Wind-driven stand-alone DFIG with battery and pumped hydro storage system

A wind-driven doubly fed induction generator (DFIG) along with the battery and pumped hydro storage plant (PHSP) has been devised for supplying isolated loads. PHSP-based storage system is economical and viable for the MW level wind-turbine system. The proposed scheme employs a squirrel-cage induction machine (SCIM) coupled with reversible pump turbine for PHSP. The battery storage is also included in this system to cope up with the intermittent nature of wind and fast-changing load. A simple control strategy has been implemented for maintaining the set values of voltage magnitude and frequency at the stator terminals of DFIG, which serve as a virtual grid for connecting ac loads and SCIM. Based on the availability of power in the wind, PHSP and battery, various operating modes of the proposed system have been clearly identified for supplying the isolated loads. These operating modes are clearly demonstrated through the analysis developed for this purpose and validated through experimental results. The salient features of the proposed system over the existing stand-alone wind-driven generators are (i) structural simplicity, i.e., employing only one power electronic converter, (ii) wide speed operation of wind-driven DFIG, (iii) reduced battery capacity, (iv) high energy storage using PHSP and (v) availability of continuous power to the isolated loads.     

基于PSCAD的双馈感应式风力发电系统低压穿越能力仿真研究

在电网故障条件下,风电并网导则要求风电发电机具备低压穿越能力。为了保护发电机及其变流器,DFIG需要采用Crowbar保护电路为转子过电流提供旁路通道,同时抑制直流母线过电压。本文在PSCAD平台下搭建了2MW双馈感应式风力发电系统,并对有无Crowbar电路的DFIG在三相短路条件下进行了仿真。结果表明：具备Crowbar电路的DFIG有较好的暂态特性,并且具各较强的低电压穿越能力。     

Designing optimal controllers for doubly fed induction generators using a genetic algorithm

This work presents a design procedure based on evolutionary computation, more specifically on a genetic algorithm combined with the formal pole placement project, to obtain optimal controllers to the rotor-side converter of doubly fed induction generators (DFIGs), in variable-speed wind generation systems connected to the electrical grid. With this procedure it is intended to improve the global system dynamic behaviour during and after the fault period, also increasing the transient stability margin of the power system and the fault ride-through capability. The control action of the DFIG converters is accomplished by proportional and integral controllers, whose gainspsila adjustment is not a trivial task, because of the high complexity of the system. The results obtained confirm the efficiency of the proposed control design procedure.     

电压型虚拟同步发电机控制策略下的双馈风电机组阻抗及次同步振荡特性

针对双馈风电机组（doubly-fed induction generators,DFIG）经串补送出系统存在次同步振荡（sub-synchronous oscillation,SSO）的问题,以电压型虚拟同步发电机（virtual synchronous generator,VSG）控制策略下的DFIG为研究对象,首先基于三相静止坐标系建立了其阻抗模型,推导了机组正、负序阻抗解析式;其次搭建了PSCAD/EMTDC模型,对理论推导阻抗特性和频率扫描结果进行了对比验证;最后基于奈奎斯特稳定判据定量分析了VSG控制策略下的DFIG经串补送出系统SSO特性,通过仿真验证了所建立模型和稳定性分析结论的正确性。研究结果为SSO的抑制提供了参考。     

含不同机组风电场低电压穿越能力仿真研究

在PSCAD/EMTDC仿真环境下建立双馈风力发电场及恒速恒频风力发电场交流并网仿真模型,通过交流系统三相短路故障仿真,研究对比2种不同风力发电机组的低电压穿越能力。仿真得出恒速恒频风力发电机组避免飞车的极限切除时间,故障持续时间小于极限切除时间便可维持恒速恒频风力发电机组的稳定不脱网运行。通过在不同点设置短路故障对比得出,故障点距离风电场电气距离越远,风电场低电压穿越能力越强。     

