Phase Detector for Brushless DC Motor Using Back-EMF Signal Comparison
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Solution Overview
Problem
Conventional phase detection systems for brushless DC motors suffer from reduced accuracy and increased costs due to the need for additional components and potential phase errors caused by sensor mounting errors.
Innovation Solution
A phase detector comprising a crossing-point phase detection circuit, a crossing-point level detection circuit, a signal selection circuit, a phase detection circuit, and a threshold-level correction circuit, which compares signal levels of multiple sensor signals, selects a signal based on threshold levels, and corrects these levels to enhance accuracy and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotary encoder with additional components is used for phase detection, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts the essential phase detection function from the complex rotary encoder system by using only the back-EMF signals already present in the motor system. The phase detection is achieved by comparing the back-EMF signals from different phases, eliminating the need for separate encoder components while maintaining detection accuracy.
Solution Approach 2:
The back-EMF signals, which are already generated by the motor during operation, are utilized for dual purposes: both for commutation control and for phase detection. This multi-functional use of existing signals eliminates the need for dedicated detection components, reducing system complexity while maintaining measurement precision.
2Device complexity
If conventional threshold comparison is used for phase detection, then device complexity is reduced, but measurement precision deteriorates due to phase errors from sensor mounting errors
Solution Approach 1:
The invention changes the detection parameter from fixed threshold levels to dynamic reference signals derived from the back-EMF signals themselves. By using the actual signal characteristics (crossing points between phase signals) as reference levels, the system adapts to mounting errors and signal variations, improving measurement precision while keeping the detection circuit relatively simple.
Solution Approach 2:
The system uses feedback from the back-EMF signals to dynamically adjust the reference levels for phase detection. The crossing points between phase signals provide real-time feedback about the actual signal levels, allowing the detection circuit to compensate for mounting errors and maintain high measurement precision without increasing complexity.
3Measurement precision
If multiple threshold levels are used for fine phase detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The invention replaces static multiple threshold levels with dynamic reference signals that are continuously updated based on the back-EMF signal characteristics. The reference levels are derived from the actual signal crossing points, allowing fine phase detection resolution without requiring a fixed array of multiple thresholds, thus reducing circuit complexity while maintaining measurement precision.
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
The phase detector achieves higher accuracy in rotational phase detection with lower additional costs by correcting threshold levels and compensating for sensor mounting errors, thereby improving motor control precision.
Implementation Method 1
The crossing-point phase detection circuit compares signal levels of respective pairs of sensor signals and outputs crossing-point phase detection signals indicating phases of crossing points between the respective pairs of the sensor signals
Implementation Method 2
The phase detection circuit detects that a signal level of the selection signal has reached a threshold level, and outputs a phase data signal indicating a phase of the rotor corresponding to the threshold level which the signal level has reached
Data Source
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AI summary
A phase detector (1) includes a crossing-point phase detection circuit (10) to compare signal levels of pairs of sensor signals (U1, V1, W1) and output crossing-point phase detection signals (UV, VW, WU) indicating phases of crossing points between the pairs of the sensor signals, each having a signal level corresponding to a rotational position of a rotor of a motor having coils, a crossing-point level detection circuit (50) to output crossing-point level signals (Y) indicating crossing-point levels detected, a signal selection circuit (20) to select one of the sensor signals as a selection signal, a phase detection circuit (30) to detect that a signal level of the selection signal has reached a threshold level, and output a phase data signal indicating a phase of the rotor corresponding to the threshold level, and a threshold-level correction circuit (60) to correct the threshold level based on the crossing-point level signals (Y).