Brushless Motor Control via Periodic Conduction Waveforms
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Solution Overview
Problem
Brushless motors with active power factor correction (PFC) circuits face high costs and require large, expensive DC link capacitors to achieve sinusoidal current draw, which is difficult to control due to back EMF in permanent-magnet motors.
Innovation Solution
A method of controlling brushless motors by varying the conduction period of the winding excitation periodically, allowing the current waveform to approach sinusoidal without the need for PFC circuits or high-capacitance capacitors, by defining the conduction period waveform to achieve specific current and magnetic flux profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an active power factor correction (PFC) circuit is used to achieve sinusoidal current draw, then the power factor is improved, but the cost and device complexity increase significantly
Solution Approach 1:
The patent extracts and removes the active PFC circuit from the control system, replacing it with a simplified approach that varies the conduction period of the winding excitation. This eliminates the complex PFC circuitry while achieving the desired sinusoidal current draw through periodic conduction period variation defined by a waveform.
Solution Approach 2:
The patent changes the conduction period parameter from a fixed value to a periodically varying value defined by a waveform. By varying the conduction period according to a specific waveform pattern, the system achieves sinusoidal current draw and high power factor without requiring complex active PFC circuitry.
2Power
If a high-capacitance DC link capacitor is used to provide regular feedback voltage, then the power factor is improved, but the device size and cost increase
Solution Approach 1:
The patent removes the requirement for a high-capacitance DC link capacitor by eliminating the active PFC circuit. The system achieves stable operation and high power factor through periodic conduction period variation without needing large energy storage capacitors to smooth the DC link voltage.
Solution Approach 2:
The patent employs periodic action by varying the conduction period according to a waveform pattern. This periodic variation in conduction timing achieves sinusoidal current draw and high power factor without requiring continuous voltage smoothing that would demand large capacitor sizes.
3Power
If the conduction period is varied periodically to achieve sinusoidal current waveform, then the power factor is improved, but the control complexity increases
Solution Approach 1:
The patent implements periodic action by varying the conduction period according to a defined waveform pattern. This periodic variation in conduction timing naturally produces sinusoidal current draw and high power factor. The control complexity is managed by using a systematic waveform-based approach rather than complex real-time calculations.
Solution Approach 2:
The patent applies dynamics by transitioning from a fixed conduction period to a dynamically varying conduction period defined by a waveform. This dynamic adjustment of the conduction period enables the system to achieve sinusoidal current draw and high power factor while adapting to different operating conditions.
4Loss of energy
If the conduction period waveform is optimized to reduce peak magnetic flux density, then the motor efficiency is improved and size is reduced, but the control complexity increases
Solution Approach 1:
The patent changes the conduction period from a fixed parameter to a waveform-defined parameter that varies periodically. By optimizing the waveform shape and timing, the system reduces peak magnetic flux density, improving motor efficiency and enabling smaller motor size while maintaining manageable control complexity through systematic waveform design.
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 enables high power factor and efficient operation with reduced motor size and cost, while maintaining low harmonic content and compliance with harmonic standards, achieving constant average power over a range of speeds and voltages.
Implementation Method 1
exciting a winding of the motor for a conduction period over each electrical half-cycle of the motor... the waveform of the conduction period may be defined such that the waveform of current drawn from the power supply approaches that of a sinusoid
Implementation Method 2
The length of the conduction period also influences the magnitude of the magnetic flux density in the motor. The waveform of the conduction period may therefore be defined so as to achieve a particular envelope for the magnetic flux density
Implementation Method 3
a permanent-magnet rotor (5) that rotates relative to a stator (6)... The rotor (5) comprises a plurality of permanent magnets (7) arranged around its circumference
Implementation Method 4
an inverter (10) that converts the DC voltage to a variable frequency AC voltage... by controlling the switching of the power semiconductor devices in the inverter
Implementation Method 5
a rectifier (8) that converts the AC voltage to a DC voltage
Implementation Method 6
When driven by an AC supply, the control system often includes an active power factor correction (PFC) circuit... difficult to control due to back EMF in permanent-magnet motors
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method of controlling a brushless motor, the method comprising exciting a winding of the motor for a conduction period over each electrical half-cycle of the motor. The length of the conduction period is defined by a waveform that varies periodically with time. Additionally, a control system that implements the method, and a motor system that incorporates the control system.