Kexun Yu

Investigation of Self-Excitation and Discharge Processes in an Air-Core Pulsed Alternator

The air-core pulsed alternator has advantages in the application of pulsed power region, such as in electromagnetic launchers. The self-excitation and discharge processes in an air-core alternator are more complicated than traditional iron-core generators. In this paper, a mathematical model of an air-core pulsed alternator is built and several critical problems are analyzed, such as the conditions for successful self-excitation, the time needed for self-excitation, the waveforms of electromagnetic torque, discharge current and load voltage, and the compensation action during discharge, the effect of triggered angles, the rotational speed curve, and the energy reclaiming. Investigation of self-excitation and discharge processes in an air-core pulsed alternator is helpful for understanding the operation principle, predicting the performance, and analyzing and designing the system.

Investigation of a Novel Pulse CCPS Utilizing Inertial Energy Storage of Homopolar Inductor Alternator

This paper presents the investigation of a novel capacitor-charging power supply through inertial energy storage of a homopolar inductor alternator (HIA). The structure of a new 18/16-pole HIA is proposed, and we introduce the theory and advantages of HIA. The characteristics of the static magnetic field distributions are calculated by finite-element analysis, and a basic mathematic model of HIA is set up. We propose an efficient and stable capacitor-charging circuit topology to meet the requirements of this system. A functional model of the key device, namely, IGCT, is also established. Finally, we verify its feasibility and advantages through analysis of the system simulation.

Two-Reaction Theory of Homopolar Inductor Alternator

This letter aims to settle the controversy about whether or not the two-reaction theory is applicable to homopolar inductor alternator (HIA). First, the prerequisite of two-reaction theory is introduced. The direct and quadrature axes of HIA are defined and the corresponding armature reaction fields are calculated respectively based on finite element method. A conclusion that two-reaction theory is applicable to HIA is made using spatial overlay analysis.

Investigation of Pulse Excitation in Air-Core Pulsed-Alternator System

An air-core pulsed alternator is made of nonferromagnetic materials, which needs very high field current. Self-excitation is usually applied in these systems. This is a positive-feedback progress, which takes tens of milliseconds to reach the desired large field current. The field loss is one of the main limitations of the machine design. This paper presents a new excitation mode, which is the pulse-excitation mode. The main idea is that a pulsed current charges the field coil so that the field coil and the armature coil conduct electricity only for a short time around the main discharge pulse. The field-current pulse is supplied by a pulse capacitor. Generally speaking, the pulse-excitation mode is a combination of pulsed alternator and capacitor. Compared with the self-excitation operation mode, the pulse-excitation operation mode reduces the field loss in each discharge process. This increases the discharge frequency of the air-core alternator pulse-power system. In addition, the repeat discharge-current pulses could have similar peak value. In this paper, the pulse-excitation mode in a pulsed-alternator system is investigated. The simulation results of this scheme are presented. The discharge current, field current, voltage of the field capacitor, and rotational-speed changes are analyzed. Finally, the advantages and disadvantages of this mode are discussed.

Inductance Mathematic Model of a Homopolar Inductor Alternator in a Novel Pulse Capacitor Charge Power Supply

The investigation of inductance mathematic model of a homopolar inductor alternator (HIA) in a novel pulse-capacitor charge power supply (CCPS) is presented. We study the characteristics of the inductance parameters based on the HIA theory and 3-D finite element analysis, establish the inductance mathematics model of HIA, and build a novel pulse-CCPS with 12/10-pole HIA. We also establish the simulation model of the power supply and compare the simulation results with the experimental one. The results prove the correctness of the inductance mathematic model. Finally, the problem of parameters-matching between the charging circuit and the HIA inductance is discussed.

