| Summary: | 碩士 === 國立交通大學 === 機械工程學系 === 101 === Nowadays, the solar energy has gained importance in recent years with the development of the renewable energy sources. For a single-phase dc-ac pulse-width modulated (PWM) inverter in grid-connected photovoltaic (PV) system, the system output current, which is injected into the utility grid, is expected to be a sinusoidal waveform of desired fundamental frequency and magnitude after filtering. However, the harmonics in the PWM inverter output voltage are often generated as a result of voltage source disturbances. The high-frequency harmonics are relatively easier to filter out; nevertheless, the low-frequency voltage harmonics induced by the fundamental component can cause the ac current, which is injected into the utility grid, to be distorted. In addition, the variation of system parameters is also a major problem that can affect the inverter performance.
In this thesis, a Doubly Coprime Factorization Disturbance Observer (DCFDOB) structure is applied in order to solve the problems mentioned above effectively. This structure provides a sufficient flexibility to reject different types of disturbances without complicated calculations or adding extra circuit components. In addition, its design procedure contains the H∞-loop shaping method to guarantee the robust stability and robust performance. Some simulations are given to illustrate the effectiveness of the DCFDOB. The results reveal that with the application of the proposed DCFDOB scheme, the total harmonic distortion (THD) of the system output current in both nominal and practical cases are improved and the effects of system parameter variations in practical cases are reduced.
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