Sensorless BLDC Motor PWM Control for Rotor Stop Position Detection
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Solution Overview
Problem
Existing motor control systems for sensorless DC brushless motors face challenges in accurately determining the rotor stop position due to slow exciting current attenuation and voltage fluctuations, leading to increased time requirements for position determination and reduced accuracy.
Innovation Solution
A motor control apparatus with an excitation unit, measurement unit, determination unit, and control unit that uses PWM signals to drive switching elements connected to motor coils, controlling the duty ratio of the PWM signal to manage exciting current flow and power supply voltage, thereby reducing the time needed to determine the rotor stop position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exciting current attenuation rate is slow, then the waiting time until the exciting current becomes 0 is longer, but the rotor stop position determination accuracy is improved
Solution Approach 1:
The patent changes the parameter of exciting current attenuation rate by controlling the duty ratio of PWM signals applied to switching elements. By adjusting this parameter, the system achieves faster current attenuation while maintaining measurement accuracy through controlled excitation sequences.
Solution Approach 2:
The patent implements dynamic control of the exciting current attenuation process by varying the duty ratio of PWM signals in real-time. This allows the system to adaptively manage the decay rate of exciting current, optimizing both speed and accuracy of rotor position determination.
2Loss of time
If the exciting current is regenerated into the power supply to cause rapid attenuation, then the time needed for determination is shortened, but the power supply output voltage rises due to regenerated energy
Solution Approach 1:
The patent employs feedback control by monitoring the power supply output voltage and adjusting the duty ratio of PWM signals accordingly. When voltage rise is detected due to current regeneration, the system reduces the duty ratio to dissipate excess energy, maintaining voltage stability while achieving rapid current attenuation.
Solution Approach 2:
The patent converts the potentially harmful effect of power supply voltage rise into a beneficial control mechanism. By detecting voltage changes caused by current regeneration, the system uses this information to dynamically adjust PWM duty ratios, transforming a problem into an opportunity for optimized control.
3Measurement precision
If multiple coil combinations are excited in order to determine rotor stop position, then the determination accuracy is improved, but the time required for excitation of all phases increases
Solution Approach 1:
The patent applies periodic action by exciting multiple coil combinations in a systematic sequence with controlled timing. Each coil combination is excited for a predetermined period with specific PWM duty ratios, allowing accurate position determination through multiple measurements while maintaining efficient operation through optimized excitation cycles.
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 approach reduces the time required to determine the rotor stop position and enhances accuracy by managing exciting current flow and power supply voltage fluctuations, improving the efficiency of motor control in image forming apparatuses.
Implementation Method 1
the control unit drives, in a first time period and in accordance with a first pulse width modulation (PWM) signal, a first switching element connected to a first phase coil corresponding to a first phase of the excitation phase targeted for excitation and, in a second time period after the first time period and in accordance with a second PWM signal
Implementation Method 2
an excitation unit having a plurality of switching elements respectively connected to a power supply and respectively connected to different coils of a motor, wherein the excitation unit is configured to excite an excitation phase targeted for excitation among a plurality of excitation phases of the motor
Data Source
AI summary
A motor control apparatus includes an excitation unit and a control unit. The excitation unit includes switching elements connected to a power supply and to different motor coils. The excitation unit excites an excitation phase targeted for excitation among motor excitation phases by the control unit driving the switching elements. When the excitation phases are excited, the control unit drives, in a first time period and based on a first PWM signal, a first switching element connected to a first phase coil corresponding to a first phase of the excitation phase targeted for excitation and, in a second time period and based on a second PWM signal, drives a second switching element connected to a second phase coil corresponding to a second phase of the excitation phase. The control unit controls outputting a duty ratio of the second PWM signal to the second switching element in the second time period.