Wind Power Inverter Control Using Negative-Sequence Current Balancing
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Solution Overview
Problem
Wind power installations face challenges in balancing asymmetrical network voltages, which can occur due to long overhead lines, as symmetrical feed-in methods are ineffective in eliminating such asymmetries in three-phase electrical networks.
Innovation Solution
A method involving the measurement of phase voltages, calculation of symmetrical negative-sequence voltage systems, and predefined setpoints for negative-sequence currents is implemented to balance network voltages, using an inverter to feed an asymmetrical three-phase AC current into the network, thereby counteracting asymmetrical voltages and improving network symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a symmetrical feed-in method is used in a wind power installation, then the control system operates simply and the current feed-in is straightforward, but the asymmetrical network voltage cannot be eliminated and network symmetry deteriorates
Solution Approach 1:
The patent applies asymmetry by intentionally generating an asymmetrical current component (negative sequence current) to counteract the asymmetrical voltage. The control system calculates negative sequence voltage components and generates corresponding negative sequence current components that are asymmetrical in nature, which then balance the overall network voltage when injected into the grid.
Solution Approach 2:
The control system performs preliminary anti-action by calculating the negative sequence voltage components from the measured asymmetrical voltage and pre-defining setpoints for negative sequence current before the asymmetry causes problems. This proactive approach prevents voltage instability by counteracting the asymmetry before it propagates through the network.
2Stability of the object's composition
If an asymmetrical current feed-in is implemented to balance network voltages, then network voltage symmetry is improved, but the current feed-in becomes more complex and requires additional control mechanisms
Solution Approach 1:
The patent implements feedback by continuously measuring the three-phase network voltage, calculating the negative sequence voltage components, and using these calculations to dynamically adjust the negative sequence current setpoints. The control system monitors the asymmetry level and adjusts the compensating current in real-time, creating a closed-loop feedback mechanism that manages complexity through intelligent control.
Solution Approach 2:
The control system changes parameters by transforming the measured voltage parameters into negative sequence voltage components and then into negative sequence current setpoints. This parameter transformation approach systematically manages the complexity by using mathematical relationships to convert the control problem into a solvable form with defined setpoints for the inverter.
3Stability of the object's composition
If negative sequence current components are injected to counteract asymmetrical voltage, then voltage balancing is achieved, but additional current components increase the overall current complexity
Solution Approach 1:
The patent applies segmentation by separating the current feed-in into two independent components: a positive sequence current component for normal power transmission and a negative sequence current component for voltage balancing. This segmentation allows each current component to be controlled independently with its own setpoints, managing the complexity by dividing the overall current system into manageable segments that can be optimized separately.
Data Source
AI summary
Provided is a method for controlling a wind power installation and/or a wind farm having at least one wind power installation, particularly in the case of asymmetrical network voltages, comprising: measuring a first voltage of a first phase, a second voltage of a second phase and a third voltage of a third phase of a three-phase electrical system, calculating a symmetrical negative-sequence voltage system from the measured voltages including a first negative-sequence voltage, a second negative-sequence voltage and a third negative-sequence voltage, predefining setpoints for a negative-sequence current system depending on the calculated, symmetrical negative-sequence voltage system including a first negative-sequence current component, a second negative-sequence current component and a third negative-sequence current component, wherein the setpoints are defined such that a balancing of the measured voltages is achieved, feeding an asymmetrical three-phase AC current into a wind farm network or an electrical supply network depending on the predefined setpoints.