Adaptive Filter for DC Motor Ripple Detection
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Solution Overview
Problem
Existing methods for determining the system dynamics and position of permanent-magnet direct current motors are prone to instability and inaccuracies, especially during the start-up phase, due to frequency jumps and harmonic components, leading to incorrect ripple counting and filtering.
Innovation Solution
An adaptive filter method with an adjustable band center frequency is used to detect and filter motor current signals, calculating instantaneous frequency using exponential functions and a mechatronic time constant, which improves accuracy and stability by weighting real-time measurements and modeled step responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ripple counting method is used for sensorless position detection, then costs are reduced by eliminating Hall sensors, but measurement precision deteriorates due to frequency jumps and harmonic components during start-up phase
Solution Approach 1:
The patent applies dynamics by making the filter frequency adaptive rather than fixed. The band center frequency of the filter is continuously adjusted based on the instantaneous frequency estimation, allowing the system to track frequency changes during motor operation, particularly during the critical start-up phase where frequency jumps occur.
Solution Approach 2:
The patent changes the parameter of filter frequency from a static value to a dynamically varying parameter. By estimating instantaneous frequency and using it to adjust the filter's band center frequency, the system adapts to changing operating conditions, eliminating measurement errors caused by fixed frequency filters during transient states.
2Device complexity
If adaptive filter with fixed frequency is used, then device complexity is reduced, but reliability deteriorates due to incorrect ripple detection during start-up and speed changes
Solution Approach 1:
The system performs self-service by automatically estimating its own instantaneous frequency from the motor current signal and using this estimation to adjust its filter parameters. This self-adjustment mechanism eliminates the need for external frequency control systems while maintaining reliable ripple detection across all operating conditions.
Solution Approach 2:
The patent implements feedback by continuously monitoring the motor current signal, estimating instantaneous frequency, and using this information to adjust the filter's band center frequency. This closed-loop approach ensures the filter remains synchronized with the actual signal characteristics, preventing detection errors during transient operations.
3Measurement precision
If instantaneous frequency estimation is performed during start-up phase, then measurement precision improves, but device complexity increases due to additional calculations and modeling
Solution Approach 1:
The patent replaces complex mechanical or hardware-based frequency measurement systems with software-based instantaneous frequency estimation. By using mathematical models and signal processing algorithms to estimate frequency from the motor current signal, the system achieves high precision without requiring additional physical measurement devices or complex hardware circuits.
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 enhances the accuracy and stability of frequency determination, reducing interference from harmonic components and allowing precise position and speed measurement without additional sensors, even in motors with inclined slots, and improves robustness against aging and manufacturing fluctuations.
Implementation Method 1
an electrical signal, in particular a motor current signal I Motor, of the permanently excited direct current motor is detected and by means of an adaptive filter device with an adjustable band center frequency f B is filtered
Implementation Method 2
a mathematical model with an exponential function for the instantaneous current IM and an exponential function for the calculation of the instantaneous frequency f M instantaneous frequency f M is used
Data Source
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AI summary
The method involves detecting an electrical signal i.e. motor current signal (Imotor), of a permanently excited direct current motor. The electrical signal is filtered using an adaptive filter device (1), and a filtered electrical signal is generated. A ripple of the filtered electrical signal is detected. An actual frequency of the ripple is determined. An instantaneous frequency of the ripple is calculated. An expected frequency value is calculated from the actual frequency of the ripple, the instantaneous frequency of the ripple and a weighting factor, during an initial phase of the motor.