Research On Dual Mode Inverter Control Of Distributed Wind And Solar Complementary Microgrid System

Under the microgrid system condition of two types of dual mode inverters,which can be island and connected to the grid,it is inevitable that the three-phase voltage imbalance will be encountered.As an important index of power quality in microgrid,three phase voltage symmetry plays an important role in the normal operation of microgrid.In addition,under the conditions of the actual user's power consumption,it is very easy to cause the unbalance of the three phase voltage of the load side due to the uneven distribution of the user's power or the external caused by various faults.At present,there is a more mature method to control the inverter under the balance grid and load.For example,from the grid operation of constant voltage constant frequency Vf control method,as well as the constant power PQ control method,in addition to droop control method.These methods are based on the three-phase voltage balance on the basis of proportional integral or proportional resonance and other tracking control methods.However,when the voltage is unbalanced,the negative sequence component of the voltage will appear with respect to the three-phase balanced condition.At present,most of the control methods are based on three phase voltage balanced condition,which is only contain positive sequence voltage and no negative sequence component.If the voltage is unbalance and we are still only control the positive sequence component,can lead to problems such as harmonic distortion,increase the output voltage and current,regardless of the load or the inverter will have a great impact.So it is necessary to separate the positive sequence and negative sequence voltage components under unbalanced voltage conditions and extract them separately.The methods used in this paper are filter separation method,symmetrical component method and delay signal method.In addition,the grid system,but also consider the design of grid PLL,the negative sequence component exists,if PLL with positive sequence component of the conventional phase locked there will inevitably be a failure,therefore,this paperstudies the phase lock methods of second order generalized integrator and decoupled double synchronous reference frame PLL to track phase in unbalanced grid.Base on the appeal method of positive and negative sequence component separation and PLL,these paper use the positive and negative sequence double loop control method of grid voltage and current,the instantaneous power control and negative sequence component suppression method,reduce the ooutput harmonics,maintain the stability and efficiency the maximum power in order to improve the effect of unbalanced load and grid environment for the inverter.Finally,according to the topological structure of inverter dual mode with load and grid,Matlab/Simulink simulation model is built based on grid and island mode,and the inverter operation simulation verification under the condition of the power unbalanced grid and load.In addition,this paper also introduces the circuit experiment platform with DSP28335 as the control core and the experimental work of the above theory and simulation.The simulation and experiment verify the correctness and feasibility of the control strategy.