K.T. Chau

The University of Hong Kong | HKU · Department of Surgery

Wireless motors offer significant advantages in terms of installation flexibility and cable-free features but inevitably require multiple power semiconductors and electronic components at the receiver side to achieve wireless movement. Moreover, motor speed information is difficult to capture due to technical impediments in realizing wireless speed...

For multistorey car parks, this paper proposes and implements an integrated sensorless wireless charging (SWC) system of electric vehicles (EVs) using a symmetric high-order network that is designed to mirror the electrical parameters of the onboard receiver and battery. The proposed SWC control can avoid the need of communicating and sensing the r...

This paper proposes and implements a wireless hybrid stepper motor (HSM) system, which offers high controllability of speed, direction, and position without physical contact and electrical connection between the power source and the motor. By transmitting electrical pulses to each motor winding in different frequencies, duty ratios, and sequences,...

Multilevel converters have attracted more and more attention for their advantages over the two-level converters in breaking voltage limitation and multichannel wireless power transfer (WPT), but their switching loss is unbearable due to the lack of an effective soft-switching modulation method. To fill this gap, this article proposes and implements...

Hybrid electric vehicles (HEVs) and electric vehicles (EVs) have been advocated by global governments’ policies in recent decades. Besides combating the climate crisis and urban air pollution, great contributions of developing the HEVs and EVs have been identified to accelerate the process of green transportation and smart city. Battery management...

Superconducting rotating machines are more efficient, smaller and lighter than conventional ones. Thus, they can reduce energy consumption and can be an enabling technology in applications that require light-weight machines. Using high temperature superconducting (HTS) materials in machines simplifies cooling designs compared to using low temperatu...

Recently, wireless power transfer for electric motor technology has been studied, where the primary side can drive the motor without physical contact, so the load motor can be employed in isolated environments. This paper proposes a wireless permanent-magnet brushless DC (PM-BLDC) motor. Prominently, the secondary side does not involve any motor co...

The integration of high-precision robotics and magnetic resonance imaging (MRI) exhibits the potential to enhance the accuracy and safety of MRI image-guided surgery. However, the potential hazards associated with conventional electromagnetic servomotors in strong magnetic fields have hindered the development of MRI-compatible robotics. To address...

In order to provide differential action for electric vehicles performing reliable cornering, the axial-field (AF) double-rotor (DR) flux-reversal (FR) motor shows a good ability of torque output along with magnetic differential (MagD) control on its two rotors. Apart from using the permanent magnet (PM) excitation, which suffers from high PM cost a...

This paper proposes a dynamic wireless charging scheme for electric vehicles (EVs) using autonomous frequency control. The key is to make the receiver circuit of an EV always operate in the splitting region by adopting proper transmitter coils and displacement between adjacent transmitter coils. Then, by sensing the primary current, the autonomous...

In this article, a quantitative analysis of the cross-coupling effect for multi-objective wireless power transfer (WPT) is presented, and a relevant cancellation method to eliminate the influence is implemented. Based on the exemplified two-pickup and three-pickup WPT systems, the wirelessly transmitted power and efficiency are significantly affect...

A novel periodic energy control (PEC) strategy for DC-DC converters is proposed in this letter, where the port nearest to the load is selected as the energy control target, considering the loss of switching and passive components. A simplified energy calculation method is derived to replace the integration methods in terms of the possible error dur...

Superconductors in practical use can be subjected to spatially non-uniform and time-varying external field as well as carrying a transport current, for example, in an electrical machine. This paper verifies that the integral method can be used in situations in which the external field is spatially non- uniform, by providing both theoretical reasoni...

Popularization of wireless power transfer (WPT) has promoted the multi-disciplinary explorations and integration. It gradually incubates numerous attractive solutions for industrial, domestic and medical scenarios. Therefore, a series of smart WPT emerges, and these state-of-the-arts will bring a great impact on the modern technology and human soci...

This paper proposes a novel wireless universal motor. By eliminating the motor controller and position sensor, the secondary side is very simple and robust. Besides, bidirectional movement can be achieved. The key is to employ a self-driving circuit at the secondary side. Also, the advantages of the small size and large starting torque of universal...

This Special Issue aims to focus on advances in EV technologies: 1) the high torque density of electric machines, high efficiency of electric propulsion systems and high reliability of electric drivetrains; 2) the high power density of chargers and power converters; 3) the high energy density of energy storages and high convenience of energy refuel...

This paper proposes a direct three-phase single-stage AC-AC system based on pulse density modulation (PDM) for the series resonant load. Compared with the traditional multi-stage AC-DC-AC system, the bus capacitors among the DC stage can be eliminated, and good grid-side current quality is achieved. Unlike pulse width modulation, PDM has fewer swit...

