Line Current Total Harmonic Distortion Research Articles

Comparison of the effect of output filters on the total harmonic distortion of line current in voltage source line converter - simulation study.

Two different output filter topologies are considered, namely the LCL- and L+LC-filter. The space vector modulation (SVM) is used to control the power switches of the converter. Design methods for both filter types are proposed. The methods are used to dimension the filter components. The performances of the filters designed are verified by simulations to meet the given line current total harmonic distortion (THD) requirement. The study reveals that the LCL-filter is more effective a filter topology in attenuating line current harmonic components than the L+LC-filter.

A 24-Pulse Rectifier With a Passive Auxiliary Current Injection Circuit at DC Side

In this article, a simple series-connected 24-pulse rectifier with a passive auxiliary current injection circuit (ACIC) is proposed. The proposed rectifier consists of a 12-pulse rectifier and an ACIC. The ACIC includes a circulation current forming circuit, an auxiliary single-phase transformer (AST), and an auxiliary single-phase full-bridge rectifier (ASFR). The ASFR extracts alternating square-wave current from the dc side and injects it into the outputs of three-phase rectifier bridges to increase the output state of these bridges. The operating mode of the proposed rectifier is analyzed, and the functional relationship between the input current and turns ratio of AST is established. The AST turns ratio that minimizes the input line current total harmonic distortion (THD) is derived. The voltage and current rating of AST are calculated, and the design method of capacitors C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in ACIC is given. Under the optimal turns ratio, the ACIC extends the 12- to a 24-pulse rectifier. The resulting 24-pulse rectifier draws near-sinusoidal input currents with less than 5% THD. The AST in ACIC has a very low kilovolt-ampere rating (1.96% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ), and the current ratings of ASFR are small. The theoretical analyzes are provided and experimentally verified using a 1.7 kW experimental prototype.

Input Current Step-Doubling for Autotransformer-Based 12-Pulse Rectifier Using Two Auxiliary Diodes

To significantly decrease the input line current total harmonic distortion (THD) under simple circuit configuration conditions, this article propose an input current step doubling scheme for autotransformer-based 12-pulse rectifier using two auxiliary diodes. The auxiliary diodes are installed between the two retrofitted double-tap interphase reactors, and they inject specific square wave currents to increase the output current states of the rectification bridges. This modification extends the 12-step input line current to a 24-step input line current, and the near sinusoidal input line current with THD below 5% is obtained. As the proposed scheme only requires two low current stress (3.4% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) auxiliary diodes, it achieves high-cost performance, is easy to implement and has a simple circuit configuration. A 2.2 kW simulation and experimental prototype is built to verify the theoretical analysis.

A 12-pulse rectifier with passive harmonic reduction based on UIPT in more electric aircrafts

PurposeThe purpose of this paper is to provide a T autotransformer based 12-pulse rectifier with passive harmonic reduction in more electric aircraft applications. The T autotransformer uses only two main windings which result in volume, space, size, weight and cost savings. Also, the proposed unconventional inter-phase transformer (UIPT) with a lower kVA rating (about 2.6% of the load power) compared to the conventional inter-phase transformer results in a more harmonic reduction.Design/methodology/approachTo increase rating and reduce the cost and complexity of a multi-pulse rectifier, it is well known that the pulse number must be increased. In some practical cases, a 12-pulse rectifier (12PR) is suggested as a good solution considering its simple structure and low weight. But the 12PR cannot technically meet the standards of harmonic distortion requirements for some industrial applications, and therefore, they must be used with output filters. In this paper, a 12PR is suggested, which consists of a T autotransformer 12PR and a passive harmonic reduction (PHR) based on the UIPT at direct current (DC) link.FindingsTo show the advantage of this new combination over other solutions, simulation results are used, and then, a prototype is implemented to evaluate and verify the simulation results. The simulation and experimental test results show that the input current total harmonic distortion (THD) of the suggested 12PR with a PHR based on UIPT is less than 5%, which meets the IEEE 519 requirements. Also, it is shown that in comparison with other solutions, it is cost effective, and at the same time, its power factor is near unity, and its rating is 29.92% of the load rating. Therefore, it is obvious that the proposed rectifier is a practical solution for more electric aircrafts.Originality/valueThe contributions of this paper are summarized as follows. The suggested design uses a retrofit T autotransformer, which meets all technical constraints, and in comparison, with other options, has less rating, weight, volume and cost. In the suggested rectifier, a PHR based on UIPT at its dc link of 12PR is used, which has good technical capabilities and lower ratings. In the PHR based on UIPT, an IPT is used, which has an additional secondary winding and four diodes. This solution leads to a reduction in input current THD and conduction losses of diodes. In full load conditions, the input line current THD and power factor are 4% and 0.99, respectively. The THD is less than 5%, which satisfies IEEE-519 and DO-160G requirements.

