Two-Stranded EC Motor PWM Control for Temperature Mapping
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Solution Overview
Problem
Existing two-stranded electronically commutated motors used in compact fans face challenges in accurately mapping temperature information from PWM signals to rotation speed, leading to loss of temperature information and potential overheating due to non-conformal mapping, especially in duty factor ranges from 15% to 50%.
Innovation Solution
The use of a commutation controller to actuate semiconductor switches in series with motor stator winding strands and periodically interrupt power supply, allowing decaying loop currents to drive the rotor, ensuring energy stored in the magnetic circuit is utilized efficiently, and a diode connection to ground bus for PWM signal control, enabling effective conversion of duty factor into corresponding rotation speed without information loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PWM control is used to regulate fan speed based on temperature, then the fan can operate at different speeds, but the rotation speed does not accurately reflect the temperature information due to non-conformal mapping in certain duty factor ranges
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to periodically interrupt power supply to the motor windings. The third semiconductor switch periodically blocks and releases power to the windings, creating decaying loop currents during switch-off intervals that drive the rotor. This periodic control enables precise mapping of duty factor to rotation speed across the full range, including the previously problematic 15-50% range, thereby preserving temperature information accuracy.
Solution Approach 2:
The patent changes the operational parameters of the motor by controlling the duty factor of PWM signals applied to the third semiconductor switch. By varying the duty factor from 0% to 100%, the system achieves conformal mapping where rotation speed directly corresponds to temperature information. The decaying loop current mechanism allows the motor to respond linearly to duty factor changes across all ranges, eliminating information loss.
2Loss of energy
If the fan runs slowly at low temperatures, then energy consumption is reduced and service life is extended, but temperature information may be lost leading to potential overheating
Solution Approach 1:
The patent implements feedback by using temperature sensors to generate PWM signals whose duty factor depends on the temperature of the object being cooled. This closed-loop control ensures that the fan speed accurately reflects the temperature information, allowing the system to run slowly at low temperatures to save energy while maintaining reliability by preserving complete temperature information for decision-making.
3Productivity
If the duty factor is increased to achieve higher rotation speeds, then more heat can be dissipated, but the mapping between duty factor and rotation speed becomes non-linear causing information loss
Solution Approach 1:
The periodic interruption of power supply through the third semiconductor switch creates decaying loop currents that maintain a linear relationship between duty factor and rotation speed even at high speeds. This allows the fan to achieve high productivity for heat dissipation while preserving temperature information accuracy throughout the entire operating range.
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 a wide-range, low-noise, and almost linear control of motor current and rotation speed, ensuring accurate temperature-driven fan operation without overheating, improving efficiency and extending the service life of compact fans.
Implementation Method 1
a decaying loop current flows in the windings, and continues to drive the rotor of the motor
Implementation Method 2
the current acts in driving fashion in the other winding strand as well
Implementation Method 3
energy stored in the magnetic circuit of the motor continues to be used to drive the rotor
Data Source
AI summary
A two-stranded electronically commutated DC motor has a permanent-magnet rotor (36), power supply terminals (28, 30) for connecting the motor to a current source (22) and a stator (102) having a winding arrangement which includes first and second winding strands (52, 54). The latter are controlled by respective first and second semiconductor switches (70, 80). The motor also has a third controllable semiconductor switch (50), arranged in a supply lead from one of the terminals (28, 30) to the winding strands (52, 54), which third switch is alternately switched on and off by applying to it a PWM (Pulse Width Modulated) signal 24. During switch-off intervals, magnetic flux energy stored in the motor causes a decaying loop current (i2) to run through the windings, continuing to drive the rotor. This facilitates conformal mapping of temperature information in the PWM signal onto a target motor rotation speed.