Magnetic Pole Detection Circuit for Brushless DC Motors
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Solution Overview
Problem
Brushless DC motors face challenges in reliable magnetic pole detection due to the high manufacturing costs and reliability issues of Hall sensors or rotary encoders, and the susceptibility of back EMF detection to interference and low-speed operation limitations.
Innovation Solution
A magnetic pole detection circuit comprising a multi-phase voltage divider unit, filter unit, DC level compensation unit, amplifying unit, and hysteresis comparison unit, which detects and filters back EMF signals to generate a zero-crossing point signal for controlling the excitation mode of a multi-phase motor, eliminating the need for Hall sensors or rotary encoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall sensor or rotary encoder is used to detect magnetic pole position, then detection accuracy is improved, but manufacturing cost increases and reliability decreases due to additional components and wiring
Solution Approach 1:
The patent extracts the magnetic pole position detection function from external components (Hall sensors, rotary encoders) and implements it through the existing back EMF sensing circuitry. By processing the back EMF signal that already exists in the motor system, the invention eliminates the need for separate detection components, thereby improving reliability while maintaining detection accuracy.
Solution Approach 2:
The back EMF sensing circuit, originally designed for voltage measurement and control, is made multi-functional by enabling it to perform magnetic pole position detection as well. The same circuit that monitors motor operation voltages now also extracts position information through signal processing, eliminating dedicated detection components and reducing system complexity.
2Ease of manufacture
If back EMF is used for magnetic pole position detection, then manufacturing cost is reduced, but detection precision deteriorates due to interference from PWM switching voltage and low signal amplitude at low speeds
Solution Approach 1:
The patent introduces an intermediary signal processing stage that includes filtering and amplification between the back EMF sensing and position detection. The filter removes PWM switching interference, and the amplifier boosts the weak low-speed signal, enabling precise position detection while maintaining the cost advantage of using back EMF instead of external sensors.
Solution Approach 2:
The invention changes the parameters of the back EMF signal through filtering (frequency domain) and amplification (amplitude). By adjusting these parameters, the useful position information is enhanced while interference is suppressed, solving the precision problem without changing the fundamental detection method.
3Device complexity
If back EMF signal is directly used for detection, then device complexity is reduced, but detection reliability worsens due to signal interference and insufficient amplification at low speeds
Solution Approach 1:
The patent applies preliminary signal conditioning (filtering and amplification) to the back EMF signal before it is used for position detection. This preliminary processing ensures that the signal is clean and sufficiently strong before entering the detection logic, improving reliability while keeping the overall circuit relatively simple by using standard signal processing techniques.
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
This solution enables precise control of rotation speed and torque output across a wide speed range, reducing system costs and improving reliability by accurately detecting magnetic pole positions at both high and low speeds without the need for additional components.
Implementation Method 1
The filter unit is configured to filter the back EMF signal to generate a filtered signal
Implementation Method 2
The amplifying unit is configured to amplify the compensation signal to generate an amplified signal
Implementation Method 3
The hysteresis comparison circuit is configured to perform a hysteresis comparison on the reference signal and the amplified back EMF signal to avoid signal bounce due to switching noise
Data Source
AI summary
A magnetic pole detection circuit includes a multi-phase voltage divider unit, a filter unit, a DC level compensation unit, an amplifying unit, and a hysteresis comparison unit. The multi-phase voltage divider unit is configured to detect a back electromotive force (EMF) signal of a multi-phase motor. The filter unit is configured to filter the back EMF signal to generate a filtered signal. The DC level compensation unit is configured to compensate a DC level of the filtered signal to generate a compensation signal. The amplifying unit is configured to amplify the compensation signal to generate an amplified signal. The hysteresis comparison unit is configured to generate a zero-crossing point signal according to the amplified signal and a reference signal. The zero-crossing point signal is adapted to control an excitation mode of the multi-phase motor.