Variable-speed Generation System Research Articles

Development of a low-harmonic vector hysteresis current controller

The increasing interest in the use of renewable energy sources for the generation of electrical energy makes it necessary to ensure that these type of installations do not jeopardize the global operation of the electrical system to which they are connected. Up until now, this safety has been achieved by imposing very strict limits to the percentage of “non-controllable” renewable energy that can be connected to the grid. In order to increase these limits, new control schemes must be developed, focusing in power quality and, if possible, in trying to help grid stability. The paper proposes two new control methods for the current injected by a variable-speed generation system and compares them to a traditional hysteresis control. The first one obtains a table by using an algorithm that calculates the switching state that minimises switching frequency. The commutation is determined by a single comparator applied to the error vector, achieving a circular error area. The use of this table, along with the selection of a circular error area for the current vector makes that the current error remains always inside the specified error area. The second method is a predictive one, based on the previous one, that decides the optimum switching vector in the precise time when the commutation occurs, taking into account the present state of the system.

Pitch A ngle Control through PI and PID Controller based for Wind Energy Conversion System

The worldwide electrical energy consumption is growing day by day and also increasing the demand of power generation. So in addition into the electrical power system network for power production units a large number of renewable energy units is being combined. A wind energy generation system is the economical of all safe renewable energy sources and the environmentally clean in worldwide. The acceptance of variable speed generation systems the recent evolution of variable frequency drive and power semiconductors technology has been aided. Pitch angle control techniques is best factor to improve the efficiency as well as protection of the wind turbine blade. Therefore, presented in the work a comprehensive model of permanent magnet machines in wind turbine system. Modelling and simulation permanent magnet machines with wind turbine system of PI and PID controller based pitch angle control figuring performance is done by using MATLAB software. The significant result of these controller performance is being compared and also shown with validate approach with the existing survey.

Control of a BDFIG Based on Current and Sliding Mode Predictive Approaches

The Brushless Doubly Fed Induction Generator (BDFIG) is a great attraction nowadays thanks to its high reliability and high low voltage ride-through capability. In variable speed generation systems, the most used control techniques are the vector control, direct torque/power control. Vector control is highly sensitive to parameters variations, while the two others offer high amount of ripples reducing power quality. This paper therefore proposes a Sliding Mode Power Predictive Control (SMPPC) and an Indirect Model Power Predictive Control (I-MPPC) for a simple and efficient power control of the BDFIG. The SMPPC takes current components in the αβ frame as sliding surfaces derived from the I-MPPC based on current predictions to track the desired active and reactive powers in the BDFIG. A cost function defined as currents’ quadratic errors is used to choose the appropriate voltage vector for control winding supply, and the Particle Swarm Optimization algorithm is used to determine the optimal gain for the SMPPC. Simulations on MATLAB/Simulink are carried out to show the effectiveness of the control schemes as well as their robustness to some parameters variations. More so, power compensation is used to improve the capability of the control strategy to provide sinusoidal and balanced currents under unbalanced grid conditions. The proposed methods compared to direct power control show good performances in terms of total harmonic distortion reduction, low ripples and robustness, strengthening the idea of using the BDFIG as an alternative to new generation of wind energy conversion systems.

가변속 발전기 적용에 따른 컨테이너선박 에너지 효율성 비교

가변속 발전기 적용에 따른 컨테이너선박 에너지 효율성 비교

Maximum Power Point Tracking Control of IPMSG Incorporating Loss Minimization and Speed Sensorless Schemes for Wind Energy System

In the variable-speed generation system, the wind turbine (WT) can be operated at maximum power operating points by adjusting the shaft speed optimally. This paper presents a novel maximum power point tracking (MPPT)-based control of interior permanent-magnet (IPM) synchronous generator incorporating loss minimization algorithm (LMA). In the proposed method, without requiring the knowledge of wind speed, air density, or turbine parameters, MPPT algorithm generates optimum speed command for speed control loop of vector-controlled machine side converter. The MPPT algorithm uses the estimated active power output of the generator as its input and generates command speed so that maximum power is transferred to the dc link. The proposed control system also incorporates a LMA to minimize the losses in the generator and hence to improve the efficiency of the wind energy conversion system (WECS). A speed sensorless scheme is also incorporated to increase the reliability of the system. The performance of the proposed adaptive MPPT control of wind generator incorporating loss minimization and speed sensorless schemes is tested in both simulation and experiment at variable wind speed conditions.

