Brushless Motor Control via Zero-Crossing Conduction Updates
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Solution Overview
Problem
Brushless motor control systems face challenges in efficiently managing conduction periods to maintain stable current waveforms and power profiles across varying motor speeds and voltages, often requiring expensive and complex controllers to adjust timing frequently.
Innovation Solution
A method that rectifies alternating voltage and updates the conduction period in response to zero-crossings, allowing for regular updates irrespective of motor speed, using a simple and cost-effective controller, and defines the conduction period as a waveform varying periodically to achieve a stable current waveform and efficient motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the timing of control signals is adjusted for each edge of the rotor signal to respond quickly to changes in motor speed or excitation voltage, then the response speed is improved, but the controller cost increases due to the need for a faster and more expensive controller
Solution Approach 1:
The patent segments the control signal adjustment into two parts: (1) coarse adjustment done less frequently based on rotor signal edges, and (2) fine adjustment done more frequently based on zero-crossings of the alternating voltage. This segmentation allows the system to maintain good response characteristics while reducing the overall processing burden on the controller, thereby lowering controller cost.
Solution Approach 2:
The patent introduces periodic action by using zero-crossings of the alternating voltage as an additional trigger for conduction period adjustment. Since zero-crossings occur at a fixed frequency determined by the power supply, this provides regular periodic updates that supplement the rotor-signal-based adjustments, improving response without requiring the controller to process every rotor edge at high speed.
2Device complexity
If the timing of control signals is adjusted after a fixed number of edges of the rotor signal to reduce controller requirements, then the controller cost is reduced, but the performance is adversely affected due to less frequent adjustment at lower speeds and more frequent adjustment at higher speeds
Solution Approach 1:
The patent introduces periodic action by using zero-crossings of the alternating voltage as an additional trigger for conduction period adjustment. Since zero-crossings occur at a fixed frequency determined by the power supply, this provides regular periodic updates that supplement the rotor-signal-based adjustments, improving response without requiring the controller to process every rotor edge at high speed.
Solution Approach 2:
The patent implements feedback by continuously monitoring both rotor position (via rotor signal edges) and power supply voltage phase (via zero-crossings). This dual feedback mechanism ensures that the controller can adjust the conduction period based on both mechanical state and electrical state, maintaining performance across varying operating conditions while using a less expensive controller.
3Adaptability or versatility
If the conduction period is updated at different points in the cycle of the alternating voltage to accommodate varying motor speeds, then the motor speed adaptability is improved, but the harmonic content of the current waveform increases
Solution Approach 1:
The patent introduces periodic action by using zero-crossings of the alternating voltage as an additional trigger for conduction period adjustment. Since zero-crossings occur at a fixed frequency determined by the power supply, this provides regular periodic updates that supplement the rotor-signal-based adjustments, improving response without requiring the controller to process every rotor edge at high speed.
Solution Approach 2:
The patent applies preliminary action by pre-synchronizing the conduction period updates with the zero-crossings of the alternating voltage. This ensures that updates occur at predictable, standardized points in the voltage cycle, which helps maintain consistent current waveform characteristics and reduces harmonic content while still allowing adaptation to different motor speeds through the rotor signal edge triggering.
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 results in a more stable current waveform, reduced harmonic content, and efficient motor operation, enabling a high power factor and smaller motor design without the need for active power factor correction circuits or high-capacitance link capacitors.
Implementation Method 1
rectifying an alternating voltage to provide a rectified voltage
Implementation Method 2
Owing to the back EMF induced in the winding by the permanent-magnet rotor
Data Source
AI summary
A method of controlling a brushless motor that includes rectifying an alternating voltage to provide a rectified voltage, exciting a winding of the motor with the rectified voltage for a conduction period over each electrical half-cycle of the motor, and updating the conduction period in response to a zero-crossing in the alternating voltage. Additionally, a control system that implements the method, and a motor system that incorporates the control system.