Peak current mode control of three-phase boost rectifiers in discontinuous conduction mode for small wind power generators

This paper presents a peak current mode control scheme of a boost rectifier with low distortion of the input current for wind power systems based on permanent magnet synchronous generators with variable speed operation. The three-phase boost rectifier is operated in discontinuous conduction mode (DCM), and power factor correction techniques are applied. It is shown that the DCM operation significantly reduces the total harmonic distortion of the currents in the permanent magnet synchronous generator, increasing the power factor of the system, so that the vibrations and mechanical stress of the generator are minimized. The characteristics of the DCM boost rectifier are studied considering: (1) the series resistance of the inductors; (2) the modeling and adjustment of peak current mode control yielding a stable loop; (3) the design of an input filter that reduces the switching noise in the currents of the generator.     

Low power wind energy conversion system based on variable speed permanent magnet synchronous generators

This paper presents a low power wind energy conversion system (WECS) based on a permanent magnet synchronous generator and a high power factor (PF) rectifier. To achieve a high PF at the generator side, a power processing scheme based on a diode rectifier and a boost DC–DC converter working in discontinuous conduction mode is proposed. The proposed generator control structure is based on three cascaded control loops that regulate the generator current, the turbine speed and the amount of power that is extracted from the wind, respectively, following the turbine aerodynamics and the actual wind speed. The analysis and design of both the current and the speed loops have been carried out taking into consideration the electrical and mechanical characteristics of the WECS, as well as the turbine aerodynamics. The power loop is not a linear one, but a maximum power point tracking algorithm, based on the Perturb and Observe technique, from which is obtained the reference signal for the speed loop. Finally, to avoid the need of mechanical sensors, a linear Kalman Filter has been chosen to estimate the generator speed. Simulation and experimental results on a 2‐kW prototype are shown to validate the concept. Copyright © 2013 John Wiley & Sons, Ltd.     

Neural network controller for a permanent magnet generator applied in a wind energy conversion system

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system (WECS) employing a permanent magnet synchronous generator, is proposed. The permanent magnet generator (PMG) supplies a DC load via a bridge rectifier and two buck–boost converters. Adjusting the switching frequency of the first buck–boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck–boost converter allows output voltage regulation. The on-times of the switching devices of the two converters are supplied by the developed neural network (NN). The effect of sudden changes in wind speed, and/or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simultaneously with the developed NN controller. The results proved also the fast response and robustness of the proposed control system.     

An integrated control method for a wind farm to reduce frequency deviations in a small power system

Output power of wind turbine generator (WTG) is not constant and fluctuates due to wind speed changes. To reduce the adverse effects of the power system introducing WTGs, there are several published reports on output power control of WTGs detailing various researches based on pitch angle control, variable speed wind turbines, energy storage systems, and so on. In this context, this paper presents an integrated control method for a WF to reduce frequency deviations in a small power system. In this study, the WF achieves the frequency control with two control schemes: load estimation and short-term ahead wind speed prediction. For load estimation in the small power system, a minimal-order observer is used as disturbance observer. The estimated load is utilized to determine the output power command of the WF. To regulate the output power command of the WF according to wind speed changing, short-term ahead wind speed is predicted by using least-squares method. The predicted wind speed adjusts the output power command of the WF as a multiplying factor with fuzzy reasoning. By means of the proposed method, the WF can operate according to the wind and load conditions. In the WF system, each output power of the WTGs is controlled by regulating each pitch angle. For increasing acquisition power of the WF, a dispatch control method also is proposed. In the pitch angle control system of each WTG, generalized predictive control (GPC) is applied to enhance the control performance. Effectiveness of the proposed method is verified by the numerical simulations.     

A unity power factor front-end rectifier with hysteresis current control

A three-phase front-end rectifier capable of sustaining sinusoidal input currents in phase with their corresponding input phase voltages, and performing a wide dc link voltage regulation, is analyzed and presented in this paper. It makes use of three bidirectional switches between the rectifier ac side and dc link. An output power estimator, a dc link voltage regulator and a hysteresis current controller are applied in the proposed control algorithm to obtain and track the reference currents. This control algorithm, based on hysteresis current control technique, can enable the proposed rectifier-inverter ac motor drive to function within a wide output power range and large input inductance variations, yielding low current harmonics and unity power factor. Theoretical results of its analysis are verified initially through digital simulation, and confirmed by using an experimental prototype.     

