A review on power electronics technologies for power quality improvement

Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.This work has been supported by FCT-Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017 and by the FCT Project newERA4GRIDs PTDC/EEIEEE/30283/2017

Bridgeless Step/Up Unity Power Factor Rectifier for High Voltage Applications

Power electronic devices with front- end rectifier are widely used in computer, communication and electric vehicle industries. These rectifiers are nonlinear in nature and generate current harmonics which pollute utility power. International harmonic standards (e.g., IEC 61000-3-2 and EN 61000-3-2) have been put in place to confine power pollution. These standards limit the current harmonics generated by loads to a specified threshold depending on load power and application. In other words, a high power factor is required. Power supplies with active power factor correction (PFC) techniques are becoming necessary for many types of electronic equipment to meet the harmonic regulations and standards. However, classical PFC schemes have lower efficiency due to significant losses in the diode bridge. Several bridgeless topologies have been introduced to decrease diode bridge conduction losses. Most of the step-up PFC rectifiers utilize boost converter at their front end due to its natural PFC capability. In this thesis, a new bridgeless PFC topology based on Cuk converter is presented. Similar to Cuk converter, the proposed topology offers several advantages in PFC applications, such as easy implementation of transformer isolation, inherent inrush current limitation during start-up and overload conditions, and lower electromagnetic interference (EMI). These advantages make the proposed topology a viable solution for high voltage DC loads such as electric vehicle battery charger. Chapter III presents steady state analysis for the proposed rectifier. The rectifier is analyzed only during the positive half of the line frequency due to symmetry. Design procedure, simulation and measurements to verify the capability of the rectifier are presented in Chapter IV. Harmonics content and efficiency of the proposed rectifier versus conventional Cuk full bridge PFC rectifier are also presented

Active converter based on the VIENNA rectifier topology interfacing a three-phase generator to a DC-bus

AC-DC converters find application in every day life as a front-end to DC-DC and DC-AC converters. Active three-phase converters shape the three-phase input current to be sinusoidal and to be in-phase with the input voltage, as well as to provide a steady DC output voltage. This thesis investigates various active three-phase rectifier and control topologies and identifies a rectifier and control topology most suitable for use in converting a variable voltage variable frequency generator output to a DC voltage. In this dissertation, design relations are derived for determining the plant transfer response (for the suitable topology/controller), design equations are derived for designing/choosing the filter components, and guidelines are derived that will assist in choosing the right semi-conductor components and to give an estimation of expected system efficiency. The dissertation investigates the implementation of both analogue and digital control and provides implementation methodologies for both controllers. Expected results are verified by simulation and a build-up prototype. It was shown that the VIENNA rectifier is able to convert a generator type input, with variable input voltage amplitude and variable frequency, to a constant DC-bus voltage whilst controlling the input current to be sinusoidal and in phase with the input voltage. The rectifier was able to maintain a constant DC voltage at the output for input voltages as low as half the rated input voltage and for an equivalent output power of half the rated output power. This suggests that the VIENNA rectifier, controlled as a dual-boost rectifier, is suitable for applications that require power factor corrections and simultaneously operate from a wide input voltage range.Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2007.Electrical, Electronic and Computer EngineeringMEngunrestricte

Dynamic modeling of pwm and single-switch single-stage power factor correction converters

The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters operating in continuous conduction mode (CCM) and under small ripple conditions. Modeling of conductor losses under large ripple conditions has not been reported in the open literature, especially when the converter operates in discontinuous conduction mode (DCM). In this dissertation, new models are developed to include conduction losses in the non-ideal PWM switch model under CCM and DCM conditions. The developed model is verified through two converter examples and the effect of conduction losses on the steady state and dynamic responses of the converter is also studied. Another major constraint of the PWM switch modeling approach is that it heavily relies on finding the three-terminal PWM switch. This requirement severely limits its application in modeling single-switch single-stage power factor correction (PFC) converters, where more complex topological structures and switching actions are often encountered. In this work, we developed a new modeling approach which extends the PWM switch concept by identifying the charging and discharging voltages applied to the inductors. The new method can be easily applied to derive large-signal models for a large group of PFC converters and the procedure is elaborated through a specific example. Finally, analytical results regarding harmonic contents and power factors of various PWM converters in PFC applications are also presented here

Low-power PFC and forward converters : methods to improve performance

The number of power electronic appliances is growing. Power electronic converters can be used to convert the ac line voltage to a dc voltage, and further through dc-dc conversion stages to desired dc voltages for different loads. This Thesis deals with three single-stage power factor correction converters and a forward type dc-dc converter. Single-stage converters can be considered as low cost solutions for power factor correction. This is because only one active switching stage is used in the converters. Small signal and steady state analysis are performed for the dither converter. A resonant type snubber is analyzed for the BIFRED and BIBRED converters and a new type of clamp circuit is developed for the BIFRED converter. The dc-dc conversion part of the Thesis deals with a forward converter with active clamp circuit and self-driven synchronous rectifiers. Resonant transition of the converter is analyzed in detail. Emphasis of the research is on improving the efficiency of the converter. Findings show that the minimization of the turn-on losses in the converter is not necessarily advantageous. The analysis is verified with a 3.4 V and 30 A prototype converter.reviewe

Data Center Power System Emulation and GaN-Based High-Efficiency Rectifier with Reactive Power Regulation

