【作者】 李达义；

【导师】 贾正春； 陈乔夫；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2005， 博士

【摘要】 电力系统冲击性、非线性负载容量的不断增加使电力系统出现了电压电流波形畸变、电压波动、闪变和三相不平衡等电能质量问题,而现代化生产过程中所使用的各种先进的精密仪器与设备对供电质量要求越来越高。在全面总结现有研究成果的基础上作者将变压器理论和现代电力电子技术的结合,研究了用于电力系统动态谐波抑制的有源滤波器和电力系统中可以实现多种功能的可调电抗器,并对几种含有变压器的柔性输电装置进行了分析,主要研究成果为: 1)对电力系统谐波电压(或电流)进行了分析,得出基于连续信号傅立叶级数的各次谐波系数的计算公式,并根据欧拉公式推导了该计算公式与Matlab 中的FFT 函数计算出的谐波系数的关系,实例应用证明了这种分析的正确性。通过仿真解释了两种典型的谐波源的物理本质和分类依据。简要分析了包含无源滤波器在内的串联混合型有源滤波系统的整体参数设计方案。2)介绍了一种基于磁通可控的可调电抗器,这种可调电抗器中包含一个串联变压器,当在变压器的二次侧采用有源的方式注入一个与一次侧电流频率相同、相位相反的电流时,随着注入电流的幅值的变化,变压器的主磁通会发生连续变化,从而可以实现变压器的一次侧阻抗的连续无级可调。本文详细分析了二次侧注入电流与一次侧注入电流在相位和幅值变化时所必需满足的稳定性条件,根据该稳定性条件解释了该可调电抗器之所以能稳定工作的原因。当基于磁通可控的可调电抗器的两种特殊工作状态应用到有源滤波器时,可以得到一种基于基波磁通补偿的混合型有源电力滤波器。这种滤波方案通过检测变压器一次侧的基波电流,并采用电压型PWM逆变器来产生一个基波补偿电流。将此基波补偿电流注入串联变压器的二次侧,当二次侧注入基波电流和电网电流中的基波成分满足基波补偿条件时,串联变压器对基波呈现变压器一次侧漏阻抗,而对谐波呈现励磁阻抗。这种有源滤波器通过提高了系统对谐波的阻抗从而迫使谐波电流流入无源滤波器支路,真正起到了谐波隔离的作用。与国内外现有串联型有源滤波器方案完全不同,这种方案只需检测、跟踪基波电流,补偿基波磁通,因此对电流跟踪控制方式的频带要求很低,且性能稳定,电路结构简单,易于在工程中实现。本文还分析了有源滤波系统在什么条件下可以不加高次无源谐波滤波器和高通滤波器,同时对这种基于基波磁通补偿有源电力滤波器如何用于三相谐波源的滤波做了详细介绍。3)为了解决大容量有源滤波器,提出了一种变压器二次侧采用多绕组的结构的方案。这种变压器结构二次侧采用多绕组,每个绕组与一个用来产生基波补偿电流的PWM 逆变器相接,当多个补偿电流共同作用产生的基波磁势与一次侧基波磁势完全更多还原

