Parallel operation of inverter modules is the solution to increase the reliability, efficiency, and redundancy of inverters in microgrids. Load sharing among inverters in distributed generators (DGs) is a key issue. This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid. PQ control and droop control techniques are established to control the microgrid operation. P-f and Q-E droop control is used to attain real and reactive power sharing. The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge. To address these issues, two DGs are interfaced with two parallel inverters in an islanded AC microgrid. PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references. The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics. A dual control strategy is proposed for the AC microgrid under islanded operation without communication link. Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.
- Inverter parallel operation control strategy
- Droop control strategy
- Frequency restore
- Power sharing
In this paper, the enhanced droop and PQ control strategies for controlling parallel DGs in islanding mode of AC micro-grids were investigated to achieve flexible power regulation. The main advantage of this dual control strategy is to enable operation without any communication between the parallel DGs. The power tracking error for PQ control based inverters was investigated and the enhanced droop control implemented with predefined droop characteristics for power reallocation was proposed. To improve and restore the frequency, a frequency restoration scheme (FRS) implemented among the distributed generators was developed. The proposed droop controller provides stable operating under different control strategies in islanded operation and the DG voltage can quickly respond to the required voltage demand. The PQ controller can effectively track the active and reactive power and the droop control provides voltage control in islanded mode. The simulation results obtained from MATLAB/SIMULINK verified the stability of the load voltage and frequency.
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