I don't know if there's more special word for it in general, but in the US it's known as [the](https://en.wikipedia.org/wiki/Connecticut_Compromise) 

> Connecticut Compromise (also known as the Great Compromise of 1787 or Sherman Compromise) was an agreement that large and small states reached during the Constitutional Convention of 1787 that in part defined the legislative structure and representation that each state would have under the United States Constitution. It retained the bicameral legislature as proposed by Roger Sherman, along with proportional representation of the states in the lower house, but required the upper house to be weighted equally among the states. Each state would have two representatives in the upper house.

Also, this form of compromise is rather common in other [federations with bicameral legislature](https://en.wikipedia.org/wiki/Federalism#Bicameralism):

>  A federal upper house may be based on a special scheme of apportionment, as is the case in the senates of the United States and Australia, where each state is represented by an equal number of senators irrespective of the size of its population.

> Alternatively, or in addition to this practice, the members of an upper house may be indirectly elected by the government or legislature of the component states, as occurred in the United States prior to 1913, or be actual members or delegates of the state governments, as, for example, is the case in the German Bundesrat and in the Council of the European Union.