Grid Forming Stator Flux Control of Doubly-Fed Induction Generator

Abstract

The doubly fed induction generator is widely used in wind power applications. For stand-alone operation of this machine, the control of the stator flux with fixed voltage and frequency has been proposed. This paper extends the stator flux control of the doubly fed induction machine by droop mechanisms, which vary the setpoint of flux magnitude and frequency depending on active and reactive power. This gives the doubly fed induction generator system unknown grid supporting and grid forming performance. The validation of the proposed control scheme has been conducted on a 10kVA testbed system. The closed-loop behavior of the system has been proven to enable grid-tied and islanded operation with the same control structure. The system response to load changes and islanding events show no disruptive transients in both conditions.

Control Systems for Low-Inertia Power Grids: A Survey on Virtual Power Plants

“…A comprehensive review of PC techniques for islanded MGs is presented in [270]. In [271], it was shown that wind energy plants equipped with doubly fed induction generators can achieve excellent grid forming and grid supporting capabilities using stator flux control with droops for frequency and magnitude. The idea of adaptive dynamic participation factors was presented in [272] to design grid-forming controller for dynamic virtual power plants.…”

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

“…with modified normalized DFIM angular velocity Ω m,H0 defined in the following, see (18). Assuming Ω m,H0 = Ω m in (17), M m,ref decreases if the rotor decelerates, counteracting the desired inertial response [6,24]. A simple MPPT compensation is to sample and hold the MPPT input when detecting active inertia emulation, i. e.…”

“…However, this control is not based on the VSM concept and it is not stated, how to adapt the gains for different DFIM operating points. Moreover, [17] does not achieve decoupling of the responses to grid frequency changes and to power reference changes, as proposed in this paper.…”

“…This is a common configurations used worldwide [10]. Despite similar VSM grid synchronization loops, the electro-magnetic DFIM control loops differ: There exist VSM controls with (i) no inner current or magnetic flux control loop [11][12][13], i. e. applying the VSM voltage amplitude and angle directly to the RSC, (ii) inner current control loop [14,15], (iii) inner magnetic rotor flux control loop [16], (iv) outer magnetic stator flux and inner stator current control loop [17]. The inner magnetic rotor flux control in [16] 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 rotor current control with the reference vector angle depending on the VSM rotor position, motivated by the fact that the excitation or rotor current vector of a SM is fixed to its rotor position.…”

“…Moreover, [6] does not consider type 3 WECS. In [17], a feedforward path is added to the active power droop control to decrease the response time. The control error is multiplied by a gain and the resulting feedforward angle is added to the Park angle, used for magnetic stator flux linkage control.…”