Static Var Compensating Device And The Analysis Of Its Voltage Stability

With the application of new craft and technology, and the improvement of the automation and intelligentization of electric devices, more and more people choose to use the devices with high precision, high performance, high efficiency high technology which require better power quality. Reactive power compensation and harmonic suppression are of the best ways of improving the power quality. Of all the reactive power compensating devices, the Static Var Compensator(SVC) which composed of Thyristor Controlled Reactor(TCR) and Fixed Capacitors(FC) has the advantage of high stability, small overshoot and high cost performance thus it is widely used. But its grid compensation would have an effect on the stability of the voltage of power system without detailed analysis, in the worst case, it can cause voltage instability and even voltage collapse. Above all, this thesis designed the SVC with the ability of compensating reactive power, and provided an objective analysis of the negative effect of SVC on voltage stability.Firstly, this thesis did a research on the design of SVC system, which is divided into two parts, FC and the control system of the TCR. The FC over compensates the inductive load which appears the most in the power grid. The TCR offsets the over compensated part of capacitive reactive power while at the same time injects harmonic to the system, so the design of FC must take into consideration of the filtering function. Based on the analysis of the harmonic injected by TCR, the respective FC filters are designed and the performance of these filters is verified by simulink simulation.Secondly, this thesis did a research on the control method of the thyristor in TCR, and based on the instantaneous reactive power theory, the calculation method of the three phase unbalance compensating susceptance is derived using p-q method. The thesis also established the control model of SVC. To obtain a stable and reliable triggering control over the thyristors in TCR, the design of hardware of the SVC controller use the dual-processor structure, in which the MCU takes charge of the peripheral interfaces and DSP executes the data process procedure. The SVC designed is verified in simulink simulation.At last, this thesis analyzed the impact of the SVC system on the system voltage. The voltage-current feature indicates that SVC can stabilize the bus voltage, however through the analysis of the voltage stability, this thesis reach a conclusion that if the adjusting rate of SVC is too slow or the compensating location is inappropriately chosen, the load would likely to be forced to work in the voltage instable zone, moreover, the system bus voltage may collapse.