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The paper presents a study on synchronous machine that can operate as a generator and a compensator simultaneously. Modifying the field current, the reactive power injected into the supplying network is changed. An automated system is described which injects the maximum reactive power for a given amount of electrical active power, under the following conditions: the stator current is limited to the rated value, the field current is maximum admissible, the grid voltage is limited to a maximum reference and over-excited state of the machine is assured.

The paper presents a functional analysis of a singlephase inverter of mid-range power and its optimization based on three performance criteria. The studied inverter is an IMD (Inverter Mono-Phase Digital) with a bridge of IGBT transistors used for supplying vital consumers for guiding, control and safety of railway transport. The inverter operation is analyzed under different load situations together with options for maximizing the efficiency, diminishing the total harmonic distortion factor and reducing the intake current of the adapting transformer, by varying the capacity and inductance of the filter. The results are obtained through experimental tests using high performance measuring apparatus.