Static Converter Precharge Device for Inrush Current Control
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Solution Overview
Problem
Static converters face challenges in precharging capacitors to the minimum voltage required for startup, leading to potentially high inrush currents and undesirable loading on the network when directly connected to the supplying system, especially when the phase angle of the system voltage is unfavorable.
Innovation Solution
A precharge device with power electronics provides an adjustable and constant precharge current, using power controllers or rectifiers connected via a precharge transformer to bypass direct precharging, limiting and controlling the precharge current to avoid peak currents and voltage dips, allowing capacitors to be charged to the necessary voltage for submodule activation and system synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If capacitors are precharged directly from the supplying system, then precharge time is reduced, but high inrush currents occur causing voltage dips and network loading
Solution Approach 1:
A precharge device with power electronics is introduced as an intermediary between the supplying system and the converter capacitors. This device provides controlled precharge current through power controllers or rectifiers, preventing direct connection and thus avoiding inrush currents while maintaining efficient charging
Solution Approach 2:
The precharge device dynamically controls the precharge current parameters, adjusting the current magnitude and timing to optimize charging speed while preventing harmful inrush currents. The power electronics enable precise parameter management during the precharge phase
2Use of energy by moving object
If power semiconductors are activated at low voltage, then energy consumption is reduced, but submodules cannot be activated without minimum voltage
Solution Approach 1:
The precharge device performs preliminary voltage buildup on the capacitors before the main power conversion operation begins. This preliminary action ensures that minimum voltage requirements are met for reliable submodule activation and power semiconductor operation, preventing activation failures
3Ease of operation
If phase angle of system voltage is unfavorable, then synchronization is complicated, but direct connection causes high inrush currents
Solution Approach 1:
The precharge device serves as a mediator that decouples the synchronization process from direct system connection. It enables controlled voltage buildup independent of system phase angle, allowing synchronization to be achieved without the harmful effects of direct connection during unfavorable phase conditions
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
This solution enables efficient precharging of capacitors to the minimum voltage required for submodule activation, minimizing precharge time and avoiding high inrush currents, thus smoothly connecting the power converter to the system without significant network loading.
Implementation Method 1
connected via a precharge transformer to bypass direct precharging, limiting and controlling the precharge current
Implementation Method 2
Each submodule is in the form of a half-bridge or full-bridge circuit and has an associated capacitor as energy store
Data Source
AI summary
A static converter that includes a power converter circuit having a plurality of interconnected module branches. Each module branch may have one or more electrically series-connected two-pole submodules as switchable voltage sources which each include a capacitor as an energy store and power semiconductors as electronic switching elements. A device for precharging the capacitors is included that has at least one power electronics device for providing an adjustable precharge current. The at least one power electronics device, being supplied with power by an auxiliary supply system and being connected to a converter bridge via a precharge transformer, can be used to achieve a sufficiently high voltage level for the capacitors of the submodules when the converter is started up so as to achieve firstly the minimum voltage for supplying power to the power semiconductors and secondly the minimum voltage for synchronization to the systems.