الفهرس | Only 14 pages are availabe for public view |
Abstract The thesis is concerned with applying a convenient simulation technique for studying the performance of an on-line static UPS system under different steady state and transient conditions. The PSPICE simulation package is found to be a convenient tool for simulating and analyzing on-line static UPS systems. Each part of the UPS system is modeled and simulated as an individual element. These submodels are then integrated to give the complete model of the system. The modeling covers semiconductor power switches (Thyristors and MOSFETS), power transformers, filters, batteries and sinusoidal pulse width modulation (SPWM) generators. Feedback and feedforward controllers are considered to regulate the output voltage and suppress the undesired low order harmonics. The steady state and transient performance of an on-line static UPS system feeding a resistive load are analyzed. This includes the steady state performance for normal as well as for standby operations. The transient behaviour is determined for different cases; namely, transients from normal to standby condition and vice-versa, the application of a sudden pulse spike appearing in the normal supply, the application of a sudden short circuit in some battery cells, and the application of a sudden load or short circuiting the load. A computer load is also considered. The main requirements for a UPS system feeding a computer load are discussed, and the reflection of the computer load on the UPS performance is studied. By the help of simulation, the effect of different UPS output waveforms on the crest factor and efficiency is investigated. Different steady state and transient simulations are performed to identify the behaviour and critical conditions that may encounter the computer system fed from a UPS system under severe supply interruption conditions and UPS transients. The PSPICE simulation package is proved to be a very effective tool in studying the steady state and transient behaviour of on-line static UPS systems under different control strategies, with feedforward and feedback controllers, and when feeding different types of loads. The simulation package provides the time response as well as the frequency spectrum of the different system variables. It helps in investigating many features of UPS systems, such as total harmonic distortion, voltage stabilization and regulation, and efficiency. |