GPRS在水利调度系统中的应用

为实现工程作业环境恶劣条件下的用水要求,本文设计了基于GPRS通信的变频恒压供水系统,采用GPRS通信模块作为通信的主要设备,对工程作业环境恶劣的地方进行实时监控,解决了传统的布线、架线的难题。实现了管网压力的准确采集,自动调节某台水泵的转速和多台水泵的投入及退出,使管网主管道出口端的压力基本保持在一定的范围内。供水控制系统投入运行后,各项指标达到了设计要求,解决了恶劣环境下居民生活用水难的问题。     

Robust MPC-based current controller against grid impedance variations for single-phase grid-connected inverters

Recently, LCL filters have been widely used in the output of single phase inverters. Since, the grid side inductor in these filters is in series with the grid impedance at the Point of Common Coupling (PCC), it may create new resonances. This phenomena may take the control loop toward instability. In this case, in order to have a reliable operation, the current controller should be insensitive to the grid impedance variation. In order to damp these resonances, researchers have presented some methods using active or passive damping. These methods added an extra loop to the control loop, an extra passive component in the filter or extra sensor in the control process. But in most of them, the complexity and the cost of controller have been increased. Therefore, presenting a simple control method without extra sensor, passive component or extra arrangement can be a promising approach. This paper presents an MPC-based current controller, which is simple and robust against the grid impedance variation and even the variation of the LCL filter parameters. In contrast to classical multi-loop controller like Proportional-Resonant (PR) controllers, the proposed control method does not need any parameter tuning. In the proposed controller, the switching plan and duty cycles are determined by a cost function and a switching table. Therefore, at the same time with any variation in grid impedance, the proposed controller changes the next switching state and duty cycle. Operating performance like look-up table, searching in all possible switching states to find the best state for the next switching period, makes the controller adaptive and robust against the variation of LCL filter parameters. In order to confirm the effectiveness of the proposed controller, simulations and experimental results of the proposed controller are compared with a classical PR controller.     

An Analysis Approach for the Assessment of Pulse-width Modulated Carrier Frequency Spectral Components in Power Distribution Systems with Photovoltaic Resources

Power distribution systems may have photovoltaic resources, and these resources may interface with the AC system via pulse-width modulated inverters. The pulse-width modulated currents have high-frequency spectra due to the switching frequency, which is typically 2.0–20 kHz. These carrier frequency components are asynchronous to the “power frequency” (the “baseband,” which is 50 or 60 Hz). Residential photovoltaic resources are in the 2–5 kW range, and “utility-scale” photovoltaic resources may be in the range of 500 kW. The pulse-width modulated carrier frequency components of voltage and current propagate in the power distribution system, and the details of this propagation are described. Note that the pulse-width modulated voltages are not harmonics of the 60-Hz baseband frequency, nor are the several pulse-width modulated voltages generally synchronous with each other. The objective is to describe an analytical approach for the assessment of carrier frequency spectra in distribution systems with photovoltaic resources. Analysis tools and experience with those tools are given. Information is given to distribution engineers faced with systems with pulse-width modulated inverter resources and advice on frequency ranges of study, potential modeling inaccuracies, and software tools. The results of a study on an actual high penetration solar photovoltaic feeder are given.     

一种适用于低压微电网的改进型下垂控制器

针对低压微电网中采用传统下垂控制器多微源之间功率分配精度不高和非线性负载影响的问题,通过虚拟阻抗的设计,将等效线路阻抗设计为在工频附近呈现阻性,满足低压微电网的线路阻抗特点,同时降低了微源逆变器功率均分控制对输出线路阻抗的敏感性;等效线路阻抗在高频谐波段呈感性,有效抑制非线性负载造成的高频谐波。同时改进了功率控制环,避免了较大的阻性等效输出阻抗造成电压降低的问题,加入的并网自动跟踪相角控制器在计划并网前自动调整微源输出电压相角,保证并网过程平滑过渡。仿真结果验证了提出的改进下垂控制器可以消除微源之间的环流,同时抑制高频谐波,输出电压与设定值无静差且并网过程平滑无冲击;基于DSP的样机实验结果也验证了该方法的正确性和可靠性。     

