Current injection method to eliminate harmonics

This article proposes a method to eliminate AC harmonic currents by injecting equal-but-opposite harmonic compensating currents. This method is applicable to any type of load considered a harmonic source. This article describes a system involving a hardware interface, a PC, and advanced software to measure, analyze, and report the condition of harmonics on the power system. This system is used to generate all the necessary harmonic currents for compensation. Digital simulation and experimental results from a single and three phase AC/DC converters are shown to verify the effectiveness of this technique     

磁链追踪PWM法中的谐波分析

从反变换的角度对磁链追踪PWM法中的谐波情况进行了分析。推导了定子磁链多边形的径向误差△R、相位误差△Ф与谐波的分布以及各次谐波含量之间的关系，并通过仿真研究了径向误差△R和相位误差△④对谐波影响的特点。     

State-of-the-art carrier PWM techniques: a critical evaluation

With the introduction and wide acceptance of gate-turnoff power drives, e.g., bipolars, power FETs, GTOs, the switching behaviour of converters has reached the point where further improvements in firing and switching networks bring out only marginal benefits. Consequently, the research interests in the area of static converters have been shifting toward improving the process of power conversion through a combination of novel circuit topologies and improved voltage and harmonic control PWM (pulsewidth modulation) techniques. As a result, several such techniques have been proposed lately. Although these techniques are clearly superior to the original sine PWM technique, little or conflicting data is available about their merits relative to each other. A critical evaluation of the aforementioned PWM techniques on the basis of application is provided, thereby giving the framework and guidelines for the selection of the best technique for each area of application     

Developing a novel sinusoidal pulse width modulation (SPWM) technique to eliminate side band harmonics

In this study, an enhanced SPWM modulation scheme is developed in order to minimize total harmonic ratio (THD) by eliminating the side band harmonics that are not paid attention in regular modulation schemes. Unlike the conventional SPWM, the developed modulation scheme considers the elimination of harmonics that are located at the carrier frequency and at the side bands of carrier frequencies. Therefore, the harmonic elimination feature of SPWM that eliminates the base harmonic orders but not considers the side band harmonics in frequency domain is improved with the developed analytical definition. The side band harmonic elimination feature of the proposed SPWM scheme eliminates higher order harmonics. The elimination of high-ordered attenuated harmonics decreases the harmonic contents seen in the THD spectrum. The simulation of inverter is carried out with Matlab/Simulink and experimental studies are performed utilizing TMS320F2812 DSP. The proposed SPWM schemes is tested according to various control strategies such as switching frequency (f_sw) and modulation index (m_i) terms by using a full bridge inverter. The analytical model improved to calculate and generate switching intervals is simultaneously operated in DSP instead of managing a look-up table. The experimental studies of the inverter verify that the developed SPWM modulation scheme mitigates the side band harmonics successfully. The higher order harmonics are eliminated and the THD ratios are decreased owing to proposed SPWM scheme.     

Reduced harmonics PWM controlled line-side converter for electricdrives

The concept for a reduced-harmonics PWM modulator, as applied for the control of a line-side power converter for a variable speed AC motor drive, is described. The PWM algorithm determines the on-state duration of each switching vector based on the observation of the time-variable voltage reference vector. Since there is no reference made to a constant-frequency carrier signal, the generated pulse patterns become asynchronous. It is the essential property of this method to produce a quasicontinuous harmonic spectrum in which all frequency components have more or less equal magnitudes. This is an advantage as compared with carrier-based PWM control schemes that exhibit high-amplitude carrier and side-band components in their harmonic spectra. The emission of acoustic noise radiated from the AC filter inductor is reduced     

Space vector control and current harmonics in quasi-resonantsoft-switching PWM conversion

The paper presents an analysis of the behavior of the modulation schemes useful for the soft-switched, quasi-resonant VSI power inverter in comparison with standard PWM techniques (sine-triangle and space-vector). Although the presence of a purely capacitive snubber across each power device in such kinds of converters allows true PWM, this is affected by some constraints in the switching sequence depending on the load current polarities, which result in a ripple content much higher than that obtained from conventional PWM schemes with the same switching frequency. However, it is also shown that the location and duration of the zero-vector state is a degree of freedom which can be useful to obtain different switching sequences, so reducing substantially the ripple. The above criteria have been adopted in developing a PWM technique based on space vectors, which is also described in the paper. Such a technique determines the optimum vector sequence which gives the wanted voltage vector, while reducing the ripple content. Results of simulations are reported, illustrating the differences between the various schemes and validating the effectiveness of the proposed modulation method     

Elimination of low-frequency harmonics caused by PWM in athree-phase soft-switched boost rectifier

This paper presents three major causes of low-frequency harmonics in a high-frequency soft-switched three-phase pulsewidth modulation (PWM) boost rectifier: pulsewidth limits; an improper space-vector modulation scheme; and dead time. Among these, the pulsewidth limits are related to soft-switching techniques. To eliminate undesirable low-frequency harmonics, each cause is illustrated and a solution is provided. Both simulation and experimental results prove the effectiveness of the proposed solutions. Due to the similarities between boost rectifiers and voltage-source inverters, the conclusions of this paper are also applicable to high-frequency PWM voltage-source inverters     

