Access control method for parallel direct current power supplies and device thereof

An access control device for parallel direct current power supplies, applied to a grid-connected inverter, wherein,

• a direct current side of the grid-connected inverter is connected with n direct current power supplies in parallel via 2n switches;
• and
• the access control device for the parallel direct current power supplies comprises:
• a control unit and an insulation resistance detection circuit, and n is a positive integer greater than 1;
• wherein,
• one ends of n of the 2n switches are connected with positive output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a positive input terminal of the insulation resistance detection circuit and a positive input terminal of the grid-connected inverter;
• one ends of the other n of the 2n switches are connected with negative output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a negative input terminal of the insulation resistance detection circuit and a negative input terminal of the grid-connected inverter;
• the insulation resistance detection circuit is configured to detect single insulation resistances to ground of the n direct current power supplies and a total insulation resistance to ground of direct current power supplies currently in parallel;
• and
• the control unit is configured to:
• control the 2n switches to be open or closed, and determine whether the single insulation resistance to ground each meet a first preset condition;
• control, in a case that the single insulation resistances to ground fail to all meet the first preset condition, each switch connected with a direct current power supply, a single insulation resistance to ground of which fails to meet the first preset condition, to be open;
• control each switch connected with a direct current power supply, a single insulation resistance to ground of which meets the first preset condition, to be closed;
• determine whether the total insulation resistance to ground meets a second preset condition;
• control, in a case that the total insulation resistance to ground fails to meet the second preset condition, a switch connected with a direct current power supply, a single insulation resistance to ground of which is smallest of the direct current power supplies currently in parallel, to be open;
• and repeatedly determine whether a total insulation resistance to ground of direct current power supplies currently in parallel meets the second preset condition, and control, in a case that the total insulation resistance to ground fails to meet the second preset condition, a switch connected with a direct current power supply, a single insulation resistance to ground of which is smallest of the direct current power supplies currently in parallel, to be open, till the total insulation resistance to ground meets the second preset condition.