Research Of The Improved Droop Control Strategy Based On The Common Point Voltage In Microgrid

Distributed generation is one of the most effective ways to use clean energy.With the increase of the permeability of distributed generation,many scholars put forward the concept of microgrid.The use of microgrid can improve the system stability and energy efficiency.As an important part of energy conversion,it is of great significance to study the control strategy and the safe and stable operation of the inverters.First of all,the development and control strategies of the micro grid are analyzed in this paper,and the droop control is introduced in detail.The mathematical model of three-phase inverter is established and the parameters of power,voltage and current are controlled.It can reduced from the analysis of power distribution conditions that some situation factors,such as geographical location,load condition,will lead to the consequence that the inverters is unable to realize power distribution reasonably and cause the circulation in the islanding operation mode,which would affect the safe operation of micro grid seriously.Secondly,aiming at this problem,two kinds of improved droop control strategies are adopted,which are distributed secondary control strategy and the robust droop control strategy based on common point voltage.the principle of the distributed secondary control is relatively simple,but the usage of many PI controllers makes it difficult to adjust parameters,and difficult to realize.In addition,when the inverters' capacity are not equal,the reasonable distribution of the power can not guaranteed.In the robust droop control strategy based on common point voltage,the virtual negative impedance algorithm is adopted to reach power decoupling.The equality of the output voltage between each inverters is ensured by sampling the public voltage.to make the output voltage be stable around the rated value,the voltage secondary regulator is added.Regardless of the inverters' capacity equal or unequal between each other,as long as the droop coefficient is proper regulated,the reasonable distribution of power can always be achieved.Besides this scheme need to adjust a few parameters are needed to be adjusted and it is easy to implement.In this paper,the simulation model of micro grid is established in the MATLAB/Simulink software environment,and the simulation results of the control method are used to verify the better applicability of the second methods.Finally,a DSP control experimental platform composing of two three-phase inverters is constructed,and the control strategy is verified by experiments.the experimental results show that the control strategy used in this paper can not only achieve a reasonable distribution of power,but also improve the steady-state voltage value.