Six-pulse Rectifier Research Articles

An Original Method Based on Simulink to Model and Simulate A.C.-D.C. Converters Taking into Account the Overlap Phenomenon

This paper presents a simple and original method to simulate the behaviour of a.c.-d.c. converters with Matlab-Simulink. This approach takes into account the overlap phenomenon with continuous and discontinuous conduction modes. The a.c. to d.c. converter is presented as a block (voltage input and voltage output) which can be inserted in a complex structure. The simplicity of the method makes it easy to understand and its short computing time makes it an interesting alternative to the Matlab SimPower Systems toolbox and PSIM software for teaching power electronics simulation. The method is designed in order to be user-friendly and easy to implement for students. In this paper, it is used for a six-pulse rectifier and extended to a twelve-pulse rectifier with delta/wye-delta transformer. Experimental results are provided to validate the proposed modelling method.

Variants of rectifiers with near sinusoidal input currents – a comparative analysis with the conventional diode rectifier

Based on the characteristics of the rectifiers with near sinusoidal input currents [rectifier with near sinusoidal input current-1 (RNSIC-1), with capacitors connected on the DC side and RNSIC-2, with capacitors connected on the AC side], the study proposes a comparative analysis between the performances (generated capacitive current, costs, efficiency, dimensions and other considerations) of the two variants of RNSIC converters with three-phase six-pulse full-bridge diode rectifiers with passive filters. Therefore the technical and economical advantages of the RNSIC converters are demonstrated. The inductors and the capacitors of the RNSIC converters do not belong to the category of resonant circuits tuned to specific frequency. This is the reason why the design requirements for the capacitors are not very stringent as they can have a tolerance range of ±10% without inflicting severe performance degradations. These converters can be used for a wide power range, practically mitigating the current harmonics generated by a three-phase diode rectifier, without being influenced by the harmonics generated by other consumers.

A Hybrid 18-Pulse Rectification Scheme for Diode Front-End Rectifiers With Large DC-Bus Capacitor

Diode rectifiers with large dc-bus capacitors, used in the front ends of variable-frequency drives (VFDs) and other ac-to-dc converters, draw discontinuous current from the power system, resulting in current distortion and, hence, voltage distortion. Typically, the power system can handle current distortion without showing signs of voltage distortion. However, when the majority of the load on a distribution feeder is made up of VFDs, current distortion becomes an important issue since it can cause voltage distortion. Multipulse techniques to reduce input current harmonics are popular because they do not interfere with the existing power system either from higher conducted electromagnetic interference, when active techniques are used, or from possible resonance, when capacitor-based filters are employed. In this paper, a new 18-pulse topology is proposed that has two six-pulse rectifiers powered via a phase-shifting isolation transformer, while the third six-pulse rectifier is fed directly from the ac source via a matching inductor. This idea relies on harmonic current cancellation strategy rather than flux cancellation method and results in lower overall harmonics. It is also seen to be smaller in size and weight and lower in cost compared to an isolation transformer. Experimental results are given to validate the concept.

A novel particle swarm optimisation self-regulating stand-alone wave energy conversion scheme

The paper presents a novel stabilisation scheme system for a wave energy converter (WEC) using permanent magnet linear generator (PMLG) connected to a six-pulse diode rectifier. The proposed controller of WEC-battery renewable energy system is based on multi-objective particle swarm optimisation (MOPSO) technique. The optimisation algorithm is implemented to control a novel low cost dynamic AC side filter/capacitor compensation scheme. The novel dynamic modulated filter capacitor compensation (MPFC) scheme serves as an AC side voltage stabilisation regulator and wave energy utilisation enhancement. The objective is to extract available power from the wave energy system (WES) and transfer this power efficiency to the local isolated DC side electric load. The performance and dynamic characteristics of the controllers to any load non-linear J, B parameters and load torque excursions is examined for PMDC motor drives. A tri-loop error-driven dynamic controller is used to adjust the PWM switching of the two dynamic filter compensator schemes. A multi-objective optimisation MOPSO technique is used to find the dynamic optimal control settings of the control signal to the PWM activation/triggering block that dynamically minimises the global dynamic error for all components, three SPWM, switched filters and motor.

Input Impedance Modeling of Multipulse Rectifiers by Harmonic Linearization

Multipulse rectifiers are used in large industrial drives, aircraft, electric ships, and other systems, where limits on harmonic currents prohibit the use of conventional three-phase, six-pulse rectifiers. The large power rating of these rectifiers and the dynamic nature of the loads often necessitate the study of their dynamic interactions with the source, which can lead to system stability and power quality problems if not properly designed. This paper presents input impedance models for multipulse rectifiers that can be used for such system stability and dynamic power quality analysis. The modeling method is based on the concept of harmonic linearization and makes use of analytical mapping functions that describe voltage and current transfer through multiphase diode rectifiers. Input impedance models are developed first for general N-phase rectifiers, and then combined with a model of the phase-shifting transformer to define the three-phase input impedance. Magnetizing inductance and line commutation due to transformer leakage inductance are also considered. Details of the modeling method are presented using an 18-pulse rectifier as example, and experimental measurement results are also presented to validate the models.

