Virtual synchronous machine control for doubly-fed induction machine based wind energy conversion systems [long version]

Abstract

<p>Facing the climate crisis, more and more renewable inverter-based resources (IBRs), such as wind energy conversion systems (WSs), replace grid-connected synchronous machines (SMs). SMs inherently provide balanced and sinusoidal grid voltages but also power system inertia, whereas standard grid-following (GFL) control of IBRs leads to decreasing power system inertia. This paper proposes grid-forming (GFM) control for doubly-fed induction machine (DFIM) based wind energy conversion systems (WSs) based on the virtual synchronous machine (VSM) concept with the following extensions: (i) Maximum power power tracking (MPPT) compensation for accurate inertia emulation, (ii) feedforward torque control (FTC) for fast power reference tracking, (iii) de-rated operation or reference power point tracking (RPPT) to provide additional power reserves, (iv) dynamic droop power saturation control to avoid excessive power overshoots (as available power reserves are taken into account), and (v) grid voltage control utilizing reactive power from both, DFIM stator and rotor-side back-to-back inverter. The modeling and control of the DFIM-based WSs is shown in detail and the grid model is based on the IEEE 9-bus test system. Comprehensive simulation results show that the GFM control enables unlimited power penetration of IBRs and that the grid frequency dynamics of VSM-based power systems can be interpreted and handled analogously to SM-based power systems. During normal operation, compared to existing VSM control without FTC, the proposed VSM control with FTC increases the wind energy yield, i. e. typical MPPT or RPPT performance is achieved, similar to the performance of GFL control. For high power penetration of IBRs, the proposed VSM control enables stable operation due to its inertia emulation or GFM capability, whereas GFL control tends to instability. During faults and system splits, the VSM provides higher power system damping than a real SM due to (i) virtual/internal damping that can be adapted by software (hence almost independently from the hardware, whereas the response of SM damper windings depends on the physical machine design and cannot be altered during operation), and due to (ii) faster droop control which adapts the virtual turbine power without the mechanical delays that dominate real turbine dynamics.</p>

Virtual Synchronous Machine Control for Doubly Fed Induction Machine-Based Wind Energy Conversion Systems

“…The results for VSM control without FTC, GFL control and a comparison to VSM control with FTC (similar to Fig. 11) are shown in [2, but not here due qualitatively similar conclusions as in the previous scenario which are (cf. Sec.…”

“…Reference [14] takes the pitch actuation delay into account for modeling but also solely uses PI-control. In contrast to those references, the proposed feedback improves the control performance by requiring less (transient) pitch actuation, see [2,Fig. 15].…”

“…. , a 3 , is Hurwitz (proven for the considered WS parameters from [2] using Matlab) if the proportional and integral gains are chosen as follows…”

“…The simulation results for VSM control without FTC and for GFL control are shown in [2, but not here due to nearly identical power system dynamics. However, Fig.…”

“…This paper summarizes the long version [2] and extends the VSM control with FTC for DFIM-based WSs in [28] by the following contributions: (i) RPPT based on the maximum rotation strategy [23] to maximize the kinetic energy reserves, (ii) dynamic droop power saturation to mitigate power overloading, (iii) improved MPPT compensation for accurate inertia emulation during severe RoCoF events, (v) WS modeling, including not only the DFIM with RSI but also the RSI power supply via the dc-link, the GSI and the LC(L)-filter, (v) WS control, including not only the DFIM power control but also the dc-link voltage and grid voltage control, (vi) simulations, including the grid connection to take interactions with the transmission system or other generation units into account, which may lead to power oscillations. In this regard, it is important to note that both, the DFIM stator and the GSI, may provide reactive power for grid voltage support.…”