This paper now a control action for an islanded medium voltage microgrid to coordinate hybrid power source (HPS) units and to control integrate multilevel inverters under unbalanced and nonlinear load conditions. The planned HPS systems are related to the loads done a cascaded H-bridge (CHB) multilevel inverter. The CHB multilevel inverters increase the output voltage level and improve power quality.
The HPS employs fuel cell (FC) and photovoltaic sources as the main and supercapacitors as the integral power sources. Fast temporary response, high performance, high power density, and low FC fuel use are the main advantages of the planned HPS system. The planned control action consists of a power management unit for the HPS system and a voltage controller for the CHB multilevel inverter.
Each distributed generation unit employs a multiproportional resonant controller to regulate the buses voltages even when the loads are unbalanced and/or nonlinear. Digital time-domain simulation research are carried out in the PSCAD/EMTDC environment to verify the work of the overall planned control system.
- Cascaded H-bridge (CHB) multilevel inverter
- Fuel cell (FC)
- Hybrid power source (HPS)
- Multiproportional resonant (multi-PR)
- Photovoltaic (PV)
- Supercapacitor (SC)
Fig. 1. Single-line diagram of MV microgrid consisting of two DG units.
Fig. 2. Proposed structure of the hybrid FC/PV/SC power source.
EXPECTED SIMULATION RESULTS:
Fig. 3. Microgrid response to unbalanced and nonlinear load changes in feeder F1 . (a) and (b) Instantaneous real and reactive powers of feeders.
Fig. 4. Microgrid response to the unbalanced and nonlinear load changes applied to feeder F1 ; positive-sequence, negative-sequence, and harmonic components of loads currents at (a) feeder F1 and (b) feeder F2 .
Fig. 5. Dynamic response of DG units to unbalanced and nonlinear load changes applied to feeder F1 . (a) and (b) Real and reactive power components of DG units.
Fig. 6. Microgrid response to the unbalanced and nonlinear load changes applied to feeder F1 ; positive-sequence, negative-sequence, and harmonic currents of (a) DG1 and (b) DG2 .
Fig. 7. (a) Instantaneous current waveforms, (b) five-level-inverter output voltage, and (c) voltage waveforms of each phase of DG1 ’s CHB inverter due to the nonlinear load connection to feeder F1 .
Fig. 8. (a) Instantaneous current waveforms, (b) five-level-inverter output voltage, and (c) voltage waveforms of each phase of DG1 ’s CHB inverter due to the single-phase load disconnection from feeder F1 .
Fig. 9. (a) Voltage THD and (b) VUF at DG1 ’s terminal.
Fig. 10. Voltages of dc links for DG1 ’s units.
Fig. 11. Dynamic response of DG1 to load changes; currents of FC stacks and PV units for each HPS. (a) Phase a, (b) phase b, and (c) phase c.
Fig. 12. Dynamic response of DG1 to load changes; average current of SC module of each HPS. (a) Phase a, (b) phase b, and (c) phase c.
This paper now an sufficient control strategy for an islanded microgrid including the HPS and CHB multilevel inverter under unbalanced and nonlinear load environment. The proposed method includes power executive of the hybrid FC/PV/SC power source and a voltage control method for the CHB multilevel inverter.
The main features of the planned HPS include high work, high power density, and fast transient response. Furthermore, a multi-PR controller is given to regulate the voltage of the CHB multilevel inverter in the presence of unbalanced and nonlinear loads. The work of the planned control strategy is examined using PSCAD/EMTDC software. The results show that the proposed method:
1) regulates the voltage of the microgrid under unbalanced and nonlinear load conditions,
2) reduces THD and improves power quality by using CHB multilevel inverters,
3) enhances the dynamic response of the microgrid under fast temporary conditions,
4) correctlly balances the dc-link voltage of multilevel inverter modules, and
5) efficiently manages the powers among the power sources in the HPS system.
 H.Zhou,T. Bhattacharya,D.Tran,T. S. T. Siew, and A. M. Khambadkone, “Composite energy storage system involving battery and ultracapacitor with dynamic energymanagement in microgrid applications,” IEEE Trans. Power Electron., vol. 26, no. 3, pp. 923–930, Mar. 2011.
 W. S. Liu, J. F. Chen, T. J. Liang, and R. L. Lin, “Multicascoded sources for a high-efficiency fuel-cell hybrid power system in high-voltage application,” IEEE Trans. Power Electron., vol. 26, no. 3, pp. 931–942, Mar. 2011.
 A. Ghazanfari, M. Hamzeh, and H. Mokhtari, “A control method for integrating hybrid power source into an islanded microgrid through CHB multilevel inverter,” in Proc. IEEE Power Electron., Drive Syst. Technol. Conf., Feb. 2013, pp. 495–500.
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