Electromagnetic Launch System Research Articles

Theoretical model of lithium iron phosphate power battery under high‐rate discharging for electromagnetic launch

AbstractDue to the large error of the traditional battery theoretical model during large‐rate discharge for electromagnetic launch, the Shepherd derivative model considering the factors of the pulse cycle condition, temperature, and life is proposed by the Naval University of Engineering. The discharge rate of traditional lithium‐ion batteries does not exceed 10C, while that for electromagnetic launch reaches 60C. The continuous pulse cycle condition of ultra‐large discharging rate causes many unique electrochemical reactions inside the cells. The traditional model cannot accurately describe the discharge characteristics of the battery. The accurate battery theoretical model is an important basis for system efficiency calculation, precise discharge control, and remaining capacity prediction. To this purpose, an experimental platform for electromagnetic launch is built, and discharge characteristics of the battery under different rate, temperature, and life decay are measured. Through the experimental test and analysis, the reason that the traditional model cannot accurately characterize the large‐rate discharge process is analyzed. And a novel battery theoretical model is designed with the help of genetic algorithm, which is integrated with the electromagnetic launch topology. Numerical simulation is compared with the experimental results, which verifies the modeling accuracy for the large‐rate discharge. On this basis, a variety of discharge conditions are applied to test the applicability of the model, resulting in better results. Finally, with the continuous cycle‐pulse condition in the electromagnetic launch system, the stability and accuracy of the model are confirmed.

Research on current decoupling control of six‐phase permanent magnet linear synchronous motor for electromagnetic launch

AbstractSix‐phase permanent magnet linear synchronous motor (PMLSM) for electromagnetic launch (EML) system presents the characteristics of a high order, nonlinearity, multivariable, strong coupling, and nonperiodic transient operation in the synchronous rotating coordinate system, posing a great challenge to the dynamic response ability of the current loop. Existing research on current decoupling control (CDC) mainly focuses on cross decoupling within a three‐phase system, even though there are neither decoupling methods for multiphase systems nor effective evaluation criteria for the decoupling and dynamic response performances. From this perspective, this paper first presents an equivalent reduced‐order complex‐matrix dynamic mathematical model of six‐phase PMLSM and analyze its transient coupling characteristics during the process of EML. Then, the CDC methods of six‐phase PMLSM based on direct compensation and matrix diagonalization principles are realized, respectively, to accomplish the cross decoupling and back electromotive force decoupling within and between different three‐phase windings. Finally, an all‐round method is proposed, for the first time, to evaluate the decoupling performances and dynamic response performances of different CDC strategies for six‐phase PMLSM. Significant superiority of deviation decoupling regulator in decoupling performance and robustness are verified based on high‐speed EML experimental platform of six‐phase PMLSM.

An Experimental Study on Sensorless Determination of the Projectile Position by Artificial Neural Network in Magnetic Launcher Systems

Electromagnetic launchers are systems in which energy is converted from one form to another. The energy applied to the launcher is converted into magnetic energy in the coil and then into motion energy. The object to be launched follows the magnetic field created in one or more fixed coils. The coil can be fed by direct current (dc) or alternative current (ac) source. In dc systems, the capacitor charging time delays the serial launch. In ac systems, the absence of capacitors enables serial launching. In this study, the application of an ac electromagnetic launch system, which provides a serial launch, is proposed. The maximum force acting on the projectile can be achieved by timely cutting off the energy applied to the coil. Therefore, in electromagnetic launchers, it is critical to know the position of the projectile in the coil. In launcher systems fed with alternating current, the projectile position can be predicted from current changes without the need for an additional setup. In the study, TMS320F28335 digital signal processor (DSP) microprocessor with high processing capacity was used to detect the trigger moment from coil current. Time-delayed artificial neural network was used to estimate the position of the projectile within the coil by using the obtained current differences. The normalized values of the current differences were applied to the time-delayed multilayer neural network (MLNN) algorithm and the projectile position was estimated with 94.67% accuracy. The proposed system increases efficiency compared to systems using conventional sensors, as it prevents or reduces the retraction force.

Modeling of the Rail Type Electromagnetic Launch System With Superconducting Pulsed Power Supply Considering Resistance

In the rail type electromagnetic launch system, when the projectile accelerates in orbit, it is affected by not only the electromagnetic force, but also various resistances, such as sliding friction, air resistance and so on. These resistances affect the characteristics of the pulsed power supply (PS). Nowadays, in order to analyze and design the pulsed PS conveniently, researchers usually ignore the influence of various resistors, and use fixed loads including resistors and inductors to simulate the rail load module, which will cause large errors. So, the mathematical model of the orbital electromagnetic launch system with superconducting is established, including the pulsed PS model with the multiple high-temperature superconducting pulsed power transformer (HTSPPT) and the dynamic rail load model considering various forces. The simulation results indicate that the dynamic rail load model considering various forces can reduce the error of capacitor voltage, load current and other parameters, the features of pulsed PS can be studied more precisely.

