Electromagnetic Launch Applications Research Articles

Design of Multilayer Winding-Based Halbach Array PM Compulsator

Compulsator provides higher energy density and comparable power density for pulse power supply than capacitor-based sources. With the added feature of natural current, zero-crossing capabilities make compulsator the ideal choice for pulse power supply to electromagnetic launch applications. A multilayer Halbach array permanent magnet (PM) compulsator is designed to achieve the desired performance. The multilayer winding arrangement is considered to minimize the self-inductance and to maximize the short-circuit current capability of the compulsator. Thus, different winding configurations with series and parallel connections in the compulsator are presented in detail. The mathematical modeling of the designed compulsator is also presented in brief. The designed compulsator is simulated by considering temperature rise, PM demagnetization effect, and so on. The designed compulsator performance in a dead short circuit of all phases and with single-phase short-circuit condition is presented. The obtained results show that the designed compulsator achieves the target objective.

Design Aspects and Thermal Characteristics of Single-Sided Linear Induction Motor for Electromagnetic Launch Application

This paper presents the design aspects and thermal characteristics of single-sided linear induction motor (SLIM) for Electromagnetic launchers. It is designed to accelerate a 50 kg mass through a distance of 3 meters within a minuscule time to an exit velocity of 50 m/s. A study of the motor’s parametric variation based on the launching requirement has been performed. Its performance characteristics are obtained using 3D FEM and verified analytically using Parseval’s method. The FEM, analytical and experimental verification of the thrust characteristics of different secondary conductive sheet materials namely, aluminum, beryllium copper and German silver shows that, the latter exhibits superior characteristics than the former two, because its thrust-velocity curve is close to inverse linear relationship (stable region of operation of LIM), which significantly reduces the accelerating time during the launch. The designed SLIM is assessed for its thermal performance with materials having temperature-dependent electrical properties by carrying out a coupled-field FEM simulation. The conclusions demonstrate that the electromagnetic and thermal assessments are in tandem with each other as required for launching.

Discussion on Topologies of Quick Response IPPS Suitable for Closed-Loop Control of EML

High energy density makes inductive pulsed power supply (IPPS), a research focus of supplies for electromagnetic launch (EML). However, in existing IPPS topologies, the charging and discharging stages of the inductors cannot be separated, so the response time of IPPS can be as long as ten or even tens of milliseconds. For this reason, the real-time closed-loop control of the output current and muzzle velocity based on IPPS is nearly impossible, which might be one of its biggest drawbacks compared to the capacitive pulsed power supply (CPPS). In this article, a novel current maintainable meat grinder (CMMG) circuit capable of fast response for EML applications is proposed, in which the antiparallel diode can provide a current maintaining path. After the inductor completes its charging process, the current can be maintained for a period of time. Thus, the circuit can be in a hot standby state and can be triggered with a very short delay. Subsequently, two commutation methods for the CMMG circuit are explored. The first one is to introduce the inverse current commutation with semiconductor device (ICCOS) branch. In its experiment with an inductance energy of 22 kJ, the circuit maintains 77% of the charging energy in the first 10 ms and is triggered successfully after 28 ms with almost zero response delay. The second method is the superconducting switching technology, based on which the CMMG with self-shutdown circuit is proposed and simulated.

Research on the Compensation Matching Design and Output Performance for Two-Axis-Compensated Compulsators

Compulsators are popular choices for various high-power electromagnetic launch applications, especially for the electromagnetic railgun. A two-axis-compensated compulsator with lower internal impedance and higher power density was proposed in the authors’ previous paper. The field windings and compensating windings are allocated electrical orthogonally, providing the opportunity to design the direct-axis and quadrature-axis compensations independently. Due to the excitation function of the field windings, as well as field windings and compensating windings at the same rotor periphery, the ratio between $d$ -axis and $q$ -axis compensation is determined not only by the waveform of the air-gap flux density but also by the occupied space of windings, electromagnetic force during discharge and temperature rise and cooling condition. All these aspects mentioned above were analyzed in this paper. Furthermore, the output performance for single pulse discharge of a 2-m railgun with 100-g armature and multiple pulses discharge of a 5-m railgun with 300-g armature was simulated and compared. The results indicated that the two-axis compensation could obtain benefits by introducing more sinusoidal discharge currents for single pulse mission comparing to traditional compensation structure, whereas no obvious advantages for a flat-topped current waveform for multiple pulses mission.

