Hi Micha,
In order to use d3 provided out of the box you have to use jQuery.sap.require("sap.ui.thirdparty.d3") or specify D3 in libs attribute inside UI5 bootstrap tag. In order to use different version of D3 lib eliminate this code and link necessary d3_v3.js file via <script> (or put it into you'rs project folder and use jQuery.sap.require() ).
Denis.