Abstract
This aim of this paper is to design controller for Doubly Fed Induction Generator (DFIG) converters and MPPT for turbine and a sensor-less rotor speed estimation to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages. It is also aimed to meet desired reference real and reactive power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The turbine blade angle changes with variations in wind speed and direction of wind flow and improves the coefficient of power extracted from turbine using MPPT. Rotor side converter (RSC) helps to achieve optimal real and reactive power from generator, which keeps rotor to rotate at optimal speed and to vary current flow from rotor and stator terminals. Rotor speed is estimated using stator and rotor flux estimation algorithm. Parameters like tip speed ratio; coefficient of power, stator and rotor voltage, current, real, reactive power; rotor speed and electromagnetic torque are studied using MATLAB simulation. The performance of DFIG is compared when there is in wind speed change only; alter in reactive power and variation in grid voltage individually along with variation in wind speed.
Highlights
Wind and solar electric power generation systems are popular renewable energy resources and are getting significance due to retreating of primary fuels and because of ecofriendly nature and is available from few kilo-watt power to megawatt rating [1]
The dynamic performance of the Doubly Fed Induction Generator (DFIG) system is shown in Figure 9 is investigated under three different cases and the rating specifications for DFIG and wind turbine parameters are given in appendix
Case A: Change in tip speed ratio (TSR) and coefficient of power (Cp) with wind speed, reactive power and grid voltage The changes in tip- speed ration and power coefficient Cp with change in wind speed alone is shown in Figure (a), with both reactive power and wind speed variation in Figure (b) and variation with grid terminal voltage and wind speed both is shown in Figure 10 (c)
Summary
Wind and solar electric power generation systems are popular renewable energy resources and are getting significance due to retreating of primary fuels and because of ecofriendly nature and is available from few kilo-watt power to megawatt rating [1]. The reference rotor speed is derived from the wind turbine optimal power output PmOpt as shown in Figure 4 and grid power demand. The reference power input to the lookup table as shown in Figure 6b is Pm,gOpt. Based on the value of Pm,gOpt , the rotor is made to rotate at optimal speed so as to extract maximum power from DFIG set. To achieve better response during transient conditions, decoupling d-axis voltage is added as in case of separately excited DC motor This decoupling term helps in controlling steady state error and fastens transient response of DFIG during low voltage ride through (LVRT) or during sudden changes in real or reactive powers from/ to the system. The electrical power from DFIG changes when mechanical power changes or rotor speed changes or load demand from grid varies
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