Design of a Compulsator to Drive a Railgun

Compulsators are ac generators which are used for electromagnetic launch applications over the past few decades. This paper presents the work carried out by the authors to design a compulsator for a railgun which has been built and tested with a capacitor bank of 20 kJ as the pulsed-power source in the author’s laboratory. The generator topology selected for the compulsator is a single phase, two-pole machine with iron core and passive compensation. The design is based on the criterion of achieving maximum projectile exit velocity with the additional condition that natural current zero is synchronized with the instant of the projectile’s exit. The effect of varying the different parameters of the compulsator on the performance of the system has also been studied and discussed in this paper. By means of performance analysis, the necessary background for the design of the actual compulsator has also been achieved.

Research on Superconducting Induction Maglev Linear Machine for Electromagnetic Launch Application

Linear induction machines (LIMs) are widely used in the electromagnetic launch systems. Based on the MgB2 type superconducting wires, a superconductive LIM with an electrodynamic type structure (EDS) is proposed in this paper. The moving primary magnetic field induces eddy current in the conductor plate and the inductive eddy magnetic field acts back on the primary field. The lift force and thrust force will be produced between the primary and the secondary. Referred to the analysis of some famous researchers’ theory and achievements, an improved method is proposed and applied to MgB2 type superconducting LIM. The calculation results are obtained and compared with finite-element analysis. The results indicate the method is practical and valid, which can lead the design and save design time.

Inductances and Phase Coupling Analysis of Tubular Permanent Magnet Machines With Transverse Flux Configuration

This paper performs the inductance and phase coupling analysis of a tubular permanent magnet machine with transverse flux configuration for electromagnetic launch (EML) applications. Self-inductance and mutual inductance are calculated by employing a frozen permeability finite element technique, and the results are validated by measurement on a prototype machine. The analysis of phase coupling problem is then undertaken, and it has been shown that the tubular transverse flux machine has the merit of magnetic decoupling between phases, and thus shows a brilliant prospect in EML applications. The influence of armature reaction on the inductance is also investigated, and it indicates that at higher current, the inductance fluctuates once instead of twice within one electrical cycle, which is quite different from that in conventional machines.

Evaluating Material Performance Between High-Current Contacts

A high-current test fixture (HiCTF) was developed to examine material response to repulsive forces generated between electrically conducting material pairs during short pulses of high current, similar to conditions experienced in Electromagnetic Launch applications. Based upon Holm's contact theory with additional preload and pressure distribution parameters, this test fixture was designed to use a loading press to apply preload to the test specimens while conducting current through the specimen contact interface. The fixture uses an aligned mechanical loading device to provide a preload across the contact interface of the specimen. The HiCTF will allow for investigation of contact response sensitivity as a function of its degradation, impact of geometry variation, surface conditions, material pairing, preload, and contact integrity. Statistically based experimental designs have been constructed and analysis methodologies developed that incorporate likelihood ratio analysis and the Neyer method. The Neyer D-optimal design method, used in sensitivity testing of explosives, shows promise as an appropriate test method for HiCTF results and will be used to provide sufficient information for comparisons and developmental thresholds. Results from HiCTF testing provide insight into the electrical contact phenomenon and high-current material response. This paper provides an overview of the HiCTF, its motivation, analysis methodology, results, observations, and lessons learned.

Design Considerations of Tubular Transverse Flux Linear Machines for Electromagnetic Launch Applications

Due to the achievable high force densities, permanent magnet linear machines with transverse flux configurations are gaining increased interest in electromagnetic launch (EML) applications, in which the force density demand is crucial. This paper deals with the design of a tubular transverse flux linear machine (TFLM) targeting EML applications, and the issues pertinent to its topology selection, design optimization, and thermal modeling are discussed. By overall comparison of practical topologies and technologies of the TFLM, a tubular moving-magnet topology with separated flux paths is believed to be more appropriate. Design optimization is then performed to maximize the thrust force under specific volumetric constraints. It is shown that the thrust force is more sensitive to the stator segment length, instead of the magnet thickness. Regarding the overload requirement inherent in EML systems, special focus is given on the thermal characteristics of the TFLM at overload conditions, and it is proved that the machine shows appreciable overload capability. Measurements carried out on a prototype TFLM have validated the predictions.

