Weiduo Zhao

Investigation of Multiphase Compulsator Systems Using a Co-Simulation Method of FEM-Circuit Analysis

As power supplies, compulsators are popular choices for electromagnetic railguns. Compared to a single-phase system, multiphase compulsator can provide more flexibility in current waveform and higher power density. However, the accurate simulation method of a multiphase compulsator is still not clear enough for researchers since both the machine and the external circuit become more complex. With this background in mind, this paper describes a finite-element method combined with circuit analysis. The compulsator is modeled in Maxwell while the railgun launcher and external circuits are modeled in Simplorer, each with their respective advantages. Based on this model, the performances of the two- and three-phase air-core compulsator powered railgun systems are analyzed. The compensation modes, trigger control, and output characteristics are also discussed. The co-simulation model and analysis results can provide the theoretical guides for multiphase compulsator investigation in the future.

Design, Simulation, and Testing of a Dual Stator-Winding All-Air-Core Compulsator

The focus toward advanced mobile tactical configurations for railgun power supplies has resulted in the evolution of five compulsator generations in the past 30 years from iron-core to air-core prototypes. However, the exact air-core field simulation and the complicated fabrication technique of an air-core compulsator are not clear enough for researchers. This paper presents a detailed description of a small-scale all-air-core compulsator, which has a novel topology. The unique feature of the all-air-core compulsator is that there are two armature windings in the stator, the primary armature winding for providing the main output pulse and the secondary armature winding for providing the voltage for self-excitation. This approach allows the optimization of each armature winding to its specific duty cycle for increasing the overall efficiency of the compulsator. The two armature windings are located in the stator and not in the rotor. The advantage of this configuration is that it is unnecessary to equip the large-energy-level brush- and slip-ring mechanism. It is necessary to improve the power density, stability, and life span of a system. The no-load and discharge simulation results of the all-air-core compulsator were presented. Then, the electrical and mechanical parameters were given. The process technology of the slotless windings and the subassembly of the stator and rotor were presented. The results of the pulse-excitation experiment validate the results of the simulation.

Discussion of electrical discharge machining in gas

Summary form only given. For the microcosmical understanding of electrical discharge machining (EDM) in gas (dry EDM), the influences of such parameters as polarity and gas pressure on EDM in gas were discussed based on theory of gas discharge and experiments; meanwhile, the influencing factors of material remove rate (MRR) in dry EDM and reasons for the low relative wear ratio (RWR) are analyzed mainly according to the gas medium characteristics. Positive polarity was recommended in dry EDM because electrodes play main roles in collision and ionization; the notable feature of dry EDM is very low RWR and the reasons for low RWR are analyzed as follows: (1) the passage developing to anode is stronger than the passage toward cathode, which can be used to explain that the energy absorbed by anode is larger than the energy absorbed by cathode, and that is main reason for lower RWR. (2) Tool electrode was protected by the debris adheres on the tool. Additionally, discharge passage extends rapidly in gas medium although it is limited by liquid in conventional EDM, which leads to weaker workpiece cool effect and low MRR in dry EDM; Finally, to ensure machining process stable at the sparkle discharge state, a certain gas pressure is necessary to strengthen deionization in dry EDM and to keep discharge points disperse in gap.

Sensitivity Analysis and Regulation Strategy of Current Waveform for Two-Axis-Compensated Compulsators

Compulsators have been considered appropriate pulsed power supplies for electromagnetic railguns. In order to ensure a high projectile mean to peak acceleration ratio, it is desirable to provide a flat-topped pulse for the railgun. This paper analyzes a two-axis-compensated compulsator, which is a refined selective passive compulsator having an orthogonal displacement between compensating winding and field winding. During the discharge process, the quadrature-axis compensation is provided by the compensating winding, when direct-axis compensation is provided by the field winding. Compared to the traditional selective passive configuration, this arrangement is able to provide another degree of freedom to compensate the armature reaction, thus an output of a current waveform with more flexibility. In this paper, the self-excitation and discharge process of a two-axis-compensated air-core compulsator is simulated based on a finite-element model. Analysis of the current waveform sensitivity to compulsator design parameters is also carried out, as well as the regulation strategy to generate a flat-topped pulse. The research process mentioned in this paper could help to optimize the design of compulsators in future applications.

Design and Analysis of a Two-Phase Two-Axis-Compensated Compulsaor

As power supplies, compulsators are popular choices for electromagnetic railguns. In this paper, a two-phase two-axis-compensated compulsator (2P2AC compulsator) with lower internal inductance and higher power density was designed and analyzed. Two-phase armature windings are allocated on the stator, and discharge pulse currents to the load via a rectifier. This arrangement decouples the machine speed from the pulsewidth, thus enables a higher tip speed. Two sets of windings with electrical orthogonal displacement are allocated on the rotor. The bigger one is the field winding that freewheels via a diode and provides the direct-axis compensation during the discharge process, while the smaller one is the short-circuit compensating winding providing the quadrature-axis compensation. The effect of the composition of the d- and q-axis compensation is equivalent to a passive compensation using a continuous conductive shield, which compresses the flux for all rotor positions. Compared with the passive compensation, this arrangement has no conductive path to couple with the field winding due to the orthogonal displacement, thus speeding up the charging process. This paper presents the design methodology of the 2P2AC compulsator, along with its system performance of driving railgun load.