Investigation on Design of Novel Step-Up 18-Pulse Auto-Transformer Rectifier

The multi-pulse rectifier has gained a wide range of applications in the high-power rectification system due to the advantages like simple structure, high efficiency, and high reliability. In this paper, an 18-pulse auto-transformer rectifier unit (ATRU) with adjustable output DC voltage was studied, to meet the requirements of high efficiency and low harmonic pollution of ATRU. Firstly, the basic operating principle of the proposed ATRU was analyzed in detail. The essential relationship between the step-up ratio factor and the output DC voltage, the total harmonic distortion (THD) of the input line current, and the equivalent kVA rating of the transformer was deduced considerately, which provides a theoretical basis for the optimization design of the system. Finally, the correctness of the theoretical analysis was verified by simulation and experiment. The experimental results show that under the 6kVA rating condition when the step-up ratio is 1.137, the transformer equivalent kVA rating is only 27.8% of the load output power, the input line current THD of ATRU is 6.58%, and the efficiency is 98.5%.

Comparative study of multi‐objective finite set predictive control methods with new max–min strategy applied on a seven‐level packedU‐cell inverter

This article studies the design and implementation of multi-objective predictive control (MO-PC) of a grid-connected seven-level packed U-cell (PUC7) inverter for minimising the line current total harmonic distortion (THD) and capacitor voltage error simultaneously. The weighting factor method is usually used as a simple method for solving the control problem in the literature. However, there are some difficulties and shortcomings in the calculation of weighting factors. Here, max–min selection strategy with together priority is adopted to reduce these deficiencies and improves the system performance. The switch model of the PUC inverter is derived and then applied in designing the MO-PC for grid-connected applications, where a controlled active or reactive power is injected into the utility. A comparative study among three strategies of weighting factor, fuzzy decision-making and max–min selection is performed to distinguish the proposed method superiority. Experimental results are given to validate the practicality of the applied controller in regulating the line current and capacitor voltage of the grid-connected PUC7 inverter.

A Simple Harmonic Reduction Method in Multipulse Rectifier Using Passive Devices

This paper proposes a novel and passive harmonic reduction method at dc link of multipulse rectifier (MPR). The proposed method uses a single-phase diode-bridge rectifier to generate circulating current, which can shape the input line current of MPR. The input side of the single-phase diode-bridge rectifier is connected with the secondary winding of interphase reactor (IPR), and its output side is connected with load, which can recycle the harmonic energy and feed to load. The operation mode of the single-phase diode-bridge rectifier is analyzed, and the turn ratio of the IPR is designed optimally. Under ideal condition, the proposed MPR operates as a 24-pulse rectifier, and its total harmonic distortion (THD) of input line current is about 7.6%. Most of all, the proposed method is easy to be used in different 12-pulse rectifier topologies, and its conduction losses are far less than that of the conventional double-tapped IPR. Simulation and experiment results show that the THD of input line current is less than 5%.