Design, Analysis, and Testing of a Novel Permanent Magnet Compulsator

In electromagnetic launch (EML) applications, a compensated pulsed alternator is an effective form of pulsed power supply because of its high energy density and power density. The basic advantages of compensated pulsed alternators for EML applications are their higher energy density than capacitors and their export ac output that is suitable for transmission and transformation. In general, external excitation is adopted as a form of self-excitation or pulse excitation in compensated pulsed alternators with an iron core or air core. Using this form not only results in heavy and bulky components but also complicates and reduces the reliability of the system. This paper proposes a novel compensated pulsed alternator that is excited by permanent magnets (PMs) and equipped with an iron core or air-core stator. This system does not require any excitation converter or brush–slip ring, thereby making it more reliable, less massive, and less voluminous than the system with self-excitation or pulse excitation. In addition, analytical models are introduced to simulate the air-gap magnetic distribution, back-electromotive force, pulsed current wave, discharge torque, and energy exchange of this machine. A scale-model prototype of the PM-compensated pulsed alternator is designed, fabricated, and tested. The actual output voltage waveform and pulsed current waveform are sampled and compared with the predicted ones. The results show that the design of the PM compulsator is feasible and reliable.

Numerical Analysis and Design Optimization of a Homopolar Inductor Machine Used for Flywheel Energy Storage

This paper investigates a homopolar inductor machine (HIM) for flywheel energy storage in electromagnetic launch applications. An equivalent 2-D finite-element model is presented to predict the machine behavior, and the effectiveness of the equivalence is validated by the comparison of 2-D and 3-D results. Based on the 2-D model, the rotor tooth shape is then optimized to achieve high fundamental value of the air-gap flux density for a given rotor diameter. It is shown that the proposed 3-D to 2-D equivalence can predict the performance of the HIM in an accurate and fast way, which is quite valuable in the design stage of a HIM.

Analytical Modeling and Design Optimization of Linear Synchronous Motor With Stair-Step-Shaped Magnetic Poles for Electromagnetic Launch Applications

In this paper, a stair-step-shaped magnetic pole structure is proposed to use in a permanent-magnet linear synchronous motor (PMLSM) for its application in an electromagnetic launch system. The aim of this configuration is to shape the air-gap flux density distribution produced by poles to be as close to a sine waveform as possible for the reduction of thrust ripple and the increase of motor controllability. An analytical model is derived for the PMLSMs by solving Maxwell equations and applying the superposition theorem for calculating the magnetic field, electromotive force, and thrust/torque of the motor. Magnet dimensions are then optimized using the analytical method and genetic algorithm, where the reduction of air-gap flux density harmonics is considered as the optimization target. Finally, the effectiveness of the proposed technique to enhance the motor performance is investigated by a time-stepping transient finite-element method. The results show an improvement in the optimal motor performance.

Analytical Modeling and Design Optimization of Linear Synchronous Motor With Stair-Step-Shaped Magnetic Poles for Electromagnetic Launch Applications

Analytical Modeling and Design Optimization of Linear Synchronous Motor With Stair-Step-Shaped Magnetic Poles for Electromagnetic Launch Applications

Design of a 3-m-Long Electromagnetic Launcher

A 3-m-long 30-mm square bore launcher has been constructed for electromagnetic launch application at the Institute of Electrical Engineering, Chinese Academy of Sciences. The main purpose of the launcher is to conduct the basic and applied research in electromagnetic launch. An optimum structure of the insulators was adopted through the stress analysis using the software ANSYS. In order to know about the variation of the gap under a certain stress, an air pressure piston (maximum air pressure of 5 MPa) and a position sensitive detector were adopted. The measuring results have shown that the rail gap decreases gradually from breech to muzzle; this kind of design can abate the erosion of the rails caused by arc discharge effectively. A total of 85 tests has been performed, including 17 tests of single-module discharging and 68 tests of nine-module sequential discharging, and a highest muzzle velocity of 1.9 km/s with a 45-g mass was achieved, operating at a current of 410 kA and 2-ms pulse duration. This launcher is now used for the fundamental research on armature structure, performance of the pulsed power supply, and the diagnostic system. A novel launcher based on the previous experimental results is under development.

