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This article presents an interleaved buck-type rectifier with pseudo-dc-link capacitors featuring automatic current balancing, soft-switching operation, efficient ac-dc conversion, and tight output regulation. The ac-input-current-synchronized modulation scheme that hybridizes for cycle-by-cycle phase-shift and duty ratio adjustment is adopted for zero-voltage switching (ZVS) operation and output regulation. In addition, the pseudo-dc-link capacitors facilitate the convergence and current balancing between output inductors. Mathematical models are provided to quantitatively describe the mechanism of current balancing, steady-state performance, and dynamic response. A lab prototype is built, and the experimental results are provided to verify the features. [ABSTRACT FROM AUTHOR]

Harmonic current estimation is required in active power filters for compensation purposes. The most efficient way of calculating the total harmonic current up to the infinite order is to subtract the fundamental component from the distorted current. Direct determination of the fundamental component of a distorted current of mains frequency was realized recently with a third-order modulation integral observer. This article shows that using an exponential modulation function (Exp-MF) for the integral observer will: 1) significantly enhance the robustness of the observer against noise and 2) automatically remove the low-frequency envelope arising from the D/A and A/C sampling processes compared to previous polynomial modulation function. These new and advantageous features are supported with detailed analysis and experimental verification. The robust observer can be implemented in grid-connected power electronics circuits that require the instantaneous information of the fundamental and/or harmonic currents. Practical comparative tests with the adaptive notch filter and recursive discrete Fourier transform (DFT) methods in an active power filter have confirmed the good performance under both the steady and dynamic states of the proposed Exp-MF integral observer. [ABSTRACT FROM AUTHOR]

This article proposes a simple multivector predictive direct power control (P-DPC) using geometric modulation. Different from the conventional counterpart using two active and one zero vector, the proposed multivector P-DPC uses a primary and a secondary equivalent vector having the opposite angular position to synthesise the voltage reference acquired from the deadbeat calculation. The generic equation of the rectifier voltage is established to calculate the primary and the secondary equivalent vectors as the weighted sum of two active vectors. The duty cycle optimization is achieved by combining the coefficients of the two equivalent vectors and the length ratio of the reference amplitude compared with the maximum rectifier voltage. The proposed multivector P-DPC offers a simple solution of duty cycle optimization that circumvents the calculation of instantaneous power rates and complex differential equations prevalent in conventional multivector approaches. This significant reduction of control complexity makes the proposed approach suitable to be implemented in low-cost microcontroller units. Experimental and simulation results have demonstrated the effectiveness of the new method. [ABSTRACT FROM AUTHOR]

A generic red, green, and blue (RGB) LED system encompasses complex interactions of power, heat, light, and color, which pose a major challenge for achieving precise control over luminance and color-mixing in high-quality lighting applications. In this article, new nonlinear empirical models of a practical RGB LED system with closed-loop control are formulated. They enable precise prediction of luminous flux and color coordinates by using the three distinct reference voltages as the control variables for independent current regulation across the RGB LED strings. The proposed empirical models are experimentally verified by using a hardware prototype of a dc–dc single-inductor three-output LED driver with proportional–integral compensators and time-interleaving control scheme. The measured values of luminous flux and color coordinates agree closely with the predicted values from the models. [ABSTRACT FROM AUTHOR]

Starting from the principle of instantaneous power theory, this article explores various direct power control (DPC) strategies for three-phase two-level pulsewidth modulation (PWM) converters. After summarizing the fundamental power formula of PWM rectifiers, this article studies the operating principle of the conventional table-based approach and its related improvements. It further looks into the advanced counterparts employing space vector modulation and different nonlinear control strategies. The emphasis is put on the prevailing predictive DPC. Besides, the voltage-sensorless and robust DPC methods based on the virtual flux concept and the state observer or estimator are investigated. Critical issues, including the sample delay, constant switching frequency, duty cycle optimization, objective function, and unbalanced operation are examined. [ABSTRACT FROM AUTHOR]

The energy efficiency of an inductive wireless power transfer (WPT) system will deviate from the possible peak value if the magnetic coupling of the transmitter and receiver coils or the load resistance changes. To achieve maximum-efficiency tracking regardless of coupling or load changes, on–off keying (OOK) modulation is used. However it has the issue of large surge current in the circuits during OOK modulation. The current overshoots of a series–series (SS) compensated WPT system at the startup stage might be much higher than the rated current. The current overshoots not only increase the stress on the power switch devices but also cause high voltage spikes across the windings and the resonant capacitors which is a challenge for insulation design. A soft-start scheme is proposed to address the current overshoot problem. The principle of the soft-start scheme can be essentially applied to WPT systems with different compensation topologies. The experimental results of a 3.3-kW prototype verify that the proposed soft-start scheme effectively suppress the current overshoots. [ABSTRACT FROM AUTHOR]

