AC Brushless Power Tool Startup Using Zero-Crossing Control
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Solution Overview
Problem
Alternating current power tools using large electrolytic capacitors face issues with large size, reduced lifespan due to heat generation, and voltage pulsation leading to startup failures.
Innovation Solution
A brushless motor system with a voltage conversion module, drive circuit, and controller that utilizes a small filter capacitor and precise timing or zero-crossing detection to manage alternating current input, ensuring accurate rotor position calculation and continuous torque generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large electrolytic capacitor is used to stabilize input voltage, then voltage stability is improved, but the overall device size increases and heat generation reduces capacitor lifespan
Solution Approach 1:
The patent extracts the large electrolytic capacitor from the system and replaces it with a small filter capacitor combined with a voltage stabilization module. This removal eliminates the heat generation and lifespan issues while maintaining voltage stability through alternative means (voltage stabilization module with small capacitor).
Solution Approach 2:
The patent changes the capacitance parameter from large (electrolytic capacitor) to small (filter capacitor), and compensates by changing the control strategy parameter - using zero-crossing detection and specific timing intervals to ensure stable motor operation without requiring large energy storage capacity.
2Stability of the object's composition
If a large electrolytic capacitor is used to stabilize input voltage, then voltage stability is improved, but the device structure becomes larger affecting assembly
Solution Approach 1:
The large electrolytic capacitor is extracted and replaced with a small filter capacitor, dramatically reducing the volume required for voltage stabilization while maintaining system functionality through the voltage stabilization module.
Solution Approach 2:
The capacitance value parameter is changed from large to small, and the system compensates by changing the operational parameter - using specific timing control during zero-crossing intervals to achieve stable operation with minimal energy storage capacity.
3Volume of stationary object
If no large electrolytic capacitor is used, then device size is reduced, but voltage pulsation increases causing startup failure
Solution Approach 1:
The system performs preliminary action by detecting the zero-crossing point of the AC voltage before motor startup and controlling the power module to turn on at this specific moment. This preliminary timing action ensures the motor receives stable voltage at the critical startup phase, preventing startup failure without requiring a large capacitor.
Solution Approach 2:
The system uses feedback by continuously monitoring the AC voltage waveform, detecting zero-crossing points, and adjusting the power module control signals accordingly. This feedback mechanism ensures the motor always starts at the optimal voltage point, maintaining high startup reliability with minimal capacitance.
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
Reduces the probability of startup failure and improves the assembly and lifespan of the power tool by stabilizing voltage and accurately controlling motor operation.
Implementation Method 1
The voltage conversion module is configured to receive the alternating current received by the power module and operatively output a direct current bus voltage
Implementation Method 2
The brushless motor includes a stator winding and a rotor... configured to drive the brushless motor
Data Source
AI summary
An alternating current power tool includes a brushless motor, a power module, a voltage conversion module, a drive circuit, and a controller. The power module is configured to receive an alternating current to supply power to the stator winding. The voltage conversion module is configured to receive the alternating current received by the power module and operatively output a direct current bus voltage. The drive circuit is electrically connected to the voltage conversion module and configured to drive the brushless motor. The controller is configured to start timing when the alternating current received by the power module crosses through a point of zero. In a preset time interval [T1, T2] of each half cycle, a first control signal is outputted to the drive circuit to power on the stator winding.