Wound Field Synchronous Generator Research Articles

An Expeditious Algorithm for Identification and Classification of Rotor Faults in Salient Pole Synchronous Generators

Providing secure electricity depends on the reliable operation of the synchronous generators in power plants. Inter-turn short circuit (ITSC) and dynamic eccentricity (DE) faults are among the most prevalent fault types in wound field synchronous generators (WFSGs). Among the various signals used to detect faults such as current, voltage, and vibration, the stray magnetic field provides higher sensitivity for early-stage ITSC and DE detection. The introduced detection methods rely on comparison of various signals frequency spectrum's from fault and healthy generators. However, obtaining a frequency spectrum of a healthy synchronous generator that has been operating for decades in a power plant is almost impossible. A unique pattern is introduced using fast Fourier transform that can be implemented on a low-end microcontroller and ideal for IoT solutions. The efficacy of the proposed pattern is examined by finite element modeling and validated on a 100 kVA WFSG setup in the laboratory and field test in a power plant with a power rating of 22 MVA.

Effects of Material Deformation Due to Aging of Electrical Steel on the Brushless Wound-Field Synchronous Generator

This study analyzes the material deformation of electrical steel with aging and its effects on the electromagnetic and thermal characteristics of a Brushless Wound-Field Synchronous Generator (BL-WFSG). First, in order to confirm the material deformation of electrical steel applied to the BL-WFSG, magnetic property tests are performed on the core sheets of the old and new generators. Those two generators are made of the same material, so there was no difference except for their usage time. Based on the results of the magnetic property tests, an electromagnetic field analysis is performed on the old and new generators, and analysis results are compared in order to confirm the effects of material deformation on the electromagnetic characteristics of BL-WFSG. Then, a thermal analysis is performed on the old and new generators using losses calculated by electromagnetic field analysis as heat sources, and analysis results are compared in order to confirm the effects of material deformation on the thermal characteristics of BL-WFSG. Finally, an additional electromagnetic analysis is performed on both the old and new generators, using the exact winding resistances that were calculated in the thermal analysis for each respective generator in order to calculate and compare the efficiency of the old and new generators. Through this process, the authors confirmed the effects of material deformation of the rotor and stator cores due to aging on the electromagnetic and thermal characteristics of the BL-WFSG.

Integrated Damper Cage for THD Improvements of Variable Speed Salient-Pole Synchronous Generators for the More Electric Aircraft

Wound field synchronous generators (WFSGs) have been implemented as aircraft main ac power generation for decades. The trend of moving toward more electric aircraft (MEA) made dc and variable-frequency ac buses favorable for the next-generation power systems in aircraft, as opposed to constant frequency ac grid systems. The minimization of the generators’ output voltage total harmonic distortion (THD) is an ever-more critical objective, especially for variable-frequency power systems where this target has to be met within the whole range of operating speeds. In conventional, constant speed, and WFSGs, a number of consolidated techniques are implemented to meet this requirement. In variable-speed SGs intended for the MEA, these techniques are no longer fully effective and new methodologies are thus necessary. This article replaces the conventional squirrel-type damper cage with a new integrated damper cage (IDC) located at the interpole regions. The proposed IDC, while acting as a mechanical structure to retain the field windings at high operating speeds, also achieves very low-voltage THD values at different speeds, thus complying with the power quality requirement. A 250-kVA prototype is designed, analyzed, built, and tested to prove the proposed concepts and methodologies.

Three-level Vienna Rectifier with a Brushless and Permanent Magnetless Generator for Wind Energy Conversion Systems

Abstract This paper proposes a system design and control technique for a newly developed brushless and permanent magnetless synchronous generator-based variable-speed wind energy generation system, transferring power to a constant voltage dc grid via a three-level Vienna rectifier (VR). The recently established generator named Brushless Induction excited Synchronous Generator (BINSYG) is a wound field synchronous generator (WFSG), whose excitation is developed by controlling an Induction Machine fitted to the same machine structure and sharing the same magnetic core. A new controller is proposed that ensures the stable operation of BINSYG for a wide variation of shaft speeds. VR achieves sinusoidal input current and can control the power factor at its input, which is particularly suitable for wind energy applications. The top and bottom capacitor voltages of the VR are balanced using redundant switching combinations. The system with its proposed control algorithm is modelled in MATLAB/Simulink for a 5 kW rated BINSYG feeding power to a 750 V dc grid. The steady-state and dynamic state simulation results are presented and the controller performance is verified for a wide range of wind speeds. Further, real-time results using the OPAL-RT testbed are presented for the same system to verify the effectiveness of the overall control strategy.