STUDI PENGGUNAAN PENYEARAH 18 PULSA DENGAN TRANSFORMATOR 3 FASA KE 9 FASA HUBUNGAN SEGIENAM

The 18-pulse converter, using Y or D -connected differential autotransformer, is very interesting since it allows natural high power factor correction. The lowest input current harmonic components are the 17 th and 19 th . The Transformer is designed to feed three six-pulse bridge rectifiers displaced in phase by 20 0 . This paper present a high power factor three-phase rectifier bases on 3-phase to 9-phase transformer and 18-pulse rectifier. The 9-phase polygon-connected transformer followed by 18-pulse diode rectifiers ensures the fundamental concept of natural power factor correction. Simulation results to verify the proposed concept are shown in this paper.

Performance Evaluation of a Novel Hybrid Multipulse Rectifier for Utility Interface of Power Electronic Converters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents an improved analysis of a novel Programmable Power-factor-corrected-Based Hybrid Multipulse Power Rectifier (PFC-HMPR) for utility interface of power electronic converters. The proposed hybrid multipulse rectifier is composed of an ordinary three-phase six-pulse diode-bridge rectifier (Graetz bridge) with a parallel connection of single-phase switched converters in each three-phase rectifier leg. In this paper, the authors present a complete discussion about the controlled rectifiers' power contribution and also a complete analysis concerning the total harmonic distortion of current that can be achieved when the proposed converter operates as a conventional 12-pulse rectifier. The mathematical analysis presented in this paper corroborate, with detailed equations, the experimental results of two 6-kW prototypes implemented in a laboratory. </para>

An Efficient Current Distortion Suppression Method for Six-Pulse Bridge Rectifiers

In this paper, an efficient current distortion suppression method for six-pulse bridge rectifiers is presented, whereby high-quality waveforms at both ends of the rectifier are possible. The methodology involves accurate shaping of the dc current by using two forced commutated switches. It is demonstrated, theoretically and experimentally, that this action on the dc side is reflected back on the ac side, and as a result, perfect sinusoidal input currents are achieved. In addition, ripple-free voltages and currents are obtained on the dc side by using electrolytic capacitors and smoothing reactors. Rectifying and inverting operations are possible with a simple control circuit, which is also able to both track rapid load variations and overcome failures more efficiently than other modern alternatives. Selected theoretical results are presented, which are fully validated in a laboratory prototype.

Effects of Voltage Supply Unbalance on AC Harmonic Current Components Produced by AC/DC Converters

This paper examines the main factors affecting amplitudes of the harmonic current components generated by HVDC converters operating under unbalanced voltage supply. A symmetrical firing scheme is considered and emphasis is placed on operation of the six-pulse full bridge rectifiers, which are used as the basic arrangement for assembling the twelve pulse converter widely used in HVDC transmission and as a field voltage supply for synchronous generators in large power plants. Several computer simulation results are shown in order to illustrate the effect produced by the unbalanced voltage supply on the characteristic ac harmonic current magnitudes when considering different operating conditions characterized by changes on dc current amplitudes and on the firing delay angle. Special attention is placed on the noncharacteristic triple harmonic currents arisen basically as a result of the different commutation time on phase currents produced by the negative sequence components of the phase-to-phase voltages.

Programmable PFC based hybrid multipulse power rectifier for ultra clean power application

A novel hybrid three-phase rectifier is proposed. It is capable to achieve high input power factor (PF) and low total harmonic input currents distortion (THD/sub I/). The proposed hybrid high power rectifier is composed by a standard three-phase six-pulse diode rectifier (Graetz bridge) with a parallel connection of single-phase Sepic rectifiers in each three-phase rectifier leg. Such topology results in a structure capable of programming the input current waveform and providing conditions for obtaining high input power factor and low harmonic current distortion. In order to validate the proposed hybrid rectifier, this work describes its principles, with detailed operation, simulation, experimental results, and discussions on power rating of the required Sepic converters as related to the desired total harmonic current distortion. It is demonstrated that only a fraction of the output power is processed through the Sepic converters, making the proposed solution economically viable for very high power installations, with fast investment payback. Moreover, retrofitting to existing installations is also feasible since the parallel path can be easily controlled by integration with the existing dc-link. A prototype has been implemented in the laboratory and it was fully demonstrated to both operate with excellent performance and be feasibly implemented in higher power applications.

