Research On Pot Detection And Power Control Of Multi-Load Induction Cooker

Electromagnetic induction heating is gradually replacing traditional heating methods and widely applied to industrial,domestic and medical fields for its high efficiency,cleanness safety and controllability.Induction cookers,as the typical representative of induction heating in civil field,have attracted great attention.Firstly,aiming at designing an eight-load induction cooker with an upper output power limit of 2000 W,this paper analyzes the characteristics of common inverter topology and multi-load topology of induction cookers.After comparing different topologies according to design requirements,the half-bridge series resonant inverter with parallel loads is selected as the main circuit topology of multi-load induction cooker.Secondly,to solve the problem that the traditional pulse counting method is not suitable for multi-load induction cooker due to its non-real-time characteristic,a real-time pot detection method based on current phase is proposed by analyzing the approximate relationship between current phase and load parameters.The software and hardware circuit scheme that adopt CPLD as the core chip is designed.The feasibility is verified through simulation.Then,in view of the disadvantages of traditional pulse frequency modulation such as its poor linearity of power modulation and the increasing switching loss caused by high frequency under light-load conditions,a combined modulation strategy,pulse frequency modulation and low frequency pulse density modulation(PFM & LF-PDM),is designed.Under this modulation strategy,the frequency is kept changing in a small range,and switching points of load switches are close to the zero-crossing point of the bus voltage,which effectively reduces the switching loss.The feasibility is verified through simulation.Finally,combined with the design objectives,an experiment platform of multi-load half-bridge induction cooker with parallel loads is built.Through theoretical analysis,the main parameters and device selection of the system are determined.The main protection circuit,sampling circuit and control system are designed.The system is validated experimentally.The experimental result demonstrates that the real-time pot detection method based on current phase can accurately distinguish pot materials,and the PFM & LF-PDM modulation strategy can effectively reduce the frequency change and improve the system robustness.