A novel modulation technique with interleaved‐and‐shifted shoot‐through state placement for quasi‐Z‐source inverters

In this paper, a single‐phase quasi‐Z‐source (qZS) inverter (qZSI), integrating the pulse width modulation (PWM) control with interleaved‐and‐shifted shoot‐through state (STS) placement modulation technique, is proposed to simultaneously achieve both dc voltage boost and dc‐ac inversion. Instead of placing the STS in both inverter legs simultaneously, the addressed method inserts the STS only in left/right inverter leg separately during the positive/negative half cycle of the output voltage to reduce switching losses and thermal stresses of the power devices. The STS shift is also studied to decrease the switching numbers of power devices and thus can improve the efficiency further. Theoretical analysis and design guidelines of the studied inverter are included. Improvement in effectiveness and performance of the devised scheme and modulation strategy are proved experimentally and compared with the previous studies on a built laboratory prototype.     

Data-mining model based adaptive protection scheme to enhance distance relay performance during power swing

The paper presents a data-mining model based adaptive protection scheme enhancing distance relay performance during power swing for both compensated and uncompensated power transmission networks. In the power transmission network, the distance relays are sensitive to certain system event such as power swings, which drive the apparent impedance trajectories into the protection zones of the distance relay (zone-3) causing mal-operation of the distance relay, leading to subsequent blackouts. Further, three-phase balanced symmetrical fault detection during power swing is one of the serious concerns for the distance relay operation. This paper proposed a new adaptive protection scheme method based on data-mining models such as DT (decision tree) and RF (random forests) for providing supervisory control to the operation of the conventional distance relays. The proposed scheme is able to distinguish power swings and faults during power swing including fault zone identification for series compensated power transmission network during stress condition like power swing. The proposed scheme has been validated on a 39-bus New England system which is developed on Dig-Silent power factory commercial software (PF4C) platform and the performance indicate that the proposed scheme can reliably enhance the distance relay operation during power swing.     

V2G直流充电桩检测方案与检测系统设计

针对现有V2G直流充电桩现场检测装置功能不全面、检测方案单一、控制及管理困难等问题,依据国家相关标准,设计了V2G直流充电桩检测方案和检测系统。首先,根据需要设计了3种检测方案：现场检测方案、实验室检测方案以及动力电池检测方案。不同的检测方案对应V2G充电桩不同检测环境和检测项目。然后,依据3种检测方案给出了检测系统的硬件设计和软件设计,能够实现对V2G直流充电桩充放电功能、直流输出性能、并网性能及保护功能等进行检测。同时还可以对电动汽车动力电池状态进行评估,从而判断电池潜在风险。最后,通过对V2G直流充电桩和车辆动力电池进行不同项目检测。测试结果表明所设计的检测方案和检测系统能够准确实现对V2G直流充电桩的功能和性能检测。     

电力系统次同步振荡检测与在线定位技术综述

随着电网规模扩大以及新能源发电并网容量增加,次同步振荡(SSO)问题日益凸显,对电网安全稳定运行造成了较大的威胁。及时检测出系统中的SSO并对其进行在线定位,对保障电力设备安全与系统稳定运行具有重要意义。首先对SSO的检测方法进行了介绍,并归纳总结了各类方法的优缺点。然后,介绍了SSO定位方法,并对现有研究存在的不足进行了探讨。最后,介绍了适用于SSO在线检测定位的量测系统架构以及相量测量单元/广域测量系统(PMU/WAMS)升级改造方案,并对SSO检测与定位技术未来的发展趋势进行了展望。     

Adaptive Power Control Protocol With Hardware Implementation for Wireless Sensor and RFID Reader Networks

