Sensorless Brushless DC Motor Rotor Position Detection
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Solution Overview
Problem
Conventional rotor position detection methods for brushless DC motors, especially in sensorless systems, face challenges in achieving high resolution and stability, particularly during rotor acceleration stages.
Innovation Solution
A motor driver device with a position detector that applies pulse voltages to target and non-target coil pairs, generating evaluation voltages to determine rotor position based on voltage sums and polarities, and adjusts pulse application times based on current flow, allowing for high-resolution rotor position detection in a sensorless manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional rotor position detection methods are used in sensorless systems, then the system structure is simple, but the measurement precision of rotor position is insufficient, especially during rotor acceleration stages
Solution Approach 1:
The detection process is divided into multiple discrete pulse application steps, with each pulse targeting specific coil combinations (UV, VW, WU phases) to sequentially probe different rotor position ranges. This segmentation enables high-resolution position detection through staged measurement without requiring a complex single-step detection system
Solution Approach 2:
Pulse trains are applied periodically to the motor coils at specific detection timing points during the rotation cycle. The periodic application of detection pulses to different coil combinations enables continuous high-resolution rotor position tracking throughout the acceleration phase, maintaining precision without excessive system complexity
2Measurement precision
If pulse voltages are applied to all coil combinations for position detection, then the measurement precision improves, but the loss of energy increases due to unnecessary power supply to non-target coils
Solution Approach 1:
Instead of applying pulse voltages to all possible coil combinations, the system applies pulses only to specific target coil pairs (UV, VW, or WU phases) selected based on the current detection stage and rotor position estimation. This partial action approach achieves sufficient measurement precision by focusing power application only where needed, thereby reducing energy waste from unnecessary coil excitation
3Measurement precision
If the pulse application time is fixed, then the control is simple, but the measurement precision varies during different rotor acceleration stages
Solution Approach 1:
The pulse application time is dynamically adjusted based on the rotor acceleration stage and estimated position. During different acceleration phases, the system varies the duration and timing of pulse applications to optimize the detection signal quality. This dynamic control maintains high measurement precision across varying operating conditions while using relatively simple control logic that adapts to real-time motor state
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 enables stable and high-resolution rotor position detection, improving accuracy and reliability, especially during rotor acceleration, by utilizing pulse train application processes and dynamic adjustment of pulse application times, thus enhancing motor control precision.
Implementation Method 1
the output stage circuit is further configured to, with respect to all combinations of target coil pairs, execute a first process of applying a pulse voltage from a first direction to the target coil pair and a second process of applying a pulse voltage from a second direction opposite to the first direction to the target coil pair, and stop power supply to the non-target coil in the first process and the second process. The position detector detects the position of the rotor based on voltages generated in the non-target coil in each first process and each second process of the pulse train application process.
Data Source
AI summary
A motor driver device supplies drive voltages to three phase coils of a stator in a brushless DC motor based on a detection result of a position of a rotor in a sensorless manner. In a position detection section, two phase coils are set as a target coil pair and a remaining one phase coil is set as a non-target coil, and with respect to all combinations of target coil pairs, a first process of applying a pulse voltage from a first direction to the target coil pair and a second process of applying a pulse voltage from a second direction opposite to the first direction to the target coil pair are executed. In the first and second processes, power supply to the non-target coil is stopped. The position of the rotor is detected based on voltages generated in the non-target coil in each first process and each second process.