A Simple, Passive 24-Pulse AC–DC Converter With Inherent Load Balancing

A new converter topology for a three-phase multipulse rectifier circuit is described. This converter draws almost sinusoidal currents from the ac system with very low harmonic content and typically less than 3% total harmonic distortion. The topology uses only passive components and has a lower component count than other rectifier circuits with similar performance. Two six-pulse rectifier bridges are connected in series, fed by a series connection of transformers, to form a 12-pulse system. An additional low power harmonic injection circuit enhances the performance of the circuit to obtain low harmonic current pollution levels that are comparable with those achieved from a 24-pulse rectifier. The circuit operation is explained and experimental results are presented.

Analysis and simulation of a wind-electric battery charging system

A small commercial wind-electric battery-charging system based on a three-bladed rotor has been analysed in a detailed fashion. The system consists of a synchronous generator with permanent magnets, a six-pulse rectifier and a battery bank with charge controller. A steady-state power curve is predicted based on the electric characteristics found experimentally and the aerodynamic performance of the rotor simulated with a version of blade element momentum (BEM) theory developed in our group. The BEM code has been designed to account for variable Reynolds numbers at different blade sections and stall conditions. The findings are compared with the manufacturer's specifications, and a detailed discussion is provided. A very good agreement with the steady-state power curve given by the manufacturer has been obtained after accounting for different sources of power losses, such as voltage drops in the rectifier, Joule heating in the power cables and losses in the generator's core. The system is found to operate near the aerodynamic optimum for all wind speeds studied, whereas electrical losses are significant near rated power. Some recommendations for improving the system performance are provided. Copyright © 2005 John Wiley & Sons, Ltd.

Line Current Harmonics Reduction in Multipulse Connection of Asymmetrically Loaded Rectifiers

This paper proposes a new arrangement for the multipulse connection of asymmetrically loaded six-pulse rectifiers. This arrangement is, therefore, particularly suitable for implementing the dc voltage sources of hybrid multilevel inverters in applications with active power transfer, such as medium-voltage adjustable-speed drives. A new design methodology is proposed to determine the phase shifts among the secondaries of the isolation transformer, even when the active power levels processed by each rectifier and their input and output impedances are different. A set of phase angles is obtained to minimize, and even to eliminate, undesired low-order harmonics of the input current, in particular, the 5th harmonic, because this harmonic component presents an amplitude considerably higher than the amplitude of the other harmonics. In consequence, the proposed design methodology increases the input power factor and reduces the input current total harmonic distortion. Simulation and experimental results are presented to demonstrate the feasibility of the proposed structure.

Medium-voltage transformerless ac/dc power conversion system consisting of a diode rectifier and a shunt hybrid filter

This paper proposes a 3.3-kV transformerless AC-to-DC power conversion system consisting of a three-phase six-pulse diode rectifier and a shunt hybrid filter. The hybrid filter is formed by a single tuned LC filter per phase and a small-rated three-phase active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter be. In addition, no additional switching-ripple filter is required for the hybrid filter because the LC filter functions not only as a harmonic filter tuned at the seventh harmonic frequency but also as a switching-ripple filter around 10 kHz. Experimental results obtained from a 200-V 5-kW laboratory system and simulation results of a 3.3-kV 300-kW system confirm the validity and effectiveness of the system.

A Proposal of a 3.3-kV/6.6-kV Transformerless Hybrid Filter, and Experimental Verification Based on a 200-V Laboratory System

This paper proposes a transformerless shunt hybrid filter for harmonic compensation of a three-phase six-pulse diode rectifier, where the ac line-to-line voltage is 3.3kV or 6.6kV. The hybrid filter consists of a single tuned LC filter per phase and an active filter with a dc capacitor voltage as low as 300V or 600V. The two filters are directly connected in series with each other without any transformer. The passive filter absorbs harmonic currents produced by the rectifier, whereas the active filter improves the filtering characteristics of the passive filter. The required rating of the active filter is much smaller than that of a conventional shunt active filter used alone. In addition, no additional switching-ripple filter is required for the active filter, because the LC filter acts not only as a tuned LC filter around the 7th-harmonic frequency but also as a switching-ripple filter around 10kHz. A feedforward control scheme is also proposed to improve the active filter performance. Experimental results obtained from a 200-V, 5-kW laboratory system and simulation results of a 3.3-kV, 300-kW system confirm the validity and effectiveness of the system. The hybrid filter gives satisfactory compensation performance, thus allowing us to put it into practical use.

