Abstract
Simulations done in MATLAB/Simulink together with experiments conducted at the Ångströms laboratory are used to evaluate and discuss the total harmonic distortion (THD) and total demand distortion (TDD) of a tap transformer based grid connection system. The grid connection topology can be used with different turbine and generator topologies and is here applied on a vertical axis wind turbine (VAWT) with a permanent magnet synchronous generator (PMSG) and its operational scheme. The full variable-speed wind conversion system consists of a diode rectifier, DC link, IGBT inverter, LCL-filter, and tap transformer. The full variable-speed operation is enabled by the use of the different step-up ratios of the tap transformer. In the laboratory study, a full experimental setup of the system was used, a clone of the on-site PMSG driven by a motor was used, and the grid was replaced with a resistive load. With a resistive load, grid harmonics and possible unbalances are removed. The results show a TDD and THD below 5% for the full operating range and harmonic values within the limits set up by IEEE-519. Furthermore, a change in tap, going to a lower step-up ratio, results in a reduction in both THD and TDD for the same output power.
Highlights
Installed wind power on the utility grid is rapidly increasing [1]
This paper mainly focuses on wind power where there are two strong arguments for the use of full power electronic conversion systems
The work presented in this paper aims to evaluate the total harmonic distortion (THD) and total demand distortion (TDD) of the system
Summary
Installed wind power on the utility grid is rapidly increasing [1]. This paper mainly focuses on wind power where there are two strong arguments for the use of full power electronic conversion systems. The ability to control the rotational speed almost freely giving the benefit of optimal energy absorption, reduced loads, gearless turbines, and reduced noise at low wind speeds. The power electronics give the wind turbine the ability to be an active component in the power system [6]. This allows for control of active and reactive power flow and the ability to strengthen weak grids. An evaluation of today’s most commonly used power conversion topologies for wind power can be found in [7, 8]
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