Chris Mi

San Diego State University | SDSU · Department of Electrical and Computer Engineering

In the conventional design of a double-sided LCL compensation network for the capacitive power transfer (CPT) system, two external capacitors are connected in parallel with the horizontal capacitive coupler, or a vertical capacitive coupler is required to reduce the resonant inductances. This approach results in a loosely coupled structure. The com...

This paper presents a frequency-domain analysis that models the behavior of Constant-on-Time (COT)-controlled Buck converters in wide-input-output-range scenarios. Based on this analysis, a design strategy is proposed to enable robust control with a duty-cycle-independent quality factor, also known as a constant $Q$ -value. A constant $Q$ -valu...

In this article, a novel load-independent capacitive power transfer (CPT) system with multiple constant voltage (CV) outputs is proposed. The capacitive repeater unit is designed to enhance the power transfer capability, which contains four plates where two plates are used to receive power from its previous unit and the other two plates transfer po...

This article presents the state-of-the-art electric vehicle (EV) charging technologies that benefit from the wide bandgap (WBG) devices, which is regarded as the most significant revolution in the power electronics industry in the past few decades. First, the recent WBG device technology evolution, performance comparison, and reliability issues are...

The successful commercialization of wireless power transfer (WPT) technology in mobile phones, laptops, and electric vehicles (EV), requires a safe, reliable, and efficient charging infrastructure. A metal object, such as a coin, a key, or a nail, however, may be inadvertently exposed, by close proximity, to the magnetic fields generated by the WPT...

A metal‐rim‐connected inductive coupler with series‐none compensation topology is proposed for smartwatch applications. By cross‐connecting the receiving coil to the metal rim with a 1 mm slot, the direction of the induced current on the metal rim is transformed to be the same as the current flowing on the receiving coil, leading to a strong magnet...

It is challenging to power a large number of gate drivers of the series‐connected insulated gate bipolar transistors (IGBTs) in a high‐voltage application because multiple isolated power supplies are needed. In this study, a novel wireless power transfer (WPT) system using repeater coils is designed to solve this problem. Every two repeater coils f...

This paper proposes a long‐distance multi‐load wireless power transfer (WPT) system with a constant voltage (CV) output for each load. A repeater unit consisting of two bipolar repeater coils is designed to power the load. Multiple repeater units are placed in a line and the power can be transferred from one unit to the next. Each repeater unit cor...

An NFC-CPT-combined coupler with a series-none compensation topology is proposed for metal-cover smartphone applications. To achieve capacitive power transfer through metal cover, the metal cover itself is used as receiving metal plates. To realize near field communication (NFC) through metal cover, the cross slot including a slim horizontal slot a...

Non-radiative inductive power transfer is one of the most studied and commercially applied wireless charging technologies, where the magnetic field is employed as the medium for power transfer. In the wireless charging of electric vehicles, the strong magnetic field will heat up any metal items falling in the charging area due to eddy current induc...

This paper proposes a power relay system to power multiple loads wirelessly via the magnetic coupling. Multiple power relays are placed in a line and the power can be transferred between these relays. Each power relay consists of two relay coils, which function as the receiver and transmitter respectively. In order to suppress the magnetic coupling...

A three-coil wireless charging system is proposed for full metal-cover smartphone applications. Considering the space limitation and other antennas in the smartphone, the receiver coil embedded in the smartphone is designed to be miniaturized as 16 mm × 65 mm. By integrating a series capacitance at the end of the 2 mm width narrow horizontal slot l...

A dual-coupled inductor-capacitor-capacitor and series (LCC-S) compensated wireless power transfer (WPT) system with a compact receiver size is proposed in this paper to improve the misalignment performance and achieve fault tolerant operation as well as a stable output power. The compensation coil and the main coil are integrated as two decoupled...

This paper proposes a general unified methodology for arbitrary higher-order resonant circuits. With the proposed methodology, the equivalent circuits and the general resonant methods of the higher-order resonant circuit are presented to realize the load-independent constant current (CC) and constant voltage (CV) outputs at two different load-indep...

This paper proposes a novel wireless power transfer (WPT) system for multiple loads. Multiple coils are used as power repeaters to enhance the power transfer capability over a long distance and each power repeater corresponds to a load. The LCC compensation method is used for each repeater coil in the system, which ensures load-independent currents...

