The Reactive Voltage Coordinated Control For PV Accessing To Distribution Network

With distributed PV connect to distribution network, it will bring many new issues to power system as the development of PV and one of the most critical problem is voltage and reactive power. There are some problems will face inevitably after PV access to power grid, such as voltage fluctuation caused by PV output uncertainty, how to make PV work to provide reactive power support instead of off-grid at the situation of power grid fault, voltage and reactive power coordinated control when PV system at the same area connect to distribution network.This paper reviews the research status of the field of PV voltage and reactive power control at home and abroad, and then the coordinated control of PV and DSTATCOM is proposed to achieve flexibly grid-connected. The PV system is modeled at the case of light changing, and then study the impact on the grid voltage of different PV output. In addition, DSTATCOM modeling is shown in this paper to justify DSTATCOM can generate inductive reactive power or capacitive reactive poweradapting to voltage requirements to stabilize voltage.Secondly, a method of low voltage ride through based on DSTATCOM group coordinated control for PV is proposed to solve the case of PV off-grid operation in faults and the impact on power grid after restoration. Adjust the PV output voltage to control the output power and stabilize the DC voltage of the capacitor based on the relationship between the PV output voltage and power,so that the PV operated in the DSTATCOM state under fault conditions; then adjust the slope of each DSTATCOM based on maximum reactive power capacity of the device to allocate reactive power output of each device reasonably and establish the DSTATCOM group coordinated control strategy based on the slope.Thirdly, a coordinated control method for DSTATCOM group based on slope adjustment is proposed to solve the coordinated control problem of reactive and voltage with multi-DG in the same area. With taking into account the parameters of grid,the relationship among the reactive voltage、the output active current of DG and the output reactive current of DSTATCOM is Established, Then, based on maximum capacity of the DSTATCOM, the slope adjustment of each DSTATCOM is set up to allocate reactive power output of each device reasonably; The reactive current proportional gain which is constituted by the sum of the setting slope and reactance of corresponding line to the reference voltage as a negative feedback is added to constitute DSTATCOM’s new voltage reference value and establish coordinated control strategy of DSTATCOM group based on slope adjustment.With the guiding idedogy, in the cases of the power grid in fault and in steady-state, there are two systems will be simulated, one with PV and DSTATCOM, the other with dual DGs and DSTATCOMs, and showed that the coordinated control strategy has good control effect and engineering application.The paper is subsidized by the National natural science fund program "Research on the Space-time dynamic characteristics of reactive voltage and multi-dimensional optimization control of high-sensitivity power grid".