Ventilation Airflow Control Using Segmented Motor Current Sensing
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Solution Overview
Problem
Conventional ventilating systems face challenges in maintaining a constant air flow rate across a wide range due to variations in duct resistance and external wind pressure, requiring accurate current detection to control the motor effectively.
Innovation Solution
The ventilating system employs a DC motor with a control circuit that includes multiple low-resistance resistors for precise current detection, using switching units to adjust resistance and maintain a consistent air flow rate by adjusting the duty cycle and motor voltage based on detected currents and rotating speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a DC motor is used to drive blades in a ventilating system with a wide air flow rate range (100 m3/h to 400 m3/h), then the system can operate across multiple ventilation stages, but it becomes difficult to accurately detect current and maintain constant air flow rate
Solution Approach 1:
The current detection circuit is segmented into multiple parallel branches, each containing a low-resistance resistor. This segmentation allows the system to handle a wide current range by selectively activating appropriate branches, thereby maintaining detection accuracy across different air flow rate stages (100, 200, 300, 400 m3/h) without requiring a single high-precision detector for the entire range.
2Device complexity
If conventional current detection methods are used in a wide air flow rate range, then the system structure remains simple, but the air flow rate cannot be kept constant due to inaccurate current detection
Solution Approach 1:
The system implements feedback control by continuously detecting current through the low-resistance resistors and using this information to adjust motor operation. The control unit processes signals from the detection circuit and modifies motor drive parameters accordingly, ensuring constant air flow rate despite variations in duct resistance and external wind pressure across the wide operating range.
Solution Approach 2:
Low-resistance resistors are introduced as intermediary elements in the current detection path. These resistors convert motor current into measurable voltage signals with minimal impact on motor performance. The intermediaries enable accurate current measurement across a wide range without significantly affecting the motor's operational characteristics or requiring complex direct measurement techniques.
3Productivity
If the air flow rate is controlled in a very wide range using current and rotating speed, then multi-stage ventilation is achieved, but current detection must be extremely accurate to maintain constant air flow rate
Solution Approach 1:
The current detection circuit employs dynamic switching between multiple parallel branches with different resistance values. As the air flow rate requirement changes across the wide range (100-400 m3/h), the control unit dynamically selects or combines appropriate branches to maintain optimal detection precision for the current operating stage, enabling high productivity across all ventilation levels.
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 solution allows for accurate detection of currents flowing in the DC motor, ensuring a constant air flow rate is maintained despite changes in duct resistance and external influences, effectively controlling the ventilation system across a wide range of settings.
Implementation Method 1
a first current detecting unit that detects a current flowing in the DC motor... The first current detecting unit includes a plurality of low-resistance resistors, detects a motor current by using divided voltages of the low-resistance resistors
Data Source
AI summary
A ventilating system that can make an air flow rate variable includes a DC motor that drives blades and a control circuit that controls the DC motor. The control circuit includes a first current detecting unit that detects a current flowing in the DC motor, a rotating speed detecting unit that detects a rotating speed of the DC motor, and a control unit that controls the DC motor based on a rotating speed detected by the rotating speed detecting unit and a current detected by the first current detecting unit. The current detecting unit includes a plurality of low-resistance resistors, detects a motor current by using divided voltages of the low-resistance resistors, and calculates a ventilation air flow rate based on the rotating speed detected by the rotating speed detecting unit and the current detected by the first current detecting unit.