What is meant by Loss-less economic dispatch?

Economic dispatch is the short-term determination of the optimal output of a number of electricity generation facilities, to meet the system load, at the lowest possible cost, subject to transmission and operational constraints. The Economic Dispatch Problem is solved by specialized computer software which should honour the operational and system constraints of the available resources and corresponding transmission capabilities

to Avoid this deficiency it necessary to be use " FACT Controller"

Like 

1)Series Controller

2) Shunt Controller

3)Shunt series Controller

4)Series,Series Controller