Showing papers on "Power factor published in 2017"

Extended State Observer-Based Sliding-Mode Control for Three-Phase Power Converters

Abstract: This paper proposes an extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters. The proposed control technique forces the input currents to track the desired values, which can indirectly regulate the output voltage while achieving a user-defined power factor. The presented approach has two control loops. A current control loop based on an SOSM and a dc-link voltage regulation loop which consists of an ESO plus SOSM. In this work, the load connected to the dc-link capacitor is considered as an external disturbance. An ESO is used to asymptotically reject this external disturbance. Therefore, its design is considered in the control law derivation to achieve a high performance. Theoretical analysis is given to show the closed-loop behavior of the proposed controller and experimental results are presented to validate the control algorithm under a real power converter prototype.

Enhanced Virtual Synchronous Generator Control for Parallel Inverters in Microgrids

Abstract: Virtual synchronous generator (VSG) control is a promising communication-less control method in a microgrid for its inertia support feature. However, active power oscillation and improper transient active power sharing are observed when basic VSG control is applied. Moreover, the problem of reactive power sharing error, inherited from conventional droop control, should also be addressed to obtain desirable stable state performance. In this paper, an enhanced VSG control is proposed, with which oscillation damping and proper transient active power sharing are achieved by adjusting the virtual stator reactance based on state-space analyses. Furthermore, communication-less accurate reactive power sharing is achieved based on inversed voltage droop control feature ( V–Q droop control) and common ac bus voltage estimation. Simulation and experimental results verify the improvement introduced by the proposed enhanced VSG control strategy.

Comprehensive Analyses and Comparison of 1 kW Isolated DC–DC Converters for Bidirectional EV Charging Systems

Abstract: Isolated dc–dc converters with galvanic isolation are commonly used in electric vehicle (EV) battery chargers. These converters interface between a dc voltage link, which is usually the output of a power factor correction stage, and an energy storage unit. CLLC and dual active bridge (DAB) dc–dc converters can achieve high power density, high-energy efficiency, wide gain range, galvanic isolation, and bidirectional power flow, and therefore, have potential applications as dc–dc converters for bidirectional EV charging systems. In this paper, full-bridge CLLC, half-bridge CLLC, full-bridge DAB, and half-bridge DAB dc–dc converters are evaluated and compared for their suitability for EV chargers. All the converters are designed with optimal soft-switching features. The operating principles, design methodologies, and design considerations are presented. Prototypes of the converters with power rating of 1 kW are designed and developed. The prototypes interface a 500 V dc link and a 200–420 V load, which is common for EV applications. The performances of the circuits are analyzed and a comprehensive comparison is conducted.

Distribution Voltage Regulation Through Active Power Curtailment With PV Inverters and Solar Generation Forecasts

Abstract: Distribution voltage profiles are subjected to overvoltage limit violations from high penetration of grid-connected photovoltaic (PV) systems. Such voltage rises seen at the point of PV interconnection can be mitigated by adaptively changing the active and/or reactive power injection from the PV inverter. This work proposes a local voltage regulation technique that utilizes very short-term (15 s) PV power forecasts to circumvent imminent upper voltage limit violation or an overvoltage scenario. To provide these PV generation forecasts, a hybrid forecasting method is formulated based on Kalman filter theory, which applies physical PV generation modeling using high-resolution (15 s) data from on-site measurements. The proposed algorithm employs an active power curtailment based on these PV power forecasts, when the reactive power estimate given by a droop-based method cannot provide the desired voltage regulation within predefined power factor limits. The curtailment threshold values are calculated in such a way that this voltage regulation technique can reduce possible voltage limit violations. The effectiveness of the proposed method is demonstrated with case studies developed on a standard test feeder with realistic load and PV generation profiles.

