Control of a permanent magnet synchronous general-based wind energy conversion system.
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Wind energy has proven to be a competitive and an environmentally friendly renewable energy resource for generating electricity. Wind farms are usually located far from the load centers; hence the generated power has to be transmitted over long distances to load centers. High voltage direct current (HVDC) transmission system is the preferred means for transmitting bulk power over long distances when compared to high voltage alternating current (HVAC) transmission system. An HVDC transmission system increases the transmission capacity, improves the system stability, and possesses lower transmission losses. In this research investigation, a 690V, 2MW wind turbine-driven permanent magnet synchronous generator is modelled to be integrated into a local 33kV AC grid via a three- level neutral-point-clamped voltage source converter (VSC)-based HVDC transmission system. Three control schemes were implemented, namely: pitch-angle controller, generator-side converter controller, and a grid-side converter controller to optimize the system performance. The stability analysis and controller modeling was carried out in MATLAB using bode plots and step response curves. The proposed subsystems and the control schemes were implemented in PSIM software package to evaluate the overall system's performance. The simulations were carried out on the model and it was concluded that the grid-side converter controller ensured maximum power point tracking when the wind speed was lower than the wind turbine(WT)'s rated wind speed. Conversely, as the wind speed exceeded the WT's rated wind speed, the pitch-angle controller was activated. This increased the angle of attack thereby reducing the power coefficient in order to shed off the aerodynamic power. Furthermore, the DC-link voltage was stabilized within the allowable limits to ensure a continuous flow of active power from the WT to the grid and the reactive power transfer between the grid-side converter and the AC utility grid was maintained to a minimum to ensure a unity power factor. The comparison analysis of the new control approach to the traditional control approach illustrated that for the new control approach, the ability of the DC-link voltage controller to keep the DC-link voltage within the allowable limits does not get impaired during fault conditions. Therefore, the power continues flowing from the WT generator to the grid. Conversely, it was observed that for the traditional control approach, the ability of the DC-link voltage controller to stabilize the DC-link voltage gets impaired and therefore it can no longer effectively transfer as much active power from the WT generator to the grid. Therefore, the new control approach proved to be effective in terms of stabilizing the DC-link voltage during fault conditions thereby enhancing the WT’s fault-ride-through capability.