Sensorless Motor Drive Circuit Zero Crossing Detection
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Solution Overview
Problem
Sensorless motor drive systems face challenges in accurately detecting the zero crossing point due to noise components in back electromotive voltage, leading to rotor position misdetetection, which affects rotation accuracy and stability.
Innovation Solution
A motor drive circuit with a pulse modulation signal generation unit, back electromotive detection circuit, switching control unit, and pulse adjustment unit that compares back electromotive voltage with middle point voltage to accurately detect the zero crossing point, adjusting the pulse modulation signal's duty ratio and frequency to minimize phase errors and ensure precise detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse modulation is used to control motor current, then motor control flexibility and efficiency are improved, but noise components appear in back electromotive voltage causing zero crossing point detection errors
Solution Approach 1:
The patent introduces a mask signal as an intermediary element that selectively validates back electromotive detection signals during specific time periods. The mask signal acts as a filter that allows only valid zero crossing points to pass through to the rotor position calculation, blocking invalid detections caused by PWM noise. This mediator approach resolves the contradiction by enabling continued use of PWM for efficient motor control while eliminating its harmful effect on detection accuracy.
Solution Approach 2:
The patent applies preliminary action by pre-defining valid detection periods based on PWM cycle timing before actual zero crossing detection occurs. By calculating expected zero crossing timing in advance and creating corresponding mask signals for these predetermined periods, the system prepares validation criteria beforehand, ensuring that only zero crossing points occurring during noise-free periods are accepted for rotor position calculation.
2Volume of moving object
If sensorless motor drive is implemented to miniaturize the motor, then motor size is reduced, but rotor position detection accuracy deteriorates due to noise
Solution Approach 1:
The mask signal serves as an intermediary validation mechanism that enables sensorless motor drive to achieve both miniaturization and accurate rotor position detection. By filtering detection signals through the mask signal validator, the system eliminates noise-induced errors that would otherwise prevent accurate sensorless operation, thus allowing motor size reduction without sacrificing detection precision.
3Measurement precision
If zero crossing point detection is performed continuously, then rotor position accuracy is maintained, but detection errors increase due to noise-induced false detections
Solution Approach 1:
The mask signal acts as a reliability gatekeeper that maintains rotor position accuracy by validating each detected zero crossing point against expected timing windows. This intermediary validation prevents false detections from corrupting the rotor position calculation, thereby maintaining both measurement precision and detection stability simultaneously.
Solution Approach 2:
The system employs feedback by continuously comparing actual detection timing against expected timing based on PWM cycle information. When a detected zero crossing point falls outside the valid period indicated by the mask signal, it is rejected as invalid. This feedback mechanism ensures that only reliable detections contribute to rotor position accuracy, preventing noise-induced errors while maintaining continuous position monitoring.
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
The proposed solution enables accurate detection of the zero crossing point with minimal delay, improving rotor position accuracy and stability in sensorless motor drive systems, particularly in miniaturized disc media applications like CD and DVD players.
Implementation Method 1
a back electromotive detection circuit which detects a zero crossing point by comparing a back electromotive voltage generated in at least one coil of the multi-phase motor with a middle point voltage of the coil
Data Source
AI summary
A pulse generation unit generates a PWM signal whose duty ratio changes according to a target torque of a motor. A back electromotive detection circuit compares a back electromotive voltage generated at a coil of the motor with a middle point voltage of the coil, and outputs a back electromotive detection signal that becomes high level at a timing of the zero crossing point. A phase adjustment unit compares phases of the back electromotive detection signal and a reference signal that becomes a predetermined level at a predetermined timing, and adjusts the duty ratio of the PWM signal by feedback so that the phase error becomes a minimum. A frequency adjustment unit adjusts the frequency of the PWM signal such that the frequency of the PWM signal becomes integral multiples of the frequency of the back electromotive detection signal.