Research On Voltage Stability Control Strategy Of Island DC Microgrid With Constant Power Load

With the large-scale promotion of renewable energy and the development of distributed generation(DG)technology,microgrid has been widely concerned.Compared with AC microgrid,the DC microgrid has attracted more and more attention from scholars at home and abroad,because it does not need to consider the phase and frequency of voltage.Further,a DC microgrid contains simple control structure and less power conversion links.The stable operation of DC microgrid is the premise target of practical application,and the stability of system depends on the stability of DC bus voltage.Therefore,this paper focuses on the stability of DC microgrid system bus voltage.The specific work is as follow:Firstly,the topology and operation mode of DC microgrid are introduced and the components of the system are studied.According to the mathematical model of photovoltaic,the output characteristics under different illumination and temperature are analyzed.The maximum power point tracking control(MPPT)is adopted to the unidirectional DC/DC converter of photovoltaic unit to realize the efficient utilization of photovoltaic output.For the voltage supporting energy storage unit of DC microgrid in island mode,the output characteristics of energy storage battery are studied.Then,the control strategy of bi-directional DC/DC converter based on droop and double closed-loop PI control is introduced.Meanwhile,the characteristics of constant power load(CPL)and the mechanism of voltage stability of DC bus are analyzed.Secondly,the dimension reduction model of a complex DC microgrid with multi-source and multi-load is achieved and a virtual negative inductive control strategy is proposed.The constant power source(CPS)unit based on MPPT control is defined as a kind of CPL with negative power consumption.And then,the whole dimension reduction model of a complex DC microgrid system with multiple distributed micro sources and constant power loads is realized,the equivalent steady-state model of DC microgrid is obtained.A virtual negative inductive control strategy is proposed to solve the problem of voltage instability caused by CPL in a DC microgrid.Detailed performance comparison of the proposed control and virtual capacitance are implemented through MATLAB/Simulink simulation.Moreover,the improved performance of the proposed control method has been further validated with several detailed studies.The results demonstrate the feasibility and superiority of the virtual negative inductive control strategy.Finally,the influence of time delay in a DC microgrid system is considered innovatively.For the DC microgrid system with time delay,the corresponding delay model is established.The influence of control delay in a DC microgrid is analyzed.Further,in the cases of considering only control delay and considering both delay and parameter changing,the effectiveness of the control strategy proposed in this paper is verified by simulation.