Investigation of methods for loss of mains detection for domestic scale distributed generation

Abstract

The drive to lower the environmental impact of power generation has underlined the importance of distributed generation (DG). DG allows a multitude of dispersed renewable technologies to be included within the energy supply network. The energy generation of a DG installation doesn’t necessarily coincide with local power consumption; grid connec- tion allows surplus local power to be distributed using the wider power network. This results in a variety of DG units requiring grid connection. A power electronics interface is commonly needed to achieve connection between the DG unit and the distribution network. Whilst DG units are available in a multitude of sizes, the focus of this work is domestic scale DG. Single phase power inverters are commonly used to connect DG units to the utility. An issue associated with the interconnection of generators within the distribution network is the formation of power islands. A power island is defined as a section of the power network, consisting of generators and loads, which becomes electrically isolated from the wider power network. The majority of grid connection standards stipulate that the grid con- nection power electronics interface must include a robust loss of mains (LOM) detection routine. Once a LOM event has been detected the output power of the DG unit must be reduced to zero to guarantee no power island exists. This thesis details the work carried out during the completion of an En- gineering Doctorate (EngD) Degree in Power Electronics, Machines and Drives. A low voltage laboratory test bench and associated simulation model have been designed and constructed to allow multiple in-the-loop based LOM detection methods to be presented, analysed and compared. A new LOM detection technique has been created, referred to as the proposed technique. The proposed technique is a hybrid LOM detection technique which uses a passive routine to signal when a LOM event may have occurred and an active technique to confirm the LOM event. The passive routine uses Fourier analysis to constantly monitor the magni- tude and spread of high frequency voltage components present at the DG unit connection point. The active confirmation routine is an active power shift function. A fully rated 500W laboratory test bench was created which allows the proposed technique to be verified at power levels more realistic for a standard DG unit installation.