Multi-objective Analysis And Optimization Control Of DT-STATCOM In Intelligent Distribution Grids

As an important part of smart grid,intelligent distribution grid is closely related to the needs of users.It has the characteristics of distributed generation,non-linear impact load and power-electronized,which is beneficial to make full use of renewable energy and significantly improve electrical energy efficiency.But there are still some urgent problems such as improving electric power quality and coefficient of clean energy utilization.Static Synchronous Compensator(STATCOM),a kind of typical compensation,is widely used in power quality optimization of distribution grid,owing to its excellent control performance.However,the traditional compensation equipment have the demerits of high cost and low efficiency in situations of static synchronous compensation and low voltage side decentralized compensation,which is not ideal.Therefore,in this paper,the STATCOM integrated with distribution transformer(DT-STATCOM)is employed to realize power quality compensation of the distribution grid at distribution grid power quality distribution point.Due to the complexity of the power quality problem in power distribution grid,it is necessary to simultaneously realize the comprehensive optimization compensation of reactive power,harmonics and unbalance.The existing single compensation method cannot meet the requirements of high-quality operation in the intelligent distribution grid.In order to solve the above problems and comprehensive compensate power quality in distribution grid,in this paper it's investigated about the optimization of DT-STATCOM multi-objective comprehensive compensation instruction value and the improvement of control strategy.Firstly,because the traditional DT-STATCOM mathematical model is difficult to reflect the influence of the primary leakage inductance of the distribution transformer on the STATCOM output filter design,in this paper based on the node admittance matrix,the mathematical model of DT-STATCOM is established,and the quantitative expression of STATCOM integrated tap side leakage inductance is given.The equivalent mathematical models of LCL type STATCOM in three-phase abc and dq coordinate system are established.The comparative analysis shows that the equivalent model of the three-phase abc coordinate system can be used to save the control system decoupling design and the coordinate transformation of the control variables,which simplifies the design process of the control system.Furthermore,the DT-STATCOM power quality comprehensive evaluation and command value optimization problem are studied to provide the optimal compensation component command value for the power quality integrated control strategy.Due to the limited capacity of compensation equipment,when the required compensation capacity exceeds the limit,DT-STATCOM faces the problem of selecting power quality compensation components.Combined with the concept of power quality penalty factor,the DT-STATCOM power quality multi-objective compensation command value optimization strategy based on electricity price penalty factor is proposed,which improves the efficiency of DT-STATCOM comprehensive compensation under capacity constraints.The simulation model is built in MATLAB/Simulink,which verifies the effectiveness of DT-STATCOM compensation component command value detection method and commands value optimization strategy.Finally,aiming at the problems of complex controller design,difficult parameter setting and steady-state performance guarantee when the traditional control strategy is applied to DT-STATCOM comprehensive compensation,based on the analysis of PI parallel repetitive control,a new harmonic disturbance observer is proposed in this paper.Relying on the design of a new filter,the improved current inner loop control strategy achieves zero-station tracking control of periodic signals.Combined with the command value optimization and the command value tracking control strategy,the DT-STATCOM power quality integrated control strategy is constructed.The effectiveness of the zero steady-state tracking control of the command value and the comprehensive compensation strategy of DT-STATCOM is verified by the simulation.Afterwards,the physics experiment platform was built,which results show that compared with the PI parallel repetitive control method,the improved harmonic disturbance observer integrated control strategy reduces the current THD from 4.49% to 2.68%,and the command value tracking error is reduced from 4.33% to 1.06%.In this paper,the mathematical modeling of distribution transformer based on nodal admittance matrix is established.The compensation instruction value based on price penalty factor is optimized.The integrated current loop tracking control strategy based on harmonic disturbance observer is studied.The steady-state tracking performance of DT-STATCOM is improved.The coordinated optimal control of reactive power,harmonic and load unbalance is realized.