Harmonic filtering of high-power 12-pulse rectifier loads with a selective hybrid filter system

Current distortion of 12-pulse rectifier loads is significantly lower compared to six-pulse rectifier loads. However, in passive filtering of the lowest and dominant characteristic 11th and 13th harmonics, the use of 5th and 7th filters is often required in order to prevent possible parallel and series resonance between the passive filter and source impedance which can be excited by source background distortion or by load current residual noncharacteristic harmonics at the 5th and 7th harmonic frequencies. In hybrid filter systems, an active filter (AF) can be added in series with the passive filter in order to isolate the source and load. In most proposed hybrid filter systems, AF control is based on the detection of total current distortion and high-frequency inverters. With a selective AF control system and voltage-controlled inverter, the AF can be controlled to isolate the load at the critical frequencies only while at all other frequencies the passive filter function is preserved so that lower switching frequency and AF rating is required. In this paper, the authors present a selective AF filter control system and simple hybrid filter topology suitable for the compensation of high-power 12-pulse rectifier loads. Harmonic current controllers based on the second-order infinite-impulse response digital resonant filters are used, as they can be considered as simple digital algorithms for more complex double cascaded synchronous-reference-frame-based proportional plus integral controllers. They are centered to the targeted harmonic frequencies by using an adaptive fundamental frequency tracking filter. This approach gives good results, even if the reference waveform (in our case, a load voltage) is highly distorted or unbalanced and no separate phaselocked loop is required. Test results for a laboratory model of this system and stability analysis are presented and the importance of delay-time compensation is discussed.

Sequential connection and phase control of a high-current rectifier optimized for copper electrowinning applications

This paper proposes an optimized sequential control technique for copper electrowinning high-current rectifiers. The converter comprises two series-connected six-pulse double-wye rectifiers, a step-down transformer, and a tuned input filter. The six-pulse rectifiers are fed from delta and polygon primary windings with different turns ratio and phase shifted by 5/spl deg/. Under the proposed control scheme, one rectifier is kept at nominal output voltage, and the other one is phase controlled to control the load's current. The proposed strategy greatly improves the rectifier's performance, reducing its reactive power maximum demand by 62% compared to conventional rectifiers and, therefore, reduces the input filters power rating also by 62%. This is accomplished while keeping the input power factor above 0.95 throughout the whole operating range. Further, the converter's reactive power consumption presents a low varying characteristic, allowing it to use a fixed filter, even when operating from a power system not capable of withstanding large reactive power variations. Finally, it presents a harmonic current distortion comparable to conventional 12-pulse high-current rectifiers. This paper presents the design and optimization procedure of the rectifying system. A 2.5 kVA laboratory prototype was used to validate the converter model, later employed in evaluating the converter operating in a 10.5 MVA copper electrowinning facility. The results obtained confirm the advantages of the proposed converter and its control strategy.

Improved Application of Power Acceptability Curves and Their Application to Certain Three-Phase Loads

The electric power acceptability curves are loci in the bus voltage-disturbance time plane. These loci separate regions of operation into "acceptable" and "unacceptable." Several power acceptability curves exist, and this paper discusses a constant energy model for the derivation of the curves. The application of the curves is discussed. The main foibles of the curves in the undervoltage disturbance region are that they do not model three-phase effects and they were not designed for rotating loads. The paper proposes a solution to these drawbacks. The use of power acceptability curves for three-phase induction motors and six-pulse rectifier loads is discussed.

Three-phase six-pulse buck rectifier with high quality input waveforms

The design and analysis of a three-phase, six-pulse buck rectifier is presented. The PWM modulation technique is analysed using the commuting function. Such analysis represents the main design tool for the commutation sequence, since it provides information about the harmonic behaviour of the rectifier signals with respect to the parameters involved in the modulation. The carrier signal is selected after a spectral analysis has been performed, to minimise the harmonic distortion content, thus obtaining high quality input currents. Likewise, as an additional and helpful tool for the designer, a digital circuit was developed to generate and store the commuting function, which is then applied to the rectifier. Some tests were carried out on a prototype. The results which focus on the power factor and the total harmonic distortion are presented.

ACSL/graphics modeller component models for electric power education

This paper describes the use of detailed models of power system components for undergraduate and graduate education. The models were developed in a commercial graphically oriented package (ACSL/Graphic Modeller). At the undergraduate level, the models are provided to the student to use as a tool to reinforce lecture and laboratory concepts. At the graduate level, the models can be used to introduce the student to more advanced topics such as reference frame theory and provide a beginning point for the student to develop more complex models. Included in the paper is a short tutorial on the use of ACSL/Graphic Modeller and a description of several models including a synchronous machine, induction motor, pulse-width-modulated inverter and a six-pulse bridge rectifier. Sample studies using each model are shown with suggestions for additional uses by students. Since the models are detailed, transient as well as steady-state phenomena can be demonstrated with the models. For example, the free acceleration of an induction motor and a three-phase fault on the synchronous generator are among the applications shown in the paper. The models are provided on the CDROM and can be viewed and executed with a free viewer version of ACSL.