基于动态相量法的电力电子变换器的模型与仿真分析

电力电子装置在电力系统中得到广泛应用,忽略这类快速控制器件内部动态特性的准稳态模型在进行动态分析时缺乏准确性,而基于时域模型的电磁暂态仿真的仿真规模又受到限制。本文引入动态相量法,用来建立电力电子变换器的非线性、大信号、时不变的模型。仿真结果表明,动态相量模型比传统的稳态相量模型精确,非常接近于时域模型的结果,适合于快速数值仿真。     

不对称三相电压下电压源型换流器谐波分析与抑制策略

不对称三相电压下,电压源型换流器(VSC)将产生低次谐波,给电网造成谐波污染。随着VSC在电力系统中的广泛应用,这类问题必须得到更多的关注,提出有效的解决方法。基于动态相量和序分量,推导出序分量动态相量,并对其特性进行了分析;将含开关函数描述的VSC时域模型转化为动态相量模型;定义交流电流和直流电压的各阶序分量动态相量为状态变量,建立了以状态空间描述的VSC序分量动态相量谐波分析模型,综合考虑了开关函数的详细动态特性和交直流侧谐波的相互作用,从而揭示了VSC产生谐波的机理,实现了VSC谐波的解析求解。在此基础上,提出负序补偿的不对称调制策略,以抑制低次谐波的产生。通过各种不对称情况下的仿真和计算,验证了所提出的谐波分析模型的正确性和谐波抑制策略的有效性。     

Tools for dynamic analysis of the general large power system using time-varying phasors

This paper extends the applicable range of phasors for transient analysis from the traditional slow quasi-stationary range to accommodate fast speeds up to the carrier frequency. Rigorous phasor calculus is developed for time varying low pass phasor signals whose bandwidths are less than the 60 Hz carrier frequency. Symmetrical components technique for analysing quasi-stationary unbalanced power system transients is extended to cover the low pass time-varying phasors. It is also proved that the time varying phasors can be used for computing the fast electromagnetic transients within the linear RLC lumped parameter representation of the transmission network irrespective of the transient speeds. In linear networks, this time-varying phasor concept unifies two classical approaches: (1) transient analysis using instantaneous currents and voltages, and (2) steady state analysis using traditional phasors, into analysing both behaviours precisely using the time-varying phasors.     

结合谐波特征的可控串补动态相量法建模与特性分析

该文引入动态相量法建立可控串补TCSC的系统化的大信号模型,TCSC的动态相量模型是以时变傅里叶级数中的主导项为状态变量建立的状态空间模型,可以考虑晶闸管开关的非线性动态和谐波特性。通过对时域模型和不同精细程度的动态相量模型的仿真,揭示了TCSC在容性工作区时电容电压的谐波分量主要是三次谐波和五次谐波的特征,同时表明考虑开关的动态特性、根据需要的精度建立的动态相量模型适于电力系统的快速动态分析和与频谱相关的机理研究。     

基于晶闸管控制电抗器的FACTS动态相量模型

利用电力系统变量的时变傅里叶系数得到晶闸管控制电抗器(thyristor controlled reactor,TCR)的动态相量模型,该模型忽略了对TCR动态特性影响较小的谐波分量,并通过对TCR时域模型的平均运算获得动态相量状态空间模型。应用该模型对含柔性交流输电装置的电力系统进行仿真,能在保证一定精度的同时获得较快的速度。基于TCR的动态相量模型提出了静止无功补偿器和晶闸管控制串联电容器的动态相量模型。通过与商业软件DCG/EMTP在简单测试系统上的全时域仿真结果相比较,证明了该动态相量模型的有效性和正确性。     

An improved fault analysis algorithm for unbalanced multi-phasepower distribution systems

The results of an improved method for fault calculations in unbalanced multi-phase power distribution systems containing nonutility generators and large induction motor loads are presented in this paper. The method utilizes a combined time- and frequency-domain analysis approach to produce results that are superior to those obtained in “classical” fault analysis without the large increase in computer time with complete time-domain solutions. Sources and loads can be represented by either classical frequency-domain models or detailed differential equation models. The potentially unbalanced power distribution system is represented by an admittance matrix formed using a linear graph-based application of AC circuit theory. The time-domain differential equation source and load models are interfaced with the frequency-domain distribution system model using time series analyses to estimate equivalent voltage and current phasors from discrete data sets     

非接触式电压相量测量算法

同步相量测量技术为电网动态安全监测提供了数据基础,非接触式电压传感技术具备安全、便捷、成本低的优势,有利于测量装置实现海量布点。现有非接触式电测量的缺陷在于复杂电压经探头传变后二次侧输出电压发生畸变,难以还原一次侧电压相量。为解决电压畸变问题,文中提出了一种对带内信号分频计算的相量测量算法。首先对探头输出电压进行预处理,滤除带外信号与噪声,随后采用矩阵束法计算带内信号频率,以此构建信号模型进行时域拟合求解带内信号相量,最后将带内信号相量还原至一次侧后合成得到综合相量。仿真结果表明,所提方法能够利用探头二次侧输出电压采样值计算一次侧电压相量。实验数据显示所提方法的幅值测量误差小于4.5%,相位误差小于1°,频率误差小于0.04 Hz,频率变化率误差小于4 Hz/s。     

