BLDC Motor Control Circuit Over-Current Protection
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Solution Overview
Problem
BLDC motors lack effective protection against over-current and over-torque conditions, which can damage power transistors and mechanical loads, and pose safety risks to humans, especially during excess mechanical load or faulty operation scenarios.
Innovation Solution
A control circuit with a torque-feedback loop, PWM circuit, over-current detection circuit, filter capacitor, and compensation capacitor is implemented to regulate the current and torque of BLDC motors, including a torque-control circuit, reference-signal generator, error amplifier, and over-current detection mechanism to prevent damage and ensure safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the on-period of power transistors is increased to correct speed errors, then the speed control accuracy is improved, but the current through power transistors increases causing over-current damage
Solution Approach 1:
The patent implements a dual feedback mechanism: a speed feedback loop that monitors motor speed and generates speed error signals, and a current feedback loop that monitors current through power transistors and generates current error signals. These feedback signals are processed by error amplifiers to generate appropriate drive signals, ensuring that speed correction actions do not cause over-current conditions.
Solution Approach 2:
The patent introduces preliminary protection actions through over-current detection circuits that continuously monitor current levels before damage occurs. The detection circuits generate reset signals that preemptively stop or limit current flow when threshold values are approached, preventing over-current damage before it can occur during speed correction operations.
2Force
If the current through windings is increased to increase torque, then the torque output is improved, but the power transistors and windings are damaged due to over-current
Solution Approach 1:
The patent employs current feedback loops that continuously monitor the current flowing through windings and power transistors. Error amplifiers process these feedback signals to generate drive signals that maintain torque output while preventing current from exceeding safe thresholds, thus protecting components from over-current damage.
Solution Approach 2:
Over-current detection circuits provide preliminary protection by continuously monitoring current levels and generating reset signals before damage occurs. These detection circuits establish safe operating boundaries that prevent both torque-related over-current and general over-current conditions that could damage power transistors or windings.
3Speed
If the on-period is dramatically increased to correct locked rotor, then the speed recovery is improved, but permanent damage occurs to power transistors
Solution Approach 1:
The patent implements preliminary over-current detection that continuously monitors current levels during all operating conditions including locked rotor scenarios. When current approaches dangerous levels, detection circuits generate reset signals that preemptively limit or stop current flow, preventing permanent damage to power transistors while still allowing speed recovery under normal conditions.
Solution Approach 2:
The feedback mechanism includes over-current detection circuits that provide real-time monitoring and error amplifiers that process detection signals to control power transistor operation. This feedback ensures that even during locked rotor correction attempts, the system responds to current feedback to prevent damage while attempting speed recovery.
Data Source
AI summary
A BLDC (brushless direct current) motor system of the present invention includes a control circuit, a sequencer, a driving circuit, and a BLDC motor. The control circuit determines the maximum torque and the maximum speed of the BLDC motor. The control circuit includes an over-current detection circuit to generate a reset signal in response to a switching current of the BLDC motor. The reset signal is generated when the switching current of the BLDC motor exceeds a threshold. A pulse width of the PWM signal is correlated to the level of a speed-control signal and the level of the torque-control signal. The pulse width of the PWM signal is also controlled by the reset signal generated by the over-current detection circuit.