Simulation Research of a CPA Powered Railgun System

The railgun, as a novel kinetic energy weapon, is being taken seriously by each country military. The pulse power source and railgun barrel, directly related to the performance of the total system, are important parts of the railgun system. The compensation pulse alternator, with its high energy storage density and power density, becomes one of the most potential pulse powers. The simulation of the pulse generator powered railgun system is researched in this paper. In order to accurately simulate the characteristic of the railgun system, the time-varying characteristic of the parameters and the kinetic resistance are taken into account in the process of building the raigun model. The railgun model is completed through the Matlab/simulink. The generator model is set up in FLUX. The coupling module between the two softwares is utilized to realize the co-simulation of the railgun system. The simulation results show that the optimum length (the displacement of the projectile exiting the muzzle while the current exactly reduces to zero) of the barrel has the relation with trigger moment of alternator. The velocity of the projectile will decrease when the trigger moment is delayed or the distance between the breech and the armature becomes further.

Research on the Thermal Field and Active Water Cooling System Design of an Air-Core Compulsator

Compulsators are popular choices for high-end railgun power supplies. In order to maximize energy stores and power densities, compulsators are designed as an air-core prototype. However, new problems have also been brought out by the new structure. Due to the poor thermal conductivity of composite materials and the high field current needed to maintain the magnetic potential, one of the principal limiting factors for achieving continuous discharges is the high winding temperature rise. In this paper, on the basis of electromagnetic analysis, the losses of the coils and compensating shield could be calculated first, and then, a transient 3-D finite-element thermal analysis was performed for both the stator and rotor. Finally, for the purpose of stabilizing the hottest spot temperature of the coils at a given level, an active cooling system has been designed and simulated. The presented method can be applied to other compulsators having the same thermal issues.

Design of the Halbach Hybrid-Excitation Compulsator

Pulsed alternators integrate kinetic energy storage, electromechanical energy conversion and pulse shaping in one unit, and it is the research focused on the field of pulsed power sources. The electrical excitation and the permanent magnet excitation are contained in one hybrid excitation pulsed generator together in which the advantages of two different excitation types are integrated. The brush slip ring mechanism with low reliability and high maintenance costs can be cancelled. And the electromagnetic field can be adjusted quickly by external electrical excitation source and correspondingly the performance can be quickly adjusted. An all-iron-core hybrid excitation compulsator prototype had been designed, fabricated and optimized. The hybrid excitation concept was validated in the research of compulsator. Although the compulsator researches are mainly focused on the all-air-core electrical excitation topology, there exist some bottleneck technologies which restrict the application of compulsator in actual fields. The hybrid excitation compulsator can decrease the cost, increase the reliability and widen the application scope of compulsator, especially in the middle-low power range. Halbach array is a permanent magnet arrangement structure which is a combination structure of different directions arrays. The Halbach array offers a number of attractive features in comparison with the normal array one. And the air-gap magnetic flux can be increased and the rotor yoke magnetic flux is decreased. Based on it, the Halbach array can be designed on the composite rotor core. A part-air-core compulsator which includes an air-core rotor and an iron-core stator was designed. For analyzing the electromagnetic design results, the three dimensional model was built and finite element analysis method was used. The performances simulation results of the Halbach hybrid excitation compulsator were presented.

Design and analysis of a bidirectional cross-linking transverse flux permanent magnet synchronous motor

Transverse flux permanent magnet synchronous motor is suitable for high torque applications, because it features a spatial decoupling between electric load and magnetic load. A new bidirectional cross-linking transverse flux permanent magnet synchronous motor (BCTF-PMSM) is proposed and analyzed, which can fully utilize the rotor permanent magnets and have larger space utilization ratio than the traditional transverse flux machine. First, the fundamental structure and operation principle of BCTF-PMSM is introduced. Second, based on the basic electromagnetic relations and the 3D finite element analysis, the design method of BCTF-PMSM is summed up. Last, one prototype is designed and manufactured. The no-load back-EMF and static torque experiments are carried out. The experiment results agree well with the theoretical analysis. That verifies the validity of the theoretical analysis and the rationality of motor design.

Design of Halbach hybrid excitation compulsator

Pulsed alternators integrate kinetic energy storage, electromechanical energy conversion, and pulse shaping into one unit, and it is the research focused on the field of pulsed power sources. The electrical excitation and the permanent magnet excitation are contained in one hybrid-excitation pulsed generator together in which the advantages of two different excitation types are integrated. The brush slip ring mechanism with low reliability and high maintenance costs can be cancelled. In addition, the electromagnetic field can be adjusted quickly by external electrical excitation source and correspondingly the performance can be quickly adjusted. An all-iron-core hybrid-excitation compulsator prototype was designed, fabricated, and optimized. The hybrid excitation concept was validated in the research of compulsators. Although compulsator research is mainly focused on the all-air-core electrical excitation topology, there exist some bottleneck technologies that restrict the application of compulsators in actual fields. The hybrid-excitation compulsator can decrease the cost, increase the reliability, and widen the application scope of compulsators, especially in the middle-low power range. The Halbach array is a permanent magnet arrangement structure, which is a combination structure of different direction arrays. The Halbach array offers a number of attractive features in comparison with the normal array. The air-gap magnetic flux can be increased and the rotor yoke magnetic flux is decreased. Based on this, the Halbach array can be designed on the composite rotor core. A part-air-core compulsator that includes an air-core rotor and an iron-core stator was designed. For analyzing the electromagnetic design results, the 3-D model was built and finite element analysis method was used. The performance simulation results of the Halbach hybrid-excitation compulsator were presented.