In high-power electric vehicle wireless charging systems, the charging distance is short, and the coupling is strong in order to increase the power density and reduce the coil size and the system cost. With a strong coupling, the receiver-side compensation can be eliminated, and a high efficiency can still be obtained. The inductor-capacitor-induct...

Accurate modelling is necessary for designing a wireless power transfer (WPT) system and currently, first harmonic approximation (FHA) is widely used. However, it is not accurate for WPT systems with a strong coupling, such as fast charging of electric vehicles with a coupling coefficient of 0.80, compared to the conventional wireless charging with...

The output characteristics and the transfer efficiencies of Inductive Power Transfer (IPT) systems are affected by the variation of parameters such as, but not limited to, variable load, misalignment between the primary and secondary coils, and resonance frequency detuning owing to the inevitable manufacturing tolerances. This paper first analyzes...

This paper proposes a wireless power repeater system for long-distance and multiple-load applications with equal power load at each repeater. Each repeater performs as a power relay that not only receives and transmits power but also supplies power to its local load. The main contribution of this paper is to provide the design methodology of a dist...

Electrostatic motor can work as a supplement to the electromagnetic motor due to its simple structure, low cost, light weight, and high efficiency. This paper presents a dielectric-gas-based single-phase electrostatic motor with simplified construction. The motor design is focused on increasing the capacitance, subsequently the torque, to make the...

Wireless power transfer systems in seawater inevitably suffer some energy loss as a consequence of eddy current loss. Here, we present a coil structure utilizing two transmitter coils placed symmetrically adjacent to each side of the receiver coil. This coil arrangement, termed a 1×1×1 structure, yields improved power transfer efficiency. The eddy...

This paper proposes a tightly-coupled inductive power transfer (IPT) system for the low-voltage and high-current charging of automatic guided vehicles (AGVs). There are two challenges in the system design. First, the wide varying range of the airgap introduces difficulties to design the compensation circuit. Second, the low-voltage and high-current...

In a wireless power transfer (WPT) system, voltage tuning and frequency tuning are two major methods to control the power. For the design of a WPT system at the rated power, it is crucial to understand the characteristics of a WPT system with a constant-power load (CPL) under voltage tuning and frequency tuning. The model of a series-series compens...

An automotive onboard heater-equalizer is proposed to heat low-temperature batteries and balance cell voltages without the requirement of external power supplies. The proposed integrated topology only needs one MOSFET for one cell, resulting in a compact size and low cost, which can be easily applied to electric vehicles (EVs). Particularly, all MO...

In the wireless charging of high-power electric buses or low-power consumer electronics, the charging distance is normally very small, leading to a strong coupling. Current distortion occurs for a Wireless Power Transfer (WPT) system with a strong coupling. This paper investigates the strongly-coupled Series-Parallel (SP) compensated WPT system, wh...

Wireless Power Transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency or the coil current increases. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT sy...

This paper presents a rotation-resilient wireless charging system with a reversely wound receiver that supports efficient charging for lightweight autonomous underwater vehicles. By employing a two-part reversely wound receiver coil structure, the total mutual inductance of the proposed coil structure remains relatively constant when rotational mis...

In some applications of Wireless Power Transfer (WPT) technology, such as wireless charging of consumer electronics and electric buses, the coupling between the transmitter and the receiver is strong in order to improve efficiency. With a strong coupling, the compensation on the receiver side can be eliminated to achieve a high-level integration of...

The classical switched-capacitor (SC) equalizer (CSCE) is widely used in battery management systems (BMS) because of the accurate balancing and ease of implementation. However, it only achieves the adjacent cell-to-cell (AC2C) equalization, and its balancing speed and efficiency would become extremely low for multi-cell series-connected battery str...

The double-sided LCC topology provides a highly efficient compensation method for EV wireless charging systems. However, the two compensated coils occupy a large volume. In order to address the volume increase as well as to be compatible with unipolar coil structures, which are widely applied in EV wireless charging systems, an integration method i...

In cold climates, lithium-ion batteries suffer severe power/energy loss, bad performances, and reduced life cycle. Many internal AC heating strategies have been proposed to provide fast heating with a higher efficiency and better uniformity. However, the AC current is typically generated by an off-board equipment with grid power supply, which is a...

