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This paper presents a comparative study of dynamic performance of conventional VSC based HVDC and Modular Multilevel Converter (MMC) VSC based HVDC operating in back to back configuration. Voltage and rotor angle stability of the generator during power systems fault is analyzed. The simulated power system is composed by a back-to-back HVDC based on conventional VSC and the MMC connecting two weak systems. The power source is a 100 MW generator, which is equipped with an Automatic Voltage Regulator (AVR) and without Power System Stabilizer (PSS). The rated capacity of the VSC-HVDC is 100 MW. A vector controller is implemented in dq-axis to control the rectifier DC side voltage and the AC voltage or reactive power. This same control is used in the inverter side for frequency or active power and AC voltage or reactive power control. According to the results, conventional VSC-HVDC as well as the Modular Multilevel VSC-HVDC increase damping characteristic of power oscillations modes. Additionally the converter topologies for each system are analyzed.