Heating system comprising a resistive heat element, controller for such heating system, and method of controlling a load current through such resistive heat element
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Solution Overview
Problem
Heating systems with resistive heat elements face challenges during cold-start due to inrush currents, which can damage the system or overload the power source, and existing solutions either reduce efficiency or lead to slow heating and electromagnetic interference (EMI).
Innovation Solution
A heating system utilizing a forced-closure forced-opening (FCFO) bidirectional power switch, controlled by a digital processing unit, which allows for intelligent switching schemes and limits current flow during cold-start, enabling faster heating and reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a controlled switch is used to allow load current to flow from the grid through the resistive heat elements, then the heating system can be controlled, but inrush currents occur that can damage the system or overload the power source
Solution Approach 1:
The controller initiates a controlled startup sequence that gradually increases the conduction angle from a small initial value to the full 180 degrees over multiple AC cycles. This preliminary gradual activation prevents sudden inrush currents by building up power delivery incrementally, allowing the heating elements and surrounding materials to warm up progressively rather than experiencing thermal shock from full power activation.
Solution Approach 2:
The system dynamically adjusts the conduction angle of the controlled switch based on the startup phase. During cold-start, the conduction angle is progressively increased from a small value to 180 degrees over multiple AC cycles. This dynamic control strategy adapts the switching behavior to the current temperature state of the heating elements, preventing inrush currents while maintaining full power capability once warmed up.
2Reliability
If the applied voltage is reduced to the resistive heat element during cold-start, then inrush currents are reduced, but the efficiency of the heating system is reduced
Solution Approach 1:
The controller employs periodic modulation of the conduction angle during the startup phase, increasing it in steps across multiple AC cycles. This periodic action allows the system to deliver controlled amounts of energy incrementally, preventing inrush currents while still providing continuous heating over time. The heating efficiency is maintained because the cumulative energy delivery over the startup period approaches the full power level, just distributed across multiple cycles rather than delivered all at once.
3Reliability
If conduction angle control is used with TRIACs, then inrush currents are managed, but the cold-start is very slow requiring at least 180 half cycles to reach full power
Solution Approach 1:
The system dynamically adjusts the conduction angle progression strategy to balance inrush current management with startup speed. Rather than uniformly increasing the conduction angle by minimal amounts across all 180 half cycles, the controller can accelerate the conduction angle increase once the initial thermal stabilization is achieved, reducing the total cold-start time while still preventing harmful inrush currents during the critical initial phase.
Solution Approach 2:
The controller modifies the conduction angle parameter progressively during startup, changing it from a small initial value to the full 180 degrees. By optimizing the rate and pattern of this parameter change, the system achieves a balance between preventing inrush currents and minimizing cold-start time, potentially reaching full power faster than traditional methods while maintaining reliable inrush current management.
4Reliability
If conduction angle control is used with TRIACs, then inrush currents are managed, but EMI is significantly increased particularly with conduction angles between 45 degrees and 135 degrees
Solution Approach 1:
The controller incorporates feedback mechanisms to monitor the conduction angle and adjust it to avoid problematic ranges that generate excessive EMI. By detecting when the conduction angle enters the 45-135 degree range during startup, the system can modify its progression strategy to skip or quickly traverse through these EMI-prone angles, reducing electromagnetic interference while maintaining effective inrush current management through alternative conduction angle profiles.
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
The FCFO bidirectional power switch effectively manages inrush currents, allowing for efficient and rapid heating while minimizing the risk of system damage and EMI, enabling the use of smaller circuit breakers and improving overall system control.
Implementation Method 1
Heating systems comprising resistive heat elements... the controller connected to the at least one resistive heat element and being configured for controlling a load current through the at least one resistive heat element
Data Source
AI summary
A heating system having: i) at least one resistive heat element; ii) at least two terminals for receiving a grid voltage from a power grid, and iii) a controller for being connected to the terminals for receiving the grid voltage, the controller connected to the at least one resistive heat element and being configured for controlling a load current through the at least one resistive heat element, wherein the controller is configured controlling the load current though the at least one resistive heat element. The controller comprises an FCFO-bidirectional power switch connected in series with the at least one resistive element for controlling the load current that is received from the power grid. A method is for controlling the load current through the at least one resistive element, which applies a certain algorithm to avoid inrush current, shortens the length of a cold start and solves problems such as EML.