A system and method for variable power transfer in an inductive charging or power system. In accordance with an embodiment the system comprises a pad or similar base unit that contains a primary, which creates an alternating magnetic field. A receiver comprises a means for receiving the energy from the alternating magnetic field from the pad and transferring it to a mobile device, battery, or other device. In accordance with various embodiments, additional features can be incorporated into the system to provide greater power transfer efficiency, and to allow the system to be easily modified for applications that have different power requirements. These include variations in the material used to manufacture the primary and/or the receiver coils; modified circuit designs to be used on the primary and/or receiver side; and additional circuits and components that perform specialized tasks, such as mobile device or battery identification, and automatic voltage or power-setting for different devices or batteries.

System and method for inductive charging of portable devices

Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive 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.

A Critical Review of Recent Progress in Mid-Range Wireless Power Transfer

Inductive power transfer is a practical method for recharging electric vehicles because it is safe, convenient, and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Circular couplers are the most common topology in the literature; however, they have fundamentally limited coupling. Their flux patterns necessarily limit the operational air gap as well as tolerance to horizontal misalignment. A new polarized coupler topology [referred to as a double D (DD)] is presented, which overcomes these difficulties. DDs provide a charge zone five times larger than that possible with circular pads for a similar material cost and are smaller. A 0.31-m2 DD enables 2 kW of power transfer over an oval area measuring 540 mm × 800 mm with a 200-mm air gap. Leakage magnetic fields have been investigated and show that circular and DD couplers operating under similar power transfer conditions produce similar levels. Both topologies can be designed and operated to ensure compliance with international guidelines.

Development of a Single-Sided Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems

A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive power transfer

Inductive power transfer (IPT) was an engineering curiosity less than 30 years ago, but, at that time, it has grown to be an important technology in a variety of applications. The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a $1 billion industry in the process. Since then applications for the technology have diversified and at the same time become more technically challenging, especially for the static and dynamic charging of electric vehicles (EVs), where IPT offers possibilities that no other technology can match. Here, systems that are ten times more powerful, more tolerant of misalignment, safer, and more efficient may be achievable, and if they are, IPT can transform our society. The challenges are significant but the technology is promising.

Inductive Power Transfer

In this paper, the design of a contactless charger for the lithium-ion battery of a cellular phone is presented. In this charger, the primary core of the transformer is in the charger unit and the secondary core is in the telephone. The gap (3 mm) between them is the thickness of the two plastic cases. The transformer core design for the maximum coupling coefficient with the size constraint on the secondary side is presented. Analysis of the primary-side series resonant power converter with the loosely coupled transformer is performed, and the design optimization is presented. For the battery-charging control, a simple control circuit is presented and its performance is verified from the experimental results.

Design of a contactless battery charger for cellular phone

In this paper, the design of a contactless charger for a 3.3 W lithium-ion battery of a cellular phone is presented. In this charger, the primary core of the transformer is in the charger unit and the secondary core is in the telephone. The gap (3 mm) between them is the thickness of the two plastic cases. The transformer core design for the maximum coupling coefficient and the maximum magnetizing inductance with the size constraint on the secondary side is presented. A half-bridge series resonant converter is used to compensate the leakage inductance and to achieve ZVS operation. Voltage gain, current gain analysis, and design procedure are presented. For the battery charging control, an infrared LED is used and its performance is verified from the hardware experiments.

Cold cathode fluorescent lamps (CCFLs) show complex characteristics, which make it difficult to drive them in parallel. In this paper, a backlight inverter, which can drive multiple CCFLs using single controller and single switching network, is presented. The analysis of the lamp current distribution is presented in detail. The current-balancing condition, under which the lamp currents are well balanced in the presence of the lamp voltage variation, is derived. The effect of the resonant component variation is also investigated. The analysis results are verified from experiments with two 720-mm/4-mm CCFLs for 32-in liquid crystal display televisions. Experimental results with eight CCFLs are also presented in the presence of the lamp voltage and the resonant component deviation

Analysis of Current Distribution in Driving Multiple Cold Cathode Fluorescent Lamps (CCFL)

Disclosed is a digital PWM input D class amplifier by PWM negative feedback. The amplifier includes: digital modulation part for modulating PCM signal of input audio to PWM signal; pulse width generating and correcting part for comparing difference between the PWM signal and output signal negatively fed back, with PWM ramp signal to generate PWM switching signal; output part for generating an amplified output audio signal in response to the PWM switching signal of the pulse width generating and correcting part; and voltage negative feedback loop for negatively feeding back signal of the output part and decreasing a harmonic component to provide the signal to the pulse width generating and correcting part. Thus, the invention compares the negative feedback signal with positive/negative (+/−) saw tooth PWM ramp signal to control On/Off time period of switching transistor and the PWM pulse width and thereby enhance the linearity of the output PWM.

Digital PWM input D class amplifier by PWM negative feedback

Cold cathode fluorescent lamps (CCFL) show complex characteristics, which make it difficult to drive them in parallel. In this paper, analysis of the lamp current distribution in parallel operation is presented in detail. The current balancing condition, under which the lamp currents are well balanced in the presence of the lamp voltage variation, is derived. The analysis results are verified from experiments with two 720 mm/4 mm CCFL's for 32-inch LCD TVs. Experimental results with eight CCFL's in parallel are also presented

Chang-Gyun Kim

Papers

Design of a contactless battery charger for cellular phone

Design of a contactless battery charger for cellular phone

Analysis of Current Distribution in Driving Multiple Cold Cathode Fluorescent Lamps (CCFL)

Digital PWM input D class amplifier by PWM negative feedback

Uniform Current Distribution in Driving Cold Cathode Fluorescent Lamps (CCFL) in Parallel