Sensorless Draft Inducer Motor Controller for Burner Ignition
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Solution Overview
Problem
Existing sensorless constant mass flow fan motors in draft inducers for burner systems fail to ensure sufficient airflow for ignition due to fluctuations in air temperature and barometric pressure, leading to inconsistent mass flow rates and potential failure to actuate the vacuum switch.
Innovation Solution
A motor controller system that includes a processor and inverter, which supplies specific currents to the fan motor to produce a first mass flow rate greater than the threshold for ignition and then transitions to a target mass flow rate for normal operation, accounting for changes in air density and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant mass flow fan motors are used without airflow sensors, then device complexity is reduced and cost is lowered, but mass flow rate becomes insufficient to actuate the vacuum switch when air temperature and barometric pressure fluctuate
Solution Approach 1:
The fan motor operates in two distinct dynamic modes: a first speed during ignition to generate sufficient mass flow for vacuum switch actuation, and a second reduced speed during normal operation. This dynamic speed adjustment resolves the contradiction by adapting the system's operational characteristics to different phases of burner operation, ensuring reliable ignition without requiring sensors while maintaining operational efficiency.
Solution Approach 2:
The system changes the operational parameters of the fan motor based on the operational phase. During ignition, the fan operates at a higher speed to compensate for cold, dense air conditions that reduce pressure drop. During normal operation, the fan reduces speed since the air is warmer and less dense, producing adequate pressure drop at lower speeds. This parameter change enables sensorless operation while maintaining reliability across varying environmental conditions.
2Reliability
If fan speed is increased to produce sufficient mass flow for ignition, then vacuum switch actuation is achieved, but energy consumption increases
Solution Approach 1:
The fan motor operates periodically at high speed only during the ignition phase to ensure reliable vacuum switch actuation, then transitions to lower speed during normal operation. This periodic high-speed operation ensures ignition reliability while minimizing energy consumption during the extended normal operation period, resolving the contradiction between reliability and energy use.
Solution Approach 2:
The system dynamically adjusts fan speed based on operational phase, using high speed temporarily during ignition to ensure reliability, then reducing to efficient operating speeds during normal operation. This dynamic adjustment resolves the energy-reliability tradeoff by applying high energy consumption only when necessary for reliable ignition.
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
Enables reliable ignition and operation of the burner system by ensuring sufficient airflow initially and optimizing airflow for efficient operation, eliminating the need for airflow sensors and reducing costs and complexity.
Implementation Method 1
The inverter is configured to supply current to a motor configured to rotate the draft inducer fan
Implementation Method 2
As the combustion gasses move through the burner and heat exchanger, a pressure drop is produced
Implementation Method 3
The processor is configured to instruct the inverter to supply a first current during a first period to the motor to rotate the draft inducer to produce a first mass flow
Data Source
AI summary
A motor controller for a burner system includes an inverter that supplies current to a motor that rotates a draft inducer fan. A processor is coupled to the inverter and receives a signal from a system controller, and in response instructs the inverter to supply a first current, during a first period, to the motor to rotate the fan to produce a first mass flow through the burner system, the first mass flow having a first mass flow rate greater than a threshold to actuate a vacuum switch. The processor then instructs the inverter to supply a second current, during a second period starting at an expiration of the first period, to the motor to rotate the fan to produce a second mass flow through the burner system, the second mass flow having a target mass flow rate for normal operation of the burner.