Increased demand of electric ship power with emerging requirements for serving highly dynamic loads at limited power sources, has motivated the development of medium voltage DC shipboard power systems. As different types of power converters can be involved in the same system, advanced load management scheme is required to ensure stable and optimal operation under various conditions. In this paper, a heterogeneous multi-agent system model is established for the load demand management of a zonal medium voltage DC shipboard power system, where different types of DC-DC converters with diverse conversion ratios are considered as heterogeneous agents. Then, a flocking based cooperative control protocol is designed to achieve the group objective, where navigational feedback is introduced to ensure that each agent runs within a limited range. Finally, numerical simulations are conducted to verify the performance of the proposed model. Compared with the existing work, our contribution lies in: 1) The heterogeneous multi-agent system model we formulated for a combination of DC-DC converters with different types and diverse voltage levels is more consistent with the actual power system and each converter can be controlled individually according to load ratings and priorities; 2) The modified navigational feedback with the function of confining the lower and upper bound of agents can significantly improve the control effect of the cooperative control protocol. INDEX TERMS Medium voltage DC shipboard power system, heterogeneous multi-agent system model, load demand management, DC-DC converter, navigational feedback. PEIFENG XI received the B.S. degree in electronic engineering from Shanghai University, in 2004, and the M.S. degree in electronic engineering from Shanghai Jiao Tong University, in 2010. He is currently with the Shanghai Electrical Apparatus Research Institute. He is also a member of the Shanghai Key Laboratory of Smart Grid Demand Response, Shanghai, China. His current research interests include smart grid, demand response, and energy management.
The development of powered electronic technology has made many aware of the design and control of ship power systems (SPSs), and has made medium voltage DC (MVDC) architecture the main research direction in the future. The negative impedance characteristic of constant power load (CPL) generated by the coupling of powered electronic converters will seriously affect the stability of the systems if these converters are not properly controlled. The conventional linear control method can only guarantee the small-signal stability of the system near its equilibrium point. When the operating point changes in a large range, linear control methods will be ineffective. More importantly, research for the large-signal stability of the multi-converter system with CPLs is still rarely involved. In this paper, a sliding-mode-based duty ratio controller (SMDC) is proposed for voltage regulation and current sharing of the multiple parallelly-connected DC–DC converters system loaded by CPLs. By controlling the output voltage of each converter with SMDC, large-signal stability of the coupled bus voltage is ensured. Meanwhile, proportional current sharing between the parallel converters is achieved by droop control integrated in the reference value of converter voltage. Simulation studies were conducted in MATLAB/Simulink, where two typical operating conditions, including the variation of load power and bus voltage, were designed to verify the effectiveness of the proposed method. Moreover, a traditional PID controller was used as a comparison to reflect the superiority of the former. Simulation results showed that the proposed method is able to guarantee large-signal stability of the system in the presence of large-scale variations in load power and bus voltage. The output current of the parallel converters can also be distributed in desired proportions according to the droop coefficient.
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