Variable-speed wind power generation using doubly fed wound rotor induction machine-a comparison with alternative schemes

In this paper, a wind energy conversion system (WECS) using a grid-connected wound rotor induction machine controlled from the rotor side is compared with both fixed speed and variable speed systems using a cage rotor induction machine. The comparison is done on, the basis of: (1) major hardware components required; (2) operating region; and (3) energy output due to a defined wind function using the characteristics of a practical wind turbine. Although a fixed speed system is more simple and reliable, it severely limits the energy output of a wind turbine. In case of variable speed systems, comparison shows that using a wound rotor induction machine of similar rating can significantly enhance energy capture. This comes about due to the ability to operate with rated torque even at supersynchronous speeds; power is then generated out of the rotor as well as the stator. Moreover, with rotor side control, the voltage rating of the power devices and DC bus capacitor bank is reduced. The size of the line side inductor also decreased. Results are presented to show the substantial advantages of the doubly fed system.     

含有虚拟阻抗的微源逆变器微网小信号稳定性分析

微网渗透率升高使微网系统惯性减小,受到扰动之后微网易发生振荡失稳。文章引入虚拟阻抗,提出一种适用于低压微网的改进型下垂控制,减小线路阻抗的影响。在此基础上建立微网系统的小信号模型,通过计算系数矩阵特征根的形式判断系统的稳定性,并在Matlab/Simulink软件中搭建相应的模型,通过时域仿真图判断系统的稳定性。     

Fuel-cell energy generation system based on the series-capacitor boost converter

This work introduces the development of a power-electronics customizable energy system for their application on renewable energy generation based on proton-exchange membrane fuel cells. The customizable energy system aims to regulate the output voltage from a fuel cell, which has a relatively low amplitude and wide range of variation, to a fixed voltage to feed a grid-tie inverter. The customizable energy system proposed is based on a dc-dc converter for which different configurations (topologies) are available, such as the traditional single-phase boost or the (interleaved) multi-phase boost. The dc-dc converter of the energy system is based on the series-capacitor boost converter, a recently proposed converter that has a similar configuration to the interleaved boost converter. This article shows that the series-capacitor boost topology offers benefits in the proposed application. An experimental prototype was developed and tested in order to demonstrate the advantages of the system proposed.     

适于直驱型风力发电系统的大功率变流器

直驱型变速恒频风力发电系统采用低速永磁同步发电机结构,无需齿轮箱,机械损耗小,运行效率高,维护成本低.该系统须采用的大功率变流器单元可以有不同的拓扑结构,根据每种电路拓扑的特点,整个系统的控制方法都会相应地发生变化.文章对直驱型变速恒频风力发电系统基本拓扑结构进行了对比分析,着重分析了常见的中高压变频器主电路拓扑,并对大功率变流器在风力发电系统应用中的可行性进行了相关分析与探讨.     

应用于新能源发电的有源钳位隔离型Boost变换器

传统的隔离型Boost变换器需要使用两个及以上的磁性元件,造成磁性元件数量偏多。文章提出了一种新型有源钳位隔离型Boost变换器,该变换器将变压器、输入电感和谐振电感集成在一个磁性元件中,变换器的开关管数量及增益特性与传统的隔离型全桥Boost变换器相同。通过设置原边有源钳位电路,变换器中所有开关管的电压应力不超过变换器的最高输入电压;设置副边谐振倍压网络,变换器实现了整流二极管的零电流关断。最后在一台500 W的样机进行试验,试验结果验证了该变换器的可行性。     

风力发电系统中的变流器模型简化方法

针对风电场仿真运行慢、占用内存大的缺点,分别对双馈异步风力发电机(DFIG)的机侧和网侧变流器进行分析。基于稳态条件下SPWM模型简化的思想,利用开关函数将DFIG中的机侧和网侧变流器模型简化为两个由直流电容相连理论模块,并将模块的输出结果输入到DFIG转子和电网电路中形成闭环。最后在PSCAD仿真平台下进行仿真,验证文中提出的简化模型的有效性。     

鹰式波浪能发电装置发电系统研究

文章首先对鹰式波浪能发电装置能量转换系统进行分类,分析了各系统的组成及工作原理,设计了一种液压式和直驱式组合的发电系统,通过模型试验优化了系统中的参数配置,提高了能量转换效率,最后通过实海况试验验证了"鹰式一号"波浪能发电装置的发电系统设计方案的可行性。     

