Chain-Link Converter De-Energizing via Charging Resistor Switching
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Solution Overview
Problem
The existing methods for de-energizing STATCOM converters, such as those based on chain-link topology, are time-consuming due to the slow discharge of DC capacitors, limiting the availability of the converter during maintenance or repairs.
Innovation Solution
A method involving the opening of AC circuit breakers and charging resistor switches to circulate current through the phase legs and charging resistors, accelerating the discharge of DC capacitors, and optionally using a discharge circuit and tuned zero sequence filters to further facilitate the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC capacitors are discharged using leakage current and standard circuitry, then the converter can be shut down, but the discharge time is long and the shutting down procedure is time-consuming
Solution Approach 1:
The method applies preliminary action by pre-configuring the charging resistors and switches to enable rapid discharge. Before the actual shutdown, the system prepares the discharge path by opening the charging resistor switches and connecting the charging resistors across the DC capacitors, so that when discharge is needed, the path is already ready and discharge can begin immediately at maximum rate.
Solution Approach 2:
The invention changes the discharge parameters by switching from natural leakage discharge to forced discharge through charging resistors. The charging resistors provide a controlled low-impedance path that increases the discharge current magnitude, thereby reducing the discharge time constant and accelerating the voltage decay rate of the DC capacitors.
2Ease of repair
If the STATCOM converter is shut down for repair or maintenance, then components can be serviced, but the availability of the converter is limited during the long discharge time
Solution Approach 1:
The charging resistor switches change the electrical parameters of the discharge circuit by providing a low-impedance discharge path through the charging resistors. This parameter change accelerates the voltage decay, reducing the time the converter remains in a non-safe state and thereby minimizing downtime for maintenance activities.
Solution Approach 2:
The system performs self-service discharge by using its own charging resistor circuitry, which is already part of the converter structure, to discharge the DC capacitors rapidly. This eliminates the need for external discharge equipment and enables the converter to service itself by preparing the discharge path through controlled switching of existing components.
3Loss of time
If charging resistors are used to accelerate discharge, then the discharge time is reduced, but additional circuitry and control steps are required
Solution Approach 1:
The charging resistors and their associated switches serve multiple functions: they provide DC capacitor discharge paths, enable rapid energy dissipation during shutdown, and can be controlled through existing converter control circuitry. This multi-functionality reduces the need for dedicated discharge circuitry and minimizes additional complexity while achieving fast discharge.
Solution Approach 2:
The existing charging resistor circuitry, which is already part of the converter design for capacitor charging, is repurposed to provide discharge functionality. By opening the charging resistor switches and connecting the resistors across the capacitors, the system uses its own existing components for discharge, eliminating the need for separate discharge resistors and control circuitry.
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 approach significantly reduces the time required to de-energize the converter, making it faster and more efficient, thereby reducing downtime for maintenance and repair.
Implementation Method 1
circulating a current within the chain-link converter through the charging resistors and each phase leg, whereby the DC capacitor are discharged
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a method 30 for de-energizing a chain-link converter 1 comprising one or more phase legs L1, L2, L3, each phase leg L1, L2, L3 comprising a number of series-connected converter cells 21, 22,..., 2n. The phase legs L1, L2, L3 are connected to a respective charging resistor RL1, RL2, RL3. The method 30 comprises the steps of: opening 31 AC circuit breakers 4L1, 4L2, 4L3 arranged between a power grid 3 and the chain-link converter 1, opening 32 charging resistors switches SL1, SL2, SL3 arranged in parallel with a respective one of charging resistors RL1, RL2, RL3, and circulating 33 a current within the chain-link converter 1 through the charging resistors RL1, RL2, RL3 and each phase leg L1, L2, L3, whereby the DC capacitor 71, 72,..., 7n are discharged. The invention also relates to a controller, computer program and computer program products.