Yanghong Xia

Distributed Coordination Control for Multiple Bidirectional Power Converters in a Hybrid AC/DC Microgrid

This paper proposes a distributed coordination control method for multiple bidirectional power converters (BPCs) in a hybrid ac/dc microgrid. The researched hybrid ac/dc microgrid is composed of both ac and dc subgrids connected by multiple parallel BPCs, and only the ac subgrid contains storages for the sake of economy. The proposed control method can realize the appropriate power interaction between the two subgrids and make the two subgrids to support each other, so the hybrid microgrid can operate well in both the grid-connected and islanded modes. Concretely, there are three improvements in this proposed control methods. First, a d-q-0 three-axis control strategy instead of the conventional d-q two-axis control strategy is adopted to suppress the circulating current on the ac side generated by the multiple parallel BPCs. And then the square of the dc voltage rather than the dc voltage itself is controlled, which can make the control of the dc voltage linearized and can make the BPCs provide well voltage support for the dc subgrid. Second, the dc droop control is adopted for the dc current sharing. Also, in order to relieve the storages from generating too much reactive power if the ac load reactive power is very large in the ac subgrid, the reactive power droop control is adopted to make the BPCs share some reactive power. Third, taking the capacities and load types of the two subgrids into consideration, a coordinated control strategy based on the dc voltage versus the frequency droop is designed to realize the power interaction between the two subgrids. Furthermore, the stability analysis of the proposed control method is conducted. All the conclusions are verified by the real-time hardware-in-loop tests.

A Decentralized Coordination Control Method for Parallel Bidirectional Power Converters in a Hybrid AC–DC Microgrid

In the hybrid ac–dc microgrid, the ac and dc subgrids are connected by bidirectional power converters (BPCs) that play an important role in the load power sharing and power interaction between the ac and dc subgrids. The coordination control and circulating current suppression for the parallel BPC system are very challenging. In this paper, a decentralized coordination control method is proposed for parallel three-phase BPCs, which can suppress the circulating currents, realize proper power interaction, and achieve overall load power sharing in both the grid-connected mode and the islanded mode. The performance of the proposed control methods is verified by the real-time hardware-in-loop tests.

Decentralized Multi-Time Scale Power Control for a Hybrid AC/DC Microgrid With Multiple Subgrids

To facilitate the connection of various renewable ac and dc sources and loads to power systems, the hybrid ac/dc microgrid with multiple subgrids has been grasping more and more attention, in which the rated ac frequencies and dc voltages in different ac subgrids and dc subgrids can diversify for various applications. As the interaction among these subgrids is highly complicated, the stable and efficient operation of the hybrid microgrid is very challenging. Focusing on this problem, this paper proposes a decentralized multi-time scale power control method to make the interacted subgrids operate in coordination and support each other when the power of the system is fluctuated. The proposed control method stabilizes the power fluctuation in three time scales, of which the first two are conducted at the subgrid level and the last is conducted at the system level. In the first time scale, the ac frequency or dc voltage is changed to regulate the load power through the droop control. Further, in the second time scale, the output power of distributed generations is changed according to the deviations of ac frequency or dc voltage. Through these two coordinated control strategies, the power fluctuation is primarily stabilized. In the third time scale, the ac frequencies and dc voltages of all the subgrids are changed according to a designed coordinated power control strategy with consideration of the capacities and load types of each subgrids, which can make the subgrids support each other. Through this coordinated control strategy, the proper power interaction among different subgrids can be realized and the power fluctuation is further stabilized with the support of other subgrids. The effectiveness of the proposed power control method is verified by the real-time hardware-in-loop tests.