燃料电池发电系统中新型直流变换器的研究

针对燃料电池输出端电压低且变化范围宽,需较高的直流电压增益才能实现并网发电的特点,文章研究了一种基于交错控制和平均电流控制的新型高增益直流变换器,该变换器不仅具有较高的电压增益、合适的占空比、脉动较小的输入输出电流纹波,开关管承受的电压电流应力远远低于传统的二次型Boost变换器,而且控制电路简单等特点。文章详细分析了该变换器的工作原理、稳态性能,并对其进行了小信号的建模分析,通过仿真验证了所研究的拓扑电路和控制方法的可行性。     

High-efficiency grid-connected photovoltaic module integrated converter system with high-speed communication interfaces for small-scale distribution power generation

This paper presents a high-efficiency grid-connected photovoltaic (PV) module integrated converter (MIC) system with reduced PV current variation. The proposed PV MIC system consists of a high-efficiency step-up DC-DC converter and a single-phase full-bridge DC-AC inverter. An active-clamping flyback converter with a voltage-doubler rectifier is proposed for the step-up DC-DC converter. The proposed step-up DC-DC converter reduces the switching losses by eliminating the reverse-recovery current of the output rectifying diodes. To reduce the PV current variation introduced by the grid-connected inverter, a PV current variation reduction method is also suggested. The suggested PV current variation reduction method reduces the PV current variation without any additional components. Moreover, for centralized power control of distributed PV MIC systems, a PV power control scheme with both a central control level and a local control level is presented. The central PV power control level controls the whole power production by sending out reference power signals to each individual PV MIC system. The proposed step-up DC-DC converter achieves a high-efficiency of 97.5% at 260 W output power to generate the DC-link voltage of 350 V from the PV voltage of 36.1 V. The PV MIC system including the DC-DC converter and the DC-AC inverter achieves a high-efficiency of 95% with the PV current ripple less than 3% variation of the rated PV current.     

A high efficiency photovoltaic module integrated converter with the asymmetrical half-bridge flyback converter

A module integrated converter (MIC) for a photovoltaic (PV) cell is important part of power conditioning system (PCS). It performs maximum power point tracking of a PV cell to generate the power as much as possible from solar energy. There are several methods for connection between the PV modules and the MICs. In order to avoid partial shading effects, converter-per-module approach was proposed. The MIC that performs maximum power point tracking (MPPT), if it is low efficiency, is no use. The MIC whose output is connected to the output of PV module was proposed for high efficiency. However, there are some problems. In this study, an asymmetrical half-bridge flyback converter is proposed instead of the original flyback converter with same method to solve the problems. The proposed MIC was built to verify the performance. The new topology using soft switching technique showed good performance for the efficiency. At the higher power, the efficiency of the proposed converter is higher than existing converter.     

高效屋顶光伏发电及其并网系统研究

文章针对屋顶光伏发电及并网设计了DC-DC-AC型双级式的电力变换器,即前级最大功率跟踪电路和后级单位功率因数并网逆变电路,介绍了双级电力变换器的结构与原理,研究了最大功率跟踪与单位功率因数并网问题,提出基于双环MPPT和专家PID控制的系统控制方法,通过仿真和搭建屋顶光伏发电系统实验平台,分别验证了文章方法的有效性和准确性。     

直接驱动型全功率变流风力发电系统

从等效电路的角度分析了两级联H桥输出五电平的工作模式.为了满足直驱型风电系统对变流器的大功率要求,采用载波相移正弦脉宽调制技术(CPS-SPWM)控制级联H桥变流器,并对比了常规CPS-SPWM调制方法和对称调制法在实现五电平输出上的差异,经仿真和试验验证:这种拓扑结构满足直驱型风力发电系统对变流器的要求,说明CPS-SPWM调制方法适用于直驱型风力系统中的大功率变流器,在提高装置功率容量的同时,可以有效地减小变流器输出谐波,调节输出波形,提高整个装置的信号传输带宽.     

5 kW DC/DC converter for hydrogen generation from photovoltaic sources

This paper covers the design of a DC–DC power converter aimed for hydrogen production from photovoltaic sources. Power conditioning for such application is usually driven by different constraints: high step-down conversion ratio is required if the input voltage of such equipment has to be compatible with photovoltaic sources that are connected to grid-connected inverters; galvanic isolation; high efficiency and low mass. Taking into account those factors, this work proposes a push–pull DC/DC converter for power levels up to 5 kW. The operation and features of the converter are presented and analyzed. Design guidelines are suggested and experimental validation is also given.     