Modeling and Control of Three-Phase Grid-Connected Power Supply With a Small DC-Link Capacitor for Electrolyzers

In this paper, a new feed forward dc-link voltage compensation method is proposed. The target applications are the converters built with diode bridge frontends, small capacitance in the dc-link which feeds a dc/dc converter used for electrolysis. The compensation method can be tuned in a way to minimize the grid side total harmonic distortion (THD) and partial weighted harmonic distortion (PWHD): thus, the converter can comply with the standards with less filtering at the grid side. In order to design the controllers and perform stability analysis, average model has been derived. However, the performance of the proposed control method is a trade-off between the size of the line filter, the value of the line current THD and PWHD, and the amplitude of the load current ripple. The theoretical work has been validated through experiments on a 5 kW dc power supply used for an electrolyzer. In the experiments, the THD of the grid current can be reduced from 30.5% to 29.5% (without filter and including compensation) and 28.5% (with filter and compensation), and the PWHD from 50% to 38.9% by applying the proposed method and also keeping the load current peak-to-peak ripple under 10% of its nominal value.

Capacitive Emulation for LCL-Filtered Grid-Connected Converters

This paper proposes an effective capacitive emulation (CE) technique to reduce the grid current distortion when the converter currents are controlled (converter current feedback (CCF)) in grid-connected converters with an LCL filter. Although the CCF scheme is preferable to the grid current feedback (GCF) scheme in terms of stability and inherent current limitation of the power semiconductors, the former presents a problem of additional grid-current harmonic distortion due to the LCL capacitor, which generates a distorted current by line voltage differentiation. To solve this problem, the distorting capacitive current is reproduced on the converter output, so that both cancel out each other on the grid. That is, the converter emulates a negative capacitance while delivering the active and reactive power at the fundamental frequency. This is achieved by adding an estimation of the distorting capacitive current to the converter current reference. Moreover, an effective CE technique requires a current control capable of tracking all harmonics added to the current reference and compensating for any control delay. To compensate this delay, the paper proposes a buffer-based method to advance and filter the current reference. The effectiveness of the CE method has been tested on a 10-kVA transformerless inverter with CCF and a simple proportional-integral (PI) control with grid-voltage feedforward cancellation. Experimental results prove that the proposed solution reduces the line current THD (total harmonic distortion) compared with the GCF strategy with proportional-resonant (PR) control.

Variable-Switching Frequency PWM Technique for Induction Motor Drive to Spread Acoustic Noise Spectrum With Reduced Current Ripple

Pulse-width modulation (PWM) of a motor drive at a fixed switching frequency leads to harmonic currents in narrow bands around integral multiples of the switching frequency resulting in tonal frequency acoustic noise components, which are irritating to the human ear. Random variation of carrier frequency to spread the spectrum poses challenges in device loss calculation, thermal design, and closed-loop controller design. Random pulse positioning is not quite effective at high speeds of the drive, where the problem of acoustic noise is most pronounced. This paper proposes a simple variable-frequency PWM and evaluates the performance of the same experimentally on a 6-kW induction motor drive. The experimental results show that the acoustic noise is spread uniformly over a range of frequencies without introducing low-frequency current harmonics. Compared with fixed-frequency PWM, the dominant acoustic noise is reduced significantly over a wide range of speeds. The variable-frequency PWM is further shown to reduce line current total harmonic distortion at high speeds of the drive. The computational effort required by the variable-frequency PWM is only marginally higher than that required by fixed-frequency PWM.

Effect of circulating current on input line current of 12‐pulse rectifier with active inter‐phase reactor

This study analyses quantitatively the effect of circulating current's amplitude and phase on the input line current of 12-pulse rectifier with active inter-phase reactor. The input line current and its total harmonic distortion (THD) are calculated under different amplitudes and phases of circulating current, and according to the calculation results, the effect of circulating current is analysed. Different from the previous results, it is obtained that the system has better performance when the amplitude of circulating current is slightly less than, but not equal to the half of load current. Both phase lagging and leading increase the THD of input line current. Some simulation and experiment are carried out to validate the theoretical analysis.

