Rapid developments of planar magnetics in recent years have prompted new applications of planar t... more Rapid developments of planar magnetics in recent years have prompted new applications of planar transformers in electronic industry. The low-profi’e features of planar magentics make them attractive in many electronic systems that have stringent thickness requirements. In this article, some recent progress of planar PCB transformers and their applications are described. Comparisons of canventional and pianar transformers are reviewed. New trend of integrated electronic packaging in power electronic systems is briefly discussed.
Rapid developments of planar magnetics in recent years have prompted new applications of planar t... more Rapid developments of planar magnetics in recent years have prompted new applications of planar transformers in electronic industry. The low-profi’e features of planar magentics make them attractive in many electronic systems that have stringent thickness requirements. In this article, some recent progress of planar PCB transformers and their applications are described. Comparisons of canventional and pianar transformers are reviewed. New trend of integrated electronic packaging in power electronic systems is briefly discussed.
Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the us... more 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.
Optimum energy efficiency in a wireless power transfer (WPT) system usually occurs only at a spec... more 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 re-configurable 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.
This paper discusses the recent system platforms based on planar charging as well as its critical... more This paper discusses the recent system platforms based on planar charging as well as its critical issues and related technologies. The information on the first wireless power standard ''Qi'' is then presented with future trend and development predictions.
Starting from Tesla's principles of wireless power transfer a century ago, this critical review o... more Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magnetoinductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load. Index Terms-Electromagnetic fields, human exposure, maximum efficiency, maximum power transfer, mid-range wireless power transfer, tesla's resonators.
The renewable generations (RGs) are conventionally interfaced with the utility grid through batte... more The renewable generations (RGs) are conventionally interfaced with the utility grid through battery energy storage systems (BESS). In this cascaded configuration of the gridconnected 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 non-critical 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 (ES). 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 These keynotes speeches the following: Keynote speech on “Challenges of modern power sys... more ABSTRACT These keynotes speeches the following: Keynote speech on “Challenges of modern power systems and IEEE PES”; Plenary Session on “Challenges and Opportunities of Smart Grid Development and Technologies”; The Technical Challenges and Benefits of Implementing AMI in Hong Kong; Smart Grid Features of Energy Management System &amp; Distribution Management System of HK Electric; Electric Springs - A New Smart Grid Technology for Taming the Intermittent Nature of Wind and Solar Power; Challenges and Opportunities of Distributed Energy Resource Integration; Honorary Lecture (Free-of-charge); Outdoor Insulator Flashover Problems under Icing Conditions.
With the increasing adoption of renewable energy sources into power grids, the issue of voltage a... more With the increasing adoption of renewable energy sources into power grids, the issue of voltage and frequency fluctuation of the network becomes a more critical problem that needs to be resolved urgently. The so-called demand-side management (DSM) of power system provides the opportunity for the prospective grids to intelligently balance the power supply and consumption. As one of the crucial roles of DSM, smart loads are naturally committed to manage the power flow of the network. Other than previous communication-based smart loads, the recently proposed electric springs (ES) provide an opportunity to turn some conventional loads into smart loads without the need for communication. In this paper, a simple voltage and frequency (v&f) control method is applied to such a smart load for tackling the voltage and frequency fluctuations of the power grids. Simulation results reveal that with the proposed v&f control, the smart load can achieve better voltage and frequency regulation performance than that with the conventional control and smart load. Experimental results validating the feasibility of the proposed v&f controller on regulating the voltage amplitude and frequency of the common-coupling point of a power grid are provided.
ABSTRACT In this paper, we present a brief overview of historical developments of wireless power ... more ABSTRACT In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Teslas resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter coil and the receiver coil with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and non-coaxial domino-resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at sub-Mega-Hertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal-spacing for the coaxial straight domino systems has better efficiency performance than equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated.
