Integral-type half-tangent phase-locked loop for more electric aircraft grids

In this paper, an integral-type half-tangent phase-locked loop (IHTan-PLL) is proposed for the varying-frequency AC grids of more electric aircraft (MEA). First, the performance of the synchronous reference frame phase-locked loop (SRF-PLL) and half-tangent phase-locked loop (HTan-PLL) is discussed from a large-signal viewpoint. When the frequency changes largely, the SRF-PLL has many oscillations and endures a rather long transient process. The HTan-PLL can address the large frequency jumps. However, for the varying-frequency AC grids with harmonic disturbances, the HTan-PLL still has oscillations in estimating the frequency when the frequency jumps largely. To enhance the performance of the SRF-PLL and HTan-PLL, the IHTan-PLL is developed for the varying-frequency AC grids with harmonic disturbances. The IHTan-PLL performs better than the SRF-PLL and HTan-PLL in addressing the large frequency jumps. Specifically, under any large frequency changes, the IHTan-PLL still converges to the equilibrium point (0,0), and no oscillations emerge. In addition, the IHTan-PLL has better steady-state accuracy in estimating the frequency than the SRF-PLL and HTan-PLL. The experimental results also demonstrate the superior performance of the proposed IHTan-PLL.