Control Strategy for Offshore Wind Farms with DC Collection System Based on Series-Connected Diode Rectifier
Abstract
:1. Introduction
2. System Configuration and Coupling Mechanism
2.1. Topology
2.2. Coupling Mechanism of SCUs
3. System Control Strategy
3.1. Characteristics of DR
3.2. Control Strategy of Receiving End Converter
3.3. Control Strategy of Wind Turbine Converters
4. Fault Analysis and Ride-through Strategy
4.1. Receiving End AC Fault
4.2. DC Grounding Fault
4.3. Open DC Line Fault
5. Simulation
5.1. Start-Up
5.2. Wind Speed Growth Scenario
5.3. AC Fault of Receiving End
5.4. DC Grounding Fault U
6. Conclusions
- (1)
- With the coupling mechanism analysis, it is pointed out that the CDC mode is suitable for SCUs to eliminate energy curtailment without an auxiliary control strategy or equipment during unequal wind speed. Characteristics of DR are analyzed, and the linear relationship among active power, AC voltage of the MF transformer, output DC voltage, and output DC current of SCUs is researched first. Combining DR characteristics and CDC mode, a coordinate control strategy for the DC wind farm is proposed, where the receiving end converter operates as a DC current source with the DC current controller and the offshore wind turbine operates as a DC voltage source with a triple loop mediate AC voltage control strategy. Under the coordinate control strategy, the SCUs can track its MPPT without energy curtailment or overvoltage issues.
- (2)
- The fault isolation problems caused by SCUs are analyzed. Benefiting from the unidirectional conduction characteristics of DR, the healthy SCUs can keep operating without special equipment after a grounding DC fault occurs and the AC current of fault ones is smaller than 1.2 pu without destruction of SCUs. Considering the power loss and economy, reconfiguration switches are proposed, and only 40% active power is lost before the broken DC line is repaired. In addition, the characteristics of an AC fault located at the onshore grid are analyzed. A detecting and protection strategy is proposed for onshore AC fault without communication to protect the MMC from destruction quickly with sub-module voltage smaller than 1.12 pu.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Topology One | Topology Two | Topology Three | |
---|---|---|---|
Length of DC cable | 14d | 10d | 10d |
Number of switches | 3 | 2 | 5 |
Economy (k/EUR) | 2084 | 2400 | 3720 |
Estimated power loss | 3Prate | 3Prate | 1Prate |
Onshore MMC | Rated power | 160 MW |
DC voltage | 320 kV | |
DC current | 0.5 kA | |
Onshore grid voltage | 400 kV | |
Offshore Wind Farm | Number of SCUs in a string | 8 |
Rated power of PMSG | 20 MW | |
Rated frequency | 12 Hz | |
Rated voltage | 3.6 kV | |
The output voltage of the AC/DC rectifier | 6 kV | |
The output voltage of DR converter | 40 kV | |
Output DC current of DR converter | 0.5 kA | |
Isolation transformer of SCUs | 250 Hz, Y/∆, 3.3/66, leakage inductance, 1% |
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Xie, L.; Cheng, F.; Wu, J. Control Strategy for Offshore Wind Farms with DC Collection System Based on Series-Connected Diode Rectifier. Sustainability 2022, 14, 7860. https://doi.org/10.3390/su14137860
Xie L, Cheng F, Wu J. Control Strategy for Offshore Wind Farms with DC Collection System Based on Series-Connected Diode Rectifier. Sustainability. 2022; 14(13):7860. https://doi.org/10.3390/su14137860
Chicago/Turabian StyleXie, Lijun, Fan Cheng, and Jing Wu. 2022. "Control Strategy for Offshore Wind Farms with DC Collection System Based on Series-Connected Diode Rectifier" Sustainability 14, no. 13: 7860. https://doi.org/10.3390/su14137860