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Normally, lookup-table-based methods are being utilized for loss-minimizing control of permanent magnet synchronous motors (PMSMs). But numerous repetitive experiments are required to make a lookup table, and the program size becomes bulky. In this paper, analytic methods for finding the loss-minimizing solution are studied. Since the solution lies either in the interior or on the voltage limit boundary, two different cases are dealt with separately. In both cases, fourth-order polynomials are derived. To obtain approximate solutions, methods of order reduction and linear approximation are utilized. The accuracies are good enough for practical use. These approximate solutions are fused into a proposed loss-minimizing algorithm and implemented in an inverter digtal signal processor. Experiments were done with a real PMSM developed for a sport utility fuel cell electric vehicle. The analytically derived minima were justified by experimental evidences, and the dynamic performances over a wide range of speed were shown to be satisfactory. Index Terms--Fuel cell electric vehicle (FCEV), loss minimization, permanent magnet synchronous motor (PMSM).

Small- and medium-sized distributed generation (DG) systems in a microgrid normally have inverters, and the inverter outputs are connected to the grid through an LCL filter. In this paper, we are interested in designing a DG inverter that behaves like a uninterruptible power supply (UPS) for its dedicated loads, while enabling power flow control with the microgrid. If the grid power is lost, then the DG system can be transferred smoothly to the island (stand-alone) operation. This islanding capability provides a higher reliability of the local ac bus than the conventional power system. In order to have such a UPS functionality, the inverter is desired to have a high control bandwidth, which is required for regulating the AC bus voltage at the presence of nonlinearities and unpredictable behaviors of the loads. As for a fast controller, a two-degree-of-freedom (DOF) controller is applied to the LC filter plant with the inverse dynamic model. The voltage command levels are selected considering the amount of power share with the grid. The effectiveness of the proposed control scheme is shown by experimental results. Index Terms--Distributed generator (DG), inverters, microgrid, two-degree-of-freedom (DOF) controller, uninterruptible power supply (UPS).

In the design of a parallel resonant induction-heating system, choosing a proper capacitance for the resonant circuit is quite important since both output-power maximization and capacitor heat loading should be considered. The temperature rise often blows up the water-cooled capacitors in high-power induction heaters or reduces the lifetime of capacitors significantly. This paper, therefore, presents a method of finding an optimal capacitance that maximizes the output power while considering the capacitor loss at the same time. To count the effect of the capacitor heatup, an equivalent series resistance is included in the model. Based on the equivalent circuit model, the output power and the capacitor loss are obtained as the functions of capacitance, and an optimization technique is applied treating the capacitance as a control variable. The effectiveness of the proposed method is verified by simulations and experiments. Index Terms--Equivalent series resistance (ESR), induction heater, optimal selection, parallel resonant circuit.