The development and deployment of radio frequency identification (RFID) systems render a novel distributed sensor network which enhances visibility into manufacturing processes. In RFID systems, the detection range and read rates will suffer from interference among high-power reading devices. This problem grows severely and degrades system performance in dense RFID networks. Consequently, medium access protocols (MAC) protocols are needed for such networks to assess and provide access to the channel so that tags can be read accurately. In this paper, we investigate a suite of feasible power control schemes to ensure overall coverage area of the system while maintaining a desired read rate. The power control scheme and MAC protocol dynamically adjust the RFID reader power output in response to the interference level seen during tag reading and acceptable signal-to-noise ratio (SNR). We present novel distributed adaptive power control (DAPC) as a possible solution. A suitable back off scheme is also added with DAPC to improve coverage. A generic UHF wireless testbed is built using UMR/SLU GEN4-SSN for implementing the protocol. Both the methodology and hardware implementation of the schemes are presented, compared, and discussed. The results of hardware implementation illustrate that the protocol performs satisfactorily as expected.     

Power quality improvement with an extended custom power park

This paper describes the operation principles of an extended custom power park (CPP). The proposed park is more effective when it is compared to the conventional power parks regarding the yield of improving both current and voltage quality of linear and nonlinear loads using dynamic voltage restorer (DVR), active power filter (APF), static transfer switch (STS) and diesel generator (DG). Moreover, a supervisory power quality control centre is presented to coordinate these custom power (CP) devices by providing pre-specified quality of power. A fast sag/swell detection unit is also presented to improve the system response. The ability of the extended CPP for power quality improvements is further analyzed using PSCAD/EMTDC through a set of simulation tests.     

A new adaptive PMU based protection scheme fortransposed/untransposed parallel transmission lines

This paper proposes a brand-new adaptive phasor measurement unit (PMU) based protection scheme for both transposed and untransposed parallel transmission lines. The development of the scheme is based on the distributed line model and the synchronized phasor measurements at both ends of lines. By means of eigenvalue/eigenvector theory to decouple the mutual coupling effects between parallel lines, the fault detection and location indices are derived. The two proposed indices are used in coordination such that the internal and external fault events can be distinguished completely. By on-line estimation of the line parameters under the actual power system conditions, the proposed scheme will respond more accurately to power system faults. Extensive simulation results using EMTP have verified that the accuracy of the fault location achieved is up to 99.9%. The proposed protection system responds well and fast with regard to dependability and security. All the results show that the performance of the proposed detection/location indices is independent of fault types, locations, resistance, source impedance, fault inception angles, and load flows     

Novel reactive power controllers for the STATCOM and SSSC

The paper investigates the dynamic operation of both static synchronous compensator (STATCOM) and static synchronous series compensator (SSSC) based on a new model comprising full 48-pulse GTO voltage source converter for combined reactive power compensation and voltage stabilization of the electric grid network. These key FACTS devices are power electronic GTO converters connected in parallel or series with the power system grid and are controlled by novel decoupled controllers. The complete digital simulation of the STATCOM and SSSC within the power system is performed in the MATLAB/Simulink environment using the power system blockset (PSB). The STATCOM scheme and the electric grid network are modeled by specific electric blocks from the power system blockset while the control system is modeled using Simulink. Two novel controllers for the STATCOM and SSSC are presented in this paper based on a decoupled current control strategy to ensure stable operation of the STATCOM under various load excursions. A novel control scheme for the static synchronous series compensator (SSSC) is also implemented to provide a full controllable series compensating (buck/boost) injected voltage over a specified capacitive and inductive range, independently of the magnitude of the transmission line current. The series reactive compensation scheme with an external dc power supply can also compensate for any voltage drops across resistive component of the transmission line impedance. The novel decoupled controller uses a phase locked loop (PLL) with a novel reduced inherent time delay to improve the transient performance of the SSSC. The performance of both STATCOM and SSSC schemes connected to the 230 kV grid are evaluated. The proposed novel control schemes for the STATCOM and SSSC are fully validated by digital simulation.     