While detection of foreign or unintended metallic objects is an important topic for wireless power transfer (WPT), operation of WPT systems with intended metallic objects is largely an unchartered territory. This article presents a methodology for analyzing the effects of intended metallic object on a WPT system through the study of the magnetic field distribution and the use of a reduced-order equivalent model of the systems for comparing the WPT system with and without the metallic object. The methodology is applied to a metallic corona ring of low resistance used with a WPT system. The analysis quantifies how an intended metallic object could change the magnetic coupling between the transmitter and receiver coils, and alter the equivalent resonant tank parameters of the WPT system. Recompensation of the resonant tank can only enhance the power transfer capability but not the energy efficiency. The theory and practical verification of a new performance-enhancement method based on a combination of recompensating the resonant tanks and maximizing the equivalent mutual inductance of the Tx and Rx coils is presented. Such methodology provides a general approach to analyze WPT systems with or without relay resonators in the presence of intended metallic objects. [ABSTRACT FROM AUTHOR]

In this article, a single-inductor multiple-output (SIMO) inverter with precise and independent output voltage regulation is presented. This SIMO inverter with controllable output voltage enables each individual transmitting coil in a multicoil wireless power transfer system to be driven by a tightly regulated constant-voltage source. This is especially useful for the wireless charging of rechargeable batteries when they act as a constant-current (CC) load in the CC charging phase. By precisely regulating the source voltage at each transmitting coil, a constant load current at the corresponding receiver can be achieved at a particular resonant frequency and mutual inductance between the transmitting and receiving coil. The closed-form expressions of the sinusoidal-like output voltage and resonant inductor current as a function of the duty ratio of the main switch are also analytically derived. An experimental prototype of a single-inductor three-output inverter with a single time-multiplexed analog-based controller employing the type II compensation is implemented. It is experimentally verified that the individual ac outputs can be accurately and independently controlled. The maximum error between the target and measured peak voltage values is shown to be within 1.14%. [ABSTRACT FROM AUTHOR]

The inertia of future power systems is expected to decrease with increasing penetration of renewable energy resources. Sufficient inertia is required to avoid large fluctuations in grid frequency and also limit the excessive rate of change of frequency (RoCoF). Unlike many previous works focusing on virtual inertia on the power supply side, this paper studies and quantifies potential virtual inertia from the load side. The analysis shows that, voltage-dependent loads coupled with electric spring (ES) technology can be operated as smart loads (SL) within the +/−5% tolerance of the ac mains voltage and offer virtual inertia. Following the U.K. National Grid frequency requirements, it is shown that the ES based SL can provide virtual inertia up to an inertia coefficient of $H_{SL}=2.5$ s (when $n_{p}=2$) with respect to its load power rating. The effectiveness of such virtual inertia extraction from SL has been verified by the simulation study on a CIGRE benchmark microgrid with high-resolution domestic demand model. The value of $H_{SL}$ is shown to be around 1.3 s during the most part of the day and can increase the overall system inertia coefficient by 0.53 s if all the domestic loads are transformed into the proposed smart loads. [ABSTRACT FROM AUTHOR]

In this paper, a voltage sensorless controller is developed for a two-switch single-phase rectifier that involves power factor correction and active pulsating power buffering without electrolytic capacitors. While a two-switch rectifier normally requires four sensed signals for control, only one current sensor is required in this proposal, thereby offering advantages such as low cost, high compactness, isolation between control and power circuits, and improved reliability. While the basic operating principle follows that of a conventional voltage sensorless controller for single-switch converters, several critical design considerations are the key to the success of the implementation which is explained in detail. The feasibilities of the controller are experimentally testified with a 100-W rectifier prototype regarding both steady state and dynamic performance. [ABSTRACT FROM AUTHOR]

Single-phase power converters with the active pulsating-power-buffering (PPB) function are essentially highly coupled and nonlinear systems. Advanced control techniques are needed for this emerging class of converters to achieve fast transient response and large-signal stability. Existing control solutions are based on either 1) linear control techniques that are operating-point specific or 2) nonlinear control techniques that are generally topology-dependent. The proposed work is an evolved generalized feedback-linearization (FBL) control approach that incorporates the direct Lyapunov control method. The proposed control provides good stabilization of the internal dynamics of the system (which is unviable with FBL control) while still retaining all the best features of FBL control. A kind of single-phase power conversion system with active PPB is described. It is shown that FBL control naturally destabilizes the system and that the proposed control can globally stabilize the system under various operating conditions while yielding fast dynamics. [ABSTRACT FROM AUTHOR]