Long-range underwater wireless power transfer (WPT) systems have great application prospects in many industrial fields. However, conventional WPT systems may suffer different kinds of technical issues in this highly unstable operation environment, such as large output decay when the transmission distance increases, and output fluctuation caused by...

Due to the inevitable variation of component parameters, interference of ferromagnetic foreign body, active regulation of operation frequency, and rectification effect caused virtual capacitance or inductance, zero-phase-angle (ZPA) operation and zero-voltage switching (ZVS) could hardly be maintained without extra control strategies, especially fo...

A demand-customized selective wireless power transfer system is proposed in this article. Multiple receivers can be recognized based on their positions and the magnetic field in the powering area can be controlled and regulated accordingly. For authorized receivers, the system can simultaneously deliver power to meet different output requirements f...

Popularization of electric vehicles (EVs) is an effective solution to promote carbon neutrality, thus combating the climate crisis. Advances in EV batteries and battery management interrelate with government policies and user experiences closely. This article reviews the evolutions and challenges of (i) state-of-the-art battery technologies and (ii...

In order to get rid of the bulky and lossy differential gears and to enhance the system robustness, the magnetic differential (MagD) system is proposed after the mechanical differential (MechD) and electronic differential (ElecD) systems. The MagD system is mainly composed of the double-rotor (DR) stator-permanent-magnet (PM) motor with a new set o...

Hybrid electric vehicles (HEVs) and electric vehicles (EVs) have been advocated by global governments’ policies in recent decades. Besides combating the climate crisis and urban air pollution, great contributions of developing the HEVs and EVs have been identified to accelerate the process of green transportation and smart city. Battery management...

This article proposes and implements an optimized omnidirectional wireless power transfer (WPT) system using distributed transmitter coils. Under the consideration of practical WPT applications which involve human safety concerns, such as daily home apparatus or wireless rechargeable medical implants, the proposed system can achieve the shortest ch...

This paper proposes an autonomous pulse frequency modulation (APFM) scheme for wireless battery charging in which the self-excited oscillating (SEO) wireless power transfer (WPT) system can offer output power regulation with reliable zero-voltage switching (ZVS). The key is to utilize the self-excited oscillation feature to adjust the WPT operating...

To wire, or not to wire, that is the question: Whether electric motors should go wireless. The pros and cons of wireless motors will be introduced, hence identifying the conflict and tradeoff between system reliability, transmission efficiency, electrical safety and working environment. Differing from the pseudo-wireless version which is actually a...

A wireless electric vehicle energy network (WEVEN) can offer more functionalities and opportunities for the modern power grid while having high flexibility and reconfigurability. This paper proposes a novel WEVEN to collaborate with the distributed renewable energy network, electric power network, energy storage network, and other energy networks....

A vehicular energy network (VEN) uses electric vehicles (EVs) to transport energy across a wide geographical area. EVs can charge and discharge wirelessly at road junctions whilst moving, and thus transfer energy between junctions. In this paper, we propose a method to optimally route energy from multiple energy-supplying junctions to multiple ener...

This article proposes and implements a multi-resonating-compensation (MRC)-based multi-channel multi-pickup (MCMP) wireless power transfer (WPT) system. The proposed compensation topology holds triple or more resonating points, which can establish multiple transmission channels with minimum reactive power losses without utilizing multiple transmitt...

This paper proposes and implements a long-range wireless power drive (WPD) system using a magnetic extender, which can be promisingly applied in underground pipeline transportations and in-pipe robots. Generally, the underground pipeline transportation networks usually rely on the power grid and control system to regulate the flow rate. Nonetheless...

This paper proposes and implements an advanced pulse frequency modulation (PFM) scheme to adjust the output power of the parity-time (PT) symmetric wireless power transfer (WPT) system. The key is to utilize PFM to adjust the duty ratio of the self-excited oscillating inverter for the PT-symmetric WPT system, hence transferring more power than that...

In this paper, a wireless resolver is proposed and implemented for wireless switched reluctance (SR) motors, which can detect the rotor position and transfer the information to the primary side without involving any battery storage or active components at the secondary side. The key is to integrate wireless power transfer (WPT) into a variable relu...

The wireless power transfer (WPT) technology has attracted more attention due to its convenience, electrocution-free, and safety. However, the current discontinuity characteristics of WPT systems are not sufficiently appreciated. In this paper, a unified full-load discrete-time (UFDT) model for the WPT system is established, which is both suitable...

