The cascaded H-Bridge (CHB) is a good candidate to integrate multiple PV arrays into the power grid. However, due to the internal uncertain power supply of renewable sources, it is difficult to meet the power grid power command with only PV arrays. To overcome this limitation, a CHB converter with both PV arrays and energy storage units in the DC rails is proposed in this paper. Firstly, a two-layer hierarchical control is developed for independent PQ control and power distribution among each CHB cell, while meeting with the grid PQ reference command at the same time. Then, a modified power management method is developed to adaptively modify the current power points for PV panels from their maximum power points to solve the potential over-modulation problem caused by frequent battery charging and discharging. With the proposed approach, a good harvesting of PV power can be ensured in various situations. Verification results are provided to validate the performance of the proposed system.
- Cascaded H-bridge
- Power control
- Coordinated control
- PV-Battery system
In this paper, a compact single-phase PV-battery-hybrid system is developed with a single stage CHB converter, where both PV panels and battery are connected to separate DC rails of the converter. To achieve proper MPPT of each PV array and at the same time, avoid conflicts caused by the difference between PV output power and the grid power demand, a hierarchical control power control scheme is developed. The central controller is responsible for the regulation of grid current to meet the grid demand and the local controller of each H-bridge cell is responsible for MPPT of PV arrays. The battery in the proposed system acts as a buffer to compensate the gap between PV output power and grid demand. To overcome the potential over-modulation problems when the battery is absorbing power with reference voltage angle opposite to that of the PV cells, a modified power management method which can slightly changes PV array operation point in an online manner, is also developed. This method can be used to obtain the maximum allowable output power of PV while ensure an accurate control of power transfer to the grid mains. Since this paper only gave a roughly sketched control scheme of the CHB-based PV-battery-hybrid system, there are still some limitations at present. E.g., firstly, to fit the system PV power capacity, the capacity of the battery may be fairly large as well, thus it may exceed the limitation of system construction investment. However, it should be noted that even if the capacity of the battery is limited, it is still able for this CHB-based system to provide a schedulable output power and participate in the grid power flow regulation in an acceptable region, which will still be effective to improve the energy utilization in a limited range, and help reduce the PV discarding rate. The system planning issue was beyond this topic and not discussed in detail. Secondly, In general, distributed power cells are always required to be able to plug-and-play. While this series system is highly dependent on the communication system, the plug-and-play implementation issue should also consider the communication system design in each controller, making it not only a control issue but also a communication issue. The plug-and-play operation remains a rather interesting topic to be studied in our future work.
 S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg. “A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep./Oct. 2005.
 F. Blaabjerg, Y. Yang, D. Yang, X. Wang. “Distributed Power-Generation Systems and Protection,” Proc. IEEE, vol. 105, no. 7, pp. 1311–1331, July. 2017.
 S. V. Araújo, P. Zacharias, and R. Mallwitz, “Highly Efficient Single-Phase Transformerless Inverters for Grid-Connected Photovoltaic Systems,” IEEE Trans. Ind. Electron., vol. 57, no. 9, pp. 3118-3128, Sep. 2010.
 B. Yang, Wuhua Li, Y. Zhao, X. He. “Design and Analysis of a Grid-Connected Photovoltaic Power System,” IEEE Trans. Power Electron., vol. 25, no. 4, pp. 992-1000, Apr. 2010.
 J. He and Y. W. Li, “Analysis, design and implementation of virtual impedance for power electronics interfaced distributed generation,” IEEE Trans. on Ind. Appl., vol. 47, pp. 2525-2538, Nov/Dec. 2011.