https://orcid.org/0000-0002-2799-3466
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ABSTRACT
In this paper, a coordinated power sharing strategy for multiple subgrid-based dc microgrid (DCMG) is proposed. The DCMG has an SPV (storage-PV) subgrid and two PV subgrids connected through interlinking bidirectional converters (IBCs). In the SPV subgrid, a charging/discharging power and state-of-charge (SoC) of battery-based droop strategy have been implemented for the battery controller for dc bus voltage regulation. In PV subgrid, IBC regulates its dc bus voltage. Further, for coordinated power-sharing, a correction factor-based coordination control strategy for IBC has been proposed. With the proposed coordination strategy, a small change in load demand has been taken care of by the PV subgrid without affecting the state of the battery. Moreover, the battery has been accorded the last priority to respond to the change in load demands in the DCMG. With the proposed strategy, a low SoC battery charges 1.28%/min faster than the conventional strategy. Similarly, a high SoC battery charges 1.07%/min slower than the conventional strategy. Hence, deep discharge and overcharge of the battery are avoided. With the coordination strategy, a higher capacity subgrid takes more load demand than a weak subgrid. The effectiveness of the proposed strategy is verified with MATLAB simulation and OPAL-RT real-time digital simulator.
Nomenclature
Abbreviations
| BS | = | Battery storage |
| DCMG | = | DC microgrid |
| HSS | = | High SoC state |
| IBC | = | Interlinking bidirectional converter |
| LSS | = | Low SoC state |
| MPPT | = | Maximum power point tracking |
| NSS | = | Normal SoC state |
| PCM | = | Power control mode |
| PI | = | Proportional-integral |
| PV | = | Photovoltaic |
| PVT | = | Photovoltaic thermal |
| RTDS | = | Real-time digital simulator |
| SG | = | Subgrid |
| SoC | = | State-of-charge |
| SPV | = | Storage + Photovoltaic |
| TEG | = | Thermoelectric generator |
| WT | = | Wind turbine |
Symbols
| α | = | Coordination coefficient |
| C | = | DC-link capacitor |
| ΔV | = | Coordination factor |
| Iin | = | Input current of IBC |
| Iout | = | Output current of IBC |
| kdc | = | Voltage gain constant |
| kps | = | Proportional gain of IBC secondary controller |
| kis | = | Integral gain of IBC secondary controller |
| kpu | = | Proportional gain of IBC voltage controller |
| kiu | = | Integral gain of IBC voltage controller |
| kpi | = | Proportional gain of IBC power controller |
| kii | = | Integral gain of IBC power controller |
| kpbu | = | Proportional gain of battery voltage controller |
| kibu | = | Integral gain of battery voltage controller |
| kpbi | = | Proportional gain of battery current controller |
| kibi | = | Integral gain of battery current controller |
| Lb | = | Inductor of BDDC converter of battery |
| Lij | = | Inductor of IBC between ith and jth subrids |
| NV | = | Normalized dc bus voltage of subgrid |
| n | = | Voltage constant |
| Pb | = | Power of battery |
| Pch | = | Charging power of battery |
| Pcri | = | Critical load capacity of subgrid |
| Pdis | = | Discharging power of battery |
| Pibc | = | Power flow through the IBC |
| Pin | = | Input power of IBC |
| Pmax | = | Maximum load capacity of subgrid |
| Pmpp | = | Maximum power of PV generation |
| Ppv | = | Generated power of PV |
| Pref | = | Reference power of IBC |
| Psen | = | Sensitive load capacity of subgrid |
| Pt | = | Base value of power of subgrid |
| Rdroop | = | Voltage droop coefficient |
| r | = | Power droop coefficient |
| rn | = | Nominal power droop coefficient |
| SoCl | = | Lower threshold of SoC |
| SoCm | = | Lower cut-off limit of SoC |
| SoCu | = | Upper threshold of SoC |
| T | = | Time constant |
| ub | = | Battery voltage |
| Udc | = | Nominal dc bus voltage of subgrid |
| Vdc | = | DC bus voltage of subgrid |
| Vdcpv | = | DC bus voltage of PV subgrid |
| Vdcs | = | DC bus voltage of storage subgrid |
| Vibc_ref | = | Reference dc voltage of IBC |
| Vibc_nom | = | Nominal dc voltage of IBC |
| Vlcs | = | Lower cut-off dc voltage of subgrid |
| Vlcs | = | Lower cut-off dc voltage of storage subgrid |
| Vnom | = | Nominal dc bus voltage of subgrid |
| Vnoms | = | Nominal dc bus voltage of storage subgrid |
| Vrefs | = | Reference dc bus voltage of storage subgrid |
| Vuc | = | Upper cut-off dc voltage of subgrid |
| Vucs | = | Upper cut-off dc voltage of storage subgrid |
Disclosure statement
No potential conflict of interest was reported by the author(s).