© 2016, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved. This paper presents a pretty comprehensive analysis on stability issues of control for active power filter (APF) installed in an electric grid where megawatt doubly fed induction generator (DFIG) wind farm is connected. Major objectives of this paper are to evaluate roles and impacts of main design parameters in the controller of APF. As well, the ultimate goal is to determine the stable value range and the suitable-performance value range for a proportional control coefficient in APF. Wherein, firstly, background theories of the voltage-detection control method for APF to reduce the voltage and current distortions on the electric grid are described. Furthermore, an appropriate equivalent circuit of a typical grid-connected DFIG wind farm with APF to analyze impedance in the frequency domain is introduced. After that, mathematical formulas and algorithm to determine the stable value range and suitable performance value range for the control coefficient in APF are proposed. Finally, results obtained with the suggested equivalent circuit and impedance analysis technique are shown and discussed in detail. Besides, different operation cases of the controller of APF and the illustrative DFIG wind farm, including parametric uncertainties of the electric grid, also are examined to assess effectiveness of the proposed analysis algorithm.