Sensorless BLDC Motor Startup Current Adaptation
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Solution Overview
Problem
Current sensorless driving technologies for brushless DC (BLDC) motors require large startup currents to avoid failure, leading to excessive power loss, especially under light loads, as they cannot accurately estimate rotor load conditions.
Innovation Solution
A motor control method and device that adaptively adjusts the startup current based on the load state and torque demand of the BLDC motor by sensing phase voltage and current signals, allowing for efficient startup without constant high current application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large startup current is applied to drive the BLDC motor, then the motor can avoid startup failure and maintain normal rotation, but excessive power loss occurs especially under light load conditions
Solution Approach 1:
The patent applies dynamics principle by transitioning from static open-loop current control to dynamic closed-loop control. The system starts with open-loop control to ensure reliable startup, then detects rotor position using sensorless algorithms, and switches to closed-loop control that dynamically adjusts current based on actual load conditions. This dynamic transition resolves the contradiction by maintaining high startup reliability while reducing power loss during normal operation.
Solution Approach 2:
The patent changes the control parameter from fixed large startup current to adaptively adjusted current based on load detection. By using sensorless algorithms to estimate rotor position and load conditions, the system modifies the current parameter dynamically - applying sufficient current for reliable startup detection, then reducing it to appropriate levels based on actual load, thereby resolving the power loss issue while maintaining startup reliability.
2Ease of operation
If open-loop current control is used for startup, then the motor can start without sensor feedback, but the load condition of the rotor cannot be estimated accurately
Solution Approach 1:
The patent applies preliminary action by first using open-loop control to get the motor running, then performing sensorless rotor position detection to estimate load conditions before transitioning to closed-loop control. This sequence ensures the motor starts easily without complex sensor feedback while subsequently obtaining accurate load estimation for optimized control.
Solution Approach 2:
The patent introduces feedback through sensorless algorithms that detect rotor position and estimate load conditions during startup. This feedback mechanism allows the system to transition from open-loop to closed-loop control, resolving the contradiction by maintaining startup simplicity while enabling accurate load estimation through detected electrical signals and algorithmic processing.
3Reliability
If constant large current is applied during startup, then the motor can overcome unknown load conditions, but power loss increases significantly
Solution Approach 1:
The patent applies partial action principle by using large current only partially - specifically during the initial startup phase when load conditions are unknown. Once sensorless detection confirms proper operation and estimates load conditions, the system reduces current to appropriate levels. This resolves the contradiction by applying excessive current only when necessary for reliability while minimizing energy consumption during subsequent operation.
Data Source
AI summary
A motor control method adapted for use in the startup process of a sensorless brushless DC (BLDC) motor includes the following steps. A phase voltage signal and a driving voltage signal are generated according to the startup current signal with a first predetermined value and a phase current signal. A driving current signal is generated according to the driving voltage signal to drive the BLDC to rotate. The driving current signal is sensed to generate the corresponding phase current signal. The load state of the shaft end of the BLDC is determined according to the phase voltage signal with the change of the corresponding phase current signal and the startup current signal. The magnitude of the startup current signal is adaptively adjusted according to the load state of the shaft end and/or according to the electric rotation angular velocity and the torque demand of the BLDC motor.