Improvement and application of miniature Hopkinson bar device based on series-parallel coil array electromagnetic launch

To eliminate the electromagnetic deceleration force, remove the limitations of striker bar’s length and improve the efficiency for the miniature split Hopkinson pressure bar (mini-SHPB) device, the electromagnetic launch system and energy supply system are improved. The series-parallel coil array launch structure is proposed. The multi-winding parallel coils discharge rapidly to eliminate electromagnetic deceleration force without complex control system or detecting the position of the striker bar in the electromagnetic coils, which can remove the length limitation of striker bar, adjust the stress wave width easily, simplify the multistage launch sensor component structure, and improve the launch velocity greatly without changing the coil geometry parameters. The integrative energy storage structure comprised of “lithium battery + booster module + capacitor group” is proposed. Through the booster module, the capacitor can be charged controllably and the structure can quickly complete many times tests in a single charge, which is secure, reusable and accurate. By using the improved device, the dynamic mechanical properties of Inconel 625 based on laser engineered net shaping (LENS) process are tested in two different build directions under different high strain rates. The tests show that the properties are affected by build direction because of the material anisotropy.

Design of analog electromagnetic launcher based on STM32

In order to improve the accuracy of the electromagnetic launching system, this paper designs a simulated electromagnetic launching device based on STM32 MCU, which takes the steering gear pylons as the motion system, the solenoid coil as the launching system, and the capacitor as the energy storage element. After collecting data, the microcontroller controls the deflection of the pylon steering gear to adjust the launching Angle or the control transformer to adjust the launching voltage, and then controls the charging or discharging of the capacitor to provide energy for the launching device to launch the projectile. Two modes, automatic and manual, are designed. The former takes OpenMV as the target identification and ranging device, and transmits data to SCM through serial communication. The latter can be displayed on the OLED screen by entering the target position through a manual key. The launcher simulates the real electromagnetic launcher and realizes the automatic and accurate launch of the projectile.

Design and Analysis of a High Efficient Multi-Segment Redundancy Linear Motor

Background: The electromagnetic aircraft launch system helps the carrier aircraft accelerate take-off on a short distance on the flight deck. Linear motors are required to have high efficiency and thrust / volume ratio, as the actuator of the EMALS. In addition, linear motors were required to have the fluctuation of the thrust is as small as possible to prevent impact and overstress on the airborne equipment. The thrust performance and thrust fluctuation suppression of linear motors are the current research hotspots in the field of EMALS. Objective: This paper proposes a multi-segment LPMSM to improve the efficiency of the system. Methods: We design a decentralized primary structure based on the Autonomous Decentralized System (ADS) concept. Only the coils near the moving secondary are motivated during the launch process. The others could be released from being driven after the secondary slide over; this control will save energy. Results: A multi-segment linear motor is proposed to improve the efficiency of the EMALS. This motor consists of two sections - the one with iron core for the low speed process and the one without iron core for the high speed process. Conclusion: The normal direction component of the air gap magnetic flux density is much larger than that of the longitudinal component, and their values are 80-90% and 10-20% respectively. For the normal direction component, it is mainly affected by the third, seventh, and ninth harmonics. The accelerating and energy test results show that, in the accelerating process, the efficiency of the linear motor can be more than 90%, and the acceleration is stable.

Effect of Geometric Parameters on Equivalent Load and Efficiency in Rectangular Bore Railgun

The electromagnetic launch system model provides a useful reference for the launch process and performance. Inductance gradient and resistance gradient of the rail, which reflect the equivalent load characteristics of the launcher, are related to shape, material of the rail, and other factors, making it difficult to characterize in the circuit model. Therefore, a method combining equivalent network with finite element analysis is proposed to solve this problem. A segmentation-based real-time trigger strategy is applied to the 4 MJ pulse power supply (PPS) system consisted of 28 modules to shoot the 0.15 kg armature on a 6 m long rail. The width, height of the rail, or separation between two rails increase individually from 20 to 180 mm. After computing the resistance and inductance gradients of the specific rail in ANSYS, the rapid system-level simulation is carried out in MATLAB-Simulink to deliver the railgun's performance. The results show that both the resistance gradient and the inductance gradient contribute to the launch efficiency. In order to obtain a larger inductance gradient, the width of the two rails should be narrower, the height should be shorter, and the separation between the two rails should be farther. Nevertheless, in the perspective of decreasing resistance gradient, the rail should be wider, taller, and farther. Although the resistance gradient increases with the decrease of height and width, the promotion in the inductance gradient has much more significant impacts on the electromagnetic force under the same geometric change. Therefore, for the sake of a higher launching efficiency, the rails should be narrower, shorter, and farther.

