The growing installation of distributed generation (DG) units has brought structural changes of modern power distribution systems. Conventional solutions, where multiple DG units are connected in parallel, are not very cost-effective because of the two-stage power conversion configuration. To simplify the system structure, reduce cost, and improve efficiency, the series-connected converters have been widely investigated to meet the requirements of high-voltage PV and battery applications, and recently been explored for PV-battery hybrid systems.
However, there are still certain limitations in present applications and investigations on the series-connected converter systems, such as less redundancy, higher communication burden (as the number of cells increase), over-modulation risks, power flow coordination between PV units and batteries, harmonic distribution between series cells, and so on. To address these issues and enhance the performance of the series-connected converter systems, this Ph.D. project is initiated to address but not limited to the following aspects in high-voltage power converters for PV-battery systems:
1) Modifications on modulation schemes. This project aims to develop PWM methods suitable for series PV-battery hybrid systems of different scales based on conventional phase-shifting PWM and level-shifting PWM methods.
2) Stable operation boundary expansion methods. The stable operation boundaries of series PV-battery systems will be analyzed, and the operation boundary expansion method will be proposed correspondingly to realize maximized DC voltage utilization.
3) Fault identification and fault-ride-through methods. Fault–ride-through methods for the series PV-battery systems will be proposed considering cell fault, grid fault, communication system fault, etc.
4) Harmonic management methods. A multi-target harmonic management method will be formulated to simultaneously cope with grid harmonic power flow scheduling, grid and converter unbalance, over-modulation risk of each cell, and harmonic power distribution among cells.