The Study On Smooth Switching Control Strategy Of Multifunction Active Power Filter

With power electronic technology develops rapidly in recent years,a lot of power electronic devices are applied in the power system of generating equipment and electric equipment.The harmonic pollution is more and more serious.Governance harmonic problem is around the corner,so the research of active power filter is increasingly valued.On the other hand,micro-grid is developing rapidly for sources of energy such as solar energy,wind energy.Its core structure is the inverter.Due to the structure of inverter is only different on DC-side load compared with active filter.If the inverter and the active filter is implemented on the same set of equipment,it can greatly reduce the cost,and so this paper studies multifunctional active filter with the active power filter and inverter.Firstly,the mathematical model of the traditional active filter is introduced and deduced,controller of AC-side current and DC-side voltage is current inner loop and voltage outer loop of the double closed loop control strategy.As the process impacts on power grid which the DC-side capacitor voltage reaches the stable process quickly,a way of charging the capacitor to a reference value is adopted.Secondly,grid controller strategy and off-grid controller strategy are separately studied for active filter with the energy storage system.In the grid,the PQ control strategy is used,making multifunctional active filter compensate harmonic and reactive power and inject power to the grid,realized the power factor of 1.For the off-grid control,the traditional voltage frequency control and virtual synchronous generator control are studied and analyzed.Voltage frequency control maintains voltage and frequency constantly so that they could not being affected by the fluctuation of the load,but it is very high requirements for energy storage system;Virtual synchronous generator control can dynamically adjust the frequency and voltage according to the load,namely the droop is maintained at the steady state and synchronous generator mechanical inertia is maintained at the transition state.Then models are built in Simulink platform,and the simulation results demonstrate the effectiveness of the three kinds of control strategies.Finally,this paper studies the voltage amplitude tracking,phase tracking and current tracking control strategy for the voltage and current shock produced by multifunctional activefilter when multifunction active filter is switched back and forth between grid and off-grid.Under voltage amplitude tracking and phase tracking,virtual synchronous generator controller has the characteristics of the secondary frequency modulation and voltage regulation.Phase tracking notices the phase fluctuations near 0 and near 2?which the traditional phase tracking doesn't notice,this paper puts forward the improvement strategies accordingly.Phase difference passes sine link first,then passes PI regulator.PI regulator outputs compensation frequency,and fluctuations is solved near 0 and 2?.When system switches,voltage outer loop controller of the system output reference value and the current inner ring current value differ too big,tracking grid load current is adopted.The control strategy is verified by simulation.The simulation results show the correctness of the seamless switching control strategy.