基于复转矩系数法研究并网双馈风电场引发电力系统次同步振荡问题综述

风能作为一种可持续的清洁能源,近年来在我国得到迅猛的发展。双馈感应型风力发电机（doubly-fed induction generator,DFIG）具有灵活的控制特性,得到了广泛的应用,但由于其结构的特殊性,并网双馈风电场容易引发次同步振荡问题。该文首先介绍了并网双馈风电场引发电力系统次同步振荡（sub-synchronous oscillation,SSO）的机制。其次,对基于复转矩系数法的3类SSO问题的研究情况进行了系统性综述,并讨论了复转矩系数法的推广形式及其适用领域。最后,基于风力发电的前景和复转矩系数法的特性,对今后的研究方向进行了展望。     

新型双馈变速凸极同步电机

提出一种新型双馈变速凸极同步电机,阐述了它的基本原理和结构,电机的转子采用分裂磁极和正交绕组, 结构简单、可靠。转子绕组由低频交流变频电源供电,使电机具有变速恒频的特性。通过原型样机的试验,验证了该项发明的正确性和实用性,它将在大型水电、风电中得到广泛应用。     

Integrated power management circuit for piezoelectronic generator in wireless monitoring system of orthopaedic implants

Piezoelectric (PZT) materials are capable of converting the mechanical energy of compression into electrical energy. With the recent advent of extremely low-power electrical devices, PZT generators have become attractive in many kinds of applications, especially for biomedical applications. Piezoelectronic generators are used in a wireless monitoring system of orthopaedic implants. Due to their poor source characteristics, the efficiency of PZT generator is low. A hybrid direct current (DC)?DC, comprising a switched capacitor (SC) DC?DC converter and a low dropout (LDO) linear voltage regulator, is presented to improve conversion efficiency. A bandgap reference (BGR) circuit which works in sub-threshold region is also presented. Because SC DC?DC converter works in the highest voltage region in this system, small power supply current, including supply current through BGR and other auxiliary modules, means low power consumption. BGR?s power supply voltage can be varied from 3 to 16 V. Its supply current is only 3.2 μA at 125 C and its temperature coefficient is 46 ppm. Stacked switches technique is proposed to reduce leakage current in switching process of SC converter. Simulation results show that the efficiency of SC?s converter can reach 88%, that of LDO can reach 80% and that of the overall system can reach 66%, including power consumption of all auxiliary components, which is far higher than previous work.     

Negative sequence compensation within fundamental positive sequence reference frame for a stiff micro-grid generation in a wind power system using slip ring induction machine

An isolated wind power generation scheme using slip ring induction machine (SRIM) is proposed. The proposed scheme maintains constant load voltage and frequency irrespective of the wind speed or load variation. The power circuit consists of two back-to-back connected inverters with a common dc link, where one inverter is directly connected to the rotor side of SRIM and the other inverter is connected to the stator side of the SRIM through LC filter. Developing a negative sequence compensation method to ensure that, even under the presence of unbalanced load, the generator experiences almost balanced three-phase current and most of the unbalanced current is directed through the stator side converter is the focus here. The SRIM controller varies the speed of the generator with variation in the wind speed to extract maximum power. The difference of the generated power and the load power is either stored in or extracted from a battery bank, which is interfaced to the common dc link through a multiphase bidirectional fly-back dc-dc converter. The SRIM control scheme, maximum power point extraction algorithm and the fly-back converter topology are incorporated from available literature. The proposed scheme is both simulated and experimentally verified.     

可将机械能转变成电能的介电弹性体研究进展

弹性体材料具有轻质,易加工,价格低廉的优点,广泛用于生产生活各个领域.本文简要介绍了介电弹性体材料发电的基本原理,相比传统利用电磁感应原理的发电机的优势.重点介绍了几种目前研究比较广泛的介电弹性体材料:丙烯酸酯类、硅橡胶、聚氨酯和天然橡胶等,并分析了介电弹性体材料的介电常数、击穿电压和断裂伸长率等因素对发电量和发电效率的影响,及它们作为介电弹性体发电材料的优势和不足.此外,提出了作为介电弹性体发电机所需材料在未来应该重点开展的工作方向.     

