Virtual synchronous control of grid-connected DFIG-based wind turbines

Abstract

This paper proposes a virtual synchronous control strategy for Doubly-Fed Induction Generator (DFIG)-based wind turbines. On the basis of the proposed excitation control model orientated by rotor flux, and the P-f, Q-V droop control models which emulate the governor and exciter of synchronous machine, this paper established the basic virtual synchronous control structure for DFIG. This control strategy can provide DFIGbased wind turbines with intrinsic regulation ability of frequency and voltage without using the phase-locked loop (PLL) of the grid. Considering the power limitation under certain wind speed, the proposed adaptive droop control method realized the maximum power point tracking (MPPT) of wind turbines in steady state. Simulation results demonstrate the feasibility and effectiveness of the presented virtual synchronous control for grid-connected DFIG. This control strategy can not only provide the possibility of unifying the grid-connected wind turbines as the standard synchronous power, but also decrease the negative effect on the grid frequency and voltage with high penetration of wind energy.

Injecting positive‐sequence current virtual synchronous generator control under unbalanced grid

“…where the DC part is the positive-sequence component, the doublefrequency part is the negative-sequence components. From (12), the double-frequency components are removed by the following trap filter…”

“…The traditional synchronous machine-based generation systems use inertia stored in its rotating mass. With the idea of emulating virtual inertia to the inverter-interfaced generation systems, the concept of Virtual Synchronous Generator (VSG) has been developed during the last decade [4][5][6][7][8][9][10][11][12][13][14]. Beside VSG proposed in [4][5][6][7][8][9][10][11][12][13][14], several other control methods, including VISMA [7], Synchronverters [8], and VSG [9] have been proposed to emulate virtual inertia.…”

“…One approach was to introduce the inertial response function based on the traditional vector control [5][6][7][8][9], while the grid side converter (GSC) output was still equivalent to a current source [10]. Another approach was to control the GSC as a voltage source by imitating the synchronous generator (SG) swing equation [4,11,12]. Since SG is naturally friendly to the power system and the typical SG is a voltage source [13], the voltage-source VSG control method has been adopted for DGs to emulate the rotor inertia and droop characteristics of synchronous generators [4][5][6][7], especially in a very week AC system condition [12].…”

Inertial response characteristics analysis and optimisation of PMSG‐based VSG‐controlled WECS

“…For the inertial response operation, the WT KE releases and the WT rotor speed decreases. According to (8), the VSG reference value decreases. The equivalent inertia constants are expressed as follows:…”

“…VSG schemes for different wind turbine (WT) types have been proposed in [7][8][9] to realise the basic frequency support function in the WECS. These studies missed exploring the influence of WECS on the VSG characteristics.…”