Battery Power Tool DC-DC Converter for Inrush Current Limiting
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Solution Overview
Problem
Conventional power tools suffer from damaging current pulses when a battery pack is connected, which can harm components, and existing solutions like pre-charging via a resistor cause losses and delay usability.
Innovation Solution
Incorporating a DC-DC converter unit between the battery unit and power electronics, which limits inrush current through an intermediate circuit capacitor, preventing damage and maintaining quick operational readiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate circuit capacitor is connected directly to the battery unit, then DC voltage stabilization is achieved, but damaging inrush current pulses occur when the battery pack is connected
Solution Approach 1:
A current limiting circuit is introduced as an intermediary component between the battery unit and the intermediate circuit capacitor. This mediator limits the inrush current when the battery pack is connected while allowing the capacitor to perform its DC voltage stabilization function, thus resolving the contradiction between reliability and harmful factors.
2Object-affected harmful factors
If a pre-charging resistor is inserted to limit inrush current, then damage to components is avoided, but energy losses increase and operating time decreases
Solution Approach 1:
The current limiting circuit is designed to dynamically adjust its characteristics: it limits current only during the initial connection phase when inrush current occurs, then becomes transparent to normal operation. This dynamic behavior prevents component damage without causing continuous energy losses that would reduce battery operating time.
3Object-affected harmful factors
If a pre-charging resistor is used to limit inrush current, then current pulses are reduced, but waiting time until power tool usability increases
Solution Approach 1:
The current limiting circuit is designed to perform its current limiting function only during the brief connection moment, automatically transitioning to a non-intrusive state. This preliminary action approach reduces current pulses without creating a sustained waiting period, allowing the power tool to become usable immediately after connection.
4Reliability
If conventional electrolytic capacitors are used for DC voltage stabilization, then capacitance is achieved, but self-heating and power loss occur
Solution Approach 1:
The patent specifies using polypropylene film capacitors instead of conventional electrolytic capacitors. This parameter change in capacitor technology provides equivalent or superior capacitance for DC voltage stabilization while significantly reducing self-heating and power loss, thus resolving the contradiction between reliability and temperature.
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 DC-DC converter unit mitigates damaging current pulses with minimal losses, ensuring rapid and safe power tool readiness.
Implementation Method 1
the DC-DC converter unit controls its output voltage U 2 such that the output current I 2, representing the inrush current, is limited to a damage-free maximum output current I 2_max
Implementation Method 2
an intermediate circuit capacitor for DC voltage stabilization in the electrical power supply line from the connection point for the battery unit to a power electronics unit
Data Source
Figure 1
Figure 2
AI summary
The invention relates to an electronic device for supplying energy to a power tool, comprising a two-pole connection interface for a battery unit, which is connected to an electric motor as a drive by means of associated electrical lines via a controlling power electronics unit, wherein at least one intermediate circuit capacitor connecting the two electrical lines for DC voltage stabilization is arranged between the connection interface and the power electronics unit, wherein the two-pole connection interface is connected on the input side to a DC voltage converter unit, which is connected on the output side to the power electronics unit, wherein the intermediate circuit capacitor is connected to the electrical lines in the section between the DC voltage converter unit and the power electronics unit.