Stator voltage harmonics and unbalance compensation of the sensorless standalone doubly fed induction generator

Purpose – Doubly fed induction generator (DFIG) is widely used in wind energy conversion systems and it can operate with other primary movers. The purpose of this paper is to focus on the standalone operation of DFIG which may expand the area of possible applications and increase capabilities of the generation system in terms of power quality. Design/methodology/approach – Synthesis of the control method was preceded by analysis of mathematical model of the machine. The control method based on the negative sequence and high harmonics extraction has been developed and verified in the laboratory unit. Control of the fundamental frequency component uses neither rotor speed nor position sensors. Findings – The original method allows to compensate negative sequence and high harmonics of the generated voltage. At the same time, due to the active filtering capability of the grid side converter, the stator phase current shape is close to sine wave. Thus, it is seen by the machine as a linear load, what eliminates the electromagnetic torque ripples. Practical implications – The system and control method can be applied in variable speed generation systems, e.g. wind turbines or diesel engines operating in the standalone mode. Originality/value – Although the selective compensation of negative sequence and harmonics are known in the literature, until now the methods have been verified for the system with a rotor position sensor. Moreover, the stator current feed-forward improving the transient properties, as well as results of transient states caused by the load step change, have not been proposed in publications.

A Study on Variable Speed Generation System with Energy Saving Function

This paper presents development of variable speed generation (VSG) system with energy saving function. The rubber tyred gantry crane (RTGC) requires the power from diesel-engine. Significant fuel savings by reducing the engine speed can be achieved, because all of operation modes except hoisting are required lower power than rated value of engine. When low speed operation output voltage of generator is decrease until acceptable range of motor driver inverters and auxiliary load supplier. According to power demand engine speed is varying from 20 to 60Hz, and voltage is varying between 210Vac and 480Vac. When idle mode or low power operation dc/dc converter operates by constant output voltage control and inverters dc site voltage is compensated by it. This paper proposed 3-phase interleaved boost converter which has the same structure as the commercially available 3-phase inverter and current sharing capability. 400kW interleaved converter is designed and a performance of converter is evaluated through several experiments with a RTGC system. Energy saving VSG system can cut down fuel consumption by 36% and 21.3% at idle and unidirectional load operations.

Design and Practical Implementation of a Novel Variable-Speed Generation System

This paper investigates a novel variable-speed generation system. A new integrated power circuit with voltage clamp protection and self-excitation function is presented. Conventionally, due to the large internal impedance of a generator, oscillations are produced by the resonances of the filter in armature currents which may cause unstable behavior of the generation system. In this paper, an active damping control algorithm cooperated with matrix converter (MC) instantaneous value synthesizing modulation strategy is proposed to suppress oscillations of MC input currents effectively. In addition, a closed-loop voltage control scheme with MC constant transfer ratio and hybrid excitation synchronous generator excitation current regulation is studied. At last, the feasibility of the overall system and schemes has been verified by the experimental results.

Experimental Validation of a Space-Vector-Modulation Algorithm for Four-Leg Matrix Converters

Most variable-speed AC generation systems use back-to-back converters to supply electrical energy, with fixed electrical frequency and voltage, to a stand-alone load or grid. Matrix converters (MCs) are a good alternative to back-to-back converters because they have several advantages in terms of size and weight. Therefore, MCs can be advantageously used in any variable-speed generation system where high efficiency, reliability, small size, and low weight are considered important factors. Nevertheless, to interface an MC-based generation system to an unbalanced 3φ stand-alone load, a four-leg MC is required to provide a path for the zero-sequence load current. Space-vector-modulation (SVM) algorithms for the operation of four-leg MCs have been proposed in the literature. However, these modulation methods have high computational burdens, and they are difficult to implement, even in fast DSP-based control platforms. Therefore, only simulation results have been reported in these publications. In this paper, an SVM algorithm is optimized and experimentally tested. Moreover, the harmonics produced in the input current when a four-leg MC is feeding an unbalanced or nonlinear load are also mathematically analyzed in this paper, with experimental verification being provided.

