Motor Winding Resistance Estimation for Accurate Ripple Counting
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Solution Overview
Problem
Existing methods for determining the number of revolutions in electric motor assemblies are inaccurate due to issues with ripple detection errors, and they require precise temperature and resistance measurements, which can be complex and unreliable, especially in varying environmental conditions.
Innovation Solution
An electric motor assembly with a current sensor, temperature sensor, and processing circuit that determines motor resistance values based on temperature measurements and current values, selecting the appropriate method for resistance calculation based on the relative positions of brushes and commutator sections to improve ripple counting accuracy and reduce false alarms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ripple counting is used to determine motor revolutions, then the method is simple and does not require additional sensors, but the accuracy is reduced due to ripple detection errors
Solution Approach 1:
The patent uses feedback by measuring the actual motor resistance during operation and comparing it with expected resistance values at different brush-commutator positions. This feedback mechanism allows the system to identify and correct false ripple detections, thereby improving revolution counting accuracy without adding complex hardware
Solution Approach 2:
The patent replaces the mechanical/physical ripple detection method with an electrical measurement approach. By measuring motor resistance through voltage and current measurements and comparing with pre-stored resistance maps, the system substitutes the purely mechanical ripple counting method with an electrical field-based measurement and comparison system
2Measurement precision
If temperature sensors are installed for each motor to accurately measure temperature, then temperature estimation accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent implements self-service by using the motor's own electrical parameters (voltage, current, and derived resistance) to estimate its temperature. The motor assembly itself provides the measurement data needed for temperature estimation through resistance measurements, eliminating the need for external temperature sensors
Solution Approach 2:
The patent uses motor resistance as an intermediary parameter to indirectly measure temperature. Instead of directly measuring temperature with sensors, the system measures resistance (which can be obtained from voltage and current measurements) and uses pre-stored resistance-temperature relationships to estimate temperature, serving as a mediator between electrical measurements and temperature information
3Measurement precision
If resistance measurements are taken at different brush and commutator positions, then the accuracy of resistance determination is improved, but the measurement process becomes more complex
Solution Approach 1:
The patent applies preliminary action by pre-storing resistance maps that contain expected resistance values for different brush-commutator positions and temperatures. During operation, the system only needs to measure current resistance and compare it with the pre-stored values, eliminating the need for complex real-time measurements at multiple positions and reducing the measurement process complexity
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 enhances the reliability of motor revolution counting and temperature estimation, reducing the risk of false over-temperature alarms and allowing for accurate motor control without the need for precise temperature sensors for each motor, thus improving overall motor performance and safety.
Implementation Method 1
a predetermined dependence of variation of the motor resistance dependent on the temperature value
Implementation Method 2
determine an electric current value measured by the current sensor, when the electric motor is at least substantially at standstill
Data Source
AI summary
An electric motor assembly is configured to determine a motor winding resistance value. Predicted values are determined for a first and second position of motor commutator sections relative to the motor brushes, with at least one of the brushes contacting different numbers of the sections in the first position and the second position. The predicted values are based on a temperature value measured by the temperature sensor and a predetermined dependence of variation of the motor resistance dependent on the temperature value. An electric motor current value is measured by a current sensor when the electric motor is substantially at standstill. A selection is made between different factors for determining the motor resistance value using the electric current value, dependent on which of the predicted values most closely corresponds to the electric current value. The motor resistance is determined using said electric current value according to the selected factor.