Improved virtual DC generator technique for PV power generation units in railway field

Abstract

The power-electronics-based DC microgrid system composed of new energy sources in railway field has low inertia, weak damping characteristics, and the voltage fluctuation microgrid systems caused by the power disturbance of solar. In order to improve the inertia of the DC microgrid system, a virtual DC generator technology is adopted in the interface converter of photovoltaic (PV) power generation unit, so that it has the external characteristics of DC generator. However, the influence of PV maximum power point tracking(MPPT) is not considered in the traditional virtual DC generator control. Therefore, an improved control strategy for virtual DC generator is proposed, and its small signal model is established to analyze the influence of inertia and damping coefficient on stability. The results show that the proposed method effectively weakens the impact on DC bus voltage when the output of PV power unit changes suddenly, which improves the stability of the microgrid. Meanwhile, the correctness and feasibility of the method are verified.

Keywords

renewable energy / photovoltaic (PV) system / power-electronics-based DC microgrid system / virtual DC generator control / virtual inertia

References

[1] HU H T, CHEN J Y, GE Y B, et al. Research on regenerative braking energy storage and utilization technology for high-speed railways. Proceedings of the CSEE, 2020, 40(1): 246-391.

[2] LI X L, GUO L, WANG C S, et al. Key technologies of DC microgrids: an overview. Proceedings of the CSEE, 2016, 36(1): 2-17.

[3] ZHU X R, HAN D H, MENG F Q, et al. Grid converter series virtual impedance method for improving DC microgrid stability. Power System Technology, 2019, 43(12): 4523-4531.

[4] ZHENG T W, CHEN L J, LIU W, et al. Multi-mode operation control for photovoltaic virtual synchronous generator considering the dynamic characteristics of primary source. Proceedings of the CSEE, 2017, 37(2): 454-464.

[5] CHOOPANI M, HOSSEINIAN S H, VAHIDI B. New transient stability and LVRT improvement of multi-VSG grids using the frequency of the center of inertia. IEEE Transactions on Power Systems, 2020, 35(1): 527-538.

[6] CHAI J Y, ZHAO Y Y, SUN X D, et al. Application and prospect of virtual synchronous generator in wind power generation system. Automation of Electric Power Systems, 2018, 42(9): 17-68.

[7] ALIPOOR J, MIURA Y, ISE T . Stability assessment and optimization methods for microgrid with multiple VSG units. IEEE Transactions on Smart Grid, 2018, 9(2): 1462-1471.

[8] ZHU Z B, ZHANG C Y, ZENG X B. Photovoltaic energy storage microgrid system based on adaptive rotating inertia VSG control strategy. Proceedings of the CSU-EPSA, 2021, 33(3): 67-72.

[9] RAVADA B R, TUMMURU N R. Control of a supercapacitor, battery and PV based stand-alone DC microgrid. IEEE Transactions on Energy Conversion, 2020, 35(3): 1268-1277.

[10] MANANDHAR U, WANG B, ZHANG X, et al. Joint control of three-level DC–DC converter interfaced hybrid energy storage system in DC microgrids. IEEE Transactions on Energy Conversion, 2019, 34(4): 2248-2257.

[11] E Z J, WANG G L, LI Z B, et al. Optimization control method for hybrid energy storage system to enhance the renewable energy absorption level of power grid. Proceedings of the CSU-EPSA, 2021, 33(3): 132-137.

[12] AUGUSTINE S, MISHRA M K. A unified control scheme for a standalone solar-PV low voltage DC microgrid system with HESS. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(2): 1351-1360.

[13] LI X L, GUO L, WANG C S, et al. Robust and autonomous DC bus voltage control and stability analysis for a DC microgrid//IEEE 8th International Power Electronics and Motion Control Conference, May 22-26, 2016, Hefei, China. New York: IEEE, 2016: 3708-3714

[14] GAVRILUTA C, CANDELA J I, ROCABERT J, et al. Adaptive droop for control of multiterminal DC bus integrating energy storage. IEEE Transactions on Power Delivery, 2015, 30(1): 16-24.

[15] ZHI N, ZHANG H. Improved hierarchical control strategy for DC microgrid. High Voltage Engineering, 2016, 42(4): 1316-1325.

[16] WANG C S, LI X L, GUO L, et al. A nonlinear disturbance observer based DC bus voltage control for a hybrid AC/DC microgrid. IEEE Transactions on Power Electronics, 2014, 29(11): 6162-6177.

[17] ZHANG H, ZHANG K T, XIAO X, et al. Control strategy of energy storage converter for simulating DC generator characteristics. Automation of Electric Power Systems, 2017, 41(20): 126-132.

[18] ZHANG X Y, LI H, FU Y. Dynamic stability analysis and self-adaptive voltage inertia control of DC microgrids with novel virtual machine. High Voltage Engineering, 2021, 47(8): 2865-2874.

[19] ZHI N, DING K, DU L, et al. An SOC-based virtual DC machine control for distributed storage systems in DC microgrids. IEEE Transactions on Energy Conversion, 2020, 35(3): 1411-1420.

[20] SAMANTA S, MISHRA J P, ROY B K. Virtual DC machine: an inertia emulation and control technique for a bidirectional DC-DC converter in a DC microgrid. IET Electric Power Applications, 2018, 12(6): 874-884.

[21] CHENG Q M, YANG X L, CHU S Y, et al. Research on control strategy of PV system based on virtual DC generator. High Voltage Engineering, 2017, 43(7): 2097-2104.

[22] MA Y C, WANG S T, LIU G C, et al. Research on virtual DC generator-based control strategy of DC microgrid with wind/energy storage. High Voltage Engineering, 2020, 46(11): 3819-3831.

[23] HE F Q, LI Z Y, YANG R F, et al. Active virtual DC generator technique for new-energy unit of offshore platform. Ship Engineering, 2020, 42(10): 90-96.