Optical measurements based on integrating sphere are primary suitable for steady-state measurements and unsuitable for dynamic real-time measurements. This paper presents an alternative method using the combination of a photodetector system and the dynamic photo-electro-thermal theory for real-time optical measurements. It is demonstrated that the voltage output of a photodetector can be correlated to the optical power in real time. Such method has been successfully applied to analyze a phosphor-converted white light-emitting diode (PC white LED) using an extended dynamic model with separate calculations of optical power from the blue LED chips and phosphor layer. Both calculated and practical results are included to confirm the validity of the new method. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) has been proposed as an effective control method for pulsewidth modulated (PWM) converters. The recent development focuses on the integration of the model predictive (MP) control and DPC to obtain better steady-state performance. In most MP-DPCs, duty cycle optimization (DCO) is a common technique to achieve the power error minimization. However, the periodic occurrence of a duty cycle larger than one (D > 1) deteriorates the performance of the PWM converter by inducing current spikes and power surges. To address this problem, this paper conducts an in-depth examination on the “D > 1” case common in MP-DPC using DCO. It is found the “D > 1” case is caused by the wrong control action of the active power in the starting period of each sector. Furthermore, a new table containing an additional pre-calculated interval in every sector is developed to eradicate the “D > 1” case and its associated power quality issues. Both simulation and experimental results are provided to demonstrate the effectiveness of the new table. [ABSTRACT FROM AUTHOR]

A component-minimized and low-voltage-stress single-phase power factor correction rectifier without electrolytic capacitor is proposed in this paper. Component minimization is achieved by embedding an active pulsating-power-buffering (PPB) function within each switching period, such that typical add-on power electronic circuits for PPB are no longer needed. Additionally, with a three-level flying-capacitor configuration, the voltage stresses of switching devices can be reduced more than 50% as compared to existing solutions that are based on embedded PPB. The relationship between the inductance requirement and the patterns of the modulation carriers, and how it can be utilized to minimize the magnetics of the rectifier, is also discussed. A 110 W hardware prototype is designed and tested to demonstrate the feasibilities of the proposed rectifier. An input power factor of more than 0.97, peak efficiency of 95.1%, and an output voltage ripple of less than 4.3% across a wide load range have been experimentally obtained. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions. [ABSTRACT FROM AUTHOR]

In this paper, a nonisolated buck-boost single-inductor multiple-output (SIMO) dc–ac inverter for driving multiple independent high-frequency ac outputs of medium power is proposed. Compared with traditional bridge-type inverters, the proposed buck-boost SIMO inverter achieves 1) a smaller component count, 2) fully independent power control of its outputs, 3) better scalability in increasing the number of ac output channels, and 4) higher power efficiency. Operating in pseudo-continuous conduction mode, the rated power of each output channel of this inverter can be high while attaining zero cross regulation. The scalability factor of the proposed inverter is formally investigated and the theoretical maximum number of ac outputs is analytically derived. The targeted application of this SIMO-based inverter is for driving multiple transmitter coils to realize versatile multidevice medium-power wireless power transfer. A hardware prototype of a single-inductor three-output buck-boost inverter delivering a medium power of 8.4 W per output channel has been constructed. It is experimentally verified that precise and independent current regulation of individual transmitter coil is achievable with the proposed inverter. [ABSTRACT FROM AUTHOR]

The renewable generations (RGs) are conventionally interfaced with the utility grid through battery energy storage systems (BESS). In this cascaded configuration of the grid-connected inverter, battery, and RG, the power of the battery is passively governed by the power difference between the RG and the grid. This compromises the state-of-charge (SoC) control of the battery and increases the storage capacity. To address this issue, a hybrid electric spring (HES), which is integrated with the RG and noncritical load (NCL), is proposed in this paper for the grid-tied power control and reduction of battery storage capacity in ac microgrids. Such an integrated configuration enables a flexible control of the power flow among battery, NCL, and grid. On top of that, the proposed HES can achieve an extended operating region of grid-tied power control compared with the conventional BESS and the existing electric springs. The operating principle, steady-state analysis, and control design of the HES are discussed. The functions of the grid-tied power control and battery SoC control are verified experimentally and through simulations. [ABSTRACT FROM AUTHOR]