Performance evaluation of thyristor based static transfer switch

Industrial customers are becoming more sensitive to variations of utility supply systems due to the growing demand for process controls in automated plants. One option to increase reliability and quality of AC power is to provide sensitive customers with access to two independent power sources. In this paper, a fast thyristor based static transfer switch (STS) is proposed which employs fast voltage-detection and thyristor gating strategies to connect the customer to either of the two sources. Performance of the designed STS system is evaluated using the Electromagnetic Transients for DC (EMTDC). Simulation results are verified by comparing them with experimental results     

Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.     

Near optimal MIMO detection with reduced search space

A multi-input multi-output (MIMO) detection scheme that requires considerable low complexity but still achieves the near optimal performance is proposed. The fundamental idea of the proposed MIMO detection scheme consists of two points: 1) the computational complexity is restrained by a complexity limit in low signal-to-noise ratio (SNR) region; 2) while in high SNR region, the complexity is significantly reduced by the proposed search space method. Comparing with existing fixed-complexity techniques of MIMO detection (e.g., K-best sphere detector and reduced-search maximum-likelihood (RS ML) detection), the significant benefit of proposed detection scheme is that less computational power will be spent for the given data rate, or the throughput of detector can be increased for high SNR cases. According to the simulation results, the near optimal performance can be obtained while the detection complexity is kept considerable small.     

一种基于DSP的高精度谐波检测改进方案设计

介绍了一种基于同步旋转坐标系的以DSP为核心的数模混合型谐波检测设计方案。针对常规方案的缺陷提出了改进信号流的新方案。它有效地整合了模拟和数字的优势，基于低速率采样的低通滤波器解决了DSP字长和精度的矛盾，并针对数字系统的时间延迟提出了补偿策略。实验结果表明，该方案硬件简单、成本低，可实现高精度、无延迟的谐波检测。     

Efficient detection for cooperative communication with two alternating relays

A two-path amplify-and-forward (AF) relaying scheme, which uses two relays to retransmit for the source alternately, was proposed by Rankov [Rankov et al. IEEE Journal on Selected Areas in Communications, 2007, 25 (2): 379–389]. This scheme can avoid half-duplex loss in spectral efficiency, but it cannot work well when the interrelay channel gain is strong. An efficient detection scheme for two-path AF relaying system is proposed in this paper. In the proposed scheme, interference cancellation is first performed at the destination so that the received signal after interference cancellation is the superposition of two symbols with noise. Then, a low complexity soft maximum a posteriori (MAP) decoder and an iterative soft decoder are employed to extract the diversity of the two relay-destination links. The proposed detection scheme can efficiently improve the system performance compared to the detection scheme presented by Rankov (2007), especially when the inter-relay channel gain is strong.     

主动探测式保护关键技术概述及展望

以新能源为主体的新型电力系统中广泛应用的电力电子设备引入了新的故障特征,对继电保护性能提出了更高的要求,传统继电保护技术难以适用。主动探测式保护利用可控的电力电子设备生成特定的探测信号,引入了更为清晰明确的故障特征,可以构造更为简便、灵敏、可靠的保护新原理。基于扰动的故障分析方法为主动探测式保护提供了理论基础,电力电子技术的发展为主动探测式保护提供了应用基础。针对主动探测式保护的具体实现方案,详细分析了探测信号的选择、生成、注入时机和处理等关键技术,归纳整理了主动探测式保护在直流系统和新能源发电等典型场景下的应用。对未来的研究方向和工程实践中可能遇到的问题进行了总结评述,期望能为主动探测式保护的深入研究提供参考。     

基于TMS320F2801的PMSM矢量控制的数字实现

提出一种以低成本的TMS320F2801为主控芯片,180 ppr的低分辨率混合式编码器为位置定位及速度采集单元,IGBT逆变器为功率驱动电路的永磁同步电机(PMSM)调速系统设计方法.详细介绍了系统的硬件设计方案,包括DSP控制电路、功率驱动电路及信号检测电路.应用矢量控制算法及SVPWM技术,并采用硬件与软件相结合...     

