Power Tool Motor Control With Overmodulated SVPWM
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Solution Overview
Problem
Conventional square wave modulation control for direct current motors in power tools results in low output power, low motor efficiency, and poor energy utilization due to limited torque vectors.
Innovation Solution
A power tool system that includes a motor, a speed regulation mechanism, a driver circuit, and a control module. The control module calculates a voltage vector based on measured rotational speed, phase current, and target speed, and overmodulates this vector to output a PWM signal to the driver circuit, maintaining a constant phase voltage for a preset time and ensuring at least two peaks in the voltage waveform per cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional square wave modulation control is used to drive the motor, then the control is easy to implement, but the output power is low and motor efficiency is poor
Solution Approach 1:
The patent changes the control parameter from conventional square wave modulation to space vector pulse width modulation (SVPWM). This parameter change transforms the control method from switching between six discrete torque vectors to generating continuous torque vectors through voltage vector synthesis, thereby increasing output power and motor efficiency while maintaining implementation feasibility through systematic control strategies.
Solution Approach 2:
The patent transitions from one-dimensional square wave modulation (single duty cycle adjustment) to two-dimensional voltage vector control in the complex plane. By representing voltage vectors as phasors with magnitude and phase angle, the system can independently control torque magnitude and rotor flux, enabling higher output power and improved efficiency through optimized vector synthesis.
2Device complexity
If conventional square wave modulation control is used to drive the motor, then the control structure is simple, but the motor efficiency is low and energy utilization is poor
Solution Approach 1:
The patent changes the control approach from simple duty cycle modulation to space vector-based PWM control. By calculating optimal voltage vector magnitudes and phase angles based on motor operating conditions, the system achieves superior energy utilization through precise control of stator current vectors, reducing copper losses and improving overall motor efficiency despite increased control complexity.
Solution Approach 2:
The patent implements feedback control by continuously monitoring motor current and position to calculate the required voltage vectors. The control system adjusts voltage vector synthesis in real-time based on actual motor state, ensuring optimal energy utilization and efficiency across varying operating conditions through closed-loop control.
3Device complexity
If six discrete torque vectors are used in conventional control, then the control method is simple, but the output performance is poor
Solution Approach 1:
The patent segments the voltage control space into multiple sectors based on rotor position, with each sector having optimized voltage vector combinations. By dividing the control range and applying sector-specific PWM strategies, the system generates continuous torque vectors that smoothly traverse the entire operating range, significantly improving output performance compared to discrete six-state switching.
Solution Approach 2:
The patent transitions from static six-state switching to dynamic voltage vector synthesis that continuously adapts to rotor position and speed. The control system dynamically calculates optimal voltage vector magnitudes and directions based on real-time motor state, enabling smooth torque production and high-performance operation across the entire speed and load range.
Data Source
AI summary
A power tool includes a motor, a speed regulation mechanism, a driver circuit, and a control module. The motor includes a stator winding and a rotor. The speed regulation mechanism is at least used for setting a target rotational speed of the motor. The driver circuit is used for delivering electrical energy provided by a power supply device from a direct current bus to the motor, where the driver circuit includes multiple electronic switches connected between the power supply device and the motor. The control module is configured to calculate a voltage vector according to a measured rotational speed of the motor, a phase current of the stator winding, and the target rotational speed and overmodulate the voltage vector to output a pulse-width modulation (PWM) signal to the driver circuit. A per-unit value of an amplitude of the voltage vector ranges from 0 to 1.15.