Review of harmonic analysis, modeling and mitigation techniques

Abstract: Power quality problems are manifested in voltage, current or frequency deviations causing malfunction of sensitive equipment. Integration of inverter connected PV and wind power plants, and rampant rise in nonlinear loads have led to harmonic problem in power system. Nonlinear loads and switched devices energized by sinusoidal sources or linear loads and switched devices with non-sinusoidal sources, produce harmonics in distribution system. Academic harmonic analysis study consists of modeling nonlinear loads to develop Norton and Thevenin equivalent circuits of devices for integration into harmonic analysis software. Experimental researchers often use harmonic analyzers to measure the harmonics in real systems to evaluate suitable mitigation alternatives. The distortive power losses force utilities to increase apparent power to maintain reliable and uniform power supply. Harmonic analyzers use data acquisition hardware and inbuilt software algorithms to perform onsite measurements. Harmonic analyzers help find true power factor, total harmonic distortions, reactive and distortive power losses. Use of shunt capacitance at unity power factor worsens the situation instead of supplying distortive power compensation. Active power factor correction techniques, using smart algorithm to cancel the distortive power, have been reviewed for further research. Nonlinear physics of harmonic phenomenon is described to explore its applications. Harmonic mitigation technologies have been compared, current state of the art technology reviewed and demonstrated by designing a harmonic filter. Measurement of harmonics, waveform distortions, and true power factor (TPF) of single and three phase electronic loads is carried out to test their compliance to harmonic standard limits. Energy conservation concept requires reduction of harmonics in distribution networks. This study found 60±10% reduction in power factor and more than 2% increase in line losses due to widespread use of nonlinear loads. Utility apparent power demand increases due to consumers’ inadvertent violation of IEC Standard 61000-3-2 and IEEE Standard 519–1992.

The Benefits of SiC MOSFETs in a T-Type Inverter for Grid-Tie Applications

Abstract: It is well known that multilevel converters can offer significant benefits in terms of harmonic performance and reduced switching losses compared to their two-level counterparts. However, for lower voltage applications the neutral-point-clamped inverter suffers from relatively large semiconductor conduction losses because the output current always flows through two switching devices. In contrast, the T-type multilevel inverter has less conduction losses because only a single outer loop switching device is required to connect the converter output to the upper and lower dc buses, albeit at the expense of increased switching losses since these outer switches must now block the full dc link voltage. Silicon carbide (SiC) mosfet devices potentially offer substantial advantage in this context with their lower switching losses, but the benefit of replacing all switching devices in a T-type inverter with SiC mosfets is not so clear-cut. This paper now explores this issue by presenting a detailed comparison of the use of Si and SiC devices for a three-level T-type inverter operating in grid-tie applications. The study uses datasheet values, switching loss measurements, and calibrated heat sink thermal measurements to precisely compare semiconductor losses for these two alternatives for a T-type inverter operating at or near unity power factor. The results show that replacing only the dc bus connection switches with SiC devices significantly reduces the semiconductor losses, allowing either the converter power level or the switching frequency to be significantly increased for the same device losses. Hence, the use of SiC mosfets for T-type inverters can be seen to be an attractive and potentially cost-effective alternative, since only two switching devices per phase leg need to be upgraded.

Low-Frequency Power Decoupling in Single-Phase Applications: A Comprehensive Overview

Abstract: This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic.

A Novel Nine-Level Inverter Employing One Voltage Source and Reduced Components as High-Frequency AC Power Source

Abstract: Increasing demands for power supplies have contributed to the population of high-frequency ac (HFAC) power distribution system (PDS), and in order to increase the power capacity, multilevel inverters (MLIs) frequently serving as the high-frequency (HF) source-stage have obtained a prominent development. Existing MLIs commonly use more than one voltage source or a great number of power devices to enlarge the level numbers, and HF modulation (HFM) methods are usually adopted to decrease the total harmonic distortion (THD). All of these have increased the complexity and decreased the efficiency for the conversion from dc to HF ac. In this paper, a nine-level inverter employing only one input source and fewer components is proposed for HFAC PDS. It makes full use of the conversion of series and parallel connections of one voltage source and two capacitors to realize nine output levels, thus lower THD can be obtained without HFM methods. The voltage stress on power devices is relatively relieved, which has broadened its range of applications as well. Moreover, the proposed nine-level inverter is equipped with the inherent self-voltage balancing ability, thus the modulation algorithm gets simplified. The circuit structure, modulation method, capacitor calculation, loss analysis, and performance comparisons are presented in this paper, and all the superior performances of the proposed nine-level inverter are verified by simulation and experimental prototypes with rated output power of 200 W. The accordance of theoretical analysis, simulation, and experimental results confirms the feasibility of proposed nine-level inverter.

