Increased Wind Energy Yield and Grid Utilisation with Continuous Feed-In Management

Abstract

This paper presents a study to assess how wind turbines could increase their energy yield when their grid connection point is not strong enough for the rated power. It is state of the art that in such situations grid operators impose feed-in management on the affected wind turbines, i.e., the maximum power is limited. For this study a 5 MW wind turbine is introduced in a small grid that has only limited power transfer capabilities to the upstream power system. Simulations of one particular day are conducted with the electric load, the temperature, and the wind speed as measured on that day. This simulation is conducted twice: once with the 5 MW wind turbine controlled with conventional feed-in management, and a second time when its power is controlled flexibly, i.e., with continuous feed-in management. The results of these two simulations are compared in terms of grid performance, and in terms of mechanical stress on the 5 MW wind turbine. Finally, the conclusion can be drawn that continuous feed-in management is clearly superior to conventional feed-in management. It exhibits much better performance in the grid in terms of energy yield and also in terms of constancy of voltage and temperature of grid equipment. Although it causes somewhat more frequent stress for the wind turbine, the maximum stress level is not increased.

Simultaneous Inertia Contribution and Optimal Grid Utilization with Wind Turbines

“…The 1 st Eigenmodes model of a wind turbine represents the generator-converter unit as a first order low pass filter (PT1). In the previous study on continuous FIM [5] the time constant of this PT1 filter (T_PT1_geno_substi [21]) was set to 150 ms, which is a reasonable value for normal power control of a WT. In the inertial response study shown here, this time constant has to be reduced to a lower, but yet realistic value, to allow more rapid power variations as this is needed for effective inertial response.…”

“…Consequently, FIM becomes necessary in situations of high wind speeds, and/or very low local consumption in the campus grid. The FIM controller, which is shown in Figure 6 addresses the thermal loading of the transformer as well as VC [5].…”

“…(Since here only the interference between FIM and inertia contribution are assessed the steady state operating point of the transformer is irrelevant.) Further considering the heat dissipation at the surface of the transformer leads to the power that is stored in the transformer in the form of heat [5]. Hence, the transfer function from power transfer in pu to transformer temperature in °C is given in Equation 8.…”

“…For economic reasons grid connection of dispersed renewable energy generation develops slower, and often not to the same extent, as the installation of the generators. Consequently, the power infeed of these generators has to be restricted in weather situations that allow the production of large amounts of renewable power [5,11]. The transition to renewable energies is only economically feasible if conventional power plants are replaced; i.e.…”

“…For this study PC, PE30, wind speed, grid frequency, fgrid, and the ambient temperature were measured on 05 April 2017, which was a day with changing and eventually quite good wind conditions and a typical load profile for the campus. The measurements of PC, PE30, wind speed, and the ambient temperature are already published [5]; hence, they are not reproduced here.…”