Criteria-Based Modulation for Multilevel Inverters

Pulse width modulation schemes are aimed at adjusting the fundamental component while reducing the harmonic content of an inverter output voltage or current. This paper addresses the topic of optimal inverter operation in reference to a given objective function. The objective function could embody either a single performance criterion, such as voltage or current total harmonic distortion (THD), or a weighted sum of multiple criteria. The proposed method ensures primacy of the chosen solution while imposing no restriction over its modulation index. In particular, operating the inverter by the chosen solution would result in performances superior to any other modulation scheme commutating in an equal number of switching angles per fundamental cycle. The proposed method allows for the consideration of practical inverter constraints and prevents the possibility of impractical switching sequence. A detailed investigation of the method is given, accompanied by two practical cases minimizing, respectively, phase-voltage THD and line-current THD of a three-level inverter. Selected simulation and experimental results are presented to validate the theoretical part.

Voltage sensorless control of the three‐level three‐switch Vienna rectifier with programmable input power factor

The three-level, three-switch Vienna rectifier is fast emerging as the preferred topology for the high-power factor front end converter in many applications. Conventional control algorithms for the Vienna rectifier requires sensing of both the supply voltage and the line current. However, in many applications, where an electrical generator feeds the rectifier, the ‘supply voltage’ is not available for measurement. Even for grid-connected applications the supply voltage may contain significant harmonic distortion which, in turn, increases the harmonic distortion of the rectifier input current. To mitigate these disadvantages, this study presents a novel voltage sensorless control algorithm for the Vienna rectifier. Voltage sensorless control algorithms reported in the literature for this rectifier, so far permit only unity rectifier terminal power factor operation. In contrast, the proposed control algorithm can operate the rectifier at programmable power factor. For the verification of the algorithm, experiments were conducted on a laboratory prototype of the Vienna rectifier using both voltage sensorless and sensor-based control algorithms. Performances of both these algorithms were found to be similar under transient conditions. The voltage sensorless controller achieved better input line current total harmonic distortion in steady state.

A Comparative Performance Investigation of Single-Stage Dimmable Electronic Ballasts for Electrodeless Fluorescent Lamp Applications

This paper presents a comparative investigation, design and development issues about six different single-stage topologies, applied as electronic ballasts, for electrodeless fluorescent lamps. The ballast is intended to feed a 100 W lamp at 250 kHz, with dimming feature. The proposed topologies use different converters for the power factor correction (PFC) stage: Buck-Boost, SEPIC, Zeta, Cúk, Flyback, and Boost. All of them operate in discontinuous conduction mode. A resonant half-bridge inverter is used as lamp power control (PC) stage. The integration of both stages (PFC and PC) is proposed in this paper. In this way, it is possible to reduce the number of active switches, as well as simplify the required driving and control circuitry. Experimental results demonstrate the feasibility of the proposed dimming technique that achieved around 56% lamp power dimming, from 100 W down to 44 W. The implemented topologies attained high average power factor (>0.98), and low line current average total harmonic distortion (<;15.3%). A comparison among all the proposed topologies in terms of power factor, harmonic distortion, efficiency and number of components is presented. Finally, a comparison between an integrated and a nonintegrated SEPIC half-bridge converter is also performed.

Indirect Matrix Converters' Enhanced Commutation Method

This paper introduces an enhanced commutation method applied to the indirect matrix converter topology. It is based on the detection of the load current polarity so as to cancel the turn-on delay times of the load-side converter's switches. The proposed method allows the grid-side converter devices to commutate at zero current with larger time interval widths provided for this safe commutation. Moreover, it has been shown through experimental results, carried out on a laboratory prototype of the matrix converter, that a substantial improvement of line current total harmonic distortion is achieved.

