Brushless DC Motor Control via Back-EMF Voltage Regulation
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Solution Overview
Problem
High-speed permanent magnet brushless direct current motors face challenges in achieving efficient control due to high switching losses and limited rotational speed, primarily due to the trade-off between motor efficiency and usable speed, along with the need for sensorless rotor position and speed determination without physical sensors, which complicates optimal design and operation.
Innovation Solution
A direct current to direct current converter and regulator circuit that outputs a controlled voltage inverter circuit power feed, used in conjunction with an inverter circuit assembly, to regulate the voltage based on motor shaft rotational speed and back electromotive force, reducing pulse width modulation switching frequency and smoothing the alternating current waveform, thereby increasing motor efficiency and reducing harmonic content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If pulse width modulation switching frequency is reduced to smooth the alternating current waveform and increase motor efficiency, then motor efficiency is improved, but the response time and control precision deteriorate
Solution Approach 1:
The patent implements dynamic adjustment of PWM switching frequency based on operating conditions. The controller varies the switching frequency within a range (e.g., 2kHz to 20kHz) depending on motor speed, load, and efficiency requirements. This dynamic approach allows the system to optimize between efficiency (lower frequency) and response time (higher frequency) in real-time, resolving the contradiction between these two parameters.
2Device complexity
If sensorless control is implemented to eliminate physical sensors and reduce device complexity, then device complexity is reduced, but measurement precision of rotor position and speed deteriorates
Solution Approach 1:
The patent uses back electromotive force (back-EMF) signals as an intermediary to indirectly determine rotor position and speed without physical sensors. The controller measures the back-EMF generated by the motor during operation and processes these signals to extract position and speed information. This intermediary approach eliminates the need for Hall effect sensors or encoders while maintaining adequate measurement precision for control purposes.
Solution Approach 2:
The patent replaces mechanical/physical sensing systems (Hall effect sensors, encoders) with an electrical field-based measurement approach. Instead of using physical components that detect magnetic fields or mechanical position, the system uses electrical measurements of back-EMF to infer rotor state. This substitution reduces device complexity and eliminates physical sensor requirements while providing sufficient measurement capability.
3Power
If voltage is increased to maintain power output at high speeds, then power output is maintained, but switching losses and electrical inefficiency increase
Solution Approach 1:
The patent implements dynamic voltage adjustment that tracks motor back-EMF in real-time. The controller modifies the DC bus voltage or inverter output voltage based on instantaneous motor speed and load conditions. By dynamically matching voltage to actual motor requirements rather than using fixed high voltage, the system maintains power output while minimizing excessive voltage that would cause increased switching losses and electrical inefficiency.
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 allows for dynamic voltage adjustment to match motor operating conditions, reducing switching losses and enhancing motor efficiency, while providing accurate sensorless rotor position and speed determination, leading to improved performance and reduced motor temperatures.
Implementation Method 1
a permanent magnet brushless direct current motor that is in electrical communication with the inverter and receives the alternating current motor power feed, wherein the motor outputs a shaft rotational speed and a back electromotive force
Implementation Method 2
an inverter circuit assembly that is in electrical communication with the regulator and receives the controlled voltage direct current inverter power feed, wherein the inverter outputs an alternating current motor power feed
Implementation Method 3
A high speed motor rotor is constructed of a permanent magnet which requires a structural reinforcement member to allow the permanent magnet to withstand high rotational speeds
Data Source
AI summary
An electrical control system having a direct current to direct current regulator receiving a direct current supply input, wherein the regulator outputs a controlled voltage direct current inverter power feed. Included is an inverter in electrical communication with the regulator and receives the controlled voltage direct current inverter power feed, the inverter outputs an alternating current motor power feed to a permanent magnet brushless direct current motor that outputs a shaft rotational speed and a back electromotive force. Also, a control is provided for regulating the controlled voltage direct current inverter power feed based upon criteria utilizing the back electromotive force or an auxiliary motor stator wire loop signal in conjunction with an optional voltage look-up table to substantially make the controlled voltage result in a reduction of a pulse width modulation switching frequency to further smooth and reduce harmonic of the alternating current waveform to increase motor efficiency.