Lightweight autonomous underwater vehicles (AUVs), powered by rechargeable batteries, are widely deployed in inshore surveying, environmental monitoring, and mine countermeasures. While providing valuable information in locations humans have difficulty accessing, limited battery capacity of such systems prevents extended mission times. In order to...

This paper proposes a dual-coupled LCC-compensated IPT system with a compact magnetic coupler to improve misalignment performance. In the magnetic coupler, the main coils form the first coupling and compensation inductors are integrated with the main coils to form a second coupling. In the design presented in this paper, the main coils are unipolar...

This letter proposes a two-plate capacitive wireless power transfer (CPT) system for electric vehicle charging applications. The vehicle chassis and the earth ground are used to transfer power, which can replace two plates in a conventional four-plate CPT system. Therefore, only two external plates are required in the proposed CPT system. The coupl...

The conventional state-of-charge (SoC) estimation methods based on the equivalent circuit model (ECM) integrate all state variables into one augmented state vector. However, the correlations between RC voltages and SoC degrade the stability and accuracy of the estimates. To address this problem, this paper presents an adaptive SoC estimation method...

This paper presents a non-integer order (fractional) derivative model for modeling Lithium-ion (Li-ion) battery dynamics and where direct continuous-time (CT) model identification methods are used to estimate the battery model parameters. In particular, the CT least squares-based state-variable filter (lssvf) identification method is extended to be...

This paper presents a non-integer order (fractional) derivative model for modeling Lithium-ion (Li-ion) battery dynamics and where direct continuous-time (CT) model identification methods are used to estimate the battery model parameters. In particular, the CT least squares-based state-variable filter (lssvf) identification method is extended to be...

This paper presents a non-integer order (fractional) derivative model for modeling lithium-ion (Li-ion) battery dynamics in which direct continuous-time (CT) model identification methods are used to estimate the battery model parameters. In particular, the CT least squares-based state-variable filter (lssvf) identification method is extended to be...

This paper presents a battery model with non-integer order derivatives for modeling the dynamics of a lithium-ion battery over a large operating range. The non-integer or fractional differential model includes a constant phase element term to approximate the non-linear dynamical behavior of the battery. The proposed fractional differential model is...

Increasing use of wireless power transfer (WPT) in electric vehicles (EVs) is stationary charging, referred to as static charging in this chapter. This is because of the large number of passenger cars that are ready to be used by many potential customers. Automatic refueling of a vehicle is a wonderful thing for the person bored with repeated daily...

As a further step to go forward to a more improved performance on the inductive power transfer system (IPTS) for road-powered electric vehicles (RPEVs), an ultra-slim S-type power supply rail, which has a width of only 4 cm, is explained in this chapter. The cross-section of the core has a thin S-shape, and a vertical-wound multiturn coil is displa...

The 5 m off-distance inductive power transfer systems that have optimally shaped cores in the primary and secondary coils are explained. Instead of conventional loop-type coils for a magnetic resonance scheme, magnetic dipole-type coils with cores are used for a drastic reduction in deployment space and quite long wireless power transfer. An optimi...

The core of an inductive power transfer (IPT) system can be said to be coupled inductors. In this chapter, the coupled coils are modeled as equivalent circuits. We will start from the general distributed inductor case and then derive a lumped element circuit model. Furthermore, we will derive the transformer model and M-model, which correspond to a...

Due to strong and high-frequency magnetic field between transmitting (Tx) and receiving (Rx) coils of wireless stationary electric vehicle (EV) chargers, there is the possibility of them catching fire from debris of a metal piece in the magnetic field, which is inductively heated during charging. Position detection (POD) of misalignment between Tx...

Compensation circuits in the inductive power transfer system (IPTS) vary depending on applications. A basic and widely used compensation scheme with single magnetic coupling and two capacitors is explained in this chapter. The characteristics of series–series (SS), series–parallel (SP), parallel–series (PS), and parallel–parallel (PP) compensation...

In this chapter, the concept of mobile power electronics is explained with a general classification of this field. The history of mobile power electronics is briefly introduced and a few examples of mobile power electronics such as RF, optical, and tethered power transfer techniques are explained. Conventional wireless power transfer techniques suc...

In addition to the asymmetric coil structure in the previous chapter, another idea of increasing tolerance is to use DQ power supply coil sets for wireless stationary electric vehicle (EV) chargers. Two coil sets having a 90 phase difference can increase tolerances for longitudinal, lateral, as well as diagonal displacements. Each power supply coil...

