Publications
496 results found
Li S, Guo Y, Tan S-C, et al., 2016, An Off-line Single-Inductor Multiple-Output LED Driver With High Dimming Precision and Full Dimming Range, IEEE Transactions on Power Electronics, Vol: 32, Pages: 4716-4727, ISSN: 0885-8993
This paper presents a single-inductor multiple-output (SIMO) LED driver with precise dimming and full dimming range. Based on the coordination of a string-level scheme and a system-level dimming scheme, the proposed SIMO LED driver can overcome practical constraints of existing SIMO LED drivers such as limited dimming range and needs for high-current switches. The proposal can achieve dimming precision up to an accuracy of 0.8% and also full dimming range. It has the flexibility of using either phase-shift or synchronous pulsewidth-modulated (PWM) switching for dimming control. The proposed circuit and control operations have been practically verified with a 25-W off-line SIMO-driven LED system. Practical evaluations of its power quality and energy efficiency are also provided.
Akhtar Z, Chaudhuri B, Hui SYR, 2016, Smart loads for voltage control in distribution networks, Power and Energy Society General Meeting (PESGM), 2016, ISSN: 1944-9933
Luo X, Akhtar Z, Lee CK, et al., 2016, Distributed voltage control with electric springs: Comparison with STATCOM, Power and Energy Society General Meeting (PESGM), 2016, ISSN: 1944-9933
Zhang C, Lin D, Hui SY, 2016, Basic control principles of omnidirectional wireless power transfer, IEEE Transactions on Power Electronics, Vol: 31, Pages: 5215-5227, ISSN: 0885-8993
This paper presents the basic control principles of omnidirectional wireless power transfer (WPT) based on the current amplitude control. The principles involve 1) an “omnidirectional” scanning process for detecting the power requirements in a 3-D space and 2) a “directional” power flow control for focusing the wireless power toward the targeted areas. Such principles apply to any WPT system comprising three orthogonal transmitter coils and multiple receivers with coil resonators. A current amplitude control method capable of generating a magnetic vector at a set of points evenly distributed on a spherical surface is explained. Based on the voltage and the current information in the transmitter circuit, the power involved in each vector over the spherical surface can be obtained. By scanning the vector over the spherical surface, the collective power flow requirements for the targeted loads can be determined. Based on the power requirements for the vectors over the spherical surface, a weighted time-sharing scheme is adopted to focus the wireless power toward the targeted areas. This method has been successfully applied to a hardware prototype. Both theoretical and experimental results are included to confirm these principles.
Chen HT, Tan SC, Lee ATL, et al., 2016, Precise color control of red-green-blue light-emitting diode systems, IEEE Transactions on Power Electronics, Vol: 32, Pages: 3063-3074, ISSN: 0885-8993
© 1986-2012 IEEE. The complex nature and differences of the luminous and thermal characteristics of red, green, and blue (RGB) light-emitting diodes (LEDs) make precise color control of RGB LED systems a great technological challenge. This paper presents a nonlinear model that includes coupling effects among LED devices for predicting color in RGB LED systems. A control method is included to demonstrate that this model can be used for precise color control. The proposed model and control method have been successfully evaluated in practical tests. The measurements agree well with model predictions. They form a new design tool for precise color control of RGB LED systems.
Chen B, Pin G, Ng WM, et al., 2016, A fast-convergent modulation integral observer for online detection of the fundamental and harmonics in grid-connected power electronics systems, IEEE Transactions on Power Electronics, Vol: 32, Pages: 2596-2607, ISSN: 1941-0107
Harmonics detection is a critical element of activepower filters. A previous review has shown that the RecursiveDiscrete Fourier Transform and the Instantaneous p-q Theory areeffective solutions to extracting power harmonics in single-phaseand three-phase power systems, respectively. This paper presentsthe operating principle of a new modulation function integralobserver algorithm that offers a fast solution for the extraction ofthe fundamental current and the total harmonic current whencompared with existing methods. The proposed method can beapplied to both single- and three-phase systems. The observerbasedalgorithm has an advantageous feature of being able to betuned offline for a specific application, having fast convergenceand producing estimated fundamental component with highcircularity. It has been tested with both simulations and practicalmeasurements for extracting the total harmonic current in ahighly efficient manner. The results have confirmed that theproposed tool offers a new and highly effective alternative to thesmart grid industry.
