Research On Control Strategy Of High Power Three Level Static Reactive Compensator

In recent years,energy demand has been increasing,and under the background of the dual carbon goal,the proportion of new energy such as wind energy has increased year by year,in order to stabilize the grid voltage,improve power quality,improve load efficiency,how to quickly and stably achieve reactive power compensation has become a top priority.Compared with the two-level static reactive power compensator,under the same conditions,the three-level static reactive power compensator has the advantages of low switching frequency,low voltage stress of the power device,and better output waveform quality,and has received widespread attention in the application of medium voltage and high-power reactive power compensation.In this thesis,the phase-locked loop of the three-level stationary reactive power compensator and the control strategy of reactive power compensation are studied in depth.Firstly,this thesis takes the three-level static reactive power compensator of the Neutral Point Clamped(NPC)topology as the research object,introduces its working principle,and builds the corresponding mathematical model.Secondly,the working principle of the phase-locked loop of the three-phase synchronous coordinate system and the second-order generalized integral phaselocked loop is introduced,and the corresponding mathematical model is constructed.When there is grid amplitude imbalance,harmonics,and DC bias voltage,the first two phase-locked loops have the problem of not being accurately locked.In view of their problems,an improved second-order generalized integral phase-locked loop is proposed,which can accurately track the phase angle of the grid voltage under the above three conditions,and the interference is negligible,and verify the correctness of the theoretical analysis through simulation.Then,the working principle and mathematical model of traditional doubleclosed-loop PI control,SVPWM modulation strategy and model prediction reference value tracking control in three-level static reactive power compensator are introduced,and both control strategies can output reactive current to achieve reactive power compensation under the condition of controlling the midpoint potential.In the steadystate case,compared with the traditional double-closed-loop PI control,the model prediction reference value tracking control is more flexible,and the coefficient realization of the value function can be adjusted according to the control performance requirements,and the current with better waveform quality can be output.Finally,the feasibility and correctness of the theoretical analysis are verified by simulation.Finally,a three-level static reactive power compensator system is designed,the hardware parameters and software of the system are introduced,and the modulation strategies mentioned in this thesis,double closed-loop PI control and model prediction reference value tracking control,are experimented on the experimental platform,and the experimental results verify the correctness and feasibility of the dual closed-loop PI control and model prediction reference value tracking control in the three-level static reactive power compensator.