Research on Detent Force Characteristics of a Linear Flux-Switching Permanent-Magnet Motor

Linear flux-switching permanent-magnet (LFSPM) motors have been proposed for electromagnetic launch system (EMLS). Benefiting from the permanent magnet (PM) settled on the long double-sided primary and the yokeless secondary, the proposed structure has the advantage of high thrust force density and simple structure compared with the traditional linear permanent-magnet synchronous motor (LPMSM) and linear induction motor (LIM), which makes it more suitable for the EMLS. However, it suffers from the deficiency of relatively high detent force due to the permanent magnets (PMs) settled on the primary, which will also exert an influence on the thrust ripple. Different from the traditional rotary motor, the linear motor also suffers from the end force caused by the end effect. So, a new structure of secondary, which is called symmetric unequally spaced (SUS) secondary in this paper, is proposed to improve the electromagnetic performance from the point of the detent force and thrust ripple for the motor. The thrust ripple and detent force are effectively declined by applying the proposed method without the sacrifice of the average thrust force. The validity of the method is verified by finite element analysis (FEA). A prototype with SUS secondary is manufactured to verify the simulation result.

Electromagnetic Launching System as an Alternative to Non-Destructive Sonic Wave Generation for Steel Bar Length Determination

Soil nailing system is widely used along highways in Brazil. Non-destructive techniques have been used to estimate the length of installed soil nails. Sonic Echo and Impulse Response techniques evaluate the bar length using sonic wave propagation. The methods are similar and consists in generate an impact with a hammer. Results may be affected by this non-standard procedure. This paper aims to propose an automated sound wave generation in order to carried out tests quickly, with reproducibility and without operator dependence. An electromagnetic launching system was developed, which uses a projectile in place of the hammer, and the electromagnetic force instead of human force. The sound data was received by a microphone and sent to the computer by a microcontroller, making the system compact and portable. Projectile output speed optimization and impact reproducibility were analyzed. Nails length were obtained by both time and frequency domain data analysis. Results showed high reproducibility under the same initial condition. Propagation velocity presented a relative error less than 1% for steel bar with length of 1 m.

Combined Fuzzy Time Series Prediction Method for Fault Prediction of EML Pulse Capacitors

Metallized film capacitors are an important part of the electromagnetic rail launch system. It is of great significance to predict its failure. In engineering, the failure law of capacitor is obtained by cyclic pulse accelerated life test of capacitor module with a small number of samples, and is used to predict the actual failure of capacitor in electromagnetic launch (EML) system. This method has the following problems: first, there are few samples of capacitor in life test at affordable cost, which cannot include all capacitor characteristics; second, the time interval of actual EML missions and the voltage of the capacitors are both changing and inconsistent with the conditions used in the life test; third, the statistical law is affected by the measurement and other errors. For these reasons, the prediction accuracy of the existing methods is limited. In this article, a new combined time series prediction method is proposed by using the high-order fuzzy time series prediction theory. Based on the capacitor used in the prototype of an electromagnetic railgun, the life test data of 20 pulse capacitors are used as the prior knowledge input, and the prediction model is obtained. Five groups of capacitor life test data simulating real launch conditions are used as test data to verify that the prediction accuracy of the proposed method is better than that of the traditional method, and the prediction accuracy of capacitor capacitance, which made by different processes, is much higher than that of the traditional method.

Loss Analysis of Air-Core Pulsed Alternator Driving an Ideal Electromagnetic Railgun

