Variable Speed Constant Frequency Generation Research Articles

Finite-Set Model Predictive Power Control of Brushless Doubly Fed Twin Stator Induction Generator

This paper presents a finite-set model predictive power control (FS-MPPC) method for the brushless doubly fed twin stator induction generator (BDFTSIG) in variable speed constant frequency generation applications. The FS-MPPC controller is developed in a general reference frame from which all other reference frames can be deduced readily. The invariant feature of the predictive power model in various reference frames contributes to the reference frame-free characteristic of the developed FS-MPPC controller, enabling its application more flexible and universal. Besides, the arduous process of control winding flux estimation is avoided in the FS-MPPC controller by choosing state variables that are easy to be obtained. Moreover, the influence of rotor circuit that has long been neglected in the existing controllers for the brushless doubly fed induction machines is embedded within the predictive power model and inherently considered in the FS-MPPC controller, which contributes to accurate power control of the BDFTSIG. Furthermore, the feasibility and effectiveness of the developed FS-MPPC controller regarding different power levels and grid fault conditions are briefly discussed. Finally, numerical simulations and experimental tests are carried out, which demonstrates the effectiveness of the developed FS-MPPC controller.

Voltage Control of a Stand-Alone Cascaded Doubly Fed Induction Generator

This paper studies the cascaded doubly fed induction machine, operating as a brushless variable speed constant frequency generator supplying an isolated load. In isolated electric supply, the amplitude and frequency of the output voltage of the generator should be stabilized during the speed and/or load changing. Despite the complexity of the generator model, a simple indirect field-oriented vector control is elaborated to meet the output voltage requirements. Experimental results validate the proposed control approach. The study is extended to reveal the behavior of the controlled system under unbalanced load.

Dual-Electrical-Port Control of Cascaded Doubly-Fed Induction Machine for EV/HEV Applications

This paper presents a dual-electrical-port control scheme for four-quadrant operation of cascaded doubly-fed induction machine (CDFIM), which has conventionally been used as a variable-speed drive or variable-speed constant-frequency generator for limited-speed-range applications. The proposed control method enables the synchronous control of both power winding (PW) and control winding (CW) currents, and as a consequence, not only the control complexity but also the rotor slip frequency and related core losses are significantly reduced in comparison with the previously proposed single-electrical-port control scheme. It is for the first time revealed that the CDFIM drive that indirectly couples PW and CW through induction behavior can be readily controlled like a conventional induction motor to achieve the highest torque density. The torque density–speed region of the CDFIM falls within that of the power machine in singly-fed operation mode, and only a half of that of the power machine in doubly-fed operation mode, which shows the urgent need for torque density enhancement of brushless doubly-fed machines for electric vehicle/hybrid electric vehicle applications. Computer simulations and experiments are implemented to verify the dynamic performance of the proposed control method.

Operation and Control of Stand-alone Brushless Doubly Fed Induction Generator Using Control Winding Side Converters

The brushless doubly fed induction generator has wide applications as a stand-alone variable-speed constant-frequency generator in some embedded generation systems. In this article, a controller for a stand-alone brushless doubly fed induction generator using control winding side converters is introduced, which was implemented as a ship shaft generation system located in a container ship. The primary goal of the control system is to obtain constant output voltage and frequency of the brushless doubly fed induction generator, regardless of the load and speed condition variation. The main obstruction of working with the brushless doubly fed induction generator is its inherent complexity. To overcome this problem, the mathematical description, power flow, and performance evaluation of the stand-alone brushless doubly fed induction generator is comprehensively developed and analyzed. The experiments presented in this article were implemented on a 2/6-pole 250-frame-size wound-rotor brushless doubly fed induction generator.

Distortion Analysis and Duty Ratio Correction Algorithm for Asymmetric Modulation of Two-Stage Matrix Converter

When applying the two-stage matrix converter (TSMC) to the aero variable-speed constant-frequency generation system, the high input frequency varying between 360 and 800 Hz becomes a great challenge to its control. One of the most commonly used modulation methods for TSMC is the dual space vector modulation (DSVM). Simulation and experiments show that despite its advantages such as simplicity and low switching loss, the asymmetric DSVM causes distortion both in the output voltages and input currents of the TSMC. In this paper, the conception of “pulse orthocenter” (PO) is introduced via a BUCK model, and the influence of PO's fluctuation upon the actual output is revealed. Based on the PO theory, the spectra of TSMC's output voltages and input currents are then analyzed, indicating that asymmetric modulation causes $3n\omega_{\rm in}\pm(3m\pm 1)\omega_{o}$ harmonics in the output voltages and $(3n\pm 1)\omega_{\rm in}$ harmonics in the input currents. In order to suppress these harmonics, a duty ratio correction (DRC) algorithm is proposed to improve the waveform quality without increasing switching loss. The DRC formula is provided and the available range of related parameters discussed. The correctness of distortion analysis is testified via simulation, and the validity and feasibility of the DRC algorithm is verified via experiments.