Electrical power system essentials

Abstract: Preface 1 Introduction to Power System Analysis 11 Introduction 12 Scope of the Material 13 General Characteristics of Power Systems 14 Phasors 15 Equivalent Line-To-Neutral Diagrams 16 Power in Single-phase Circuits 17 Power in Three-phase Circuits 18 Per Unit Normalization 19 Power System Structure 2 The Generation of Electric Energy 21 Introduction 22 Thermal Power Plants 23 Nuclear Power Plants 24 Renewable Energy 25 The Synchronous Machine 3 The Transmission of Electric Energy 31 Introduction 32 Transmission and Distribution Network 33 Network Structures 34 Substations 35 Substation Concepts 36 Protection of Transmission And Distribution Networks 37 Transformers 38 Power Carriers 4 The Utilization of Electric Energy 41 Introduction 42 Types of Load 43 Classification of Grid Users 5 Power System Control 51 Introduction 52 Basics of Power System Control 53 Active Power and Frequency Control 54 Voltage Control and Reactive Power 55 Control of Transported Power 56 Flexible AC Transmission Systems (FACTS) 6 Energy Management Systems 61 Introduction 62 Loadflow or Power Flow Computation 63 Optimal Powerflow 64 State Estimator 7 Electricity Markets 71 Introduction 72 Electricity Market Structure 73 Market Clearing 74 Social Welfare 75 Market Coupling 8 Future Power Systems 81 Introduction 82 Renewable Energy 83 Decentralized Or Distributed Generation 84 Power-electronic Interfaces 85 Energy Storage 86 Blackouts and Chaotic Phenomena Appendices A Maxwell's Laws A1 Introduction A2 Power Series Approach To Time-varying Fields A3 Quasi-Static Field Of A Parallel-plate Capacitor A4 Quasi-Static Field Of A Single-turn Inductor A5 Quasi-Static Field Of A Resistor A6 Circuit Modeling B Power Transformer Model B1 Introduction B2 The Ideal Transformer B3 Magnetically-Coupled Coils B4 The Non-ideal Transformer B5 Three-phase Transformer C Synchronous Machine Model C1 Introduction C2 The Primitive Synchronous Machine C3 The Single-phase Synchronous Machine C4 The Three-phase Synchronous Machine C5 Synchronous Generator In The Power System D Induction Machine Model D1 Introduction D2 The Basic Principle of The Induction Machine D3 The Magnetic Field In The Air-Gap D4 A Simple Circuit Model For The Induction Machine D5 Induction Motor In The Power System E The Representation of Lines And Cables E1 Introduction E2 The Long Transmission Line E3 The Medium-length Transmission Line E4 The Short Transmission Line E5 Comparison of The Three Line Models E6 The Underground Cable References List of Abbreviations List of Symbols Index

DC Grid Voltage Regulation Using New HESS Control Strategy

Abstract: The power generation from renewable power sources is variable in nature, and may contain unacceptable fluctuations in case of the wind power generation. High fluctuations in power generation may negatively impact the voltage stability of the microgrid. This problem can be alleviated by using hybrid energy storage system consisting of batteries and supercapacitors (SCs) at dc grid. A new control scheme is proposed to control the power sharing between batteries and SCs to match the generation-demand mismatch and hence to regulate the grid voltage. In the proposed control strategy, the SC supplies error component of the battery current in addition to the fast transient power demand. This added feature not only improves the dc grid voltage regulation capability but also reduces the stress levels on the battery and hence increases the life span of the battery. The main advantage of the scheme is that, the uncompensated power due to slow dynamics of the battery is diverted to the SC and keeps the state of charge within the limits for longer duration, as compared to the conventional strategy. The proposed scheme is validated through detailed experimental studies.

