【作者】 王磊；

【导师】 杨洪耕；

【作者基本信息】 四川大学 ， 电力系统及其自动化， 2005， 硕士

【摘要】 随着社会的进步和发展,电能质量问题逐渐引起人们的重视。一方面,随着非线性负荷的不断增加,以及电力电子设备的广泛应用,使得电网中的电压和电流发生畸变,配电系统中谐波污染问题日益严重,造成电能质量的严重恶化;另一方面由于工业自动化水平的提高,微处理器和PLC等智能器件大量应用于工业控制过程,而这些精密控制过程更容易受到电能质量的影响,因此现代工业对电能质量的要求越来越高。由于电力系统中谐波源具有随机性,所以用统计方法描述谐波更为准确,许多国际标准及建议采纳一种评估的方法作为谐波限值的标准,例如IEC采取日值的95%和周值的最大值作为评估标准。 由于谐波源具有时变特征,很多情况下采用统计方法估计其影响程度。电力系统中不可能在所有节点位置安装谐波检测装置,通常对未测节点用随机矢量求和的方法进行评估,所以多谐波源求和问题就提了出来。本文提出了一种新的方法处理电力系统中随机谐波矢量(电压和电流)在具有不同相角分布时的求和问题。首先将几个随机谐波矢量进行X-Y轴正交分解求和,得到分量和的2k阶矩后利用Laguerre多项式求其近似概率密度函数(pdf: probability density function)。然后根据分量和的pdf及概率学定义进行X-Y轴矢量合成,实现以Laguerre多项式形式表达的谐波和的幅值的概率密度函数。 为了保证供电质量,确保系统和用户在额定的范围内正常交易,对用户投入系统运行所产生的影响进行合理的奖惩,体现系统和用户对电能质量状况的共同责任,因此,有必要对公共联接点各谐波源所产生的谐波污染问题进行责任的明确划分。非线性负荷对公共联接点PCC(Point of Common Coupling)的谐波发射水平定义为在没有其它非线性负荷或谐波源存在时,由此非线性负荷单独作用在PCC产生的谐波电压。由于系统侧背景谐波的存在,在PCC的谐波电压更多还原

【Abstract】 With the rapid growth of economics, power quality issue has increasingly captured considerable attention from both utility companies and their customers. The extensive applications for power electronic apparatus and nonlinear equipment distort the waveforms of voltages and currents. As a result, power quality is going much worse. In addition, due to the improvement of industrial automatization, such parts of an apparatus as MPU and PLC are applied to industrial process controls, which are disturbed easily by stirs from power system. Therefore modern industry needs higher power quality than old one does. Because of the random of the harmonics recourses in power system, it is exactly to use the method of statistic to describe them. Many international standards and advices use an evaluation as a limit to the level of harmonics. For example the IEC has taken on a standards to limit distortion levels define the compatibility levels of distortion 95% a day or the maximum a week.Because of the random of the harmonics recourses in power system, sometimes the effect was estimated using the method of statistic. It is impossible to fix detected devices on every node in system. It is usually used the summation of the random vectors to estimate the levels of harmonics of the node which didn’t fix detected devices. So the question of summation of the random vectors was brought forward. This paper presented a new method to get the sum of random harmonic vectors (voltage or current) which phases have different probability distribution functions in the power system. Several vectors are decomposed with X-Y axis. The probability density functions (pdfs) of the sum of X-Y axis ponderances can be obtained byusing Laguerre polynomials after getting the 2kth moments of the sum of them. Basing on the pdfs of the sum of X-Y axis ponderances, the pdfs of the length of the sum of vectors are obtained.In order to assure the quality of power supply, and ensure the normal dealings between utility companies and customers in rated limits, it is indispensable to put a penalty or a premium due to the effect of a customer, which embodies the corporate responsibility for power quality. There for it is the sticking point for solving the problem about separating the duty to find methods of assessing the harmonic emission level. The effect of nonlinear loads harmonics levels on PCC was defined without other harmonics recourses. The voltage of single nonlinear loads harmonics was defined. The harmonics voltages of a given nonlinear loads is the sum of all the harmonics on the PCC. It is difficult to measure it directly because of the background harmonics. A new approach for assessing harmonic emission levels from nonlinear loads is proposed with inverse sum of probability. The model of sum of probability is based on the figure characteristics of harmonics from nonlinear load disconnected and connected. The 2k order moments are used to determine Laguerre polynomials expansion for simulating the sum probability density function (pdf): A recursive algorithm is used to calculate 2k order moments of measurements on X-Y components. The 2k order moments of sum of vectors are deduced from it.At the end of the paper the pdfs of the sum of two harmonic voltage vectors that were obtained by using true dates are compared with those obtained by using Laguerre polynomials. The method was proved validity.更多还原