Research on Robust PIMD Control for Brushless Doubly Fed Machine

As a kind of novel machine, the brushless doubly fed machine (BDFM) without the electric brush and slip ring has gained more and more attention in its AC speed regulation and variable-speed constant-frequency generation system applications due to its good operation performance. For the speed regulation of the BDFM as the external disturbance existing, a proportional integral minus delay (PIMD) controller combining with the H robust control method is proposed. The PIMD controller utilizes the minus delay method and adjusts the delay time to eliminate the known external sinusoidal disturbance input signal. The controller combining with the H∞ robust control strategy can effectively restrain the unknown uncertainties of the system, and further enhance the system robustness. The simulation results show that the proposed PIMD controller can enable the system to have better robustness against external disturbances, and greatly improves the interference rejection performance of the system. Keywords: Brushless doubly fed machine, H∞ control problem, PIMD controller, robust control, speed regulation.

Comparing Study on Performance of Brushless Doubly-Fed Generator with Different Rotor Structures

In order to study comparatively the effect of different rotor structure on variable speed constant frequency generation. The simulation performance comparisons between ALA reluctance rotor and cage rotor generator are presented in this paper by MATLAB software. It is indicated that ALA reluctance rotor and cage rotor exhibits fine variable speed constant frequency generation, however, the voltage harmonic of reluctance rotor generator is more than that of cage rotor generator.

Unbalance and harmonic voltage compensation for a stand‐alone variable speed constant frequency double‐output induction generator supplying non‐linear and unbalanced loads

This study presents an improved control algorithm for a stand-alone double-output induction machine-based variable speed constant frequency generator. The algorithm ensures sinusoidal load voltage and machine stator current for all types of loads such as balanced, unbalanced, linear and non-linear in any arbitrary combination. This is achieved by incorporating harmonic and unbalanced load compensation function to the stator side converter. Unlike other control strategies reported in the literature for this purpose, the proposed algorithm does not require extraction or compensation of individual harmonic/unbalance components of the load voltage/stator current. Harmonic compensation performance of the algorithm is thoroughly analysed theoretically and design guidelines provided. The experimental results obtained from a laboratory prototype demonstrate excellent load voltage regulation property during severe transient operating conditions. Total harmonic distortion and unbalance of the load voltage and stator current even with large unbalanced non-linear loads are also found to be much smaller compared with similar systems reported earlier in the literature.

Study on the New SVPWM Method for Three-Level Inverter of Brushless Doubly-Fed Machine

Brushless doubly-fed machine (BDFM) is a new type of AC induction motor.It has a good applicable prospect as the variable frequency motors or the variable speed constant frequency generators. Although the advantage of the three-level inverter, there are also some problems of neutral point voltage balance in this method such as the unbalance of neutral point voltage. And the traditional principle of Three-level inverter space vector pulse width modulation method is to estimate the sectors and calculating a lot of trigonometric functions. To solve these problems, a novel method for the virtual space vector concept in G-H coordinate system is presented in this paper. The method proposed can omit the judging process of the sectors, reduce the calculating burden, and maintain the balance of neutral-point voltage between capacitances within a certain index modulation. The results of simulation are given to validate the improved virtual space vector modulation.

A New Method to Estimate the Magnetic Field Modulation Effect of Brushless Doubly-Fed Machine with Cage Rotor

Brushless doubly-fed machine (BDFM) doesn't use brush and slip ring, and has advantages such as high system reliability, small capacity of its frequency converter, low system cost, adjustable power factor and speed, etc. At the same time, it has good applicable potentials on the variable frequency motors and the variable speed constant frequency generators. However, due to the complicacy and particularity of BDFM in the structure and operating mechanism, the effect of magnetic field modulation directly influences the operating efficiency of BDFM. To study the effect of different cage rotor structures on the magnetic field modulation of BDFM, the rotor magnetomotive force (MMF) of BDFM with cage rotor is studied by the analytical method. The components and features of rotor harmonic MMFs are discussed. At the same time, the method to weaken the higher harmonics is analyzed by the theoretic formulae. Furthermore, the magnetic field modulation mechanism is expounded on in detail and the relationship between the magnetic field modulation effect and the operating efficiency of BDFM is established. And then, a new method for estimating the magnetic field modulation effect is proposed. At last, the magnetic field modulation effects of four BDFM prototypes with different cage rotor structures are compared by the MMF analysis and the efficiency data of electromagnetic design. The results verify the effectiveness of the new method for estimating the magnetic field modulation effect of BDFM with cage rotor.

