A Closed Loop Control Strategy for a Frequency-Only Converter with High Efficiency

A. Benaboud and A. Rufer (Switzerland)


NPC, three level converter, Square Wave Modulation, high efficiency, angle shift control, closed loop control.


Many electric power generators use gas turbines as power sources, coupled through a mechanical gearbox in order to adapt their synchronous speed to the optimal rotation speed of the turbine. This paper proposes to replace the mechanical gearbox with a flexible electronic solution which would offer a higher efficiency. A new control strategy is proposed for the three level Neutral Point Clamped converter, which is characterized by its high efficiencydue to the use of square-wave modulation. The main advantage of this modulation is the quasi absence of switching losses. In this modulation, only the frequency can be adapted between the input and the output voltages, but their magnitudes are not freely controllable. The active and reactive powers produced can be controlled by the generator’s excitation, as well as both the angle shift be tween the generator’s and rectifiers's voltages and between the inverter’s and network’s voltages. The simulation and a partial experimental results for different operating points highlight the capabilities of the proposed control strategy.

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