Frequency Regulation of a Synchronous Generator in Association with a Back-to-Back Converter

Abstract

The synchronous generator in the power system controls the mechanical input power to regulate the frequency under normal operation, thereby delaying the speed of frequency regulation. This paper presents a frequency-regulating scheme of the synchronous generator that mitigates the frequency fluctuations caused by continuous output power fluctuations of a wind turbine generator. To achieve this, a back-to-back (BTB) converter is connected between the synchronous generator and the transformer. In the machine-side converter (MSC), to regulate the frequency within a narrow band, a control scheme that decreases the active power in the over-frequency section and increases the active power in the under-frequency section is implemented. In addition, to maintain the rotor speed of the synchronous generator within a narrow band, the speed controller adjusts its mechanical input power depending on the rotor speed variation. The power control scheme in the BTB converter uses the kinetic energy stored in the rotating masses of the synchronous generator for regulating the frequency. As a result, the rotor speed of the synchronous generator further fluctuates; however, the rotor speed controller can maintain the rotor speed within a narrow band. The simulation results in the modified IEEE 14-bus system indicate that the proposed scheme can significantly mitigate the frequency fluctuations caused by wind speed variations under normal operation.