Modified Deloading Strategy of Wind Turbine Generators for Primary Frequency Regulation in Micro-Grid

Abstract

In this work, the contribution of wind turbine generator (WTG) to support micro-grid (MG) during depressed frequency condition has been studied with a modified strategy for improving the primary load frequency response of MG. The majority of existing deloading techniques to estimate the reference power are based on the linear relationship. Hence they are not so accurate to mimic the actual speed versus power dynamics of turbine rotor during deloading operation which is inherently nonlinear in nature. In this work, the existing methods have been analyzed in detail with an aim to improve the performance. Based on the analysis a modified deloading method assuming non-linear relation between rotor speed and power of WTG system has been proposed which shows the improved load frequency response in MG. The proposed deloading technique is simulated and validated using real-time digital simulator (OP4510) for the variation in load and generation inside an islanded MG. The results obtained using modified deloading method are compared with existing deloading method and it is found that proposed deloading method handles the non-linearity of the system during deloading operation and also it contributes more power to MG in response to load demand at the cost of slight increase in the speed of turbine rotor.

Challenges and potential solutions of grid-forming converters applied to wind power generation system—An overview

“…Based on the above analysis, three possible energy reserving schemes are shown in Figure 2, which are suitable for either type-3 or type-4 wind generators. As shown in Figure 2A, if there is no additional BESS in the wind generator, the wind turbine (WT) needs to operate in the deloading mode to reserve some wind energy (Vidyanandan and Senroy, 2013;Ducar et al, 2017;Krpan and Kuzle, 2020;Kumar et al, 2020;Dong et al, 2021). This is a possible way for the wind generator to achieve the GFM function, but it is not the best way from an economic point of view, because some potential wind energy is wasted.…”

“…As shown in Figure 3, the generalized GFM control structure consists of inner voltage/current control loops and outer power control loops, where the active power is related to the phase angle and the reactive power is related to the voltage magnitude. Besides, a voltage reference E∠θ is generated by the active power and reactive power controller at the outer loop, which can (Vidyanandan and Senroy, 2013;Ducar et al, 2017;Krpan and Kuzle, 2020;Kumar et al, 2020;Dong et al, 2021); (B) Adding an energy storage system on the dc-side (Chen et al, 2021); (C) Adding an energy storage system on the ac-side (Kouassi and Francois, 2016;Chen et al, 2021;Zhao et al, 2022).…”

“…Thus, different dc-link voltage control methods are worth being compared (Nguyen et al, 2022). Besides, to provide frequency support to the grid, the wind generator should reserve some additional energy, so that the deloading operation of the generator may be necessary (Kumar et al, 2020). In this paper, several energy reserving schemes, dc-link voltage control schemes, and overcurrent protection schemes for wind generators are reviewed, where type-3 and type-4 wind generators are the study focus.…”

Optimal active power control of wind turbines in grid-forming mode

“…De-loading operation can be achieved by shifting the operating point below the MPP. Thus, converting a part of the available power from the wind to kinetic energy and storing it in the rotor [6], [7]. In this case, wind turbines can increase their output power following any frequency disturbance by converting the additional stored kinetic energy, whether partially or entirely to active power and sending it to the grid.…”

Viability of providing spinning reserves by RES in Spanish island power systems

“…The authors employ a fuzzy control method to sense the frequency deviations and adjust the amount of deloading subsequently. In [27], the authors argue that existing linear deloading techniques lack accuracy, and the nonlinear relation between rotor speed and output power during deloading practice should not be overlooked. Then they've proposed a nonlinear formulation to enhance stability and frequency regulation participation of wind turbines in micro grid.…”