Power Distribution Control Of Interlinking Converter Considering Voltage-Frequency Correlation Coefficient In Hybrid Microgrid

With the extensive utilization of clean energy,the new energy technology has been developed widely.The concept of "Microgrid" has also been put forward.The operation characteristics and control scheme of microgrid are widely studied by scholars.At present,the distribution network in China is still dominated by AC.Therefore,AC/DC hybrid microgrid becomes the mainstream of microgrid technology.The interlinking converter(IC)is the bridge connecting AC bus and DC bus,which is the key equipment to realize bidirectional energy flow in microgrid.However,the control strategy of IC is more complex than inverters or rectifiers.Firstly,for the requirements of power balance on both sides of IC,the droop characteristics of AC and DC subgrids should be coordinated and controlled.The power balance characteristics of AC and DC sections are analyzed according to the power operation characteristics.Combining the virtual synchronous machine characteristic and the virtual capacitance characteristic of IC,the DC voltage and AC frequency are related.A novel hybrid droop control of IC considering voltage-frequency correlation coefficient is proposed in this paper.The three typical operating conditions in islanding state are simulated.The power can flow between AC subgrid and DC subgrid.The power distribution function of IC is realized.Secondly,when the power is transmitted by IC,capacity of both sides should be considered to properly distribute power flow.So,the capacity weight factor is introduced into the power balance equation.The capacity constraints are derived according to the voltage-frequency range of the hybrid microgrid.Then the power distribution control of IC is optimized.Through the analysis of droop characteristics of subgrids,the equivalent droop coefficient of the subgrid is obtained.Combining the new hybrid droop control equation,the power reference value of IC is calculated.The simulation results show the power distribution between AC/DC microgrid is optimized by introducing the capacity weight factor.Power can be properly shared and flow between subgrids.The regulation ability of distributing generations is full used.Finally,the hybrid microgrid system has many controllers and poor ability to resist frequent loads switching because of its complexity.The voltage feed-forward control is added in the design of the controller to reduce the impact of voltage fluctuation on output current of IC during load switching and improve stability of the system.The effect of stability optimization is simulated.And the effect of feed-forward control is verified.