Fast, transient energy extraction from high-frequency AC alternators for use in electromagnetic launch applications

This paper describes work toward transient energy extraction from high-frequency alternators to drive electromagnetic launchers through intelligent triggering of thyristors or silicon controlled rectifiers (SCR). The work was done using a three-phase, 75 kVA level motor-generator set with a dc machine acting as the load. This system serves as a scale model to develop control techniques for full-scale, multimegajoule applications. With the use of a microcontroller and advanced sensors, the system is able to maintain synchronization of the SCR converter with the generator voltage despite dynamically changing frequency and voltage distortion.

Compact, lightweight, superconducting power generators

Many future military systems will depend heavily on high electrical power input ranging from hundreds of kilowatts up to the multimegawatt level. These weapon systems include electromagnetic launch applications as well as electrically driven directed energy weapons (DEW), such as high-power microwaves and solid-state lasers. These power generation subsystems must often be packaged using limited space and strict weight limits on either ground mobile or airborne platforms. Superconducting generators made of high-temperature superconductors (HTS) will enable megawatt-class airborne power systems that are lightweight and compact. Also discussed briefly are new advances in HTS conductors and refrigeration systems furthering the development of HTS power systems.

Investigation of a 3-D hybrid finite-element/boundary-element method for electromagnetic launch applications and validation using semianalytical solutions

The hybrid finite element/boundary element (FE/BE) computational scheme is advantageous in that it satisfies boundary conditions at infinity while avoiding meshing and computations in the air regions. Of numerous hybrid schemes, one using the fundamental solution of Poisson's equation as the weighting function has been employed successfully in many fields. Analyses in electromagnetic (EM) launch usually involve strong coupling among EM, thermal, and structural equations. The hybrid method has the added benefit that it may be fashioned to incorporate the effect of structural deformations on EM fields. Here, a three-dimensional (3D) hybrid algorithm using the fundamental solution of Poisson's equation as the weighting function is investigated and implemented in the parallel version of the code electromechanical analysis program in 3D (EMAP3D). The method is validated using two examples with semianalytical solutions: a 3D ring conductor with rectangular cross section carrying uniform current, and a quadrupole configuration with four independent, closed-ring conductors excited by imposed potential differences. The solutions obtained using the hybrid method match the semianalytical solutions within approximately four percent deviations.

Compact capacitor technology for future electromagnetic launch applications

Advanced power systems for electromagnetic propulsion depend on capacitor banks as the first stage of pulsed power. Significant electrical energy is required to support a number of anticipated launch applications. In support of successful integration of these technologies, TPL has developed an improved dielectric material for high energy density capacitors. Recent developments have led to a novel dielectric film that can be fabricated and incorporated into innovative, high-voltage designs using conventional manufacturing processes. Full-scale (100 kJ) capacitors incorporating TPL's established film technology is projected to provide an energy density between 3.5 and 4.0 J/cm/sup 3/.

A compound opening switch for electromagnetic launch applications

The authors describe a repetitive compound opening switch capable of carrying mega-ampere currents and holding tens of kilovolts while opening in the submillisecond regime. The switch is made up of three elements. First, a wide foil to carry large currents for long periods of time is ripped open at sonic velocities to transfer the current to a fuse. The fuse then provides commutation and voltage holding, also allowing time for the foil opening to clear. The third element is a CVR (constant voltage resistor) with an I-V characteristic like that of back-to-back Zener diodes. The CVR limits the voltage excursion of the fuse. The current is transferred to the CVR from the fuse before it explodes, and the required switch dissipation is provided in the CVR. Analysis of this compound switch, including fundamental limitations and design issues, is presented. Preliminary experimental results for foil ripping and the fuse/CVR combination are included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>