DC-link Charging Arrangement with Parallel Capacitor
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Solution Overview
Problem
Existing DC-link charging systems face inefficiencies due to direct connection to the grid when uncharged, leading to overloading and high energy dissipation as heat through resistors.
Innovation Solution
A charging capacitor is arranged in parallel to the contactor, allowing current to pass and limit charging, with a filter arrangement and active rectifier control to manage power angle and voltage, maximizing charging power while minimizing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the DC-link capacitor is directly connected to the grid when uncharged, then the charging process is simple and fast, but this causes a large current which overloads the remaining components
Solution Approach 1:
A contactor is introduced as an intermediary switching device between the grid and the DC-link capacitor. The contactor controls the connection timing, allowing the system to safely manage the charging process by initially connecting through the contactor and then establishing the main grid connection, thereby preventing component overload while maintaining charging efficiency
2Reliability
If charging resistors are used to limit the charging current, then component overload is prevented, but a large amount of charging energy is dissipated as heat resulting in very poor efficiency
Solution Approach 1:
The harmful function of the charging resistor (energy dissipation) is extracted and removed from the system. Instead of using resistive current limiting, the patent employs a contactor-based switching mechanism that enables direct charging without energy-wasting resistors, thereby preventing component overload while eliminating heat loss
3Reliability
If a contactor is introduced to control the charging connection, then component overload is prevented, but the charging efficiency remains low due to energy loss in traditional resistor-based charging
Solution Approach 1:
The contactor is merged with the main grid connection switch, combining the protective function and the main power connection function into a single integrated switching mechanism. This eliminates the need for separate charging resistors and enables efficient direct charging while maintaining component protection, thereby resolving the contradiction between reliability and productivity
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 solution enables efficient charging of the DC-link capacitor with reduced energy losses, allowing for a stable voltage supply and efficient energy transfer, even when the contactor is open, by forming a voltage divider and optimizing power angle and voltage amplitude.
Implementation Method 1
a charging capacitor (Cch1, Cch2, Cch3) arranged in parallel to each of the contactors (13, 14, 15)... The charging capacitor limits the current and supplies the necessary electrical energy to the input of the rectifier means
Implementation Method 2
The charging capacitor and the filter capacitor form a voltage divider. When the main voltage is applied to the input side of the charging capacitors, the charging capacitors will limit the current but charge the DC-link to a level determined by the ratio of the charging capacitor and the filter capacitor
Implementation Method 3
rectifier means, in particular active rectifier means... the control means being configured to adjust a power angle between a voltage and the supply ports and a charging voltage at active rectifier ports
Data Source
AI summary
A DC-link charging arrangement is described having a DC-link capacitor, rectifier means, and contactor means arranged between supply voltage ports and the rectifier means and having at least one contactor. Such a charging arrangement should enable charging of a DC-link capacitor in a simple way with low losses. To this end a charging capacitor is arranged bridging the at least one contactor.