ABSTRACT A new design of low-cost and low-profile power transformer is presented in this paper. T... more ABSTRACT A new design of low-cost and low-profile power transformer is presented in this paper. The manufacturing cost of a power transformer can be reduced using the proposed printed-circuit board (PCB) transformer. The transformer windings are etched on the opposite sides of a double-sided PCB. Self-adhesive ferrite polymer composite (FPC) sheets are stuck on the two PCB surfaces to shield the magnetic flux induced from the transformer windings. The PCB transformer does not require manual winding and bobbin. A power converter prototype employing the PCB transformer has been implemented. The technique of choosing the optimum switching frequency of the power converter using PCB transformer is addressed in this paper. The maximum power delivered from the prototype is 94 W. The maximum efficiency of the power converter is 83.5%
With increasing installations of grid-connected power electronic converters in the distribution n... more With increasing installations of grid-connected power electronic converters in the distribution network, there is a new trend of using distributed control in a cyber layer to coordinate the operations of these power converters for improving power system stability. However, cyber-attacks remain a threat to such distributed control. This paper addresses the cyber-attack detection and a countermeasure of distributed electric springs (ESs) that have emerged as a fast demand-response technology. A fully distributed modelbased architecture for cyber-attack detection in the communication network is developed. Based on a dynamic model of ES with consensus control, a local state estimator is proposed and practically implemented to monitor the system. The estimator is fully distributed because only local and neighboring information is necessary. A countermeasure for the distributed ESs to ride through the cyber-attack and maintain regulatory services in a microgrid is demonstrated successfully. Experimental results are provided to verify the effectiveness of the proposed cyber-attack detection method and its ride-through capability. INDEX TERMS Electric springs, cyber-attack detection, distributed state estimator.
An investigation into the effects of the structures of both LED devices and systems on the lumino... more An investigation into the effects of the structures of both LED devices and systems on the luminous performance is presented. Single-chip and multichip LED structures and concentrated and distributed LED systems are studied and compared. Practical tests on both of the device and system levels have confirmed the theoretical predictions that parallel LED structures can lead to much lower thermal resistance and thus higher luminous output. The results of this paper contribute to new information for both LED device manufacturers and system designers toward the optimization of the LED technology. Index Terms-General photo-electro-thermal theory, lightemitting diodes, thermal design for LEDs.
Rapid developments of planar magnetics in recent years have prompted new applications of planar t... more Rapid developments of planar magnetics in recent years have prompted new applications of planar transformers in electronic industry. The low-profi’e features of planar magentics make them attractive in many electronic systems that have stringent thickness requirements. In this article, some recent progress of planar PCB transformers and their applications are described. Comparisons of canventional and pianar transformers are reviewed. New trend of integrated electronic packaging in power electronic systems is briefly discussed.
Rapid developments of planar magnetics in recent years have prompted new applications of planar t... more Rapid developments of planar magnetics in recent years have prompted new applications of planar transformers in electronic industry. The low-profi’e features of planar magentics make them attractive in many electronic systems that have stringent thickness requirements. In this article, some recent progress of planar PCB transformers and their applications are described. Comparisons of canventional and pianar transformers are reviewed. New trend of integrated electronic packaging in power electronic systems is briefly discussed.
Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the us... more 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.
Optimum energy efficiency in a wireless power transfer (WPT) system usually occurs only at a spec... more 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 re-configurable 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.
This paper discusses the recent system platforms based on planar charging as well as its critical... more This paper discusses the recent system platforms based on planar charging as well as its critical issues and related technologies. The information on the first wireless power standard ''Qi'' is then presented with future trend and development predictions.
Starting from Tesla's principles of wireless power transfer a century ago, this critical review o... more Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magnetoinductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load. Index Terms-Electromagnetic fields, human exposure, maximum efficiency, maximum power transfer, mid-range wireless power transfer, tesla's resonators.
The renewable generations (RGs) are conventionally interfaced with the utility grid through batte... more The renewable generations (RGs) are conventionally interfaced with the utility grid through battery energy storage systems (BESS). In this cascaded configuration of the gridconnected 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 non-critical 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 (ES). 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 These keynotes speeches the following: Keynote speech on “Challenges of modern power sys... more ABSTRACT These keynotes speeches the following: Keynote speech on “Challenges of modern power systems and IEEE PES”; Plenary Session on “Challenges and Opportunities of Smart Grid Development and Technologies”; The Technical Challenges and Benefits of Implementing AMI in Hong Kong; Smart Grid Features of Energy Management System &amp; Distribution Management System of HK Electric; Electric Springs - A New Smart Grid Technology for Taming the Intermittent Nature of Wind and Solar Power; Challenges and Opportunities of Distributed Energy Resource Integration; Honorary Lecture (Free-of-charge); Outdoor Insulator Flashover Problems under Icing Conditions.