Data centers are indispensable for today\u27s computing and networking society, which has a considerable power consumption and significant impact on power system. Meanwhile, the average energy usage efficiency of data centers is still not high, leading to significant power loss and system cost. In this dissertation, effective methods are proposed to investigate the data center load characteristics, improve data center power usage efficiency, and reduce the system cost. First, a dynamic power model of a typical data center ac power system is proposed, which is complete and able to predict the data center\u27s dynamic performance. Also, a converter-based data center power emulator serving as an all-in-one load is developed. The power emulator has been verified experimentally in a regional network in the HTB. Dynamic performances during voltage sag events and server load variations are emulated and discussed. Then, a gallium nitride (GaN) based critical conduction mode (CRM) totem-pole power factor correction (PFC) rectifier is designed as the single-phase front-end rectifier to improve the data center power distribution efficiency. Zero voltage switching (ZVS) modulation with ZVS time margin is developed, and a digital variable ON-time control is employed. A hardware prototype of the PFC rectifier is built and demonstrated with high efficiency. To achieve low input current total harmonic distortion (iTHD), current distortion mechanisms are analyzed, and effective solutions for mitigating current distortion are proposed and validated with experiments. The idea of providing reactive power compensation with the rack-level GaN-based front-end rectifiers is proposed for data centers to reduce data center\u27s power loss and system cost. Full-range ZVS modulation is extended into non-unity PF condition and a GaN-based T-type totem-pole rectifier with reactive power control is proposed. A hardware prototype of the proposed rectifier is built and demonstrated experimentally with high power efficiency and flexible reactive power regulation. Experimental emulation of the whole data center system also validates the capability of reactive power compensation by the front-end rectifiers, which can also generate or consume more reactive power to achieve flexible PF regulation and help support the power system

High Current Density Low Voltage Isolated Dc-dc Converterswith Fast Transient Response

With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel\u27s CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel\u27s roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs

HA 컨버터를 응용한 AC-DC 및 DC-AC 전력 변환

학위논문 (박사)-- 서울대학교 대학원 : 전기공학부, 2013. 2. 조보형.This dissertation proposes a new topology H-bridge converter with additional switch legs (HA converter). The proposed topology has simple circuit structure with expandability and flexibility. With six semiconductor devices and single inductor, the topology is capable of operating as buck, boost, and buck-boost converter. Theoretically, it demonstrates low common mode current and electromagnetic interference (EMI) by solidly connecting grounds of input and output terminals. The proposed topology is advantageous not only in grid-connected power conversion application but also in stand-alone power system such as electric vehicle, because these systems include large parasitic capacitances and are prone to high common mode EMI due to the wide mechanical structure of the conductor. Among many offspring circuits of the HA converter, a boost-buck-boost (B3) rectifier for off-line power supply with active power factor correction and a buck-buck-boost (B3) inverter for grid-connected photovoltaic system are proposed as two practical examples. Principle of operations, dedicated control algorithms, and filters for the new circuits are analyzed and designed in detail. Experimental results based on the laboratory prototype hardware prove that the proposed circuits outperform their conventional counterparts by showing low common mode noise and comparable efficiency.Abstract............................i Contents...........................ii List of Figures....................iv List of Tables......................x 1. Introduction.....................1 1.1. Motivations and Backgrounds....1 1.2. Objectives.....................2 1.3. Dissertation Outlines..........4 2. H-bridge Converter with Additional Switch Legs (HA Converter)......................7 2.1. Review of Common Mode EMI......7 2.1.1. In Off-line AC-DC Rectifier.11 2.1.2. In Grid-connected DC-AC PV Inverter...........................16 2.2. Topology Derivation...........24 2.2.1. Dual H-bridges..............29 2.2.2. HA Converter................31 2.3. Feature of HA Converter.......34 3. B3 Rectifier for AC-DC Conversion.........................40 3.1. Advantage of B3 Rectifier.....40 3.2. Operation.....................43 3.3. Control.......................45 3.3.1. Power Imbalance in a Line Cycle..............................47 3.3.2. Inductor Current Reference Calculation........................51 3.3.3. Compensator Design..........56 3.4. Differential Input Filter Design.............................67 3.5. Experiments...................75 3.5.1. Implementations.............75 3.5.2. Results and Discussions.....81 4. B3 Inverter for DC-AC Conversion.........................88 4.1. Advantage of B3 Inverter...........................88 4.2. Operation.....................91 4.3. Control.......................93 4.3.1. Inductor Current Reference Calculation........................93 4.3.2. Compensator Design..........98 4.4. Differential Output Filter Design............................104 4.5. Experiments..................111 4.5.1. Implementations............111 4.5.2. Results and Discussions....117 5. Flexibility of HA Converter.........................125 6. Conclusion and Further Works...134 Appendix..........................137 A.1. Correction Factor of B3 Rectifier in Small Signal Model.............................137 A.2. Input Impedances of Boost and Buck-boost Converter.........................139 A.3. Loss Estimation of B3 Rectifier Switches..........................144 A.4. H5 and HERIC Inverter Operations........................153 References........................160 국문 초록.........................168 감사의 글.........................169Docto

Analysis, Design and Control of a Modular Full-Si Converter Concept for Electric Vehicle Ultra-Fast Charging

L'abstract è presente nell'allegato / the abstract is in the attachmen

Power Quality Issues in Distributed Generation

This book deals with several selected aspects of electric power quality issues typically faced during grid integration processes of contemporary renewable energy sources. In subsequent chapters of this book the reader will be familiarized with the issues related to voltage and current harmonics and inter-harmonics generation and elimination, harmonic emission of switch-mode rectifiers, reactive power flow control in power system with non-linear loads, modeling and simulation of power quality issues in power grid, advanced algorithms used for estimating harmonic components, and new methods of measurement and analysis of real time accessible power quality related data