Tang Renyuan

Combined strategy of improved simulated annealing and genetic algorithm for inverse problem

A combined strategy of an improved simulated annealing (SA) algorithm and genetic algorithm is presented, with the goal of reducing the computational expenses. The improvements made on the SA algorithm include two parts, i.e., the adaptive regulating for the step vector, and the dynamic testing for the equilibrium of the Metropolis process. The proposed strategy has both the advantage of SA algorithm, the ability to avoid being trapped in a local optimum, and that of genetic algorithm, the ability to use the information about the searched states for the next iteration. A practical application on geometry optimization of pole shoes in large salient pole synchronous generators is effectively implemented using the strategy. The numerical results show that the number of iterations used by executing the combined strategy are only about 75% of those by executing basic SA algorithm.

Transient simulation of power transformers using 3D finite element model coupled to electric circuit equations

This paper presents a three-dimensional coupled approach for transient simulation of electromagnetic devices. The approach is based on the A-V-A formulation, in which the eddy current field and the electric circuit equations are solved simultaneously. The Newton-Raphson procedure has been used to take the magnetic non-linearity into account. The transient short-circuit state of a 240000 kVA power transformer is simulated by the coupled approach.

Interior composite-rotor controllable-flux PMSM - memory motor

A new class of interior composite-rotor controllable-flux permanent magnet synchronous machine (PMSM) for true wide-speed operation is proposed. It can operate in wide-speed without overmuch armature loss and sacrifices in other machine characteristics. The tangential-set permanent magnets (PMs) are NdFeB that has high remanent flux density B/sub r/ and high coercive force H. The radial-set PMs are AlNiCo that has high B/sub r/ and low H. By applying the pulse of d-axis stator current vector i/sub d/, the magnetized intensity and direction of AlNiCo can be controlled. The flux created by NdFeB is repelled by AlNiCo to stator and air-gap PM-flux is intensified, or is partially bypassed by AlNiCo in the rotor and the air-gap PM-flux is weakened. The structure can adapt for memory motor with more pole-pairs. The interior magnetic field distribution in two extreme magnetized conditions was analyzed by finite element method. And the proposed assumption is proved.

Numerical calculation of 3D eddy current field and short circuit electromagnetic force in large transformers

The improved T- Omega method is employed to calculate the three-dimensional transient eddy current field in large transformers, as well as the short-circuit electromagnetic forces acting on the transformer windings. The effects of the magnetic shielding and initial angles of currents are studied, and the nonuniform distribution of ampere-turn along the height of the windings is taken into account. Thus, a common software package is developed. Two different transformers are analyzed, and the computed results show agreement with measured ones. >

Computation of transient electromagnetic torque in a turbogenerator under the cases of different sudden short circuits

A method for the computation of the transient electromagnetic torque in turbogenerators is given in which the iron saturation and the relative motion of the rotor and stator are taken into account. This method is based on the finite-element computation using a dynamic model coupled with the equations of external electric circuits. To avoid the airgap mesh distortion caused by the movement of the rotor, moving boundaries are introduced in the airgap. An example is given that involves the computation of the distribution of transient magnetic field and the electromagnetic torque of a 200-MW turbo-generator following different types of sudden short-circuits. The computed results agree with the measurements very well. >

Calculation of end region magnetic field and circulation losses for turbo-generators using a coupled field and circuit equations method

A method using coupled fields and circuit equations is presented to calculate the end-region magnetic field, the current distribution in stator winding strands, and the circulating losses of the stator winding in large turbogenerators. In the calculation, the nonuniform distribution of current density in the stator winding and the influence on the end-region magnetic field of the copper shield are considered. Finally, the effect of the transposed angle on the circulating losses is analyzed. The method is used to calculate the end-region magnetic field and the current of the stator winding strands in a two-pole 300-MW generator. Numerical results are presented. >

Eddy current fields and overheating problems due to heavy current carrying conductors

Large complex problems, eddy current fields and local overheating due to heavy current carrying conductors (HCCC) including leads and connecting bus bars in a 360 MVA/500 kV power transformer, are analyzed by the boundary element method. To improve numerical accuracy, this paper chooses triangle polar coordinate mapping and addition-substraction techniques to evaluate singular integrals. The distributions of magnetic flux and eddy current densities in metallic parts of different materials are discussed. According to the criterion of overheating, permissible lead current and limiting distance between HCCC and metallic parts and arrangements of HCCC are suggested. >

Development of permanent magnet synchronous motor used in electric vehicle

Permanent magnet synchronous motor (PMSM) has a excellent performance and will see a wide use in electric vehicle (EV) application. But some improvements should and can be done to make it more suitable in an EV drive. In this paper, asymmetric airgap and its optimal design, field and circuit coupled design method and winding switch of PMSM are put forward and analyzed, and are verified to be valid by experiment or simulation.

Computation of eddy current losses by heavy current leads and windings in large transformers using IEM coupled with improved R- Psi method

A method combining the improved R- Psi method (in which the electrical vector potential R only exists in the conducting region) and the IEM (integral equation method) is described which synthesizes the advantages of the two methods and reduces the CPU time and the storage space required to solve 3-D eddy-current problems in open regions. The IEM is used to compute the magnetic field and losses due to heavy-current leads and the improved R- Psi method is used to calculate the magnetic field and losses due to windings. The coupled method is used to calculate the three-dimensional sinusoidal eddy-current field related to the open region in a 360 MVA/500 kV power transformer. The eddy current and loss computation and the estimation of the local hot spots makes it possible to prevent a large transmitter from local overheating. >

Theory and design of hybrid excitation permanent magnet synchronous generators

On the basis of a conventional permanent magnet (PM) synchronous generator’s construction, a novel kind of Hybrid Excitation Permanent Magnet Synchronous Generator (HEPMSG) is introduced by inserting exciting winding in the stator or rotor. Firstly, the construction of HEPMSG is improved with the addition of PM excitation on the ferromagnetic pole, and its working principle and design method are studied in detail. Then, an appropriate exciting current control system is presented considering the characteristics of HEPMSG. Finally, a prototype is made, and test results confirm the analysis and design.