Abstract
In DC microgrids, distributed energy storage plays a key role in stabilizing the DC bus voltage. The bidirectional DC/DC converter in the distributed energy storage system should be designed according to the voltage level and electromagnetic isolation requirements, and multiple energy storage units should be coordinated for load current distribution according to the state of charge (SOC). This paper proposes a SOC power index droop control strategy by communication lines to coordinate the fast and high-precision distribution of load current among multiple energy storage units, and the SOC between energy storage units quickly converges to a consistent state. Considering that communication lines are susceptible to interference, this paper further proposes an improved SOC power index droop control to overcome the effects of communication line failures. Considering the high cost of the energy storage unit, it should be connected to the DC microgrid in layers to achieve a reasonable allocation of resources in practical applications. In order to provide high-quality power to a large power grid, the quantification standards of the DC bus fluctuation range and the working range of each converter are further discussed to maximize the stability of the DC bus voltage and grid-connected power fluctuation.
Highlights
Distributed energy storage is the key issue to solve the issue of grid-connected renewable energy generation
Comprehensive analysis of Figure 10k in the fast and accurate distribution of load current DC bus voltage shows that the deviation is smaller; once the communication line fails, it automatically switches to Figure 10f mode to continue running
This paper has presented a distributed drooping control of state of charge (SOC) power exponents and considers the emergency state when communication faults occur
Summary
Distributed energy storage is the key issue to solve the issue of grid-connected renewable energy generation. To stabilize bus voltage fluctuations and solve energy supply volatility issues, adding energy storage devices can improve the device’s voltage sag and the inrush issues caused by load-switching, changes in natural conditions, and instantaneous faults in DC microgrid systems; this improves the reliability and scheduling flexibility of the distributed generation grid connection. The main functions of the high-frequency transformer are (1) to achieve electrical isolation of the DC bus and energy storage components, to reduce electromagnetic interference (EMI); (2) to adjust the voltage conversion level;.
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