Fault Tolerance Control And Coordination Control Strategies Of Distributed Generators In PV/Storage/Hydrogen Microgrid

Photovoltaic(PV)/storage/hydrogen Microgrid can effectively absorb PV renewable energy and promote the development of comprehensive energy.PV acts as the main power source in Microgrid,and its operation reliability will affect the stability of the whole system.Hydrogen production unit(HPU)can absorb PV energy in large scale and long period,but the energy conversion efficiency of electricity-hydrogen energy and the coordination control are very important.This thesis first studies the operation characteristics of each unit in the PV/storage/hydrogen microgrid,then studies the fault-tolerant control strategy of the PV power generation system,and finally studies the coordination control strategy of the microgrid.The main work is as follows.Firstly,based on the PV/storage/hydrogen microgrid,their operation characteristics are analyzed.The engineering application model of HPU and the conversion efficiency model are proposed.The energy conversion efficiency from electric energy to chemical energy determines the application feasibility of electrochemical load in microgrid.The external electrical characteristic models of HPU is analyzed,and the energy conversion efficiency model is proposed to guide the operation strategy of HPU.Secondly,there exists common ground circulating current(CGCC)problem of parallel Hbridge DC/DC converters in PV dominated DC microgrid.The differential mode control strategy is proposed to effectively improve the fault tolerance of PV system.The PV generators achieve power convergence through parallel converters,and the common ground loop is generated due to the negative grounding fault on the power side,which leads to the CGCC.Especially,the difference of line resistance and input voltage will cause great CGCC and crash the PV system.The differential mode control strategy is proposed to effectively improve the fault tolerance ability of PV system.Then this chapter analyzes the undesired influence of the shadow shading problem,open-circuit fault and short-circuit fault in PV module.An improved topology based on BuckBoost converter is proposed to suppress these harmful fault phenomenon.The compared experimental results show that the proposed topology outperforms the conventional topology and the Boost converter based topology in the existing literature.Thirdly,the proportional-resonant(PR)control strategy is proposed to solve the grounding fault problem in PV modules and improve the system operation ability when PV system is connected into the AC microgrid.The grounding fault in different positions of PV modules will produce the DC bias component and the third harmonic component in the AC side voltage.Meanwhile,the output voltage of the DC-side converter fluctuate violently and the CGCC is also generated.According to the characteristics of the fault components,the PR control strategy is proposed and the rich experimental results show its effectiveness.Then,as for the grounding fault problem of PV modules in parallel PV systems,the 0-axis based control strategy from the view of AC side and the differential mode control strategy as well as improved topology from the view of DC side are proposed respectively.The grounding fault in parallel PV systems not only produces CGCC but also degrades the stability of the system seriously.From the view of AC side,the CGCC can be embodied through the zero-sequence component of the three-phase inductive current,thus a 0-axis based control strategy is proposed to suppress the ground current.From the view of DC side,the CGCC will result in the difference between the output and input currents of PV modules,thus the differential mode control strategy based on an improved topology is proposed to solve the problem.Fourthly,based on the DC bus voltage and AC bus frequency signal,the decentralized coordination controls are proposed with consideration of the operation characteristics of different units respectively in the PV/storage/hydrogen microgrid.As for storage battery,the functions with variables of So C and instantaneous power are proposed to guarantee that the remaining capacity of battery and the charging or discharging power are in the safe range.As for PV generator,the P-V and P-f droop control strategies are proposed to make the PV generator work off from maximum power point mode to reference power point mode seamlessly.As for HPU and fuel cell,the adaptive transition control between maximum efficiency point operation mode and maximum power point operation mode is proposed.The stable operation of microgrid system and the high efficiency of PV power consumption can be realized based on the above-mentioned control strategies.