The pulsed power supply based on air-core pulsed alternators, with advantages in terms of miniaturization and lightweight, has been a preferred power source for electromagnetic launch (EML) systems in all-electric vehicles or ships. However, when an air-core pulsed alternator is used to drive the electromagnetic railgun, the bulk of the inertial energy storage converts into energy losses. These losses not only reduce the efficiency of the system but also cause temperature rising of the alternator, leading to a limit on its repetitive output performance, affecting the performance of the electromagnetic railgun, and ultimately, the alternator's volume and weight will also increase. Therefore, it is necessary to develop research relating to those losses. In this article, the operation principle of the EML system is explained first, and four typical operating stages are described. Then, the influence of the rotor eddy current on the performance of the alternator is analyzed. After that, the various losses generated in the pulsed power supply system are analyzed in detail. The eddy current losses are obtained from simulation. The copper losses and switch losses are calculated by formulas derived in different stages and different members. The formulas of windage and mechanical losses are obtained too. Based on these analyses, losses can be calculated by the parameters of the EML system or derived from a cosimulation model. Also, the influence of alternator parameters and structures on losses is studied. Finally, a seven-phase six-pole air-core prototype is introduced, and the windage and mechanical losses are tested on the prototype. Moreover, the cosimulation model of the EML system is built, its losses are evaluated, and the efficiency of the EML system is derived.

Thermal Analysis of the Pulse Inductor for Electromagnetic Launch Under Continuous Discharge Condition

The solenoid pulse inductor is a key component of the electromagnetic launch (EML) system, and effective thermal management is a necessary condition for reliable and stable operation under continuous discharge condition. A 3D transient coupling heat transfer model for the solenoid pulse inductor with liquid cooling mode was established, and the temperature distribution and the characteristics of heat dissipation of the inductor under continuous discharge condition has been analyzed. A temperature measurement system was designed, and the accuracy of the 3D coupling model has been verified. In addition, effects of the flow rate, the inlet temperature and the coolant on the efficiency of liquid cooling were analyzed by using this model. The results show that during continuous discharge, the maximum temperature and maximum temperature difference of the inductor continue to increase, but the rising speed rapidly slows down. Raising the flow rate can effectively improve the efficiency of the liquid cooling and decrease the temperature difference in the inductor during continuous discharge, but the marginal benefit of raising the flow rate is gradually reduced. Dropping the inlet temperature has little effect on the efficiency of the liquid cooling, and ethylene glycol solution can replace deionized water as the liquid cooling coolant for the pulse inductor under low temperature condition. This paper is expected to help to improve the thermal management and optimize the performance of the solenoid pulse inductor.

Optimal Design of High-Speed Double-Sided Linear Permanent Magnet Motors With Segmented Trapezoidal Magnetic Poles

For the kilometer-level electromagnetic launch system, a high-speed double-sided linear permanent magnet (PM) linear motor is presented in this paper. To enhance the average thrust force, reduce the thrust ripple and normal force of linear motor, a segmented trapezoidal PM shaping method is proposed. Compared with conventional PM shaping method, the segmented trapezoidal PMs achieves less force ripple, greater average force and lower manufacturing difficulty. The risk of PM demagnetization fault has been taken into account. To reduce the losses in the mover of the linear motor, a non-metallic light-weight mover structure is proposed. The effectiveness of segmented trapezoidal PMs and non-metallic light-weight mover are verified by the finite element method and experiment.

Research on Discharge Timing Control of Multi-Parameter Pulse Forming Network

To solve the complicated timing control caused by the mixed-use of multi-generation pulse power sources in the system, a timing trigger control system with a PID controller was designed. According to the nonlinear characteristics of the armature state during the launch process, the circuit model and the dynamic model of the electromagnetic launch system were established, and the PID controller and command processing and distribution system were designed. The results showed that the PID controller can precisely control the discharge timing of the multi-parameter pulse power module so that the armature acceleration can precisely track the set value.

Fault Prediction of Electromagnetic Launch System Based on Knowledge Prediction Time Series

The fault prediction of the electromagnetic launch (EML) system is an important guarantee to improve the reliability of the system, but there is no mature method that can be directly applied. Combined with the engineering practice of large-scale EML system, a fault prediction method based on knowledge prediction time series is proposed. First, the high-frequency waveform collected in each launch is extended into a time series along the number of launches; second, an intelligent waveform features extraction expert system is constructed to realize feature extraction; third, multidimensional feature sequence prediction and waveform prediction are realized by using two neural networks, respectively; finally, fault prediction is realized by associating the fault diagnosis knowledge. The temperature rising test data of a railgun system for 15 consecutive launches and the recoil stroke test data of noncontinuous 78 launches are used as the input source of the proposed algorithm. The results show that the proposed algorithm can automatically extract the features with fault trend. The single step prediction error of features is less than 1.47%, and the mean square error of curve prediction is half of the results of SARIMA prediction algorithm. Through the temperature rise curves, the proposed algorithm can predict the fault free of the 14th and 15th launch. According to the recoil stroke curves, the fault of the launcher of the 75th launch is predicted. The actual analysis shows that the fault prediction accuracy is high, and the algorithm can significantly improve the system reliability after being applied to engineering.

