Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

New Stationary Frame Control Scheme for Three Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions

A new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple. This paper's novelty is the development of a new current-reference generator implemented directly in stationary reference frame. This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator. Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme. A comparison with two other existing control techniques is also performed. Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating conditions

Harmonic current extraction of shunt active power filter based on prediction current technique - Hysteresis PWM

Due to the wide spread of power electronics equipment in modern electrical systems, the increase of the harmonics disturbance in the ac mains currents has became a major concern due to the adverse effects on all analysis and simulation using MATLAB-SIMULINK of a three-phase shunt active equipment. This paper presents the Shunt Active Power Filter (SAPF) to compensate the generated harmonics by 3-phase Rectifier Bridge fed R-L load. The harmonic current extraction is based on prediction current extraction technique -hysteresis PWM generation pattern

New techniques to improve power quality and evaluate stability in modern all-electric naval ship power systems

This dissertation focuses on two crucial issues in the design and analysis of the power electronic systems on modern all-electric naval ships, i.e., power quality control and stability evaluation. It includes three papers that deal with active power filter topology, active rectifier control, and impedance measurement techniques, respectively. To mitigate harmonic currents generated by high-power high-voltage shipboard loads such as propulsion motor drives, the first paper proposes a novel seven-level shunt active power filter topology, which utilizes tapped reactors for parallel operations of switching devices. The multi-level system has been implemented in both regular digital simulation and real-time digital simulator for validation. In the second paper, a harmonic compensation algorithm for three-phase active rectifiers is proposed. Based on the theory of multiple reference frames, it provides fast and accurate regulation of selected harmonic currents so that the rectifier draws balanced and sinusoidal currents from the source, even when the input voltages are unbalanced and contain harmonics. Extensive laboratory tests on a 2 kW prototype system verifies the effectiveness of the proposed control scheme. The last paper presents a new technique for impedance identification of dc and ac power electronic systems, which significantly simplifies the procedure for stability analysis. Recurrent neural networks are used to build dynamic models of the system based on a few signal injections, then the impedance information can be extracted using off-line training and identification algorithms. Both digital simulation and hardware tests were used to validate the technique --Abstract, page iv

A back to back multilevel converter for driving low inductance brushless AC machines

Traditionally, multilevel converters are utilised in medium voltage applications, allowing the DC-link voltage to exceed the switch maximum blocking voltage. Here, their application to control high- efficiency brushless permanent magnet synchronous machines exhibiting low phase inductance is explored, the relative advantages being shown to include reduced current ripple and improved harmonic spectrum. A cost benefit analysis is included along with experimental results from a prototype 5-level back-to-back converter

High-performance motor drives

This article reviews the present state and trends in the development of key parts of controlled induction motor drive systems: converter topologies, modulation methods, as well as control and estimation techniques. Two- and multilevel voltage-source converters, current-source converters, and direct converters are described. The main part of all the produced electric energy is used to feed electric motors, and the conversion of electrical power into mechanical power involves motors ranges from less than 1 W up to several dozen megawatts

STEROWANIE ORAZ SYNCHRONIZACJA DWUPOZIOMOWEGO FALOWNIKA NAPIĘCIA W WARUNKACH PRZEJŚCIOWEJ ASYMETRII NAPIĘĆ SIECI

This paper presents the operation of grid tied, two level voltage source inverter (VSI) during network voltage unbalance. The control system was implemented in synchronous rotating reference frame dq0 (SRF). Two types of control structures were investigated herein. First utilizes the Double Decoupled SRF Phase-locked loop (DDSRF-PLL) synchronisation with positive and negative sequence currents control. Second one is simplified system that does not provide symmetrical components decomposition and decoupling for synchronisation. Simulation results exhibited a superior performance of the DDSRF-PLL control system under grid voltage unbalance.Niniejszy artykuł przedstawia pracę dwupoziomowego falownika napięcia współpracującego z siecią, podczas przejściowej asymetrii napięć. System sterowania został zaimplementowany w wirującym układzie synchronicznym dq0. Przeanalizowano dwa typy sterowania. W pierwszym zastosowano metodę synchronizacji z odprzęganiem DDSRF-PLL wraz z możliwością kontroli prądów składowej zgodnej i przeciwnej. Drugi natomiast w swoje uproszczeni formie nie pozwalała na sterowanie obu składowych symetrycznych, zabrakło również odprzęgania podczas synchronizacji z siecią. Wyniki symulacji pokazały o wiele lepsze działanie pierwszej metody sterowania

Sliding mode approach for control and observation of a three phase AC-DC pulse-width modulation rectifier

