Gas Modulating Valve PWM Control for Ultra-Low Burner Flow
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Solution Overview
Problem
Conventional methods for regulating gas flow in condensation boilers face limitations in achieving high power modulation, particularly in delivering precise gas metering at low flow rates and adapting to different gas types, due to restricted ranges of modulation and inadequate sensor detection of combustion quality.
Innovation Solution
A method for driving a modulating valve that uses pulse-width modulation (PWM) signals to control the gas flow rate, allowing for controlled delivery of gas flow rates below the minimum flow rate by adjusting the duty cycle and frequency of the PWM signal, thereby extending the range of modulation and ensuring stable combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional gas-modulation valve is used with a Venturi mixer, then the system can operate in a limited range of air flow rates, but the depression signal is too low to be detected by the gas-modulation valve at low air flow rates, resulting in imprecise gas metering
Solution Approach 1:
The patent replaces the pneumatic control system (Venturi mixer generating pressure depression) with an electronic control system. A flow sensor directly measures the air flow rate and generates an electrical signal that controls the gas-modulation valve, eliminating the need for the Venturi mixer's pressure-based control mechanism. This substitution enables precise measurement and control across a wider range of air flow rates.
Solution Approach 2:
The patent changes the control parameter from pressure depression (pneumatic) to electrical signal (electronic). By using a flow sensor to generate an electrical signal proportional to air flow rate, the system can accurately detect and respond to low air flow rates that were previously undetectable by pressure-based systems, thereby improving measurement precision across the full operating range.
2Adaptability or versatility
If electronic fuel control with closed-loop regulation is implemented, then the range of power modulation can be increased, but the ability to deliver air and gas within this wide range of modulation remains limited by conventional valve design
Solution Approach 1:
The patent implements a closed-loop control system where a flow sensor continuously monitors the air flow rate and feeds back an electrical signal to the control unit. The control unit adjusts the gas-modulation valve based on this feedback to maintain the desired air-fuel ratio across a wide range of power modulation, ensuring reliable gas delivery despite the expanded operating range.
Solution Approach 2:
The patent makes the gas-modulation valve dynamically adjustable through electronic control. The valve's opening position is continuously varied based on the electrical signal from the flow sensor, enabling the system to adapt to different power levels and maintain proper air-fuel mixing across the entire modulation range, from minimum to maximum power.
3Adaptability or versatility
If the valve is designed for worst-case gas types, then it can support a range of gases, but the minimum flow rate is higher than necessary, reducing the modulation range
Solution Approach 1:
The patent changes from fixed mechanical valve design to electronically controlled valve operation. By using PWM signals to control the valve, the system can deliver precisely controlled low flow rates regardless of gas type characteristics. The electrical control allows the valve to operate in a pulsed manner at very low duty cycles, achieving minimum flow rates much lower than what conventional mechanical designs permit.
Solution Approach 2:
The patent employs pulse-width modulation (PWM) to control the gas-modulation valve. The valve operates in periodic on-off cycles with variable duty cycle, allowing the system to deliver average flow rates below the valve's minimum continuous flow rate. This periodic action enables the system to achieve the required low minimum flow rates while maintaining compatibility with various gas types.
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 enables a wider range of modulation for gas flow rates, improving the precision and adaptability of gas delivery to different gas types, enhancing combustion efficiency and reducing emissions, without requiring substantial modifications to the valve or control hardware.
Implementation Method 1
A method for driving a modulating valve regulating the flow of gas to a burner of a condensation boiler is known from document WO 2014/060991 A1. This approach enables a wider range of modulation for gas flow rates, improving the precision and adaptability of gas delivery to different gas types
Data Source
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AI summary
Method for driving a device for modulating a valve (1) regulating the flow rate of gas towards a burner (3), in particular of a condensation boiler having high power modulation, the valve together with the associated closure member thereof being designed so as to operate with a predetermined characteristic curve, the flow rate (Qgas) delivered being proportionally related to the strength of a first current signal (Imod) sent to the modulator such that the flow rate can be modulated, using said characteristic of proportionality, within a range of modulation between a maximum flow rate (Qgas_max) and a minimum flow rate (Qgas_min), and, so as to deliver controlled gas flow rates that are below said minimum flow rate (Qgas_min), thereby extending the range of modulation into minimum deliverable flow rate values, provision being made to drive the modulator with a second PWM voltage signal capable of generating a particular second PWM current signal (Imod'), so as to move the closure member of the valve according to the second signal. Furthermore, the terms first (Ta) and second (Tb) time interval being given to the successive durations of the high signal and the low signal, respectively, the sum of which is equal to the period (T) of the second signal, with a duty cycle (dc) equal to the relationship Ta/T, the strength of the second current signal (Imod') is modulated: - by amplitude modulation of the second signal (Imod'), leaving the duty cycle constant, so as to vary the flow rate accordingly, or - by modulation of the duty cycle in the period (T), keeping a preset amplitude of the second signal constant relative to the first time interval, so as to vary the flow rate delivered accordingly.