| Influenced by the energy crisis and environmental pollution,cheap and clean renewable energy has gradually entered people’s vision,and then micro-grid based on distributed generation emerges as the times require.Because the power flow of DC micro-grid is only DC bus voltage without precise control of frequency,phase and reactive power,it not only makes the control of DC micro-grid simple and flexible,but also reduces its loss.Because of its low cost and high economy,DC microgrid has been widely studied at home and abroad.The safe and stable operation of DC micro-grid depends strictly on the power electronic converters.Aiming at stabilizing the DC bus voltage,this paper coordinates the working modes of the converters,proposes a simplified hierarchical control strategy,and suppresses the bus voltage fluctuation through grid-connected converters.A control strategy of DC micro-grid grid grid-connected converter based on differential feedforward of bus voltage is proposed.The details are as follows:In the first part,taking the typical grid-connected mode of photovoltaic and energy storage DC microgrid as the research object,the working mode of each converter in traditional bus voltage hierarchical control is analyzed,and the conclusion is drawn that there are many working modes and complex switching between modes in traditional bus voltage hierarchical control.The simplified bus voltage hierarchical control is put forward.There is no voltage source and current in the control of photovoltaic unit.The switching between sources works at the maximum power tracking point,the grid-connected converter and energy storage unit stabilize the DC bus voltage,and the energy utilization rate is improved.The power-voltage characteristic curves of the simplified micro-source converters and the control block diagrams of the micro-source converters are given.Finally,the traditional bus voltage hierarchical control and the simplified bus voltage hierarchical control are simulated and verified.In the second part,in order to solve the problem of low inertia and poor anti-disturbance ability of DC microgrid,the current control strategy of DC microgrid grid-connected converter based on bus voltage differential feedforward is proposed.Taking three-phase half-bridge grid-connected converter as the research obj ect,the linear control relationship between DC bus voltage and inductance current is established according to inequality constraints.The change rate of bus voltage is combined with the steady-state current value of the inductance of the connected network as the control instruction value of inductance current.To reduce the excessive voltage drop of the bus under disturbance,the virtual capacitor is designed by using the energy-power relationship and introduced into the bus.Line voltage control loop can improve the anti-disturbance ability of DC micro-grid without increasing the actual capacitance,and stability analysis of DC micro-grid after adding virtual capacitance is given.Finally,the effectiveness of the proposed control method before and after adding virtual capacitors is compared and analyzed. |
