Multi-pulse Transformer Research Articles

FCS-MPC with Nonlinear Control Applied to a Multicell AFE Rectifier.

The use of controlled power converters has been extended for high power applications, stacking off-the-shelve semiconductors, and allowing the implementation of, among others, AC drives for medium voltages of 2.3 kV to 13.8 kV. For AC drives based on power cells assembled with three-phase diode rectifiers and cascaded H-bridge inverters, a sophisticated input multipulse transformer is required to reduce the grid voltage, provide isolation among the power cells, and compensate for low-frequency current harmonics generated by the diode-based rectifiers. However, this input multipulse transformer is bulky, heavy, and expensive and must be designed according to the number of power cells, not allowing total modularity of the AC drives based on cascade H-bridges. This study proposes and evaluates a control strategy based on a finite control set-model predictive control that emulates the harmonic cancellation performed by an input multipulse transformer in a cascade H-bridge topology. Hence, the proposed method requires conventional input transformers and replaces the three-phase diode rectifiers. As a result, greater modularity than the conventional multicell converter and improved AC overall input current with a THD as low as 2% with a unitary displacement power factor are achieved. In this case, each power cell manages its own DC voltage using a nonlinear control strategy, ensuring stable system operation for passive and regenerative loads. The experimental tests demonstrated the correct performance of the proposed scheme.

Modeling, Simulation and Design of Prototype Three Phase 6, 12, 18 and 24 pulse converters with Phase Shifting Transformer for Power Quality Improvement

This research paper presents the, 6,12,18 and 24 pulse converters with Phase Shifting Transformer Configuration for power quality improvement, as it highly reduces the Total Harmonics Distortions current in main ac supply. Interconnection of conventional transformers are used to make Four 3-φ systems to obtain different phase shifts is presented and obtained performance is compared between of a 6,12,18 and 24 -pulse Transformer Rectifier Configuration. Such multi pulse topologies consist on the various 6-pulse converter units connected either in parallel or series on the DC side. Each units phase shifted by the auto transformer or individual designed isolated transformers to compensate the harmonics content in the order of (nP±1), n = 1,2, 3, and P = Pulses. This proposed work is mainly based on the two objectives (1) to simulate the various multi pulse transformer (up to 24 pulse) with R-Load, using the matlab software. (2) Prototype hardware model. In both cases analysis the Total Harmonic Distortions current in main ac supply by FFT Analysis and FLUKE 43 Power Quality Analyzer. Finally, Simulation based results have been validate with Gutor and IEEE 519-1992 Standard. Experimental results compared with IEEE Standard and additionally improves the THDs voltage, Crest Factor and K Factors.

Finite Control Set—Model Predictive Control with Non-Spread Spectrum and Reduced Switching Frequency Applied to Multi-Cell Rectifiers

Multi-cell converters are widely used in medium-voltage AC drives. This equipment is based on power cells that operate with low-voltage-rating semiconductors and require an input multipulse transformer. This transformer cancels the low-frequency current harmonics generated by the three-phase diode-based rectifier. Unfortunately, this transformer is bulky, heavy, expensive, and does not extend the existing power cell (three-phase rectifier—Direct Current (DC) voltage-link—single-phase inverter) to the transformer. In this study, a harmonic cancelation method based on finite control set-model predictive control (FCS–MPC), extending the power cell’s modularity to the input transformer. On the other hand, it considers treating the two disadvantages of the FCS–MPC: High switching frequency and spread spectrum. The details were developed in theory and practice to obtain satisfactory experimental results.

Multicell AFE Rectifier Managed by Finite Control Set–Model Predictive Control

Multicell converters, based on power cells that use low-voltage semiconductors, implement AC motor drives for medium-and high-voltage applications. These converters feature an input multipulse transformer, which performs low-frequency harmonics cancelation generated by three-phase diode rectifiers in the power cells. Despite this advantage, the multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells required by a specific case, limiting the modularity of the topology. This work proposes a multicell converter based on power cells that requires a standard input transformer and uses active front-end rectifiers controlled by employing a finite control set-model predictive control algorithm. The proposed approach emulates the multipulse transformer harmonic cancelation owing to the predictive algorithm operation combined with input current references that are phase-shifted for each active front-end rectifier. Simultaneously, the DC voltages of the power cells are regulated and equalized among the cells using PI regulators. Experimental results confirm the feasibility of the proposed system as input currents in each Multicell AFE rectifier with a unitary displacement factor, and a low THD of 1.87% was obtained. It is then possible to replace the input multipulse transformer with standard ones while reducing the copper losses, reducing the K factor, and extending the modularity of the power cell to the input transformer.