Second‐order sliding mode control of wind turbines to enhance the fault‐ride through capability under unbalanced grid faults

AbstractThe integration of wind generation to the grid is growing rapidly across the world. As a result, grid operators have introduced the so‐called grid codes (GC), which nowadays include a range of technical conditions and requirements, which wind generators must fulfill. Among these, the low‐voltage ride through (LVRT) is a requirement for wind turbines to stay connected to the grid and continue to operate during the disturbance. In this study, a control structure, combining inertial kinetic energy storage with a crowbar circuit, is proposed to enhance the ride through capability of a wind turbine generator (WTG) based on a wound‐field synchronous generator (WFSG) under unsymmetrical voltage dips. For the grid‐side converter (GSC), a decoupled double synchronous reference frame (DDSRF) d‐q current controller is used. Furthermore, a second‐order sliding mode controller (SOSMC) with super‐twisting (ST) algorithm is proposed for the GSC and the machine‐side converter (MSC) to improve the response speed and achieve an accurate regulation of the dq‐axis current components simultaneously. The main objectives of the GSC are to achieve a balanced, sinusoidal current and smooth the real and reactive powers to reduce the influence of the negative‐sequence voltage. A series of simulations are presented to demonstrate the effectiveness of the proposed control scheme in improving the LVRT capability of the WFSG‐driven wind turbine and the power quality of the system under unbalanced grid voltage conditions.

Challenges and Opportunities for Wound Field Synchronous Generators in Future More Electric Aircraft

Electrical machines and drives keep moving away from traditional technologies such as brushed machines and wound field machines toward lighter, “easier to maintain” machines. A very interesting aspect is that certain transport applications, especially the aerospace industry, still favor the classical wound field machine for its main generating system such as Boeing 787. This article focuses on investigating this particular trend by presenting a detailed overview of the historical power-generation systems on aircraft. This article compares the current state of the art of wound field machines with other generator families. The results of this analysis are then projected into the needs of the electrical power generation and distribution system on aircraft. Although power density is a major objective for any aerospace application, however, the extra benefits associated with wound field systems are still essential in modern aircraft. This article then focuses on the main challenges for improving the power density of wound field machines. Recommendations, opportunities, and improvements related to wound field machines are discussed. In conclusion, if robust designs for higher speed wound field generators were consolidated, it would be very probable that these classical machines might still be implemented on future More Electric Aircraft (MEA) platforms.

Simplified Damper Cage Circuital Model and Fast Analytical–Numerical Approach for the Analysis of Synchronous Generators

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical–numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes.

Accuracy improvement for complex harmonic analysis modelling of a wound field synchronous generator

Complex harmonic analysis (CHA) provides a computationally efficient alternative to finite element analysis (FEA) for modelling multi-phase wound field synchronous machines. This paper presents three methods that could improve the accuracy of the CHA: by improving the equivalent air gap, by including a saturation factor, and by using image methods for computing end-winding inductance. The comparison against a finite element method and experiment shows the improved complex harmonic method could predict waveforms reliably, where a dynamic finite element method would be time-consuming. This paper shows the method is valid for a five-phase generator.

Excitation System Technologies for Wound-Field Synchronous Machines: Survey of Solutions and Evolving Trends

WFSM are included in the majority of large power generating units and special high-power motor drives, due to their high efficiency, flexible field excitation and intrinsic flux weakening capability. Moreover, they are employed in a wide range of high-end solutions in the low-to-medium power range. This contribution presents a comprehensive survey of classical and modern methods and technologies for excitation systems (ESs) of (WFSMs). The work covers the fundamental theory, typical de-excitation methods and all the modern excitation equipment topologies in detail. It also includes a description of the state-of-the-art and the latest trends in the ESs of wound-field synchronous motors and generators. The purpose of the paper is to provide a useful and up-to-date reference for practitioners and researchers in the field.

