Induction Heating Frequency Converter Discharge Control
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Solution Overview
Problem
Induction heating devices experience high starting currents and noise due to the charging of intermediate circuit capacitors, leading to reduced component lifespan and user dissatisfaction with audible noise.
Innovation Solution
Discharge the intermediate circuit capacitor to a threshold value before activating the induction coil, using a controllable switching element to limit the initial current and prevent noise, allowing for a low-noise and component-protecting operation by controlling the switching element with a pulse-width modulated square-wave signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the intermediate circuit capacitor is charged to no-load voltage during first supply half-wave, then the capacitor buffers the intermediate circuit voltage, but high starting current flows through the IGBT and resonant circuit causing audible noise and reduced component service life
Solution Approach 1:
The patent applies preliminary action by discharging the intermediate circuit capacitor before the induction coil is activated. The control unit discharges the capacitor in a time interval prior to the zero passage of the alternating supply voltage, ensuring the capacitor is substantially discharged before power generation begins. This prevents high starting currents and the associated audible noise and component stress.
Solution Approach 2:
The patent applies preliminary anti-action by actively discharging the intermediate circuit capacitor before it can charge to no-load voltage. The control unit monitors the supply voltage and initiates discharge before the zero passage, creating a counter-action that prevents the harmful charging effect from occurring in the first place.
2Power
If the switching element is switched on to generate heating power, then the induction coil produces adjustable heating power, but high current flows from the charged capacitor causing noise and component stress
Solution Approach 1:
The control unit performs preliminary discharge of the intermediate circuit capacitor before the induction coil is activated for heating power generation. This ensures that when the switching element is turned on, the capacitor does not discharge through the resonant circuit, eliminating high starting currents while allowing full heating power to be generated subsequently.
3Object-generated harmful factors
If the intermediate circuit capacitor is discharged prior to zero passage, then high starting current is prevented and noise is reduced, but the capacitor must be controlled during a specific time interval
Solution Approach 1:
The control unit uses feedback by monitoring the alternating supply voltage and detecting its zero passage. Based on this feedback, the control unit determines the appropriate time interval for discharging the intermediate circuit capacitor - specifically before the zero passage of the supply voltage. This feedback mechanism automates the timing control and ensures reliable operation.
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 method reduces start-up noise and extends the lifespan of power components by ensuring a pulsed current-free converter startup, enabling reliable and quiet operation with adjustable heating power control.
Implementation Method 1
the input supply voltage initially is rectified with the aid of a rectifier into a direct supply voltage or intermediate circuit voltage
Implementation Method 2
an induction coil is supplied with an alternating voltage or an alternating current, so that in a cooking utensil coupled magnetically to the induction coil and which is to be heated, eddy currents are induced, which give rise to a heating of the utensil
Implementation Method 3
eddy currents are induced, which give rise to a heating of the utensil
Implementation Method 4
Normally there is a so-called intermediate circuit capacitor for buffering the intermediate circuit voltage at the output of the rectifier
Implementation Method 5
subsequently processed for generating the high frequency control voltage with the aid of one or more switching elements, generally insulated gate bipolar transistors (IGBTs)
Data Source
AI summary
The invention relates to a method for operating an induction heating device. The induction heating device comprises an induction coil and a frequency converter for producing a control voltage for the induction coil. The frequency converter comprises a rectifier rectifying an alternating supply voltage (UN), an intermediate circuit capacitor, looped in between output terminals of the rectifier and equalizing the rectified voltage (UG), and at least one controllable switching element, looped in between the output terminals of the rectifier. According to the invention, in a predetermined discharge interval (INT) before a zero crossing (ND) of the alternating supply voltage (UN), the intermediate circuit capacitor is discharged to a threshold value by controlling the at least one switching element before the induction coil is controlled in order to produce an adjustable heating capacity.