Generalized Mathematical Modeling of N-Phase Power Systems

ABSTRACT

The analysis of the polyphase power systems is normally carried out by assuming a perfectly balanced system. However, power system is generally unbalanced because of various reasons. Therefore, it is desirable to analyse the power system taking imbalances into account. Hence, it is necessary to develop mathematical formulations of various components of the power systems in phasor co-ordinates. In this paper, detailed mathematical models for general n-phase components have been developed. These models will be useful for conducting the steady state as well as the transient analysis of the multiphase systems in phasor co-ordinates. Finally, the paper concludes with the discussion on the findings based upon these models.     

面向宽频振荡抑制的宽频相量测量装置

快速实时测量宽频相量对于宽频振荡抑制有着重要意义。然而,已有宽频相量测量装置主要面向监测类应用,响应速度慢。研制了一种面向宽频振荡抑制的宽频相量测量装置。该装置采用加窗插值离散傅里叶变换算法,实现多模式宽频相量测量;采用较短时间窗缩短算法的动态响应时间;通过2个数字信号处理器并行计算分别完成基波和谐波/间谐波相量测量。通过性能测试发现,所研制的宽频相量测量装置响应速度快、准确度高,能满足宽频振荡抑制等应用对相关性能的要求。     

动态条件下的同步相量测量算法的研究

考虑到电力信号的动态特性,利用泰勒级数对电力信号的时变相量进行建模,并利用相邻采样数据窗的相量测量值来表示相量导数,以此相量导数来修正系统动态特性对相量测量精度的影响。仿真计算以及现场数据的分析研究表明：该同步相量测量算法提高了多种动态条件下(如低频振荡和频率偏移等情况)对信号相量进行测量的精度,与传统相量测量方法相比,虽然运算量有所增加,但仍能够满足现场在线应用的要求。     

变压器励磁涌流的相移比较鉴别方法

为了满足现代变压器保护动作快速性的要求，针对变压器铁心饱和的过程中具有非线性特性，提出了一种利用相移比较的短数据窗算法。该方法利用前一段波形估计出的基波相量经移相后与后一段波形估计的相量相比较来判别故障和励磁涌流，并给出了具体的故障判别方案。动模试验表明：该方法原理简单、易于实现，能够迅速、可靠地切除各种情况下变压器的内部故障。     

基于改进泰勒加权最小二乘法的相量测量算法

大部分相量测量算法将信号相量作为一个静态模型,因此对电网中经常发生的电压幅值和相角波动特别敏感。基于标准频率下动态相量模型的泰勒加权最小二乘法(Taylor Weighted Least Squares, TWLS)不仅提供了相量值,还提供了相量导数值,可以提高对电网动态状况的监测。在此基础上,提出了一种基于基波频率值的改进泰勒加权最小二乘法。首先用非线性最小二乘法得到基波频率值。然后介绍了基于测量基波频率值的改进泰勒加权最小二乘法推导过程,并对该算法所涉及的窗函数、数据窗长度和泰勒多项式阶数进行分析选择。最后采用不同的信号模型和实际数据来检验算法的性能。仿真结果表明:提出的改进泰勒加权最小二乘法的测量精度满足要求。     

计及电抗器支路电阻的TCSC动态相量法模型

为研究含TCSC的电力系统的稳定性和动态特性及设计TCSC的实用化控制策略,提出了计及电抗器支路电阻影响并结合动态相量法的TCSC建模方法。动态相量模型是随时间缓慢变化的非线性、大信号模型,适合暂态过程快速而又精确地仿真,但传统动态相量法存在状态空间方程阶数随着计及频率成分增加而迅速增长的问题。故在分析模型的状态变量特性,忽略快速变量的动态变化过程后,由动态相量与傅立叶系数间的关系建立了计及电抗器支路电阻影响的TCSC动态相量法模型。仿真算例验证了所提出模型的精确性和有效性。     

Hybrid-model transient stability simulation using dynamic phasors based HVDC system model

A novel hybrid-model transient stability simulation algorithm for ac/dc power systems is suggested in this paper, where dynamic phasors theory is applied for HVDC transmission system modeling, and traditional electromechanical transient models are used for ac system. A detailed dynamic-phasors-based HVDC system model is derived first, and the algorithm for interface of the dc dynamic phasors model to ac network is proposed next. Computer simulation results show that the HVDC dynamic phasors model has very good accuracy as compared with its electromagnetic transient model; the test results from a 2-area ac/dc power system and a multi-infeed HVDC power system show clearly that the suggested interface algorithm works effectively in system transient stability analysis. The proposed hybrid-model simulation algorithm provides a new approach for dynamic simulation of large-scale ac/dc power systems.     

