This paper describes power system stabilization with a VSG (virtual synchronous generator) control scheme by using VSC (voltage source converter) type HVDC (high-voltage DC transmission) with SMES (superconducting magnetic energy storage). Power system stabilization schemes that prevent instability due to the disturbance in grids that are connected to renewable power sources were studied. This paper further discusses the effect of SMES connected to the DC link of the VSC-HVDC system for the compensation of power fluctuation caused by distributed generators in one AC newtork of HVDC for eliminating the influence on the network on the other side to which the HVDC is connected. Simulations using PSCAD/EMTDC were carried out to evaluate the performance of the applied control system.

The hybrid AC/DC microgrid systems have been popular and being developed as the next generation power systems because of the comprehensive combination of both AC and DC microgrid systems. Power management scheme is one of the most critical operation aspects for hybrid microgrids because the system is operating with various generation sources and loads such as renewable energy sources, energy storage systems and AC and DC loads. Therefore, in this research, control strategies and power management scheme is considered for all possible operation modes of standalone and grid-connected conditions. In the existing microgrid system in Electrical Power Engineering department in Yangon Technological University, rooftop PV plant and battery are cooperating to supply the electricity. The inverter in this system allows the unidirectional power flow from DC to AC and there is no specific power management system for grid-connected and standalone operation mode. To provide bidirectional power flow in the existing system, the configuration of converter and control strategies for power management system are developed in this research. To provide the bidirectional power flow between AC bus and DC bus, the bidirectional interlink power converter with high frequency isolation is applied. The control system including the power balancing between generation and demand, DC link voltage control and AC link voltage and frequency control is considered. By applying droop control method in the developed system, power flow balancing between AC bus and DC bus is maintained. And also, using high frequency isolation transformer in interlink converter provides fast response of the system performance and maintaining continuous power supply within each AC system and DC system during disturbance condition in one subsystem. The performance of the proposed power management system is demonstrated by using MATLAB/Simulink.

This paper presents the small signal stability of multi-machine power system over the 58-Bus, 26-Machine, Yangon Distribution Network and is validated with MATLAB software under various disturbance conditions. Time-domain solution analysis is employed to determine the small signal dynamic behavior of test system. Transtability model is used to perform time-domain simulation in SIMULINK. The simulation is carried out for normal condition, reference voltage of regulator (Vref) disturbance, mechanical torque (Tm)disturbance and network (fault) disturbance and the conditions of change in center of inertia for rotor angle (delta COI),  slip for center of inertia (slip COI), field current and mechanical torque are observed. According to the simulation results, perturbation of Vref shows only instability on the system. But ramping of Tm and network disturbance can cause large disturbance on the system and unstable conditions can be observed.

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