The bridge between the materials and devices of thermoelectric power generators

Abstract: While considerable efforts have been made to develop and improve thermoelectric materials, research on thermoelectric modules is at a relatively early stage because of the gap between material and device technologies. In this review, we discuss the cumulative temperature dependence model to reliably predict the thermoelectric performance of module devices and individual materials for an accurate evaluation of the p–n configuration compared to the conventional model used since the 1950s. In this model, the engineering figure of merit and engineering power factor are direct indicators, and they exhibit linear correlations to efficiency and output power density, respectively. To reconcile the strategy for high material performance and the thermomechanical reliability issue in devices, a new methodology is introduced by defining the engineering thermal conductivity. Beyond thermoelectric materials, the device point of view needs to be actively addressed before thermoelectric generators can be envisioned as power sources.

AC Stability Analysis and dq Frame Impedance Specifications in Power-Electronics-Based Distributed Power Systems

Abstract: Small-signal stability in balanced three-phase systems is typically investigated by means of the generalized Nyquist stability criterion (GNC) that involves operations on the source and load subsystems’ impedance matrices. Eigenvalues of the ratio of these impedance matrices should be calculated for stability judgment. This paper shows that for a power-electronics-based distributed power system, impedance matrices of subsystems can be designed as diagonal dominant. Therefore, stability, in this case, is fully determined by the scalar ratios formed by the impedance elements seen across the ${d}$ -axis and ${q}$ -axis interfaces. A three-phase ac system can then be treated as two decoupled dc systems. As a result, the ac stability analysis can also be conducted based on insightful impedance quantities; impedance specification criteria developed for dc systems can be readily applied to ensure stability in ac systems. The major contribution of this paper is related to the simplification of the GNC analysis with good experimental validations. Limitation of the proposed method is that the systems have to work under high power factor condition. However, such limitation is not a problem for many power-electronics-based distributed power systems.

Operation and Control of an Improved Hybrid Nine-Level Inverter

Abstract: This paper proposes a new nine-level inverter for medium- and high-power applications. The proposed topology comprises of a three-level (3L) active neutral-point-clamped (ANPC) inverter connected in series with a floating capacitor (FC) fed H-bridge. Besides, two additional switches operating at line frequency are appended across the dc link of the 3L ANPC structure. Compared with conventional hybrid cascaded inverters, the primary advantage of this addition is doubling of the resulting root mean square output voltage. This amelioration is achieved while preserving the standard 3L ANPC and H-bridge structures with minimum topological modification. A simple logic-gate-based voltage balancing scheme is developed to regulate the FC voltage. The proposed voltage balancing method is independent of load power factor, inverter modulation index, and can balance the voltage across FC instantaneously. The step-by-step formulation of logical expressions for the generation of gating pulses is deliberated in detail and can be generalized for any $n$ -level inverter. Further, simulation results as well as the experimental measurements obtained from the laboratory prototype are presented to validate the effectiveness and practicability of the proposed configuration. Finally, the notable merits of the proposed inverter over the prior art topologies is established through a comprehensive comparative study.

Review of GaN totem-pole bridgeless PFC

Abstract: Switching-mode AC/DC converters are widely used in modern power supplies for computers, data centers and telecommunication equipment. Achieving Power Factor Correction (PFC) and high efficiency are the two most important requirements. In many cases, high power density is also of tremendous interest. Both power efficiency and power density are greatly influenced by the power devices, the topology and the control used. Compared with conventional Si power MOSFET and Si super-junction MOSFET, the newly introduced 600 V GaN devices not only eliminate the reverser recovery, but also have much lower switching and driving losses. These excellent properties enable the emergence of the totem-pole bridgeless AC/DC converter as the next generation preferred solution for PFC instead of the state-of-the art Si-based boost PFC. In this paper, the key technologies and designs for both hard-switching and soft-switching GaN totem-pole PFC are reviewed and the key performance metrics are compared. A soft switching, 3.2 kW totem-pole PFC prototype with 99% efficiency and 130 W/inch3 power density has been achieved in the author's group as a proof of the concept. Based on the power density comparison, the high frequency soft-switching GaN totem-pole PFC is the preferred choice to achieve both high efficiency and high power density at the same time.

