Generalized DC electromotive force control strategy for AC/DC hybrid microgrid interface converter

Bidirectional Interface Converter (BIC) connecting the AC and DC buses is the hub of the hybrid microgrid in the energy interaction between the AC and DC subnets. Therefore, the research on the control strategy of BIC is of great significance for the stable operation of the microgrid. Rural distributed power supply and power load are complex and decentralized. AC/DC hybrid microgrid is very suitable for the rural distributed energy consumption and power supply. However, the access of a high proportion of new energy and power electronic equipment has made the power supply and load of rural AC/DC hybrid microgrid appear the multi-power electronics, leading to the low inertia and damping problems of BIC. In this study, Generalized Direct Current Electromotive Force (G-DCEMF) control strategy was proposed to effectively solve the problem of low inertia and damping in hybrid microgrids. Power sharing was also realized in the AC-DC side of the hybrid microgrid for better inertia and dynamic performance. Firstly, a connection was established between the AC bus frequency and the DC motor angular velocity, where the terminal voltage was equivalent to the DC bus voltage, while the BIC transmission power was expressed by the DC side voltage and current. Then, the electromotive force balance equation of the DC motor was incorporated into the BIC control to derive the G-DCEMF control equation. Secondly, the relationship was obtained between the virtual resistance value and the rated capacity of BIC in the generalized DC electromotive force control strategy. The virtual resistance was used to determine the active power deficit or surplus state between DC and AC subnets. The judgment results show that the BIC was used to control the power distribution, in order to verify the autonomous bidirectional power regulation of generalized DC electromotive force control. The power distribution was also achieved in the multi-BIC parallel operation. Thirdly, the stability of the system was evaluated using a small signal model. The improved control strategy was simple in structure and easy to model. Only the external control loop of BIC was modified without switching between control modes, thereby reducing power loss and instability caused by mode switching. Then, the dynamic response of BIC was analyzed under the control of generalized DC electromotive force. The value of the virtual inductance was obtained during this time. The virtual inductance was adjusted to improve the inertia of the system. The power distribution and dynamic response between subnets were adjusted to reduce the influence of the frequency of the AC bus or the voltage fluctuation of the AC/DC subnets. The anti-interference characteristics and dynamic performance of the AC/DC hybrid microgrid were improved effectively for better stability of the hybrid microgrid operation. Finally, compared with the traditional bidirectional droop control, the generalized DC electromotive force control can be expected to better adjust the power transmission, according to the load fluctuation of the AC/DC subnet. The finding can provide the inertia for the entire microgrid system, and then weaken the impact of unilateral microgrid power disturbance on other microgrids in the system. The AC/DC hybrid microgrid was established in the PSCAD/EMTDC simulation software. The effectiveness of the G-DCEMF control strategy was also verified. The G-DCEMF control can be expected to realize the bidirectional power flow of BIC for better system inertia, dynamic response and anti-disturbance performance in the stability of the microgrid. © 2023 Chinese Society of Agricultural Engineering. All rights reserved.