Brushless DC Motor Current Modulation Without a PFC Stage
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Solution Overview
Problem
Existing brushless DC motor control methods for power tools require power factor correction filters, which increase technical complexity and reduce power factor, while pulse-like charging currents from rectifiers degrade AC mains performance and reduce converter lifespan.
Innovation Solution
A cascaded control system superimposes an internal motor current controller with an external speed controller, using a modulation signal based on intermediate circuit voltage to amplitude-modulate the motor current, maintaining a constant mean value for optimal power factor without a PFC stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power factor correction filter (PFC) stage is connected upstream to charge the DC link capacitor, then the AC mains performance is improved and torque fluctuations are prevented, but the technical complexity increases and the power factor decreases
Solution Approach 1:
The invention extracts and eliminates the PFC stage from the system by implementing a control method that directly shapes the motor current to follow the intermediate circuit voltage profile, thereby achieving power factor improvement without the additional hardware complexity of a PFC filter stage
Solution Approach 2:
The invention changes the control parameters by amplitude-modulating the motor current setpoint value according to the intermediate circuit voltage, transforming the current waveform to match the voltage profile and achieving optimal power factor without additional filtering hardware
2Stability of the object's composition
If a power factor correction filter (PFC) stage is connected upstream, then torque fluctuations due to interference are prevented, but the power factor is reduced
Solution Approach 1:
The invention uses feedback by continuously monitoring the intermediate circuit voltage and using it to modulate the motor current setpoint, creating a closed-loop control system that maintains optimal power factor while ensuring stable torque delivery
Solution Approach 2:
The invention implements dynamic current modulation where the motor current amplitude is continuously adjusted to follow the intermediate circuit voltage profile, creating a dynamic control system that adapts to varying operating conditions while maintaining optimal power factor and torque stability
3Ease of manufacture
If pulse-like charging currents are used to charge the DC link capacitor, then the rectifier operation is simplified, but the AC mains performance is degraded and converter lifespan is reduced
Solution Approach 1:
The invention converts the potentially harmful pulse-like charging currents into beneficial shaped current waveforms by using the intermediate circuit voltage profile to modulate the motor current, transforming what would be harmful current spikes into useful torque-producing current while improving overall system reliability
Data Source
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AI summary
The invention relates to a method and an electronic device for controlling a brushless DC motor which is operated on an AC network with a passive rectifier without power factor correction filtering, wherein the DC motor is operated according to a cascaded control by an internal motor current controller being superimposed by an external speed controller, wherein a modulation signal is added to a setpoint value of the motor current in order to use the amplitude-modulated setpoint value as a reference variable of the motor current controller.