Model Predictive control design for switched inductor quasi-Z-source inverter in comparison with the traditional two-stage inverter based on Photovoltaic.

• Applicant: Professor Dr.-Ing. Ralph Kennel
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2015 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262773038

The shortage in the global fossil fuels and the increase in environmental concern have initiated a major interest for discovering renewable energy sources. PV generation systems have shown the potential to become a main source of electrical power generation for the whole world with powerful and persistent increase. Several power electronic converters have been employed in order to provide AC power to the utility grid. The cost of power electronic systems represents a substantial portion of the overall installation costs. With the development of solar cell technology, the price of solar modules has dropped dramatically. However, the prices for the power converters almost remain the same. Lowering the cost of the power converters has become a very urgent issue for grid connected PV systems.Voltage source inverters (VSI) have been widely used for DC/AC power conversion but due to their limitations, the Z-source inverter (ZSI) was introduced. ZSI has an additional zero vector, shoot-through switching state, which is forbidden in the traditional VSI. The new ZSI advantageously utilizes the shoot through states to boost the DC bus voltage by turning on both upper and lower switches of a phase leg. Therefore, the ZSI can boost the voltage and produce a desired output voltage which is greater than the available DC bus voltage. In addition, the reliability of the inverter is greatly improved because the shoot-through due to misgating or EMI can no longer destroy the inverter. Thus it provides a reliable and efficient single stage structure for buck-boost power conversion. However the ZSI draws a discontinuous current from the DC source, thus it is not suitable for PV applications. Quasi Z-source inverter (qZSI) is an improved version of the classical ZSI which is proposed to replace it with the same limited boost factor. But PV systems have a wide range of output voltage which needs also a high inverter boost range. To increase the boost factor and utilize the advantages of qZSI, the switched inductor qZSI will be designed in this project as a single-stage inverter to interface PV system with the utility grid and the AC loads.The main objective of this project is to realize the model predictive control (MPC) of the new switched inductor qZSI based on PV system. The proposed inverter will be compared with the traditional two-stage inverter in light of inverter efficiency, the requirement of the passive components and voltage and current stress on the power switches. For a fair comparison, two 3 kW inverters will be designed using the same components and evaluated under the same conditions. Moreover, the MPC will be assessed in comparison with the conventional PI controller during the transient and the steady-state operation. At the end a potential, cheaper, simpler, and robust single-stage inverter for PV applications is expected. These new technologies will help increase the solar power in a more efficient and economical way.

• DFG Programme: Research Grants