Voltage and frequency control of parallel operated synchronous generator and induction generator with STATCOM in micro hydro scheme

Parallel operation of synchronous and induction generators in micro hydro scheme is presented. The synchronous generator has an exciter, which provides a fixed excitation to produce normal rated terminal voltage at full resistive load. On the other hand, the induction generator has neither exciter nor speed controller. Static compensator (STATCOM) is connected to the common bus for terminal voltage and frequency control. A resistive dump load is connected across the DC link capacitor of STATCOM through a chopper to control active power. Simulink model is developed to perform transient analysis of the proposed scheme. Experimental results are presented to compare with the simulation results. It is found that connection of an induction generator in parallel with the synchronous is much simpler than connecting two synchronous generators in parallel.     

Advanced control for PWM converter and variable-speed induction generator

The paper describes a simple control structure for a vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Deadbeat current control is developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with newly designed phase-locked-loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to build up the voltage of the IG without the need for a battery and to reduce the rating of the PWM converter with the need for only three sensors. This proposed scheme can be used efficiently for variable speed wind or hydro energy conversion systems. The measurements of the IG system at various speeds and loads are given and show that this proposed system is capable of good AC and DC voltages regulation     

Mathematical Morphology-Based Artificial Technique for Renewable Power Application

This paper suggests a combined novel control strategy for DFIG based wind power systems (WPS) under both nonlinear and unbalanced load conditions. The combined control approach is designed by coordinating the machine side converter (MSC) and the load side converter (LSC) control approaches. The proposed MSC control approach is designed by using a model predictive control (MPC) approach to generate appropriate real and reactive power. The MSC controller selects an appropriate rotor voltage vector by using a minimized optimization cost function for the converter operation. It shows its superiority by eliminating the requirement of transformation, switching table, and the PWM techniques. The proposed MSC reduces the cost, complexity, and computational burden of the WPS. On the other hand, the LSC control approach is designed by using a mathematical morphological technique (MMT) for appropriate DC component extraction. Due to the appropriate DC-component extraction, the WPS can compensate the harmonics during both steady and dynamic states. Further, the LSC controller also provides active power filter operation even under the shutdown of WPS condition. To verify the applicability of coordinated control operation, the WPS-based microgrid system is tested under various test conditions. The proposed WPS is designed by using a MATLAB/Simulink software.     

A nine-level hybrid symmetric cascaded multilevel converter for induction motor drive

A nine-level hybrid symmetric cascaded multilevel converter (MLC) fed induction motor drive is proposed in this paper. The proposed converter is capable of producing nine output voltage levels by using the same number of power cells as that of conventional five-level symmetric cascaded H-bridge converter. Each phase in this configuration consists of one five-level transistor-clamped H-Bridge (TCHB) power cell and one three-level H-bridge power cell with equal dc link voltages, and they are connected in cascade. Due to cascade connection and equal dc link voltage, the power shared by each power cell is nearly equal. Near-equal power sharing enables the feature of improving input current quality by using an appropriate phase-shifting multi-winding transformer at the converter input. In this paper, the operation of the converter is explained using staircase and hybrid multi-carrier sine PWM techniques. Further, a detailed analysis for the variations in the dc link capacitor voltages and the dc link mid-point voltage in TCHB power cell is carried out, and the analytical expressions thus obtained are presented. The performance of proposed system is analysed by simulating a 500 hp induction motor drive system in MATLAB/Simulink environment. A laboratory prototype is also developed to validate the claims experimentally.     

