Xianfei Xie

Optimized Design and Simulation of an Air-Core Pulsed Alternator

The air-core pulsed alternator has been studied for more than three decades. However, its optimized design theories are still rarely reported. The performance of the air-core pulsed alternator-based pulsed-power system is often closely associated with the electrical machine parameters, the system structure, and the load requirements. The parametric optimization of this type of alternator has a very important influence on the performance. This paper focuses on the optimization theory of the air-core pulsed alternator design, including the optimization of the magnetic field distribution, the turn number of armature winding, and the turn number of field winding. The features of the magnetic field distribution in the air-core pulsed alternators are analyzed based on the analytical expressions. By designing a ferromagnetic shield put on the outside of the stator, the radial magnetic field component increases and the circumferential one decreases. The optimization principles of the winding turn numbers are also deduced based on the system circuit and operation mode. The optimization theories are verified by system-level dynamic simulation. Finally, some rules are summarized, which are beneficial to the optimized design of the air-core pulsed alternator.

Discharge Process of the Multiphase Air-Core Compulsator-Based Railgun Systems

Along with the ever-increasing requirement of power and energy density in the electromagnetic launch field, the air-core compulsator has been the research focus for the last two decades. However, when considering the multiphase air-core compulsators designed for railguns, no existing published papers have investigated the different discharge processes and different performances caused by different phase numbers. This paper has investigated the different performances influenced by the phase number of the air-core compulsator. The current commutation is of great importance especially in the fast electromechanical energy conversion. The current commutation and pulse regulation in the discharge process of the multiphase air-core compulsator have been studied in detail. Three different railgun systems have been discussed in which a three-phase, a four-phase, and a novel five-phase compulsator are adopted. Besides, three sets of corresponding parameters have been designed and proposed for simulation under the premise that all compulsators have the same volume and weight. Different from the traditional applications in which the current commutation is always avoided, the key point in this paper is the utilization of the current commutation process. A new idea for the design of the phase number of the air-core compulsator is presented. The conclusion is pioneering and instructive to the design of the multiphase compulsator for railgun systems.

Analytical Calculation of Synchronous Reactances of Homopolar Inductor Alternator

In this paper, the direct-axis (d-axis) and quadrature-axis (q-axis) synchronous reactances of homopolar inductor alternator (HIA) are calculated. First, an approximate 2-D model of HIA is developed and its relative air-gap permeance function is described. Then, the analytical expressions for the synchronous reactances in the d-axis and q-axis are derived from magnetomotive force-relative air-gap permeance function theory, including armature reaction reactance and armature leakage reactance. Finally, theoretical results are compared with the simulation and experimental results.

Design Considerations of an Air-Core Pulsed Alternator in an Electromagnetic Railgun System

An air-core pulsed alternator is extremely attractive for driving the electromagnetic launchers. The reason is that the machine can offer high voltage and current performance in a single-element energy storage device, a smooth pulse profile, and naturally cycled current zeros, which can allow for extremely low muzzle currents and simplifies switching requirements. But because of the short history of the air-core pulsed alternator in China, the relevant theoretical research is not enough and the experience in fabrication is absent. It is really necessary to summarize a preliminary design method in order to rapidly determine the size and approximately evaluate the electrical performance of the machine. The optimization will be based on this first-stage design scheme. In this paper, based on the requirements of the railgun, some important design considerations of a seven-phase and six-pole air-core pulsed alternator are presented in detail. In addition, it is significant to obtain the analytical formulas for the first-stage design requiring less costs; these formulas intuitively allow us to expedite the design process and optimize the design scheme. Finally, some basic output parameters of the machine are given for the preliminary design; the designed pulsed alternator will generate 1.4 kV and drive a train of 1-MA pulses into a 5-m railgun, accelerating 200-g masses at 2 km/s.

Optimized design and simulation of a GW-scale Multiphase Air-Core Pulsed Alternator

Multiphase Air-Core Pulsed Alternators have been studied for almost two decades. However, its design and optimization theories are still rarely reported. The main parameters of this type of alternators have very important influence on the performance. These parameters are often closely associated with system performance parameters, the system structure and the load requirements. This paper begins with describing the basic design theory of the GW-scale air-core pulsed alternator. Then, the relationships of major parameters are analyzed, including the main dimensions, the magnetic field, the armature turns in series per phase, the number of turns per pole of the field winding, the load parameters and etc. Finally, the optimization theories are verified by system-level dynamic simulation.

