Control of grid side inverter for wind turbine

Abstract

Nowadays, the renewable energy sources are a topic of interest in our society. Wind energy has many advantages facing the fossil fuel which explain why it has grown so fast in the last years. Wind energy is a clean fuel source that does not pollute the air as power plants are doing with combustion of fossil fuels. The low environmental impact of wind energy makes it a very attractive solution, which in last years demand has grown a lot. In 1985 the commercial wind turbines had a power of 20􀀀60 kW with a diameter of 20m and already in 2005 had increased to 5MW with a diameter of 125m [9]. Different configurations can be used for a wind turbines. The design of a wind turbine can have a gearbox or not, the generator can be an asynchronous or synchronous machine and the connection to the grid can be directly or through power conversion. Two modes of operation can be used in function of the wind turbine configuration. These types of operation are fixed speed and variable speed. In the past, fixed speed which can get maximum efficiency for one wind speed was used. But, the power conversion is not efficient for this reason nowadays the topology most used is variable speed. It is designed to achieve the maximum efficiency over a wide range of wind speeds. In 20 years, the cost of wind power generation has decreased by around 80% [10]. This has been possible because of the development in power electronics.The full scale power converter is the type which has become more popular where the generator is connected to the grid via a back to back converter. Back to back converter is used to control the reactive power and voltage too [4; 19]. Improving the performance of control in power electronics goals can be achieved, such as: – Reliability: where the control of power quality is necessary to fulfill the grid codes requirements. – Efficiency: to have a better use of the wind turbine capacity. – Cost. Self commutated converter system is the most used [6]. A typical converter is with insulated gate bipolar transistor (IGBTs) and its modulation can be done by pulse width modulation (PWM). It can control both active and reactive power, depending of the modulation, LCL filter and control method used. The high switching frequency used in the modulation may produce harmonics. In order to reduce them filters should be used. Filters are used between converter and grid because is not possible to have connect two voltage sources in parallel, in this case the back to back converter and the grid. LCL filter is the most common

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Control of grid side inverter for wind turbine