Abstract
To meet the challenge of large-scale renewable energy penetration and take full advantage of existing AC infrastructure, the bipolar DC distribution system is of interest. In this article, the system structure and characteristics of the bipolar DC distribution network are proposed. The three-level Neural Point Clamped Converter (NPC) is used in the proposed system to construct the bipolar DC system. To optimize the DC system performance, an improved cooperative control and energy management strategy is proposed mainly to mitigate DC voltage fluctuation and balance the positive and negative phase voltage. The improved strategy consists of (1) 2-degree of freedom (2DOF) PID controller in traditional voltage control loop; (2) cooperative controller to take full advantage of storage system; (3) voltage equalization controller to balance two-phase voltages; and (4) the energy management system to dispatch the response job to batteries and supercapacitors. Experiments and simulations are performed to validate the effectiveness of the proposed strategy.
Highlights
In recent years, due to the demand for clean and sustainable energy, the large-scale penetration of renewable energy has made it a challenge for the traditional distribution system
The integration of most renewable energy sources in the AC distribution network needs additional power electronics devices to perform the power transformation, e.g., DC/DC, DC/AC converters for photovoltaic systems and AC/DC, DC/AC converters for wind power systems
In a future DC distribution network, reliable communication between a three-level Neural Point Clamped Converter (NPC) converter and a storage system with affordable time delay can be assured by advanced communication devices
Summary
Due to the demand for clean and sustainable energy, the large-scale penetration of renewable energy has made it a challenge for the traditional distribution system. Compared with AC distribution systems, DC distribution systems can integrate the renewable energy sources with improvements in dynamic performance, complication of control design, power quality, losses of transmission, and the cost of distribution network [2,3,4,5,6]. The DC micro-grid structure, bus voltage control, power management and bidirectional power flow problem are studied in [3,4,10,19,20]. The research on the DC micro-grid are beneficial to renewable sources integration and DC distribution network research; some new problems in DC distribution systems should be further researched. To fully utilize the storage system, including battery and supercapacitor, the cooperative control and energy management strategy of the DC distribution network is proposed. The experiment and simulation results are presented to demonstrate the effectiveness of the proposed strategy
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