Light-emitting diode (LED)-based visible light communication (VLC) has recently been promoted by the lighting industry for providing services and information for consumers in shopping malls. Communication system designs require well-defined signal-to-noise ratio (SNR). Being semiconductor devices, both LEDs and photodetectors are highly temperature-sensitive. This paper explores the electrical and thermal sensitivities of LED and photodetector together for VLC applications, and highlights the discoveries that the SNR of LED-based VLC could vary substantially over the full operating power range of the LED lighting systems. A new analysis of the SNR based on the photoelectrothermal theory has been developed. It can be used as the theoretical and design tool to predict such SNR variations. The validity of the new analysis has been confirmed with practical measurements that are consistent with theoretical predictions. The analytic approach can in principle be used as a design tool for LED-based VLC. [ABSTRACT FROM AUTHOR]

In this paper, the smart load formed by the back-to-back electric springs (ES-B2B) is evaluated for improving the fault-ride through (FRT) capability of the wind turbine generation system with fixed speed induction generator (FSIG) for the first time. The characteristic of the ES-B2B in providing fast reactive power compensation is found to be highly useful in recovering the rotor speed of FSIGs when a fault event occurs. This is a new function in addition to the original function of stabilizing mains voltage against renewable generations. A simple and yet effective controller is then developed for the ES-B2B in order to ensure fast response. The ES-B2B-based smart load and the proposed control have been tested in MATLAB/Simulink and real-time digital simulator to evaluate: 1) the reactive power compensation capability of ES-B2B; 2) the effectiveness of the proposed control of ES-B2B for FRT support; and 3) the comparison of distributed ES-B2Bs with centralized STATCOM in providing distributed FRT support in different grid topologies. [ABSTRACT FROM AUTHOR]

Optimum energy efficiency in a wireless power transfer (WPT) system usually occurs only at a specific load value while the load such as a battery is normally not constant. A major challenge in WPT is, therefore, to achieve high energy efficiency over a wide load range. Previously, impedance transformation methods such as dc–dc converters and use of a relay coil have been used to transform the practical load resistance to the optimum (or near-optimum) value. In this paper, a new approach based on reconfigurable magnetic resonant structures is proposed to achieve high energy efficiency and low volt-amp ratings. This basic principle is to create more than one efficiency–load curve. The WPT system is controlled to be operated within the top regions of the energy efficiency curves of the reconfigurable circuits so that high energy efficiency can be achieved over a very wide load range. The principle of this new approach is explained with an analysis and verified with practical measurements. [ABSTRACT FROM PUBLISHER]

Three-phase electric spring (3-ph ES) has recently been proposed as a fast demand response technology for applications in unbalanced power systems fed with a mixture of conventional and renewable power generation. Using the instantaneous power theory as the theoretical framework, this paper presents the criteria and conditions for minimizing the average and oscillating power of the 3-ph ES for the first time. A detailed analysis of the use of 3-ph ES is included for providing multiple control objectives of voltage regulation and power balancing of the 3-ph power system, and minimization of the average and oscillating ac power of the ES. A corresponding control scheme implementable in a single controller is included and explained. The control scheme has been practically verified with experiments. [ABSTRACT FROM PUBLISHER]

High-power light-emitting diodes (LEDs) having properties of high luminous efficacy and long life span are becoming a major light source for general illumination. To fully utilize the advantages of LED in lighting applications, the offline power supply that drives the LED should possess the following features: high efficiency, long life span, high input power factor, and (COC). In this paper, high efficiency is achieved by using a minimal power processing (MPP) configuration. Near perfect power factor correction (PFC) is achieved by a simple dual-output disc-ontinuous-conduction-mode (DCM) pulse-width-modulated (PWM) front-end converter. One output of the front-end converter is connected to the LED load using a control switch. The other output is connected directly to a dc storage capacitor cascaded with a downstream DCM PWM converter driving the same LED load to achieve COC driving. The power flow is controlled to achieve the required MPP that can also reduce the storage capacitance by balancing only the ac input ripple power and the dc output power without power recycling. Thus, the design requires no electrolytic capacitor, hence extending the system life span. The achievement of input PFC, MPP, and COC requires design tradeoff among design freedom, ease of control and component count. LED drivers having all these properties are developed, designed, and tested. [ABSTRACT FROM PUBLISHER]