Decoupled Power Control of Doubly-Fed Induction Generator Based on an Implicit Position and Speed Estimation Algorithm without the Flux Computation

Owing to the increased attention on the need for deployment of renewable energy sources such as the wind energy, there is a growing interest in Doubly Fed Induction Generators (DFIG) which are suitable for variable speed constant frequency generation. Accurate information of the rotor position with respect to the stator is central to the effective decoupled control of real and reactive power in the DFIG. Typically sensorless estimation of the rotor position involves complex signal processing. This paper presents the implementation of a simple and implicit sensorless algorithm for estimating the rotor position and speed for decoupled control of the doubly-fed induction generator. The proposed algorithm does not involve the computation of stator magnetic flux directly or indirectly using the voltage integration, recursive techniques, re-computations or programmable low pass filters etc. Instead, it employs simple analytical equivalents for the resolved components of the stator flux which are derived from the basic equations governing the machine operation. Since the flux terms are replaced with other equivalent terms, the estimation process is devoid of computing any flux terms and requires only the measured stator voltage and the currents in stator and rotor windings apart from the machine parameters. Starting on the fly, accurate estimation near synchronous speed, immunity against variation in stator and rotor resistances or in the magnetizing inductance are the principal advantages of the algorithm. Reduced complexity and the computational burden facilitate the easy implementation of the algorithm on a low cost fixed point processor. Excellent agreement between the simulation and test results on a laboratory doubly-fed induction machine validates the proposed estimation algorithm. Further MATLAB/Simulink based simulation results are presented to validate the efficacy of the position estimation algorithm based vector control of a doubly-fed induction generator.

Effect of wind speed and load power factor variation on optimal sizing of the machine and converters for double output induction generator based stand-alone wind energy conversion systems

In this paper, an algorithm for finding out the optimal ratings of the machine and power electronic converters of a wind turbine driven stand-alone double output induction generator based variable speed constant frequency generation system is reported, which seeks to minimize the cost of energy generation. The nonlinear constrained optimization technique employed includes, among others, the reactive power balance constraints, which are not often considered for stand-alone systems. For this purpose, the load power factor is modeled as a random variable with known probability density function. The total energy captured is calculated for a given wind velocity density function and load power factor density function. The proposed method finally finds the optimum combination of machine and converter ratings, which results in minimum cost of energy. The effects of changes in load power factor and wind velocity distribution are also discussed in detail.

00/02746 New self-excited variable speed constant frequency generator for wind power systems

00/02746 New self-excited variable speed constant frequency generator for wind power systems

00/01482 Operation of new variable speed constant voltage and frequency generator connected to the grid

Aedes (Stegomyia) aegypti is the vector responsible for the transmission of the viruses that cause zika, yellow and chikungunya fevers, the four dengue fever serotypes (DENV – 1, 2, 3, 4), and hemorrhagic dengue fever in tropical and subtropical regions around the world. The present study investigated the genetic differentiation of the 15 populations of this vector in the Brazilian state of Maranhão, based on the mitochondrial ND4 marker. A total of 177 sequences were obtained for Aedes aegypti, with a fragment of 337 bps, 15 haplotypes, 15 polymorphics sites, haplotype diversity of h = 0.6938, and nucleotide diversity of π = 0.01486. The neutrality tests (D and Fs) were not significant. The AMOVA revealed that most of the variation (58.47%) was found within populations, with FST = 0.41533 (p < 0.05). Possible isolation by distance was tested and a significant correlation coefficient (r = 0.3486; p = 0.0040) was found using the Mantel test. The phylogenetic relationships among the 15 haplotypes indicated the existence of two distinct clades. This finding, together with the population parameters, was consistent with a pattern of genetic structuring that underpinned the genetic differentiation of the study populations in Maranhão, and was characterized by the presence of distinct lineages of Aedes aegypti.