A novel PWM scheme to eliminate the diode freewheeling In the Inactive phase in BLDC motor

The brushless DC motor (BLDCM) with trapezoidal electromotive force (back-EMF) waveform is used widely. In principle, when the motor runs in the 120° conduction mode, two of the three phases are active while the other phase is inactive at all times. However, a ripple current occurs in the inactive phase due to the diode freewheeling during the non-commutation period in the traditional pulse width modulation (PWM) methods, which aggravates the torque ripples. A new PWM method is proposed in this paper to eliminate the diode freewheeling during the non-commutation period in the inactive phase. As a result, the torque ripple is suppressed using the proposed method. The simulation and experimental results are demonstrated to verify the validity of the proposed PWM method. __________ Translated from Proceedings of the Chinese Society for Electrical Engineering, 2005, 25(7): 104–108 (in Chinese)     

Application of differential evolution for cascaded multilevel VSI with harmonics elimination PWM switching

Harmonic elimination pulse width modulation (HEPWM) method has been widely applied to multilevel voltage source inverter (MVSI) to remove low frequency harmonics from its output voltage. However, the computation of the HEPWM switching angles for MVSI is very challenging due to several constraints, namely angle sequencing, very tight angular spacing and the numerous possibilities of angles distribution ratio. Realizing the potential of Differential Evolution (DE) to handle complex problems, this work proposes its application to solve the HEPWM problem for cascaded MVSI. Its emphasis is on improving the availability of HEPWM for higher output voltage by extending the maximum range of modulation index (M). It also removes the discontinuities in the switching angles and reduces the number of distribution ratio required to obtain the required solution. Compared to the most advanced (similar) work, i.e., 7-level MVSI with seventeen switching angles, DE covers a wider range of M; the maximum achievable M is 2.80. Furthermore, it exhibits very low second order distortion factor (DF₂): for the worst case, the value of DF₂ is 0.0014%. To verify the viability of the proposed algorithm, simulation is carried out and hardware prototype is constructed. Both results show very good agreement with the theoretical prediction.     

A PWM rectifier/inverter system capable of suppressing both harmonics and EMI

This paper proposes a new PWM rectifier/inverter system that is capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). The conversion system consists of a PWM rectifier and inverter, and an active common‐noise canceler (ACC) which has been proposed by the authors. The ACC developed for this system is characterized by the sophisticated connection of a common mode transformer which can compensate for common mode voltages produced by both the PWM rectifier and inverter. As a result, the size of the common mode transformer can be reduced to one‐third, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 59–68, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10062     

几种PWM闭环控制方案的一致性分析研究

PWM闭环控制在电力电子技术等领域中有着广泛的应用,对几种常用的PWM闭环控制方案工作原理和闭环传递函数进行分析,得出了它们之间的转换关系.通过对各个闭环系统中控制参数的合理配置,可以使这些方法的控制效果趋于一致.最后通过Madab/Simulink建模仿真比较了它们的输出电压稳态和动态性能,验证了几个方案的本质一致性...     

Behavioral modeling of permanent magnet synchronous motor fed by PWM inverters considering iron losses due to carrier harmonics

This paper proposes a new method for behavioral modeling of a permanent magnet synchronous motor (PMSM) fed by a PWM inverter considering the iron losses due to carrier harmonics. In the proposed method, an inductance is connected in series with an iron loss resistance in the equivalent circuit of the PMSM to suppress the harmonic current due to carrier harmonics. The effectiveness of the proposed method is investigated by comparing the numerical results of iron losses of the PMSM obtained using a finite-element method and the newly derived equivalent circuit.     

Comparative investigation of PWM techniques for a new drive for electric vehicles

Results of a comparative investigation of deterministic and random pulsewidth modulation (PWM) techniques to be employed in a new ac drive for electric vehicles are presented. The study, employing the advanced simulation package SABER from Avant! Corporation, was focused on the reduction of electromagnetic interference (EMI) when a deterministic PWM strategy is replaced with an RPWM method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques characterized by random variations of switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good EMI-mitigating potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected.     

单元串联多电平逆变器PWM方法比较研究

探讨了几种现有的多电平逆变器的脉冲宽度调制PWM(Pulse Width Modulation)方法,提出了一种多电平最优空间矢量方法,该方法通过选取最优空间矢量确定三相最佳电平组合,得到三相电压实际电平值,从而生成三相PWM控制模式。并与现有的PWM方法进行了比较。仿真结果说明多电平最优空间矢量方法具有开关频率低、总谐波含量低的优点。     

