POWER CONTROLLER FOR A WIND-TURBINE-DRIVEN TANDEM INDUCTION GENERATOR

ABSTRACT

A controller for delivering either constant power or maximum power from a wind-turbine-driven grid connected induction generator with double stator windings, one fixed and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. The load torque of the generator is controlled by varying the angular displacement between the two stators. The generator can feed power to the grid at variable speed and constant frequency and is termed a Tandem Induction Generator.

Dynamic models for the wind energy conversion system are proposed for both controlled and uncontrolled operation to predict changes in shaft speed to shifts in wind speed using data pertaining to a commercial wind turbine. Results based on laboratory tests on a 1hp tandem machine driven by a dc motor demonstrating the feasibility of both controllers are presented. A steady state model of the tandem generator is also proposed and compared to measurements made on the test machine.     

PERFORMANCE ANALYSIS OF SELF-EXCITED INDUCTION AND RELUCTANCE GENERATORS

ABSTRACT

The paper presents a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines. The proposed arrangement is adapted to use one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors. Operational and steady-state equivalent circuits for both types are developed and used to predict the dynamic and steadystate behaviours under load conditions. This analysis depends mainly upon the computation of the power angle for a given machine parameters, capacitor ratings, and load conditions at a constant speed. Further, stability limits of both generators are investigated by developing the active-reactive power (P-Q) diagram for each generator. Conditions required to achieve self-excitation are also given. Performances of the two generator types are evaluated theoretically and experimentally.     

CORRESPONDENCE: VARIABLE-SPEED,CONSTANT-FREQUENCY HYSTERESIS GENERATOR

ABSTRACT

The hysteresis generator has been mentioned in the literature [1,2], but analytical studies seem to be absent. The supersynchronously operated hysteresis machine offers promise of a simple infinite bus generator for use with a prime mover characterized by either speed fluctuation or poor speed regulation.

In this note, a previously presented asynchronous equivalent circuit model [3] and example machine data [4] are utilized to predict asynchronous hysteresis generator performance for speeds from 1.0 to 1.5 per unit. The example hysteresis generator is seen to be a near constant output power device over a wide range of supersynchronous speeds when operated on an infinite bus.     

Improved Performance of a Schrage Motor by Tertiary Tuning

ABSTRACT

Tertiary capacitor tuning in the stator of the schrage machine is developed to increase the air gap mmf, improve the generating and motoring efficiency and power factor, increase the full-load torque of the machine, and keep the machine as a wide range speed transducer.

The system analysis based on a developed equivalent circuit is given with experimental verification.

The analysis and characteristic curves show the effect of the brush axis variation. The advantages of tertiary capacitor tuning over brush axis shifting are shown.     

Synchronous Machines Adapted for Six Step Converters–Part II: Experimental Evidence

ABSTRACT

An investigation has been carried out to evaluate converter driven synchronous machines including a machine which is specially adapted for use with converters. The adapted machine has been designed so that the internally generated voltage is tailored to produce a desired current waveform when the machine is driven by a six step voltage source inverter. In this manner, the energy flows associated with commutation are supplied by electromechanical means. In the specific example presented, an armature current waveform is produced which is congrument with the applied armature voltage.

A short design study has been carried out which compares a conventional machine and an adapted machine of similar volume under converter driven operation. The rating of the adapted machine is slightly better than the conventional machine, although both are derated compared to the sinusoidal operation of the conventional machine.The adapted machine has a significantly improved power factor as well as smaller armature currents and reduced variations in shaft output power. Because of the reduced requirements for reactive power and armature current, it is expected that a simpler converter could be utilized. In addition to the design study, an experimental program has been carried out to demonstrate that the adapted machines will operate as predicted. An experimental machine in the 6 kw range was constructed and tested in a variety of conditions. The results of the experimental work agreed well with predicted behavior.     

ON-LINE ESTIMATION OF SYNCHRONIZING AND DAMPING TORQUE COEFFICIENTS USING AN ARTIFICIAL NEURAL NETWORK BASED APPROACH

ABSTRACT

This paper presents an artificial neural network based on-line approach to assess the dynamic stability of a single machine connected to an infinite bus system. The proposed approach is based on estimating the synchronizing and damping torque coefficients of the synchronous machine from voltage and power on-line measurements. Test results show that the proposed approach is very encouraging for fast evaluation of the dynamic stability.     

THE DOUBLY-FED MACHINE WITH PASSIVE ROTOR SUPPLY IMPEDANCE OPERATING AS A VSCF GENERATOR-A SLIP DEPENDENT MATHEMATICAL MODEL

ABSTRACT

The paper presents a mathematical model for a doubly-fed induction generator driven by a variable-speed prime mover. The primary circuit of the generator is supplied at rated frequency and output power is obtained from the secondary circuit. The components of power generated by the machine are presented. The steady-state stability limits of the generator are investigated. Comparison between the predicted and experimental results shows that although the model is simple, good agreement is obtained.     

