Converter Unit Inrush Current Synchronization via Third Contactor
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Solution Overview
Problem
In high-capacity converter unit systems where multiple converter units are connected in parallel, variations in voltage detection thresholds lead to uneven distribution of inrush currents during power-on or restoration, potentially causing excessive current flow through diode elements in one unit, and existing solutions complicate the system with external voltage detectors and controllers.
Innovation Solution
A converter unit system with a third contactor that synchronizes the operation of second contactors across units, using a second inrush-current suppression resistor in parallel to the third contactor, and a control unit that manages the first and second contactors based on DC voltage detection, allowing for averaged inrush current distribution without external voltage detection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple converter units are connected in parallel to construct a high-capacity system, then the system power capacity is improved, but variation in voltage detection thresholds causes uneven inrush current distribution leading to excessive current through diode elements in certain units
Solution Approach 1:
A third contactor is introduced as an intermediary component that coordinates the switching of multiple converter units. The third contactor receives control signals and synchronizes the opening/closing of individual contactors in each converter unit, ensuring that inrush currents are distributed evenly across all parallel-connected units rather than concentrating in a single unit due to threshold variations.
Solution Approach 2:
The control system monitors the operational state of each converter unit and dynamically adjusts the switching parameters of the third contactor. By changing the control parameters based on real-time voltage detection and contactor status, the system optimizes inrush current distribution and prevents excessive current flow through diode elements during power-on or restoration events.
2Object-affected harmful factors
If external voltage detectors and controllers are added to manage inrush current distribution, then inrush current suppression is improved, but the system complexity increases
Solution Approach 1:
The third contactor serves multiple functions: it acts as a switching device for individual converter units, a coordination mechanism for synchronizing parallel units, and a control interface for managing inrush current distribution. By making the third contactor multi-functional, the system achieves effective inrush current suppression without adding separate external voltage detectors and controllers, thus avoiding increased system complexity.
Solution Approach 2:
The converter units utilize their own internal voltage detection units and control units to monitor and manage inrush currents. Each unit's control unit detects voltage thresholds and communicates with the third contactor to coordinate switching actions. This self-service approach eliminates the need for external control systems while maintaining effective inrush current suppression across all parallel-connected units.
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 configuration effectively averages inrush current flow across parallel converter units, reducing the risk of excessive current through any single unit and simplifies the system by eliminating the need for external voltage detection circuits, thereby protecting diode elements and enhancing system reliability.
Implementation Method 1
an inrush-current suppression circuit for suppressing flow of a high inrush current through diode elements within the diode bridge of the converter unit at the time of power-on to charge the smoothing capacitor
Implementation Method 2
a contactor connected in parallel to the inrush-current suppression resistor
Implementation Method 3
a converter circuit that converts an alternating current to a direct current by a diode bridge
Implementation Method 4
a smoothing capacitor that removes ripple components from the DC voltage into which the converter circuit has converted the AC voltage
Data Source
AI summary
In a converter unit system, converter units are connected in parallel. The converter unit includes a converter circuit connected to an AC power supply and a DC bus, a first inrush-current suppression resistor connected to the DC bus, a first contactor connected in parallel to the first inrush-current suppression resistor, a smoothing capacitor provided after the first inrush-current suppression resistor and the first contactor, a second contactor externally outputting ON/OFF signal, a voltage detection unit measuring a DC voltage value across the smoothing capacitor, and a control unit controlling the first contactor and the second contactor. The converter unit system includes a third contactor connected to the converter units, and a second inrush-current suppression resistor connected in parallel to the third contactor. When contacts of the second contactors are all closed, a contact of the third contactor is closed.