Sensorless DC Motor Controller Adaptive Overcurrent Threshold
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Solution Overview
Problem
Sensorless DC motors face challenges in starting, particularly with motors having small torque characteristics and heavy inertia, where setting the overcurrent detection threshold too low leads to prolonged startup times, and with large torque characteristics and light inertia, setting the threshold too high results in overdrive and potential motor burnout.
Innovation Solution
A controller that generates different overcurrent detection voltages based on the motor's starting or steady-state conditions, using a digital signal generator and DAC to produce distinct overcurrent detection voltages for each state, allowing for adaptive control of PWM signals to prevent overcurrent and ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overcurrent detection threshold is set low to prevent motor burnout, then motor safety is improved, but startup time increases significantly for motors with small torque characteristics and heavy inertia
Solution Approach 1:
The patent applies dynamics by making the overcurrent detection threshold variable rather than fixed. The threshold dynamically changes based on the motor's operating state (starting vs. steady-state), allowing the system to adapt to different operational requirements and resolve the contradiction between safety and startup speed.
Solution Approach 2:
The patent changes the parameter of overcurrent detection threshold based on operating conditions. By switching between a first threshold value during starting and a second threshold value during steady-state, the system optimizes both motor protection and startup performance according to the actual operational phase.
2Productivity
If the overcurrent detection threshold is set high to enable quick startup, then startup speed is improved, but the motor may experience overdrive and burnout for motors with large torque characteristics and light inertia
Solution Approach 1:
The system dynamically adjusts the detection threshold based on the motor's operational phase. During starting, a higher threshold enables faster startup, while during steady-state, a lower threshold ensures safety, thus resolving the contradiction between productivity and reliability through temporal differentiation.
Solution Approach 2:
The patent implements preliminary action by detecting the motor's operating state in advance and pre-setting the appropriate threshold value before overcurrent conditions occur. This allows the system to be prepared with the correct threshold setting, preventing both overdrive and burnout through proactive adaptation.
3Device complexity
If a constant overcurrent detection threshold is used, then device complexity is reduced, but the system cannot adapt to different motor characteristics and operating states
Solution Approach 1:
The patent introduces dynamics into the control system by implementing state-dependent threshold selection. The controller detects whether the motor is in starting or steady-state and automatically selects the appropriate threshold, providing adaptability without requiring complex external adjustment mechanisms.
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
Enables quick and stable startup of sensorless DC motors by adjusting overcurrent detection thresholds according to the motor's state, preventing burnout and ensuring efficient operation regardless of inertia and torque characteristics.
Implementation Method 1
a DAC 12 converts the digital signal Vd to the overcurrent detection voltage Vth
Data Source
AI summary
According to one embodiment, a controller of a motor includes a driving signal output module, a position detector, a determiner, and an over current detector. The driving signal output module is configured to generate a driving signal for generating a driving current of a motor, a duty ratio of the driving signal being depending on an over current detection signal. The position detector is configured to generate a position detection signal for determining an operating status of the motor by comparing an induction voltage generated by a rotation of a rotor of the motor by the driving current with a predetermined reference voltage. The determiner is configured to determine whether the motor is in a starting state where a rotating frequency of the rotor is smaller than a predetermined value or in a steady state where the rotating frequency of the rotor is equal to or higher than the predetermined value based on the position detection signal. The over current detector is configured to output a comparison result as the over current detection signal in accordance with a determination result of the determiner.