Abstract

In order to solve the problems brought upon by off-shore wind-power plants, it is important to improve fault ride-through capability when an on-shore fault occurs in order to prevent DC overvoltage. In this paper, a coordinated control strategy is implemented for a doubly-fed induction generator (DFIG)-based off-shore wind farm, which connects to on-shore land by a modular multilevel converter (MMC)-based high voltage direct current (HVDC) transmission system during an on-shore fault. The proposed control strategy adjusts the DC voltage of the off-shore converter to ride through fault condition, simultaneously varying off-shore AC frequency. The grid-side converter detects the frequency difference, and the rotor-side converter curtails the output power of the DFIG. The surplus energy will be accumulated at the rotor by accelerating the rotor speed and DC link by rising DC voltage. By the time the fault ends, energy stored in the rotor and energy stored in the DC capacitor will be released to the on-shore side to restore the normal transmission state. Based on the control strategy, the off-shore wind farm will ride through an on-shore fault with minimum rotor stress. To verify the validity of the proposed control strategy, a DFIG-based wind farm connecting to the on-shore side by an MMC HVDC system is simulated by PSCAD with an on-shore Point of Common Coupling side fault scenario.

Highlights

  • In the proliferation of renewable energy, worldwide total wind-power installations in 2017 were about 52 GW, bringing the global total to nearly 540 GW

  • The objective of the proposed fault ride-through (FRT) strategy is to ride through an on-shore fault by rotor and minimize the burden on the rotor by DC voltage control of the DC capacitor

  • The grid side converter (GSC) of doubly-fed induction generator (DFIG) picks up the changed offand the rotor side converter (RSC) current reference order changes for deloading

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Summary

Introduction

In the proliferation of renewable energy, worldwide total wind-power installations in 2017 were about 52 GW, bringing the global total to nearly 540 GW. A DC chopper can expend excessive energy by using a chopper resistor implemented in a DC link [10] They are not necessary if the kinetic energy controls studied by Yang et al [11] are implemented. Yang et al [11], if surplus energy was stored in a rotor mass, even in the absence of the crowbar or DC chopper, a wind farm could ride through on-shore faults. The proposed coordinated control strategy stores excessive generated power in two energy storage mediums when an on-shore fault occurs in both a VSC converter DC link and a wind turbine rotor, while signaling control references in frequency droop. DC chopper, crowbar-free operation by energy control in a DC link and a wind turbine.

Control and Modeling of the OSWF System
Off-shore
MMC HVDC Outer Loop and Energy Control
DFIG Power and Current Control
Advanced FRT Strategy
Unbalanced Power Calculation for DC Voltage Control
Voltage-Frequency Droop Control
Deloading by Rotor Current Droop
Simulation
Study Cases
Case A
Case B
Case C
Simulation Result
Scenario A
Scenario B
10. Simulation
11. Simulation
Scenario C
15. Simulation
17. Simulation
18. Simulation
Conclusion
Findings
Conclusions
Full Text
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