Variable speed genset with full rated power converter using readily available industrial products

Although a classic diesel genset may reach 35% efficiency at nominal load, it has very poor efficiency at low load conditions. Still, these conditions often occur in real world applications when combining gensets with variable autonomous loads. Previously, the authors built a hybrid genset prototype achieving fuel consumption reductions of over 30%. As an alternative to this hybrid genset, this paper reports on a variable speed genset prototype. To demonstrate a higher fuel efficiency, a prototype 50 kVA variable speed genset has been built using readily available industrial products. A diesel internal combustion engine supplies power to a PM synchronous generator to produce variable voltage, variable frequency AC. Using a four-quadrant variable-frequency drive and transformer this electrical energy is converted to produce an autonomous 4-wire 50 Hz 3×400 V grid. Operation principle, prototype implementation, first load tests (speed response and power quality) and possible improvements are discussed in this paper.