Effectiveness Evaluation of Missile Electromagnetic Launch System Based on ADC Model Improved by EWM-FAHP-ICWGT

To solve the key problems of strong infrared radiation, poor continuous combat capability of the system, serious ablation of the launching device, and environmental pollution during missile launch, the electromagnetic launch system (EMLS) has been studied for missile launching tasks. However, most of the current research studies are aimed at specific technical points and lack the overall design and evaluation of the system. Therefore, the designed system may have problems such as excessive cost, lack of economy, or low overall efficiency. In order to complete the overall evaluation of the missile electromagnetic launch system (MEMLS), this article established an ADC model improved by entropy weight method-fuzzy analytic hierarchy process-improved combination weighting model of game theory (EWM-FAHP-ICWGT). The established model integrates subjective and objective weights, eliminating the problem of negative combination coefficients that traditional CWGT may bring, and the average difference in combination weights is the smallest. Difference analysis and differential analysis are also used here to discuss the requirements for the reliability indicator which is mean time between failure (MTBF) and maintainability indicator which is mean time to repair (MTTR) to further improve the effectiveness of the system. Finally, the indicators that have a significant impact on the performance of MEMLS are analyzed, which provides a direction for further research on the system.

Large-Scale PFN Fault Diagnosis Method Based on Multidimensional Time Series Anomaly Detection Using Convolutional Neural Network

The fast fault diagnosis of large-scale pulse-forming network (PFN) of electromagnetic rail launch system is of great significance. It is an important research direction to diagnose the PFN fault by detecting the anomaly of multidimensional time series in each pulse-formatting unit (PFU). Due to the high sampling rate of time series and the characteristics of aperiodic instantaneous pulse, the current time series diagnosis method is not suitable. Multidimensional coupling aggravates the complexity of the problem. In order to solve the problem, this article proposes a method of multidimensional time series anomaly detection based on convolutional neural network. First, the multidimensional time series is transformed into a gray-scale image, which can reflect the health status of a PFU. Second, a deep convolution neural network is constructed to identify the abnormal images based on the existing data trainers. Finally, a convolution neural network is constructed to locate the fault. The results show that the model can identify 100% of the abnormal PFU waveform, and the fault classification model can also accurately locate the fault, which proves the effectiveness of the proposed algorithm.

DC‐link capacitor voltage balance strategy of independent double three‐phase common bus five‐level NPC/H‐bridge inverter based on finite control set

This study aims at the DC-link capacitor voltage imbalance problem of independent double three-phase common bus five-level neutral point-clamped/H-bridge inverter, which is applied to an electromagnetic launch system under instant high-power and high-current conditions. First, the traditional method of voltage balance strategy based on redundant vectors is described, and the key factors leading to the DC-link capacitor voltage fluctuation is analysed in detail. Second, the objective function is constructed to predict the variation trend of DC-link capacitance voltage difference. Third, an optimised voltage balance strategy is proposed. At first, the optimised strategy calculates the variation trends of the voltage difference for all three-phase switch vector combinations. Then, the results make up a voltage balance finite control set. At last, compare the results in the set to select the vector combination corresponding to the minimum variation for output. Finally, tested by the semi-physical real-time simulation platform, and the proposed optimised voltage balance strategy is verified effective for improving DC-link capacitor voltage imbalance and inhibiting the voltage difference fluctuation.

A Novel Permanent Magnet Linear Motor for the Application of Electromagnetic Launch System

The surface-mounted permanent magnet linear synchronous motor (PMLSM) is a good candidate for the Electromagnetic Launch System due to its merits of high-power density, power factor and efficiency. However, this kind of machine needs a lot of permanent magnets (PMs) on the long stator, which is costly. To solve this problem, a novel PMLSM is proposed in this paper. The stator of novel PMLSM has the consequent poles structure and the mover of novel PMLSM has two iron cores, which sandwiches a mover PM. Firstly, the structure and operation principle of the proposed PMLSM have been investigated. Then, the analytical calculation of thrust and detent force is analyzed and the structural parameters of the motor are optimized for larger thrust and less detent force. Finally, for a fair comparison, the proposed motor is designed and built based on an existing PMLSM with similar electromagnetic and geometrical parameters. The thrust performance indexes of the novel PMLSM are estimated and compared with the conventional surface-mounted PMLSM, which indicates that the proposed PMLSM can keep similar performances with the exciting PMLSM. Moreover, it has a simple structure, less thrust ripple and can save many PMs, which can help reduce costs.