Power Converter Current Limiting During Asymmetric AC Faults
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Solution Overview
Problem
Existing power converter control methods in HVDC systems fail to effectively manage positive and negative phase sequence currents during AC system faults, leading to potential overloading and incorrect operation of protection systems, as they either ignore voltage symmetry restoration or introduce delays in current limiting responses.
Innovation Solution
A method that dynamically regulates both positive and negative phase sequence currents by setting amplitude limits, allowing the negative phase sequence current to flow naturally while ensuring the total AC current amplitude does not exceed the converter's limits, thereby maintaining voltage balance and preventing overloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the converter maintains purely positive phase sequence AC voltage profile during asymmetric faults, then the converter operates in standard SGFM control mode, but large negative and positive phase sequence current flows occur that can overload semiconductor devices
Solution Approach 1:
The control method dynamically adjusts the converter's voltage profile by introducing a negative phase sequence voltage component during asymmetric faults. This dynamic modification allows the converter to deviate from standard SGFM operation when needed, controlling current flow to prevent semiconductor device overload while maintaining stability during fault conditions
Solution Approach 2:
The invention changes the voltage profile parameters by adding a negative phase sequence voltage component (Vneg) during asymmetric faults. This parameter change modifies the current characteristics, ensuring that the resultant current amplitude remains within safe limits for semiconductor devices while still providing fault response
2Reliability
If the converter provides transient current to counteract voltage and frequency changes during AC system perturbations, then system stability is strengthened, but current limits may be exceeded
Solution Approach 1:
The control method employs feedback mechanisms that continuously monitor system conditions during AC perturbations. When voltage or frequency changes are detected, the controller adjusts the converter output to provide stabilizing transient current while simultaneously ensuring current limits are not exceeded, balancing system support with device protection
Solution Approach 2:
The converter dynamically adjusts its output characteristics during AC system perturbations, providing transient current support when needed while modulating the amplitude to remain within safe operating limits. This dynamic response allows the converter to strengthen system stability without causing current limit violations
3Power
If the converter allows large current exchange during insulation faults to counteract voltage deviation, then voltage support is provided, but semiconductor devices may be overloaded
Solution Approach 1:
During insulation faults, the converter changes its voltage profile parameters by introducing negative phase sequence voltage components. This parameter modification enables the converter to provide voltage support during faults while controlling the amplitude and characteristics of the current exchange to prevent semiconductor device overload
Solution Approach 2:
The control method dynamically adjusts the converter's response to insulation faults by modulating the voltage profile and current characteristics in real-time. This dynamic control allows the converter to provide necessary voltage support while simultaneously protecting semiconductor devices from overload conditions
Data Source
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AI summary
A computer-implemented method (400) of controlling a power converter in a power transmission network. A first amplitude limit value for a first AC current output from an AC side of the power converter is received (410). A second amplitude limit value for a negative phase sequence component of the first AC current is received (420). The negative phase sequence component is measured (430) to provide a measured second amplitude. The negative phase sequence component is regulated (440) to flow with a regulated second amplitude that is the lesser of the measured second amplitude and second amplitude limit value. A positive phase sequence component of the first AC current is regulated (450) to flow with an amplitude not exceeding a regulated third amplitude. The regulated third amplitude is set using a function of the first amplitude limit value and the regulated second amplitude, such that the regulated second amplitude and the regulated third amplitude, when combined, provide a first amplitude for the first AC current that is substantially equal to the first amplitude limit value.