Induction drive system with DSTATCOM based asymmetric twin converter

High power demands are usually met by advanced power electronics converters in several large utility and electric drives applications. Applications from high power drives commonly uses solution based multi pulse and multilevel converters. A common DC link with atleast one voltage source converter (VSC) working with almost fundamental switching frequency are used in converters of multipulse type, and each output module is connected with the multipulse transformer in series. When compared to that of solution with single-VSC, Several VSCs generating different triggering pulses are adjused in order to achieve current injected with low specified total harmonic distortion (THD) with losses of abridged switching. Huge structure in complexity and expensive cost expenditure of the multipulse transformer is the major limitation of this scheme. DC link split capacitors in addition are eliminated by modifying the topology of the circuit. Thus, the independent voltages of the DC capacitor are controlled and decreased in number and the flow of third harmonic current component in the transformer is eliminated. The scheme of the designed controller is depending on the derived mathematical system model. Simulaion observation is used to check the scheme performance and efficiency in a detailed way with drive control technique.

Inclusive Design and Development of Front-End Multiphase Rectifier With Reduced Magnetic Rating and Improved Efficiency

This article proposes a 20-pulse asymmetric multiphase converter (AMPC) suitable for medium- and high-power applications. Unlike the other state-of-the-art 20-pulse delta-connected autotransformers, the proposed delta-connected AMPC has an ability to reduce input harmonics, maintains high efficiency, and requires a magnetic rating of only 30.12% of the nominal load; thereby, a significant reduction in space, weight, and overall cost required is the salient features of the proposed AMPC. A detailed power quality performance analysis and an efficiency calculation are discussed. First, the proposed AMPC configuration is simulated in MATLAB/Simulink environment for evaluating its viability under different loading conditions, and the results are illustrated. A detailed comparison of the proposed AMPC configuration with other multipulse transformers is included, which confirms the merits of the proposed system. Also, a prototype is developed, and the experimental measurements obtained are presented to validate the feasibility and operability of the proposed AMPC. The proposed AMPC offers a total harmonic distortion of 3.7% and can operate at near-unity power factor complying with the IEEE and IEC standards.

Analysis of 6-Pulse and 12-Pulse in Conversion of the 115VAC/400Hz to 270 VDC for Application on Fighter

The development of aircraft secondary power technology is moving from mechanical power, pneumatic power and hydraulic power to electric power. The trend toward electric power is known as More Electric Aircraft (MEA). Modern military aircraft are designed using 270VDC for electric power system. Today, some military aircraft still use 115VAC/400Hz for their electrical power system. If this type of aircraft need provides 270VDC electrical power, then they require Multi-Pulse Transformer Rectifier Unit (TRU). The development of this type TRU has not been aimed to comply with aircraft military standards. This research investigates the variation of the number of pulses (p) and firing angle (α) to the amplitude ripple voltage, output voltage, and distortion factor in order to comply with the MIL-STD-704F standards. The multi-pulse transformer rectifier unit being analyzed consists of 6-Pulse and 12-Pulse. The research shows that the amplitude ripple voltage and distortion factor of the 6-Pulse TRU do not comply MIL-STD-704F. The amplitude ripple voltage and distortion factor of 12-Pulse comply MIL-STD-704F with firing angle (α) ≤4°.Keywords: Transformer Rectifier Unit, thyristor, ripple voltage, distortion factor, firing angle

Methodology to qualify marine electrical propulsion system architectures for platform supply vessels

Conventional diesel-electric propulsion systems in platform supply vessels (PSVs) use low-voltage AC (LVAC) supply-based architecture with multiple diesel-generators feeding busbars at 690 V, 60 Hz. The busbars distribute power to thruster motor drives via multi-pulse transformers and diode bridge rectifiers. Advancements in electrical power conversion and distribution technologies offer possibilities of AC or DC distribution at low/medium voltage (LV/MV) for reduced fuel consumption (FC), emissions, and equipment footprint. This study presents methodology to qualify propulsion system architecture for PSV application. Potential architectures, besides conventional one, are active front end (AFE) converter-based LVAC (690 V), MVAC (3.3 kV), LVDC (1000 V), and MVDC (5000 V). Performances of these architectures are assessed quantitatively based on FC, emissions, weight, volume, efficiency, and reliability. FC is estimated based on brake-specific FC data of diesel engine. NO x , SO 2 , and CO 2 emissions are assessed based on their emission factors. The weight, volume, and efficiency are estimated based on parameters of individual components. Reliability is assessed based on component failure data using DIgSILENT Power Factory. The architectures are ranked based on performance parameters using a Pugh matrix. The most suitable architecture for the target PSV is LVDC, followed by MVDC, LVAC with AFE, MVAC, and conventional LVAC.

