Electric Power Systems Research 89 (2012) 23–30 Contents lists available at SciVerse ScienceDirect Electric Power Systems Research jou rn al h om epage: www.elsevier.com/locate/epsr Minimization of powers ripple of direct power controlled DFIG by fuzzy controller and improved discrete space vector modulation Mohammad Verij Kazemi a , Morteza Moradi b , Reza Verij Kazemi c a Institute for Higher Education, Pooyandegan Danesh, Chaloos, Iran b Islamic Azad University, Nowshahr Branch, Mazandaran, Iran c Islamic Azad University, Chalos Branch, Chaloos, Mazandaran, Iran a r t i c l e i n f o Article history: Received 12 August 2011 Received in revised form 5 February 2012 Accepted 7 February 2012 Available online 6 March 2012 Keywords: Constant switching frequency Direct power control Discrete space vector modulation Doubly fed induction generator Fuzzy logic controller a b s t r a c t This paper presents a new direct power control (DPC) strategy for a double fed induction generator (DFIG) based wind energy generation system. The strategy of the discrete space vector modulation (DSVM) that is on the basis of the DPC, is implemented. The algorithm to select voltage vector can effectively change the response of the system. So, a new analysis is done and a new switching table is proposed. The proposed switching table is presented to optimize the performance of the voltage vectors by accurately designing the sequence of the voltage vectors. Rearranging the sequence of the voltage space vectors has an influence on active power ripple. To enhance the performance of the closed loop system, fuzzy system is proposed in place of the switching table and hysteresis system. The four variables, rotor speed, errors of the active and reactive powers and stator flux position are exerted to the fuzzy system and the output is the vector that should be implemented to the switching devices. The outperformance of the proposed method is demonstrated by performing simulations in Matlab Software. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The most important advantages of variable speed wind turbines versus a conventional constant speed system are the improved dynamic behavior, resulting in the reduction of the mechanical stress and fluctuation of the electrical power, and also the increase of the power capture [1]. One of the generation systems, com- mercially available in the wind energy market, is the doubly fed induction generator (DFIG) which its stator winding is directly con- nected to the grid and its rotor winding is connected to the grid through a frequency converter (Fig. 1). One of the advantages of this system is that the rating of the power converter is one-third of that of the generator, also operation and four quadrant active and reactive powers. Direct torque control (DTC) of induction machine was devel- oped in the mid-1980s [2,3]. DTC is an active research control schemes which is on the basis of the decoupled control of flux and torque. DTC provides a very fast and precise torque response with- out a complex field-orientation block and inner current regulation loops. Some DTC based strategies are voltage vector selection using switching table [2], direct self-control [3], space vector modulation [4], discrete space vector modulation [5] and fuzzy logic [6]. As an intelligent method, fuzzy control does not need the accurate math- ematic model of the process. Fuzzy logic controllers were used in direct torque control systems in the past few years. Wei et al. [7] combined DSVM and Fuzzy and gained a good response. Base on the principles of DTC strategy, direct power control (DPC) was developed for three-phase pulse width modulation (PWM) rectifier. DPC directly controls the stator active and reac- tive powers. It is possible to control the amplitude of the rotor flux space vector and its relative distance from the stator flux space vector, i.e., a necessary condition for the control of the DFIG. Several researchers focused on the progress of the DPC tech- niques that operate at a variable switching frequency [8,9]. Expensive and complicated AC harmonic filters and power convert- ers are the consequence of using the variable switching frequency. DPC at a constant switching frequency was recently developed for the DFIG by [10,11]. But the practical implementations of these methods are more complicated and expensive than conventional DPC. Verij kazemi et al. [12] presented a new DPC on the basis of the DSVM technique. Number of voltage vector generated by this method is more than conventional DPC method. The increase of the number of voltage vectors allows designing more accurate switch- ing tables. The DSVM-DPC achieves a sensible reduction of power ripples and constant switching frequency without increasing the complexity of the conventional DPC. In this paper, power ripples in DSVM-DPC are analyzed and the optimized switching tables are defined. Then, a new DPC control strategy for DFIG on the basis of fuzzy logic is presented and the per- formance of the proposed fuzzy system is compared with switching table. Mamdani’s min-max method [15,16] is used to compute the inference strategy in the fuzzy system. The rules of the fuzzy 0378-7796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.epsr.2012.02.008