Abstract
Considering the increasing requirements of the AC-DC hybrid microgrid (HMG) for the transmission power capacity and voltage level, the several bus interface converters (BICs) with the two-level PWM converter topology, need to be connected between AC bus and DC bus in parallel, which could generate circulating current and cycle power. The cost of the modular multilevel converter topology based BIC is too high. Hence, this paper proposes to apply the BIC with three-level topology to the HMG, and a droop control strategy with the midpoint potential hysteresis regulation link is designed, which can effectively suppress the fluctuation of midpoint potential without affecting the normal operation of the BIC in the grid connected or off mode. In addition, the principle of neutral point fluctuation and the process of hysteresis control are introduced, and the detailed design of dual-mode control strategy based on droop curve are also given. Finally, the effectiveness of the improved control strategy is verified by simulation.
Highlights
With the rapid development of the new energy power generation, research on the microgrid has been received more and more attention
The proposed droop control strategy with the midpoint potential hysteresis regulation link of the bus interface converters (BICs) is shown in Fig. 6 and the proposed control strategy is implemented as follows: 1) Detect the AC and DC bus voltage, generate the reference value Ptref of the transmitted active power through the droop or constant voltage regulator (VR)
Aiming at the disadvantages of the BIC with the two-level PWM topology in the AC-DC hybrid microgrid (HMG), this paper proposes to apply the three-level topology based BIC to the system, which requires the large transmission power and the high voltage level
Summary
With the rapid development of the new energy power generation, research on the microgrid has been received more and more attention. The BIC based on the three-level topology has many advantages compared to the two-level topology, but it has inherent problems of the neutral point potential fluctuation [18]. It will cause the DC bus voltage fluctuation in the AC-DC HMG, which through the BIC affects the power quality of the AC subnet. For the neutral point potential fluctuation caused by the three-level topology, a droop control scheme with midpoint potential hysteresis regulation link is designed. The effectiveness and feasibility of the proposed method are verified by simulation
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