New General Multilevel Voltage Source Converter Topology And Its Application In D-STATCOM

The grid in nonlinear and unbalanced load frequency phenomenon with the further development of modern science and technology will become increasingly high,is now regarded as a compensation device has a great advantage,namely the distribution static synchronous compensator(D-STATCOM).What's most worth mentioning is that it can compensate reactive power as well as compensate for three-phase imbalance by issuing negative sequence current.For the current development trend,cascaded form D-STATCOM has become the main selection topology of reactive power and imbalance compensation in distribution network because of its many advantages.The chain D-STATCOM based on star type connection has been paid more attention and applied.But it also has its shortcomings.And for this kind of topological structure of the D-STATCOM,the DC side capacitor is connected to each other and the active energy cannot flow smoothly between the three phase bridge arms,so if there is a negative sequence component will directly affect the phase equilibrium of DC voltage.Based on this,this dissertation takes three-phase H bridge cascade STATCOM device as the research object,and proposes a new type of universal multilevel voltage source converter topology D-STATCOM,which is composed of a chain H bridge inverter unit and a DC side common capacitor inverter unit.For the DC side shared energy storage capacitor,the active energy can be freely circulated between the three phase bridge arms,and the realization of the controller is simple.The two kinds of common topology combination has become a new topological structure of the D-STATCOM.This dissertation starts from the main circuit topology as a starting point,analyzed the main circuit topology of several common STATCOM,introduces the advantages of the new structure of the main circuit topology of and modulation strategy,but also the new topology to compensate unbalanced condition,several common STATCOM main circuit topologies are compared and analyzed.The basic principle of compensation imbalance is described in detail,and a fast algorithm for detecting sequence components is presented.The negative sequence components in the system can be detected quickly and accurately.In order to study the control strategy more conveniently,the mathematical model of the new topology is established under certain conditions.In order to make the controller realize the coordination and compensation of the chain H bridge inverter circuit and the DC side common capacitor inverter unit,the two control strategies are combined to achieve the current control based on the robust L2 performance criterion.The two control methods are the repetitive control based on the internal model principle and the passivity control with dissipative characteristics.Finally,based on the above theory,a simulation model is built in MATLAB/Simulink,and the effectiveness of the designed circuit is verified by setting parameters and showing the results of some experimental waveforms.The experimental platform is set up.By observing the relevant parameters and experimental waveforms,we verify the feasibility of the new universal multilevel voltage source converter topology applied in D-STATCOM.