BLDC Back-EMF Detection Circuit for Accurate Zero-Crossing Commutation
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Solution Overview
Problem
Existing BLDC motors face challenges in accurately detecting the back-electromotive force (back-EMF) zero crossing point, especially when the back-EMF voltage is close to zero, leading to inaccuracies in rotor position tracking.
Innovation Solution
A motor system incorporating a BLDC motor, driving circuit, voltage divider circuit, and analog-to-digital converter (ADC) with specific switch configurations and bypass diodes to process back-EMF feedback signals, allowing precise detection of zero crossing points without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional back-EMF detection methods are used in BLDC motors, then the system structure remains simple, but the detection precision deteriorates when back-EMF voltage is close to zero
Solution Approach 1:
The patent introduces an intermediary voltage divider circuit between the back-EMF detection point and the ADC. This circuit uses resistors and a bypass diode to condition the back-EMF signal, providing a stable reference voltage and protecting against voltage extremes. The intermediary circuit enables accurate detection of zero crossing points by transforming the raw back-EMF signal into a form suitable for ADC conversion, thereby improving measurement precision without requiring complex additional sensors.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the reference voltage level used for zero crossing detection. The bypass diode changes the electrical parameters of the detection circuit based on the back-EMF voltage state, allowing the system to accurately detect zero crossing points even when the back-EMF voltage is close to zero. This parameter adjustment enables precise detection without increasing device complexity.
2Measurement precision
If additional sensors are added to improve rotor position tracking accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent implements self-service by enabling the BLDC motor system to detect rotor position using its own existing back-EMF signals without requiring external sensors. The voltage divider circuit processes the naturally generated back-EMF signal from the motor windings, allowing the system to track rotor position autonomously. This approach improves measurement precision while avoiding the added complexity of external sensors and their associated circuitry.
Solution Approach 2:
The voltage divider circuit serves multiple functions: it conditions the back-EMF signal for ADC conversion, provides a stable reference voltage, protects against voltage extremes through the bypass diode, and enables zero crossing point detection. By making this single circuit multi-functional, the patent achieves accurate rotor position tracking without requiring additional specialized sensors, thereby improving measurement precision while maintaining simple device architecture.
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
Enables accurate detection of back-EMF zero crossing points, enhancing rotor position tracking and commutation precision in BLDC motors.
Implementation Method 1
The voltage divider circuit includes a first resistor, a second resistor, and a bypass diode. The first resistor includes a first terminal coupled to the third winding, and a second terminal. The second resistor includes a first terminal coupled to the second terminal of the first resistor, and a second terminal configured to optionally connect to a control voltage or ground via a switch.
Implementation Method 2
The bypass diode is in parallel with the first resistor. The bypass diode includes a first terminal coupled to the first terminal of the first resistor, and a second terminal coupled to the second terminal of the first resistor.
Implementation Method 3
The ADC is coupled to the voltage divider circuit and is used to receive the processed back-EMF feedback signal from the second terminal of the first resistor. According to the back-EMF feedback signal, the zero crossing point of the back-EMF could be determined.
Implementation Method 4
The motor system may track the rotor position according to the back-electromotive force (back-EMF) zero crossing point of the BLDC motor.
Data Source
AI summary
A motor system includes a brushless direct current motor, voltage divider circuits, a switch and an analog-to-digital converter. The brushless direct current motor includes 3 sets of windings, one set of windings being floating during each commutation. There are 3 voltage divider circuits, and each voltage divider circuit includes a first resistor, a second resistor and a bypass diode. The first resistor includes a first terminal coupled to the set of floating windings. The second resistor includes a first terminal coupled to the first resistor, and a second terminal coupled to the switch to receive a control voltage at the second terminal of the second terminal or grounding the second terminal of the second terminal. The bypass diode is coupled in parallel to the first resistor. The analog-to-digital converter receives a divided back-electromotive force signal to determine back-electromotive force zero crossing, so as to perform the commutation.