Wenbin Yuan

An f-P/Q Droop Control in Cascaded-Type Microgrid

In cascaded-type microgrid, the synchronization and power balance of distributed generators become two new issues that needs to be addressed urgently. To that end, an f-P/Q droop control is proposed in this letter, and its stability is analyzed as well. This proposed droop control is capable to achieve power balance under both resistive-inductive and resistive-capacitive loads autonomously. Compared with the inverse power factor droop control, an obvious advantage consists in extending the scope of application. Finally, the feasibility of the proposed method is verified by simulation results.

Improvement of transient stability in inverter-based AC microgrid via adaptive virtual inertia

Unlike centralized synchronous generator (SG) in conventional power system, distributed micro-sources are parallel connected to neighbors by inverters, which are less-inertia. To improve the transient stability, inverter-based distributed generators (DG) can draw an analogy between the storage and rotor rotational kinetic energy of SG in inertia function. Instead of emulating a fixed virtual inertia, this study proposes adaptive virtual inertia to alleviate the frequency response. In the transient process, a large inertia is implemented when the frequency will deviate from the normal value, and a low inertia is adopted when its necessary to recover the frequency. The proposed method can enhance the anti-interference and over-load capacity, so that frequency stability is strengthened. Lyapunov stability analysis is utilized to prove the convergence. Simulation results are presented to verify the effectiveness of the method.

A novel operation mode for PV-storage independent microgrids with MPPT based droop control

In microgrids, photovoltaic (PV) and storage are integrated as a droop-controlled ideal source, which is not practical and challenges the system efficiency. Instead, PV-storage can be allocated separately. This PV-storage independent system is more flexible and easier to optimize. But, the conventional PQ-controlled PVs rely on master voltage-controlled storage sources. In this paper, a novel operation mode is proposed for the PV-storage independent microgrids. PVs operate as current controlled voltage sources (CCVS). A maximum power point tracking (MPPT) based droop control scheme is introduced to explain the proposed operation mode. Thus, this mode enables PVs to supply an auxiliary service of frequency regulation and a maximum utilization of renewable energy. The small signal stability of entire system is analyzed to design the physical and control parameters. Finally, simulations are presented to verify the system effectiveness.

A decentralized SOC balancing method in cascaded H-bridge based storage modules

Due to different initial state of charge (SOC) of energy storage system, the SOC of cascaded storage module is unbalanced in microgrid. Many conventional methods realize SOC balance of cascaded storage module based on centralized communication. In this paper, a decentralized SOC balancing method is proposed without any communication. In this scheme, the modified P-f curves are changed by the local SOC information in real-time, which can change the out-inputting power for balancing SOC. Moreover, regardless of charging mode or discharging mode, the unified SOC balancing is guaranteed without changing control structure. Compared with Centralized communication, this scheme has a higher reliability and fault tolerance. The stability of this scheme is verified through small signal analysis of the complete system. Finally, the effectiveness of SOC balancing and transient response are verified through simulations.