Voltage Source Converter Sub-Module Connection Integrity Testing
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Solution Overview
Problem
The existing methods for testing the integrity of connections in voltage source converters, particularly after installation or maintenance, are laborious and time-consuming, involving visual inspection and individual testing of numerous sub-modules, which is inefficient and risky due to high operating voltages.
Innovation Solution
A method and apparatus for testing series connected cells in a voltage source converter using a low-voltage electrical test stimulus that is sufficient to forward bias freewheeling diodes, allowing for safe and quick monitoring of electrical characteristics without requiring the sub-modules to be fully powered, thereby ensuring connection integrity without risking catastrophic failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If visual inspection and individual testing of each sub-module are performed, then connection integrity can be verified, but the testing process becomes laborious and time-consuming
Solution Approach 1:
The patent combines multiple individual sub-module tests into a single integrated testing procedure. By applying a low voltage stimulus across the entire series-connected string of sub-modules, the method simultaneously verifies the integrity of all connections and components in one operation, rather than requiring separate tests for each sub-module.
Solution Approach 2:
The testing apparatus performs multiple verification functions simultaneously using a single low voltage stimulus application. It checks for proper series connection, verifies diode functionality, detects open circuits, and validates overall string integrity all in one test sequence, making the testing process universally applicable to various VSC configurations.
2Measurement precision
If high operating voltage is applied for testing, then comprehensive electrical characteristics can be monitored, but catastrophic failure risk increases
Solution Approach 1:
The patent changes the voltage parameter from the normal high operating voltage to a low voltage level for testing purposes. This parameter change allows sufficient electrical measurement and monitoring of diode conduction and connection integrity while reducing the energy available to cause catastrophic damage, thus decoupling measurement capability from damage risk.
Solution Approach 2:
The low voltage stimulus acts as an intermediary that indirectly tests the high voltage system without subjecting it to full operating conditions. The stimulus is sufficient to forward-bias diodes and reveal connection issues but serves as a safe mediator that prevents catastrophic failure by limiting maximum energy exposure.
3Object-affected harmful factors
If low voltage test stimulus is applied to forward bias diodes, then safe testing is achieved, but voltage must be greater than threshold voltage
Solution Approach 1:
The patent applies a voltage that is partially sufficient for full operating conditions but excessive enough to achieve the specific testing objective of forward-biasing diodes. The voltage exceeds the diode turn-on threshold to ensure reliable conduction and connection verification, while remaining below the level that would cause damage, thus applying just the right amount of stress needed for the test.
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 a safe, efficient, and rapid assessment of connection integrity, allowing for the validation of series connected cells without exposing them to high voltages, thus reducing the time and expense of commissioning or maintaining voltage source converters.
Implementation Method 1
the electrical test stimulus has a voltage that is lower than the rated operating voltage of the voltage source converter but which is greater than a threshold voltage which is sufficient to forward bias freewheeling diodes of each of the first plurality of series connected to provide a conduction path through the plurality of series connected cells
Data Source
Figure 1~2b
Figure 3~4
AI summary
This application relates to methods and apparatus for testing the connection integrity of a plurality of series connected cells/sub-modules (103) of a voltage source converter (100), such as a valve (101 a,b) of a multi-module converter (MMC). Each cell comprises an energy storage element, for example a capacitor (105), and a plurality of switch elements (106), e.g. connected in a half-bridge arrangement. Each switch element has an associated freewheeling diode (107). The method comprises applying an electrical test stimulus (VSTIM+, VSTIM-) to the plurality of series connected cells, wherein the electrical test stimulus has a voltage that is lower than the rated operating voltage of the voltage source converter, but which is greater than a threshold voltage, which is sufficient to forward bias freewheeling diodes of each of the first plurality of sub-modules to provide a conduction path through the plurality of series connectedcells/ sub-modules. The electrical characteristics of the plurality of series connected cells to the electrical test stimulus is monitored and used to determined whether the cell/sub-moduless are connected correctly, for example by comparing to an expected characteristic.