Synchronous Generator Brushless Field Excitation and Voltage Regulation via Capacitive Coupling Through Journal Bearings

Wound field synchronous generators (WFSG) are the standard electromechanical converter for back-up and utility scale power generation. Maintenance costs may be minimized by adopting noncontact or “brushless” technologies to replace sliding slip ring connections for rotor field excitation. This paper presents a brushless excitation approach using ceramic insulated sleeve (journal) bearings with oil lubrication to form capacitively coupled slip rings, in contrast to more traditional inductive brushless exciters and rotary transformers. This capacitive power transfer (CPT) approach exhibits advantages including low weight, low volume, and has a relatively simple construction using off-the-shelf components. Analysis, design, and prototype construction of the CPT system are presented. Experimental results demonstrate that 1.7 nF of capacitive coupling transfers 340 W to the rotor field winding of a 10 kW 208 V WFSG. Voltage regulation of a WFSG is demonstrated during steady state and 1 per unit load step changes yielding a NEMA-MG1 class G2 rating.

Improved Damper Cage Design for Salient-Pole Synchronous Generators

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions.

Online Model-Based Condition Monitoring for Brushless Wound-Field Synchronous Generator to Detect and Diagnose Stator Windings Turn-to-Turn Shorts Using Extended Kalman Filter

In this paper, a model-based approach is proposed to detect and diagnose stator winding fault in the Brushless wound-field synchronous generator (BWFSG). The extended Kalman filter is used as a state and parameter estimation technique for the proposed model-based approach. The mathematical model of the BWFSG with stator winding fault is developed and simplified for online implementation. An experimental test-rig is used to acquire the required inputs for the developed state estimation technique. The estimated rotor currents and fault parameter are analyzed to identify key signatures for condition monitoring (CM). The harmonic components such as the second harmonic components of the estimated field and damper currents, and the rms value of the estimated fault parameters are identified as suitable signatures for winding fault and diagnose. Based on the identified signatures, a model-based CM algorithm is proposed and validated in real time. The validation results confirmed that the proposed algorithm is able to detect and diagnose winding inter-turn short-circuit faults in real-time reliably.

A new control strategy of WFSG-based wind turbine to enhance the LVRT capability

This paper proposes a competent and effective scheme to enhance the low voltage ride through (LVRT) capability of wound field synchronous generator (WFSG) based wind turbines (WTs) under unbalanced voltage dip conditions. A technique for grid synchronization against voltage excursions, i.e., a PLL using positive grid voltages with a high selectivity filters (HSFs) is utilized to extract a robust grid voltage synchronization signal irrespective of the mains condition to enhance the overall system performance. Besides, a new controller (adaptive fuzzy RST) for both the stator side converter (SSC) and grid side converter (GSC) current regulation are employed to further improve dynamic performance. Also, a reactive power support scheme to manage the WFSG reactive power during contingencies and fulfill the grid codes obligations is presented. Moreover, an additional device such as braking chopper (BC) circuit is used in the DC-link circuit for stable operation of the wind energy conversion system (WECS) under-line fault. Effectiveness of the proposed control strategy is verified by the numerical simulations.

Winding Configurations for Five-Phase Synchronous Generators With Diode Rectifiers

Wound-field synchronous generators are widely used in aircraft and marine electrical systems. As the electric power requirements increase, there is renewed interest in dc power networks, but the electrical source remains a synchronous generator. The combination of a diode rectifier with a wound-field multiphase generator reduces the voltage ripple on the dc network and increases fault tolerance, compared with an equivalent three-phase system. It also increases the options in terms of the winding design and configuration. This paper uses circuit modeling, including harmonics, informed by static finite-element results, to understand the wound-field generator performance for star and polygon connections of both short- and fully-pitched coils. Experimental results are used to validate the models. A polygon connection of short-pitched coils is shown to give good generator utilization for a healthy machine. However, careful design is required to prevent circulating harmonic currents. Under winding open-circuit faults, the polygon connection requires significant derating, making the star connection the preferred option.

Unity power factor operation and neutral current compensation of diesel generator set feeding three‐phase four‐wire loads

This study deals with power quality improvement in a diesel generator (DG) set-based standalone supply system feeding three-phase four-wire(3P4W) loads. The proposed system consists of a diesel engine, three-phase wound field synchronous generator, a four-leg voltage source converter (VSC) and3P4W loads. The four-leg VSC with a capacitor connected on its DC link is used for neutral current compensation and unity power factor operation of the DG set. In addition, the VSC provides harmonics elimination and the load balancing. The voltage of the DG system is controlled by excitation control of the synchronous generator and the frequency is controlled by speed regulating system of the diesel engine. The speed of the engine is regulated by controlling the fuel injection of the diesel engine. An adaptive theory-based notch filter algorithm is used to extract fundamental component of the load currents for estimation of reference source currents.