具有功率精确分配能力的逆变器电压谐波 分频下垂控制方法研究

微网中有可能存在电压谐波问题。设计具有能量转换和电压谐波治理的复合型逆变器有助于降低微网的成本。同时当多逆变器并联时,希望各逆变器能在基波和谐波域依照各自容量分配功率。现有方法是采用下垂控制和虚拟阻抗技术。首先建立包含谐波域的逆变器并网模型,阐述了谐波抑制的基本原理。然后讨论了设计逆变器的输出阻抗为阻性的方法。随后应用下垂控制策略,提出了逆变器基波和谐波的分频下垂控制器设计方法。最后通过PSCAD验证了该方法不仅能有效地抑制电压谐波,而且也能依照容量合理分配基波域和谐波域的功率。     

基于电流跟踪的并联逆变器控制系统的性能分析

多逆变器并联运行是提高电机传动系统逆变器容量的一种有效方法。以多逆变器并联带三相电机负载的传动系统为研究对象,针对跟踪参考电流的主从式矢量控制系统,研究了并联逆变器的多控制器参数设计方法,建立了控制系统的传递函数,分析了跟踪参考电流的控制方式对电机传动系统性能的影响。研究结果表明该控制系统结构简单,多电流调节器可进行简化设计;但与相同容量单个逆变器供电的电机传动系统相比,采用该控制系统会影响电机电流的动态响应性能和抗干扰能力。     

并网逆变器LCL接口直接输出电流控制建模及稳定性分析

并网逆变器LCL接口直接输出电流控制存在不稳定的现象。为了揭示其本质,建立了系统线性控制模型,推导出系统特征方程,根据Routh-Hurwitz稳定判据得出重要结论:并网逆变器LCL接口直接输出电流无论采用P、PI还是PID控制,系统均不稳定。该问题简单直接的解决方案是在LCL上串联电阻,以增大相角裕度,提高系统稳定性。本文在系统线性模型的基础上,针对电阻三种可能的串联位置,深入分析了电阻大小、调节器参数以及稳定裕度之间的内在联系并得出精确量化的结论,最后探讨了系统非线性因素如开关动作和过调制饱和等对结论有效性的影响。     

Photo-patternable high-k ZrOx dielectrics prepared using zirconium acrylate for low-voltage-operating organic complementary inverters

Solution-processed dielectric materials with a high dielectric constant (k) have attracted considerable attention due to their potential applications in low-voltage-operating organic field-effect transistors (OFETs) for realizing large-area and low-power electronic devices. In terms of device commercialization, the patterning of each film component via a facile route is an important issue. In this study, we introduce a photo-patternable precursor, zirconium acrylate (ZrA), to fabricate photo-patterned high-k zirconium oxide (ZrO_x) dielectric layers with UV light. Solution-processed ZrA films were effectively micro-patterned with UV exposure and developing, and transitioned to ZrO_x through a sol-gel reaction during deep-UV annealing. The UV-assisted and ∼10 nm-thick ZrO_x dielectric films exhibited a high capacitance (917.13 nF/cm² at 1 KHz) and low leakage current density (10⁻⁷ A/cm² at 1.94 MV/cm). Those films could be utilized as gate dielectric layers of OFETs after surface modification with ultrathin cyclic olefin copolymer layers. Finally, we successfully fabricated organic complementary inverters exhibiting hysteresis-free operation and high voltage gains of over 42 at low voltages of ≤3 V.     

A New Approach to H-Infinity Control for Grid-Connected Inverters in Photovoltaic Generation Systems

Abstract

The present study investigates the stability problem of the grid-connected inverters (GCIs) for possible variations in grid impedance. A new type of H∞ control method is proposed for the current control loop of inverters, where the third weighting function is determined using the game theory. The proposed method is applied to the GCI in a photovoltaic system and its response to variations in grid impedance is investigated. Computer simulations conducted for comparison of H∞ and PI controller indicate the effectiveness of the proposed control algorithm. Simulation results also show that the proposed algorithm significantly outperforms the PI controller under the conditions of varying grid impedance.