scholarly journals Fast Frequency Response of a Doubly-Fed Induction Generator for System Inertia Support

2020 ◽  
Vol 10 (8) ◽  
pp. 2934
Author(s):  
Dejian Yang ◽  
Hong-Chao Gao ◽  
Lei Zhang ◽  
Jingjiao Li ◽  
Xinsong Zhang ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Recovery Process ◽  
Test Results ◽  
Rotor Speed ◽  
Short Term ◽  
Induction Generators ◽  
Doubly Fed Induction Generators ◽  
Frequency Drop ◽  
Doubly Fed ◽  
System Inertia

Converter-interfaced doubly-fed induction generators (DFIGs) can provide short-term frequency support (STFS) capability by releasing rotating kinetic energy. After arresting the frequency decrease, the rotor speed should return to its initial operating condition. During the rotor speed recovery process, special attention should paid to the performance of the rotor speed restoration duration and size of the second frequency drop (SFD). This paper suggests an enhanced STFS method of DFIGs to preserve better performance of the frequency nadir with less released rotating kinetic energy and accelerate the rotor speed restoration. To this end, a rotor speed-varying incremental power is proposed and is added to the maximum power tracking (MPT) operation reference during STFS, thereby releasing less rotating kinetic energy from DFIGs; afterward, the power reference smoothly decreases to the reference for MPT operation during the preset period. Test results clearly demonstrate that since even less rotating kinetic energy is utilized, the proposed method can preserve better performance of heightening the frequency nadir; furthermore, the proposed method accelerates the rotor speed restoration when the proposed strategy produces the same SFD as the conventional method, thereby improving the power grid resilience.

scholarly journals Fast Stepwise Inertial Control Scheme of a DFIG for Reducing Second Frequency Drop

2021 ◽  
Vol 11 (17) ◽  
pp. 8259
Author(s):  
Yien Xu ◽  
Dejian Yang ◽  
Jiejie Huang ◽  
Xinsong Zhang ◽  
Liang Hua
Keyword(s):  
Wind Speed ◽  
Rotor Speed ◽  
Induction Generators ◽  
Doubly Fed Induction Generators ◽  
Frequency Drop ◽  
Control Scheme ◽  
Grid Codes ◽  
Inertial Control ◽  
Doubly Fed ◽  
System Frequency

With the fast growth in the penetration of wind power, doubly fed induction generators (DFIGs) are recommended for their ability to enforce grid codes that provide inertial control services by releasing rotational energy. However, after supporting the system frequency, a second frequency drop (SFD) is prone to occurring to regain the rotor speed caused by the sudden reduction in output. In this article, we propose a torque limit-based fast stepwise inertial control scheme of a DFIG using a piecewise reference function for reducing the SFD while preserving the frequency nadir (FN) with less rotor energy released. To achieve the first objective, the power reference increases to the torque limit and then decays with the rotor speed toward the preset operating point. To achieve the second objective, the power reference smoothly lessens over time based on the exponential function. The performance of the proposed stepwise inertial control strategy was studied under various scenarios, including constant wind speed and ramp down wind speed conditions. The test results demonstrated that the frequency stability is preserved during the frequency support phase, while the second frequency drop and mechanical stress on the wind turbine reduce during the rotor speed restoration phase when the DFIG implements the proposed stepwise inertial control scheme.

scholarly journals Torque Limit-Based Inertial Control of a DFIG for Rapid Frequency Stabilization

2021 ◽  
Vol 9 ◽  
Author(s):  
Yien Xu ◽  
Hongmei Wang
Keyword(s):  
Kinetic Energy ◽  
Power Grid ◽  
Frequency Stabilization ◽  
Rotor Speed ◽  
Point Tracking ◽  
Frequency Drop ◽  
Inertial Control ◽  
Power Point ◽  
Doubly Fed ◽  
High Level

With the increasing penetration of renewable energy generation, the frequency stability of a power grid can be significantly threatened. A doubly-fed induction generator (DFIG) participates in the frequency support of a power grid by releasing kinetic energy (KE) to boost the frequency nadir (FN). However, during rotor speed restoration, it is difficult to counterbalance the size of a second frequency drop (SFD) and the rotor speed recovery duration. This paper proposes an improved torque limit-based inertial control (TLBIC) to raise the FN by releasing less kinetic energy while guaranteeing rapid frequency stabilization with reduced SFD. To this end, when detecting a disturbance, the DFIG enhances the active reference power to the torque limit, and then the active power reduces smoothly based on an exponential function until the maximum power point tracking (MPPT) curve is met, and the rotor speed reverts to the initialization operating condition along the MPPT curve. A simulation system model with various wind power penetrations is established in EMTP-RV. Results show that the proposed scheme boosts the FN at a high level with less KE and guarantees rapid frequency stabilization.

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

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3697
Author(s):  
Xiangwu Yan ◽  
Xuewei Sun
Keyword(s):  
Kinetic Energy ◽  
Control Strategy ◽  
Power Loss ◽  
Frequency Control ◽  
Frequency Regulation ◽  
Doubly Fed Induction Generator ◽  
Rotor Speed ◽  
Frequency Drop ◽  
Doubly Fed

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.

scholarly journals Dynamic Low Voltage Ride through Detection and Mitigation in Brushless Doubly Fed Induction Generators

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4461
Author(s):  
Ahsanullah Memon ◽  
Mohd Wazir Mustafa ◽  
Muhammad Naveed Aman ◽  
Mukhtar Ullah ◽  
Tariq Kamal ◽  
...  
Keyword(s):  
Fuzzy Logic ◽  
Fuzzy Logic Controller ◽  
Low Voltage ◽  
Voltage Drop ◽  
Low Voltage Ride Through ◽  
Induction Generators ◽  
Doubly Fed Induction Generators ◽  
Reactive Current ◽  
Doubly Fed ◽  
Rotor Side Converter

Brushless doubly-fed induction generators have higher reliability, making them an attractive choice for not only offshore applications but also for remote locations. These machines are composed of two back-to-back voltage source converters: the grid side converter and the rotor side converter. The rotor side converter is typically used for reactive current control of the power winding using the control winding current. A low voltage ride through (LVRT) fault is detected using a hysterisis comparison of the power winding voltage. This approach leads to two problems, firstly, the use of only voltage to detect faults results in erroneous or slow response, and secondly, sub-optimal control of voltage drop because of static reference values for reactive current compensation. This paper solves these problems by using an analytical model of the voltage drop caused by a short circuit. Moreover, using a fuzzy logic controller, the proposed technique employs the voltage frequency in addition to the power winding voltage magnitude to detect LVRT conditions. The analytical model helps in reducing the power winding voltage drop while the fuzzy logic controller leads to better and faster detection of faults, leading to an overall faster response of the system. Simulations in Matlab/Simulink show that the proposed technique can reduce the voltage drop by up to 0.12 p.u. and result in significantly lower transients in the power winding voltage as compared to existing techniques.

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