Brushless Motor Control via Adjustable Overrun Period
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Solution Overview
Problem
Conventional brushless motor control systems require expensive active power factor correction (PFC) circuits and high-capacitance DC link capacitors to achieve a high power factor, which increase costs and physical size.
Innovation Solution
A method of controlling a brushless motor by exciting the winding until current exceeds a threshold, then continuing for an adjustable overrun period that varies with elapsed time, motor speed, and excitation voltage, allowing for a sinusoidal current waveform without the need for a PFC circuit or high-capacitance capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an active power factor correction (PFC) circuit is used to achieve high power factor, then the power factor is improved, but the cost and device complexity increase significantly
Solution Approach 1:
The patent extracts and eliminates the complex active PFC circuit from the motor control system. Instead of using a dedicated PFC circuit, the invention achieves power factor correction through simplified control of the inverter switching, thereby reducing device complexity and cost while maintaining high power factor performance
Solution Approach 2:
The inverter control system performs multiple functions simultaneously: it drives the motor and also corrects the power factor. By making the inverter control serve both motor drive and PFC functions, the patent eliminates the need for separate PFC circuitry, reducing overall system complexity
2Power
If a high-capacitance DC link capacitor is used to provide regular feedback voltage, then the power factor is improved, but the physical size and cost increase
Solution Approach 1:
The patent changes the control parameters of the inverter switching to achieve power factor correction without relying on large capacitance values. By adjusting switching timing and duration dynamically, the system achieves sinusoidal current draw and high power factor with minimal capacitor size
Solution Approach 2:
The patent removes the requirement for high-capacitance DC link capacitors from the system design. Instead of using large capacitors to smooth voltage and enable PFC, the invention achieves the same effect through intelligent inverter control, dramatically reducing the physical size and cost of capacitive components
3Ease of operation
If the winding is excited until current reaches maximum value, then the current control is simplified, but the power factor deteriorates due to harmonic content
Solution Approach 1:
The patent makes the excitation duration dynamic rather than fixed. The overrun period is adjusted continuously based on motor speed, load conditions, and electrical cycle position. This dynamic control allows the system to maintain simple current threshold-based control while achieving sinusoidal current waveforms and high power factor through variable excitation timing
Solution Approach 2:
The patent employs periodic excitation cycles with variable overrun periods that sync with the electrical cycles of the motor. By adjusting the excitation duration periodically according to the electrical cycle phase and motor operating conditions, the system achieves both simple control implementation and high power factor performance
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 achieves a high power factor and stable current waveform, reducing costs and physical size by eliminating the need for expensive PFC circuits and large capacitors, while maintaining efficient energy use.
Implementation Method 1
exciting a winding of the motor until current in the winding exceeds a threshold... using an alternating voltage that is rectified and used to excite the winding
Data Source
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AI summary
A method of controlling a brushless motor, the method comprising exciting a winding of the motor until current in the winding exceeds a threshold, and continuing to excite the winding for an overrun period. The length of the overrun period is then adjusted in response to a change in one of time, motor speed and excitation voltage. Additionally, a control system that implements the method, and a motor system that incorporates the control system.