Motor Power Limiting During Cold-Load Startup in Power Tools
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Solution Overview
Problem
Power tools, such as plate compactors, experience increased resistance and load due to cold temperatures and environmental factors, leading to excessive power demands that can damage batteries and motors, particularly during startup.
Innovation Solution
A power limitation algorithm that adjusts motor control parameters to maintain power within a limit, activating a power limitation mode when motor speed is below a threshold and deactivating it 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 may cause damage
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 gradually increased rather than maintained at full operating speed, allowing the motor to accelerate smoothly while staying within battery power capabilities. This dynamic adjustment resolves the contradiction between fast startup and power limitation.
Solution Approach 2:
The control system continuously monitors actual motor speed and compares it to the reference speed, adjusting control parameters accordingly. This feedback mechanism ensures the motor reaches operating speed as quickly as possible without exceeding the battery's power capability, resolving the contradiction between startup speed and power demand.
2Productivity
If the motor operates at full power to overcome increased cold load, then the startup performance is improved, but the battery and motor may be damaged
Solution Approach 1:
The control system prepares for cold condition startup by implementing a controlled power ramp-up sequence. Before reaching full power, the system gradually increases motor power output, allowing the battery and motor to warm up and reducing thermal shock. This beforehand cushioning protects components while still achieving successful startup in cold conditions.
3Reliability
If the power limitation mode is activated early in startup, then the battery is protected, but the motor speed may not reach the threshold to deactivate the mode
Solution Approach 1:
The control system implements a preliminary warm-up phase where the motor is driven at controlled speeds to generate heat and reduce lubricant viscosity before the power limitation mode is fully engaged. This preliminary action allows the motor to overcome the initial cold threshold and reach speeds where the power limitation mode can be safely deactivated, ensuring both battery protection and speed achievement.
Data Source
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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.