The issue of high efficiency had to be dealt with with appropriate converter design; more specifically, the research team studied and developed the following solutions:

1. AC/DC conversion was implemented by the use of parallel converters. These converters were hierarchically controlled, depending on the recovered energy amount, so each time the number of “active” converters was one that matches electrical power generation. This way the converters always operated close to their nominal power, where they perform maximum efficiency, also maximizing the whole AC/DC conversion efficiency under any point of operation. Moreover, this was a modular design approach, which enabled the implementation of different power levels. The exact power level for each converter module and its dynamic behaviour was determined during simulation and evaluation process.
2. AC/DC modules had unity power factor and low THD (less than 5%) at the generator side (PFC converters); this way, synchronous generator was not charged with reactive power and electromagnetic compatibility issues are eliminated. ECRG-UP has significant experience in the development of high-efficiency PFC converter topologies and control techniques, based on PWM DC/DC topologies, as well as by the development of a 2kW PFC on board charger for electric vehicles. The selection of the PFC converter topology initially depended on the output rms voltage value of the PM generator. More specifically, if the peak AC voltage is always lower than DC bus voltage (270V) then boost type topologies can be considered; otherwise step-down configurations have to be adopted. Generally, boost type topologies were considered to be more suitable for PFC applications in the range of 1 – 10kW, due to the continuous input current shape that they produce. Moreover, the production of low AC voltage (100Vrms – 160Vrms) by the PM generator eases human security against electric shock.