New self-excited variable speed constant frequency generator for wind power systems

In this work, the possibility of using a new single-phase commutator machine as a stand alone self-excited generator is investigated. The performance of this generator is tested under variable speed operation to simulate the practical case of variable wind turbine speed. The generator is self-excited through a resonance capacitor. The effect of varying the capacitance of this capacitor on the generated voltage and its frequency is studied. Load tests under a wide range of operating conditions are conducted to explore the capability of this type of generator. It has been found that this machine can operate as a variable speed constant frequency generator simply by varying the capacitance of the excitation capacitor. This important property makes this type of generator suitable for use in wind driven power systems. Finally, a mathematical model for the generator is obtained and a simulation program is developed to predict the performance of the generator. Close agreement between the simulation and the experimental results is obtained.

Operation of new variable speed constant voltage and frequency generator connected to the grid

Wind is an uncontrolled and stochastic source of power because its speed is continuously changing in magnitude and direction. In order to maximise the obtainable power, wind driven power systems must be able to generate power at all wind speeds whether this speed is low or high. This is not possible when conventional generators are used unless complicated control systems or electronic circuits are used. In this paper, the feasibility of using an AC commutator machine as a generator for wind power plants is experimentally investigated. The machine is connected as a shunt generator in parallel with the grid. It can be operated in a wide range of speeds without any stability problems. Hence, the speed can be controlled such that the maximum output power is obtained at all wind speeds. This type of machine generates a constant frequency voltage irrespective of the shaft speed when excited from a separate constant frequency source. The experimental set has been prepared in the lab such that all variables which affect the generated power can be controlled. These variables include shaft speed, grid coupling voltage and brush angle. The effects of these variables on the amount and quality of power generated are carefully tested. The results obtained show that this machine is a suitable power converter for wind power applications.

Vector Control of a Variable Speed Doubly-Fed Induction Machine for Wind Generation Systems

SummaryControl techniques suitable for a doubly fed induction generator applied to a wind generation system are presented. A Scherbius scheme using two back-to-back voltage-fed current-regulated inverters in the rotor circuit is employed allowing subsynchronous and supersynchronous operation with low distortion currents. A vector control scheme using a reference frame oriented along the stator flux vector is used for the machine. This leads to independent control of the electrical torque and the rotor excitation current. A vector scheme aligned with the stator voltage vector is used to control the stator-side converter; this gives independent control over the active and reactive power flow between the supply and the stator-side converter. The control strategies are tested with the machine working as a variable speed constant frequency generator driven by a wind turbine emulator. Two approaches for optimum speed tracking of the wind turbine are implemented and experimental results for a prototype system ar...

BRUSHLESS CONSTANT-FREQUENCY GENERATION USING SINGLE-FRAME CASCADED INDUCTION MACHINES

ABSTRACT Brushless variable-speed constant-frequency generation finds its place in numerous situations such as aerospace and wind energy applications. In the past, cascade connected induction machines have been considered for aircraft applications due to their reliability compared to existing generating systems. The Single-Frame Cascaded Induction Machine (SFCIM) in variable-speed constant-frequency generating applications is a more favourable solution compared to a two machine system. This paper presents the application of a novel steady-state model of SFCIM to analyse a brushless, variable-speed constant-frequency generating scheme proposed for aircraft applications. The SFCIM considered in this paper consists of two independent stator windings and a rotor with a ‘multicircuit single-layer bar winding’ which is simple and robust. The theoretical results obtained using the new model are compared with the experimental results.

Transient state analysis of a doubly-fed induction generator under three phase short circuit

The doubly fed induction generator (DFG) is a variable-speed constant-frequency generator operating in either subsynchronous or supersynchronous mode. The transient behavior of a symmetrically loaded DFG after a three-phase short circuit is presented. Both speed and rotor excitation voltage and frequency remain unchanged during short circuit. The complete mathematical model of the transient state and experimental results are given, along with the transient state equivalent circuit. >

Aircraft VSCF generator expert system

VSCF (variable-speed constant-frequency) electrical systems are designed using standard modules to reduce the manufacturing cost and improve the product quality and services. An expert system that automatically configures the modules required for a particular application is described. It is a rule-based synthesis system with a domain that encompasses the matrix of standard modules. The module functions include electrical generation, conversion, the control. All the modules must be placed in a proper package to fit the space available inside the particular airplane. The configuration system is built by using a rule-based expert system development tool, OPS5, in a VAX 11/750 computer. It has the domain-specific knowledge necessary to configure the generators embedded in its rulebased and exhibits expertise to place the modules in the proper arrangement based on customer specifications and design criteria. The system can also help the engineers and salespersons to determine the configuration at quotation time and to point out any new design which is required.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>