DC microgrids fed with substantial intermittent renewable energy sources (RES) face the immediate problem of power imbalance and the subsequent DC bus voltage fluctuation problem (that can easily breach power system standards). It has recently been demonstrated that DC electric springs (DCES), when connected with series non-critical loads, are capable of stabilizing the voltage of local nodes and improving the power quality of DC microgrids without large energy storage.
In this paper, two centralized model predictive control (CMPC) schemes with (i) non-adaptive weighting factors and (ii) adaptive weighting factors are proposed to extend the existing functions of the DCES in the microgrid. The control schemes coordinate the DCES to mitigate the distribution power loss in the DC microgrids, while simultaneously providing their original function of DC bus voltage regulation. Using the DCES model that was previously validated with experiments, simulations based on MATLAB/SIMULINK platform are conducted to validate the control schemes. The results show that with the proposed CMPC schemes, the DCES are capable of eliminating the bus voltage offsets as well as reducing the distribution power loss of the DC microgrid.
- DC microgrids
- DC electric springs (DCES)
- Centralized model predictive control (CMPC)
- Non-adaptive weighting factors
- Adaptive weighting factors
- Distribution power loss
Fig. 1. An m-bus DC microgrid with n RES units.
EXPECTED SIMULATION RESULTS:
Fig. 2. Waveforms of the power supply by RES and the bus voltages of the DC microgrid without DCES.
Fig. 3. Waveforms of the bus voltages of the DC microgrid when the DCES is installed at the five buses.
Fig. 4. Waveforms of the bus voltages of the DC microgrid with three DCES installed at bus 1, bus 4 and bus 5.
Fig. 5. The comparisons of the power loss on the distribution lines between α=1 and α=0.9 when three DCES are installed.
Fig. 6. Waveforms of the bus voltages of the DC microgrid with four DCES installed at bus 1, bus 2, bus 4 and bus 5.
Fig. 7. Comparisons of the power loss on the distribution lines for different values of α when four DCES are installed.
DC electric springs (DCES) is an emerging technology that can be used to stabilize and improve the power quality of DC microgrids. In this paper, a centralized model predictive control (CMPC) with both non-adaptive weighting factors and adaptive weighting factors is proposed for multiple DCES to further mitigate the power loss on the distribution lines of a DC microgrid.
Using a DCES model previously verified with experiments, simulation studies have been conducted for a DC microgrid setup. Simulation results on a 48 V five-bus DC microgrid show that the energy is saved about 49.4% in the 5 seconds when three DCES are controlled by the CMPC with non-adaptive weighting factors and is saved about 58.5% in the 5 seconds when four DCES are controlled by the CMPC with non-adaptive weighting factors. It is also demonstrated that the power loss on the distribution lines of the DC microgrid can be further reduced by the CMPC with adaptive weighting factors, as compared to the CMPC with non-adaptive weighting factors.
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