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A Control Method for Integrating Hybrid Power Source into an Islanded Microgrid through CHB Multilevel Inverter ABSTRACT: This paper proposes a control strategy for an islanded microgrid to effectively coordinate hybrid power source (HPS) units and to robustly control individual interfaced inverters under unbalanced and nonlinear load conditions. Cascaded H-bridge (CHB) multilevel inverters are flexibly deployed in order to enhance the power quality and redundancy. The HPS employs fuel cell (FC) as the main and super capacitors (SC) as complementary power sources. Fast transient response; high performance; and high power density are the main characteristics of the proposed HPS system. The presented control strategy consists of a power management strategy for the HPS units and a voltage control strategy for the CHB multilevel inverter. A multi proportional resonant (multi-PR) controller is employed to regulate the load voltage at unbalanced and nonlinear load conditions. The proposed multi-PR controller includes a fundamental voltage controller with harmonic compensators. Digital time domain simulation studies in the PSCADIEMTDC environment are given to verify the overall proposed system performance.
KEYWORDS: 1. Hybrid power source 2. Fuel cell 3. Supercapacitor 4. CHB multilevel inverter 5. Multi-PR
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0-9347143789/9949240245 CIRCUIT DIAGRAM:
Fig. I. Proposed structure of the hybrid FC/SC power source.
CONTROL SYSTEM
Fig. 2. Proposed control strategy of hybrid FC/SC power source
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EXPECTED SIMULATION RESULTS:
Fig. 3. Microgrid response to unbalanced and nonlinear load changes; (a) Instantaneous real and reactive power. (b) Positive-sequence, negativesequence, and harmonic components of load
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Fig. 4. (a) Instantaneous current waveforms, (b) switching patterns of the output voltage, and (c) voltage waveforms of each phase of the DG unit's CHB inverter due to the nonlinear load connection.
Fig. 5. (a) Instantaneous current waveforms, (b) switching patterns of the output voltage, and (c) voltage waveforms of each phase of the DG unit's CHB inverter due to the single-phase load disconnection.
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Fig. 6. (a) voltage THD, and (b) voltage unbalance factor at DG unit terminal.
Fig. 7. The dc-link voltage waveforms to the unbalanced and nonlinear load changes.
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Fig. 8. Dynamic response of the DG unit to load changes: currents of FC stacks and SC units of each HPS, (a) phase a, (b) phase b, and (c) phase c.
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CONCLUSION: This paper presents an effective control strategy for an autonomous microgrid considering the HPS and CHB multilevel inverter under unbalanced and nonlinear load conditions. The proposed strategy includes power management of the hybrid FC/SC power source and the CHB multilevel inverter voltage control. The main characteristics of the proposed HPS are high performance; high power density; fast transient response. Furthermore, a multi-PR controller is presented to regulate the voltage of the CHB multilevel inverter in the presence of unbalanced and nonlinear loads. The performance of the proposed control strategy is investigated using PSCADIEMTDC software. The results show that the proposed strategy: • robustly regulates the voltage of the microgrid under unbalanced and nonlinear load conditions; • reduces THD and improves power quality by using CHB multilevel inverters; • enhances the dynamic response of the microgrid; • accurately balances the dc-link voltage of each H-bridge cell; and • effectively manages the power among the power sources in the HPS system.
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0-9347143789/9949240245 REFERENCES: [l] W. Liu, J. F. Chen, T. Liang, and R. Lin, "Multicascoded sources for a high-efficiency fuelceU hybrid power system in high-voltage application," IEEE Trans. Power Electron., vol. 26, pp. 931-942, Mar. 2011. [2] IEEE Recommended Practice for Electric Power Distribution for Industrial Plants. ANSIIIEEE Std. 141, 1993. [3] IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power System. IEEE Std. 519, 1992. [4] J. Pereda and J. Dixon, "23-level inverter for electric vehicles using a single battery pack and series active filters," IEEE Trans. Veh. Techno!., vol. 61, pp. 1043-1051, Mar. 2012. [5] A. Ghazanfari, M. Hamzeh, H. Mokhtari, and H. Karimi, "Active power management of multihybrid fuel celIlsupercapacitor power conversion system in a medium voltage microgrid," IEEE Trans. Smart Grid, vol. 3, pp. 1903-1910, Dec. 2012.
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