In this article, a half-tangent phase-locked loop (HTan-PLL) is proposed for variable-frequency grids of more electric aircrafts. First, the pros and cons of the synchronous reference frame PLL (SRF-PLL) are discussed in a nonlinear framework. To address the disadvantages, a half-tangent phase detector (PD) is developed and a novel PLL is then proposed. Subsequently, a phase portrait-based analysis and a Lyapunov function-based argument are provided. It is proven that the HTan-PLL has a good performance in terms of steady-state accuracy and fast dynamics, even under large frequency changes. Compared with the conventional SRF-PLL, the proposed HTan-PLL outperforms with the following features: faster dynamics than the SRF-PLL when the frequency varies largely; no unstable equilibrium points, while the SRF-PLL has infinite unstable equilibrium points; and when the grid frequency jumps widely, the HTan-PLL converges to the unique equilibrium point (0,0). By contrast, the SRF-PLL goes to different equilibrium points. Experimental tests are provided, which verify the superior performance of the HTan-PLL.