Comparison Between Self-Excitation and Pulse-Excitation in Air-Core Pulsed Alternator Systems

Air-core pulsed alternators greatly enhance the power density capabilities of pulsed power supply for electromagnetic launchers. Compared with iron-core electric machines, they require very high-excitation currents. Usually, the self-excitation mode is adopted in these systems. However, the self-excitation mode is a positive feedback process that should be precisely controlled to avoid the system being destroyed. The excitation losses are very large during the process of establishing the large field current. To solve these problems, a new excitation mode, the pulse-excitation mode, is presented in this paper. The main idea is that a pulsed current charges the field coil so that the field coil and the armature coil conduct only for a short time around the main discharge pulse. This will avoid the machine being overheated and the risk of positive feedback process. Compared with the self-excitation mode, the pulsed alternator can be operated in a higher discharge frequency and the circuit schematic of the system is simpler. A larger field capacitor is used that charges the field coil to the desired current just by a pulse. As the energy density of pulse capacitor is enhanced rapidly, the volume and mass of the field capacitor are acceptable. The pulse-excitation mode is a combination of pulsed alternator and pulsed capacitor. In this paper, the characteristics of self-excitation and pulse-excitation are analyzed, respectively. The performances of both systems are simulated, and the main waveforms are presented. Finally, there is a practical comparison between them.

Performance of Homopolar Inductor Alternator With Diode-Bridge Rectifier and Capacitive Load

This paper presents the performance of homopolar inductor alternator (HIA) with diode-bridge rectifier and capacitive load. According to the conduction and commutation rules, all the operational modes included in the bridge rectified capacitive load are considered. A simplified average-value mathematical model is established; furthermore, we derive the load characteristic under every operation mode. Using the fundamental machine differential equations and the connecting characteristics between alternator and rectifier, we establish a port-network state model of the system. The performance of the HIA with bridge rectifier and capacitive load can be predicted from charging current, commutating angle, and given parameters of the alternator. Theoretical results are compared with the simulation results obtained from numerical procedure.

Optimal Design and Experimental Research of a Capacitor-Charging Pulsed Alternator

The high power pulsed charging power supply is usually necessary for the pulsed power devices with high power repetitive discharge. This paper first introduces a new topology structure of a charge and discharge system for high voltage capacitor and its operating principle, then comes up with technical requirements for the pulsed alternator. Afterward, design features of the inductor pulsed alternator, including the structure, main dimensions, and sizes of rotor teeth and slots are studied, and the main parameters of homopolar inductor pulsed alternator (HIPA) prototype are provided. The choice of rotor material and bearing failure phenomenon are also investigated to find a responsible solution. Finally, the experimental waveforms of HIPA prototype without and rated load when charging capacitor are given. The research shows that the pulsed power supply based on the inductor pulsed alternator is competitive for its high energy storage density, moderate power density, and high reliability, which is suited to the charging power supply of pulsed capacitor.

Analysis of the Soft-Start Circuit of the High Voltage Power Supply Based on PSM Technology

The power supply based on pulse step modulation technology has been widely used as the high-voltage power supply (HVPS) for additional heating systems. The topology contains numbers of converters and multisecondary transformers. For the magnetizing inrush of the transformer and charging current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. There are resistor branches series with the transformer and each converter is used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, and as a result the dissipation and electromagnetic interference inside the module are serious. In this paper, the soft-start circuit is simplified to only one resistor branch. The precharge circuits of the converters, which are connected to the secondary, are diverted from the inside of the modules to the primary winding of transformer. Since the multisecondary transformer powers up at the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft-start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2-kV power supply, contains 12 converters, with soft start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft-start circuit of 100-kV HVPS system was designed.

Design of a novel pulse capacitor charge power system based on inertial energy storage

In this paper, a novel high-voltage generator-Homopolar Inductor Alternator (HIA) pulse-charge for the capacitor bank with repetitive frequency though inertial energy storage system has been designed. A diesel engine provides energy as a prime motor in this system, and then drives the HIA to the rated speed by the flywheel energy storage device, the AC pulse-charge for the capacitor bank with repetitive frequency through power electronic conversion. We have introduced the theory of the HIA and the operation mode of this system, and we have analyzed the rotor speed change according to the principle of energy conservation. Based on the main physical characteristics of IGCT, a functional model has been investigated and realized with the simulation tool of PSIM package. Finally, we have set up the main circuit topology for this system, and verified its feasibility though the analysis of the circuit simulation by Simulink package.