Generalized State Estimation of Flexible AC Power Systems Considering Wind Generators and Primary Frequency Control

This paper proposes a practical approach to incorporate the mathematical models of both fixed-speed and variable-speed wind turbine generators, automatic load frequency controls as well as voltage magnitude and frequency dependent loads into a weighted least squares-based state estimation algorithm suitable for the analysis of flexible alternating current (AC) transmission systems. As opposed to conventional static state estimators, where the inclusion of these electric components has been neglected so far, the proposed approach permits the determination of the steady state operation of a power system in the event of a supply-demand unbalance by estimating the magnitude of the frequency deviation from its nominal value. The state estimation is based on measurements related to those that should be obtained by a supervisory control and data acquisition (SCADA) system and phasor measurement units. For the purpose of this paper, the set of values associated with SCADA measurements (nodal power injections, power flows, and voltage magnitudes) and phasor measurement unit (PMU) measurements (voltage and current phasors) are generated from a power flow analysis of the network under study. Lastly, numerical simulations are reported to demonstrate the effectiveness of the proposed approach.     

Low-order dynamic equivalent estimation of power systems using data of phasor measurement units

This paper utilizes data measured by phasor measurement units (PMUs) to extract a low-order dynamic equivalent model for power system stability studies. The estimated model is a 2-order model for synchronous machines. This model has the advantage of simplicity of classical model and considerably reduces the oversimplifying error of classical model. This method offers an alternative approach to analytical model reduction techniques based on the detailed system models. The proposed method uses the synchronized bus voltage and current phasors measured by PMUs. Using post disturbance data, electrical and mechanical parameters of the equivalent generator are estimated sequentially. Furthermore, a new approach for estimation of two-machine and single machine infinite bus (SMIB) equivalent systems are presented for analysis of electromechanical oscillations. To evaluate the performance of the proposed approach, simulations are performed on a two area 13-bus test system and real measured PMU data. Simulation results show that the estimated model can represent the dynamic behavior of the studied system with good approximation.     

利用卫星时间作基准的电力系统同步相量测量

本文首先对同步相量测量的思想进行阐述，然后给出一种新的同步相量测量方案，该方案将基于ＧＰＳ时间信息的时钟同步技术与离散付氏变换算法相结合，能在统一参考基准下实时测量电力系统各节点的电压电流相量。文章对该方案涉及到的算法、同步采样技术、硬件构成以及可行性等进行了详细描述。     

Power quality analysis of STATCOM using dynamic phasor modeling

Modeling of synchronous static compensator (STATCOM) of a power system based on the dynamic phasor model to investigate the performance of STATCOM for power quality analysis is described. It is compared with electromagnetic transient program (EMTP) like simulation. The dynamic phasor model and electromagnetic transient (EMT) model of the STATCOM including the power system are implemented in Matlab/Simulink toolbox and PSCAD/EMTDC, respectively. STATCOM dynamic phasor model including switching functions and their control system are presented. A satisfactory solution for power quality problems on typical distribution network is analyzed using the dynamic phasor model and EMTP like PSCAD/EMTDC simulation techniques. The simulation results revealed that the dynamic phasor model of STATCOM is in excellent agreement with the detailed time-domain EMT model of PSCAD/EMTDC simulation. The dynamic behavior of STATCOM using phasor model can be applied for analyzing power quality issues. It is found faster in speed and higher accuracy can be obtained and correlates well with PSCAD/EMTDC simulation results.     

A novel hybrid state estimator for including synchronized phasor measurements

State estimator is crucial for on-line power system monitoring, analysis and control. With the increasing use of synchronized phasor measurement units (PMU) in power grids, how to utilize phasor measurements to improve the precision of state estimator becomes imperative. Since there are lots of traditional measurements in SCADA system and it is hard for phasor measurements to replace them in the near future, the best way is to develop hybrid state estimator which includes both phasor and traditional measurements to get better behavior. In this paper, a novel state estimator for including voltage phasors, branch current phasors and traditional measurements is proposed. The detailed model and how to calculate covariance matrix of PMU measurements are described in detail. New England 39-bus system and IEEE 118-bus system are used as test systems and the simulation results demonstrate that the proposed state estimation algorithm improves the precision greatly and gets better behavior as compared with other state estimators with or without phasor measurements.     

三相分布参数线路动态相量法的建模与仿真

传统的机电暂态模型由于建立在"准稳态"假设基础之上,因此不能用来仿真变化迅速的电磁暂态过程,而电磁暂态模型,虽然能准确反映电磁暂态过程,但由于仿真步长很小,仿真速度受到限制,不适合用来仿真大型电力系统。该文基于动态相量理论,对三相分布参数的线路进行推导和建模,提出一种适用于分布参数线路的大步长动态相量模型,并分析了其产生的误差。通过对算例的仿真和与电磁暂态模型仿真结果的比较,验证了动态相量模型能突破电磁暂态模型对分布参数线路仿真步长的限制,用来仿真三相分布参数线路上的电磁暂态过程。