This paper suggest a hierarchical active power management method for a medium voltage (MV) islanded microgrid containing a multihybrid power conversion system (MHPCS). To promise excellent power management, a modular power conversion system is completed by parallel connection of small MHPCS units. The hybrid system includes fuel cells (FC) as main and supercapacitors (SC) as integral power sources.
The SC energy storage satisfy the slow temporary response of the FC stack and hold the FC to meet the grid power demand. The planned control method of the MHPCS contain three control loops; dc-link voltage controller, power board controller, and load current giving controller.
Each distributed generation (DG) unit uses an flexible proportional resonance (PR) controller for control the load voltage, and a droop control method for average power giving among the DG units. The work of the planned control method is confirmed by using digital time-domain simulation learning in the PSCAD/EMTDC software situation.
- Fuel cell (FC)
- Multihybrid power conversion system (MHPCS)
- MV microgrid
- Supercapacitor (SC)
Fig. 1. (a) MV microgrid consisting of two DG units. (b) Proposed structure of hybrid FC/SC power conversion system.
Fig. 2. Proposed structure of the hybrid FC/SC power source.
EXPECTED SIMULATION RESULTS:
Fig. 3. Balanced load changes in feeders F3 and F1. (a) Instantaneous real and (b) instantaneous reactive powers of the feeders.
Fig. 4. Instantaneous voltages at the DG unit terminals during balanced load changes in feeder F1, (a) DG1 and (b) DG2 .
Fig. 5. Frequency of islanded microgrid during balanced load changes.
Fig. 6. Dynamic response of the DG units to balanced load changes: (a) real power, and (b) reactive power components.
Fig. 7. Dynamic response of DG1 units to balanced load changes: (a) FC stack and SC module power of first hybrid unit; (b) FC stack and SC module power of second hybrid unit; and (c) dc-link voltage.
Fig. 8. Unbalanced load change in feeder F1. (a) Instantaneous real and (b) instantaneous reactive powers of the feeders.
Fig. 9. Dynamic response of the DG units to unbalanced load change with conventional PR controller: (a) real power, and (b) reactive power components
Fig. 10. Dynamic response of the DG units to unbalanced load change with adaptive PR controller: (a) real, and (b) reactive power.
Fig. 11. Dynamic response of DG1 units to unbalanced load change: (a) FC stack and SC module power of first hybrid unit; (b) FC stack and SC module power of second hybrid unit; and (c) dc-link voltage.
This paper presents a hierarchical active power management method for a MV islanded microgrid considering the MHPCS. The planned method includes power authority of the FC/SC hybrid system, current sharing among the MHPCS components, voltage control of the ac-side, and power sharing among the DG units.
The SC energy storage satisfy the slow temporary reaction of the FC stack. An flexible PR controller and a droop controller are, usually, used to efficiently manage the load voltage and to share the average power among the DG units. The work of the proposed control method in both balanced and unbalanced load switching is examined using PSCAD/EMTDC software. The results show that the planned method:
- improve the dynamic reaction of the microgrid in fast transients;
- correctly divide the load current among the FC/SC hybrid units;
- strongly manage voltage and density of the microgrid;
- is able to share the average power among the DG units even under unbalanced environment;
- efficiently remove the low density temporary of power components; and
- locally satisfy the unbalanced loads.
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