In this chapter, the well-known coupled magnetic resonance system (CMRS) is explained, stating that it is nothing but new and is a sort of conventional inductive power transfer system (IPTS). There are three major magnetic couplings between coils in CMRS: source–transmitter (Tx), Tx–receiver (Rx), and Rx–load couplings, respectively. Except for Tx–...

To minimize the greenhouse effect caused by emission of CO2 , many automobile manufacturers are developing battery-powered automobiles that typically use rechargeable lithium ion batteries. However, the future of these battery electric vehicles (BEVs) is less than certain. The rechargeable lithium batteries are heavy and expensive with a limited li...

Contrary to the well-known dispersing magnetic field distribution characteristic, it is possible to some extend to focus on the magnetic field by synthesizing the magnetic field generated from multiple coils. A novel synthesized magnetic field focusing (SMF) technology is explained in this chapter and a non-radiative but focused magnetic field is e...

To have a large lateral tolerance is crucial for commercialization of road-powered electric vehicles (RPEVs). If you produce a large pick-up to meet the large tolerance, then EMF will increase and efficiency will decrease. A good design that allows large tolerance as well as low EMF and high efficiency is therefore required. Self-decoupled dual pic...

In this chapter, it is explained that not only the magnetically coupled inductors but also all inductive power transfer systems (IPTSs) inherently have the nature of a gyrator. Widely known characteristics of IPTSs such as impedance inversion and source-type conversion are proved to be the nature of the gyrator. A graphical approach that utilizes t...

Very often the dynamics of AC circuits such as AC power converters, AC power circuits (filters, power lines, etc.), AC motors, and inductive power transfer (IPT) systems should be identified to design the main circuit and controller. In this chapter, phasor transformation theory applied to the static analysis of linear AC converters is extended to...

How to deal with the dynamics of dynamic chargers is introduced in this chapter. A large signal dynamic model of the inductive power transfer system (IPTS) for the on-line electric vehicle (OLEV) is developed using the complex Laplace phasor transform introduced in Chapter 7. With the help of this dynamic model, the effect of the output capacitor a...

Improved magnetic mirror models (IM3) for mono and dual coils with a finite width and infinite permeability are explained in this chapter [47]. By introducing a mirror current, which is located at the same distance from a source current but with a smaller magnitude than the source current, the magnetic flux density of the mono and dual coils can be...

In this chapter, an advanced version of on-line electric vehicles (OLEVs) is introduced as an introductory example of road-powered electric vehicles (RPEVs). Because the author is heavily involved in the development of OLEVs, this chapter will guide readers to how practical problems are dealt with. This chapter is based on the paper by J. Huh, S.W....

The IPTS for mobile robots, which has a single wire layer of easily fabricable power floor structure and an evenly displaced multi pick-up structure for receiving uniform power, is explained. Due to its simple structure, a wide area power floor of 3.15 m 2 (1.5 m×2.1 m) could be fabricated as a prototype. Three pick-ups with an evenly displaced ang...

As an extended work of a previous chapter, a dipole-coil-based extremely loosely coupled inductive power transfer system (IPTS) for wireless sensors over a wide range is explained in this chapter. The overall superiority of dipole coils for a long-distance power delivery over loop coils with an identical configuration of a square core is verified b...

In this chapter, the fundamental principles of wireless power transfer (WPT) are explained. As introduced in Figure 1.2 of Chapter 1, WPT includes inductive power transfer (IPT), capacitive power transfer (CPT), RF power transfer (RF PT), and optical power transfer (optical PT). Because RF PT and optical PT have been briefly introduced in Chapter 1...

As an extended work of the single dipole coil in the previous chapters, crossed dipole coils for the wide-range three-dimensional omnidirectional inductive power transfer (IPT) are explained in this chapter. Free positioning of a plane receiving (Rx) coil is obtained for an arbitrary direction within 1 m from a plane transmission (Tx) coil. Both th...

In the inductive power transfer systems (IPTS) of wireless electric vehicles (WEV), the electromagnetic field (EMF) should be lowered for the safety of pedestrians. In general, the EMF should be canceled for every space, time, and load condition of interest. Three generalized design methods for canceling the EMF of WEV are explained in this chapter...

