Academic literature on the topic 'Multi-level active rectifiers'

Power electronic converters are widely used in wind energy conversion system (WECS) applications. Therefore, with the increasing manufacturing capacity of multi-MW wind generators, multi-level converters, or parallel configuration of converters are becoming more attractive solutions towards DC collection from the wind generator. Among the multilevel converters, three-level full-scale neutral point diode clamped (3L-NPC) converter are using extensively for such applications in order to reduce the voltage stress on the semiconductor devices. In this article, a comparative study based on several devices used by NPC, capacitor clamped (CC) as well as Vienna rectifier has been done. Furthermore, their estimated cost comparison and complexity of control switches have been debated. By keeping in view the merits and demerits of these rectifiers, a low cost three-level active rectifier having a smaller number of active switches with a simple control scheme have been implemented. Considering a three-phase electric grid as a generated source, a 2.2KW low-cost three-level Vienna rectifier is simulated using MATLAB/Simulink. DSP (TMS320F28335) based experimental results ratify the simulated circuit with THD<5%.

The rapid development of electric vehicle ultra-fast battery chargers is increasingly demanding higher efficiency and power density. In particular, a proper control of the grid-connected active front–end can ensure minimum passive component size (i.e., limiting design oversizing) and reduce the overall converter losses. Moreover, fast control dynamics and strong disturbance rejection capability are often required by the subsequent DC/DC stage, which may act as a fast-varying and/or unbalanced load. Therefore, this paper proposes the design, tuning and implementation of a complete digital multi-loop control strategy for a three-level unidirectional T-type rectifier, intended for EV ultra-fast battery charging. First, an overview of the operational basics of three-level rectifiers is presented and the state-space model of the considered system is derived. A detailed analysis of the mid-point current generation process is also provided, as this aspect is widely overlooked in the literature. In particular, the converter operation under unbalanced split DC-link loads is analyzed and the converter mid-point current limits are analytically identified. Four controllers (i.e., dq-currents, DC-link voltage and DC-link mid-point voltage balancing loops) are designed and their tuning is described step-by-step, taking into account the delays and the discretization introduced by the digital control implementation. Finally, the proposed multi-loop controller design procedure is validated on a 30 kW, 20 kHz T-type rectifier prototype. The control strategy is implemented on a single general purpose microcontroller unit and the performances of all control loops are successfully verified experimentally, simultaneously achieving low input current zero-crossing distortion, high step response and disturbance rejection dynamics, and stable steady-state operation under unbalanced split DC-link loading.

Two of the main challenges of recent electric vehicles (EVs) are the charging time and high initial cost. To solve the problem associated with long charging time, the car manufacturers are moving from 400 V battery EV (BEV) to 800 V BEV, which enables the utilization of multi-level converters in EV applications. This paper presents a power conversion system consisting of a Vienna rectifier and a two/three level hybrid inverter as a machine-side inverter to drive a permanent-magnet synchronous motor (PMSM). The Vienna rectifier improves the quality of the grid-side current and provides a regulated DC-link voltage. The proposed inverter, known as a 10-switch inverter, offers high output current quality with a lower number of active switches, making it compact and cost-effective. The field-oriented control (FOC), along with the SPWM modulation, is implemented to control the system. A reliable and cost-effective PMSM drive system demands sensorless control; therefore, a sliding mode observer (SMO) is used to estimate the rotor position and velocity. The accuracy of the proposed system was proved through the simulation results from MATLAB/Simulink.

This work presents the design of a control law based on the average model of a shunt active power filter considering an H-bridge neutral point clamped topology and its experimental validation. Therefore, the proposed controller is formed by three control loops, namely current (inner), regulation (outer), and balance control loops. The current loop aims to compensate both the displacement power factor and the harmonic distortion produced by nonlinear loads connected to the point of common coupling. To deal with harmonic current distortion, the current loop involves an adaptive mechanism based on a bank of resonant filters tuned at odd harmonics of the fundamental grid frequency. The regulation and balance loops are aimed to maintain the voltage of the capacitors forming the DC-link at a desired constant level. For this, proportional-integral controllers are designed. The design of all three loops considers the average model of the system. The performance of the proposed multi-loop control law is evaluated through numerical results and real-time experimental implementation, both considering a 2 kW academic benchmark with a constant switching frequency of 7 kHz. In order to provide harmonic distortion, a nonlinear load based on an uncontrolled diode bridge rectifier is considered. Additionally, step-load changes from 0.5 kW to 1 kW are considered for the nonlinear load. As a result, a suitable current tracking, voltage regulation, and balance are observed despite parametric uncertainties, load variations, and harmonic distortion. As a consequence, in steady state, simulation results indicate that the compensated grid current THD is 1.75%; meanwhile, the nonlinear load current THD is 52.5%. Experimental results indicate that the compensated grid current THD is 2.32%; meanwhile, the nonlinear load current THD is 53.8%.

At distribution side most type of loads connected are non-linear types. These loads adversely affect the power quality of the system. If not rectified at times they may distort the sine wave at source side. This paper presents a power quality conditioner which is designed using multi-level inverter (MLI). The advantage that the proposed MLI has over conventional one is that it requires less number of components as compared to the conventional. Also it improves the utility profile by improving harmonic content at output side. The proposed MLI based Unified power Quality Conditioner (UPQC) improves the grid profile at non-linear loading by prohibiting the propagation of high content harmonic load current at source side. The proposed topology has inherent active filtering capability by virtue of which there has been seen a good mitigation of power quality issues at point of common coupling. Comparative analysis of the proposed topology with the conventional MLI is also presented. The comparison of results is also presented in terms of linear and non-linear loading in a UPQC compensated distribution system.

