Sensorless DC Motor Speed Measurement via Current Gradient
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Solution Overview
Problem
Existing methods for sensorless speed determination of brush-commutated DC motors are prone to interference from supply network disturbances and require complex filtering, making them inefficient and computationally costly, especially in environments like motor vehicles.
Innovation Solution
A method that determines the rotational speed of a brush-commutated DC motor by activating it with pulse-width modulated voltages, measuring current and current gradients at specific times when the motor voltage is 0 volts, and using internal resistance and winding inductance information to calculate the induced voltage, which is proportional to the speed, thereby avoiding the need to filter current ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current ripple evaluation is used for sensorless speed determination, then speed information can be obtained without position sensors, but the measurement is influenced by supply voltage fluctuations and requires complex filtering
Solution Approach 1:
The invention extracts the speed information from a different signal source - specifically from the current gradient during voltage transitions rather than from continuous current ripple analysis. By taking the derivative of the current signal and evaluating it during specific time windows when voltage transitions occur, the method separates the speed-related information from supply voltage disturbances, eliminating the need for complex filtering while maintaining reliability
Solution Approach 2:
The method performs preliminary differentiation of the current signal to obtain the current gradient before evaluating speed information. By pre-processing the current signal to compute its time derivative, the invention transforms the measurement approach to capture transient current changes during voltage transitions, which directly relate to induced voltage and speed without being affected by steady-state supply fluctuations
2Measurement precision
If current ripple measurement is performed on supply lines, then speed determination is possible, but high supply current makes ripple detection difficult and creates load on the supply network
Solution Approach 1:
Instead of measuring speed from the amplitude and frequency of current ripples in the time domain, the invention transitions to measuring the time derivative of current (current gradient) during specific transition periods. This dimensional change from measuring steady-state ripple characteristics to measuring transient current slopes provides a clearer, more precise signal that is easier to detect accurately despite the high supply current background
3Object-affected harmful factors
If filter circuits are used to remove current ripples, then supply network interference is reduced, but speed determination becomes impossible
Solution Approach 1:
The invention extracts speed information from the transient current gradient during voltage transitions rather than from continuous current ripples. By focusing on the derivative of current during specific time windows when voltage changes occur, the method obtains speed information without requiring filter circuits, thus maintaining both speed determination capability and reducing supply network interference
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 provides a more robust and computationally efficient method for determining motor speed, resistant to supply voltage interference and capable of accurately measuring speed without the need for complex filtering, thus reducing load on the supply network.
Implementation Method 1
determining an indication of an induced voltage as the rotational speed indication using the one or more current indications and the one or more current gradient indications using information provided about an internal resistance and a winding inductance of a rotor winding of the DC motor
Data Source
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AI summary
The method involves controlling a direct current motor (2) with a pulse width modulation control. Current information indicating a flow through the motor is determined at specific time in a time slot. Current gradient information indicating temporal current gradients is determined at the specific time in the time slot. Information about induced voltage is determined as rotation speed information of the motor based on the current information and the current gradient information using information concerning internal resistance and coil inductance of a runner coil of the motor. Independent claims are also included for the following: (1) a device for determining rotation speed information of a direct current motor (2) a computer program product comprising a computer programs for executing a method for determining rotation speed information of a direct current motor.