Methods and apparatus for measuring sensorless brushless DC motor load
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Solution Overview
Problem
Existing methods for detecting laundry weight in washing machines using sensorless brushless DC motors are inaccurate due to reliance on optical couplers and zero-crossing information of counter-electromotive force, increasing manufacturing costs and reducing accuracy.
Innovation Solution
A method and apparatus that utilize phase voltage information to calculate the deceleration time of a BLDC motor, correlating this with pre-built lookup tables to predict laundry weight without the need for position sensors, thereby simplifying the main control board design and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical coupler and comparison amplifier circuit are used to measure motor deceleration, then the measurement can be performed, but the manufacturing cost increases
Solution Approach 1:
The patent extracts and eliminates the optical coupler and comparison amplifier circuit from the measurement system. Instead of using these complex components to process counter-electromotive force signals, the invention directly uses the existing phase voltage information from the three-phase bridge circuit to calculate motor deceleration and infer laundry weight, thereby removing unnecessary hardware complexity while maintaining measurement capability
Solution Approach 2:
The patent makes the phase voltage detection circuit serve multiple functions: it simultaneously provides both motor control signals and laundry weight measurement data. The same three-phase voltage detection that is already present for motor commutation is also used to calculate deceleration characteristics, eliminating the need for separate measurement circuits and reducing overall system complexity
2Measurement precision
If zero-crossing information of counter-electromotive force is used for measurement, then the weight detection can be performed, but the accuracy is low
Solution Approach 1:
The patent changes the measurement parameter from zero-crossing information of counter-electromotive force to phase voltage information. By using the amplitude and timing of phase voltages during motor deceleration, the system obtains more accurate deceleration characteristics. This parameter change enables direct calculation of deceleration rate without relying on indirect zero-crossing detection, thereby improving measurement accuracy
Solution Approach 2:
The patent replaces the mechanical/electrical signal processing method (counting pulses from counter-electromotive force through optical couplers) with a direct electrical calculation method. By using phase voltage information and computational algorithms to determine deceleration characteristics, the system achieves higher accuracy without the information loss inherent in pulse counting and zero-crossing detection methods
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 allows for more accurate and cost-effective laundry weight measurement by leveraging phase voltage information to calculate rotational speed and weight, reducing the complexity of the main control board and enhancing measurement precision.
Implementation Method 1
a change in rotational speed occurs when the motor is freely decelerating, and it is usually measured by counting the number of pulses of the counter-electromotive force of the motor
Data Source
AI summary
A method for measuring sensorless brushless-DC motor load, adapted to a home appliance, including: accelerating, through the use of a driving circuit, a BLDC motor from an initial rotational speed to a first rotational speed; disabling, through the use of a control circuit, the driving circuit; obtaining, through the use of a detecting circuit, phase voltage information corresponding to each phase of the BLDC motor when the BLDC motor is decelerated from the first rotational speed to a second rotational speed; obtaining, through the use of the control circuit, a first time period during which the BLDC motor decelerates from the first rotational speed to the second rotational speed according to at least one piece of the phase voltage information; obtaining, through the use of the control circuit, a first predicted weight of a load according to the first time period and a first lookup table.