Abstract
Fractional frequency transmission is a promising technology for medium distance offshore wind power transmission. The key component in the fractional frequency transmission system (FFTS) is the modular multilevel matrix converter (M3C). It is regarded as the next generation AC/AC converter for high voltage and high power applications due to various advantages such as high-quality waveforms, scalability, and controllability. It is important to fully study its impact on the power network. The key to the understanding and impact is the development of a suitable model, which is the focus of this paper. A small signal model of the M3C taking into account the dynamics of the capacitor voltage, AC currents, and the control system is developed. Electrical quantities from both AC sides at different frequencies couple in the M3C since there is no DC link. The complicated nonlinear terms in ABC frame are isolated and transformed in DQ frame. The model is convenient to interface with the control system and external AC systems. Small signal analysis is carried out on the influence of the controller parameters and sub-module capacitance. The correctness of the proposed model is verified by comparing to a detailed electromagnetic transient model of the M3C simulated in RTDS.
Highlights
Offshore wind power develops rapidly in recent years
Traditional high voltage AC (HVAC) is not capable of long distance offshore transmission [2], while fractional frequency transmission (FFT) proposed in [3] is able to overcome its cable shortcoming and it is an economical solution for medium distance offshore wind power transmission [4]
This paper focuses on offshore wind fractional frequency transmission system (FFTS) application
Summary
Offshore wind power develops rapidly in recent years. Its penetration keeps growing and the market witnesses increasing investments and decrease of product prices [1]. J. Luo et al.: Small Signal Model of Modular Multilevel Matrix Converter for FFTS was proposed for M3C on medium voltage motor drives. A small signal analysis is carried out, giving insights to system stability and parameter selection on controller and sub-module capacitors Frequencies from both AC sides mingling in the M3C are isolated and decoupled. Multilevel converters for transmission applications contain up to several hundred sub-modules, making it mathematically inefficient to consider dynamics on every single sub-module for a small signal model. The differential equations of the AC currents are computed as: Id20
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