3-D FEM Analysis on Electromagnetic Characteristics of an Air-Core Pulsed Alternator

In pulsed power supply for electromagnetic launchers, air-core pulsed alternators have obvious advantages to enhance the power and energy densities with a compact and lightweight structure, and it is gradually to be the prime candidate for pulsed power supply. Compared with conventional machines, an air-core pulsed alternator will supply large amounts of energy over millisecond time with a huge current as high as 1 MA and a high voltage reached several kilovolts. Since the short history of the air-core pulsed alternator in China, the related theoretical research is not enough and the fabrication experience is absent. At present, research has shown that the performance of the air-core machine cannot be evaluated by the 2-D method due to the nonexistence of ferromagnetic materials, and it is very necessary to carry out the 3-D analysis by a finite-element method (FEM). This paper will present a 3-D model of the machine according to the accurate geometric size, and the model is used to develop electromagnetic analysis by the FEM and a transient simulation about the no-load EMF is carried out too. In order to understand the mechanism and process of electromechanical energy conversion, it is obviously important to figure out the magnetic field distribution in the machine. Meanwhile, in order to evaluate the strength of the windings, the calculation of electromagnetic forces and torques is developed when the machine drives the electromagnetic rail gun with a current of 1 MA.

Research on the Excitation Control of Brushless Doubly-Fed Alternator in a Novel Pulse Capacitor Charge Power Supply

Brushless doubly-fed alternator (BDFA) has good application prospects in pulsed alternator. It works through the rotor’s pole pairs transformation function to get excitation indirectly. Since there are no brush and slip ring, BDFA is expected to have high reliability and long service life. This paper studies on the excitation control of BDFA in pulse capacitor charge power supply system. A mathematic model of BDFA is established. The power angle characteristic of BDFA and flux changing condition during discharging process is analyzed with this model. Based on the analysis, a novel excitation control theory is proposed. Simulation results are presented to illustrate the performance of this control strategy.

Simulation of a Seven-Phase Air-Core Pulsed Alternator Driving the Electromagnetic Rail Gun

As the most efficient and compact sources in pulsed power supply for electromagnetic launchers, the air-core pulsed alternator can supply a current as high as 1 MA with a voltage reached several kilovolts. The machine performs various functions, such as kinetic energy storage, electromechanical energy conversion, and power conditioning, making the electromagnetic launch system compact and lightweight. But due to the short history of the machine and the absence of fabrication experience in China, the air-core pulsed alternator is still in an exploratory stage, and there are lots of key technologies and problems needed to be researched deeply. Taking technical risks and manufacturing costs into consideration, a seven-phase air-core pulsed alternator has been proposed and the machine is under development. In this paper, operation principles of the electromagnetic launch system are presented in detail. The mathematical models of the seven-phase alternator and the rail gun are introduced. Based on the mathematical models, a simulation model about the electromagnetic launchers is built, and it is useful to help us figure out the operation characteristic when the self-excitation machine drives the electromagnetic rail gun with a 200-g projectile. As a result, it is convincing by simulation to prove the drive current can be as high as 1 MA and the projectile is with a velocity of 2 km/s at the exit. Simultaneously, violent transient situations will be illustrated in this text, such as the electromagnetic torque and the rotor speed. Meanwhile, simulation results can verify the analytical method and present the current and voltage straightforwardly. They also have great significance on choosing the proper high power switching devices.

Transient Analysis of Air-Core Pulsed Alternators in Self-Excitation Mode

In pulsed-power supply for electromagnetic launchers, air-core pulsed alternators have obvious advantages to enhance the power and energy densities. Compared with conventional machines, self-excitation mode is usually adopted due to the requirement of the large excitation current to establish the high flux densities in the air-core magnetic circuits. In this paper, a detailed description of the transient process involved with the air-core pulsed alternator operating at self-excitation mode is presented. First, it is necessary to supply a seed current rapidly prompting the alternator into the self-excitation mode. The capacitance and precharged voltage of the capacitor in excitation initialization module, which determine the seed current, are analyzed, and reasonable value ranges of the capacitance and the voltage are obtained. Then, when the machine is in self-excitation mode, a detailed study about the current and the voltage of the windings is carried out. Some innovational concepts, such as the equivalent impedance of the excitation winding R feq and the growth rate of the excitation current K fi , are proposed to simplify the transient analysis. They play a significant role to guide the optimization of our systems. Finally, the analysis is verified through the comparison with the Saber simulation results.

Design and simulation of a novel brushless Doubly-Fed Alternator for the pulse Capacitor Charge Power Supply

This paper presents a novel brushless doubly fed alternator (BDFA) based on the differential mode and conducts research on its applications in a pulse capacitor charge power supply (CCPS). Since there are no brushes, the brushless doubly-fed alternator is expected to have high reliability and long service life. The excitation winding of the BDFA that is placed in the stator slots can be supplied with either dc or ac. In previous studies, regardless of the rotor configuration, the natural speed of BDFA is 60 f/(p1 + p2), i.e., based on the additive mode. To increase the alternators natural speed, expand the alternators operation as well as control range and to promote the alternators power density, this paper presents the differential mode, i.e., natural speed is equal to 60 f/ρ1 - ρ2|. The author will introduce the detailed design method of the BDFA based on the differential mode. Utilizing the finite-element model of the alternator, we will analyze the magnetic field distribution and calculate inductance parameters of the BDFA. Subsequently, the inductance mathematic model of the BDFA will be established. We also establish the simulation model of the pulse CCPS. Finally, we will verify the feasibility of the design scheme for the BDFA through the simulation results in a pulse CCPS system.