Induction Heating Inverter Harmonic Control via Dynamic Frequency Modulation
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Solution Overview
Problem
Induction heating cooking apparatuses face issues with non-linear effects and harmonic generation, particularly at higher power levels, which exceed regulatory limits, necessitating methods to control the induction generator to maintain harmonic levels within acceptable ranges.
Innovation Solution
A method and device that detect deviations in the supply current's shape or frequency spectrum, adapting the induction current to bring it within predetermined tolerance ranges by modifying the switching frequency or duty-cycle of the inverter, ensuring harmonics are minimized and power output is optimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power output of the induction generator is increased above 3.3 kW, then the heating efficiency and performance are improved, but the harmonic generation exceeds regulatory limits
Solution Approach 1:
The patent applies dynamics by continuously varying the switching frequency of the inverter during each half-wave of the supply voltage. Instead of using a fixed switching frequency, the frequency is dynamically adjusted - increased from the base frequency toward a maximum frequency as the half-wave progresses, then decreased back to the base frequency. This dynamic frequency modulation prevents the generation of excessive harmonics while maintaining high power output capability.
Solution Approach 2:
The patent implements parameter changes by modifying the switching frequency parameter of the inverter. The switching frequency is changed from a constant value to a time-varying parameter that follows a specific profile during each half-wave cycle. This parameter change transforms the supply current waveform to maintain sinusoidal shape with reduced harmonics, enabling operation at power levels above 3.3 kW without exceeding harmonic limits.
2Device complexity
If a fixed switching frequency is used in the inverter, then the control system is simple, but the supply current develops excessive harmonics at high power levels
Solution Approach 1:
The patent applies periodic action by implementing a switching frequency variation pattern that repeats each half-wave of the supply voltage. The frequency increases and decreases in a periodic manner synchronized with the supply voltage cycles, creating a systematic approach to harmonic reduction that maintains simplicity while being effective at reducing harmonics in the supply current.
3Power
If the switching frequency is varied to reduce harmonics, then the power output can exceed 3.3 kW, but the control algorithm becomes more complex
Solution Approach 1:
The patent implements feedback by continuously monitoring the supply voltage zero-crossings and using this information to control the switching frequency variation. The control algorithm uses the detected zero-crossings as reference points to initiate and terminate the frequency modulation cycle, providing a simple yet effective feedback mechanism that enables high power operation with harmonic control.
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 effectively reduces harmonics and maintains a sinusoidal shape of the supply current, allowing for higher power output while adhering to regulatory limits, thereby improving the efficiency and performance of induction heating.
Implementation Method 1
a magnetic field or induction filed is generated in order to induce eddy currents in the object to be heated which is electrically conducting and mostly also ferromagnetic
Implementation Method 2
induce eddy currents in the object to be heated
Implementation Method 3
The induction or magnetic field is generated by an induction generator
Data Source
Figure 1
AI summary
A method for controlling an induction heating cooking apparatus, comprises the steps of a) transforming a supply current (Iin) having a base frequency, for example 50 Hz or 60 Hz, into an induction current (IW) having a higher frequency than the base frequency of the supply current, b) feeding the induction current into at least one inductor of the induction heating cooking apparatus to generate a magnetic induction field, c) detecting a deviation or distortion of the actual shape or frequency spectrum of the supply current or a rectified supply current from a predetermined admissible shape or frequency spectrum lying outside of a pre-given tolerance range, d) adapting the induction current or the electrical power associated with the induction current until the detected deviation or distortion of the actual shape or frequency spectrum of the supply current or a rectified supply current from the predetermined shape or frequency spectrum lies within the pre-given tolerance range again.