Permanent-magnet machines

This paper explores the use of an interior permanent-magnet synchronous machine (IPM) as a source of controlled DC power. A three-phase diode rectifier converts the generated AC power into DC, which is further processed by a buck or boost DC-DC converter with a pulse-width modulation voltage controller for load voltage and output power regulation. The modeling and analysis of the generator system set forth are confirmed to accurately predict the generator characteristics by experimental results derived from a 2 hp interior permanent-magnet generator controlled separately by a buck and a boost DC-DC converter     

Hybrid wind/PV/diesel hybrid power systems modeling and South American applications

This paper presents an applications case study and comparison of performance results between two computational models for simulating the performance of hybrid power systems. The first model, HYBRID2, was developed at the University of Massachusetts under National Renewable Energy Laboratory (NREL) sponsorship. The second model, SOMES, was developed at Utrecht University in the Netherlands. Both models have been designed to predict the technical and economical (life cycle cost) performance of hybrid power plants that typically might be comprised of renewable energy sources, a battery bank, and a diesel generator. A South American (Brazil) based hybrid power system used to power a remote telecommunications system was used for the applications case study. A final system configuration be used as a basis for model prediction comparison was established as a result of HYBRID2 parametric evaluation. Both codes yielded similar performance results, and this work points out that the predicted performance discrepancies are due basically to different subcomponent models and differences in control strategy. The generalized nature of this work is intended to be of interest to engineers involved with the design and analysis of hybrid power systems.     

Sensorless direct torque control for salient-pole PMSM based on extended Kalman filter fed by AC/DC/AC converter

In this paper, a new sensorless interior permanent magnet synchronous motor (IPMSM) drives method with extended Kalman filter (EKF) for speed, rotor position and load torque estimation is proposed. The direct torque control (DTC) technique for permanent magnet synchronous motor (PMSM) is receiving increasing attention due to the important advantages of the low dependence on motor parameters when compared with other motor control techniques. The Kalman filter is an observer for linear and non-linear systems and is based on the stochastic intromission, in others words, noise. The PMSM is fed by an indirect power electronic converter which is controlled by a sliding mode technique. The simulation tests performed for different operating conditions have confirmed the robustness of the overall system; and it is shown that the sliding mode technique has successfully minimized the different harmonics introduced by the line converter.     

Characteristics of a highly efficient propeller type small wind turbine with a diffuser

We studied the improved effects a diffuser had on the output power of small wind turbine systems, aiming to introduce these systems to radio relay stations as an independent power supply system. A frustum-shaped diffuser was chosen from an economical standpoint and wind speed distribution. The effect the diffuser's shape had on the wind speed was analyzed by simulation and showed that the wind speed in the diffuser was greatly influenced by the length and expansion angle of the diffuser, and maximum wind speed increased 1.7 times with the selection of the appropriate diffuser shape. The wind speed in the diffuser was fastest near the diffuser's entrance. We conducted field tests using a real examination device with a diffuser and confirmed that the output power of the wind power generator increased by up to 2.4 times compared to that of a conventional turbine. Moreover, it was confirmed that the diffuser was especially useful where the wind direction was constant.     

Design and experimental validation of a high voltage ratio DC/DC converter for proton exchange membrane electrolyzer applications

This paper deals with hydrogen production via water electrolysis, which is considered the most attractive and promising solution. Specifically, the use of renewable energy sources, such as wind electric power generators, is hypothesized for supplying the electrolyzer, aiming to strongly reduce the environmental impact. In particular, micro-wind energy conversion systems (μWECSs) are attractive for their low cost and easy installation. In order to interface the μWECS and the electrolyzer, suitable power conditioning systems such as step-down DC-DC converters are mandatory. However, due to the requested high conversion ratio between the DC bus grid, i.e. the output of a three-phase diode rectifier connected to the output of the electric generator, and the rated supply voltage of the electrolyzer, the classic buck converter alone is not suitable. Therefore, a converter is proposed and designed, consisting of a buck converter, a full-bridge IGBT converter, a single-phase transformer, and a diode bridge rectifier; LC filters are also included between buck and full-bridge converters, and at the output of the diode bridge rectifier with the aim of reducing the ripple on currents and voltages. The components of the described physical system from the output of the three-phase rectifier up to the electrolyzer are then modeled assuming the transformer as ideal, and the model is employed for designing a PI-type controller. Experimental results are provided in order to demonstrate the effectiveness of the developed converter and its control for these applications.     

基于派克变换算法的空冷电厂，厂用电谐波分析

对空冷发厂厂用电系统的谐波进行了测试,依据空冷变低压侧变频器的谐波测试数据,采用派克变换算法对空冷变高压侧谐波进行了合成。结果表明,当2台接线为O／yn11和Y/yn12的空冷变并联运行时,低压变频器产生的谐波在高压侧能够有效抵消。对发电机和厂用高压设备无显著影响。     

Simulations and experiments on a 12 kW direct driven PM synchronous generator for wind power

A direct driven permanent magnet (PM) synchronous generator has been designed and constructed and results from the first experimental tests are presented. The generator has been designed using the finite element method (FEM) and dynamic simulations have been performed to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface mounted, arched PMs. A complete experimental setup has been constructed consisting of a motor, a frequency converter, a gearbox and electrical loads. Oscilloscopes are used to measure the voltage and the current for each phase. Measurements have been performed for both full load and no load at rated speed. The harmonic content of the voltage is analyzed and compared to results from simulations. Furthermore, the generated electric power has been calculated from knowing the voltage and current and is compared to the simulated power. The agreement between experimental results and results from simulations based on finite element calculations is very high, especially considering harmonics. Several sources of error are suggested that could cause the small differences between the simulated results and the measured data for the constructed generator.     