Power Management for a Hybrid AC/DC Microgrid With Multiple Subgrids

This paper proposes a new topology of a hybrid ac/dc microgrid, where there are multiple subgrids connected to the common bus by bidirectional ac/dc converters (BADCs) and bidirectional dc/dc converters (BDDCs) in the system. The rated ac frequencies in different ac subgrids and the rated dc voltages in different dc subgrids can be different for different applications. All the storages in the system are concentrated to form a storage subgrid for convenient management and high efficiency, which maintains the common bus voltage. To ensure the hybrid microgrid operates well, a proper power management method is necessary to control the power flow among multiple subgrids. This paper proposes a decentralized power management method for the hybrid microgrid to make the interacted subgrids operate in coordination and support each other. First, taking the characteristics of the common bus configuration into consideration, a

Hierarchical control for parallel bidirectional power converters of a grid-connected DC microgrid

{P_{{\rm{dc}}}} - v_{{\rm{dc}}}^2

Decentralized Coordination Control for Parallel Bidirectional Power Converters in a Grid-Connected DC Microgrid

droop control strategy is proposed to maintain the common bus voltage and to realize power sharing among storages in the storage subgrid. Second, as the interaction among multiple subgrids is more complicated compared to the conventional hybrid, a coordinated power control strategy based on the common bus voltage, ac subgrid frequency, and dc subgrid voltage is designed for the BADCs and BDDCs to realize the power interaction among different subgrids. Furthermore, the proposed strategy takes the capacities and load types of each subgrid into consideration; hence, it is still suitable when the capacities of subgrids are mismatched and it can ensure the power quality of the subgrids with high proportion of critical loads. The effectiveness of the proposed power management method is verified by the real-time hardware-in-loop tests.

Decentralized control for parallel bidirectional power converters of a grid-connected DC microgrid

The DC microgrid is connected to the AC utility by parallel bidirectional power converters (BPCs) to import/export large power, whose control directly affects the performance of the grid-connected DC microgrid. Much work has focused on the hierarchical control of the DC, AC, and hybrid microgrids, but little has considered the hierarchical control of multiple parallel BPCs that directly connect the DC microgrid to the AC utility. In this paper, we propose a hierarchical control for parallel BPCs of a grid-connected DC microgrid. To suppress the potential zero-sequence circulating current in the AC side among the parallel BPCs and realize feedback linearization of the voltage control, a d-q-0 control scheme instead of a conventional d-q control scheme is proposed in the inner current loop, and the square of the DC voltage is adopted in the inner voltage loop. DC side droop control is applied to realize DC current sharing among multiple BPCs at the primary control level, and this induces DC bus voltage deviation. The quantified relationship between the current sharing error and DC voltage deviation is derived, indicating that there is a trade-off between the DC voltage deviation and current sharing error. To eliminate the current sharing error and DC voltage deviation simultaneously, slope-adjusting and voltage-shifting approaches are adopted at the secondary control level. The proposed tertiary control realizes precise active and reactive power exchange through parallel BPCs for economical operation. The proposed hierarchical control is applied for parallel BPCs of a grid-connected DC microgrid and can operate coordinately with the control for controllable/uncontrollable distributional generation. The effectiveness of the proposed control method is verified by corresponding simulation tests based on Matlab/Simulink, and the performance of the hierarchical control is evaluated for practical applications.

Advanced unified decentralised control method with voltage restoration for DC microgrids

In the grid-connected mode, the dc microgrid is connected to the utility by parallel bidirectional power converters (BPCs), which provide voltage support for the dc microgrid. The coordination control for these parallel BPCs is very challenging. First, for the parallel BPCs, there is circulating current among them, which limits the total system capacity and may damage switching devices. Second, taking the constant power load into consideration, the performance especially the stability of the dc microgrid is degraded if the conventional

Triple droop control method for ac microgrids

{\mathbf i}_{\boldsymbol {dc}}{\mathbf -}{\mathbf v}_{\boldsymbol {dc}}

Stability Analysis and Stability Enhancement Based on Virtual Harmonic Resistance for Meshed DC Distributed Power Systems with Constant Power Loads

droop is adopted to share the power. Third, the voltage restoration should be faster for the better quality of dc voltage, and the restoration strategy should be scalable to the changes of the dc microgrid topology for the better flexibility. For these problems, this paper proposes a decentralized control method for the parallel BPCs, which can make the BPCs operate in coordination and provide voltage support for the dc microgrid well. Furthermore, the reliability of the proposed control method is illustrated by the stability analysis. All the conclusions are verified by the real-time hardware-in-loop tests.