Starting Control Techniques Of Aviation Brushless Synchronous Integrated Starter/Generator System

Integrated Starter/Generator(ISG)system is an important development direction for future aviation power supply system.Currently,the aircraft engine,used in high-power aviation AC power system in our country,is still started by a specialized starter.Traditional three-stage brushless synchronous generators do not have the function to start an aircraft engine.Independent starter and generator make the system bigger,heavier,less reliable and more complex.Thus,the research on the starting characteristics of three-stage brushless synchronous generators to realize ISG system is very meaningful.During the start process of the three-stage synchronous machine,the ability and smooth of output torque are affected by the control method of exciter and the excitation characteristics,such as weak,variable and pulsed excitation,of the main generator.At the same time,the load characteristics of aircraft engine is also affected by the environment.Therefore,the ability to start with large and variable load is required.Based on the excitation characteristics of the exciter,initial rotor position estimation for the main generator,excitation control method for the exciter and start control method for the main generator were studied in detail and a set of methods related to the start control for the aircraft three-stage brushless synchronous starter/ generator were proposed.Firstly,since the inductance parameters and saliency of the main generator is influenced by the pulsed field current,the initial rotor position estimation methods for constant-filed electric machines are no longer appropriate.According to the current response equations of the main generator windings injected with pulse voltage within the range of 360 electrical degrees and the effect of response current on magnetization/ demagnetization characteristics of the main generator,the current curve equation which can indicate the positive direction of the rotor unambiguously was derived.Then data fitting method was used to estimate the accurate initial rotor position of the main generator online.The proposed method simplified traditional two-step rotor position estimation methods,which need to estimate the rotor position first and then determine the positive direction of the rotor.Besides,the influence of the field current ripple on the detection accuracy is reduced effectively in this method.Secondly,stable output torque is required during different start stages to meet different starting characteristics,which sets rigorous requirements for single-phase AC excitation method,DC excitation method and switching method between them of the exciter.A normalized vector calculation method for both single-phase AC excitation and DC excitation was studied in this dissertation to solve the current impact problem during the switching from single-phase AC excitation and DC excitation.Then smooth switching was achieved and start stability of the main generator was improved.In order to increase the field current of the main generator and improve the start torque in stationary and low-speed states,dynamic switching excitation control method for the exciter was proposed based on the combination of AC and DC excitation output characteristics of the exciter.Thirdly,a Voltage Torque Closed-loop Control(VTCC)method,which is able to control the output torque large and smooth during the change of excitation and load conditions,for three-stage brushless synchronous starter/generators was proposed in this dissertation.Aiming at this situation,a Voltage Torque Closed-loop Control(VTCC)method for three-stage brushless synchronous starter/generators was proposed in this dissertation.The amplitude and angle of the voltage vector for the main generator were controlled separately in this method.The requirements that the main generator should have ability to output large torque with weak field current and smooth torque with variable and pulsed field current are met by the proposed method.Since that the load characteristics of the aircraft engine is affected by the environment,an ADRC-based control method for speed,current and phase angle was analyzed.The proposed method improved the adaptability of the start control system under variable load situation effectively,and realized the smooth start of the main generator.Finally,the start control system for the three-stage brushless synchronous starter/generator was designed and dead-time compensation method for the main generator was studied.The proposed excitation control method and VTCC start control method were verified in experiments,and start control performances of the main generator with traditional vector control method,V/F control method and proposed VTCC method were compared.Experimental results showed that the VTCC method can not only restrain the disturbance of the rotor harmonic current effectively,but also achieve effective regulation for the current vector of the main generator.Therefore,the proposed VTCC method had a better starting performance compared with vector control method and V/F control method.