In the recent years multiple European and national initiatives for support of “green” renewable generation, reduction of emissions and innovation in power section has led to huge expansion of Distributed Generation (DG) in Europe. However, distribution systems do not always keep up with rates of growth of DG. In fact, distribution systems are starting to face problems, like reverse power flow and increased voltage. Not uncommon, when the limits are reached and no more generation can be connected to the system without special measures, putting at risk “green” energy targets. To understand the scale of DG extension, this thesis presents an overview of different DG type development tendencies. Moreover, it is analysed why each DG type is present in the network and why it is profitable for developers to invest in this business. A survey was undertaken between real developers of existing and planned DG of different types to understand what tariff they are going to use and what connection conditions are economically viable to them. It gave a clear indication of potential connection scenarios and behaviour of DG on the network and helped to build accurate models. The author has analysed the existing power system modelling tools and distribution system planning methods and found drawbacks or even inability to DG planning in present conditions. A unique complex approach is proposed within this thesis, which allows modelling, settings targets, analysing behaviour and making decisions related to DG planning. The proposed models are not only based on fine mathematics, but also incorporate deep practical aspects and analysis of large amount of real data. For completeness, all models are brought to a single scale and full calculation algorithm together with a test case is presented. The algorithm not only offers known expensive means of overcoming network issues caused by DG, but also review elegant approaches based on modern digital and telecommunications technologies. Multiple calculation targets are specified, which will be of particular interest to users, including Distribution Network Operators and authorities. The doctoral thesis has been written in English, it contains 155 pages, 73 figures, 23 tables and 75 references.