Wang Shanming

Steady-state performance of synchronous generators with AC and DC stator connections considering saturation

Synchronous generators with ac and dc stator connections are widely used in systems where simultaneous ac and dc power supplies are needed. For these systems the voltage harmonic distortion of ac voltage, dc voltage ripple, and dc voltage varying range are of special interest. Because of the commutation of rectifier and the saturation of magnetic circuit, the accurate calculation of voltage harmonic distortion and dc voltage varying range is comparatively difficult. This paper describes a mathematical model on the basis of the multiloop method and FEM, which aims at calculating the steady-state characteristics and the voltage waveforms of ac winding accurately. With this method, the full synergic effects of space harmonics resulting from the magnetic circuit geometry, saliency, saturation, winding layouts, and slotting are included. The calculated results are compared with those of experiments.

Research on internal faults of generators and their protection schemes in Three Gorges hydro power station

Based on the multi loop method, the internal faults of generators in Chinas Three Gorges hydroelectric power station, including the interturn short circuit in the same branch, the short circuit of two branches of same phase and the short circuit of two branches of different phases are calculated. According to the calculated data of 60 short circuits of 2 generators, protection schemes are presented. Single element transverse protection is more the attractive scheme owing to its high sensitivity and simplicity. The high sensitivity single element transverse differential, noncomplete or complete longitudinal differential protections constitute multiple protection functions.

A Variable Pole Pitch Linear Induction Motor for Electromagnetic Aircraft Launch System

A variable pole pitch linear induction motor (VPPLIM) is proposed as a new member of the family of electromagnetic aircraft launch system (EMALS). With proper designing of the variation of the pole pitch, the VPPLIM could accelerate the aircraft almost uniformly at the condition of the usual ac supply, avoiding the use of large-scale power electronic converters. Special considerations in the design of VPPLIM, such as the structure topology, the variation of the pole pitch, and the winding arrangement are discussed in detail in this paper. The acceleration performance of the VPPLIM fed by a constant-voltage constant-frequency supply is analyzed by means of the quasi-steady-state 2-D magnetic field model and the difference model of movers dynamics. A two-stage method is proposed to simulate the acceleration performance of the VPPLIM based on a 2-D thrust table of the motor achieved by the finite-element method. The calculated features of the prototype VPPLIM consist well with those expected for EMALS.

Simulation and operational protection of three-phase/twelve-phase hybrid AC-DC supply generator system

The hybrid AC-DC supply has been applied to various situations. It provides simultaneous AC and DC power with least weight, volume and cost to meet the special requirement of mobile power networks. In this paper, a mathematical model, based on the multiloop method, including speed regulator and excitation regulator, is established to reflect the system operation aspect. The simulation results of voltage harmonics are compared with experiments to verify the validity of the mathematical model. The DC side power oscillation and short circuit may result in system breakdown. The simulation program provides the guideline for system operation and protection. The simulation results showed the factors that affect the amplitude and frequency of the DC side power oscillation. The q-axis winding and feedback control of the DC load current on the excitation voltage can increase system stability. The DC side short circuit currents are also calculated for the tuning of the relays.

Multi-loop model of synchronous generators with AC and DC stator connections

Synchronous generators with AC and DC stator connections are widely used in systems where AC and DC power supplies are simultaneously needed. For these systems, not only the steady-state characteristics, such as the voltage harmonic distortion of AC voltage, but also the stability and transient performance are very important. In this paper a mathematical model on the basis of multi-loop method is described to calculate the steady-state, the stability and the transient characteristics of this kind of generator efficiently and accurately. With this method, the full synergic effects of damper winding and space harmonics resulting from the magnetic circuit geometry, saliency and winding layouts are included. The calculated results are compared with those of experiments

Research on internal fault of generator including saturation

In order to improve the performance of protection systems of generators against armature faults, it is desirous to study the operation of synchronous machines with internal faults in stator windings. For this purpose, based on the multi-loop model and FEM, a saturate model of synchronous generators is established. The state equation of the multi-loop model is time-stepped forward, during which FEM is used to calculate the winding EMF under saturate condition. The full synergic effects of space harmonics resulting from the magnetic circuit geometry, saliency, saturation, winding layouts, slotting, and time harmonics resulting from the nonsinusoidal currents, are included in the simulation. At last, the results of simulation are compared with those of experiments.

Research on field current control of hybrid excitation permanent magnet synchronous generator

In order to adjust the air-gap magnetic field of the permanent magnet(PM) machine, one hybrid excitation permanent magnet synchronous generator(HEPMSG) utilizing tooth harmonic for excitation was proposed. This paper introduced the structure and principle of the HEPMSG, and the wireless transmission technology was applied for the field current control of the tooth harmonic excitation system. The rotor tooth harmonic excitation control circuit of the HEPMSG was studied, including the excitation main circuit, the driving circuit, the wireless signal receiver and its processing circuit, and the power supply circuit. Finally, some experiments were performed for one HEPMSG utilizing tooth harmonic for excitation, and the experimental results verified the correctness and effectiveness of the proposed HEPMSG.

A novel linear induction motor for electromagnetic aircraft launch system

A variable pole pitch linear induction motor (VPPLIM) is proposed as a new member of the family of electromagnetic aircraft launch system (EMALS). With proper designing of the variation of the pole pitch, the VPPLIM could accelerate the aircraft almost uniformly at the condition of usual AC supply, avoiding use of large scale power electronics converters. The special considerations in the design of VPPLIM, such as the structure topology and the variation of the pole pitch are discussed detailedly in the paper. The acceleration performance of the VPPLIM fed by a constant voltage constant frequency supply is analyzed by means of the quasi-steady-state 2D magnetic field model and the difference model of movers dynamics. A two stage method is proposed to simulate the acceleration performance of the VPPLIM based on a 2D thrust table of the motor achieved by finite element method (FEM). The calculated features of the prototype VPPLIM consist well with those expected for EMALS.

Estimation of saturation characteristic of induction motors by injecting sinusoidal currents with customized low frequency

To keep ac magnetized state of iron core same as actual working condition and use steady-state information, a novel method for saturation characteristic estimation of induction motors at stand-still is proposed. The saturated mutual inductance is estimated according to measured stator-side reactance, when a low-frequency sinusoidal current is injected in single-phase mode. The frequency of sinusoidal current is customized according to the rotor time constant, which is a key point for successful estimation. Besides, no voltage sensor is included by using a voltage compensation technique, suitable for hardware setup of common inverters. Both simulation and experiments have been implemented to demonstrate the feasibility and validity of the proposed method.

Research on voltage harmonic distortion of synchronous generators

This paper investigates the effects of the parameters as well as the operating conditions on the waveform and the harmonic analysis of AC voltage. On the basis of the multi-loop method and FEM, a mathematical model of synchronous generators is described. With this method, the full synergic effects of space harmonics resulting from the magnetic circuit geometry, saliency, saturation, winding layouts, and slotting are included. The calculated results are compared with those of experiments.