Sensorless Brushless Motor Start-Up via Dynamic Excitation Control
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Solution Overview
Problem
Existing brushless DC motor start-up methods, particularly those using Back Electro-Motive Force (BEMF) detection, often require brute-force drive techniques that consume high currents, potentially damaging motor windings and lack effective feedback mechanisms, leading to inefficient and potentially destructive start-up conditions.
Innovation Solution
A system and method that control the rotation of a brushless three-phase motor by adjusting the excitation levels and rotation periods of electromagnets using a non-monotonic drive profile, reducing current consumption and susceptibility to over-current conditions during start-up, and utilizing a processor-based control logic to manage commutation timing and excitation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brute-force drive techniques are used during motor start-up, then motor rotation is initiated, but high currents are consumed that can damage motor windings
Solution Approach 1:
The patent applies dynamics by making the excitation level variable rather than fixed. The control system dynamically adjusts the excitation level of electromagnets during the start-up process, transitioning from high excitation to lower excitation as the rotor accelerates. This dynamic adjustment allows the motor to overcome initial inertia with high torque while reducing current consumption during continued acceleration, resolving the contradiction between reliable start-up and energy efficiency.
Solution Approach 2:
The patent changes the excitation level parameter during motor operation. By varying the excitation level of stator electromagnets based on rotor position and speed, the system optimizes the balance between torque production and current consumption. This parameter change enables effective start-up without sustained high current that would damage windings, addressing the reliability versus energy consumption contradiction.
2Force
If high excitation levels are maintained during start-up, then sufficient torque is produced for rotation, but over-current conditions occur that reduce efficiency
Solution Approach 1:
The patent employs periodic action through commutation, where the excitation of electromagnets is switched in periodic sequences as the rotor rotates. The control system activates specific electromagnet pairs in alternating phases, creating periodic torque pulses that drive rotor acceleration. This periodic excitation pattern provides sufficient average torque for start-up while allowing rest periods that reduce overall current consumption and improve energy efficiency.
Solution Approach 2:
The system dynamically adjusts excitation levels based on real-time rotor position and speed feedback. During initial start-up when torque is most needed, high excitation levels are applied. As the rotor gains speed, the excitation level is reduced, optimizing the balance between force production and energy efficiency throughout the acceleration process.
3Measurement precision
If BEMF detection is used for commutation control, then precise rotor position feedback is obtained, but the method fails when the rotor is not moving
Solution Approach 1:
The patent applies preliminary action by using an alternative commutation method during the start-up phase when BEMF detection is not yet viable. The system uses open-loop commutation or Hall effect sensor-based commutation to initiate rotor motion. Once the rotor reaches a sufficient speed where BEMF signals become detectable, the system transitions to BEMF-based closed-loop commutation. This preliminary action ensures the motor can start reliably while enabling precise position detection once operational conditions are met.
Solution Approach 2:
The patent uses Hall effect sensors as an intermediary detection method during the transition phase. These sensors provide rotor position feedback independent of BEMF, enabling commutation control during low-speed start-up conditions. This intermediary detection mechanism bridges the gap between standstill and the speed threshold required for BEMF detection, expanding the overall adaptability of the control system across the full operational range.
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 initiates motor rotation with reduced current consumption, minimizes the risk of over-current damage, and is suitable for efficient operation in applications like fans and impellers, offering improved efficiency and reliability compared to prior art designs.
Implementation Method 1
The stator generally operates as a field magnet (e.g., electromagnet), interacting with an armature to induce motion in the rotor
Implementation Method 2
The armature carries current in the motor and is generally oriented normal to the magnetic field and the torque being generated
Implementation Method 3
The rotor comprises one or more permanent magnets... interacting with an armature to induce motion in the rotor
Data Source
AI summary
System and method for initiating rotation of a rotor in a motor. The motor may include the rotor and a plurality of pairs of electromagnets. A rotation period may be determined. One or more pairs of electromagnets of the plurality of pairs of electromagnets may be excited at a first excitation level. The excited one or more pairs of electromagnets may be determined based on the rotation period. The excitation level may be decreased, over a first period of time, to a second excitation level. The second excitation level may be a lower excitation level than the first excitation level. The excitation level may be increased, over a second period of time, to a third excitation level. The third excitation level may be a higher excitation level than the second excitation level. The rotation period may be decreased over the first and second periods of time.