Ventilation Fan Control Using AC Voltage Estimation
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Solution Overview
Problem
Conventional air blowing devices struggle to precisely control air volume due to fluctuations in AC power supply voltage and load, making it difficult to accurately detect the required AC voltage for target air volume computation.
Innovation Solution
A ventilation device that includes an AC-DC conversion circuit, an inverter circuit using three-phase pulse width modulation (PWM) to convert DC voltage back to AC, and an AC voltage estimation unit, which detects the DC voltage applied to the inverter and computes the AC voltage based on motor current, allowing precise control of motor rotation speed to maintain a constant air volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC voltage is detected by a voltage detection unit to determine target air volume, then air volume control is achieved, but voltage fluctuations from AC power supply or load changes cause inaccurate air volume detection
Solution Approach 1:
The patent introduces an AC voltage estimation unit as an intermediary that computes the actual AC voltage based on the detected DC voltage and motor current. This intermediary calculation allows the system to distinguish between voltage fluctuations caused by AC power supply changes versus those caused by load variations, thereby enabling accurate target air volume determination despite voltage instability.
Solution Approach 2:
The system employs feedback by continuously monitoring the DC voltage and motor current, then using this information to estimate the AC voltage in real-time. The estimated AC voltage feeds back into the air volume computation, allowing dynamic adjustment of the target air volume to compensate for voltage fluctuations, thus maintaining measurement precision under varying conditions.
2Device complexity
If conventional air volume control is implemented without AC voltage estimation, then device complexity is reduced, but air volume control precision deteriorates under voltage fluctuations
Solution Approach 1:
The AC voltage estimation unit serves as a computational intermediary that adds minimal complexity to the control circuit. By calculating the AC voltage from readily available measurements (DC voltage and motor current), it provides precise air volume control without requiring additional sensors or complex hardware modifications.
3Loss of information
If AC voltage is not accurately detected, then computation resources are saved, but target air volume computation becomes inaccurate
Solution Approach 1:
The system uses feedback from DC voltage and motor current measurements to continuously estimate AC voltage, ensuring accurate target air volume computation without requiring direct AC voltage sensing. This approach maintains computational efficiency while improving precision by using information already available in the control system.
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 device effectively maintains a constant air volume regardless of AC power supply voltage fluctuations, ensuring precise air volume control without the need for extensive reference tables covering all possible AC voltages, thus reducing resource waste and manufacturing costs.
Implementation Method 1
an AC-direct current (DC) conversion circuit that converts an AC voltage supplied externally into a DC voltage to output the DC voltage
Implementation Method 2
an inverter circuit that converts the DC voltage output from the AC-DC conversion circuit into an AC voltage through a three-phase pulse width modulation (PWM) method
Implementation Method 3
a motor that drives the blades
Data Source
AI summary
A ventilation device includes AC voltage estimation unit (32) for estimating an AC voltage, based on a DC voltage detected by voltage detection unit (30) and a current detected by current detection unit (20). Air volume computation unit (24) determines a rotation speed of a motor, based on the AC voltage estimated by AC voltage estimation unit (32) and a target air volume output from a target air volume computation unit.