Inertia and Droop Frequency Control Strategy of Doubly-Fed Induction Generator Based on Rotor Kinetic Energy and Supercapacitor

Abstract

The large-scale application of wind power eases the shortage of conventional energy, but it also brings great hidden danger to the stability and security of the power grid because wind power has no ability for frequency regulation. When doubly-fed induction generator (DFIG) based wind turbines use rotor kinetic energy to participate in frequency regulation, it can effectively respond to frequency fluctuation, but has the problems of secondary frequency drop and output power loss. Furthermore, it cannot provide long-term power support. To solve these problems, a coordinated frequency control strategy based on rotor kinetic energy and supercapacitor was proposed in this paper. In order to ensure the DFIG provides fast and long-term power support, a supercapacitor was used to realize the droop characteristic, and rotor kinetic energy was used to realize the inertia characteristic like synchronous generator (SG). Additionally, the supercapacitor is also controlled to compensate for the power dip of the DFIG when rotor kinetic energy exits inertia support to avoid secondary frequency drop. Additionally, a new tracking curve of DFIG rotor speed and output power was adopted to reduce the power loss during rotor speed recovery.

Inertial Response and Inertia Emulation in DFIG and PMSG Wind Turbines: Emulating Inertia from a Supercapacitor-based Energy Storage System

“…In case of implementing NIC or SIC strategies, when the WT exits frequency regulation and starts the recovery process, additional power falls directly to zero, and output active power decreases instantaneously. This power shortage leads to an undesired Secondary Frequency Drop (SFD) after the frequency Nadir [11]. With VIC, during the recovery process, the VIC curve coefficient is continuously changed till reaching kopt, due to the continuous variation of the frequency deviation.…”

“…In the second one, firstly employs SC energy and then rotational kinetic energy via a cascading control, the latter being the source of greater weight when generating the response. Techniques for emulating inertia in a DFIG by connecting a SC in the DC link via an additional DC/DC converter, that regulates the SC operation, have been also proposed [11], [16]. Unlike all the referenced similar works, with the strategy proposed in this contribution, IE is achieved exclusively from the stored energy in a SC directly connected to the DC link (without an additional DC/DC converter).…”

Cooperative Primary Frequency Regulation Strategy of Wind Storage System Based on Variable Inertia Coefficient

“…Therefore, the integrated control of additional energy storage and wind turbines has been widely studied. In [7], combined with the advantages of more cycles of supercapacitors and high power density, the supercapacitor is configured in parallel to the DC bus of the wind turbine to provide inertia support. But the required capacity is large, and the economic cost is high.…”

Inertia Control Strategy of DFIG-Based Wind Turbines Considering Low-Frequency Oscillation Suppression

“…The virtual inertia control (IC) technology is one of the hot research directions of WTs participating in system frequency regulation and providing inertia support. Referring to the external characteristics of synchronous generators, the virtual IC of DFIG-based WTs adds the control link related to system frequency in the control of the power converter to achieve inertia support for the system [4][5][6][7][8].…”