Modelagem e controle de conversor multinível modular para sistema de transmissão em corrente contínua (HVDC)

Abstract

Due to the increase in energy demand, there is a need to study more effective solutions for electrical energy transmission, such as High Voltage Direct Current (HVDC) transmission systems, an alternative to current transmission systems, which are predominantly Alternating Current (AC). Among the main advantages of HVDC systems, the possibility of transmitting large amounts of energy over long distances with low losses stands out. In this context, this work presents a study of HVDC with Modular Multilevel Converter (MMC). This topology is suitable for several applications, as a result of lower switching losses, due to the lower switching frequency of the IGBTs, low harmonic distortion in the alternating current and modular structure that allows scalability in the construction. However, more complex control strategies are needed to control the power flow between the converters, in addition to the circulating current, to compensate for the voltage imbalance of the submodules in order to keep the voltage of the capacitors constant. For this purpose, independent control of active and reactive power was implemented through current vector control. Furthermore, in order to control the voltages on the capacitors of the submodules, an algorithm capable of hierarchically ordering the submodules according to the voltages of their capacitors was proposed. At each new work voltage cycle, it is determined which submodules must remain active and which must remain inactive. Furthermore, a circulating current controller was also implemented in the dq reference. Finally, computer simulation results were evaluated, via PSCAD software, to validate the dynamic response of the proposed controllers.