BLDC Motor Position Detection Using High-Frequency Inductance
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Solution Overview
Problem
Conventional BLDC motor control techniques face challenges in accurately detecting motor position at zero speed due to the unavailability of BEMF information and noise issues in existing Initial Position Detect methods, leading to potential reverse rotation and increased startup time.
Innovation Solution
The use of complementary driving and detect (CDD) signals, specifically CDD-PACI and CDD-slight move, which involve high-frequency signal injection to detect inductance differences and magnet polarity, allowing for precise motor position determination within a narrower range (30 degrees) without generating significant torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional IPD techniques inject current into six combinations of stator phases to detect motor position, then motor position can be detected at zero speed, but acoustic noise and vibration increase significantly due to torque generated during current injection
Solution Approach 1:
The patent applies periodic action by using high-frequency carrier signals (e.g., 25kHz) for position detection instead of conventional low-frequency current injection. The high-frequency signals are applied periodically to the motor phases, allowing position detection through inductance measurement without generating audible torque noise. This transforms the detection mechanism from mechanical torque-based to electromagnetic inductance-based, eliminating the harmful acoustic noise and vibration while maintaining position detection capability.
2Loss of information
If conventional IPD techniques compare six relatively close inductance signals to determine motor position, then position information can be obtained, but measurement precision deteriorates due to signal similarity and noise
Solution Approach 1:
The patent replaces the mechanical torque-based measurement system with an electromagnetic inductance measurement system. Instead of comparing six close inductance signals that are difficult to distinguish, the system uses high-frequency carrier signals to excite the motor windings and measures the resulting inductance variations. This substitution provides clearer, more distinguishable signals for position detection, significantly improving measurement precision by eliminating the signal similarity problem inherent in conventional IPD techniques.
3Device complexity
If open loop startup is used without position estimation, then device complexity is reduced, but reliability decreases due to potential reverse rotation and increased startup time
Solution Approach 1:
The patent implements self-service by enabling the motor control system to automatically determine its own initial position using the high-frequency inductance measurement method. The system independently detects rotor position and magnet polarity without requiring external sensors or complex startup procedures. This self-positioning capability allows the motor to start reliably in the correct direction while maintaining relatively simple control logic, achieving both low complexity and high reliability.
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 significantly reduces acoustic noise and vibration, enhances accuracy, and reduces the time needed for motor position detection, providing a more reliable and efficient startup process compared to conventional methods.
Implementation Method 1
An inductance difference is detected based upon the motor position after which inductor saturation is detected from magnet polarity
Implementation Method 2
inductor saturation is detected from magnet polarity
Data Source
Figure 1
Figure 1A~1B
Figure 2~2A
AI summary
Methods and apparatus for determining a position of a rotor in motor, such as a three-phase motor by determining first and second ones of sectors in which a first one of the magnetic poles of the rotor may be positioned by driving phase pairs with complementary signals and examining a voltage of a floating one of the phases. Embodiments can further include driving first and second currents towards the first and second ones of the sectors and analyzing a time for each of the first and second currents to reach a threshold to identify a sector. Embodiments can further include applying torque to the motor by driving at least one phase pair with respective signals aligned in phase and unequal duty cycles to move the rotor for determining the position of the rotor.