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

Induction heating (IH) technology is nowadays the heating technology of choice in many industrial, domestic, and medical applications due to its advantages regarding efficiency, fast heating, safety, cleanness, and accurate control. Advances in key technologies, i.e., power electronics, control techniques, and magnetic component design, have allowed the development of highly reliable and cost-effective systems, making this technology readily available and ubiquitous. This paper reviews IH technology summarizing the main milestones in its development and analyzing the current state of art of IH systems in industrial, domestic, and medical applications, paying special attention to the key enabling technologies involved. Finally, an overview of future research trends and challenges is given, highlighting the promising future of IH technology.

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Induction Heating Technology and Its Applications: Past Developments, Current Technology, and Future Challenges

Embodiments of the invention relate to a method and system for transferring power wirelessly to electronic devices. The system can utilize magnetic coupling between two coils at close proximity to transfer sufficient power to charge an electronic device. Embodiments of the invention pertain to an array of spiral coils that can be used to transmit power for transfer to receiver coils. Potential applications of this technology include charging consumer electronic devices (cell phones, laptops, PDAs, etc), developing hermetically sealed devices for extreme environments, and less invasive transcutaneous energy transfer (TET) systems. Various embodiments of the subject system can be referred to as PowerPad system. Embodiments can incorporate one or more of the following: planar inductors, PCB transformers, and very high frequency power supplies. Embodiments of the invention also pertain to planar inductors having characteristics that allow the production of even magnetic field, as well as systems that incorporate such planar inductors.

Method and apparatus for wireless power transmission

This paper proposes a boost converter with coupled inductors and a buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate the voltage spike that is induced by the trapped energy in the leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero-voltage switching, switching loss can be reduced, and conversion efficiency therefore can be improved significantly. A 200 W prototype of the proposed boost converter was built, from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for low-input-voltage applications, such as fuel cell and battery power conversion.

Boost Converter With Coupled Inductors and Buck–Boost Type of Active Clamp

Solid-state switch mode AC-DC converters having high-frequency transformer isolation are developed in buck, boost, and buck-boost configurations with improved power quality in terms of reduced total harmonic distortion (THD) of input current, power-factor correction (PFC) at AC mains and precisely regulated and isolated DC output voltage feeding to loads from few Watts to several kW. This paper presents a comprehensive study on state of art of power factor corrected single-phase AC-DC converters configurations, control strategies, selection of components and design considerations, performance evaluation, power quality considerations, selection criteria and potential applications, latest trends, and future developments. Simulation results as well as comparative performance are presented and discussed for most of the proposed topologies.

Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation

When a pan made of a nonmagnetic material, such as aluminum, is used for cooking while the is being controlled, notification is made to the user to the effect that the temperature control function has been stopped and that the temperature should be manually adjusted. When the material detection section detects that the pan is made of a non-magnetic material or a pan-floating phenomenon has occurred, in order to prevent abnormal increase in the temperature of the pan due to incorrect, temperature detection caused by the pan-floating phenomenon, a set temperature is lowered.

Induction Heating Apparatus

This paper presents a new prototype of a voltage-fed quasi-load resonant inverter with a constant-frequency variable-power (CFVP) regulation scheme, which is developed for the next-generation high-frequency high-power induction-heated (IH) cooking appliances in household applications. This application-specific high-frequency single-ended push-pull inverter using new-generation specially designed insulated gate bipolar transistors (IGBTs) can efficiently operate under a principle of zero-voltage switching pulsewidth modulation (ZVS-PWM) strategy. This low-cost soft-switching inverter using reverse-conducting and reverse-blocking IGBTs is more suitable for multiple-burner-type induction-heating cooking appliances. The operating principle and unique features of a new resonant ZVS-PWM inverter circuit topology is originally described, together with its steady-state power regulation characteristics, which are illustrated on the basis of its computer-aided simulation and experimental results. The ZVS operation condition on power regulation, loss analysis of new IGBTs incorporated into this inverter, and its active filtering performance are discussed for IH cooking appliances.

Induction-heated cooking appliance using new quasi-resonant ZVS-PWM inverter with power factor correction

This paper deals with the 1st generation prototype of one-stage boost-half bridge (B-HB) series load resonant (SLR) soft-switching high-frequency (HF) inverter with a lossless snubbing capacitor for a variety of induction heating (IH) appliances. The B-HB SLR HF inverter treated here is based upon a simple dual SLR frequency selection strategy changed automatically in accordance with various metal materials of IH loads. In the first place, the triple SLR frequency (three times of switching frequency) operated B-HB inverter is demonstrated for IH of non-magnetic and low resistivity metallic pans/utensils fabricated by aluminum, copper and multi-layer of aluminum and stainless steel. In the second place, the fundamental resonant frequency (switching frequency) operated B-HB SLR HF inverter for IH is also demonstrated of magnetic and high resistivity metallic pans/utensils fabricated by iron, iron cast and stainless steel. Finally, the principle of operation control, implemental and inherent unique features of the B-HB SLR HF inverter employing automatically dual resonant frequency selection scheme for a variety of IH metallic pans/utensils is described from an experimental point of view, along with its operating performance. This 1st generation HF SLR inverter type built-in IH cooktop with two ranges/three ranges has been put into practice in home energy utilizations in all electricity residential systems.

Latest developments of high-frequency series load resonant inverter type built-in cooktops for induction heated all metallic appliances

In this vacuum heat insulator, an excellent heat insulating performance is obtained even at high temperature, and this excellent heat insulating performance is maintained for a long period. The hot insulating device and electric water heater using this vacuum heat insulator exhibit an excellent hot insulating performance, and are decreased in the power consumption for hot insulation. The vacuum heat insulator includes a laminate bag, and an insulating core placed in the laminate bag, and the inside of the laminate bag is evacuated in a vacuum state. The laminate bag is made of a laminate film. The laminate film includes a support layer, a deposition layer evaporated on the surface of the support layer, a protective layer placed at the surface side of the deposition layer, and a seal layer placed at the back side of the deposition layer. The deposition layer is formed of at least one material of metal and metal oxide. In this laminate film, (i) the support layer has a plastic film having a glass transition point of 87° C. or higher, (ii) the protective layer has a plastic film having a glass transition point of 87° C. or higher, (iii) the deposition layer has a property of transmitting high frequency magnetic field, or (iv) the laminate bag has a seal portion formed by junction of the seal layer, and the laminate film further as a metal foil placed at a position excluding the seal portion.

Vacuum heat insulator, hot insulating device using vacuum heat insulator, and electric water heater

A boiling-over detection unit (22) of an induction cooking device is constructed so as to detect boiling over and inhibit heating output when there has been a change equal to or exceeding a specified value in the electrostatic capacitance of an electrode (4), and also to not inhibit heating output when it is detected that there has been a change equal to or exceeding the specified value in the electrostatic capacitance of the electrode (4) due to the heating output of another heating coil (3b), which is in a heating region other than the boiling-over detection target, having changed by specified variation width or more.

Izuo Hirota

Papers

Induction Heating Apparatus

Induction-heated cooking appliance using new quasi-resonant ZVS-PWM inverter with power factor correction

Latest developments of high-frequency series load resonant inverter type built-in cooktops for induction heated all metallic appliances

Vacuum heat insulator, hot insulating device using vacuum heat insulator, and electric water heater

Induction cooking device