Single-phase operation of a three-phase induction generator using a novel line current injection method

By using two capacitances and a current injection transformer, a three-phase induction generator can operate with good phase balance and line power factor while delivering power to a single-phase power grid. This paper presents a systematic analysis on this novel induction generator configuration. The solution of the system's inspection equations using the method of symmetrical components enables the steady-state generator performance at any speed to be computed. The conditions for achieving perfect phase balance are deduced from the phasor diagram. It is shown that the capacitances that result in perfect phase balance depend on the generator admittance, power factor angle, as well as the turns-ratio of the current injection transformer. Where possible, the computed results are verified by experiments conducted on a 2-kW induction machine. An experimental investigation on the system waveforms and harmonics is also carried out.     

基于虚拟磁链DPC的电压型整流器控制系统研究

对电压型PWM整流器(VSR)的直接功率控制(DPC)系统进行研究,针对采用虚拟磁链实现无电压传感器电压观测存在的模型预测误差问题,提出一种基于牛顿插值原理对模型观测电压进行修正的虚拟磁链模型预测直接功率控制策略,通过牛顿插值法修正电网电压估算值,同时引入内模反馈校正环节对模型预测相邻时刻瞬时功率所产生的误差进行修正,...     

A review of energy storage technologies for wind power applications

Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.     

2001 International Symposium on Lightning Protection

In this letter an investigation of the harmonics of the slip energy recovery drive is presented. The analysis takes into consideration not only the rotor-side rectifier, as is customary, but also accounts for the harmonics introduced by the recovery inverter. Simple relations are provided that predict all harmonic frequencies of the drive currents and torque as a function of its supply frequency and operating slip.     

Modelling of a 5-kW wind energy conversion system with induction generator and comparison with experimental results

A 5-kW wind energy conversion system (WECS) having induction generator is designed and implemented. The induction machine is connected to the power system through PWM inverter and PWM rectifier. Two digital PI controllers are used, one of them is for regulating dc link voltage and the other is for speed control of induction machine. The whole system is governed by a single fixed point digital signal processing unit (DSP). A detailed simulation program is prepared by using Matlab facilities in order to predict the performance of the controllers before implementation.     

Power limits of grid-connected modern wind energy systems

Wind energy is a prominent area of application of variable speed generators operating on the constant grid frequency. A modern wind energy system of this type consists of a surface mounted permanent-magnet generator with a frequency converter, which allows variable speed operation. The maximum power capability of the wind energy system is limited by the grid inverter. The theoretical formulation for active and reactive power limits is given. This formulation is used to set power reference limits to the inverter. Two different regions are distinguished depending on the tolerable Ac current harmonic distortion. Experimental results in a variable frequency wind energy generation system are shown.     

Power Quality Improvement in Conventional Electronic Load Controller for an Isolated Power Generation

This paper deals with the power quality improvement in a conventional electronic load controller (ELC) used for isolated pico-hydropower generation based on an asynchronous generator (AG). The conventional ELC is based on a six-pulse uncontrolled diode bridge rectifier with a chopper and an auxiliary load. It causes harmonic currents injection resulting distortion in the current and terminal voltage of the generator. The proposed ELC employs a 24-pulse rectifier with 14 diodes and a chopper. A polygon wound autotransformer with reduced kilovolts ampere rating for 24-pulse ac–dc converter is designed and developed for harmonic current reduction to meet the power quality requirements as prescribed by IEEE standard-519. The comparative study of two topologies, conventional ELC (six-pulse bridge-rectifier-based ELC) and proposed ELC (24-pulse bridge-rectifier-based ELC) is carried out in MATLAB using SIMULINK and Power System Blockset toolboxes. Experimental validation is carried out for both ELCs for regulating the voltage and frequency of an isolated AG driven by uncontrolled pico-hydroturbine.      

浓缩风能型风力发电机自动迎风控制系统

浓缩风能型风力发电机具有起动风速低,单机输出功率大,风能利用率高,度电成本低,安全性好等优点,文章针对其特有的形体流场设计了一套可以编程控制器IP612为主控单元的自动迎风控制系统,并能过大量实验此系统能够实现运转平稳,自动切入,准确对风等功能,并且高效节能。