Research On The Grid-connected And LVRT Control Strategy Of High Power Inverter For Photovoltaic Generation

With the increasing of oil and energy consumption, and shortage of traditional fossil energy, the development of renewable energy sources more and more attention, solar energy as the most promising new green energy, occupy a very important position in the development of new energy. In recent years, with the increase of PV installed capacity, more and more solar energy will be connected into the power grid. Due to the randomness and volatility characteristics of photovoltaic energy, so the impact of improved penetration of photovoltaic power system will not be ignored. Therefore, in order to ensure the safety and stability of power system operation, the state proposed the corresponding technical requirements for photovoltaic energy grid-connected, such as requirements of islanding detection, low voltage ride through, frequency/amplitude response and so on. Papers will be based on the topology of large-capacity single-stage three-phase grid-connected PV system, research the grid-connected control algorithm research. According to the issues to be addressed during the fault, low voltage ride through control strategies proposed to achieve the inverter uninterrupted grid-connected operation during the grid fault conditon.The main research topics of this paper are the grid-connected and LVRT control strategy of high power inverter for photovoltaic generation, the main contents are as follows:According to the PV inverter power grid operating conditions required for the design of the LCL filter, and according the impact of various parameters on the filtering performance of the design parameters were optimized; In order to improve system stability and efficiency of the PV inverter, solve the problem of LCL filter resonance, choose the active damping control; according to the unbalance fault control strategy to adjust the damping control algorithm to ensure the stability control system.In view of the power grid fault cause voltage sags, in order to achieve the stability during the fault ride through, research the synchronously under power fault conditions. Based on the positive sequence component extracted method which is widely discussed recently, in contrast to its under several conditions currently widely discussed unbalanced way, compared the separation effect under different unbalanced fault condition. According to the actual requirements of the LVRT test and simulation results, select the appropriate fault ride through control phase synchronization method. For realization of the zero-voltage ride through problem, verify that the selected phase synchronization can be quickly and accurately obtain the grid voltage synchronization signals under different fault conditions.For the LVRT requirements in the photovoltaic grid-connected rules, Paper analysis of the problems which should be solved in process of fault ride through. According to the fault condtion, drop for unbalanced conditions, using the positive-sequence component and the negative sequence component controlled independently unbalance controlled strategy, and by real-time adjustment the positive sequence active and reactive current to achieve the reactive power support. Using Matlab/Simulink to build a500kW single-stage photovoltaic grid-connected inverter model, setting different fault conditions to verify proposed control strategy achieve grid-connected PV systems LVRT.Based on the experimental prototype, the photovoltaic inverters grid-connected and low voltage ride through capability was tested to verify the effectiveness of the proposed control scheme under different testing environment. Currently the inverter platform based on the proposed control scheme has passed the CQC quality certification and low voltage ride through certification.