Sensorless BLDC Motor Position Control via Zero Crossing Detection
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Solution Overview
Problem
Detecting zero crossings in AC voltage and current waveforms is challenging due to noise in switching nodes, particularly when MOSFETs are used in half-bridge circuits for motor control, as the inductive load and capacitance cause ringing, making accurate detection difficult.
Innovation Solution
An electronic circuit with a zero crossing detector and position estimator that uses a counter to track logic level transitions and generate angular position and frequency signals, allowing for accurate detection of zero crossings without relying on position sensors or blanking time, and adjusts control signals based on these signals to maintain constant frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If MOSFETs are employed as power switches in half-bridge circuits for motor control, then switching performance and power control capability are improved, but switching node noise and ringing increase, making accurate zero crossing detection difficult
Solution Approach 1:
The patent introduces an intermediary signal processing stage between the noisy switching node and the zero crossing detector. This includes filtering circuits and signal conditioning stages that mediate the transition from the high-noise power switching domain to the precision detection domain, allowing accurate zero crossing detection without directly exposing the detector to switching node noise
Solution Approach 2:
The patent creates a clean copy or representation of the switching node signal through filtered voltage detection circuits. Instead of directly detecting the noisy current or voltage at the switching node, the system generates a cleaned version of the signal that preserves zero crossing information while eliminating switching noise and ringing artifacts
2Ease of operation
If traditional zero crossing detection methods are used in noisy switching environments, then detection simplicity is maintained, but detection reliability and accuracy deteriorate due to noise and ringing
Solution Approach 1:
The patent inserts signal conditioning and filtering intermediaries between the switching node and detection circuitry. These intermediaries maintain the simplicity of the overall detection architecture while significantly improving reliability by eliminating noise and ringing before the actual zero crossing detection occurs
3Measurement precision
If position sensors are used to achieve accurate motor position detection, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent enables the motor control system to detect its own position and speed by monitoring its own back-EMF and switching node voltages. This self-service approach eliminates the need for external position sensors, reducing device complexity and cost while maintaining accurate position detection through intelligent signal processing of internally available signals
Solution Approach 2:
The patent makes the existing power switching nodes and voltage detection circuits serve multiple functions: they continue to provide power control while simultaneously enabling position and speed detection. This multi-functionality eliminates the need for separate sensor systems, reducing overall device complexity while maintaining measurement precision
Data Source
AI summary
Described embodiments provide circuits, systems and methods for controlling operation of brushless direct current motors that include a plurality of windings. A gate driver provides control signals to switching elements that control a voltage applied to each of the windings of the motor. A zero crossing detector detects zero crossings of a voltage applied to the windings and transitions a zero crossing signal between a first logic level and a second logic level based on the detected zero crossings. A position estimator estimates an angular position of the motor, and counts in a first direction based on the first logic level of the zero crossing signal, and in a second direction based on the second logic level of the zero crossing signal. An observer determines a value of the counter after an elapsed time, and generates an angular position signal based upon the value of the counter.