BLDC Motor Control Using Dead-Time Back-EMF Zero-Crossing Detection
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Solution Overview
Problem
Existing BLDC motor control methods using sinusoidal commutation face challenges such as higher torque ripple, acoustic and electric noise, and increased computational load due to the need for dedicated time windows to detect back-EMF zero crossings.
Innovation Solution
A method and control circuit that calculates the rotor position based on zero-crossing times of back electromotive forces without requiring a dedicated time window, by generating PWM signals with dead-time and performing zero-crossing time measurements during the dead-time interval, allowing for simultaneous driving of all three phases and reducing the need to stop motor phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sinusoidal commutation with Space Vector Modulation is used to drive all three phases simultaneously, then motor performance is improved, but back-EMF zero crossing detection becomes difficult and computational load increases
Solution Approach 1:
The patent extracts the back-EMF detection function from the active PWM driving periods and relocates it to the dead-time intervals. By taking out the detection requirement from the main driving sequence and placing it in the naturally occurring dead-time windows, the system avoids increasing computational load while maintaining accurate rotor position sensing for sinusoidal commutation.
Solution Approach 2:
The patent ensures continuous motor operation by performing back-EMF detection during dead-time intervals without stopping any motor phase. The useful action of motor driving continues uninterrupted while the detection function is executed simultaneously during the necessary dead-time periods, eliminating the need to open dedicated time windows that would interrupt motor operation.
2Measurement precision
If dedicated time windows are opened for back-EMF detection, then zero crossing detection accuracy is improved, but motor phase interruption increases causing torque ripple
Solution Approach 1:
The patent converts the harmful dead-time intervals (which are necessary to prevent shoot-through but create measurement opportunities) into beneficial detection windows. Instead of viewing dead-time as wasted or harmful periods that cause torque ripple, the system utilizes these intervals to perform back-EMF detection, thereby eliminating the need to open additional dedicated time windows that would cause further motor phase interruptions and increase torque ripple.
3Loss of information
If back-EMF detection is performed during active PWM phases, then detection capability is maintained, but electrical noise increases
Solution Approach 1:
The patent extracts the detection function from the noisy active PWM driving periods and relocates it to the quieter dead-time intervals. By taking out the back-EMF measurement requirement from the high-noise PWM active phases and performing it during the naturally occurring dead-time windows, the system maintains full detection capability while significantly reducing electrical noise interference.
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 approach reduces computational load, torque ripple, and electric noise while enabling efficient detection of back-EMF zero crossings for sinusoidal commutation without stopping motor phases, enhancing the control of BLDC motors in applications like power steering and HVAC systems.
Implementation Method 1
sensing back-electromotive forces at said three-phase driving terminals of said motor and performing a zero-crossing time measurement on each of said back electromotive forces
Data Source
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AI summary
A method for controlling a BLDC motor (11), comprising controlling the rotational speed and/or position of said BLDC motor (11) on the basis of a position of the rotor (θ) of the motor, said position of the rotor (θ) being computed sensing the back electromotive force (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3), said BLDC motor (11) being driven with three driving phases (VP1, VP2, VP3) supplied to three-phase driving terminals ((N1, N2, N3) by a three-phase inverter (13), comprising three arms (BR1, BR2, BR3) comprising each a high side and a low side switch (MH1, ML1; MH2, ML2; MH3, ML3), operating with a sinusoidal commutation, wherein said method comprises calculating a current position of the rotor (θ) on the basis of zero-crossing times (ZC1, ZC2, ZC33) of back electromotive forces (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3), by the following steps: generating a PWM signal (PWM1, PWM2, PWM3) comprising three PWM phases comprising each a pair of complementary signals (TH1, TL1; TH2, TL2; TH3, TL3) with dead-time (DT) which duty cycle (DC) value depends on a current position of the rotor (θ), driving said three-phase inverter (13) supplying each signal of said pair of complementary signals (TH1, TL1; TH2, TL2; TH3, TL3) with dead-time (DT) to a respective high side and low side switch (MH1, ML1; MH2, ML2; MH3, ML3), sensing back-electromotive forces (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3) at said three-phase driving terminals ((N1, N2, N3) of said motor (11) and performing (151, 152, 153) a zero-crossing time measurement on each of said back electromotive forces (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3) obtaining corresponding signals indicating zero-crossing times (ZC1, ZC2, ZC33) which are supplied to said operation of calculating a current position of the rotor (θ) on the basis of zero-crossing times (ZC1, ZC2, ZC33) of back electromotive forces (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3), computing (122) triggers signals (TR1, TR2, TR3), which activate said performing (151, 152, 153) said zero-crossing time (ZC1, ZC2, ZC33) measurement on each of said back electromotive forces (BEMF1, BEMF2, BEMF3; BEMF'1, BEMF'2, BEMF'3), identifying the occurrence of a time interval corresponding to the dead time (DT) in the respective PWM phase (PWM1, PWM2, PWM3; TH1, TL1; TH2, TL2; TH3, TL3), and performing said zero-crossing time (ZC1, ZC2, ZC33) measurement during the occurrence of said dead-time (DT).