Research On Finite-time Control Of Parallel Photovoltaic/Storage Converter System For New Energy Power Generation

The utilization of renewable energy plays an important strategic role in the energy transformation.Solar photovoltaic power generation has been widely used in the world with its significant advantages.With the development of large-scale photovoltaic power generation,challenges have been brought to the improvement of the power generation efficiency of photovoltaic system and the consumption of photovoltaic power generation.Because of the influence of material and process,improving the photoelectric conversion efficiency of photovoltaic modules and photovoltaic grid inverter power conversion efficiency has technical bottlenecks in a certain period of time.Paralleling photovoltaic inverters with shared dc bus can improve system efficiency in the condition of existing solar cells and inverter.However,it also brings the problem of zero sequence current among grid connected converters problem and dc voltage regulation problem.Energy storage is an effective means to solve the problem of photovoltaic absorption.In order to guarantee the power supply quality to users,the parallel frequency recovery of multiple energy storage converters is a problem that must be solved under the isolated island operation mode of the photovoltaic microgrid.Therefore,this paper extracts the aforementioned three problems from the parallel operation mode of photovoltaic microgrid multiple converters,and conducts in-depth theoretical analysis and experimental research on the system based on the finite time control theory,which has important theoretical significance and engineering application value.Based on review the state of the art relevant solutions,this paper studies the finite time control method for related problems of grid-connected converter.The main research work and achievements are summarized as follows:1)In order to suppress the zero-sequence circulation of the parallel photovoltaic converter,the influencing factors of the zero-sequence circulation are firstly revealed,and an improved passive filter is proposed to effectively reduce the high-frequency component of the circulation.For the low frequency circulation component,the distribution of the zero vector which does not generate the actual power flow is selected as the controlled variable,and a finite time controller is proposed.In the case of the random fluctuation of the output power of photovoltaic array caused by the change of illumination,the controller can suppress the low frequency component and obtain good dynamic characteristics.2)A new leader-following architecture of parallel photovoltaic converter system is proposed for photovoltaic voltage control of parallel photovoltaic converters,which transforms the photovoltaic voltage control and array power sharing problems into the distributed consensus problem of multi-agent systems.An independent leader only has the maximum power tracking function,providing the target value of the dc voltage.Photovoltaic inverter is treated as a follower.A new method of hierarchical control,a pv voltage droop and distributed quadratic finite time consensus,is put forward,which not only ensures the dc bus voltage control is not affected by the communication delay,but also drives the state of the follower of convergence,eliminating the droop control error and minimizing photovoltaic power loss.3)For the frequency synchronization control of the micro power grid formed by the parallel energy storage converter,the equivalence between the two control methods of energy storage converters developed in different backgrounds,namely droop and VSG,is firstly revealed,which provides a new perspective for the complete dynamics modeling of microgrid based on converters.Based on the homogeneous theory,fixed time control of frequency synchronization with the micro grid second-order Kuramoto model is proposed,which ensures the followers tracking to the leader trajectory in a certain period of time without influenced by the initial state.So the convergence rate of synchronization is optimized.Frequency synchronization control provides a new train of thought to the islands of the secondary frequency of micro network under the running system restore control.