Li S, Lee ATL, Siew-Chong-Tan, et al., 2016, A plug-and-play ripple mitigation approach for DC-links in hybrid systems, APEC 2016, Publisher: IEEE, Pages: 169-176
In this paper, a plug-and-play ripple mitigation technique is proposed. It requires only the sensing of the DC-link voltage and can operate fully independently to remove the low-frequency voltage ripple. The proposed technique is nonintrusive to the existing hardware and enables hot-swap operation without disrupting the normal functionality of the existing power system. It is user-friendly, modular and suitable for plug-and-play operation. The experimental results demonstrate the effectiveness of the ripple-mitigation capability of the proposed device. The DC-link voltage ripple in a 110 W miniature hybrid system comprising an AC/DC converter and two resistive loads is shown to be significantly reduced from 61 V to only 3.3 V. Moreover, it is shown that with the proposed device, the system reliability has been improved by alleviating the components' thermal stresses.
Yang Y, Tan SC, Hui SY, 2016, Adaptive reference model predictive control for power electronics, APEC 2016, Publisher: IEEE, Pages: 1169-1175
An adaptive reference model predictive control (ARMPC) approach is proposed as an alternative means of controlling power converters in response to the issue of steady-state residual errors presented in power converters under the conventional model predictive control (MPC). Differing from other methods of eliminating steady-state errors of MPC based control, such as MPC with integrator, the proposed ARMPC is designed to track the so-called virtual references instead of the actual references. Subsequently, additional tuning is not required for different operating conditions. In this paper, ARMPC is applied to a single-phase full-bridge voltage source inverter (VSI). It is experimentally validated that ARMPC exhibits strength in substantially eliminating the residual errors in environment of model mismatch, load change, and input voltage change, which would otherwise be present under MPC control. Moreover, it is experimentally demonstrated that the proposed ARMPC shows a consistent erasion of steady-state errors, while the MPC with integrator performs inconsistently for different cases of model mismatch after a fixed tuning of the weighting factor.
Chung H, Hui SY, 2016, Sustainable lighting technology, Power Electronics and Motor Drives, Pages: 28.1-28.21, ISBN: 9781138077478
Hui SY, 2016, General photo-electro- thermal theory and its implications for light- emitting diode systems, Power Electronics and Motor Drives, Pages: 29.1-29.12, ISBN: 9781138077478
Chakravorty D, Chaudhuri B, Hui SYR, 2016, Rapid Frequency Response from Smart Loads in Great Britain Power System, IEEE Transactions on Smart Grid, Vol: 8, Pages: 2160-2169, ISSN: 1949-3053
Flexibility in certain types of loads could be exploited to provide fast and controllable power reserve if the supply voltage/frequency is controlled using existing power electronic interfaces (e.g. motor drives) or additional ones like recently proposed Electric Springs. Such a load together with its power electronic interface forms a so called ‘smart load’. Effectiveness of static smart loads for primary frequency response provision has been shown in previous papers through case studies ona segment of the LV/MV distribution network. In this paper, collective contribution of both static and motor type smart loads to rapid frequency response provision is demonstrated through a case study on the Great Britain (GB) transmission system. The active power reserve available from such smart loads are quantified and aggregated at each node at the transmission level (275/400 kV). The study shows that the smart loads collectively offer a short-term power reserve which is comparable to the spinning reserve in the GB system and thus can ensure acceptable frequency deviation and its rate of change (RoCoF) following a large infeed loss.
