High-Power Transformer-Less Wind Energy Conversion System with Permanent Magnet Wind Generator

For grid integration, a low-frequency (i.e. 50 or 60 Hz) transformer is placed inside the nacelle of the offshore wind turbine to step-up the voltage to the grid voltage levels of 11?33 kV. The heave weight and large size of the transformer significantly increase the weight and volume of the turbine. These penalties are critical in offshore applications, where cost of installation and regular maintenance are extremely high. As an alternative approach to achieve a compact and lightweight offshore and onshore wind turbine a medium voltage converter is proposed. The converter modules are cascaded to achieve medium voltage output. Each converter module is fed by a pair of generator coils with 90 phase shift to get the stable dc-link power. The power factor correction (PFC) circuit enables the generator to achieve unity power factor operation and the generator armature inductance is used as ac-side PFC boost inductance. At the grid-side, H-bridge inverters are connected in series to generate multilevel medium voltage output and the voltage-oriented vector control scheme is adopted to regulate the converter active and reactive power transferred to the grid. This new technology will enable transformer-less compact and lightweight turbine design, and has a great potential to be implemented in the future offshore wind farms and smart grid applications. The simulation is done by MATLAB/SIMULINK software.