Combining virtual synchronous machine and feedforward torque control for doubly-fed induction machine based wind energy conversion systems

Abstract

<p>With the decreasing number of directly grid-connected synchronous machines (SMs) forming the grid voltage, the risk of power system instability increases, especially regarding the grid frequency due to the decreasing power system inertia. Grid-forming (GFM) control of inverter based resources (IBRs) with inertia emulation capability is required to face these challenges and to guarantee reliable operation of the future power system. This paper proposes virtual synchronous machine (VSM) control for doubly-fed induction machine (DFIM) based wind energy conversion systems (WECS) that (i) enables feedforward torque control (FTC) and thus, does not degrade the WECS performance during normal operation, (ii) adapts the VSM damping based on the DFIM operating point, and (iii) protects the VSM against overloading to avoid loss of synchronism.</p>

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

“…Utilizing ( 13), power factor κ p := 2 3κ 2 (depending on the Clarke transform scaling factor κ; e.g. κ = 2/3 for amplitude-correct scaling), and load angle δ, the DFIM torque simplifies to [27]…”

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

“…Despite the research trend towards VSM control for inverters [11] or for type 4 WSs, based on full-scale backto-back converter configurations [17,21,22], the public research on VSM control for DFIMs or type 3 WSs is limited. There exist a few VSM control methods for DFIMs with grid synchronization loops [15,19,[23][24][25][26][27][28], but the electro-magnetic DFIM control loops in these papers differ significantly from those proposed in this paper. Usually, the following electro-magnetic DFIM control loops are employed: (i) no inner current or magnetic flux control loop [23][24][25], i. e. applying the VSM voltage amplitude and angle directly to the RSI, (ii) inner current control loop [19,26,27], (iii) inner magnetic rotor flux control loop [15], (iv) outer magnetic stator flux and inner stator current control loop [28].…”

“…There exist a few VSM control methods for DFIMs with grid synchronization loops [15,19,[23][24][25][26][27][28], but the electro-magnetic DFIM control loops in these papers differ significantly from those proposed in this paper. Usually, the following electro-magnetic DFIM control loops are employed: (i) no inner current or magnetic flux control loop [23][24][25], i. e. applying the VSM voltage amplitude and angle directly to the RSI, (ii) inner current control loop [19,26,27], (iii) inner magnetic rotor flux control loop [15], (iv) outer magnetic stator flux and inner stator current control loop [28]. For instance, the inner magnetic rotor flux control in [15] sets the active power by changing the angle between rotor and stator magnetic flux linkages and sets the reactive power by changing the magnetic rotor flux linkage amplitude, while this paper uses the inner rotor current control with the reference vector angle depending on the VSM rotor position based on [27].…”

“…Thus, a compromise between inertial support and MPPT performance has to be found. Lately, [27] proposed a feedforward torque control (FTC) for fast MPPT in combination with a freely spinning VSM, which achieves decoupling of the inertial response to RoCoF events and the MPPT during normal operation. However, [27] only considers ideal RoCoF events, i. e. neglects the interaction with the grid, whereas [11] considers the interactions of (V)SMs but only for VSM-controlled inverters, i. e. not for VSM-controlled DFIMs.…”

“…Lately, [27] proposed a feedforward torque control (FTC) for fast MPPT in combination with a freely spinning VSM, which achieves decoupling of the inertial response to RoCoF events and the MPPT during normal operation. However, [27] only considers ideal RoCoF events, i. e. neglects the interaction with the grid, whereas [11] considers the interactions of (V)SMs but only for VSM-controlled inverters, i. e. not for VSM-controlled DFIMs. Moreover, [27] only considers MPPT, but also RPPT or de-reated operation is desirable to provide additional power reserves for inertia emulation or droop control [22].…”