Research On Brushless DC Starter-Generator System For Aircraft Engine

Starter-generator system for the aircraft engine is an important part in the electricity systems of the aircraft. Some starter-generator systems during different phases of the aircraft electric power development are introduced in this paper subseaquently, and their characters are analyzed. Next, doubly salient electro-magnetic machine (DSEM) was selected as the starter-generator and the basic theory of the starter-generator system were researched in this paper. Then, an 18kW brushless DC starter-generator system for the aircraft engine was made successfully.According to the different rectifiers, three generating modes were given in this paper firstly. Then, mathematical model of DSEM was built, and basic characteristic of the generator and short circuit malfunction in different generating modes were studied by experiments and finite element simulation. Subseaquently, armature action, commutation overlap and load character in different generating modes were analyzed and calculated by finite element analysis software ANSOFT. The calculation method of the commutation inductance and formulars about commutation time, overlap angle were deduced. Next, a dual output voltages regulated technology of the doubly salient electro-magnetic generator was studied, and the dual output voltage regulator was made in this paper successfully.In order to keep the advantage of DSEG and improve the system efficiency, Doubly Salient Hybrid Excitation Genenrator (DSHEG) was performed. The structure of DSHEG was illustrated and its mathematical model was built. Basic characteristic of the generator—output characteristic at no load and under load, the characteristic between the exciting current and the load, short circuit character were researched by experiments and Finite Element Analysis. Armature action and commutation influencing on the load character in different generating modes were researched. Then, three working stages of DSHEG were studied and the boundary conditions of three stages were solved in this paper. Next, the design principle of DSHEG based on bidirectional symetrical exciting current and a bidirectional excitation voltage regulator were performed. The voltage regulator makes the output voltage of the generator stable by adoptig bipolar pulse width modulation control strategy. In the end, the stable and the dynamic experimental results of the DSHEG show that the character of the DSHEG is better than DSEG.Some important problems about the starting control were solved in this paper based on the requirements of the starting engine. The ripple of the torque at motoring is reduced greatly by improving the structure of the machine. The motor starting control algorithms based on the speed and the time was peformed. Then, the truth that Advanced Angle Control Mode (AACM) can improve output torque and power got verified by theory analysis and experiments. The table about the advanced angle value and the rotor speed was built by optimizing tne mechanical character at standard angle control mode and AACM. According to the table, DSEM can work at the best condition all the time by changing control strategy at different speed. In the end, the starter-generator system was built, and the experiments of the starting and generating were fullfilled successfully.