Proposal of a new hybrid control strategy for dynamic performance improvement of wound field synchronous generator-based wind turbines

This paper presents a simulation study of the control of a variable speed wind energy conversion system (WECS) using a wound field synchronous generator (WFSG). The proposed scheme is based on an RST controller with adaptive fuzzy gain scheduling (AFGS-RST) and regulates the active and reactive powers exchanged between the stator of the WFSG and the grid to ensure a Maximum Power Point Tracking of the WECS. The overall system model was implemented in MATLAB/Simulink with three different power controllers (the polynomial RST, the fuzzy logic controller, and the AFGS-RST controller). The performances of these controllers are evaluated under different operating conditions of the WECS power system. The results demonstrate that AFGS-RST controller is very effective in improving the power flow and very robust against variable transmission line parameters compared to the two other controllers.

Solid‐state control for reactive power compensation and power quality improvement of wound field synchronous generator‐based diesel generator sets

This paper presents the use of pulse-width modulated voltage source converter (PWM-VSC) for power quality improvement of a wound field synchronous generator-based diesel generator (DG) set realising standalone supply system. The system consists of a diesel engine driven wound field synchronous generator, a three-leg PWM-VSC with a capacitor on the DC link and linear/non-linear loads. The PWM-VSC supplies the leading kilo volt-amphere reactive (kVAR) to the loads and maintains the unity power factor of the DG set. In addition, it eliminates the harmonics from the source currents and provides load balancing. The terminal voltage is controlled by field excitation control of the generator and the supply frequency is controlled by the speed regulating system of the diesel engine. A variable step size filter-x least mean square-based control algorithm is used for estimation of reference currents for control of VSC.

Power Control of Wind Turbine Based on Fuzzy Sliding-Mode Control

This paper presents the study of a variable speed wind energy conversion system (WECS) using a Wound Field Synchronous Generator (WFSG) based on a Fuzzy sliding mode control (FSMC) applied to achieve control of active and reactive powers exchanged between the stator of the WFSG and the grid to ensure a Maximum Power Point Tracking (MPPT) of a wind energy conversion system. However the principal drawback of the sliding mode, is the chattering effect which characterized by torque ripple, this phenomena is undesirable and harmful for the machines, it generates noises and additional forces of torsion on the machine shaft. A direct fuzzy logic controller is designed and the sliding mode controller is added to compensate the fuzzy approximation errors. The simulation results clearly indicate the effectiveness and validity of the proposed method, in terms of convergence, time and precision.

Interior PM Generator for Portable AC Generator Sets

For portable ac electric generator sets, it is desired to maintain a constant output voltage under load. With wound-field synchronous generators, this is done using field current (excitation) control. This type of control is not possible with permanent magnet (PM) machines; however, theoretical analysis is used to show that acceptable output voltage regulation can be obtained by two alternative design approaches for interior PM machines. The design of an example 4-pole 16-kW machine is described, and experimental results are provided, demonstrating its sinusoidal output waveform, high voltage regulation, and high efficiency.

Variable speed wind turbine generator system with current controlled voltage source inverter

The present popular trend of wind power generation is to use variable speed wind turbine (VSWT) driving a doubly fed induction generator (DFIG), wound field synchronous generator (WFSG) or permanent magnet synchronous generator (PMSG). Among them, stability analyses of DFIG type of VSWT have already been reported in many literatures. However, transient stability and low voltage ride through (LVRT) characteristics analyses for synchronous generator type of VSWT is not sufficient enough. This paper focuses on detailed LVRT characteristic analysis of variable speed wind turbine driving a PMSG (VSWT–PMSG) with current controlled voltage source inverter (CC-VSI). Modeling and suitable control strategies for overall system are developed to augment the low voltage ride through capability of variable speed wind generator, considering recent wind farm grid code. Both symmetrical and unsymmetrical faults are analyzed as network disturbances in this paper. The permanent fault due to unsuccessful reclosing of circuit breakers is taken into consideration, which is a salient feature of this study. Moreover, the dynamic characteristic is analyzed using real wind speed data measured in Hokkaido Island, Japan. The proposed control scheme is simulated by using the standard power system simulation package PSCAD/EMTDC and results are verified by comparing that of voltage controlled voltage source inverter scheme available in power system literature.