| Photovoltaic new energy power generation has been booming in recent years, but a large number of photovoltaic energy into the large power grid, but also to the stable and reliable operation of the power grid has brought a lot of problems. Photovoltaic microgrid has become a research hotspot because of its good coordination to solve these problems,and photovoltaic DC microgrid has more advantages in the utilization and control of photovoltaic power generation than photovoltaic AC microgrid.Therefore, in this thesis, the photovoltaic DC microgrid as the object of study, for the system in the grid-on and grid-off steady-state, grid-on and grif-off switching between the switching transient, large power grid fault ride through and other three different conditions of energy coordination control started the study.(1) The photovoltaic DC microgrid structure used in this paper is put forward, and the basic theory of interface converters which constitute microgrid structure is described in detail. On this basis, the control method of each interface converter under different working conditions is put forward, which lay the foundation for the design of the overall coordinated control strategy of microgrid.(2) In order to solve the problem of stable operation for two kinds of steady-state conditions of grid-on and grid-off, Based on the idea of DC bus voltage stratification, divided the system running state. According to the running state of the system, an energy coordination control strategy is proposed to completely disperse and communicate without communication. To ensure that the stability of the DC bus voltage stability and load safe and reliable power supply with steady state conditions of microgrid.(3) In order to solve the problem of command signal source for grid-on switching to grid-off, a systematic mode conversion control strategy with active islanding detection is designed and implemented to realize the smooth switching of the grid-on to grid-off. For the system how to switch from grid-off to grid-on, the paper designs a pre-synchronous grid-connected control scheme to realize the smooth and stable grid.(4) Aiming at the problem that the conventional phase-locked loop is difficult to obtain the phase of the power grid in the process of microgrid fault traversing, research and design of a new phase-locked loop program to achieve accurate fast phase-locked. Aiming at the different requirements of the output power of the grid side converter when the system is in steady state and the main network fault, an active and reactive power coordination control strategy is designed to ensure the smooth operation of the micro-network steady state and the reliable crossing of the main network fault.Finally, through the simulation results, it is shown that the design scheme of Photovoltaic DC microgrid in this paper guarantees the efficient and reliable operation of the system steady-state mode, and realizes the smooth and stable conversion between the system grid-on and grid-off conditions, realizes the reliable crossing of the system when a large power grid fault. |
