Kazumasa Ide

Output Power Smoothing and Hydrogen Production by Using Variable Speed Wind Generators

This paper presents a combination system of wind energy conversion and hydrogen production. Hydrogen is expected as an alternative energy source in the future, and this is the best way to produce it from renewable energy like wind energy. On the other hand, the output of a wind generator, in general, fluctuates greatly due to wind speed variations, and thus the output fluctuations can have a serious influence on the power system operation. In the proposed system, a variable speed wind generator is adopted, and an electrolyzer is installed in parallel with it for hydrogen production. Output power from the wind generator is smoothed and supplied to the power system as well as to the electrolyzer based on the cooperative control method. The performance of the proposed system is evaluated by simulation analyses, in which simulations are performed by using PSCAD/EMTDC.

Analysis of saturated synchronous reactances of large turbine generator by considering cross-magnetizing reactances using finite elements

This paper describes a method to calculate saturated reactances of synchronous machines at various loads under steady-state operation by considering influence of cross-magnetizing phenomenon between d- and q-axis circuits. In the method, mutual reactances x/sub dq/ due to the cross-magnetizing phenomenon can be calculated on the basis of two-dimensional magnetic field analysis. The validity of analysis is shown by good agreement between measured and calculated field current values of a 592 MVA turbine generator at various loads. It is clear that quantitative accuracy requires the magnetic coupling between d- and q-axis circuits be considered. Subsequently, steady-state reactances at various loads are analyzed by considering mutual reactances x/sub dq/ due to cross-magnetizing phenomenon. The relation between the load angle /spl delta/ and mutual reactance x/sub dq/ is clarified, and the difference between equivalent synchronous reactances that are obtained by considering x/sub dq/ and conventional defined synchronous reactances that do not consider x/sub dq/ is shown numerically.

Dynamic harmonic field analysis of a cage type induction motor when magnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors.

Calculation of leakage inductances of a salient-pole synchronous machine using finite elements

An analysis method for calculating three components of leakage inductances, i.e. the stator, rotor and winding distribution differential leakage inductances, which properly represent the amount of each leakage flux in a salient-pole synchronous machine is presented. The winding distribution differential leakage inductance has a positive value mainly arising from the difference between the armature and field winding distributions. The value of the turns ratio must be changed as the saturation condition changes in order to transform leakage inductances into the proper armature base values. Calculated leakage inductances are shown to validate the method. Further investigations using the presented analysis may generate useful knowledge for pole designs.

Steady-state magnetic circuit analysis of salient-pole synchronous machines considering cross-magnetization

A simple magnetic circuit of salient-pole synchronous machines is presented. A method for calculating steady-state electrical performances using the circuit is described. Magnetic saturation including the cross-magnetizing phenomenon is considered in the method. The saturated reactances, field currents, and load angles are calculated easily from the method without much computational effort as compared with the finite element method. Despite the simplicity of the magnetic circuit, the calculated reactances at various load conditions using the method are close to the measured and FEM values.

Efficiency calculation of wind turbine generation system with doubly-fed induction generator

This paper presents a method to calculate various losses in wind turbine generation system (WTGS) as a function of wind speed, which is based on the steady state analysis. Variable speed WTGS using a doubly-fed induction generator (DFIG) and power converters (inverter and converter) is mainly considered in this paper. By using the proposed method, wind turbine power, generated power, generator losses, gearbox loss, power converter losses and energy efficiency can be calculated quickly. Moreover, annual energy production and capacity factor of the wind farm can be obtained by using the wind speed characteristic expressed by Weibull distribution function. Therefore, if the Weibull distribution function of wind speed is available, we can calculate the annual energy production without using real annual wind speed data. Using the data of Weibull distribution function of some different areas, capacity factor of each area is calculated and compared with those of other types of WTGSs such as Permanent Magnet Synchronous Generator (PMSG) and Squirrel-Cage Induction Generator (IG).

Higher harmonics calculation of synchronous generators on the basis of magnetic field analysis considering rotor movement

A simple analysis method is proposed for output voltage waveforms and magnetic flux waveforms passing through the main stator parts of synchronous generators. The method considers the rotor movement in order to analyze the higher harmonic sequences and some techniques for simplifying the calculation using the symmetry of armature windings and stator slot arrangements. The effectiveness of the higher harmonics analysis method under saturated conditions, is verified by 50-MV A-class generator analysis. It is useful for quantitative evaluation of the voltage and magnetic flux waveforms and no-load saturation characteristics of synchronous generators. >

Transient-torque analysis for line-starting permanent-magnet synchronous motors

Using the analysis method for resolving the starting torque of line-starting permanent magnet (PM) synchronous machines with starting cage, the electromagnetic torque can be separated into two components, the driving ldquocage torquerdquo and the braking ldquomagnet torquerdquo. The correct saturation of the iron must be considered, when calculating the separate torque components. The sum of the two torque components exhibits a good agreement with the originally calculated starting torque with the Finite Element time stepping technique. This novel method also helps to have a better knowledge of the synchronization mechanism. Results are given for a two-pole prototype motor with PN=5 kW, nN=3000 min-1, VN=200 V, Y-connection.

Analysis of leakage flux distributions in a salient-pole synchronous machine using finite elements

It is important to understand the relationship between iron core configurations and leakage flux distributions to get a better design of synchronous machines. This paper presents a method for calculating the steadyand transient-state leakage flux distributions in salient-pole synchronous machines. The method provides information on leakage flux distributions that cannot be obtained by terminal quantities. The method analyzes the leakage inductances that properly represent the corresponding leakage fluxes. They are calculated using the gap flux distributions by finite elements with magnetic saturation. The calculated leakage inductances of a synchronous machine under various loads are also shown and the relationship between the inductances and magnetic saturation is discussed.

Finite-element calculation of leakage inductances of a saturated salient-pole synchronous machine with damper circuits

It is important to understand the relationship between leakage flux distributions and machine characteristics for better design of synchronous machines. This paper presents a calculation method for leakage inductances of saturated salient-pole machines with damper circuits. Leakage inductances are divided into the self-leakage, gap leakage, and winding-differential leakage inductances. The leakage inductances correspond directly to the leakage flux distributions in the machines. Cross-magnetizing inductances are also calculated. The method is applied to a 300 MVA class generator. The relationship between the winding distributions, flux distributions, saturation, and inductances is discussed. Weak magnetic influence of the damper circuits on the armature in the d-axis is quantitatively illustrated through values of the winding-differential leakage inductances. The cross-magnetizing inductances, except for the d-axis damper circuits, are relatively large. Variations of the armature self-leakage inductances with saturation are small, and variations of the field and damper self-leakage inductances are larger.