Wu FF, Varaiya PP, Hui RSY, 2016, Smart Grids with Intelligent Periphery: An Architecture for the Energy Internet, Engineering, Vol: 1, Pages: 436-446, ISSN: 2095-8099
A future smart grid must fulfill the vision of the Energy Internet in which millions of people produce their own energy from renewables in their homes, offices, and factories and share it with each other. Electric vehicles and local energy storage will be widely deployed. Internet technology will be utilized to transform the power grid into an energy-sharing inter-grid. To prepare for the future, a smart grid with intelligent periphery, or smart GRIP, is proposed. The building blocks of GRIP architecture are called clusters and include an energy-management system (EMS)-controlled transmission grid in the core and distribution grids, micro-grids, and smart buildings and homes on the periphery; all of which are hierarchically structured. The layered architecture of GRIP allows a seamless transition from the present to the future and plug-and-play interoperability. The basic functions of a cluster consist of ① dispatch, ② smoothing, and ③ mitigation. A risk-limiting dispatch methodology is presented; a new device, called the electric spring, is developed for smoothing out fluctuations in periphery clusters; and means to mitigate failures are discussed.
Mok KT, Wang MH, Tan SC, et al., 2016, DC electric springs - A technology for stabilizing DC power distribution systems, IEEE Transactions on Power Electronics, Vol: 32, Pages: 1088-1105, ISSN: 0885-8993
There is a growing interest in using dc power systems and microgrids for our electricity transmission and distribution, particularly with the increasing penetration of photovoltaic power systems. This paper presents an electric active suspension technology known as the dc electric springs (DC-ES) for voltage stabilization and power quality improvement. The basic operating modes and characteristic of a DC-ES with different types of serially connected non-critical loads will first be introduced. Then, the various power delivery issues of the dc power systems, namely bus voltage variation, voltage droop, system fault, and harmonics, are briefly described. The operating limits of a DC-ES in a dc power grid is studied. It is demonstrated that the aforementioned issues can be mitigated using the proposed DC-ES technology. Experiment results are provided to verify the feasibility of the proposed technology.
Xiong S, Huang Y, Tan SC, et al., 2016, Morphing Switched-Capacitor Converters with Variable Conversion Ratio, IEEE Transactions on Power Electronics, Vol: 31, Pages: 5680-5693, ISSN: 0885-8993
High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss.
Hui SYR, 2016, Magnetic resonance for wireless power transfer, IEEE Power Electronics Magazine, Vol: 3, Pages: 14-31, ISSN: 2329-9207
Magnetic resonance has been a cornerstone of nonradiative wireless power transfer (WPT) since the late 19th century. However, some researchers have the misconception that magnetic resonance for WPT was developed recently. This article traces some early work of Tesla and other researchers related to the use of magnetic resonance in WPT. Included are some examples of magnetic resonance-based WPT projects conducted by researchers in the biomedical and power electronics communities over the last few decades. Two principles used in WPT are reiterated in this article, and their advantages and disadvantages are addressed. Some issues that may affect future trends of short- and midrange applications are discussed.
Guo Y, Li S, Lee ATL, et al., 2016, Single-Stage AC/DC Single-Inductor Multiple-Output LED Drivers, IEEE Transactions on Power Electronics, Vol: 31, Pages: 5837-5850, ISSN: 1941-0107
Various ac/dc LED driver topologies have been proposed to meet the challenges of achieving a compact, efficient, low-cost, and robust multistring LED lighting system. These LED drivers typically employ a two-stage topology to realize the functions of ac/dc rectification and independent current control of each LED string. The choice of having two stage conversions involves additional hardware components and a more complicated controller design process. Such two-stage topologies suffer from a higher system cost, increased power loss, and large form factor. In this paper, a single-stage ac/dc single-inductor multiple-output LED driver is proposed. It uses only one single inductor and N + 1 active power switches (N being the number of LED strings) with reduced component count and smaller form factor. The proposed driver can achieve both functions of ac/dc rectification with a high power factor and precise independent current control of each individual LED string simultaneously. A prototype of an ac/dc single-inductor triple-output LED driver is constructed for verification. Experimental results corroborate that precise and independent current regulation of each individual LED string is achievable with the proposed driver. A power factor of above 0.99 and a peak efficiency of 89% at 30-W rated output power are attainable.