Installation of a hydraulic kiln drive to eliminate a resonantvibration problem

Large, dual electromechanical drive systems have been shown to often experience vibration problems due to the high inertia of the components of these systems and the large number of resonant frequencies experienced by these drives. Hydraulic drives, by comparison, are extremely low inertia drives that have fewer resonant frequencies and benefit from the damping characteristic of the hydraulic oil used to transmit power. Additional benefits include the ability to isolate components while operating the drive and smooth speed control starting at extremely low speeds and full rated torque. This paper outlines the vibration problems that were experienced in the dual drive of a 655-ft long with 22-ft and 19-ft diameter section rotary cement kiln between 1979 and 1993. A number of analytical and empirical studies were performed, and various modifications were made or considered, to reduce the vibration in the drive train. Finally, in 1994 when the existing drive reached the end of its life, it was replaced with a hydraulic system. The methods used and considered to reduce the vibration are discussed, as well as the critical elements in deciding on a hydraulic drive, and the design issues encountered including questions of drive efficiency, reliability, maintenance, and control. Results to date of the hydraulic drive are discussed, including the elimination of the vibration problem and added flexibility in speed control     

On-screen synthesis and analysis of harmonics: a student-orientedpackage

The implementation of an interactive approach to the display and manipulation of power system harmonics is described. The resulting microcomputer program, which was developed primarily for educational use within the electrical engineering curriculum, allows both synthesis of waves from harmonic (sinusoidal) components and analysis of specified periodic waveforms in terms of their harmonic content. Data may be interactively modified, and cases may be stored for later retrieval. Some of the means employed for making such a program user-friendly and student-oriented, as well as several examples of program use, are cited     

Neuro-evolutionary approaches to power system harmonics estimation

This paper focuses on exploiting two computational intelligence techniques such as artificial neural network and evolutionary computation techniques in estimation of harmonics in power system. Accurate estimation of harmonics in distorted power system current/voltage signal is essential to effectively design filters for eliminating harmonics. No standard design is available for handling of local minima and training of NN but Evolutionary Computation (EC) techniques are capable of resolving local minima. Neural Network and Evolutionary Computing (Bacterial Foraging Optimization (BFO)) are combined to achieve accurate estimation of different harmonics components of a distorted power system signal. First estimation of unknown parameters are carried out using BFO, then optimized output of BFO are taken as initial values of the unknown parameters for Adaline. Amplitude and phase of fundamental and harmonics components are determined from final updated values of unknown parameters using Adaline. This Adaline based Bacterial Foraging Optimization (Adaline-BFO) hybrid estimation algorithm addresses the problems of slow convergence and reduction of time generation of off-springs happening in Genetic Algorithm (GA), and to avoid local minima in Particle Swarm Optimization (PSO). The proposed Adaline-BFO algorithm has been applied for estimation of harmonics of the voltage obtained across the inverter terminals of a prototype Photovoltaic (PV) system. From the obtained results, it is confirmed that the proposed Adaline-BFO algorithm provides superior estimation performance in terms of improvement in % error in estimation, processing time in computation and performance in presence of inter and sub-harmonic components when compared with the Discrete Fourier Transform (DFT), Kalman Filter (KF) and BFO algorithms.     

Oscillator analysis with respect to higher harmonics

Contents The modified harmonic balance method has been worked out to describe the behaviour of oscillators generating output signal not on the first harmonic, as it is usual, but on the higher one. The main assumptions are: All higher harmonics are considered small compared to the first one and there is only one dominant resistive nonlinearity limiting amplitude of oscillations. The approximate solution of a microwave oscillator with Gunn diode is presented as an example. The results are in accordance with experimentally observed phenomena in the oscillator such as discontinuities and power drops in its characterstics.

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Oszillator-Analyse mit höheren Harmonischen

Übersicht Die Methode der modifizierten Harmonischen-Bilanzierung wurde weiterentwickelt, um das Verhalten von Oszillatoren zu beschreiben, die nicht wie üblich Signalleistung auf der Fundamentalen abgeben, sondern auf höheren Harmonischen. Dabei wird als wesentlich angenommen, daß die Amplituden der höheren Harmonischen klein sind, verglichen mit der ersten, und daß nur eine resitive Nichtlinearität dominierend die Schwingamplitude begrenzt.Als Beispiel wird die Näherungslösung eines Mikrowellenoszillators mit Gunn-Element vorgestellt. Die Lösungsergebnisse stimmen mit experimentelll beobachteten Erscheinungen im Oszillatorbetriebsverhalten überein, wie Kurvensprüngen und Leistungseinbrüchen.

     

Triplen harmonics: Myths and reality

In a symmetrical and balanced three-phase system with distorted waveforms, a well-known rule states that each harmonic order corresponds to a specified sequence (positive, negative or zero). In this ideal case, the current in the neutral conductor (or more generally in the return path) contains only triplen harmonics. However, this rule is no longer valid in practical distribution systems subject to unbalance and waveform distortion, in which phase and neutral currents at any sequence generally contain components of any harmonic order. Possible improper extension of the ideal case concepts to general situations may create a sort of myth, to be removed by providing tutorial and practical examples.This paper provides a direct quantification of the extent to which non-triplen harmonics are present in the zero-sequence current components and triplen harmonics are present in the positive and negative sequence current components. An original set of indicators, built on the basis of the theoretical symmetrical component-based framework developed by the authors, is introduced for assessing the specific impact of the triplen harmonics at the different sequences. Some classical myths based on the ideal case are illustrated and discussed on specific examples including theoretical cases and experimental analyses, quantifying the actual role played by the triplen harmonics in these applications.