Induction Heating of Aluminum Cookware
Induction heating has become a popular alternative to other heat sources for stovetop cooking applications due to performance, efficiency, control response, and safety. The main drawback is that extreme difficulty is encountered when trying to head low-resistivity, non-ferromagnetic metals such as aluminum and copper, which are commonly used for cookware in several societies. The lack of ferromagnetic properties, resulting in no hysteresis dissipation, and low resistivity of such metals results in an impractically low resistance reflected through the work coil. The resultant impedance complicates inverter design, as it is too low to be efficiently driven with conventional inverter topologies. The magnitudes of current involved in exciting this impedance also severely impact the efficiency of the coil and resonant components, requiring extreme care in coil design. This work explores various techniques that have been proposed and/or applied to efficiently heat low-resistivity cookware and the associated limitations. A transformer-coupled series-load-resonant topology driven by a full-bridge inverter is proposed as a means of efficiently heating aluminum cookware within practical design constraints. The experimental circuit is built and successfully tested at an output power of 1.66kW. The procedure of optimizing the work coil for improved efficiency is also presented along with the procedure of measuring coil efficiency. An improved circuit incorporating switch voltage detection to guarantee zero-voltage switching is then built in order to overcome limitations of this design.