Enhanced Control Algorithm in PMSMs with Machine Current Sensor FDI and Current Management for Hardware Protection

Abstract

This paper proposes an enhanced control algorithm in permanent magnet synchronous machines (PMSMs) with machine current sensor fault detection and isolation (FDI) and current management for hardware protection. Different from existing work on machine current sensor FDI, the proposed method addresses the sensor FDI problem under co-existence of PMSM current sensor and non-sensor imbalance faults, and thereby help prevent the controller performance degradation caused by a faulty machine current sensor signal. Meanwhile, hardware protection is achieved through the proposed algorithm which has a unique feature of providing online overcurrent regulation and source power management at the same time to enhance protection of power inverter and power source. Benchmark comparison of the proposed sensor FDI method to state-of-the-art techniques is carried out to validate the good performance of the proposed FDI method in terms of fault detection time, false detection rate and missed detection rate. Sensitivity analysis of the proposed current management algorithm with overcurrent regulation and source power management is performed under changing rotor flux linkage and machine stator d-axis self-inductance, as an example to demonstrate the robustness of the proposed algorithm for hardware protection against system parameter variations. The effectiveness of the proposed algorithm is confirmed by simulation results in MATLAB for a PMSM.     

MODIFIED ASYNCHRONOUS CASCADE MACHINE SYSTEM

ABSTRACT

The modelling of the modified asynchronous cascade machine system is done in order to study the features of such system under field-oriented frame of reference. The modified machine system has two stator windings and two sections of rotor winding on the same shaft One of the stator windings is connected to the ac network while the other winding is connected to an inverter capable of controlling power flow in both directions. This system can be operated in a wide speed range and both sections of the rotor winding can produce useful torque.     

INDUCTION MOTOR DRIVE STABILIZATION WITH STATOR CURRENT FEEDBACK

ABSTRACT

The use of state feedback to control Induction motor drive systems is examined. Using the machine currents and speed as the system states, a general linearized formulation of the problem is derived. This formulation has the advantages of previous forms based on complex variable analysis, but is not subject to the limitations of that method.

The proposed model Is used to study machine control with stator current feedback. The results show that stator current feedback can be used to improve the dynamic characteristics of the drive system. Comparisons of stator current control with the uncontrolled machine and with the slip controlled machine are presented over the range of operating speed, load, and inertia. In all cases, advantages of current controlled operation can be seen.     

Simulation Study on On-Line MTPA/MTPV Trajectory Tracking in PMSMs with Power Management

Abstract

This paper proposes an on-line maximum torque per ampere (MTPA)/maximum torque per voltage (MTPV) trajectory tracking method in permanent magnet synchronous machines (PMSMs) with power management. The on-line MTPA/MTPV machine current trajectory tracking algorithm is developed from PMSM model. Maximum source current and machine current are regulated to enhance hardware protection during machine current trajectory tracking. The maximum source current management is achieved by iterating within the current trajectory tracking algorithm over continuous torque command modifications based on power flow analysis, and the maximum machine current management is achieved by torque command limiting based on current angle modulation. Different from the existing techniques in literature, the proposed method has an unique feature of providing on-line regulation of source current, while maintaining on-line MTPA/MTPV trajectory tracking in PMSMs. It also provides machine and inverter overcurrent regulation to enhance their protection. In addition, the proposed method is flexible to tune and does not require off-line calibration. The effectiveness of the proposed method is confirmed by simulation results in MATLAB.     

TEST PROCEDURE FOR VERY HIGH SPEED SPINDLE MOTORS

Abstract

In the last ten years, the new power electronic devices and the new control techniques have allowed to open new application fields for adjustable speed/torque electrical drives. Although the traditional dc drives keep still the market supremacy, the new ac drives have performance really attractive and some additional benefits due to the machine structure and to the maintenance costs. Usually, ac drives use induction or brushless motors and the power amplifiers are driven by variable voltage/frequency in order to obtain variable speed. The authors deal with induction motors fed by non conventional supplies at very high frequency. In order to evaluate the total motor losses and the single items, a test bench with a synchronous machine capable to work up to 2 kHz with sinusoidal output voltage has been set up. As a consequence, an induction motor equivalent circuit with parameters depending on the frequency has been proposed. Today, the empirical procedure is that to use for high frequency applications shelf motors derated of a factor 10 to 20 % in order to keep into account the extra harmonic losses. On the other hand, the authors propose to design ‘ad hoc’ the motors for six-steps continuous operation in order to get about the same efficiency of standard motors. The new proposed motor equivalent circuit together with the test procedure seem to be a practical tool in order to aid the new motor design.     

A LINEAR TRANSFER FIELD MACHINE FOR ASYNCHRONOUS MODE OF OPERATION

ABSTRACT

For the first time, this paper describes a working model of a novel linear transfer field machine along with an equivalent circuit analysis method for the asynchronous mode of operation In the sinusoidal steady-state. The machine is found to have a thrust-speed characteristic like unto that of the flat linear induction machine with a conducting sheet secondary. Analysis of performance is made for values of speed across the range from standstill to synchronous speed. Laboratory measured data are compared with calculated values for standstill operation.     