风力发电并网系统次同步振荡研究

大规模风力发电并网引发的次同步振荡（subsynchronous oscillation,SSO）问题已严重威胁到电网的安全稳定运行。由于电力电子设备的广泛采用,风电参与的新型次同步振荡的产生机制和作用形态均与传统次同步振荡不同,其中双馈风电场经串补并网和直驱风电场并入弱电网2种场景下出现的次同步振荡问题引起了国内外广泛的关注。首先总结了目前常用的分析方法及其适用性,然后基于典型的工程案例,梳理了近年来风电次同步振荡建模、分析、控制和保护方面取得的理论成果和工程进展,为今后风电次同步振荡的研究提供参考。     

基于模型预测的三电平PWM变流器直接功率控制

为了满足脉宽调制型变流器功率响应速度快以及绝缘栅双极型晶体管开关频率恒定等要求,提出了基于模型预测的直接功率控制策略用于三电平PWM变流器。该控制策略采用电压外环、功率内环的双闭环控制,外环省略了锁相环环节,简化了控制系统结构;内环无需PI调节器,参数设计简单,响应速度快。利用MATLAB/SIMULINK仿真平台搭建了三电平中性点箝位型PWM变流器模型,对比分析了提出的控制策略与传统PI控制的效果。仿真结果表明,新的控制策略有效降低了交流侧电流总谐波失真率,提高了交流侧功率因数,具有良好的动态和稳态性能。     

Linear analog rotation angle converter with an error of 0.001%

Conclusions The above linear analog converter can be used for nonperiodic transformation of an angle into a voltage over a wide angular range. The simple design, simple manufacturing requirements, and reliable operation inherent to analog devices are combined with a high conversion precision.The converter can be used in compensated circuits owing to the small phase difference between its output and supply voltages. The converter has a considerable output power combined with a high precision. The converter's insensitivity to noise is very high owing to its very low (of the order of 100 m) output resistance. The low noise level simplifies the design of null indicators. This converter can be usefully and effectively applied to programmed control systems, remote transmissions, and autocompensating systems.     

同步发电机励磁系统中PWM控制的仿真研究

优良的励磁控制系统不仅可以保证发电机运行的可靠性和稳定性，而且可有效地提高发电机和电力系统技术指标。同步发电机励磁系统采用了PWM整流技术，实现励磁电流低谐波和励磁功率单元高功率因数转换，提高了发电机供电质量，并用MATLAB对设计系统做出仿真验证，证明该设计对改善发电机输出电压、提高功率单元电能利用率有明显效果。     

Comparison of synchronous PM machine types for wide constant-power speed operation: converter performance

A thorough comparison of the converter performance characteristics for four permanent magnet (PM) synchronous machine configurations is presented. Two versions of an interior PM (IPM) machine with distributed windings are included. One version has a maximum back-EMF limit at the top speed while the second does not have any constraint on back-EMF amplitude. Two types of surface PM (SPM) machines are also considered, one with fractional-slot concentrated windings, and another with conventional distributed windings. The target application is an automotive direct-drive starter/alternator requiring a very wide 10:1 constant power speed ratio (CPSR). Detailed comparisons of the converter performance below and above the base speed are presented, evaluating significant issues, including the converter switching and conduction losses, output ripple current, and DC-link current ripple. Study results show that the higher excitation frequencies required by PM machines with high pole numbers have only a modest impact on converter efficiency for comparable output current waveform quality. In constrast, the imposition of maximum back-EMF amplitude constraints at top speed raise the machine rated current, resulting in elevated converter losses and larger DC-link capacitors     

EMC of power converters: the self-compatibility approach

Analysis of the internal electromagnetic compatibility of digitally controlled power converters is discussed. In particular, the optimum layout of the circuit configuration is designed on the basis of the actual electromagnetic interference between the power and the control section of a power converter. Besides, further improvements can be achieved by means of an auto- tuning additional board, which scans all the possible converter switching frequencies and analyses the distortion on the control signals corresponding to each frequency. Its main task is to select only the ones which produce low disturbances on the control signals as operating frequencies for the converter.