The Optimal Control Method And Application Of Differential Power Processing-Based Photovoltaic System

With the continuous promotion of low-carbon transformation of energy consumption structure,solar photovoltaic(PV)has become an important source of electricity for many countries.Continuing to expand China’s leading position in the solar PV industry and accelerating iterative technological innovation will both benefit the overall interests of the country and help build an energy security system that meets national strategic needs.In order to continue to expand the scale of PV power generation and accelerate the promotion and application of PV power generation,it is crucial to solve the problem of its low cost effectiveness.At present,it is widely believed that the distributed maximum power point tracking topology can effectively improve the cost-effectiveness of PV power generation system,and the Differential Power Processing(DPP)topology is considered to be the most competitive distributed maximum power point tracking topology with its high integration and low intervention loss.Considering the lack of systematic research on DPP-based PV systems,this dissertation focuses on its optimal control and application.The main research works are as follows:The low-cost fault-diagnosis and-tolerant control strategy can optimize the output performance of the faulty PV system and improve the reliability and economy of the PV system.By analyzing the changes of PV module voltage before and after the failure of DPP converter switching devices,a redundancy-free hardware fault diagnosis method with abnormal fluctuation of PV module voltage as the fault characteristic is proposed.By analyzing the characteristics of DPP converter and central converter in PV system,a non-redundant hardware fault-tolerant control strategy based on the coordinated control of normal power converters in PV system is proposed.The control strategy can achieve targeted optimization with different fault-tolerant control schemes for different fault conditions.The experimental results show that the proposed fault-diagnosis and-tolerant control strategy can effectively detect the DPP converter fault and complete the output power optimization of the PV system after the fault,and the optimization even reaches more than 120% in the given fault scenario.The control strategy balancing reliability and power production for PV system can reasonably allocate the weights of PV system reliability and power yield under different operating conditions and improve the economy of long-term operation of PV system.By analyzing the maximum power point tracking principle of the DPP-based PV system,the mathematical model of the power handled by the DPP converter under different working conditions is established.By analyzing the factors affecting the reliability of the DPP-based PV system,a simplified mathematical model of its reliability is established.By analyzing the influence of changing the processing power of DPP converter on the reliability and power production of PV system,a flexible-value processing power-limited control strategy is proposed.The control strategy can flexibly adjust the reliability and power production of the PV system by changing the processing power of the DPP converter.Simulation and experimental results show that the proposed control strategy can adjust the processing power of the DPP converter in a targeted manner according to different operating conditions to achieve a balanced control of the reliability and power production of the PV system.Synchronous maximum power point tracking control can significantly reduce the maximum power point tracking time and improve the maximum power point tracking efficiency and power production of the DPP-based PV system.In order to solve the coupling issues in DPP-based PV systems to realize the application of synchronous maximum power point tracking control in them,a simple and easy partial decoupling method is proposed.The decoupling method is independent of system parameters and has excellent scalability.By analyzing the coupling form of the DPP-based PV system,a method of decomposing the system coupling with a double closed-loop control structure is proposed.By analyzing the dominant part of the system coupling(outer-loop control object),a partial decoupling method is proposed in which the outer-loop control object is completely decoupled and the inner-loop control object suppresses the coupling through its compensator.By analyzing the difficulty of implementing the partial decoupling method,a simple physical implementation scheme is designed for it.Based on the proposed partial decoupling method,the synchronous maximum power point tracking control scheme for the DPP-based PV system is designed.Simulation and experimental results show that the proposed partial decoupling method can effectively suppress the coupling in the DPP-based PV system;the synchronous maximum power point tracking control can effectively improve the maximum power point tracking efficiency and power production of the DPP-based PV system.The application of DPP-based PV system in DC microgrid provides a reference for the practical application of distributed maximum power point tracking topology.By analyzing the stable working mode of DC microgrid,the operation state of each power generation unit under different working environment is given.By analyzing the problems of the control method of PV system in traditional DC microgrid,a control strategy for DPP-based PV system with simple control structure and power-sharing optimization is proposed.The control parameters of this strategy are designed simply and the switching of different operating modes does not cause system oscillation.A multi-mode control strategy for energy storage system with limited charge/discharge rate is proposed for the battery capacity decay problem in the operation of energy storage system.The control strategy can effectively solve the overcharge and overdischarge problems of the battery,and the seamless switching of five operation modes can realize the economic operation of the energy storage system.By analyzing the economic operation modes of each power generation unit in DC microgrid,a power coordination control strategy for PV system and energy storage system is proposed.The control strategy can reasonably adjust the operation mode of each power generation unit under the premise of DC microgrid stability.Simulation and experimental results show that the proposed power coordination control strategy can achieve the established optimal control of each generation unit while ensuring the stable operation of the DC microgrid,which verifies the practical performance of the DPP structure photovoltaic system.