Research On Contral Strategy Of 690V Statcom With LCL Filter

In the 690 V industrial power grid,the presence of various inductive and capacitive loads leads to frequent reactive power fluctuations,low power factor,and poor power quality.Therefore,it is necessary to carry out reactive compensation to improve the power factor and improve the power quality in the system.The Static Synchronous Compensator(STATCOM)has the advantages of fast response,small footprint,and high compensation accuracy in reactive power compensation and it is widely used in low voltage distribution networks.This paper mainly studies the main circuit parameters of STATCOM,LCL filter current control and DC-side capacitor voltage control.In this paper,the L-shaped filter based on Y-linked H-bridge inverter circuit is selected as the topology structure and the model is built.Secondly,the main circuit parameters of STATCOM is calculated.The design of LCL filter parameter follows the principle that the total filter inductance is the smallest and the filtering effect is the best;and the DC-side capacitance of the inverter is selected taking into account the main double-frequency fluctuation in the capacitor voltage,limiting the voltage fluctuation within a reasonable range..Considering about the problem of unstable current feedback on the side of the LCL filter,the current feedback on the inverter side is used instead of the current feedback on the grid side.To solve the problem of large current distortion,slow response,and reduced accuracy of the grid current after compensating with the inverter side current control,this paper adopts the capacitive current negative feedback to suppress the resonant peak and uses capacitor current feed forward to correct the command current and make compensation.The post-grid power system has a low current distortion rate,high compensation accuracy,and fast dynamic response without additional losses.This control method has the advantages of higher stability and simple controller parameter design.For the DC side capacitor voltage control,a layered control strategy is applied in this paper.The first layer control is the overall DC side capacitor voltage control,and the second layer control is the phase-to-phase DC side voltage equalization control.In the overall DC-side voltage control,the second-harmonic pollution caused by the second-harmonic component is suppressed by adding filter links in the feedback channel.This control strategy only exchange the positive sequence active components in the power grid and will not cause pollution to the grid.For the phase-to-phase DC-side voltage equalization control,this paper proposes a voltage equalization control method based on zero-sequence injection voltage.The zero-sequence voltage components is also discussed,which need to be injected when the grid voltage is balanced and unbalanced.The layered control strategy proposed in this paper will not inject negative sequence and harmonic components into the grid and avoid pollution to the grid during the compensation process.