Диссертация на соискание учѐной степени кандидата технических наук по специальности 05.09.12 – полупроводниковые преобразователи электроэнергии. – Национальный технический университет "Харьковский политехнический институт" – Харьков - 2016. Диссертация посвящена исследованию электромагнитных процессов в активных четырех-квадрантных выпрямителей с системами управления построенных на базе гистерезисной и широтно-импульсной модуляции, которые обеспечивают высокие показатели электромагнитной совместимости с питающей и контактной сетью. Выполнен анализ путей улучшения электромагнитной совместимости и возможности реализации рекуперации в выпрямительных установках тяговых подстанций постоянного тока. Сделан вывод, что наиболее перспективной схемой выпрямительного агрегата тяговой подстанции является схема активного трехфазного четырехквадрантного выпрямителя напряжения построенная на базе схемы автономного инвертора напряжения. Разработаны системы автоматического управления двухуровневого и трехуровневого АВН с реализации широтно-импульсной модуляции. Преимуществом разработанных систем управления является постоянная и значительно меньшая частота коммутации ключей, что обуславливает физическую реализуемость системы, а также снижение динамических потерь в преобразователе, и как следствие повышение КПД преобразователя. При этом трехуровневый АВН в сравнении с двухуровневым обладает большим числом ступеней модуляции напряжения, что обуславливает улучшенные показатели качества электроэнергии. Разработана система автоматического управления компенсационного АВН, который состоит из нескольких параллельных мостов, которые запитаны от одной сети и работают на одну нагрузку. Синхронизация каналов управления отдельных мостов с реализацией сдвига опорного сигнала ШИМ на угол ξ, обеспечивает взаимную компенсацию высших гармоник входных токов и выходного напряжения, чем достигаетсся улучшение параметров электромагнитной совместимости: коэффициент мощности 99,83%; коэффициент гармонических искажений 1,82%; коэффициент пульсаций выходного напряжения 0,1824%; мешающее напряжение в контактной сети 1,123В.<br>Thesis for candidate degree of technical sciences of speсiality 05.09.12 – Semiconductor converters of electric energy – National Technical University "Kharkov Politechnical Institute" – Kharkov - 2016. The thesis is dedicated to investigation of electromagnetic processes and EMC parameters of the two-level, three-level and parallel three-phase four quadrant active rectifiers with power factor correction with novel automated control systems based on hysteresis modulation and PWM. Control characteristics and automated control system of active four quadrant active rectifiers with hysteresis modulation and PWM was designed. Studies have shown principle weaknesses of the hysteresis modulation. It’s high and variable switching frequency and high losses in IGBT. Automated control system based on PWM has strong advantage – constant switching frequency, that improves efficiency of convertor and EMC parameters.

Дисертація на здобуття вченого ступеня кандидата технічних наук за фахом 05.09.12 – напівпровідникові перетворювачі електроенергії. – Національний технічний університет "Харківський політехнічний інститут" – Харків - 2016. Дисертація присвячена дослідженню електромагнітних процесів в активних трифазних випрямлячах напруги з корекцією коефіцієнта потужності з системами автоматичного управління побудованих на базі гістерезисної на широтно-імпульсної модуляції, які забезпечують високі показники електромагнітної сумісності з живлячою та контактною мережами. Отримані регулювальні характеристики АВН з гістерезисною системою управління на основі яких розроблена система автоматичного управління з реалізацією двонаправленої передачею енергії. Дослідження активних випрямлячів з гістерезисною системою управління показали реалізацію високих показників електромагнітної сумісності, проте і виявили її принципові недоліки, а саме високу і змінну частоту комутації, що значно ускладнює її фізичну реалізацію на існуючий базі IGBT транзисторів та зумовлює значні втрати в перетворювачі. Визначені аналітичні співвідношення максимальної частоти комутації ключів АВН з гістерезисною системою управління від параметрів живлячої мережі, схеми заміщення АВН, навантаження та величини уставки гістерезиса. Розроблена система управління компенсаційного активного випрямляча напруги, який складається із декількох паралельних або послідовних мостів, які заживлені від однієї мережі живлення і працюють на одне навантаження. Синхронізація каналів управління окремих мостів з реалізацією зсуву опорного сигналу ШІМ на кут зсуву ψ дозволяє реалізувати взаємну компенсацію вищих гармонік вхідного струму та вихідної напруги, чим досягається покращення показників електромагнітної сумісності: коефіцієнт потужності 99,83%; коефіцієнт гармонійних спотворень 1,82%; коефіцієнт пульсацій вихідної напруги 0,1824%; заважаючи напруга у контактній мережі 1,123В.<br>Thesis for candidate degree of technical sciences of speсiality 05.09.12 – Semiconductor converters of electric energy – National Technical University "Kharkov Politechnical Institute" – Kharkov - 2016. The thesis is dedicated to investigation of electromagnetic processes and EMC parameters of the two-level, three-level and parallel three-phase four quadrant active rectifiers with power factor correction with novel automated control systems based on hysteresis modulation and PWM. Control characteristics and automated control system of active four quadrant active rectifiers with hysteresis modulation and PWM was designed. Studies have shown principle weaknesses of the hysteresis modulation. It’s high and variable switching frequency and high losses in IGBT. Automated control system based on PWM has strong advantage – constant switching frequency, that improves efficiency of convertor and EMC parameters.