Implementation of the Three-Phase Switched Reluctance Machine System for Motors and Generators

This paper presents two three-phase switched reluctance machine systems. One is the dual motors drive for the electric locomotive traction; the other is the variable-speed generator system for wind power applications. The principles of the switched reluctance machine system operated at four quadrants, the scheme of the symmetrical traction at quadrant I and quadrant III, and the scheme of the symmetrical regenerative braking control at quadrant II and quadrant IV, are given. The transient phase current analysis and the energy analysis of the switched reluctance machine system at the operational state of braking or generating are evaluated, and the rotor position and the peak value of the phase current at three different conditions are given. The closed-loop rotor speed control of the main motor, synchronization of the rotor speed, and balance distribution of loads between the main motor and the subordinate motor have been implemented by the fuzzy logic algorithm. The closed-loop output power control of the switched reluctance wind power generator system implemented by regulating the turn-on angle of the main switches with fuzzy logic algorithm and fixed turn-off angle of the main switches is also presented. The major components of the two prototypes are explained in detail. The experimental results of the dual 7.5-kW three-phase 6/4 structure switched reluctance motors (SRMs) parallel drive system prototype are included. It is shown that the maximum difference in the output torque of the two motors at the same given rotor speeds is within 10.00% and the maximum difference in the practical rotor speed of the two motors is within 5.00%. The tested results of three-phase 12/8 structure switched reluctance variable-speed wind power generator system show that the error of the closed-loop output power control is within 2.2%, while the rotor speed range is close to the ratio of 1:3 with the low rotor speed 405 r/min. The average dc line current of the power converter can be utilized as a feedback signal for the actual output torque of SRM drive or a feedback signal for the actual output power of switched reluctance generator system.

Efficiency of three wind energy generator systems

This paper presents a method to calculate the average efficiency from the turbine shaft to the grid in wind energy converters. The average efficiency of three 500 kW systems are compared. The systems are: a conventional grid-connected four-pole induction generator equipped with a gear, a variable-speed synchronous generator equipped with a gear and a frequency converter, and a directly driven variable-speed generator equipped with a frequency converter. In this paper it is shown that a variable-speed generator system can be almost as efficient as one for constant speed, although it has much higher losses at rated load. The increased turbine efficiency that variable speed leads to has not been included in this paper. It is also found that a directly driven generator can be more efficient than a conventional four-pole generator equipped with a gear.

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

AbstractThis 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:This generator is a brushless system which makes use of the multifield induction machine;Frequency converter of small capacity which is used for constant voltage and frequency in load at variable speed;The PWM inverter can supply reactive power to the self‐excited generator; andVoltage wave of load is sine wave byLCfilter 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 ofLCfilter in frequency converter are described.

Characteristics of Self-Excited Generator System at Variable Speed Constant Voltage Constant Frequency by Multi-Field Induction Machine.

In this paper we deal with a generator system by use of variable energy like a wind power. The variable energy has influence voltage and frequency of a generator system. However, load requires constant voltage and frequency. Therefore, this paper proposed that a generator system have good points as follews:(1) This generator is brushless system make used of Multi-Field induction machine.(2) Frequency converter of small capacity used for constant voltage and frequency in load at variable speed.(3) PWM Inverter can supplying reactive power to Self-Excited generator.(4) Voltage wave of load is sine wave by LC filter of the frequency converter.The Multi-Field induction machines of this generator system have 4 poles and 8 poles as a same stator winding. The rotor of Multi-Field machine is especially cage type. This rotor can transform among 4 poles field and 8 poles field on the stator.In the present paper, we described an experimental study of the brushless, Self-Excited, constant voltage, constant frequency, variable speed and sine wave generator system by Multi-Field induction machine. We described component of this generator system, operation of Multi-Field induction machine, characteristics of generator system, and effect of LC filter in frequency converter.

Variable-speed generation with the series-resonant converter

Results of study and measurements are presented for a variable-speed generation (VSG) system that uses a series-resonant converter to excite the rotor windings of a doubly-fed generator. The capabilities of this system include maximum-efficiency operation and limited converter rating for a speed range from stand-still (zero RPM) to well beyond synchronous speed, as well as flexibility for line-voltage control, reactive power generation, and synchronization at zero RPM. Measurements of the harmonic distortion are provided showing the superiority of this converter as compared with a VSG system using a conventional cycloconverter or a DC-link converter. A convenient tool for analyzing the operating modes of the system is discussed that can be developed under varying resource conditions. >