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To understand the operation principle of the modular multilevel converter (MMC) deeply, it is necessary to study the harmonic characteristics of the MMC theoretically. Besides, the analytical harmonic formulas of the MMC are useful in designing the main circuit, reducing the losses and improving the waveform quality. Based on the average switching function and the Fourier series harmonic analysis,...
A circulating current suppressing controller (CCSC) is presented to eliminate the inner balancing currents in modular multilevel converter (MMC). Based on the double-fundamental-frequency, negative-sequence rotational frame, the three phase alternative circulating currents are decomposed to two DC components, and are limited to a low level by a pair of proportional integral controllers. This control...
In HVDC systems, power converters are well known the generators of harmonics on both ac and dc side. Because of the interaction between ac and dc systems, some kinds of disturbances in the ac or dc side may cause the fundamental or second harmonic current on the dc side. When the dc loop of the HVDC system has natural resonant frequencies on the fundamental or the second harmonic frequencies, the...
In this paper, the effects of different types of excitation systems and PSS on the SSR damping characteristics are studied. The complex torque coefficient approach realized by time domain simulation - the test signal method is adopted. The studied system consists of a single-machine infinite bus system. Three types of excitation systems - IEEE AC1A, AC2A, ST1A excitation systems are selected as examples...
Voltage source converter (VSC) based HVDC is a multivariable, strongly coupled nonlinear system. It is quite difficult to establish the precise mathematic model of the VSC. This paper adopts the theory of the nonlinear transformation and the feedback linearization of nonlinear system, establishes the nonlinear mathematic model of the VSC in d-q synchronous reference frame. The decoupled control strategy...
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