| Static synchronous compensator is widely used in electric power system, which reacts on improving power factor of electric system and eliminates the harmonic. It enhances the quality of power supply remarkably, and decreases the ullage of electric line. At present, static synchronous compensator is mainly used in the area of high voltage and huge capacitance, but is rarely used for low-voltage and small capacitance of civil building. The paper tries to develop a kind of static synchronous compensator which can work at 380/220V system voltage, have 100kvar capacitance, or lower. As there are a lot of lighting and electro thermal load, which works under single alternating voltage, three-phase low-voltage power system is unusually unbalanced. Therefore, the static synchronous compensator must have ability of working normally at unbalanced power system, and act on balancing three-phase current, besides compensating unbalanced reactive power of low-voltage power system and eliminating the harmonic.Static Synchronous Compensator proposed in this paper, can be used in power supply system of civil architecture. The technique can perform effectively on compensating unbalanced reactive power of low-voltage power system and eliminating the high harmonic and zero-sequence currents. The main works and conclusions are as follows:With four-leg converter designed as the main circuit, the mathematical model of Static Synchronous Compensator with four legs is established, and the controllability of this model is theoretically analyzed. The paper proposes the concept of quasi-controllability on the basis of incomplete controllability. This concept offers theoretical bases to calculate and extract the scope of error current of Static Synchronous Compensator and is of great importance. Static Synchronous Compensator is designed by method of detecting the scope of error current based on the generalized instantaneous reactive power theory. Compared with other detection methods, this method can keep well detection precision all the same and get reference current, when the voltage wave is freaky. To control the error current, a way of controlling current directly is used in this paper which is based on nonsingular transform. It transforms the three-phase voltage and current toαβ0 coordinates, and definitely presents the coordinates composed by reactive current, active current and zero-sequence current. Finally, reference value of compensating current of each sequence and the zero-sequence current can be obtained after inverse coordinate transformation. During the research period, the paper analyzed the parameter of important organ, and listed the calculating process and results of them, which extend the preliminary design of the research.During the research period, particularly in the end, the paper did simulation with MATLAB. The simulating results show that the Static Synchronous Compensator based on this paper's theory can well compensate reactive power in the three-phase unbalanced power system, its dynamic response is highly enhanced and it can effectively eliminate the harmonic and zero-sequence current. As its feature different from other compensator, the source shows favorable balance state after this device working, in spite of the load is remarkably unbalanced in each phase, and the zero-sequence current is eliminated."Designing Criterion of Civil Building"ordains that the radius of the low-voltage distributing power system should not exceed 250 meters. So the low-voltage transformer substations distribute quite densely in the power supply system of civil buildings, and the dosage of the device used for improving power factor is huge. Finally, we can forecast that the applying foreground of the'low-voltage static synchronous compensator would be favorable.
|
PDF Full Text Request