Delta Power Control Strategy for Multistring Grid-Connected PV Inverters

Abstract: With a still increasing penetration level of grid-connected photovoltaic (PV) systems, more advanced active power control functionalities have been introduced in certain grid regulations. A delta power constraint, where a portion of the active power from the PV panels is reserved during operation, is required for grid support (e.g., during frequency deviation). In this paper, a cost-effective solution to realize delta power control (DPC) for grid-connected PV systems is presented, where the multistring PV inverter configuration is adopted. This control strategy is a combination of maximum power point tracking (MPPT) and constant power generation (CPG) modes. In this control scheme, one PV string operating in the MPPT mode estimates the available power, whereas the other PV strings regulate the total PV power by the CPG control strategy in such a way that the delta power constraint for the entire PV system is achieved. Simulations and experiments have been performed on a 3-kW single-phase grid-connected PV system. The results have confirmed the effectiveness of the proposed DPC strategy, where the power reserve according to the delta power constraint is achieved under several operating conditions.

A Seven-Switch Five-Level Active-Neutral-Point-Clamped Converter and Its Optimal Modulation Strategy

Abstract: Multilevel inverters are receiving more attentions nowadays as one of preferred solutions for medium- and high-power applications. As one of the most popular hybrid multilevel inverter topologies, the five-level active-neutral-point-clamped inverter (5L-ANPC) combines the features of the conventional flying-capacitor type and neutral-point-clamped (NPC) type inverter and was commercially used for industrial applications. In order to further decrease the number of active switches, this paper proposes a seven-switch 5L-ANPC (7S-5L-ANPC) topology, which employs only seven active switches and two discrete diodes. The analysis has shown a lower current rating can be selected for the seventh switch under high power factor condition, which is verified by simulation results. The modulation strategy for 7S-5L-ANPC inverter is discussed. A 1 kVA single-phase experimental prototype is built to verify the validity and flexibility of the proposed topology and modulation method.

A Capacitance-Minimized, Doubly Grounded Transformer less Photovoltaic Inverter With Inherent Active-Power Decoupling

Abstract: Two major challenges in the transformerless photovoltaic (PV) inverters are the presence of common-mode leakage currents, and as in most single-phase converters the need for reliable and compact double-line-frequency power decoupling. In the proposed doubly grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the capacitive-coupled common-mode ground currents. The decoupling capacitance requirement is minimized by a dynamically variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The topology uses only four switches and potentially enables a high power density solution. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100/75 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output with a wide range of power factor has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. Extensive experimental results from the prototype are presented to validate the concept, design, and superior performance of the proposed topology.

High Step-Up Interleaved Boost Converter for Distributed Generation Using Renewable and Alternative Power Sources

Abstract: This paper proposes a novel high step-up interleaved boost converter suitable for distributed generation using renewable and alternative power sources. The proposed interleaved boost converter not only lengthens the lifetime of the renewable power source by reducing the input-current ripple but also achieves high step-up conversion. In addition, the voltage stress of the main switches is lowered due to the lossless passive-clamp circuit. Hence, large voltage spikes across the main switches are alleviated and the efficiency is improved. Finally, a prototype circuit with an input voltage of 48 V, an output voltage of 380 V, and an output rated power of 3.5 kW are implemented and tested to demonstrate the functionality of the proposed converter. Moreover, satisfying experimental results are obtained and discussed in this paper; the measured full-load efficiency is 94.7%, and the highest measured efficiency of the proposed converter is 97.3%.

A Wide Input Range Dual-Path CMOS Rectifier for RF Energy Harvesting

Abstract: This brief presents a dual-path CMOS rectifier with adaptive control for ultrahigh-frequency (UHF) RF energy harvesters. The input power range with high power conversion efficiency (high PCE) of the rectifier is extended by the proposed architecture, which includes a low-power path and a high-power path. The dual-path rectifier with an adaptive control circuit is fabricated in a 65-nm CMOS process. Operating at 900 MHz and driving a 147-kΩ load resistor, the measured PCE of this work can be maintained above 20% with an 11-dB input range from -16 to -5 dBm, while only an 8-dB input range can be achieved with traditional single-path rectifiers. A sensitivity of -17.7 dBm is measured with 1-V output voltage across a capacitive load.

