Brushless Motor Control via High-Ripple Rectification
Solution Overview
Problem
Brushless permanent-magnet motors require expensive active power factor correction (PFC) circuits and high-capacitance DC link capacitors to maintain stable power delivery, which increase costs and complexity.
Innovation Solution
A method of controlling brushless permanent-magnet motors by rectifying alternating voltage with a ripple of at least 50% and adjusting the advance period and conduction period in response to changes in motor speed and RMS voltage to maintain constant average power, eliminating the need for active PFC circuits and high-capacitance capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an active power factor correction (PFC) circuit is used to provide regular DC voltage, then power control is improved, but system cost and complexity increase significantly
Solution Approach 1:
The patent removes the active PFC circuit from the system entirely. Instead of using complex active components to correct power factor, the invention extracts only the essential rectification function and relies on the natural characteristics of the motor winding inductance to handle power factor correction passively, thereby eliminating the problematic active PFC circuit while maintaining power control stability
Solution Approach 2:
The patent replaces expensive active PFC circuits with a simple passive rectifier circuit using basic diodes and capacitors. This substitution uses inexpensive, simple components that perform the essential function without requiring complex active control electronics, significantly reducing system cost and complexity while maintaining adequate performance
2Stability of the object's composition
If a high-capacitance DC link capacitor is used to provide regular feedback voltage, then voltage stability is improved, but physical size and cost increase
Solution Approach 1:
The patent employs dynamic control of the rectifier conduction angle to actively regulate the DC link voltage. By adjusting the conduction period of the rectifier switches based on feedback, the system dynamically compensates for voltage variations without requiring large capacitance, thereby maintaining voltage stability while using a much smaller capacitor
Solution Approach 2:
The patent changes the operating parameters of the rectifier circuit, specifically the conduction angle and switching timing, to optimize voltage regulation. By varying these parameters dynamically, the system achieves stable DC output voltage without relying on high-capacitance components, reducing both size and cost
3Device complexity
If rectified voltage with high ripple (at least 50%) is applied to the motor, then component simplicity is improved, but power consistency deteriorates
Solution Approach 1:
The patent implements a feedback control mechanism that monitors the instantaneous power delivered to the motor and adjusts the rectifier conduction angle accordingly. This feedback loop compensates for the effects of high voltage ripple, ensuring that the average power delivered to the motor remains consistent despite the non-smooth rectified voltage waveform
Solution Approach 2:
The patent performs preliminary adjustment of the rectifier conduction timing to anticipate and compensate for power variations. By pre-calculating and setting the optimal conduction angle based on expected load conditions, the system proactively maintains power consistency before variations occur, rather than reacting to them after the fact
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 allows for constant average power and high efficiency (at least 80%) across a broad range of motor speeds and voltages without the need for costly PFC circuits or large capacitors, achieving a high power factor and compliance with harmonic standards.
Implementation Method 1
rectifying an alternating voltage to provide a rectified voltage having a ripple of at least 50%
Implementation Method 2
exciting a winding of the motor with the rectified voltage, the winding being excited in advance of zero-crossings of back EMF
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method of controlling a brushless permanent-magnet motor, the method comprising rectifying an alternating voltage to provide a rectified voltage having a ripple of at least 50%, and exciting a winding of the motor with the rectified voltage. The winding is excited in advance of zero- crossings of back EMF by an advance period and is excited for a conduction period over each electrical half-cycle of the motor. The advance period and/or the conduction period are then adjusted in response to changes in the speed of the motor and/or the RMS value of the alternating voltage so as to maintain constant average power. Additionally, a control system that implements the method, and a motor system that incorporates the control system.