Synchronization of Multiple Pulsed Alternators Discharging into an EM Launcher

As the energy level in the projectile increases it becomes necessary to use multiple pulsed alternators discharging in parallel into the EM launcher. Another reason for having more than one machine is to compensate torque and gyroscopic effects of the pulsed alternator. This requires that machines be built in counter-rotating pairs. These machines are identical in all respects except for their direction of rotation. A study was conducted to determine how the machines can be motored so that they stay in lock step in speed and phase as they are motored to full speed. The methods of connecting these multiple machines are discussed. The aim of the connection scheme is to allow the machines to naturally stay locked in speed and phase throughout its operating range. Sensitivity of the performance of these machines to small variations in the machine parameters, which is to be expected in the machines, is discussed. Sensitivity of the discharge performance to small phase angle mismatches due to tolerances is also discussed. To verify the conclusions of the study an experiment was performed on two identical 50 kVA machines discharging into a low impedance load. The motoring system that is discussed in the study was implemented in this experiment which kept the machines in lock step. This motoring system is described. Thereafter discharges were made at various speeds and field current levels. Phase angle mismatches were introduced between the two machines to see how it affected current sharing. The results and conclusions of these tests are presented in this paper.