Li S, Tan S-C, Lee CK, et al., 2016, A Survey, Classification, and Critical Review of Light-Emitting Diode Drivers, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 31, Pages: 1503-1516, ISSN: 0885-8993
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- Citations: 164
Lin D, Zhang C, Hui SYR, 2016, Mathematic Analysis of Omnidirectional Wireless Power Transfer-Part-II Three-Dimensional Systems, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 32, Pages: 613-624, ISSN: 0885-8993
Lin D, Zhang C, Hui SYR, 2016, Mathematical Analysis of Omnidirectional Wireless Power Transfer-Part-I: Two-Dimensional Systems, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 32, Pages: 625-633, ISSN: 0885-8993
Luo X, Lee CK, Ng WM, et al., 2016, Use of adaptive thermal storage system as smart load for voltage control and demand response, IEEE Transactions on Smart Grid, Vol: 8, Pages: 1231-1241, ISSN: 1949-3053
This paper describes how a large-scale ice-thermal storage can be turned into a smart load for fast voltage control and demand-side management in power systems with intermittent renewable power, while maintaining its existing function of load shaving. The possibility of modifying a conventional thermal load has been practically demonstrated in a refrigerator using power electronics technology. With the help of an electric spring, the modified thermal load can reduce power imbalance in buildings while providing active and reactive power compensation for the power grid. Based on practical data, a building energy model incorporating a large-scale ice-thermal storage system has been successfully used to demonstrate the advantageous demand-response features using computer simulation of both grid connected and isolated power systems. The results indicate the potential of using ice-thermal storage in tall buildings in reducing voltage and frequency fluctuations in weak power grids.
Yan S, Wang MH, Yang TB, et al., 2016, Instantaneous frequency regulation of microgrids via power shedding of smart load and power limiting of renewable generation
In this paper, a collaborative control scheme is proposed to improve the stability of the microgrid with intermittent renewable energy sources. Different from other cooperative control schemes targeting mostly on regulating the generation side, the proposed operating scheme utilizes all controllable resources in the microgrid, including renewable energy sources (RESs), storage devices, and controllable loads. A modified maximum power point tracking (MPPT) scheme is proposed for RESs in limiting its power output when frequency surges over its upper limit. The adaptive/smart load enabled by the electric spring (ES) reduces the power demand when the frequency falls below the lower limit. Both operating schemes for RES and adaptive/smart load can be activated when the storage system fails to respond to disturbances. The proposed collaborative scheme can be enacted in an instantaneous manner and is easy to implement by simply modifying the control of RES and adaptive/smart load. Simulation results have confirmed that the proposed scheme is efficient in reducing the frequency oscillation in a microgrid.
Qi W, Li S, Siew-Chong-Tan, et al., 2016, A two-switch buck-boost PFC rectifier with automatic AC power decoupling capability
In this paper, a single-stage power-factor-correction (PFC) rectifier with active power decoupling function is proposed. The proposed rectifier has a low component count as compared to existing solutions. Only two active switches, one inductor and one small power-buffering capacitor are needed. High power factor, wide output voltage range and active power decoupling can be simultaneously obtained. In addition, the rectifier has an inherent automatic power decoupling capability, and no dedicated active power decoupling control is required. Therefore, the control of the rectifier is simple and easy to implement. A 100 W prototype of the proposed rectifier with 110 Vrms/50 Hz input and a regulated DC output voltage ranging from 30 V to 100 V has been constructed and tested. The results show that with only a 15 μF power-buffering capacitor, a power factor of over 0.98, peak efficiency of 93.9% and output voltage ripple of less than 3% has been achieved.
