Induction Heater Ferrite Saturation Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Induction cooking heaters face issues with ferrite core self-heating due to hysteresis energy loss, leading to saturation and potential failure of power transistors, as existing methods require ferrite saturation detection and cannot assess optimal working conditions to avoid Curie-point temperature.
Innovation Solution
Implementing a magnetic flux sensor, such as a pick-up coil wrapped around the ferrite bars, to directly sense the magnetic flux and reduce power output before reaching the Curie-point temperature, using a signal conditioning circuit to detect relative permeability changes and adjust power accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power is continuously supplied to the ferrite bars for magnetic field concentration, then the magnetic field focusing function is maintained, but the ferrite bars self-heat due to hysteresis loss and may reach Curie-point temperature causing magnetic saturation
Solution Approach 1:
The patent applies preliminary action by detecting the approach to Curie-point temperature through monitoring changes in relative permeability before actual saturation occurs. The signal conditioning circuit continuously monitors the ferrite bars' magnetic properties and triggers power reduction when permeability changes indicate approaching saturation, preventing harmful overheating before it occurs.
Solution Approach 2:
The patent implements feedback by using the signal conditioning circuit to monitor relative permeability changes in real-time and automatically adjusting the power output based on this feedback. When the ferrite bars' permeability changes indicate approaching Curie-point, the system reduces power to maintain safe operating temperature while preserving magnetic field concentration capability.
2Reliability
If power is reduced to prevent ferrite saturation, then the safe operation area is improved, but the heating power and productivity are reduced
Solution Approach 1:
The patent applies dynamics by making the power output adjustable and responsive to real-time conditions. Rather than fixed power reduction, the system dynamically modulates power based on the ferrite bars' instantaneous permeability characteristics, allowing maximum safe power delivery when conditions permit and automatic reduction only when approaching saturation thresholds.
Solution Approach 2:
The patent uses parameter changes by monitoring the relative permeability parameter of the ferrite bars and adjusting power output based on this changing parameter. The signal conditioning circuit detects permeability variations and translates them into appropriate power level adjustments, optimizing the balance between safety and productivity.
3Difficulty of detecting and measuring
If standard current ratio detection method is used to detect ferrite saturation, then the detection capability is provided, but the detection occurs too late and power transistors may already be damaged
Solution Approach 1:
The patent applies preliminary action by detecting changes in relative permeability that precede actual saturation and power transistor damage. The signal conditioning circuit monitors ferrite bar magnetic properties continuously and triggers protective action when permeability changes indicate approaching Curie-point, well before the catastrophic saturation that damages power transistors.
Solution Approach 2:
The patent replaces the mechanical/electrical current ratio detection method with a magnetic field-based detection system. Instead of measuring current ratios after saturation occurs, the system uses a signal conditioning circuit to detect changes in magnetic permeability, providing earlier and more reliable detection of approaching saturation conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach anticipates and prevents ferrite saturation, prolongs the life of power transistors, and maintains optimal performance by reducing hysteresis loss energy, thereby enhancing the safe operation area and overall performance of the induction heating system.
Implementation Method 1
a magnetic flux sensor, such as a pick-up coil wrapped around the ferrite bars, to directly sense the magnetic flux
Implementation Method 2
the magnetic field concentrator, usually in the form of ferrite bars or the like placed beneath the induction coil. The main function of these ferrite bars is to focus (i.e. concentrate) the magnetic field lines generated by the inductor
Implementation Method 3
As the ferrite bars concatenate the electro-magnetic fields generated by coil current of the induction heating half bridge converter, they start self-heating due to (mainly) the hysteresis energy loss
Implementation Method 4
Induction cooking heaters use half-bridge converters for supplying the load composed of the system induction coil+cooking vessel
Data Source
AI summary
An induction cooking heater having at least one inductor and ferrite bars as magnetic field concentrators located beneath the inductor comprises a sensing circuit associated to the ferrite bars and adapted to monitor at least one electric parameter of the sensing circuit in order to prevent the ferrite bars from reaching the Curie point temperature.