Integrated power characteristic study of DFIG and its frequency converter in wind power generation

A doubly fed induction generator (DFIG) is a variable speed induction machine. It is a standard, wound rotor induction machine with its stator windings directly connected to the grid and its rotor windings connected to the grid through a back-to-back AC/DC/AC PWM converter. The power generation of a DFIG includes power delivered from two paths, one from the stator to the grid and the other from the rotor, through the frequency converter, to the grid. The power production characteristics, therefore, depend not only on the induction machine but also on the two PWM converters as well as how they are controlled. This paper investigates power generation characteristics of a DFIG system through computer simulation. The specific features of the study are (1) a steady-state model of a DFIG system in d–q reference frame, (2) a simulation mechanism that reflects decoupled d–q control strategies, (3) power characteristic simulation for both generator and converter, and (4) an integrative study combining stator, rotor and converter together. An extensive analysis is conducted to examine integrated power generation characteristics of DFIG and its frequency converter under different wind and d–q control conditions so as to benefit the development of advanced DFIG control technology.     

凝结水泵变速运行参数的定量计算

建立了热力机组的凝结水系统模型,结合凝结水泵变速运行平衡点计算式对其变速运行工况进行了分析;从除氧器水位调节阀特性出发,结合工频状态下的相关试验,对调节阀前后压力差进行了计算;推导了凝结水系统管路损失的计算方法,得到平衡点计算式的各项系数;在些基础上,结合水泵比例定律,实现了凝结水泵变速运行理论参数的定量计算,最终可据此对北凝结水泵变频改造效果进行预评估.通过某电厂600 MW机组凝结水系统的计算实例,验证了该方法的正确性与有效性.     

Modelling and simulation of a heaving wave energy converter based PEM hydrogen generation and storage system

The research on wave energy systems has been ongoing for decades. However, there are not many operational wave energy converters in use. The hydrogen energy systems also have a great potential. The proposed solution is to combine wave energy system with hydrogen energy system. The study provides details of simulation models and related simulation results. It is environmentally friendly, safe, feasible and effective. The results indicate that the proposed system model has a very high potential. With the use of low to medium energy density sea states, it is appears to be possible to generate (for DS1, DS2 and DS3, m_H2 = 350.8 kg, 623.9 kg and 2124 kg, respectively) a considerable amount of hydrogen in 20-min. The presented results include WEC motion properties, instantaneous and moving average value of other system parameters. The future promising simulations results indicate that next generation wave energy converter systems could be accompanied by hydrogen generation and storage systems.     

双馈风力发电机网侧变流器新型拓扑控制研究

文章对大功率双馈风力发电机网侧变流器并网时,电压不平衡问题提出一种有效网侧控制拓扑结构,该结构采用3个单相变流器代替原有的三相变流器,通过补偿电压达到限制故障电流同时稳定直流电压的目的。本方法减小了变流器容量,增强了可控性和适应性,同时还可在电压跌落或波动情况下保持同步到电网。最后在MATLAB/SIMULINK环境下,验证了文章所提控制方案的有效性。     

双级式光伏并网发电前级变换器系统建模与控制器参数设计

针对双级式光伏并网发电前级变换器系统功率电压双闭环MPPT结构的控制器参数设计问题,基于前级变换器系统的等效电路,采用状态空间平均法建立了系统的非线性模型,进而采用平衡点附近线性化方法得到其线性模型。根据对象特性引入控制器结构,在频率特性和根轨迹分析的基础上,给出了前级控制器参数的系统化设计方法。12 k W双级式光伏并网发电系统仿真结果表明,在标准光强和模拟自然条件光强变化时,该控制器能快速实现前级MPPT跟踪控制及单位功率因数并网控制,获得了良好的动静态性能。     

Maximum generation power evaluation of variable frequency offshore wind farms when connected to a single power converter

The paper deals with the evaluation of power generated by variable and constant frequency offshore wind farms connected to a single large power converter. A methodology to analyze different wind speed scenarios and system electrical frequencies is presented and applied to a case study, where it is shown that he variable frequency wind farm concept (VF) with a single power converter obtains 92% of the total available power, obtained with individual power converters in each wind turbine (PC). The PC scheme needs multiple power converters implying drawbacks in terms of cost, maintenance and reliability. The VF scheme is also compared to a constant frequency scheme CF, and it is shown that a significant power increase of more than 20% can be obtained with VF. The case study considers a wind farm composed of four wind turbines based on synchronous generators.