Sensorless Starting Control of the Brushless Synchronous Starter/Generator by Using the Main Exciter as a Quasi-Resolver at Low Speed

The main generator (MG) and the main exciter (ME) are mounted on the same shaft in the brushless synchronous starter/generator (BSSG). Besides, the internal high-frequency signals, caused by the rotating rectifier, exist in the rotor windings of ME. These mechanical and electrical features of BSSG indicate that the sensorless starting control of MG could be conducted with ME. However, the existing research of this strategy is limited to extracting rotor position information from the steady-state characteristics of the rotor currents of ME and consequently has not fully exploited the potential. In this article, a dynamic sensorless starting control method of MG by using ME as a quasi-resolver is proposed. First, the injection mechanism of the excitation signals in the rotor of ME and the characteristics of the induced back electromotive force (EMF) in the stator of ME in different commutation modes are analyzed to clarify the dynamic operating principle of the quasi-resolver. Then, back EMF estimation based on extended state observer is presented and an envelope extraction method is proposed. According to the envelope features of the back EMF, a software-based resolver to digital conversion method is proposed. Finally, the effectiveness of this method is verified by experiments.

I. Introduction

For the purpose of achieving fuel consumption, noise, emission, and maintenance improvements, more electric aircraft (MEA) is gaining increased attention in aviation sector. Integrated starter/generator (ISG) system, acquiring a significant reduction in the mechanical complexity of the aircraft engine system by reusing the main generator as the engine starter, is a key technology of MEA [1], [2], [3], [4]. Three-stage brushless synchronous machines [5], [6], switched reluctance machines [7], [8], induction machines [9], [10], [11], permanent magnet synchronous machines (PMSMs) [12], [13], doubly salient electromagnetic machines [14], [15], and hybrid excitation synchronous machines [16] have all been considered for ISG. Among these machines, the three-stage brushless synchronous machine, a mature, and safe generator technology, has been widely adopted by commercial and military aircraft for many years. Therefore, there is a strong driving force in the aviation industry to operate this traditional generator also as a starter to realize the brushless synchronous starter/generator (BSSG).