BLDC Motor Control Circuit for Stable Initial Rotor Position Detection
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Solution Overview
Problem
Conventional brushless DC motor control circuits face inaccuracies in detecting the initial rotor position due to unstable input voltage, leading to unstable driving voltage and incorrect feedback current measurements.
Innovation Solution
A control circuit comprising a voltage integrator, PWM generating circuit, current receiving circuit, comparison circuit, and decision circuit that integrates input voltage to generate PWM signals, controls driving voltage angles, receives feedback currents, compares them, and detects the initial rotor position, stopping PWM signals when integrated voltages exceed a predetermined value to mitigate input voltage instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional PWM signals are output with fixed output time or fixed feedback current value to detect initial rotor position, then the detection method is simple, but the detection accuracy deteriorates when input voltage is unstable
Solution Approach 1:
The patent changes the parameter of PWM signal output time from fixed to variable based on integrated voltage threshold. The control circuit integrates the input voltage over time and compares it with a predetermined threshold, dynamically adjusting when to stop PWM signal output. This resolves the contradiction by making the detection method slightly more complex (adding integration and comparison) but significantly improving detection accuracy under unstable voltage conditions.
2Ease of operation
If the PWM signal output time is fixed to obtain maximum feedback current for detection, then the control is simple, but the feedback current measurement becomes inaccurate when driving voltage is unstable
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit continuously monitors the integrated voltage and uses this feedback to determine when to stop PWM signal output. The integration of input voltage provides real-time feedback about the actual voltage conditions, allowing the system to adjust PWM duration accordingly. This maintains operational simplicity while dramatically improving feedback current measurement accuracy by ensuring measurements are taken under standardized voltage-time conditions.
3Ease of manufacture
If no position sensor is installed to save costs and improve robustness, then the motor cost is reduced and robustness is improved, but the initial rotor position detection becomes challenging under unstable voltage
Solution Approach 1:
The patent introduces an intermediary mechanism - the voltage integration and comparison circuit - that mediates between the unstable input voltage and the position detection process. This intermediary processes the voltage information and creates standardized conditions for detection, allowing reliable sensorless operation without position sensors. This maintains the cost and robustness advantages of sensorless design while significantly improving detection reliability under unstable voltage conditions.
Data Source
AI summary
A control circuit arranged to detect an initial rotor position of a brushless DC motor includes: a voltage integrator circuit, arranged to perform integration upon an input voltage, to generate a plurality of integrated voltages; a PWM generating circuit, arranged to generate and output a plurality of PWM signals to the brushless DC motor through a drive circuit, and stop outputting a PWM signal that is any of the plurality of PWM signals to the brushless DC motor according to an integrated voltage corresponding to the PWM signal; a current receiving circuit, arranged to receive a plurality of feedback currents from the brushless DC motor; a comparison circuit, arranged to perform comparison upon the plurality of feedback currents, to generate a comparison result; and a decision circuit, arranged to detect the initial rotor position according to the comparison result.