A Comprehensive VSG-Based Onshore FRT Control Strategy for OWFs With VSC-MT-HVDC Transmission

Abstract

This paper proposes a communication-free control strategy at the offshore wind farm (OWF) level to enhance onshore fault ride-through (FRT) grid code compliance of the voltage source converter (VSC)-based multi-terminal high voltage direct current (MT-HVDC) grid. In this proposal, the emerging virtual synchronous generator (VSG) concept is employed to equip the Type 4 wind turbine generator (WTG)s with inherent grid forming ability. Accordingly, it is proposed to switch the offshore HVDC converters control mode from grid forming to grid feeding during onshore FRT period to realize direct wind power in-feed reduction as a function of the severity of MT-HVDC grid's overvoltage. The related dynamics are mainly characterized by the high-speed current control loop, so improved OWF response is achieved during onshore FRT period as conventional voltage/frequency modulation strategies are not employed. New analysis/amendments are also proposed to study and improve the transient active power reduction sharing between the WTGs in first few power cycles under wind wake effect. Finally, with the objective of a smooth transfer of HVDC converters and WTGs in several proposed operation states, a set of state machines are proposed considering whole WTG's dynamics. Comprehensive time-domain simulations are performed with averaged electromagnetic transient models to demonstrate the improved onshore FRT behavior in terms of minimizing the electrical stress at both MT-HVDC grid and OWF levels. INDEX TERMS Fault-ride-through, multi-terminal HVDC grid, offshore wind farm, power reduction method, type 4 WTG, virtual synchronous generator.

Power system stability improvement considering drive train oscillations of virtual synchronous generator‐regulated type‐4 wind turbines

“…Recent grid codes require wind turbine generators (WTGs) to provide inertial frequency response to support the stability of the power system frequency; hence, novel frequency regulation schemes have been designed [1][2][3][4]. Among the schemes, the virtual synchronous generator (VSG) concept is more feasible as it can properly connect to a weak AC grid, has grid forming ability, and provides natural frequency support and harmonious grid integration [5].…”

“…75 MW wind farm connected to power system: Load increase In this section, a detailed 75 MW wind farm comprised of 15 numbers of 5 MW WTGs is connected to a modified P.M. Anderson power system, see Figure 19. Wake effect and internal cablings and transformers of the wind farm are considered as per modeling and parameters reported in [5,38]. The power system is downscaled, modelled, and parameterized following the guidelines of [26,35] to reach a 50% penetration factor for the capacity of the installed wind farm.…”

Adaptive Virtual Capacitor Control for MTDC System With Deloaded Wind Power Plants

“…1. This topology is derived from the Zhangbei ±500 kV four-terminal HVDC power grid demonstration project (China) [3].…”

“…Notably, based on the droop controller expressed in (1) and (3), an increase in the active power decreases the DC voltage. The reduced DC voltage influences the active power distributed among the GSVSC stations.…”

“…As voltage source converters (VSCs)based (or modular multilevel converters) high-voltage DC (MTDC) transmission is economical and flexible, they are used for large-scale wind farm integration and energy transmission. Furthermore, multi-terminal high-voltage DC (MTDC) transmission is a suitable method for interconnecting multi-asynchronous power grids and wind farms [2], [3], and a four-terminal ±500 kV high-voltage DC (HVDC) system is under development to interconnect largescale onshore wind farms in the Zhangbei area [4].…”