BLDC Inverter Control Using Dead-Time Back-EMF Sampling
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Solution Overview
Problem
Existing BLDC motor control methods face challenges such as higher torque ripple, reduced maximum torque, and increased acoustic and electric noise due to six-step commutation, and higher computational load with sinusoidal commutation.
Innovation Solution
A method for controlling a BLDC motor using sinusoidal commutation, where the rotational speed or position is controlled based on the rotor position computed from back electromotive force zero-crossing times, without the need for a dedicated time window for back-EMF detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If six-step commutation method is used, then the control structure is simple, but torque ripple increases and maximum torque is reduced
Solution Approach 1:
The patent transitions from six-step commutation to sinusoidal commutation, fundamentally changing the current waveform parameter from rectangular to sinusoidal. This parameter change eliminates torque ripple while maintaining controllable structure through PWM implementation.
Solution Approach 2:
The patent implements dynamic sinusoidal current control using PWM modulation, where the commutation parameters are continuously adjusted based on rotor position feedback. This dynamic approach maintains smooth torque production while enabling adaptive control.
2Object-generated harmful factors
If sinusoidal commutation is used, then torque ripple is reduced, but computational load increases
Solution Approach 1:
The patent replaces complex computational back-EMF analysis with a simplified voltage sampling method during dead-time intervals. This substitution uses direct electrical measurement instead of computational estimation, significantly reducing processing requirements while maintaining sinusoidal commutation benefits.
Solution Approach 2:
The system uses the existing dead-time in the PWM control scheme to perform back-EMF sampling without requiring additional measurement windows or stopping motor phases. The control structure serves dual purposes: switching control and sensorless position detection.
3Measurement precision
If back-EMF zero crossing detection is performed with dedicated time window, then rotor position can be detected, but torque ripple and electric noise increase
Solution Approach 1:
The patent uses the dead-time interval as an intermediary opportunity to sample back-EMF signals. This approach leverages the natural switching gap in the control cycle, allowing position detection without requiring separate measurement windows that would disrupt motor operation and increase noise.
Solution Approach 2:
The patent merges the back-EMF detection function with the existing PWM dead-time control mechanism. The same time interval that is necessary for safe switching also serves as the measurement window, combining control and sensing functions into a unified approach that eliminates additional noise sources.
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 solution reduces computational load, torque ripple, and electric noise while maintaining efficient control of the BLDC motor, enhancing its performance and reliability.
Implementation Method 1
the position of the rotor being computed by sensing the back electromotive force
Data Source
AI summary
A method for controlling a BLDC motor includes controlling the rotational speed or position of the BLDC motor based on a position of the rotor of the motor. The BLDC motor is driven by a three-phase inverter. A PWM signal is generated for three PWM phases, each including a pair of complementary signals with dead-time and having a duty cycle based on the current position of the rotor. The complementary signals are supplied to a respective high side and low side switch of each of three arms of the three-phase inverter, and a zero-crossing time measurement is performed on each of the back electromotive forces. Corresponding signals are obtained indicating the zero-crossing times. Trigger signals are generated, and the occurrence of a time interval corresponding to the dead time in the respective PWM phase is identified. The zero-crossing time measurement is performed during the occurrence of the dead-time.