Electric Motor Startup Control Using Rotor Position Signal Injection
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Solution Overview
Problem
Cutting tools such as pole saws and hedge trimmers experience low efficiency during startup, especially when loaded, leading to abnormal motor starts and reduced user experience due to inefficiencies and potential motor failure.
Innovation Solution
A power tool system with a controller that estimates the angular position of the rotor using a high-frequency signal injection method to provide a drive signal for the electric motor, allowing for controlled restarts and preventing abnormal starts by acquiring working parameters like current and rotational speed, thereby improving startup efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electric motor starts with load directly, then the startup process is simple, but the startup efficiency is low and abnormal starts occur
Solution Approach 1:
The controller performs preliminary detection of rotor angular position and startup condition assessment before the motor actually starts. By injecting high-frequency signals to detect rotor position in advance and evaluating load conditions, the system prepares optimal startup parameters beforehand, enabling efficient and reliable startup under load conditions without direct-on-line starting problems
Solution Approach 2:
The controller continuously monitors motor current, voltage, and rotor position during the startup process. Based on feedback from these parameters, the controller dynamically adjusts the drive signals to optimize startup performance and prevent abnormal starts, creating a closed-loop control system that improves both efficiency and reliability
2Productivity
If the controller uses traditional startup control, then the control circuit is simple, but the startup efficiency is low
Solution Approach 1:
The system replaces traditional mechanical startup methods with electronic control. By using a controller that injects high-frequency signals to detect rotor position and electronically controls the motor startup sequence, the system achieves efficient startup without complex mechanical switches or starters, substituting mechanical complexity with intelligent electronic control
Solution Approach 2:
The controller dynamically changes multiple parameters during startup including injection signal frequency, drive voltage amplitude, switching frequency, and current limits. By optimizing these parameters based on detected rotor position and load conditions, the system achieves high startup efficiency without requiring overly complex circuitry, as the complexity is managed through software-controlled parameter adjustment
3Reliability
If the motor starts under load without detection, then the operation is simple, but abnormal starts cause automatic shutdown
Solution Approach 1:
Before motor startup, the controller performs preliminary detection by injecting high-frequency signals to determine rotor angular position and assesses startup feasibility by analyzing current and voltage parameters. This preliminary assessment identifies potential abnormal conditions before they cause shutdown, enabling preventive control actions
Solution Approach 2:
The controller acts as an intermediary between the power source and motor, inserting detection and control functions in the startup path. By monitoring parameters through the driver circuit and intervening with adjusted drive signals when abnormalities are detected, the controller prevents shutdown while managing the added complexity through intelligent mediation
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 system significantly enhances the efficiency of power tool startups, prevents automatic shutdowns, and ensures high reliability, improving user experience and product competitiveness by effectively managing abnormal start conditions.
Implementation Method 1
acquire the angular position of the rotor with a high-frequency signal injection method
Data Source
AI summary
A cutting tool includes: an electric motor with a stator having multiple windings and a rotor; a driver circuit electrically connected to the electric motor to drive the electric motor to run; and a controller configured to estimate the angular position of the rotor based on a working parameter of the electric motor and output a drive signal to the driver circuit based on the angular position of the rotor to control the rotation of the electric motor. At a start stage, the controller is configured to: when an abnormal start of the electric motor is detected, output a first control instruction to control the electric motor to restart, where the first control instruction includes at least the instruction to input a high-frequency signal into the driver circuit so as to acquire the angular position of the rotor.