The magnetic field calculation for axial flux motors (AFMs) is always intricate and time-consuming. To this end, a fast quasi-three-dimensional (3D) analytical model is proposed in this paper for magnetic field prediction in AFMs. By dividing the AFM into several annular slices in the radial direction, the 3D magnetic field problem can be simplifie...

A newly developed multifrequency wireless power transfer system is designed and presented in this paper. By using multiple frequency channels, the system can simultaneously deliver power to different wireless pickups with arbitrary power requirements or load characteristics. The proposed design scheme of the system topology realizes both the stable...

Popularization of electric vehicles (EVs) is an effective solution to promote carbon neutrality, thus combating the climate crisis. Advances in EV batteries and battery management interrelate with government policies and user experiences closely. This article reviews the evolutions and challenges of (i) state-of-the-art battery technologies and (ii...

Transportation electrification has been widely identified as a promising solution to combat environmental pollution and greenhouse gas emissions. The gradual popularization of electric vehicles will contribute to a green transportation network that helps to reduce carbon footprint and promote carbon neutrality. Ever-growing traffic burdens and high...

In this paper, a dual-resonating-frequency (DRF) compensation topology is adopted and implemented for exciting the decoupled-double D (DDD) transmitting coils in the dual-frequency wireless power transfer (WPT) systems. Concretely speaking, two double D (DD) coils are located orthogonally and compactly to obtain the effect of magnetically decoupled...

This paper presented a single-phase shaded pole induction motor (SPIM) system, which aims to work in an isolated environment. Compared with the previous wireless SPIM, this system employs less controlled switches and can work at full-resonant condition, while retaining the merit of secondary controller-less. The key is to employ a half-bridge inver...

This paper proposes and implements an output-controllable efficiency-optimized wireless power transfer scheme using hybrid modulation. The key is to combine pulse frequency modulation (PFM) and on-off keying (OOK) modulation and to utilize feedback control. Among them, PFM is used for the output voltage regulation of the inverter to adjust the rect...

In this paper, the split-tooth stator-slot permanent-magnet (ST-SSPM) machines with different PM arrangements are comprehensively analyzed. Four types of ST-SSPM machines are first introduced and classified by the positions and polarities of PMs. Then, the operation principles are elaborated and the slot-pole combinations are derived from the view...

This paper proposes and implements a compact wireless motor drive using orthogonal bipolar coils for the coordinated operation of robotic arms. The key is to orthogonally integrate two bipolar coils to form a compact magnetic coupler (CMC), while each CMC serves as the transmitting coil and receiving coil, respectively. Instead of adopting the one-...

This paper proposes and implements an integrated wireless motor system using the laminated magnetic coupler (LMC) and commutative-resonant control (CRC). Prominently, a unique wireless power transfer (WPT) system is developed to directly drive the switched reluctance motor (SRM) over an extendable distance with all controls centralizing in the tran...

This paper proposes and implements a novel wireless power and drive transfer (WPDT) system using orthogonal bipolar couplers and separately excited modulation (SEM). Specifically, two bipolar coils are orthogonally integrated and naturally decoupled to form a compact magnetic coupler which will be utilized in the transmitter and receiver, respectiv...

Traditionally, domestic induction heating (IH) is designed to heat the ferromagnetic (FM) pan. However, it is incompetent to heat the non-ferromagnetic (NFM) pan since the small equivalent resistance of the pan will easily result in the overcurrent on the inverter. Inspired by the compensation network in the wireless power transfer (WPT), the serie...

This paper proposes and implements a brand-new wireless power and drive transfer (WPDT) system using wireless switches. A wireless piping network is conceived especially for pipeline transportations and in-pipe robots desiring wireless motor drive. Also, a multi-frequency resonant network is newly explored to generate the variable-frequency-modulat...

Abstract With ever‐increasing concerns on energy crisis and environmental protection, there is a fast‐growing interest in wind power generation systems. As electric machines and drives are core components in wind turbines, it is a pressing need for researchers and engineers to develop advanced electric machines and drives for wind power generation....

Replacement of combustion vehicles with electric vehicles (EVs) and penetration of renewable energy sources are effective solutions to reduce greenhouse gas emissions and therefore combat climate change. Such a development of green transportation is in keeping with the theme of carbon neutral. As the energy source for electric propulsion, battery p...

Popularization of electric vehicles (EVs) can effectively improve energy efficiency, reduce greenhouse gas emissions, and therefore benefit environmental quality. Battery charging develops into a necessary daily behavior for EVs like the refueling experience of gasoline vehicles. This paper reviews the state-of-the-art technologies of chargers, arc...