Controlled Strategies Using DC Voltage for Asymmetric Twin Converter for a High Power STATCOM

The proposed controller can balance individual dc capacitor voltages when H-bridges run with different switching patterns and have parameter variations. It has two advantages: 1) the controller can work well in all operation modes (the capacitive mode, the inductive mode, and the standby mode) and 2) the impact of the individual dc voltage controller on the voltage quality is small. This topology suggests further improvement Here we have to using fuzzy logic controllers in the control scheme to reduce total harmonic distortion. A three phase cascaded H-bridge inverter this control method uses a discrete-time model of the system to predict the future value of the current for all voltage vectors, and selects the vector which minimizes a cost function. Analytical solutions of pulse width-modulation (PWM) strategies for multilevel inverters are used to identify that alternative phase opposition disposition PWM for diode clamped inverters produces the same harmonic performance as phase-shifted carrier PWM for cascaded inverters, and hybrid PWM for hybrid inverters, when the carrier frequencies are set to achieve the same number of inverter switch transitions over each fundamental cycle. In order to improve the performance, a phase-shifted carrier based pulse width modulation technique is used. A mathematical model of the system is derived, based on which a controller for the scheme is designed. The effectiveness of the scheme is verified through detailed simulation study. Index Terms: DC voltage regulation, fuzzy logic controllers, voltage source converter (VSC), Pulse width modulation (PWM), static compensator (STATCOM) I. Introduction The static synchronous compensator (STATCOM) is a flexible ac transmission system device, which is connected as a shunt to the power system, for generating or absorbing reactive power (5). A STATCOM works in the capacitive mode if it injects reactive power to the power system and in the inductive mode it absorbs reactive power from the power system. A multi pulse converter uses more than one voltage source converter (VSC), with common dc link, operating with nearly fundamental switching frequency, and the output of each module is connected in series through the multi pulse transformer. By adjusting the triggering pulses of different VSCs, specified total harmonic distortion (THD) of the injected current is achieved with reduced switching losses as compared to that of single-VSC-based solution. The major drawback of this scheme is the high cost and complex structure of the bulky multi pulse transformer. Multilevel converter technology is a very efficient alternative for medium voltage and high-power applications and also for other applications where high-quality voltages and currents are required (1), (2). The other commonly used multilevel topology, i.e., cascaded converter topology comprises several single-phase H-bridge/full-bridge converters, with separate dc links. The following are the two associated problems of this topology: 1) The size of the dc-link capacitor required is high because the instantaneous power involved with each module varies at twice the fundamental frequency. 2) Regulating voltage across a large number of self supported dc-link capacitors makes the controller design complex.

A High-Performance Multicell Topology Based on Single-Phase Power Cells for Three-Phase Systems Operating Under Unbalanced AC Mains and Asymmetrical Loads

This paper presents a multicell converter topology composed of N single-phase power cells per phase and a multipulse power transformer. The topology achieves high-power-quality waveforms in three-phase applications under the presence of severe unbalanced ac mains. Moreover, the power cells are properly arranged in order to achieve high-performance ac supply current waveforms under asymmetrical loads. The configuration is based on single-phase power cells that feature a pulsewidth-modulation rectifier in order to achieve an overall unitary displacement power factor and a controlled dc-link voltage at the power-cell level. The configuration is implemented, and different experimental tests are performed where unbalance and distortion indexes are computed.

Voltage Balance and Control in a Multilevel Unified Power Flow Controlier

The neutral-point-clamped multilevel converter is an attractive implementation of the unified power flow controller because it facilitates back-to-back operation, high-voltage operation (without direct series connection of devices), and low distortion (without the use of multipulse transformers). A UPFC using three converters is proposed. Two phase-shifted converters are required to provide a full range of voltage control of the series connection while ensuring low distortion and a balanced dc link. A single shunt converter is used. A commutation angle solution that balances the voltages of the multiple dc link capacitors is analyzed in terms of the active power balance at each node. Control of shunt reactive power requires a variable dc link voltage. Control schemes for both shunt and series converters are developed and verified in terms of voltage balancing and power flow control on a micro-scale experimental system using five-level converters.

Voltage balance and control in a multi-level unified power flow controller

The neutral-point-clamped multilevel converter is an attractive implementation of the unified power flow controller because it facilitates back to back operation, high voltage operation (without direct series connection of devices) and low distortion (without the use of multi-pulse transformers). A UPFC using three converters is proposed. Two phase-shifted converters are required to provide a full range of voltage control of the series connection while ensuring low distortion and a balanced DC link. A single shunt converter is used. A commutation angle solution that balances the voltages of the multiple DC link capacitors is analyzed in terms of the active power balance at each node. Control of shunt reactive power requires a variable DC link voltage. Control schemes for both shunt and series converters are developed and verified in terms of voltage balancing and power flow control on a micro-scale experimental system using 5-level converters.