Brushless Power Tool Speed Control Under Variable Load
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Solution Overview
Problem
Existing power tools struggle to achieve higher or more stable output power due to limitations in adjusting pulse-width modulation (PWM) duty cycle alone.
Innovation Solution
A power tool with a brushless motor, inverter circuit, and controller that adjusts PWM duty cycle and conduction angle based on workload parameters to maintain target rotational speeds, prioritizing adjustments to stabilize motor speed under varying loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If PWM duty cycle adjustment is used to control motor speed, then power output can be regulated, but the output power stability and magnitude are insufficient under varying load conditions
Solution Approach 1:
The patent implements a closed-loop control system with a load detection module that detects motor workload parameters (current, voltage, or power) and feeds this information back to the controller. The controller adjusts PWM duty cycle and conduction angle based on the detected load parameters to maintain stable output power under varying load conditions, resolving the contradiction between power regulation and power stability.
Solution Approach 2:
The patent changes control parameters by introducing conduction angle adjustment in addition to PWM duty cycle control. The controller dynamically adjusts both PWM duty cycle and conduction angle based on detected load parameters, enabling more precise and stable power output control across different load conditions, thereby improving both power magnitude and stability.
2Speed
If PWM duty cycle is adjusted to maintain motor speed, then speed control is achieved, but large speed fluctuations occur under heavy load conditions
Solution Approach 1:
The load detection module continuously monitors motor workload parameters and provides feedback to the controller. When heavy load is detected, the controller increases both PWM duty cycle and conduction angle to maintain stable motor speed, preventing large speed fluctuations that would occur with PWM duty cycle adjustment alone.
Solution Approach 2:
The patent makes the control system dynamic by introducing adaptive conduction angle adjustment based on real-time load detection. The conduction angle is dynamically increased under heavy load conditions alongside PWM duty cycle adjustment, enabling the system to adapt to varying load demands and maintain stable motor speed, thereby resolving the speed stability issue.
3Device complexity
If only PWM duty cycle control is used, then the control system remains simple, but the output power cannot meet higher or more stable requirements
Solution Approach 1:
The controller is designed to perform multiple functions: it manages PWM duty cycle control, conduction angle control, load parameter detection processing, and motor speed regulation. By integrating these multiple control functions into a single controller, the system achieves enhanced output power capability without proportionally increasing overall system complexity, as the same controller hardware handles all control tasks.
Solution Approach 2:
The patent combines PWM duty cycle control and conduction angle control into a unified control approach. The controller simultaneously manages both control parameters based on load detection feedback, merging multiple control mechanisms into a coordinated system that delivers higher and more stable output power while maintaining reasonable system complexity through integrated control logic.
4Reliability
If PWM duty cycle and conduction angle are both adjusted, then output power and speed stability improve, but the control system complexity increases
Solution Approach 1:
The load detection module provides automated feedback on motor workload parameters, enabling the controller to automatically adjust both PWM duty cycle and conduction angle based on actual load conditions. This feedback mechanism reduces the need for complex manual control logic, as the system self-regulates both parameters based on detected load levels, thereby improving stability while keeping control system complexity manageable through automated decision-making.
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
The solution prevents motor damage from large speed fluctuations and improves working efficiency by maintaining optimal rotational speeds in both light and heavy load conditions.
Implementation Method 1
a brushless motor, comprising a stator and a rotor
Data Source
AI summary
A power tool includes a brushless motor, including a stator and a rotor; an inverter circuit, including a plurality of switch components, where the plurality of switch components are configured to perform a switch action to control driving of the brushless motor; and a controller, electrically connected to the inverter circuit and the brushless motor, the controller including a load detection module configured to detect a parameter indicating a workload of the brushless motor. In response to the parameter being less than a set threshold, the controller is configured to control the brushless motor to maintain a first target rotational speed; and in response to the parameter being greater than or equal to a set threshold, the controller controls the brushless motor to maintain a second target rotational speed. The first target rotational speed may be greater than the second target rotational speed.