Transportation electrification has attracted much attention in modern society. Among all electrified transportation tools, electric vehicle (EV) is absolutely the one that has great potential to compete with and further take the place of traditional fossil fuel vehicles. This article is to outline and investigate advanced electric machines and thei...

With the rapid development of wireless power transfer (WPT), the self-resonant WPT system without using additional compensation capacitors has attracted attentions. However, most of reported self-resonant WPT systems have low power transfer (less than 100 W) and high operating frequencies at megahertz. In this paper, four multiple-layer, self-reson...

This paper proposes a new parallel-hybrid-excited permanent-magnet machine (PHEM) with harmonic-differential (HD) effect, termed HD-PHEM. The key is to place the DC-field windings in the DC pole sandwiched by the two adjacent permanent-magnet (PM) poles, thereby realizing the parallel flux paths of PM flux and DC-field flux. Moreover, the HD effect...

This paper proposes and implements a wireless power transfer (WPT) with S-CLC compensation network and pulse-frequency-modulation (PFM) control for dimmable low-pressure sodium (LPS) lamps. Considering the high-voltage ignition and long-time operation, the LPS lamp has the risk of causing electrocution especially when operating in a humid environme...

This paper proposes and implements a frequency-modulated wireless direct-drive motor control (WDMC) for a promising application of underground in-pipe pumping. Accordingly, a novel urban drainage scheme is conceived, which offers high robustness, mobility and flexibility. This scheme can help with the emergency response to prevent severe weather ha...

In this paper, the parallel-hybrid-excited harmonic-shift machine (PHE-HSM) is analyzed from the perspective of the field-modulation effect based on the air-gap field harmonics. By shifting the pole-pairs of the DC-field windings from those of the PMs, the parallel-hybrid excitation can be realized due to field modulation. The operation principle a...

This paper proposes and implements a selective wireless power transfer (WPT) system based on magnetic field editing technology. Compared with the traditional WPT without control of power regions, the proposed system can deliver the energy with higher safety, flexibility, selectivity, and can be applied to multiple receivers. The algorithms for curr...

An omnidirectional energy harvester with a multi-coil structure for the wireless power transfer (WPT) system is proposed and analyzed. Compared with the traditional single-direction receivers, this harvester can provide more homogenous output power with relatively high transmission efficiency under arbitrary transmission directions. An analytical s...

Human exposure to the electromagnetic field (EMF) has been raising concerns with the fast development of the wireless power transfer (WPT) technology. This paper proposes a double-layer coil structure for wireless rechargeable implanted medical equipment, which can effectively strain the power beam in a single direction and limit the EMF emission t...

In this paper, a wireless shaded-pole induction motor (SPIM) is proposed and implemented, which artfully integrates wireless power transfer (WPT) into a single-phase SPIM to achieve the first wireless AC motor. Prominently, there is no controller at the SPIM side, as the controlling process is fully conducted at the transmitter side. Meanwhile, the...

This paper proposes and implements a multi-topological low-frequency-switching (LFS) high-frequency-resonating (HFR) wireless power transfer (WPT) system, which can significantly improve the system efficiency and fluctuations for specific HFR-WPT applications at equal power level. To adjust the HFR wireless power, high-frequency-switching phase-shi...

This paper proposes and implements a hybrid frequency pacing (HFP) technique for resonating a high-order transformed wireless power transfer (WPT) system with robust zero-voltage switching (ZVS). As a hybrid frequency modulation, the proposed HFP can efficiently tune the innate constant-frequency resonances of WPT. It can facilitate the pulse width...

This paper proposes and implements a novel magnetic quasi-resonant coupling (MQRC) scheme to realize the concept of energy-on-demand wireless power transfer (WPT). To prevent illegal receivers harvesting wireless energy, the proposed energy-on-demand technology nominates the authorized receiver to take over the initiative and generate a well-defend...

In this paper, a novel double-rotor flux-switching permanent-magnet (DR-FSPM) motor is proposed for electric vehicles with the capability of magnetic differential (MagD). The key is to introduce a new set of winding which magnetically couples with the two rotors of the DR-FSPM motor in such a way that the magnetic coupling winding field can interac...

This paper proposes and implements a full-range soft-switching pulse frequency modulated (PFM) wireless power transfer (WPT) system, which not only offers high efficiency but also high controllability, selectivity and security. Although the phase-shift control (PSC) has been widely used in various WPT applications, the high-frequency hard-switching...

A high-order compensated wireless power transfer (WPT) system is proposed and implemented for dimmable metal halide (MH) lamps without using any ignitor or ballast. Possessing high ignition voltage and constant current output, the LCC-LC compensated WPT is identified to be more competent for MH lamps as compared with the four basic compensation net...

