Motor Power Limiting During Cold-Load Startup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power tools, such as plate compactors, experience increased load due to cold temperatures and environmental factors, leading to high power demands that can damage batteries and motors, especially during startup, resulting in safety shut-offs.
Innovation Solution
A power limitation algorithm for electric motors that adjusts motor control parameters to maintain power within a limit, activating a power limitation mode if the motor speed is below a threshold, and transitioning to an operating mode when the speed exceeds the threshold, using a speed controller and power calculation units to manage power draw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the motor attempts to reach operating speed quickly under cold conditions, then the startup time is reduced, but the power demand exceeds battery capability and causes safety shut-off
Solution Approach 1:
The control system dynamically adjusts the reference motor speed based on operating conditions. During startup in cold conditions, the reference speed is initially limited to a lower value (e.g., 3000 rpm) and gradually increased as the motor warms up and operating conditions improve, allowing the system to adapt between speed performance and battery protection requirements
Solution Approach 2:
The system performs preliminary warming-up action by limiting the reference motor speed during initial startup phase. This prevents excessive power demand on cold batteries while gradually transitioning to full operating speed, ensuring the battery is warmed up and capable of handling higher power requirements before full speed is attempted
2Reliability
If the reference motor speed is limited during startup, then battery damage is prevented, but the time to reach operating speed increases
Solution Approach 1:
The system implements periodic adjustment of the reference motor speed through defined phases: initial limited speed phase for battery protection, intermediate phase for gradual acceleration, and final phase for full operating speed. This periodic progression balances battery protection with minimizing overall startup time
3Productivity
If high power is provided to overcome increased load, then the motor can reach operating speed, but the battery may be damaged or shut off
Solution Approach 1:
The system changes the reference motor speed parameter from its normal operating value to a reduced startup value during cold conditions. This parameter modification allows the motor to operate within safe power limits while still achieving functional performance, gradually transitioning back to normal parameters as conditions improve
Data Source
AI summary
There is provided method for controlling an electric motor configured to drive a mechanical load, the method being for use in a power tool and comprising: in response to a condition being satisfied, comparing speed of the motor to a speed threshold; and if the motor speed is below the speed threshold, activating a power limitation mode. The power limitation mode comprises: monitoring motor power; adjusting one or more motor control parameters so as to maintain power at or close to a power limit; and in response to a determination that the motor speed exceeds the speed threshold, deactivating the power limitation mode and activating an operating mode in which a reference motor speed for the motor is set to an operating speed.