Heater Control Circuit Harmonic Suppression via Segmented Duty Cycling
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Solution Overview
Problem
Existing heating control techniques for heaters fail to adequately restrain harmonic current, which has become a stringent issue due to stricter standards, despite previous methods like on/off control and phase control.
Innovation Solution
The proposed solution involves a heating apparatus with a current-feed switching circuit that adjusts the duty ratio of AC power to the heater, employing a combination of wave-number control, DUTY 100% executable periods, and low-DUTY wave-number control periods to minimize harmonic current, using an ASIC to manage the triac and zero-cross detecting circuit for precise timing and duty ratio adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional on/off control or phase control is used for heating, then temperature control is achieved, but harmonic current cannot be sufficiently restrained to meet stricter standards
Solution Approach 1:
The heating control is divided into multiple distinct periods: a first period with 100% duty ratio for rapid heating, a second period with reduced duty ratio for harmonic suppression, and a third period with variable duty ratio based on temperature feedback. This temporal segmentation allows each period to optimize for its specific function, resolving the contradiction between temperature control stability and harmonic current reduction.
Solution Approach 2:
The invention implements periodic switching between different duty ratios in a structured sequence (first period → second period → third period). This periodic action with varying duty ratios enables the system to alternate between aggressive heating (when temperature is low) and harmonic-suppressing operation (when temperature is sufficient), thereby meeting both temperature control and harmonic current restraint requirements.
2Object-generated harmful factors
If duty ratio is reduced to suppress harmonic current, then harmonic current is restrained, but heating efficiency and temperature rise speed decrease
Solution Approach 1:
The first period with 100% duty ratio performs preliminary heating action to rapidly bring the heater temperature up to the required range. This preliminary action ensures that subsequent periods can operate at lower duty ratios for harmonic suppression without compromising overall heating efficiency, as the thermal mass has already been warmed during the first period.
Solution Approach 2:
The duty ratio is made dynamic rather than static, transitioning from 100% in the first period to reduced values in the second and third periods. This dynamic adjustment allows the system to optimize heating efficiency when temperature is low and suppress harmonic current when temperature is sufficient, thereby resolving the contradiction between heating efficiency and harmonic current restraint.
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 harmonic current to meet stringent standards while maintaining temperature stability, balancing power consumption and harmonic suppression.
Implementation Method 1
a heater (33) that generates heat by being supplied with AC power
Implementation Method 2
a zero-cross detecting circuit that detects a zero-cross timing of the AC voltage
Data Source
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AI summary
A heating apparatus includes a switching circuit configured to switch on/off current-feeding from an AC power source to the heater, a temperature detector configured to detect a temperature of the heater, and a current-feed controller configured to execute a first current-feed mode of changing a current-feed ratio of current-feeding time to unit time by controlling switching of the switching circuit so that the temperature detected by the temperature detector falls within a target range. The current-feed controller executes a second current-feed mode of fixing the current-feed ratio to almost 100% or almost 0% during execution of the first current-feed mode in place of the first current-feed mode.