Voltage control method for photovoltaic DC micro-grid bus

The invention provides a voltage control method for a photovoltaic DC micro-grid bus to solve the voltage stability problem of a photovoltaic DC micro-grid bus. The voltage control method comprises a first step of dividing the DC bus voltage into three layers by taking a system DC bus voltage reference value as a threshold according to the balance principle of photovoltaic array output power and load power; and a second step of conducting layered coordination and control, in which, as for the first layer, when an (i)U(/i)dc1 is in the range of 239.8-242.6V, the system is in an island operation mode, and the bus voltage control adopts a droop control method; as for the second layer, when an (i)U(/i)dc2 is in the range of 249.6V to 252.4V, the system switches to grid-connected operation, a network-side interface is at an inversion state, and the Udc2 is adjusted by directly adjusting a d axis component id of an output current of a grid-connected inverter; and as for the third layer, when an (i)U(/i)dc3 is in the range of 259.6V to 262.2V, the system enters the island operation control, a micro-grid is separated from a power grid, the bus voltage is stabilized still by the droop method, and the distribution of the load power is achieved through addition of a virtual output impedance ring.