Induction Heating Inverter Switching Loss Reduction
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Solution Overview
Problem
Existing induction heating devices face switching loss issues due to resonant current phase lead mode, which increases reverse recovery current and switching loss, especially when adjusting pulse width for power supply to induction heating coils.
Innovation Solution
The induction heating device employs a control system with capacitors connected in series to each induction heating coil, using high-frequency inverters to maintain resonant current phase lag mode by adjusting pulse width and DC voltage, ensuring zero-cross timing alignment with driving voltage, and incorporating an abnormal stop unit to prevent surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If pulse width is shortened to adjust supply power to induction heating coils, then power control is achieved, but resonant current phase lead mode occurs causing increased reverse recovery current and switching loss
Solution Approach 1:
The patent dynamically adjusts the DC voltage level based on the required pulse width. When pulse width needs to be shortened for power control, the system lowers the DC voltage to maintain resonant current phase lag mode, preventing the phase lead condition that causes excessive switching loss. This dynamic parameter adjustment resolves the contradiction between power control and energy efficiency.
Solution Approach 2:
The invention changes the DC voltage parameter in response to pulse width adjustments. By monitoring when pulse width shortening would cause phase lead mode, the system automatically adjusts DC voltage to maintain optimal operating conditions, thereby controlling switching loss while achieving the desired power supply adjustment.
2Area of stationary object
If multiple induction heating coils are disposed closely together, then space utilization is improved, but mutual induction inductances generate circulation currents between inverters
Solution Approach 1:
The patent implements a control system that monitors the current phases of multiple inverters and detects circulation currents caused by mutual induction. When circulation current is detected between closely disposed induction heating coils, the control system adjusts the current phase of affected inverters to eliminate the circulation current, thereby preventing energy loss while maintaining compact coil arrangement.
Solution Approach 2:
The control system proactively prevents circulation current by monitoring phase relationships between adjacent induction heating coils. When mutual induction is detected to potentially cause circulation current, the system preemptively adjusts current phases to prevent the harmful effect before it occurs, maintaining efficient operation in compact configurations.
3Loss of energy
If current phase synchronization is performed among inverters, then circulation current is suppressed, but control complexity increases
Solution Approach 1:
The control system automatically performs current phase synchronization among inverters without requiring external intervention or complex coordination protocols. Each inverter monitors its own current phase relative to others and self-adjusts to maintain synchronization, thereby suppressing circulation current while keeping the control system relatively simple through autonomous 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 approach reduces switching loss and surge voltage, maintaining efficient heat distribution and preventing transistor damage, regardless of pulse width, by operating in resonant current phase lag mode and controlling DC voltage and frequency.
Implementation Method 1
a plurality of induction heating coils 20-25 which are disposed adjacent with each other... each of which applies a high frequency voltage converted from a DC voltage to each series circuit of the induction heating coil and the capacitor
Implementation Method 2
generate a high-frequency magnetic flux, thereby heating the heating element
Implementation Method 3
capacitors 40-45 each of which is connected in series to each of the induction heating coils... maintain resonant current phase lag mode by adjusting pulse width and DC voltage
Data Source
AI summary
The purpose of the present invention is to minimize switching losses of an inverter. An induction heating device includes: a plurality of induction heating coils (20) which are disposed adjacent with each other; a plurality of inverters (30), each of which has a capacitor (40) serially connected to each of the induction heating coils (20), and converts a DC voltage into a square wave voltage; and a control circuit (15) which controls so as to align the phase of coil currents flowing though the plurality of the induction heating coils (20), wherein the control circuit (15) controls the timing at which the square wave voltage transitions such that an instantaneous value of the square wave voltage is preserved in either the DC voltage or a turnover voltage, when the coil current zero crosses.