With the increasing adoption of renewable energy sources into power grids, the issue of voltage a... more With the increasing adoption of renewable energy sources into power grids, the issue of voltage and frequency fluctuation of the network becomes a more critical problem that needs to be resolved urgently. The so-called demand-side management (DSM) of power system provides the opportunity for the prospective grids to intelligently balance the power supply and consumption. As one of the crucial roles of DSM, smart loads are naturally committed to manage the power flow of the network. Other than previous communication-based smart loads, the recently proposed electric springs (ES) provide an opportunity to turn some conventional loads into smart loads without the need for communication. In this paper, a simple voltage and frequency (v&f) control method is applied to such a smart load for tackling the voltage and frequency fluctuations of the power grids. Simulation results reveal that with the proposed v&f control, the smart load can achieve better voltage and frequency regulation performance than that with the conventional control and smart load. Experimental results validating the feasibility of the proposed v&f controller on regulating the voltage amplitude and frequency of the common-coupling point of a power grid are provided.
ABSTRACT In this paper, we present a brief overview of historical developments of wireless power ... more ABSTRACT In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Teslas resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter coil and the receiver coil with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and non-coaxial domino-resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at sub-Mega-Hertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal-spacing for the coaxial straight domino systems has better efficiency performance than equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated.
ABSTRACT A new design of low-cost and low-profile power transformer is presented in this paper. T... more ABSTRACT A new design of low-cost and low-profile power transformer is presented in this paper. The manufacturing cost of a power transformer can be reduced using the proposed printed-circuit board (PCB) transformer. The transformer windings are etched on the opposite sides of a double-sided PCB. Self-adhesive ferrite polymer composite (FPC) sheets are stuck on the two PCB surfaces to shield the magnetic flux induced from the transformer windings. The PCB transformer does not require manual winding and bobbin. A power converter prototype employing the PCB transformer has been implemented. The technique of choosing the optimum switching frequency of the power converter using PCB transformer is addressed in this paper. The maximum power delivered from the prototype is 94 W. The maximum efficiency of the power converter is 83.5%
With increasing installations of grid-connected power electronic converters in the distribution n... more With increasing installations of grid-connected power electronic converters in the distribution network, there is a new trend of using distributed control in a cyber layer to coordinate the operations of these power converters for improving power system stability. However, cyber-attacks remain a threat to such distributed control. This paper addresses the cyber-attack detection and a countermeasure of distributed electric springs (ESs) that have emerged as a fast demand-response technology. A fully distributed modelbased architecture for cyber-attack detection in the communication network is developed. Based on a dynamic model of ES with consensus control, a local state estimator is proposed and practically implemented to monitor the system. The estimator is fully distributed because only local and neighboring information is necessary. A countermeasure for the distributed ESs to ride through the cyber-attack and maintain regulatory services in a microgrid is demonstrated successfully. Experimental results are provided to verify the effectiveness of the proposed cyber-attack detection method and its ride-through capability. INDEX TERMS Electric springs, cyber-attack detection, distributed state estimator.
An investigation into the effects of the structures of both LED devices and systems on the lumino... more An investigation into the effects of the structures of both LED devices and systems on the luminous performance is presented. Single-chip and multichip LED structures and concentrated and distributed LED systems are studied and compared. Practical tests on both of the device and system levels have confirmed the theoretical predictions that parallel LED structures can lead to much lower thermal resistance and thus higher luminous output. The results of this paper contribute to new information for both LED device manufacturers and system designers toward the optimization of the LED technology. Index Terms-General photo-electro-thermal theory, lightemitting diodes, thermal design for LEDs.
Uploads
Papers by Ron Hui