In this paper, a nonisolated dc−ac inverter topology, which enables a true single-stage direct conversion from a single dc input supply to multiple ac output power sources by using only one inductor in the power stage, is proposed. Compared with the conventional multiple-output parallel half-bridge or full-bridge inverters, the proposed single-stage single-inductor multiple-output (SIMO) inverter topology achieves a smaller number of inductors and power switches, high power density, scalability to multiple ac outputs, and independent power controllability for each ac output. A useful application of the proposed SIMO inverter is to drive an array of transmitting coils simultaneously for wireless power transfer applications. An experimental prototype has been developed to demonstrate the effectiveness of a single-inductor three-output boost-derived inverter without cross regulation. Experimental results show that precise and independent peak voltage regulation of each individual sinusoidal ac output is attainable with the proposed SIMO inverter. [ABSTRACT FROM AUTHOR]

Battery energy storage systems are often adopted to buffer the difference between the intermittent solar power and the load demand in power grids. The costs of such photovoltaic (PV) battery systems increase as the required energy storage increases. In this paper, a new configuration comprising the PV panels, a series dc electric spring (series ES) and a noncritical load is proposed to reduce the battery storage capacity of dc microgrids that have substantial PV installations. This arrangement forms a PV-embedded series dc ES (PVES). An optimization method considering the minimization of electricity bills of the dc microgrids is included to size the storage capacity and to determine the rating of the PV that are connected to the series ES. Experiments on a 48-V isolated dc grid and simulations on a 400-kVA grid-connected dc microgrid have been conducted to verify the storage reduction feature of the PVES. Both sets of results show that the PVES can tackle the intermittency of the solar power with a smaller storage capacity than that typically required in dc grids with PV installations. [ABSTRACT FROM AUTHOR]

Electric springs (ESs) have been proposed as a distributed demand-response technology for mitigating voltage and frequency fluctuations of ac power systems fed by substantial intermittent renewable energy. This paper extends this concept to the development of DCESs for voltage regulation of emerging dc power grids. The configurations of series and shunt DCES and their respective operating modes are explained. Both types of ES and their functionalities for dc bus voltage regulation, double-line frequency harmonic compensation, and providing fault-ride-through support are discussed. The proposed DCES has been successfully applied to a 48 V dc microgrid system for experimental verification. The results show a good agreement with the theoretical analysis, confirming that the DCES can be an effective solution to provide simultaneous functions of dc microgrid bus voltage regulation. [ABSTRACT FROM PUBLISHER]

Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the use of magnetic resonance technique at a certain load resistance value. However, practical load resistance is not constant. Previously, a switched mode dc–dc converter was used in the receiver circuit to emulate an equivalent load resistance for maximum energy efficiency. In this paper, a new approach based on the On–Off Keying is proposed to achieve the high energy efficiency operation over a wide range of load power without using an impedance-matching dc–dc power converter. This simple and effective method has reduced average switching frequency and switching losses. It can be applied to any series-series resonant WPT system designed to operate at a constant output voltage. Practical measurements have confirmed the validity of the proposal. [ABSTRACT FROM PUBLISHER]

High-voltage insulation (HVI) strings are commonly used to hold high-voltage electric cables and electrically isolate them from the grounded transmission tower. In this paper, a novel concept of an electric insulation string with HVI and wireless power transfer (WPT) capabilities is presented. Based on the concept of the domino-resonator WPT system, this new structure consists of coil resonators embedded inside totally sealed insulation discs, which are then connected in series to form the new insulation string structure with the simultaneous HVI and WPT functions. This structure allows energy harvested from the ac magnetic field around the high-voltage cable to be transmitted wirelessly to power an online monitoring system in high-voltage transmission tower continuously, thereby reducing the storage requirements of the battery. The design and analysis of this new WPT structure based on the dimensions of commercially available HVI rod are included. Practical measurements obtained from a hardware prototype of about 25 W have been obtained to confirm the WPT capability of the proposal. An energy efficiency of more than 60% has been achieved for a transmission distance of 1.1 m over a wide range of load. [ABSTRACT FROM PUBLISHER]

A new wireless power transfer (WPT) system based on ball-joint structure is presented in this paper. A ball-joint WPT system consists of a ball structure with a mechanical rod attached to the ball and a ball socket that accommodates the ball structure. This ball-joint structure comprises at least one winding in the ball structure and at least one winding in the ball socket structure. The ball structure can be flexibly rotated over a wide range of angle inside the ball socket, while wireless power can still be transferred from the transmitter winding to the receiver winding through magnetic resonance. The magnetic coupling coefficient between the transmitter and receiver coil over a wide rotating angular range has been analyzed and experimentally checked. Experimental results confirm that an energy efficiency of up to 81% can be achieved. [ABSTRACT FROM PUBLISHER]