Electric Motor Control Device Zero Crossing Detection
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Solution Overview
Problem
Existing control devices for electric motors struggle to accurately detect the zero crossing of the current in windings, leading to inefficiencies in synchronizing the driving voltage with the induced back electromotive force, which affects the motor's performance and precision.
Innovation Solution
A control device that samples the polarity signal of the current during specific periods centered on the expected zero crossing, counts these samples, and calculates the phase shift between the driving voltage and the back electromotive force, allowing for precise alignment and adjustment of the driving voltage with respect to the rotor position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output stage of a winding is placed in high impedance status to detect BEMF zero crossing, then rotor position detection is enabled, but the detection precision of zero crossing is insufficient
Solution Approach 1:
The patent applies preliminary action by setting expected zero crossing periods in advance based on motor speed and electrical angle relationships. The control device predicts when zero crossings should occur and prepares detection windows before they happen, allowing proactive rather than reactive detection. This improves precision by focusing detection resources on critical moments.
Solution Approach 2:
The patent implements feedback by comparing actual zero crossing detection results with expected zero crossing times. The control device continuously monitors detected zero crossings against predicted values, calculates deviations, and uses this feedback to adjust future expected zero crossing periods. This closed-loop approach enhances both precision and reliability over time.
2Measurement precision
If sampling and counting methods are used to determine phase shift, then synchronization precision is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by using the motor's own operational characteristics (current polarity changes during zero crossings) as the detection signal. Instead of requiring external sensors or complex measurement equipment, the system uses the existing current flow patterns in the windings, which naturally provide the zero crossing information needed. This reduces device complexity while maintaining high precision.
Solution Approach 2:
The patent implements periodic action by sampling current polarity at regular intervals corresponding to expected zero crossing periods. The control device uses periodic sampling synchronized with motor rotation to accumulate multiple measurements, which improves phase shift measurement precision through statistical averaging while keeping the sampling logic relatively simple and repeatable.
3Measurement precision
If multiple samples of polarity signal are counted during centered periods, then zero crossing detection accuracy is improved, but processing time increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing expected zero crossing periods based on motor speed and winding configuration. These expected periods are prepared in advance before actual zero crossings occur, allowing the system to immediately compare detected crossings against pre-computed values without performing complex calculations in real-time, thus reducing processing time while maintaining high accuracy.
Solution Approach 2:
The patent implements partial action by sampling current polarity only during specific centered periods around expected zero crossings, rather than continuously monitoring the entire waveform. This focused sampling approach takes fewer measurements (partial action) concentrated on the most informative time windows, improving detection accuracy for zero crossings while minimizing overall processing time by ignoring irrelevant portions of the signal.
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 enables improved synchronization of the driving voltage with the rotor position, enhancing the motor's efficiency and precision by accurately determining the phase shift and adjusting the driving voltage accordingly, leading to better motor control and performance.
Implementation Method 1
A direct current brushless motor consists of a permanent magnet and of a stator consisting of a certain number of windings... generating a back electromotive force... detecting a Pbemf signal that represents the polarity of the induced back electromotive force (BEMF)
Data Source
AI summary
A control device controls an electric motor that includes a winding and generates a back electromotive force. The device comprises a first circuit suitable for setting time periods each centered on the time instant of an expected zero crossing of the winding current and a second circuit suitable for generating a signal representing the polarity in the winding in the time periods. The first and second circuits are suitable for providing samples of the polarity signal. The control device comprises a counting circuit suitable for counting the samples of the polarity signal and a further circuit receiving the count and being suitable for deducing the distance between the time instant of the expected zero crossing and the actual zero crossing instant; the further means is suitable for determining the phase shift between the driving voltage of the electric motor and the induced back electromotive force based on the distance.