DC Motor Commutation via Back-EMF Envelope Zero Crossing
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Solution Overview
Problem
Existing electronic commutation methods in direct current electric motors rely on precise detection of zero crossovers in induced voltage, which can be noisy and unreliable, especially when covered by current values, leading to inefficiencies and potential loss of commutation.
Innovation Solution
The method employs synchronous measurement of induced voltage with PWM to determine zero crossovers by analyzing the envelope of the counter-induction voltage, allowing for extrapolation and reducing the need for direct measurement, thus minimizing energization pauses and enhancing robustness by adjusting PWM increments based on motor speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of zero crossover is performed, then commutation detection accuracy is improved, but measurement reliability deteriorates when zero crossover is covered by current values
Solution Approach 1:
The patent introduces an intermediary approach by measuring the induced voltage in the sub-region before direct zero crossover detection, using this measurement to calculate and predict the zero crossover point. This intermediary measurement in a cleaner voltage region serves as a mediator to overcome the reliability issue of direct measurement when zero crossover is covered by current values.
Solution Approach 2:
The patent applies preliminary action by performing the voltage measurement in the sub-region prior to the zero crossover event, before the problematic current values cover the zero crossover point. This preliminary measurement allows the system to predict the zero crossover location in advance, ensuring reliable commutation detection even when direct measurement would fail.
2Measurement precision
If energization pause is extended to enable zero crossover detection, then measurement accuracy is improved, but productivity deteriorates due to longer commutation interruption
Solution Approach 1:
The patent applies partial action by measuring the induced voltage only in a specific sub-region (before zero crossover) rather than requiring measurement across the entire energization pause. This partial measurement approach achieves sufficient accuracy for zero crossover prediction while minimizing the required energization pause duration, thus maintaining productivity.
Solution Approach 2:
By performing the voltage measurement preliminarily in the sub-region before zero crossover, the system obtains sufficient information to predict the zero crossover point without needing to extend the energization pause to cover the actual zero crossover moment, thereby reducing commutation interruption time and maintaining productivity.
3Productivity
If PWM frequency is increased to reduce energization pause, then productivity is improved, but measurement precision deteriorates due to reduced measurement window
Solution Approach 1:
The patent applies local quality by focusing the measurement specifically in the sub-region before zero crossover, where the induced voltage has favorable characteristics for measurement. This localized measurement approach ensures sufficient precision in the critical measurement window, enabling accurate zero crossover prediction even at higher PWM frequencies with reduced overall pause duration.
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 improves commutation accuracy and robustness by reducing noise and power consumption, maintaining commutation even when zero crossovers are covered, and allows for precise motor speed and angle determination.
Implementation Method 1
The induced voltage (counter-induction voltage or back EMF) is measured synchronously with the PWM. The zero crossover of the counter-induction voltage is determined by means of the point of intersection of an envelope which is superimposed on the counter-induction voltage with the zero line.
Data Source
AI summary
In an electronic commutation method in direct current electric motors which are controlled by pulse width modulation of the energization which takes place periodically with positive and negative current values and intermediate energization pauses, the counter-induction voltage is measured, wherein the zero crossing of the counter-induction voltage is determined by means of the point of intersection of the envelope to the counter-induction voltage with the zero line. The pulse width modulation of the energization is changed if the zero crossing is covered by positive or negative current values of the energization.