Decentralized Load Sharing in a Low-Voltage Direct Current Microgrid With an Adaptive Droop Approach Based on a Superimposed Frequency

Saeed Peyghami, Hossein Mokhtari, Frede Blaabjerg
2017 IEEE Journal of Emerging and Selected Topics in Power Electronics  
Conventional droop methods for load sharing control in Low Voltage Direct Current (LVDC) microgrids suffer from poor power sharing and voltage regulation, especially in the case when operating many dc sources with long feeders. Hence, the communication based approaches are employed to improve the load sharing accuracy and voltage regulation. To avoid using such an infrastructure and the corresponding effects on the reliability and stability, an adaptive droop controller based on a superimposed
more » ... on a superimposed frequency is proposed in this paper. Load sharing accuracy is improved by adapting the droop gains utilizing an introduced ac-power. The secondary controller locally estimates and compensates the voltage drop due to the droop controller. The proposed power sharing approach can properly control the load sharing and voltage regulation without utilizing any extra communication system. The effectiveness of the proposed control system is verified by simulations and experimental tests. Index Terms-DC Microgrid, Droop Method, Frequency Injection, Adaptive Droop Control, Power Sharing. small virtual resistor, an appropriate load sharing can be achieved. However, considering the line resistance effect, large virtual resistors should be utilized to carry out the appropriate load sharing. Large virtual resistors cause large voltage drop within the grid, which in most cases are compensated by employing a secondary control layer reinforced by a communication network. Point to point communication [8], [15] as well as sparse communication among converters [4], [6] are employed to reach the power management objectives including proportional load sharing and acceptable voltage regulation. However, the communication network may affect the stability and reliability of the system [4], especially in the case of operating many sources along long feeders. Although less common, independence of communication is possible, as demonstrated in [16] , where a load-sharing approach based on frequency encoding of output current of converters has been introduced. Another technique, named as power talk, has also been mentioned in [17] , where sources in the dc microgrid "talk" to each other by modulating their respective power levels without using external communication links. The approach is however prone to line, load, and other grid parameter changes, which in practice, are unpredictable. Another frequency based control approach is presented in [18] for energy management purpose in dc microgrids without utilizing a communication network. However, the expandability of the system is limited due to the additional currents required by the converters to sustain a certain ac signal. Moreover, this approach is only suitable for energy management level which requires slow dynamic response, and hence it cannot be employed in primary control level. A frequency-based power sharing technique proposed in [19] and [20] , and later reapplied to dc microgrids in [21] , may
doi:10.1109/jestpe.2017.2674300 fatcat:oxszya7jqbaalf7fml4ktfdggy