Dual-excited Synchronous Generator Research Articles

Transient stability analysis of dual excited synchronous generator with excitation control

A Dual Excited Synchronous Generator (DESG) has two field windings. The stability enhancement of the power system can be achieved with felicitous control of these two field windings independently. Most of the work covered in the literature is on the stability analysis of DESG and the independent control of field windings. The independent control allows different amounts of current in field windings, which leads to unequal field losses and uneven rotor heating. The drawback is minimized in this work by keeping a predetermined angle between the excitation voltages. A simple excitation control similar to IEEE static exciter, regulates the d-axis and q-axis components of voltage, termed as Excitation type-1 (ET1), is presented in this paper. Also, the excitation system presented in the literature termed in this paper as Excitation type-2 (ET2) for comparison. The modified versions of both ET1 and ET2 are also presented to get overall improvement after a disturbance. The DESG connected to an infinite bus through a double-circuit transmission line is the system under study. Transient stability analysis of DESG with both types of exciters as well as Conventional Synchronous Generator for several disturbances in the system are presented, and also the results are compared.

Power Tracking Excitation Control and Its Parameter Optimization of Dual-Excited Synchronous Generator

A dual-excited synchronous generator (DESG) with two field windings on the rotor has better dynamic characteristics and high stability. However, the realization of the function needs a reasonable excitation control strategy. In this article, a power tracking excitation control (PTEC) is proposed to improve the operating performances of the DESG. The dynamic processes of a 300-MW DESG with the PTEC are calculated after the disturbance of the torque and reactive power by the time-stepping finite element model, and the results are superior to those adopting the traditional dual-channel excitation control. To further improve the dynamic characteristic of the DESG, the sensitivities of the control parameters of the PTEC to the dynamic characteristic indices are studied. The fuzzy control rules are built based on the sensitivity analysis results and the control parameters are optimized by the fuzzy control method. It revealed the variation laws of the optimized control parameters along with the active and reactive power deviations and their variable rates. The results show that the DESG adopting the optimized control parameters has better dynamic characteristics. The study can provide the theoretic basis for enhancing the system damping effect and suppressing the system oscillation.

Investigation of LVRT capability of wind driven dual excited synchronous generator

This paper proposes an effective control technique for low voltage ride through (LVRT) capability in dual excited synchronous generator (DESG) wind turbines. The proposed control technique is dependent on controlling the field circuit parameters. Where the active power is controlled by the field-current space phasor magnitude and the reactive power is controlled by the field-voltage space phasor phase. With the proposed control strategy, the DESG can generate additional reactive power to support grid voltage recovery under grid faults. The DC-link voltage is kept within an acceptable limit since the excess power, due to the power mismatch between the mechanical and armature power is stored in the generator inertia. Using the proposed control strategy, the DESG can enhance the LVRT capability efficiently without using extra protection circuits or any additional control techniques during fault conditions. To test the proposed control method, simulation, and experimental results for a 1.1 kW DESG wind turbine system were obtained.

Active and Reactive Power Control for Dual Excited Synchronous Generator in Wind Applications

This paper presents a dual excited synchronous generator (DESG) as a novel suitable alternative generation system for wind energy conversion systems. A new control strategy was proposed for the DESG wind turbine system. With this control technique, the DESG could be operated as a constant-speed constant-frequency (CSCF) generation system with the benefit of adjusting the reactive power or as a variable-speed constant-frequency (VSCF) generation system with the benefits of simple control methods and lower copper losses. Using the space phasor model of the DESG, a direct relationship between the electromechanical torque and the armature reactive power in terms of the field current space phasor magnitude and the field voltage space phasor angle is provided. The proposed control strategy is based on controlling the field-current space phasor magnitude and the field-voltage space phasor phase angle to regulate the active and reactive powers of the DESG. Simulation results, based on MATLAB/SIMULINK, for a 1.1 kW DESG wind turbine system have been executed to verify the introduced control technique under various operating conditions. Also, experimental studies have been carried out to validate the simulation results using the proposed control algorithm.

Finite‐element calculation of electromagnetic characteristics and steady‐state stability of dual‐excited synchronous generator

The Dual-Excited Synchronous Generator (DESG) has two sets of field windings. The magnitudes and directions of the two field currents can be regulated, so that the excitation magneto-motive force can be in any direction. The electromagnetic characteristics of the DESG may be different with those of the Traditional Synchronous Generator (TSG) for the different rotor structures of the two generators. To obtain better electromagnetic characteristics, a time-stepping finite element model (T-S FEM) of the DESG is established. The air-gap radial flux density, saturation, active and reactive power of the DESG in single- and dual-axis excitation modes are calculated and compared with those of the TSG. The electromagnetic characteristics affected by the different ratio of q-axis field current to d-axis field current are studied. On this basis, an excitation control strategy that can enhance the steady-state stability is proposed, and the steady-state stability limits with and without excitation control are calculated by the T-S FEM. A 10-kW DESG is developed to verify the correctness of the simulation results. The results show that the DESG with dual-axis excitation has better electromagnetic characteristics and stronger reactive power ability, and the steady-state stability limit of the DESG is increased obviously through the excitation control.

