الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
A single –phase pulse width modulated (PWM )voltage source inverter used as uninterruptible power supply (UPS) is built and tested .The main purpose of UPS systems is to provide critical loads with uninterrupted ,reliable and hogh quality power regardless of the reliability and quality of the main ac power supply .Differential equations describing the system operation in different modes of operation are give .The linearized model a steady-steady operating point using a small signal approximation for static and dynamic load is developed .Stability analysis of a UPS system using Root –locus plot and Liapunov stability criterion is presented for static and dynamic load Root –Locus plot studies the effect of the variation of system parameters on the location of closed loop poles and hence system stability .Liapunove stability criterion determines a control law of the modulation index which guarantees system stability .The dynamic load performance in both transient and steady –state operation is predicted using the proposed system modeling and simulation .When the inverter switching frequency is equal to load voltage frequency the alternate operation of the inverter switches must be identical to give symmetric waveforms of load voltage and load current in positive and negative sides ptherwise the waveforms will contain dc components and high total harmonic distortion (THD) which undesired for UPS applications .A new drive circuit ,which gives a switching frequency much higher than load voltage frequency to overcome the problem of dc components and maintain low THD in load voltage waveform is proposed .Total harmonic distortion and harmonic spectrum are analyzed at different duty ratios for the two cases of inverter switching frequency An optimal closed –loop voltage control with PI controller is proposed for the system to ensure that the output load voltage is constant and nearly sinusoidal waveform irrespective of load torque and supply voltage disturbances with fast dynamic response .The optimality condition in frequency domain is used and a weighting matrix (Q) to minimize the performance index (J) for optimal control law is selected .The simulation results are give and proved to yield good agreement when compared with the relevant experimental results .