| DC/AC inverter has been widely applied in the industry. Digital control has several advantages, e.g., it is easy to achieve complex arithmetic, upgrade and maintenance, and it is not susceptive of noise and the consistent manufacture performance is better, so the digital controlled inverters are the trend of the inverter in the future. This thesis focuses on the digital control for the SPWM inverter.Firstly this thesis introduces the advantages of digital control, and several digital control schemes. Secondly the mathematical model of the inverter is derived adopting the state space average theory, and according to the model different characteristics of closed-loop inverters are discussed based on controlled variables such as output voltage, filter inductor current and filter capacitor current of the filter. Two control schemes are selected for the SPWM inverter, one is single output voltage closed-loop, the other is a dual closed-loop consisting of outer output voltage closed-loop and inner filter capacitor current closed-loop. Thirdly the compensators are designed for the two control schemes, and the performance of two control schemes are compared. The analysis shows the dual closed-loop control scheme has a better performance over the single voltage control scheme, such as better stability and faster dynamic response. Finally this thesis presents the design of hardware of the prototypeand the software flow of the control schemes. The experimental results are concluded to validate the control schemes. |
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