Electronic technologies applied to induction cooking
Induction heating is based on the fact that certain materials, when subjected to electromagnetic fields, absorb part of the energy by transforming it into heat. These materials are usually metallic and must have any of the following properties:
- Good electrical conductivity, which allows the internal circulation of the so-called induced currents or Foucault (also known as “eddy currents”).
- Ferromagnetism, thanks to which the phenomenon of the so-called magnetic hysteresis occurs.
Both phenomena allow the transformation of the energy of the electromagnetic field into heat generated internally in the material. The required electromagnetic field is created by means of a medium / high frequency current source constituted by electronic components and an inductor system.
Induction heating is used in numerous industrial metal processes (preheating and extrusion heating, casting, welding, etc.).
The emergence of modern power semiconductor electronic devices ( BJTs, MOSFETs and IGBTs ) enabled the cheapening of induction heating systems and the subsequent introduction in the consumer market. Its application to induction cookers has a history in the 70’s, with developments and patents in the United States and Japan. The introduction in Europe occurred in the 1980s.
Due to the huge market for domestic cooking, induction cooking has aroused great interest as a substitute product for glass ceramic surface cookers, please refere to http://www.cocina-espanola.es/freidora-sin-aceite/. For this reason, some research groups work in coordination with electrical appliance companies to achieve more reliable, more economical systems, with less restrictions on use and installation and with higher performance.
Despite the time that has elapsed since the appearance of the first induction cookers, these have not had a significant presence in the market. Among the main reasons is the high initial price (between two and three times the price of a conventional kitchen) and the consideration of experimental application and still not well established that has among many potential users.
This trend is currently changing, so that all major groups of household appliances have in their catalogs domestic induction cookers, either with their own developments (figure 1) or through technology transfer markets. The greater supply has brought competition and with it a reduction prices and more information to the consumer, resulting in an increase in market share.
Induction cooking appliances are called home cooking appliances that use magnetic induction as a means of generating heat in a container of metallic material, usually ferromagnetic.
Kitchens or induction hobs require the use of high performance power electronic circuits (Figure 2) operating at frequencies in the range of 20 to 100 kHz, providing power outputs of more than 3 kW with high performance. The control of these power amplifiers and controls the device is done through digital electronic systems using microprocessors and application specific integrated circuits ( ASICs ).
Figure 3 shows the very simplified basic structure of an induction cooker. A vessel is induction heated by the generation of an electromagnetic field by a spiral flat inductor separated from the vessel by a ceramic glass. The power of the inductor is made by means of an electronic system of power controlled by the user through the controls to the effect. There are different types of controls, from the traditional rotary to the most recent digital “touch control” type.
Although outwardly very similar, the differences between a conventional glass ceramic plate and an induction plate are very important. As shown in Figure 4, in a conventional glass ceramic the heat is generated in a resistive element of the apparatus and is subsequently transmitted to the vessel. However, in an induction hob, what is transmitted is the magnetic field and the heat is generated internally in the vessel itself.
Characteristics of induction
Induction cooking has many advantages compared to traditional systems. The following differential characteristics are noteworthy.
- Quickly heating . Heat production in the material itself results in faster heating than in other systems, as shown in Figure 5.
Figure 5. Comparison between different weather technologies to heat 1.5 liters of water from 20 to 95º.
- Increased security . The risk of burns is reduced due to the lower temperature of the cooking zone.
- Ease of cleaning . The lower temperature of the cooking surface prevents the combustion of food residues (see figure 6), resulting in easier cleaning.
- Greater energy efficiency . The absence of high temperature heat sources causes an increase in efficiency by reducing heat losses to the environment. Figure 7 presents the efficiency comparison between different cooking technologies.
- Automatic detection of the container . The electronic system of induction plates incorporates the functionality of automatically detecting the vessel, avoiding unnecessary energy consumptions and adapting to the size of the vessel.
It is a mixed University-Company team, mainly addressing the research tasks from the University and the development tasks from the Company. At the University of Zaragoza, the team consists of seven professors, five of them doctors, and a variable number of research fellows, belonging to the Power Electronics Research Group, Department of Electronic Engineering and Communications. On behalf of the BSH Electrodomésticos Company, the team is made up of a variable number of engineers, two of them doctors, and support staff.