Sensorless Rotor Position Detection Circuit for Automotive Noise Immunity
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Solution Overview
Problem
Existing sensorless brushless DC motors face challenges in accurately detecting rotor position and rotation rate due to environmental noise and limitations in miniaturization, especially in automotive applications, where Hall sensors are inaccurate and high voltage PNP circuit elements occupy significant semiconductor substrate area.
Innovation Solution
A sensor-less detection circuit comprising voltage adjustment circuits, differential amplifiers, and comparators, along with active filters and level shifting circuits, is used to detect rotor position by shifting and filtering BEMF signals to improve noise immunity and accommodate high input voltage ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall sensors are used to detect rotor position, then rotor position and rotation rate can be detected, but measurement accuracy decreases due to environmental noise and operating conditions
Solution Approach 1:
The patent extracts the rotor position detection function from Hall sensors and implements it through sensorless detection using BEMF signals. The detection circuit removes dependency on physical sensors by utilizing the back electromotive force naturally generated by the motor windings, thereby eliminating susceptibility to environmental noise that affects Hall sensors.
Solution Approach 2:
The patent introduces an operational amplifier-based detection circuit as an intermediary between the BEMF signal and the control system. This intermediary circuit amplifies and conditions the weak BEMF signal, making it suitable for comparison and processing while maintaining high noise immunity and measurement accuracy.
2Measurement precision
If high voltage PNP circuit elements are used for voltage comparison, then positive voltage comparison is enabled, but semiconductor substrate area increases significantly
Solution Approach 1:
The patent changes the voltage comparison approach by using operational amplifiers with adjustable gain and offset parameters. Instead of relying on fixed high voltage PNP elements, the circuit uses programmable voltage references and differential amplification to achieve accurate comparison across the full voltage range, reducing area while maintaining precision.
Solution Approach 2:
The patent creates a scaled-down version of the voltage comparison function using standard voltage levels and operational amplifiers. By copying the essential comparison functionality at lower voltage levels and using differential signaling, the circuit achieves the same measurement precision without requiring large-area high voltage PNP elements.
3Adaptability or versatility
If BEMF signal comparison is used for rotor position detection, then sensorless operation is achieved, but detection accuracy deteriorates when rotor moves slowly or is stationary due to very small BEMF signal
Solution Approach 1:
The patent applies preliminary action by using an operational amplifier to amplify the BEMF signal before comparison. The amplification stage is prepared in advance and actively boosts even the smallest BEMF signals generated at low speeds or during startup, ensuring sufficient signal level for accurate detection without requiring the rotor to be in motion.
Solution Approach 2:
The patent implements feedback through the operational amplifier circuit that continuously monitors and amplifies the BEMF signal. The high-gain feedback mechanism ensures that even minimal BEMF signals are sufficiently amplified and fed to the comparison stage, maintaining detection accuracy across all rotor speeds including stationary conditions.
4Ease of operation
If conventional BEMF comparison circuit is used, then rotor position detection is achieved, but noise immunity is poor in automotive environments with external interruptions
Solution Approach 1:
The patent introduces operational amplifiers as intermediary components between the BEMF signal source and the comparison logic. These operational amplifiers provide signal conditioning, filtering, and isolation that protect against noise and external interruptions, enhancing reliability in harsh automotive environments while maintaining ease of operation.
Solution Approach 2:
The patent converts the potentially harmful effect of noise by using the operational amplifier's high input impedance and differential signaling to reject common-mode noise. The circuit transforms environmental noise and voltage fluctuations into beneficial differential signals that can be accurately processed, turning the harsh automotive environment's challenges into advantages for the detection system.
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 enhances the accuracy and reliability of rotor position detection, reduces noise interference, and enables miniaturization while being cost and time efficient, particularly suitable for automotive applications.
Implementation Method 1
the position of the rotor is detected using a Back ElectroMotive Force (BEMF) signal
Implementation Method 2
A sensor-less detection circuit comprising voltage adjustment circuits, differential amplifiers, and comparators, along with active filters and level shifting circuits, is used to detect rotor position by shifting and filtering BEMF signals
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.