In this chapter, the dipole coil inductive power transfer system (IPTS) is applied to a special purpose instrumentation. A highly reliable power and communication system that guarantees the protection of essential instruments in a nuclear power plant (NPP) under a severe accident is explained. Both power and communication lines are established with...

As an improved solution to the I-type power supply rail, as explained in the previous chapter, a dq I-type power supply rail is introduced in this chapter. The single-phase I-type power supply rail for on-line electric vehicles (OLEVs) has a very narrow power supply rail with 10 cm width and exposes pedestrians to a very low electromagnetic field d...

Different from previous chapters of inductive power transfer (IPT), this chapter introduces capacitive power transfer (CPT) for static wireless electric vehicle (EV) chargers. A four-plate compact capacitive coupler and its circuit model for a large airgap distance CPT is proposed. The four plates are arranged vertically, instead of horizontally, t...

In this chapter, a general overview of electric vehicles (EVs) is briefly provided because EV is one of the major applications of WPT in this book. Currently, IPT is a majority method for EV charging though CPT is being researched as a potential candidate. Neither detail nor professional introduction to EVs will be tried in this chapter because thi...

The numbers and areas of wireless power transfer (WPT) applications are already rapidly increasing and are expected to significantly increase in the future. In this chapter several possible “futures” of WPT are discussed with regard to a few viewpoints in the areas and competing technologies with two or more candidates that are in competition with...

Power supply rails, often simply referred as power rails, for road-powered electric vehicles (RPEVs) are often segmented like the conventional iron rails. We do not want to turn on the power rail with no running EVs on it and we want to turn on the power rail only for providing wireless power to EVs. There are a few power rail segmentation methods,...

As discussed in the previous chapter, large tolerance is one of the best characteristics of a static electric vehicle (EV) charger, but only if no severe penalty for the larger tolerance is found. In this chapter, an explanation is given of asymmetric coil sets for wireless stationary EV chargers, which have a significantly larger lateral tolerance...

An extensive review on road-powered electric vehicles (RPEVs) is provided in this chapter. RPEVs are attractive candidates for future transportation, as introduced in the previous chapter, because they do not rely on large and heavy batteries but directly and efficiently get power while moving along a road. The inductive power transfer systems (IPT...

This paper proposes a modularized global architecture using multi-winding transformers for battery cell balancing. The global equalization for a long series-connected battery string is achieved based on forward conversion in each battery module and based on flyback conversion among modules. The demagnetization of the multi-winding transformers is a...

This paper proposes a novel coupler structure for wireless power transfer, which takes advantage of both magnetic and electric fields. The coupler contains four metal structures, two each at the primary and secondary sides, which are capacitively coupled. Each structure consists of long strips of metal sheet to increase its self-inductance, which i...

This paper proposes an automatic any-cells-to-any-cells battery equalizer, which merges the forward and flyback converters through a common multi-winding transformer. The windings of the transformer are divided into two groups, which have opposite polarities. The principles of the proposed equalizer are that the equalization in one group is achieve...

This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effec...

This paper presents a fault detection method for short circuits based on the correlation coefficient of voltage curves. The proposed method utilizes the direct voltage measurements from the battery cells, and does not require any additional hardware or effort in modeling during fault detection. Moreover, the inherent mathematical properties of the...

This paper presents an improved battery parameter estimation method based on typical operating scenarios in hybrid electric vehicles and pure electric vehicles. Compared with the conventional estimation methods, the proposed method takes both the constant-current charging and the dynamic driving scenarios into account, and two separate sets of mode...

Due to the low cost, small size, and easy control, the switched-capacitor (SC) equalizer is promising among all types of active cell balancing methods. However, the balancing speed is generally slow and the balancing efficiency is seriously low when the SC equalizer is applied into a long battery string. Therefore, an automatic switched-coupling-ca...

This paper proposes a combined inductive and capacitive wireless power transfer (WPT) system with LC -compensated topology for electric vehicle charging application. The circuit topology is a combination of the LCC-compensated inductive power transfer (IPT) system and the LCLC-compensated capacitive power transfer (CPT) system. The working principl...

This paper proposes a four-plate compact capacitive coupler and its circuit model for large air-gap distance capacitive power transfer (CPT). The four plates are arranged vertically, instead of horizontally, to save space in the electric vehicle charging application. The two plates that are on the same side are placed close to each other to maintai...