Star Point Reactor Suppression Filter for HVDC Harmonic Mitigation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing converter arrangements in high-voltage direct current (HVDC) installations experience unwanted currents due to harmonic voltage components, which can lead to noise emission and transformer saturation, particularly when there is no fixed ground connection.
Innovation Solution
A suppression filter is introduced between the neutral point of the star point reactor and ground, comprising a parallel resonant circuit with capacitance and inductance, designed to resonate at the frequency of the harmonic to be suppressed, thereby filtering out unwanted harmonic currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a star point reactor is used to symmetrize voltages and provide a ground reference, then direct current symmetry is improved, but harmonic currents from the alternating voltage grid are not suppressed leading to transformer saturation and noise emission
Solution Approach 1:
A suppression filter is introduced as an intermediary component between the star point reactor and ground connection. This filter acts as a mediator that selectively blocks harmonic currents while allowing the star point reactor to maintain its voltage symmetrization function. The filter comprises reactive components (inductors and capacitors) arranged to create high impedance at harmonic frequencies, thereby preventing harmonic currents from flowing into the transformer.
Solution Approach 2:
The suppression filter is designed with specific impedance characteristics that change with frequency. At fundamental frequency (50/60 Hz), the filter presents low impedance to allow normal operation, while at harmonic frequencies (150 Hz, 250 Hz, etc.), the filter's impedance increases significantly to block harmonic currents. This parameter change with frequency enables selective suppression of harmonics without affecting the star point reactor's voltage symmetrization capability.
2Adaptability or versatility
If the converter operates without a fixed ground connection to maintain voltage flexibility, then adaptability is improved, but contamination layer currents create resultant direct current to ground causing transformer issues
Solution Approach 1:
The star point reactor serves as an intermediary that creates a virtual ground reference without providing a fixed physical ground connection. This allows the converter to maintain voltage flexibility while the reactor's high impedance to alternating current prevents contamination layer currents from creating significant resultant direct current. The reactor mediates between the need for ground reference and the need for voltage adaptability.
3Object-generated harmful factors
If the star point reactor provides high impedance to alternating current to prevent harmonic flow, then harmonic suppression is improved, but direct current flow capability is reduced
Solution Approach 1:
The suppression filter utilizes frequency-dependent impedance characteristics where the reactive components (inductors and capacitors) are configured to present high impedance at harmonic frequencies while maintaining low impedance at direct current and fundamental frequency. This is achieved by tuning the filter's resonant frequency to match or be near the fundamental frequency, ensuring that the filter does not impede direct current flow or fundamental frequency operation while effectively blocking harmonic currents.
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 suppression filter effectively minimizes unwanted currents in the alternating voltage grid, reducing noise emission and transformer saturation by actively regulating the DC flux in the iron core, while maintaining low impedance for direct currents and high suppression capacity for specific harmonics.
Implementation Method 1
A suppression filter is introduced between the neutral point of the star point reactor and ground, comprising a parallel resonant circuit with capacitance and inductance, designed to resonate at the frequency of the harmonic to be suppressed
Implementation Method 2
the star point reactor is so designed that it represents a current path with a high impedance to the ground potential for alternating current with a fundamental oscillation frequency of the alternating voltage grid. At the same time the star point reactor provides a current path with a low impedance to the ground potential for a direct current
Data Source
AI summary
A converter arrangement includes a converter which can be switched between an AC voltage supply system and a DC voltage circuit and which has converter valves that extend between AC voltage connections and DC voltage connections. Each converter valve has a series connection of bipolar submodules that include power semiconductor devices. The converter arrangement further includes a star point reactor which is located on the AC voltage side of the converter and which has impedance coils that are interconnected to form a grounded neutral point. A suppression filter is connected between the neutral point and a ground connection. The suppression filter is configured to suppress a harmonic of an alternating voltage in the AC voltage supply system.