In‐depth study of direct power control strategies for power converters

Direct power control (DPC) has received a significant amount of research attention because of its benefits such as simplicity, robustness and excellent dynamic response. In the last few years DPC has been widely used in power electronics and electric drives. Recently, because of the rapid increase in the penetration of distributed generation sources connected to the local AC and/or DC common buses through power electronic converters, further development of DPC strategies is highly required. In addition, given the fact that the requirements of the system performance vary in different applications, it is very useful to provide an in-depth analysis so as to select the suitable control approach. This study presents an investigation of DPC of power converters. The theoretical principles are analysed and studied. The performance of each control method is then validated by experimental tests on a laboratory power converter system. The evaluated characteristics include the power ripple, line current total harmonic distortion (THD), switching behaviour, control complexity, etc. The reported results provide engineers and researchers on the subject with valuable insights into the features and implementation constraints of the DPC strategies in power and energy systems.

Analysis and Design of a Single-Stage High-Power-Factor Dimmable Electronic Ballast for Electrodeless Fluorescent Lamp

A methodological study of an electronic ballast for electrodeless fluorescent lamps (EFLs) including design and development issues is presented in this paper. The ballast is intended to feed a 100-W EFL at 250 kHz with dimming feature. The proposed topology is composed of a single-ended primary-inductance converter, used as power-factor (PF)-correction stage, integrated with a resonant half-bridge inverter, used as lamp-power control stage. The integration of both stages is proposed in this paper, in order to reduce the number of active switches, as well as to simplify the required driving and control circuitry for this application. Experimental results demonstrate the feasibility of the proposed solution that achieves 54% lamp-power dimming (46 W). The implemented topology attained very high PF (0.989) and low line-current total harmonic distortion (14.929%), without using electromagnetic interference filter, while the measured efficiency was 87% at nominal lamp power.

An Active Damping Technique for Small DC-Link Capacitor Based Drive System

A small dc-link capacitor based drive system shows instability when it is operated with large input line inductance at operating points with high power. This paper presents a simple, new active damping technique that can stabilize effectively the drive system at unstable operating points, offering greatly reduced input line current total harmonic distortion. The proposed method requires only a first-order, high-pass filter with a gain. Active damping voltage terms, linked directly to the dc-link voltage ripple through gain units, are injected to the drive machine for stabilizing the operating points. The stabilizing effect of the active damping terms is demonstrated for an induction machine based drive system. The effects of the added damping terms on the machine current and dc-link voltage are analyzed in detail. A design recommendation for the proposed active damping terms is given. Experimental results verifying the effectiveness of the new active damping method are presented.

Comparative Evaluation of m-level Thyristor based MLCR CSC

Abstract In this paper a comparative evaluation study is carried out for a 3-level, 5-level, 7-level thyristor based multi-level current reinjection (MLCR)current source converters (CSC) in terms of line current total harmonic distortion (THD) obtained, reinjection transformer requirements, reinjection switch ratings, reinjection control circuitry complexities. MLCR concept adds self commutation capability to thyristors, produces high quality line current waveforms and provides reactive power compensation in CSCs. Multi-level conversion is applied to generate the required optimum injection current which, when reinjected to the ac side reduces the line current THD. Extensive PSCAD/EMTDC simulations are presented for the comparing the different m-level reinjection schemes.

Comparative control analysis of the Vienna rectifier based on its averaged model

This paper presents a comparative evaluation of two multiple-loops duty-cycle-based control schemes applied to a three-phase three-switch three-level boost-type rectifier. The control laws are both elaborated on the basis of a state-space averaged model of the converter, expressed in the synchronous rotating frame. On the one hand, a control scheme that uses linear regulators is designed by using the small-signal transfer functions of the converter’s model, which was linearised on the neighbourhood of a suitable steady-state operating point. On the other hand, a non-linear control scheme that uses the input-output feedback linearisation approach is also designed in order to satisfy the same requirements as for the linear control system. For comparison purpose, both control schemes are implemented numerically using the Simulink tool of Matlab, and simulation experiments are carried out in order to test and verify the tracking and regulation performance of each control law, as well as their robustness towards load or mains source disturbance. For the same operating conditions, the performance of the two control laws are analysed and compared in terms of line currents total harmonic distortion (THD) and DC voltage regulation.