This paper proposes and implements a wireless dimmable lighting system using variable-power variable-frequency (VPVF) control, which can eliminate the use of secondary converters via wireless power transfer (WPT). The proposed scheme integrates the secondary T-LCL circuit into a sealed anti-parallel light-emitting diode (LED) lamp, which takes the...

This paper proposes and implements an all-in-one induction heating system, which can accommodate both pan-shaped and wok-shaped utensils. Traditionally, the pan is heated by a planar induction cooktop while the wok is heated by a curved induction cooktop. In this paper, both magnetic inductive coupling and magnetic resonant coupling are utilized to...

This paper proposes and implements a novel continuously variable-frequency energy-encrypted wireless power transfer (WPT) system for wireless energy security in multi-receiver applications. To prevent wireless energy from being illegally stolen, the proposed chaotic 2-D frequency-and-duration encryption (FDE) technology directly generates well-defe...

This paper proposes a new hybrid-excited machine, termed parallel-hybrid-excited machine (PHEM) with harmonic-shift (HS) structure or HS-PHEM. The key is to alternately place the DC-field pole-pair and permanent magnet (PM) pole-pair in the stator, thereby achieving the DC-field harmonics shift from the PM-field harmonics. Consequently, the DC-fiel...

This paper proposes and implements a novel class of inductor-capacitor-capacitor wireless coordinative DC motor drives, which not only performs selective wireless power to motors, but also achieves power equalization to ensure the same operation for isolated robotic arms. The key is to make use of the selective wireless power transfer with several...

In this paper, a novel wireless servo motor drive is proposed and implemented, which artfully integrates wireless power transfer into the DC servo motor drive to achieve wireless bidirectional servo motion. Prominently, there is no power converter or controller at the servo motor side to realize the bidirectional rotation, while the motor control i...

In this paper, a novel kind of wireless motors, namely, the LCC compensated wireless switched reluctance motor, is proposed and implemented. The definite advantages are that there is no any power converter at the motor side and particularly no switched-capacitor array at the transmitter side to realize the multiple-frequency operation. The key is t...

This paper proposes and implements a novel multi-frequency multi-power wireless power transfer (MFMP-WPT) system based on one single transmitter for simultaneously and compatibly energizing multi-standard receivers. Generally, implementing a multi-frequency WPT often requires a compromise in system complexity, control difficulty, switching frequenc...

This paper proposes and implements a novel quasi-omnidirectional dynamic wireless power transfer (WPT) system using double 3-D coils for drone applications. In the traditional omnidirectional WPT system, the receiver direction is always facing the 3-D tra-nsmitter center to maximally pick up the magnetic flux. However, the on-drone receiver normall...

This paper proposes and analyses a magnetic coupling-strengthened energy-encrypted wireless power transfer (WPT) system for electric vehicle (EV) dynamic charging. A switched-capacitorless energy-encrypted transmitter and a chaotic 2-D frequency-and-duration encryption (FDE) are introduced to improve wireless energy security. By compacting WPT coil...

This paper proposes and implements a switched-capacitorless energy-encrypted transmitter and a 2-D frequency and duration encryption (FDE) technology for roadway-charging electric vehicles based on wireless power transfer (WPT). To prevent the encrypted energy package from being illegally decrypted by unauthorized receivers, the proposed 2-D chaoti...

This paper proposes and implements an accurate position detection method in wireless power transfer (WPT) for implant applications. Since the technique of WPT via magnetic resonant coupling makes it possible to non-invasively supply electricity for implants from an external transmitter, an accurate position detection of an invisible receiver from t...

In this paper, a quantitative comparison of five new dual-permanent magnet (PM) linear motors with fault-tolerant teeth is presented, which are promising for application to the ropeless elevator propulsion system. The proposed linear motors have PMs on both the mover and stator, leading to a new class of dual-PM linear motors. In addition, they can...

In this paper, a new permanent magnet (PM) linear machine, termed the bipolar-flux (BF) doubly salient PM (DSPM) linear machine, is proposed and implemented. This BF-DSPM machine incorporates the stator-PM structure and the mover-PM structure into the DSPM machine topology. It consists of a mover with fault-tolerant teeth (FTT) and a stator with co...

This paper proposes and implements a new move-and-charge (MAC) system for automatic guided vehicles (AGVs), which not only performs wireless charging, but also automatically navigates the AGV without using guiding sensors. The key is to make use of the dc-dc converter to maintain the equivalent load resistance and then detect the charging current v...