Sensor-less Rotor Position Detection Circuit
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Solution Overview
Problem
Brushless DC motors face challenges in accurately detecting rotor position and rotation rate, particularly with Hall sensors being influenced by their environment and BEMF signals being unsuitable for miniaturization and limited to comparing positive voltages, with low accuracy at slow rotor speeds.
Innovation Solution
A sensor-less detection circuit comprising a first and second voltage adjustment circuit, a differential amplifier, and a comparator, along with an active filter, level shifting circuits, and a determination circuit, which adjusts and compares back electromotive force (BEMF) signals to accurately detect rotor position across a high input voltage range with high noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall sensors are used to detect rotor position, then the rotor position and rotation rate can be detected, but the accuracy is influenced by the operating environment
Solution Approach 1:
The patent extracts the rotor position detection function from the motor control system and implements it separately using back-EMF signal analysis. By monitoring the back-EMF voltage generated during motor operation, the system determines rotor position without requiring additional Hall sensors that are susceptible to environmental interference.
Solution Approach 2:
The patent uses back-EMF voltage as an intermediary to infer rotor position. Instead of directly measuring position with Hall sensors, the system measures the back-EMF voltage generated by the motor windings and uses this voltage signal as a mediator to determine rotor position and speed through signal processing.
2Volume of moving object
If back-EMF signal is used for rotor position detection, then miniaturization is enabled, but the BEMF becomes very small when the rotor is moving slowly or not at all
Solution Approach 1:
The patent applies preliminary action by providing a startup sequence that initially uses alternative methods (such as applying test voltages to motor windings and measuring resulting currents) to determine rotor position when back-EMF is insufficient. Once the motor reaches a speed where back-EMF becomes detectable, the system transitions to using back-EMF-based detection.
Solution Approach 2:
The patent changes the detection parameters by switching between different measurement methods based on operating conditions. At low speeds or startup, the system uses impedance-based or current-based detection methods. When the motor reaches sufficient speed and back-EMF becomes detectable, the system transitions to voltage-based back-EMF detection, effectively changing the detection parameter from current/impedance to voltage.
3Ease of manufacture
If back-EMF signal is used for rotor position detection, then cost efficiency is improved, but the BEMF signal is limited to comparing positive voltages
Solution Approach 1:
The patent inverts the traditional approach by using a differential amplifier configuration that compares the difference between two back-EMF voltages rather than comparing each voltage to a reference. This allows the system to detect both positive and negative voltage variations, effectively doubling the detection range and enabling accurate position detection throughout the entire rotor rotation cycle.
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 solution provides accurate and efficient detection of rotor position with high noise immunity and cost-effectiveness, suitable for miniaturization and effective at slow rotor speeds, enhancing the performance of brushless DC motors.
Implementation Method 1
a differential amplifier having an inverting input terminal, a noninverting input terminal, and an output terminal, wherein the inverting input terminal of the differential amplifier is connected to the second terminal of the first voltage adjustment circuit and the noninverting input terminal of the differential amplifier is connected to the second terminal of the second voltage adjustment circuit
Implementation Method 2
a comparator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the comparator is coupled to the output terminal of the differential amplifier
Implementation Method 3
A sensor-less detection circuit comprising a first and second voltage adjustment circuit, a differential amplifier, and a comparator, along with an active filter, level shifting circuits, and a determination circuit, which adjusts and compares back electromotive force (BEMF) signals to accurately detect rotor position across a high input voltage range with high noise immunity
Data Source
AI summary
In accordance with an embodiment, a sensor-less detection circuit is provided that includes a first voltage adjustment circuit coupled for receiving an induced voltage and a second voltage adjustment circuit coupled for receiving a common voltage. A differential amplifier has an inverting input terminal coupled to the first voltage adjustment circuit and a noninverting input terminal coupled to the second voltage adjustment circuit. In accordance with another embodiment, a method for detecting a motor rotor position is provided that includes receiving a first back electromotive force that is at a first voltage level and shifting the first back electromotive force from the first voltage level to a second voltage level. The first back electromotive force is filtered to generate a first filtered voltage; and a first motor rotor position signal is generated in response to comparing the first filtered voltage with a reference voltage.