Voltage Sourced Converter Fault Current Phase-Angle Control
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Solution Overview
Problem
In high voltage direct current (HVDC) power transmission networks, the phase angle of fault current is uncontrolled and arbitrary when the magnitude of the output voltage is reduced to lower the fault current, leading to unreliable fault detection and protection in AC networks.
Innovation Solution
An electrical assembly with a controller that adjusts the voltage sourced converter to inject a target fault current with a controlled phase angle, using measurements before and after a fault to determine operating parameters, ensuring the phase angle matches the pre-fault steady-state conditions and adheres to rated current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage sourced converter reduces output voltage magnitude to limit fault current, then the fault current magnitude is controlled, but the phase angle becomes uncontrolled and arbitrary
Solution Approach 1:
The invention changes the control parameters from only voltage magnitude to both voltage magnitude and voltage phase angle. The controller is programmed to determine both the magnitude and phase angle of the reference voltage by comparing measured fault current phase angle with the expected phase angle from pre-fault conditions, thereby controlling both magnitude and phase of the injected fault current simultaneously
Solution Approach 2:
The invention implements feedback control by measuring the actual phase angle of the fault current, comparing it with the expected phase angle calculated from pre-fault voltage and current measurements, and adjusting the voltage phase angle of the converter accordingly to minimize the phase difference and achieve accurate phase control
2Device complexity
If existing technologies are used without phase control capability, then the control architecture remains simple, but fault detection and protection mechanisms become unreliable
Solution Approach 1:
The invention makes the voltage sourced converter multi-functional by enabling it to provide both fault current limitation and accurate phase angle control using the same converter hardware and control system. The controller is programmed to perform multiple functions: measuring pre-fault conditions, calculating reference values during fault, and controlling both magnitude and phase of the output voltage
Solution Approach 2:
The invention performs preliminary action by capturing and storing voltage and current measurements during the pre-fault steady state period. These pre-fault measurements are used to calculate the expected phase angle and magnitude, which serve as reference values for controlling the fault current injection during the fault condition
Data Source
AI summary
An electrical assembly including a voltage sourced converter for connection to an AC network, a controller programmed so that, responsive to detection of a fault in the AC network, the controller obtains a first set of voltage and current measurements taken at an interface connection point, change operation of the voltage sourced converter to inject a modified fault current, and then obtain a second set of voltage and current measurements, determine operating parameters of the voltage sourced converter for injecting a target fault current having a target phase angle that is substantially the same as a phase angle of a reference fault current that would have resulted from operation of the voltage sourced converter in accordance with pre-fault steady-state voltage phase and magnitude values, and operate the voltage sourced converter in accordance with the determined operating parameters so as to inject the target fault current at the target phase angle.