Energy-saving multi-stage pump frequency conversion linkage system

The invention provides an energy-saving multi-stage pump frequency conversion linkage system which comprises a first-stage pump pipeline and a second-stage pump pipeline, the first-stage pump pipeline comprises a plurality of first-stage pump branches, each first-stage pump branch is provided with a first-stage pump and a water chilling unit, the first-stage pumps are communicated with the water chilling units, and the first-stage pump branches are connected in parallel; the second-stage pump pipeline comprises a plurality of second-stage pump branches, the second-stage pump branches are connected in parallel, one or more second-stage pumps, load units and bypass pipes which are connected in parallel are arranged on the second-stage pump branches, the second-stage pumps are connected with the load units, and the bypass pipes, the second-stage pumps and the load units form a loop structure; the first-stage pump pipeline is connected with the second-stage pump pipeline; the first-stage pump pipeline control met