Although there are many studies on application of FACTS unit, especially application of reactive power generating unit for power system to enhance voltage stability amplitude and transient stability as considered, the evaluation and selection of suitable power generating unit (STATCOM or SVC) as well as optimal compensation size in the analysis of steady and transient state is not paid attention to. This article studies the above described issues to give a solution to install reasonable reactive power generating source (kind of Var source, location, size) for the power system. The analysis will be based on the technical factors rather than economic ones. 500kV grid system in Vietnam will be used in the calculation until 2015. To deeply evaluate, the implementation plan of reactive power compensation was only studied for 500kV grid in the South, where the load demand is large and can be dramatically increased. The results of power flow calculation, the analysis of characteristics of PV, OPF, and transient stability were studied through PSS/E-30 software.

This paper will discuss and demonstrate how FACTS controllers shunt Static Synchronous Compensator (STATCOM) and Static VAR Compensator (SVC) have successfully been applied to power system for effective regulating system voltage. One of the major reasons for installing a STATCOM or SVC is to improve dynamic voltage control and thus increase system load ability. In this paper a STATCOM and SVC are used to regulate voltage in a power system. When system voltage is low they generate reactive power (capacitive). When system voltage is high they absorb reactive power (inductive). In this paper comparison is also performed between SVC and STATCOM under fault condition and it is show that STATCOM have the ability to provide more capacitive power during a fault over SVC. All the simulations for the above work have been carried out using MATLAB/SIMULINK environment.

Traditional uncontrolled or phase controlled cascade multilevel inverter only can realize one-direction transmission of energy. This paper presents a complex energy feedback cascade inverter topology with full-controlled, phase controlled Power units and its control strategy. For the full-controlled units, use PWM converter to replace the traditional rectifier bridge, and then combine with H-bridge inverter, the two-direction inverter is realized. The others remain phase controlled structure. According to the pump-up voltage in the energy feedback process ,a new method using the output side DC voltage closed loop control is proposed to prevent DC voltage shock and make all energy feedback to grid .Then it was verified in a cascade inverter with five units in which only three units are full-controlled. This inverter has the merits that it can automatic realize two-way flow of energy, the input currents approximate sine, the DC voltages control stability, the output voltage waveform is good and the phase shifting transformer structure is also simplified, etc. Simulation showed its feasibility and effectiveness.

The correct and quick operation of backup power automatic switching（BPAS）devices is an effective guarantee of reliable power supply to the system. However, when transformer substations are connected to small-capacity distributed power like the local small hydropower stations, the conventional BPAS devices usually fail to get into operation, which leads to the loss of power in some parts of the system. To solve this shortage，this article comes up with an improved scheme of BPAS, which has been proved through PSCAD simulation to be effective in enhancing the stability and reliability of the power grid