A Power Flow Control Strategy for Hybrid Control Architecture of DC Microgrid under Unreliable Grid Connection Considering Electricity Price Constraint

Abstract

This paper presents a power flow control strategy for a hybrid control architecture of the DC microgrid (DCMG) system under an unreliable grid connection considering the constraint of electricity price. To overcome the limitation of the existing schemes, a hybrid control architecture which combines the centralized control and distributed control is applied to control DCMG. By using the hybrid control approach, a more optimal and reliable DCMG system can be constructed even though a fault occurs in the grid or a central controller (CC). The power flow control strategy for the hybrid DCMG control architecture also takes the constraint of electricity price into account for the purpose of minimizing the electricity cost. In the proposed hybrid control, the high bandwidth communication (HBC) link is used in the centralized control to connect the CC with DCMG power agents. On the other hand, the low bandwidth communication (LBC) link is employed to constitute the distributed control. A small size of data is used to exchange the information fast between the agents and CC, or between each agent and its neighbors, which increases the reliability and robustness of the DCMG system in case of a fault in the communication link of the centralized control. A DCMG system with 400-V rated DC-link voltage which consists of a wind power agent, a battery agent, a grid agent, a load agent, and a CC is constructed in this study by using three power converters based on 32-bit floating point digital signal processor (DSP) TMS320F28335 controller. Various simulation and experimental results prove that the proposed scheme improves the system stability and robustness even in the presence of a fault in the communication link of the centralized control. In addition, the proposed scheme is capable of maintaining the DC-link voltage stably at the nominal value without severe transients both in the centralized control and distributed control, as well as both in the grid-connected case and islanded case. Finally, the scalability of the DCMG system is tested by adding and removing additional wind power agent and battery agent during a certain period.

Decentralized Power Flow Control Strategy Using Transition Operations of DC-Bus Voltage for Detection of Uncertain DC Microgrid Operations

“…The decentralized DCMG experimental setup, depicted in Figure 20, is used to demonstrate the feasibility of the proposed PFCS with the system parameters in Table 11. The experiment was performed with a laboratory-scale prototype DCMG system which has a similar power rating to the studies in [12][13][14]. The experimental DCMG system comprises four power electronic converters, which interface the DC-link with the utility grid unit, battery unit, wind turbine unit, and EV unit.…”

“…Various methods such as time-of-use pricing (TOU), real-time pricing (RTP), and stepwise power tariff (SPT) are used worldwide to calculate electricity bills [8][9][10][11]. To optimize the power consumption cost of a DCMG system, previous studies have considered the electricity price change of the utility grid [12][13][14].…”

A Centralized Power Flow Control Scheme of EV-Connected DC Microgrid to Satisfy Multi-Objective Problems under Several Constraints

“…To ensure a DCMG operation, the reliable control of power electronics converters is an indispensable part. To effectively realize all the operating modes by each power agent in Table 1, power converter controllers are implemented by modifying the configuration in [20].…”

“…On the other hand, in the centralized control scheme, all the power agents communicate with the central controller (CC), and therefore all agents determine their operating modes according to data obtained from the CC. Amongst those three control schemes, only the centralized control scheme could achieve a global optimum solution under multiple constraints by constructing an effective energy management system (EMS) alongside the CC in the MG system [20].…”

“…To prove the feasibility of the proposed power flow control scheme, the Powersim (PSIM) software (9.1, Powersim, Rockville, MD, USA) is used in this work to carry out the simulation [32]. This software has been used to simulate a microgrid system in several works [10,18,20,33]. The simulation setups validate that the proposed scheme regulates the DC-link voltage stably and reliably regardless of a sudden EV connection and disconnection with the DCMG, even when the prime objective of the DCMG operation is immediately changed, or the electricity price conditions are varied.…”