The Relationship of Magnetomotive Force Under Different Excitation Modes of Dual-Excited Synchronous Generator

The high stability of the dual-excited synchronous generator (DESG) can enhance the reliability of power supply for critical users. Based on the traditional synchronous generator (TSG), a DESG with two sets of symmetrical field windings on the rotor is presented in this paper. The rotor slots are spaced equally over the whole rotor surface of DESG, which is different from the structure of TSG. Such structures of DESG are expected to enhance the reliability and give the electromagnetic performances, such as air-gap flux density and electromotive force (emf) that are close to those of TSG. For this purpose the relationship between the excitation magnetomotive forces (mmf) of the single- and dual-axis excited DESG is investigated. The mmf with a different rotor pitch is calculated by the finite-element simulation, and the simulation results agree with those by the theoretical derivation. The excitation air-gap flux density, emf, and the magnetic saturation in stator and rotor cores are calculated under different excitation modes, and the results are compared with those of TSG. In order to validate the simulation results, the emf of 10 kW DESG model machine is measured under different excitation modes. This paper provides the theoretical basis for the design and manufacture of large DESGs.

Damping Shaft Torsional Oscillations in Dual Excited Turbo Generators

Technical advantages of utilizing the two field systems of the Dual Excited Synchronous Generator (DESG) for damping inertial and unstable torsional modes of steam turbo-generators (T-G) are considered. This is achieved by adding two auxiliary controllers, one on each field system. The d- axis auxiliary controller is designed to enhance the stability of the inertial oscillatory mode while the q-axis controller is designed to damp the unstable torsional modes. A comparison is made between using either generator or high-pressure turbine speed deviations as the stabilizing signals for the two controllers. The study is conducted on system-1 of the second IEEE benchmark for the simulation of the sub-synchronous oscillations. A rigorous state space mathematical model has been developed and simulated using MATLAB to carry the sought investigations. The pole placement method is used to determine the controller parameters. The results indicate that coordination of the two controllers can significantly increase the power system damping for the inertial and torsional oscillatory modes.

Nonlinear Optimal Excitation Control of Dual-Excited Synchronous Generators

Abstract A new approach using differential geometric theory to nonlinear control design for dual-excited synchronous generators is presented in this paper. As an example, a novel rotor angle and voltage stabilizing nonlinear optimal excitation control law of dual-excited synchronous generators is obtained, which is based on coordinate transformers and state feedback linearization combined with dynamic system. The computer simulation results on a single-machine infinite-bus power system show that dual-excited synchronous generator with proposed controller can improve dynamic stability and transient stability of power system to a great extent and has better dynamic characteristics than conventional synchronous generator.

96/00432 Characteristics of multi-phase flow with particle evaporation in a combustor with counter-flow injection

A new approach using differential geometric theory to nonlinear control design for dual-excited synchronous generators is presented in this paper. As an example, a novel rotor angle and voltage stabilizing nonlinear optimal excitation control law of dual-excited synchronous generators is obtained, which is based on coordinate transformers and state feedback linearization combined with dynamic system. The computer simulation results on a single-machine infinite-bus power system show that dual-excited synchronous generator with proposed controller can improve dynamic stability and transient stability of power system to a great extent and has better dynamic characteristics than conventional synchronous generator.

2軸励磁同期発電機一無限大母線系統の安定化制御法

2軸励磁同期発電機一無限大母線系統の安定化制御法

On the use of a digital computer as a two-phase variable-amplitude variable-frequency oscillator

A feasibility study on the use of a digital computer as a variable-amplitude variable-frequency oscillator which generates two-phase sinusoidal excitation control signals for a dual-excited synchronous generator is described. The oscillator uses two input signals. One input signal is used to control the frequency of the oscillator outputs, and the other is used to control their amplitudes. By a single variable, the software can be configured to vary the oscillator frequency range and to greatly reduce (almost eliminate) the harmonic distortion of the output signals. The harmonic distortion is constant and independent of the output frequency for each possible oscillator frequency range. The software-based oscillator design is flexible and can be used to generate different types of multiphase signal waveforms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

励磁電圧制御を考慮した2軸同期発電機のリアプノフの直接法による過渡安定度解析

励磁電圧制御を考慮した2軸同期発電機のリアプノフの直接法による過渡安定度解析

Power system dynamic studies for improved stability and minimum rotor heating via graph-theoretic modelling of a dual-excited synchronous generator

A systematic approach based on linear graph theory is suggested for linear and non-linear state model formulation of a system comprising of a dual-excited synchronous generator, connected to an infinite bus through a transmission line, and controlled by voltage regulator, angle regulator and a speed governor. Viewing the system as an interconnection of five simple subsystems, each being represented in isolation by a directed terminal graph and a set of terminal equations, leads to the generation of a system graph. A minimal state characterization is easily obtained through selecting a maximal forest, getting constraint equations therefrom, and substituting them in suitably arranged terminal equations. The method is applicable in general for any complex system. Besides presenting some of the computed results from the model thus formulated, for comparison with the experimental data available in the literature, investigations in this paper are further directed towards studies aimed at improving the stability regions to their maximum limit and cutting down the rotor copper losses to a minimum level. The effect of system operation in these modes on the relative choice of the three controller parameters is discussed with the help of various parameter-plane stability-limit loci plots.