Research On The Parallel Control Techniques Of Inverters In Microgrid

The power production mainly depends on the thermal power generation in our nation, this way has polluted ecological environment seriously. Clean energy contains great power, like solar energy, wind, nuclear energy et al, Distributed Generation(DG) is a form of use clean energy, but the utilization of it is very low because of natural conditions and grid-connected techniques. In this situation, the concept of microgrid has played an important role of supplement for DG, with the enlargement of power generation equipments and loads power, traditional power supply method depends on one inverter has not satisfied consumer power standard, so parallel inverters have become more and more popular in microgrid.The paper focus on microgrid includes parallel inverters operation, the question of current sharing and the question of power quality influenced by line impedance characteristics is researched. Influenced by line impedance in microgrid, inverter's equivalent output impedance is combine resistive element and inductive element, traditional control algorithm has some drawbacks in this situation. In this paper we adopt improved resistive algorithm for parallel system and verify its effective by simulation.Firstly, with two parallel inverters as the model. The difference in voltage amplitude and the difference in voltage phase influence on parallel system are analyzed. The character of traditional double closed loops control is analyzed too. At the same time, three controllers include proportional integral, proportional resonant and quasi resonant are analyzed, we know their advantages and shortcomings respectively.Secondly, in order to adopt improved resistive algorithm in parallel system, we should change traditional double closed loops control structure of inverter. The methods of adopting the structure of multiple closed loops with quasi resonant controller and add virtual complex impedance are researched by us, according to theoretical analysis, with multiple closed loops as the basis, the inductive element of the inverter equivalent output impedance is eliminated and the resistive element of it is increased if quasi resonant controller and virtual complex impedance own appropriate parameters respectively. Improved resistive algorithm is introduced to analyze parallel system's dynamic performance and stable performance by small signal analysis, we know the way of different droop coefficients influence on parallel system.At last, aim at test the new algorithm's effectiveness, the simulation example is set up in Matlab/Simulink. Simulate it with improved algorithm, the parallel system's characteristics and the power quality with different controllers are simulated, the simulation results demonstrate that two points: on the one hand, the algorithm is available and efficient in parallel system, on the other hand, quasi resonant controller has more advantages than proportional integral controller in ensure load power quality with this control structure and improved resistive algorithm.