Study On Control Strategies Of Three-level DSTATCOM

With the accelerating pace of industrialization in our country,the power industry as the basic industries become more and more attention to thesociety.While the constant expansion of the power system, the constant increasing incomplexity and requirements of power quality or power supply stability is alsoincreasing, new problems and new contradictions in the power system is moreprominent, so we need advanced technology or a better way to solve the currentproblems. The principal contradiction in the power system at this stage is that, Firstly,a variety of power quality sensitive electrical equipment widely used, allowing usersthe power grid reliability and power quality requirements are getting higher andhigher; Secondly, such as electric arc furnace, electric locomotives and otherimbalances, the impact power and high randomness of the industrial load is increased,the resulting voltage fluctuations, power factor is low, three-phase voltage and currentimbalance of power quality problems. These issues will not only reduce theperformance of electrical equipment, and even affect the normal operation of theentire power system. Causing unnecessary economic losses and slow down theprocess of industrialization of society. Therefore, we must take effective measures tosolve the problem.At this stage in order to improve the quality of power supply and its stability,power electronic components based on flexible AC transmission systems (FACTS)has become a hot research direction of the power electronics disciplines. In this thesis,NPC-type three-level distribution network, static reactive power compensation ofDSTATCOM as the object of study, and to discuss the working principle of thethree-level DSTATCOM, three-level DSTATCOM SVPWM modulation method andthe control methods and strategies in the case of grid voltage and load balance.This thesis focuses on the analysis of the working principle and operatingcharacteristics of the three-level DSTATCOM,on this basis, built the mathematicalmodel of the three-level DSTATCOM in the case of balanced. In this paper, asimplified three-level SVPWM algorithm as a compensator of the modulationmethod,and by regulating the duration of action of the small vector to maintain theequilibrium of the DC bus voltage.The two basic functional of static var compensator is compensation fo reactivepower and voltage. DSTATCOM through the reactive power exchange with the pointof common coupling (PCC), it can make the PCC voltage to be supported and maintained at a given reference value, avoid large fluctuations of voltage. In thisthesis the voltage value of common connection point as the direct control of the object,get rid of complex reactive power and reactive current detection. Fixed-frequencydirect power feed forward decoupling control in the outer ring, direct voltage fuzzy PIcontroller in the inner ring and the control strategy is simulated. The simulationresults show that in the case of grid voltage drop7%or uplift7%, the feedforwarddecoupling of direct power control strategy and direct voltage fuzzy PI controller toobtain a good compensation effect.