一种基于HHT的光伏并网发电系统保护方法

当光伏发电系统所连电网发生短路故障时,光伏电源的故障电流会发生暂态突变,但由于逆变器控制电路的保护作用,短路电流的幅值较小,因而传统的保护方法对光伏并网发电系统不一定适用。为寻求适合光伏并网发电系统的保护方法,建立了基于PSCAD/EMTDC的光伏并网发电系统仿真模型,对其短路电流的特性进行了仿真分析,利用希尔伯特-黄变换(HHT)对故障电流的波形进行分解,提出一种基于HHT的光伏并网发电系统保护方法,并进行了算例分析。结果表明,在含有光伏发电的电网发生短路故障时,该保护方法具有一定的有效性和可行性。     

三相四线制系统中基于等功率法的谐波检测

有源电力滤波器(APF)补偿性能的好坏很大程度上取决于系统的谐波检测算法。介绍了三相四线制系统中的3种谐波检测法,即以瞬时无功功率理论为基础的d-q法、有功分离法和基于功率平衡的等功率法,重点阐述了等功率法。在系统电压畸变和无畸变、负荷对称和不对称4种组合情况下利用PSCAD/EMTDC软件对系统的谐波检测进行仿真,在此基础上对3种检测法在补偿效果、实时性等方面作详细比较,分析各自特性。比较可知,等功率法不需要大量的计算,程序设计简单,且在补偿效果、实时性、直流侧电压利用率方面均取得其他2种方法难以比拟的效果,且易于硬件实现。实验结果表明,等功率法实用价值高。     

Wavelet technique based islanding detection and improved repetitive current control for reliable operation of grid-connected PV systems

Recent years have witnessed a thrust towards the use of solar energy as the major renewable energy source for distributed power generation. The proposed system requires reliable detection technique and suitable current control strategy for proper operation. This paper focuses on plug-in repetitive current (RC) control strategy for grid connected inverter system and wavelet technique for electrical grid status identification. The performance of proposed current control technique employed for grid connected inverter system under distorted and unbalanced grid voltage is compared with the existing conventional methods like PI and PR controller. This controller uses the feedback control system for attenuating periodic disturbances, improving high quality sinusoidal output current and high power factor. The proposed scheme employs fourth order infinite impulse response (IIR) filter for maintaining its resonance frequency, output frequency matching with grid fundamental frequency and reduction of harmonics. The DC-DC boost converter implements incremental conductance based (INC) maximum power point tracker (MPPT) algorithm. The effects of LCL filter for improving disturbance rejection capability and dynamic performance of the proposed system is also demonstrated. Grid connected PV inverter employs wavelet technique for an islanding detection functionality in order to determine the status of the electrical grid. In order to show the effectiveness of the proposed algorithm, modeling and simulation for grid connected PV system is performed using MATLAB/SIMULINK and its PowerSim toolbox.     

Hybrid-triggered fault detection filter design for networked Takagi–Sugeno fuzzy systems subject to persistent heavy noise disturbance

In the network environment, the single time-triggered scheme wastes limited bandwidth resources due to all the sampled data are transmitted to the networks, and the single event-triggered scheme may increase system error because of ignoring factors such as changes in network utilization. To reduce the design conservatism, this paper is concerned with the hybrid-triggered L₁ fault detection filter design for a class of nonlinear networked control systems (NCSs) described by Takagi–Sugeno (T-S) fuzzy model. Taking the effects of time-triggered scheme and event-triggered scheme into consideration simultaneously, we construct a fuzzy fault detection system. New results on stability and L₁ performance are proposed for fuzzy fault detection system by exploiting the Lyapunov–Krasovskii functional and by means of the integral inequality method. Specially, attention is focused on the design of fault detection filter that guarantees a prescribed L₁ noise attenuation level . Finally, two examples are presented to demonstrate the effectiveness of the proposed method.