Wu M, Li S, Tan SC, et al., 2016, Integrated magnetics for power density improvement of differential rectifiers and inverters
In this paper, a type of low-frequency integrated AC inductor with zero inductance coupling is proposed for differential rectifiers/inverters. The objective is to increase the power density of these converters by replacing their two bulky low-frequency AC inductors with the proposed integrated AC inductor, which is much more compact. The principles of magnetic integration and the optimization procedures are explained in detail. Experimental results show that a core volume reduction of 20.4% is achievable using the proposed integrated magnetics.
Hui SYR, Mitcheson PD, 2016, Wireless power transfer, Power Electronic Converters and Systems: Frontiers and Applications, Pages: 577-600, ISBN: 9781849198264
WPT can be broadly classified as radiative and non-radiative. Power can be radiated by an antenna and propagates through a medium such as air in the form of a radio frequency (RF) electromagnetic wave. Non-radiative WPT is based on near-field magnetic coupling of magnetic circuits that are generally in the form of conductive loops with a resonant frequency. WPT can be achieved through a range of technologies, ranging from near-field magnetic coupling based technologies operating at a relatively low frequency (such as 10 kHz-15.65 MHz) to microwave technologies operating at relatively high frequency (up to a few giga-hertz). This chapter focuses primarily on the former type of research and applications based on near-field magnetic coupling. It covers WPT research and applications from low-power applications.
Dong Z, Tse CK, Hui SYR, 2016, Basic circuit theoretic considerations of LED driving: Voltage-source versus current-source driving
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 driving LEDs from the circuit theoretic viewpoint. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of duality principle in developing new current-source drivers which are mostly unknown but are theoretically more versatile compared to their conventional voltage-source counterparts. Although the study exploits very basic circuit theory, it is not always borne in mind or known by practitioners the impact of the choice of circuit topologies on the current and voltage ripples, range of duty cycle variation, sensitivity, and efficiency of LED drivers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidences supporting the major conclusions. Finally, we illustrate how these results can readily lead to an effective LED driver design.
Lee ATL, Chen H, Tan SC, et al., 2016, Precise Dimming and Color Control of LED Systems Based on Color Mixing, IEEE Transactions on Power Electronics, Vol: 31, Pages: 65-80, ISSN: 1941-0107
This paper proposes a closed-loop nonlinear scheme for precisely controlling the luminosity and correlated color temperature (CCT) of a bicolor adjustable light-emitting diode (LED) lamp. The main objective is to achieve a precise and fully independent dimming and CCT control of the light mixture emitted from a two-string LED lamp comprising warm-white and cool-white color LEDs, regardless of the operating conditions and throughout the long operating lifetime of the LED lamp. The proposed control method is formulated using the nonlinear empirical LED model of the bicolor white LED system. Experimental results show that with the proposed closed-loop nonlinear approach, both CCT and dimming control of the bicolor lamp is significantly more accurate and robust to ambient temperature variations, ambient light interference, and LED aging than the conventional linear approach used in existing products. The maximum error in luminous flux employing the proposed closed-loop nonlinear approach is 3%, compared with 20% using the closed-loop linear approach. The maximum deviation in CCT is only 1.78%, compared with 27.5% with its linear counterpart.
Lee CK, Liu H, Zhang G, et al., 2016, A Unified Converter Topology for Electric Spring, 7th IEEE International Symposium On Power Electronics for Distributed Generation Systems (PEDG), Publisher: IEEE, ISSN: 2329-5759
Wang M-H, Yan S, Tan S-C, et al., 2016, DC Electric Springs with Modified Droop Control for Storage Reduction in DC Microgrids, 8th Annual IEEE Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, ISSN: 2329-3721
Zhang C, Tang N, Zhong W, et al., 2016, A New Energy Harvesting and Wireless Power Transfer System for Smart Grid, 7th IEEE International Symposium On Power Electronics for Distributed Generation Systems (PEDG), Publisher: IEEE, ISSN: 2329-5759
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- Citations: 6
Li S, Guo Y, Lee ATL, et al., 2016, Precise and Full-Range Dimming Control for An Off-Line Single-Inductor-Multiple-Output LED Driver, 8th Annual IEEE Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, ISSN: 2329-3721
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