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A hierarchical control architecture is proposed for the optimal day-ahead commitment of multiple grid support services within a virtual power plant (VPP). The day-ahead optimization considers pricing and cost data to determine the commitment schedule, and a robust Model Predictive Control (MPC) approach is included to minimize the unbalance fees during real-time operations. The multi-level control has been demonstrated experimentally using a hybrid test system, where the VPP is formed of a commercial 240 kW, 180 kWh battery energy storage system (BESS), while the additional assets are modelled in a real-time digital simulator (RTDS). Two case studies are analyzed: the first assumes a purely-electrical VPP, with a single connection to the public network; the second involves a multi-energy approach, with the introduction of a gas-supplied Combined Heat and Power unit (CHP). Both winter and summer price scenarios are tested. The results show the superiority of the multiple-service operation compared to providing a single grid support service. For example, the net revenue is increased by 30% (winter) and 7% (summer) when compared to just frequency regulation, and by +99% (winter) and 30% (summer) when compared to only energy arbitrage. [ABSTRACT FROM AUTHOR]

This paper analyzes some operational issues of three-phase surface-mounted permanent magnet synchronous generators (PMSGs) connected to a diode rectifier. This simple configuration coupled to a single-switch dc–dc converter is used in small-scale wind energy conversion systems, as well as in energy harvesting systems, to reduce costs. The diode rectifier causes an intrinsic limit for the maximum convertible power, which is related to the load impedance matching, and additional joule losses due to the distorted currents. By using an analytical steady-state model of the rectifier and of the PMSG, this paper discusses how to achieve two particularly meaningful operating conditions characterized respectively by the maximum power transfer and the maximum power per ampere. The theory is validated by simulation and test results on a prototype. [ABSTRACT FROM AUTHOR]