Reduced Order Tracking 3-ph Phase-Locked Loops in Aerospace Applications

Modeling and analysis of a reduced order tracking 3-phase Phase-Locked Loop (PLL) based on a combined control principle (error + disturbance) to improve PLL locking performance is presented in this work. The principle is in synthesizing a feedforward control that is added to a Stationary/Floating Frame Transformation PLL or Synchronous (Delta Q) Frame Transformation PLL. The feedforward comprises a frequency-to-voltage converter based on a phase/frequency estimation using an algebraic summation while implementing an inverse feedforward control principle relative to the part of the feedback loop seen after the summing junction. The reduced order tracking PLL is shown to desensitize the system relative to the conventional part PI controller tuning parameters and is operated to lock on either linear or nonlinear load current waveform and for arbitrary frequency/phase profile while maintaining stability by minimizing system dynamics. Theoretically, for an ideal implementation of the inverse transfer function and no limitations imposed by physics, the system transfer function becomes of zero order and the phase error is zero. Practically, the steady-state phase error is close to zero and the system is of minimum dynamics/order. The PLL scheme is described and performance results are presented, demonstrating the tracking ability and stability in aerospace applications in which a 3-phase PLL is used.