Reactive current control of STATCOM based MMC inverter for wind turbines connected to grid

The function of the proposed control (MMC) inverter is to convert DC power coming from the DC link made of series connected wind turbines to generate a suitable AC power, and fix the power factor (PF) of the grid at a target PF during normal operation and dc fault contingencies. This is achieved by controlling the reactive current injected to the grid. The MMC inverter is for permanent magnet wind generators through a buck converter that not only regulates but tracks the turbines fluctuating voltages. Also as a bypass control in case of any disconnection from the wind turbines. These turbines have optimized power tracking for their independent variable voltages which depend on individual wind speeds for optimal power extraction. This MMC interface has a d.c link adjustable voltage level control. The result shows the inverter has maintained ac output voltage with an improved power factor. These were achieved by maintaining the MMC inverter dc-link voltage under different wind speeds or failure, through modulation index control despite the reduced voltage inputs. The reactive current control is based on the desired derived target reactive power equations plus the dc link active power angle control implemented using a PI controls. This control technique elegantly improved the power factor to the targeted value.