Introduction. For AC-DC conversion systems, the electrical systems typically use thyristor or diode bridge rectifiers, which have relatively poor performance. Nowadays, three-phase pulse-width modulation rectifiers are widely applied in various applications for their well-known intrinsic benefits, such as adjustable DC link voltage, unity power factor, bidirectional power flow and very low total harmonic distortion. Purpose. The objective of this work is to achieve better stability and dynamic performance using sliding mode strategy for control and observation. Methods. For that purpose, first a sliding mode controller is introduced on the DC-link side to ensure a fast and accurate response of the output load voltage. Then, the sliding mode approach is employed to control the quadrature and direct components of power to maintain the input power factor at unity. Finally, this approach is used to design two observers for grid voltage estimation and online variation of load resistance. To overcome the problem associated with the use of the classical low-pass filter, an adaptive compensation algorithm is used to compensate the attenuation of the amplitude and phase delay of the observed grid voltages. This algorithm is based on the use of the two low-pass filters in cascade and ensures the minimization of chattering. Results. Comparative studies have been carried out between sliding mode control method for controlling the three-phase AC-DC pulse-width modulation rectifier and other conventional techniques. The validation by simulation and the tests carried out gave very satisfactory results and proved the effectiveness and feasibility of the sliding mode for both control and observation of three phase pulse-width modulation rectifier.Вступ. Для AC-DC систем перетворення електричні системи зазвичай використовують тиристорні або діодні мостові випрямлячі, які мають відносно погані характеристики. В даний час трифазні випрямлячі з широтно-імпульсною модуляцією широко застосовуються з різними цілями завдяки їх добре відомим внутрішнім перевагам, таким як регульована напруга у ланці постійного струму, одиничний коефіцієнт потужності, двонаправлений потік потужності та дуже низькі загальні гармонічні спотворення. Метою даної роботи є досягнення кращої стабільності та динамічних характеристик з використанням стратегії ковзного режиму для контролю та спостереження. Методи. З цією метою спочатку на стороні ланки постійного струму вводиться регулятор режиму ковзання, щоб забезпечити швидку і точну реакцію на вихідну напругу навантаження. Потім використовується метод ковзного режиму для управління квадратурною та прямою складовими потужності, щоб підтримувати вхідний коефіцієнт потужності рівним одиниці. Нарешті цей підхід використовується для розробки двох спостерігачів для оцінки напруги мережі та зміни опору навантаження в режимі онлайн. Для подолання проблеми, пов'язаної з використанням класичного низькочастотного фільтру, використовується алгоритм адаптивної компенсації, що компенсує загасання амплітуди і фазової затримки напруг мережі, що спостерігаються. Цей алгоритм заснований на використанні двох низькочастотних фільтрів у каскаді та забезпечує мінімізацію брязкоту. Результати. Були проведені порівняльні дослідження між методом керування ковзним режимом для керування трифазним випрямлячем AC-DC з широтно-імпульсною модуляцією та іншими традиційними методами. Перевірка за допомогою моделювання та проведені випробування дали дуже задовільні результати та довели ефективність та здійсненність ковзного режиму як для управління, так і для спостереження за трифазним випрямлячем з широтно-імпульсною модуляцією

Comprehensive analysis and comparison of digital current control techniques for active rectifiers

This paper presents a comprehensive analysis and comparison of digital current control techniques for active rectifiers. These rectifiers are connect-ed to the power grid and are controlled aiming to obtain sinusoidal grid currents and unitary power factor. In this context this paper presents the principle of operation of a full-bridge full-controlled active rectifier, which is controlled by different digital current control techniques, namely, proportional-integral (PI) in stationary frame, PI in synchronous frame, PI sinewave (PIS), feedforward, sliding mode, and predictive. These digital current control techniques are explained in detail and is established a comparison in terms of their current errors in steady-state, as well as in terms of their digital implementation using the digital signal processor (DSP) TMS320F28335 from Texas Instruments.FCTCOMPETE: POCI-01-0145-FEDER-00704

Class-E rectifiers and power converters: the operation of the class-E topology as a power amplifier and a rectifier with very high conversion efficiencies

In the late 70’s, the interest in reducing the value and size of reactive components moved power supply specialists to operate dc-to-dc converters at hundreds of kHz or even MHz frequencies. Passive energy storage (mainly magnetics) dominates the size of power electronics, limiting also its cost, reliability and dynamic response. Motivated by miniaturization and improved control bandwidth, they had to face the frequency-dependent turn-on and turn-off losses associated with the use of rectangular waveforms in the hard-switched topologies of that time. Similar to approaches for RF/microwave power amplifiers (PAs), the introduction of resonant circuits allowed shaping either a sinusoidal voltage or current, with parasitic reactive elements absorbed by the topology in the neighborhood of the switching frequency. The resulting resonant power converters, obtained by cascading a dc-to-ac resonant inverter with a high-frequency ac-to-dc rectifier, first transform the dc input power into controlled ac power, and then convert it back into the desired dc output [1]. This paper provides some historic notes on the operation of the class-E topology, introduced worldwide to the RF/microwave community by Nathan O. Sokal [2], as a power inverter and as a rectifier, with very high conversion efficiencies up to microwave frequencies. Recent research advances and implementations of class-E rectifiers and dc-to-dc converters at UHF and beyond are included. Offering competitive performance in terms of efficiency for RF power recovery, together with a wide bandwidth for low-loss power conversion, their potential for some modern applications is highlighted.The authors would like to acknowledge support in part by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2017-83343-C4-1-R projects, co-funded with FEDER, and in part by Lockheed Martin Endowed Chair at the University of Colorado