A Comprehensive Approach for Analytical Modeling of Line Commutated Converter based Multiterminal HVDC Systems

This paper presents an analytical model of Line Commutated Converter (LCC) based Multiterminal (MT) High-Voltage Direct Current (HVDC) systems. The approach is based on space phasor transformation and provides a modular HVDC model, since every converter of the MT system is carried out as an independent network. For each switching state of the converter - which is either two valve conduction or commutation - the space phasor transformation provides a subsystem in the complex plane; each of this consists of a voltage source, a grid impedance and a transformer impedance. The commutation current of each converter is derived from the imaginary part network of the respective subsystem. A generalization of the real part network leads to a generic subsystem for all switching states of the converter. A succeeding connection with a state space model of the DC network is performed; applying mesh analysis yields a differential equation system in order to derive the DC current. To verify the accuracy of the developed model, a comparison with an electromagnetic transient (EMT) model is carried out, which shows the consistence of the dynamic behavior.