A Single-Phase Integrated Onboard Battery Charger Using Propulsion System for Plug-in Electric Vehicles

Abstract: Plug-in electric vehicles (PEVs) are equipped with onboard level-1 or level-2 chargers for home overnight or office daytime charging. In addition, off-board chargers can provide fast charging for traveling long distances. However, off-board high-power chargers are bulky, expensive, and require comprehensive evolution of charging infrastructures. An integrated onboard charger capable of fast charging of PEVs will combine the benefits of both the conventional onboard and off-board chargers, without additional weight, volume, and cost. In this paper, an innovative single-phase integrated charger, using the PEV propulsion machine and its traction converter, is introduced. The charger topology is capable of power factor correction and battery voltage/current regulation without any bulky add-on components. Ac machine windings are utilized as mutually coupled inductors, to construct a two-channel interleaved boost converter. The circuit analyses of the proposed technology, based on a permanent magnet synchronous machine (PMSM), are discussed in details. Experimental results of a 3-kW proof-of-concept prototype are carried out using a ${\textrm{220-V}}_{{\rm{rms}}}$ , 3-phase, 8-pole PMSM. A nearly unity power factor and 3.96% total harmonic distortion of input ac current are acquired with a maximum efficiency of 93.1%.

Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower Multilevel Structures With Low Voltage Devices for Drives

Abstract: This paper proposes a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures. An important feature of this stacked structure is the use of low voltage devices while attaining higher number of levels. This will find extensive applications in electric vehicles since direct battery drive is possible. The voltages of all the capacitors in the structure can be controlled within a switching cycle using the switching state redundancies (pole voltage redundancies). This helps in reducing the capacitor size. Also, the capacitor voltages can be balanced irrespective of modulation index and load power factor. To verify the concept experimentally, a nine-level inverter is developed by stacking two five-level inverters and an induction motor is run using V/f control scheme. Both steady state and transient results are presented.

Novel Dynamic Voltage Support Capability of Photovoltaic Systems for Improvement of Short-Term Voltage Stability in Power Systems

Abstract: The large integration of photovoltaic (PV) power generation systems into power systems causes deterioration in power system stability. In our previous work, we showed that reactive power control using the inverters of PV systems, known as dynamic voltage support (DVS) capability, is a promising approach to improve the short-term voltage stability in power systems. In this paper, we propose a novel DVS capability as a function of PV inverters. In contrast to the conventional DVS capability, the proposed method uses both active and reactive power injection to improve the short-term voltage stability. Numerical examples show that the proposed DVS capability further improves the short-term voltage stability compared with the conventional DVS capability. Furthermore, the proposed method can alleviate a frequency drop after a fault caused by interruption in PV systems.

Management of Power Quality Issues in Low Voltage Networks Using Electric Vehicles: Experimental Validation

Abstract: As electric vehicles (EVs) are becoming more widespread, their high power consumption presents challenges for the residential low voltage networks, especially when connected to long feeders with unevenly distributed loads. However, if intelligently integrated, EVs can also partially solve the existing and future power quality problems. One of the main aspects of the power quality relates to voltage quality. The aim of this work is to experimentally analyze whether series-produced EVs, adhering to contemporary standard and without relying on any vehicle-to-grid capability, can mitigate line voltage drops and voltage unbalances by a local smart charging algorithm based on a droop controller. In order to validate this capability, a low-voltage grid with a share of renewable resources is recreated in SYSLAB PowerLabDK. The experimental results demonstrate the advantages of the intelligent EV charging in improving the power quality of a highly unbalanced grid.

A Novel Grid-Connected PV System Based on MMC to Get the Maximum Power Under Partial Shading Conditions

Abstract: In the case of partial shading, the output power of the unshaded PV modules will be decreased by the influence of the shaded PV modules in one branch. In order to solve this problem, this paper proposes a novel topology for a PV power generation system by connecting a PV module to the capacitor in each submodule of a modular multilevel converter parallel. As partial shading occurs, the maximum power can be extracted by regulating the capacitor voltage to the maximum power point voltage. With this proposed topology, the maximum power tracking controller, the redundancy module controller, the voltage stability controller, and the grid-connected controller are studied. Simulation and experiment results show that comparing to the traditional topology, the proposed topology can greatly improve the output power of the PV system under the conditions of partial shading and features with low-voltage stress and high efficiency.

