Multistage Control of Weak Microgrid with Power Quality Improvement Based on APF

The power quality of weak microgrid is sensitive due to the nonlinear loads and power electronic devices are applied, and the adjusting automatically compensation function of equipment self is inadequate and ineffective. For this, the control characteristic of active power filter(APF)is studied, and the droop control is analyzed in weak microgrid especially under the isolated island, and the principles of parameter adjustment are proposed. Then the multistage control algorithm of weak microgrid is proposed that improve the power quality and reliability based on APF, the algorithm is that the APF execute multistage filtering process according to the characteristics of harmonic and the other source are designed under droop control scheme, and the constraint condition which considering the THD of load current makes it contributing for the stability and reliability between APF and sources. Further, the mutual influence between multistage control algorithm and transition loads shedding considering different degrees of importance are discussed so that the scheme achieve a higher reliability. Finally, the effectiveness of the control algorithm proposed that taking oil field microgrid as an example in this paper is demonstrated through simulation and analyses.