An Integrated Method for Three-Phase AC Excitation and High-Frequency Voltage Signal Injection for Sensorless Starting of Aircraft Starter/Generator

This paper proposes an integrated method of three-phase ac excitation and high-frequency voltage signal injection (HFVSI) for sensorless controlled starting of brushless synchronous machines (BSM) used as starter/generator in variable frequency ac power systems of civil aircraft. Fixed 400 Hz of the three-phase ac power is adopted both for the ac excitation and HFVSI in the initial starting process to eliminate the bulky rotor position sensor for BSM. The resulting 6th sequence harmonic voltage determined by the rotating rectifier is utilized as the HFVSI into the field-winding of main generator without any extra high-frequency signal injection. The rotor position is estimated by the high-frequency response signals extracted from the armature windings of main generator. Due to the nonlinear rotating rectifier linked in the HFSI chain, a novel frequency-insensitive asynchronous demodulation strategy is proposed in this paper for rotor position estimation. Furthermore, the initial rotor position detection is calibrated by polarity decision of the induced currents of the armature windings within the establishment procedure of field current of the main generator at standstill. The effectiveness of the ac excitation and feasibility of rotor position estimation for sensorless starting control of BSM are validated by the simulation and experimental results.

I. Introduction

Due to the mature structure, high reliability, and low maintenance, the brushless synchronous machine (BSM) is still the most attractive candidate generator topology for both fixed-frequency and variable-frequency ac power generation for civil aircraft. It also has the potential to be used as the starter for engine cranking [1]–[3]. In the generation mode, the ac output of the main exciter of BSM is rectified by a rotating rectifier and employed for the dc excitation of main generator. The output voltage magnitude can then be regulated through an automatic voltage regulator to compensate for the variable speed and changing load. However, in the starting mode, the main exciter cannot offer excitation power for the main generator from standstill to the low speed range by the conventional dc excitation method. Thus, excitation becomes the first key issue of BSM used as starter in variable frequency ac power system [4].