Study of Harmonic Mitigation in PMSG Wind Turbine Energy Conversion Systems

Abstract. Reduced magnet price has made synchronous generators with permanent magnet synchronous generator (PMSG) an attractive alternative in the last couple of decades. Permanent magnet synchronous generators (PMSG) applied to wind energy conversion system (WECS) using variable speed operation is being used more frequently in wind turbine application. Variable speed systems have several advantages over the traditional method of operating wind turbines, such as the reduction of mechanical stress and an increase in energy capture. To allow the variable speed operation of the PMSG WECS a conventional passive harmonic trap filter with a bulky capacitor associated with a voltage source current controlled inverter (VS-CCI) is used. This simple scheme introduces a high intensity low frequency current harmonic content into the PMSG and consequently increases the total loses in it. Subsequently, decreases the power capability of the system. This paper presents a comparative simulation study between three different approaches applied to harmonic mitigation in PMSG WECS.Keywords: Wind energy, Harmonic component, PMSG, Rectifiers, Harmonic Trap Filter.1 INTRODUCTIONNow a day's worldwide energy crisis is one of the great problem. The interest in renewable energy has been revived over last few years, especially after global awareness regarding the ill effects of fossil fuel burning. The amount of energy captured from a WECS depends not only of the wind at the site, but depends of the control strategy used for the WECS and also of the conversion efficiency. Permanent magnet synchronous generators (PMSG) on wind energy conversion system (WECS) with variable speed operation are being used more frequently in low power wind turbine application. Variable speed systems have several advantages such as the reduction of mechanical stress and an increase in energy capture. In order to achieve optimum wind energy extraction at low power fixed pitch WECS, the wind turbine generator (WTG) is operating in variable-speed variable-frequency mode. The rotor speed is allowed to vary with the wind speed, by maintaining the tip speed ratio to the value that maximizes aerodynamic efficiency. The PMSG load line should be matched very closely to the maximum power line of the WTG. MPPT control is very important for the practical WECS systems to maintain efficient power generating conditions irrespective of the deviation in the wind speed conditions. To achieve optimal power output, a sensor-less scheme including a wind turbine model was developed by Tan et al in. The developed wind turbine model will be used in this work in order to evaluate the different harmonic mitigation approaches. To build the first one a classical three phase bridge rectifier (BR) associated to a bulky capacitor is used and the second stage may be implemented by two types of converters schemes Voltage source current controlled inverter (VS-CCI) and Line commutated inverter (LCI) as shown in Fig. 1. This paper has the main focus in the first energy conversion stage the AC-DC converter, which is responsible by an injection of a high harmonic current content into the PMSG. These currents circulating into the machine will generate losses. Using these approaches is possible to minimize the current harmonic content.A software simulation model developed in using PSIMâ software, which allows easy performance evaluations, is used to estimate the behaviour of these three different schemes associated with the PMSG WECS. Simulation results showed the possibility of achieving maximum power tracking, output voltage regulation and harmonic mitigation simultaneously.2 WIND TURBINE SYSTEMThe In a wind turbine system, the kinetic energy in the wind is converted into rotational energy in a rotor of the wind turbine. The rotational energy is then transferred to a generator, either directly or through a gearbox for stepping up the rotor speed. The mechanical energy is then converted to electrical energy (variable-frequency, variable-voltage) by the generator. …