Cycle-by-Cycle Current Control for Brushless Power Tools
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Summary
Problems
Handheld angle grinders and other power tools often exceed the rating of the AC power outlet's circuit breaker, leading to tripped breakers due to high power demands, necessitating increased power output without complex and expensive power conversion circuits.
Innovation solutions
A handheld AC power tool with a brushless electric motor, a converter circuit, and a controller that enforces a current limit by comparing instantaneous current to a set limit, interrupting and resuming current flow to the motor, along with a capacitor to maintain a stable DC bus voltage, allowing for efficient power delivery within the AC power source limits.
TRIZ Analysis
Specific contradictions:
General conflict description:
Principle concept:
If the power output of handheld tools is increased to meet high current demand, then the power delivery capability is improved, but the circuit breaker trips due to exceeding AC power source limits
Why choose this principle:
The controller enforces current limits on a cycle-by-cycle basis, periodically monitoring and adjusting current delivery to the motor. This periodic control allows the system to operate at high power levels while preventing sustained overcurrent conditions that would trip the circuit breaker, by interrupting current flow in a rhythmic, controlled manner synchronized with the AC power cycle
Principle concept:
If the power output of handheld tools is increased to meet high current demand, then the power delivery capability is improved, but the circuit breaker trips due to exceeding AC power source limits
Why choose this principle:
The system dynamically adjusts the current limit enforcement based on real-time operating conditions. The controller continuously monitors current draw and modulates the duty cycle of the motor drive, enabling the power output to vary dynamically within safe limits, thus achieving high power delivery without exceeding circuit breaker ratings
Application Domain
Data Source
AI summary:
A handheld AC power tool with a brushless electric motor, a converter circuit, and a controller that enforces a current limit by comparing instantaneous current to a set limit, interrupting and resuming current flow to the motor, along with a capacitor to maintain a stable DC bus voltage, allowing for efficient power delivery within the AC power source limits.
Abstract
A power tool is provided including a brushless electric motor, a switching arrangement having motor switches and interposed between the electric motor and a power supply, and a controller configured to control a switching operation of the motor switches for driving the electric motor and enforce a current limit on the current delivered to the electric motor. The controller receives a measure of current passing from the power supply to the switching arrangement and takes corrective action to reduce current delivered to the electric motor if the measured current exceeds the current limit. The controller is further configured to initiate a protective response if a number of time intervals in which the measured current exceeds the current limit exceeds a predetermined threshold.