Assessment of losses in the field coil of the compulsator under dynamic conditions

Abstract

Abstract--Air core compensated pulsed alternators are being developed as compact power supplies for tactical electromagnetic gun systems. The field coil of the compensated pulsed alternator is a critical component that establishes the excitation magnetic field. Since the machine is air cored the number of ampere-turns required from the field coil are significant, especially considering that the excitation flux density near the armature is typically in the range of about 3 T to 4 T and that near the field conductors in the range from 7 T to 10 T. The rotating nature of the field coil requires that it be light so that it can be supported under centrifugal loads. This implies that the current density in the field coil conductors is quite large. One way of overcoming the excessive heating associated with the high current density is to charge the field coil fast (in tens of milliseconds). However charging the field coil too fast also results in transient losses due too proximity and skin effects. These must be accounted for in the design and simulation of these machines.During the discharge into the load, transient currents flow in the armature winding. These currents produce magnetic fields that interact with the field coils and produce additional losses. This calculation is complicated by the fact that there is relative motion between the conductors. This paper describes a two dimensional numerical analysis that has been conducted to evaluate the losses in the field coil under these two dynamic conditions. The method integrates circuit analysis with finite element calculations. This approach is essential because the field coil conductors have a connectivity that must be described in the calculations. The motional aspects have been accounted for by choosing a reference frame on the rotor and carrying out the calculations in the d-q frame attached to the field coil.The results of this analysis are presented, along with the means of optimizing the field coil and machine geometry in view of the transient losses.

Optimized Design and Simulation of an Air-Core Pulsed Alternator

“…The air-core pulsed alternator has been studied for more than three decades [2], [3]. However, its optimized design theories are still rarely reported [4], [5]. The performance of the air-core pulsed alternator-based pulsedpower system is often closely associated with the electrical machine parameters, the system structure, and the load requirements [6].…”

The Modeling and Calculation on an Air-Core Passive Compulsator

“…A change of variables for the rotor variables offers no advantage; however, a change of variables is beneficial to the stator variables. Because of the complexity of the PCPA, we use standard Park's transformation [14]- [17], which is often used in the analysis of rotating machines to transform the six-phase system (labeled a, b, c, and d for the four phases, labeled s1 and s2 for the compensation device) variables associated with the PCPA (e.g., current and voltage) into direct-quadrature (DQ) variables. Simulations using DQ models are often more computationally efficient 0093-3813 © 2015 IEEE.…”