane when the sample is subjected to R.F. fields of the same frequency in the transverse and in the longitudinal directions (Jepsen 1961). The longitudinal R.F. field causes the modulation of the resonance frequency and the excitation of sidebands in the transverse directions. As the sample is, in effect, subjected to the resultant of the two fields, this method of excitation may be termed oblique pumping. [ABSTRACT FROM AUTHOR]

It is shown that a circuit containing a single externally driven switch, operated at a fundamental frequency f, can give efficient conversion of d.c. to a.c. at frequency f or any specified harmonic of f. The efficiency depends in the main upon the quality of the switch, as measured by the ratio of open to closed conductance, and on the percentage of the-cycle for which the switch is opened. The circuit is compared with other forms Of amplifier and harmonic generator, including the Class C amplifier. [ABSTRACT FROM AUTHOR]