Adaptive Power System Stabilizer Design Using Optimal Support Vector Machines Based on Harmony Search Algorithm

Abstract—This article presents the application of support vector machines to adaptive power system stabilizer design in a multi-machine power system based on the harmony search algorithm. Data from a multi-machine power system are the input features of the support vector machines. Support vector machine parameters and power system features are simultaneously optimized by harmony search based on the k-fold cross-validation technique. The proposed algorithm is trained by the optimal support vector machine parameters and optimal power system features. Power system stabilizer parameters produced by the proposed algorithm can be adapted by various operating conditions when the power system operates either inside or outside the training ranges. Simulation studies in the IEEJ Western Japan ten-machine power system demonstrate that the proposed algorithm is far superior to conventional power system stabilizers with fixed parameters and those designed by a robust coupled vibration model under various operating conditions and severe disturbances.     

Design of Novel Intelligent Controller for Doubly-Fed Induction Generator-Driven Wind Turbine to Improve Transient Control Performance

Abstract

This paper presents a design for the novel intelligent control (NIC) of the stabilization of a doubly fed induction generator (DFIG)-based wind turbine. The intelligent control scheme was developed to control the rotor side voltage source converter that allowed independent control of the generated active and reactive power as well as the rotor speed to track the maximum power point (MPP). Moreover, the NIC was used to reduce the interaction between the real and reactive power flow and improve the performance. The proposed NIC consisted of an improved recurrent fuzzy neural network (IRFNN) and ant colony optimization with genetic algorithms (GACO). GACO was adopted to adjust the learning rates to improve the online learning capability of the IRFNN. Furthermore, an NIC controller was proposed for both the rotor and stator side converters to improve the steady-state and transient voltage stability of the DFIG system for different operating conditions. In addition, the method is highly simple to implement. Finally, the proposed approach stabilized the internal dynamics through rotor voltage control and improved the dynamic behavior of the DFIG after clearing a fault.     

Use of multifield induction machine to determine the characteristics of self-excited generator systems at variable speed,constant voltage and constant frequency

This paper considers a generator system using variable energy such as wind power. The variable energy influences the voltage and frequency of a generator system. However, the load requires constant voltage and frequency. Therefore, this paper proposed that a generator system have the following good points:

• (1) This generator is a brushless system which makes use of the multifield induction machine;
• (2) Frequency converter of small capacity which is used for constant voltage and frequency in load at variable speed;
• (3) The PWM inverter can supply reactive power to the self-excited generator; and
• (4) Voltage wave of load is sine wave by LC filter of the frequency converter.

The multifield induction machines of this generator system have 4 poles and 8 poles similar to stator winding. The rotor of the multifield machine is especially cage type. This rotor can transform among the 4-pole field and 8-pole field on the stator. In this paper, an experimental study of the brushless, self-excited, constant voltage, constant frequency, variable speed and sine wave generator system by multifield induction machine is described. The component of this generator system, operation of multifield induction machine, characteristics of generator system, and the effect of LC filter in frequency converter are described.     

A SINGLE PHASE LINEAR TRAVELLING WAVE INDUCTION MOTOR

ABSTRACT

A simplified analysis of a single phase linear travelling wave induction machine is described. The analysis shows that the design goodness factor is independent of variation in the width of the airgap, and predicts that the performance of the machine will not be degraded by an increase in airgap. A machine designed and constructed on the basis of the analysis, was used to investigate the possibility of varying the airgap to control the speed. The results of these investigations are fully discussed.     

Coordination of multiple adjustable speed drives for power quality improvement

The proliferation of semiconductor-based non-linear devices in power systems has caused serious concern over power quality problems. This paper proposes a control strategy to coordinate multiple adjustable speed drives (ASDs) so that harmonic currents as well as reactive power generated by non-linear loads can be compensated. Under the proposed control strategy, the power quality improvement task is distributed to multiple adjustable speed drives and their contribution to the task is determined proportionally to their instantaneous power margins. The proposed control strategy can be a fairly flexible and economical solution for power quality improvement especially for the places where multiple machine drives are already-installed or required, for example, manufacturing factories or shipboard or aircraft power systems, because the adjustable speed drives can be fully utilized to improve power quality without additional compensators as well as conditioning end-use machines. Detailed simulation results using switching-level converter models verify the performance of the proposed coordination strategy.     

AN APPROACH TO IMPROVING DYNAMIC STABILITY OF SUPERCONDUCTING GENERATOR USING Q-AXIS DAMPER WINDING FEEDBACK CONTROL

Abstract

Q-axis damper Minding feedback control offers a means for improving dynamic performance of superconducting generator.This paper is an investigation of dynamic characteristics of a machine with such a control system. A model based on Park's equations in the form of Fourier Transform of the machine is proposed and used to simulate the dynamic behaviour of the generator after the occurance of a small disturbance of torque or voltage of the power source.From the computer simulation results, it was proved that the system can offer sufficient damping effects and an optimum design can be reached by choosing parameters of the control system carefully. Also,it is a more economic method compared with those proposed by others [4,5,6].