A SiC-Based High-Efficiency Isolated Onboard PEV Charger With Ultrawide DC-Link Voltage Range

Abstract: In LLC-based onboard battery charging architectures used in plug-in electric vehicles (PEV), the dc link voltage can be actively regulated to follow the battery pack voltage so that the LLC converter can operate in proximity of resonant frequency and achieve high efficiencies over the wide range of battery pack voltage. However, conventional boost-type power factor correction (PFC) converters are unable to provide ultrawide dc link voltages since their output voltages should always be larger than their input voltages. This paper proposes a Silicon Carbide (SiC)-based onboard PEV charger using single-ended primary-inductor converter (SEPIC) PFC converter followed by an isolated LLC resonant converter. With the proposed charger architecture, the SEPIC PFC converter is able to provide an ultrawide range for dc link voltage, and consequently enhance the efficiency of the LLC stage by ensuring operation in proximity of resonant frequency. A 1-kW SiC-based prototype is designed to validate the proposed idea. The experimental result shows that the SEPIC PFC converter achieves unity power factor, 2.72% total harmonic distortion, and 95.3% peak conversion efficiency. The LLC converter achieves 97.1% peak efficiency and always demonstrates a very high efficiency across the ultrawide dc-link voltage range. The overall efficiency of the charger is 88.5% to 93.5% from 20% of the rated load to full load.

A Fully Integrated Reconfigurable Self-Startup RF Energy-Harvesting System With Storage Capability

Abstract: This paper introduces a fully integrated RF energy-harvesting system. The system can simultaneously deliver the current demanded by external dc loads and store the extra energy in external capacitors, during periods of extra output power. The design is fabricated in 0.18-μm CMOS technology, and the active chip area is 1.08 mm 2 . The proposed self-startup system is reconfigurable with an integrated LC matching network, an RF rectifier, and a power management/controller unit, which consumes 66-157 nW. The required clock generation and the voltage reference circuit are integrated on the same chip. Duty cycle control is used to operate for the low input power that cannot provide the demanded output power. Moreover, the number of stages of the RF rectifier is reconfigurable to increase the efficiency of the available output power. For high available power, a secondary path is activated to charge an external energy storage element. The measured RF input power sensitivity is -14.8 dBm at a 1-V dc output.

Low-Complexity Adaptive Multisine Waveform Design for Wireless Power Transfer

Abstract: Channel-adaptive waveforms for wireless power transfer significantly boost the dc power level at the rectifier output. However, the design of those waveforms is computationally complex and does not lend itself easily to practical implementation. We here propose a low-complexity channel-adaptive waveform design whose performance is very close to that of the optimal design. Performance evaluations confirm the advantages of the new design in various rectifier topologies, with gains in dc output power of 100% over conventional waveforms.

High-Efficiency Wireless Power Transfer System for Electric Vehicle Applications

Abstract: In this brief, a high-efficiency wireless power transfer (WPT) system for electric vehicle charging application is studied and implemented. Series–series resonant topology with RF feedback design is adopted as the WPT dc–dc stage due to the advantages of circuit simplicity, easy analysis, and control. A 500-W laboratory prototype is built and tested to verify the feasibility of the proposed design. According to the experimental results, high wall-to-battery efficiency and unity power factor can be achieved over an air gap of 15 cm and maximum sliding distance of 10 cm under various power conditions and universal input voltage from 90VAC to 264VAC.

Voltage Control with PV Inverters in Low Voltage Networks—In Depth Analysis of Different Concepts and Parameterization Criteria

Abstract: In some rural and sub-urban areas, the hosting capacity (HC) of low voltage networks is restricted by voltage limits. With local voltage control, photovoltaic generators can mitigate the voltage rise partly and, therefore, increase the HC. This paper investigates the effectiveness and general performance of different reactive and active power control concepts. It presents the findings of an extensive simulation-based investigation into the effectiveness of voltage rise mitigation, additional reactive power flows, network losses, and power curtailment. The two most common implementations of reactive power control have a similar effectiveness. The voltage rise can be compensated for by up to 25% and more than 60% for typical cable and overhead (OH) feeders, respectively. By additionally using active power curtailment of up to 3% of the annual yield, the HC can be increased by about 50% and 90% for the considered cable and OH feeder, respectively (purely rural feeders).