【Abstract】 Power quality problems such as voltage waveform distortion, voltage fluctuation, flicker and three phase unbalance become increasingly serious as the capacity of impactive and nonlinear load in electric power system continuously increases. Whereas some precise instrument and equipments used in modern production have much higher request to power quality. The author make a few researches on active power filter using for suppressing the harmonic of power systems and adjustable reactor, which have many functions, by combining the transformer with modern power electronics. At the same time the author analyzes some FACTS equipments containing transformer. The main research results are as follows: 1) The current (or voltage) of electric power system is analyzed. The amplitude calculating formulas of the fundamental and harmonics are achieved. The amplitude calculating formulas and the calculating results of one of Matlab’s functions-FFT are compared according to Euler formula and the relation of the two is achieved. The validity of these analyses is proved by practical applications. Harmonic sources are classified into two kinds: current type harmonic source and voltage type harmonic source and their physical essential is analyzed in terms of simulation. An integrated parameter design of series hybrid active power filtering system containing passive power filters is introduced. 2) A novel principle of adjustable reactor based on magnetic flux controllable is introduced. The secondary winding of a transformer is inversely in phase injected a current producing by a voltage source inverter, which has the same frequency as the current of the primary winding. According to the transformer’s voltage equations, the main magnetic flux of the transformer will vary continuously along with the continuous change of the injected current’s amplitude; therefore, the equivalent impedance of primary winding of the transformer will change continuously. The stability condition when the amplitude and phase of the injected current from the secondary winding varies is addressed in detail. According to the stability condition, the adjustable reactor can run normally. When the two special states are applied in the active power filter, we can achieve a novel series hybrid active power filter with the fundamental magnetic flux compensation (FMFC) of a series transformer. In the active power filter, the fundamental current component of power utility is detected and tracked to produce a fundamental compensation current, which is injected into the secondary winding. When the injected fundamental current and the fundamental current component of the power utility satisfy the fundamental magnetic flux compensation condition, the series transformer can really exhibit very low impedance to fundamental and naturally magnetizing impedance to harmonics. As a result, the series hybrid active power filter with FMFC really acts as “harmonic isolator”. In the active power filter, the fundamental current is detected and followed to realize the FMFC, the system bandwidth requirement is much lower and the control circuit is simple; the filtering system is more stable and more easily realized. The criterion in which the high order or high-pass filter can be omitted is addressed. The topology structure and characteristics when the series hybrid active power filter with FMFC is used in three-phase system are analyzed. 3) In order to design a high-power series active filter, a novel transformer structure with multiple secondary windings is proposed. The novel transformer structure contains one primary and multiple secondary windings, which are connected with a PWM inverter using for producing multiple fundamental compensating currents. When the overall multiple fundamental compensating currents and the fundamental current component of the electric utility in each phase satisfy the FMFC condition, the series transformer can really exhibit very low impedance to fundamental and magnetizing impedance to harmonics. The fundamental compensating current of secondary winding is provided together by multiple inverters after the transformer with multiple secondary windings is used. And then the switching devices of PWM voltage source inverter are available in the case of large capacity. The influence of the inconsistent mutual impedance and the inverter parameters is analyzed. Experimental results of active filtering system with 80kVA three-phase harmonic resource verified the validity of the novel principle of series hybrid active power filter with FMFC and the transformer structure for large capacity. 4) The timely detecting approach of the fundamental or harmonic current signal, which is specially researched in the paper, is a key technique in active power filter. The influence of the PLL influence to harmonic detection in ip-iq operation method based on the instantaneous reactive power theory is originally investigated. The conclusion is the harmonic can be detected accurately without the PLL when only harmonic instead of harmonic and reactive power is detected when the line frequency hardly change. What is more, two kinds of improved methods based on the instantaneous reactive power theory are investigated and the consistency in physical essence of both methods is proved. Furthermore, two kinds of fundamental detection approaches are introduced from the modern filter method in the paper. One is the fundamental detection method of the power systems in terms of LC parallel resonance. The other one is a simple fundamental currentdetecting approach by using Switched-capacitor filter (SCF). The principle, detection precision, dynamic response and the circuit realization of the two novel approaches are also addressed and verified in the paper. 5) The most often-used current control includes three strategies: hysteresis current control, carried modulation current control and periodical sampling method. The principle is analyzed in the light of one-phase and three-phase and simulations are made in order to verify those analysis. Their individual characteristic and suitable scope of the four strategies are explained. The parameter choosing criterion of hysteresis current control and the features of triangle comparison current control are addressed in the paper. 6)Three kinds of protecting strategies used in the series hybrid active power filter with FMFC are investigated: the secondary windings of series transformer are short-circuited, voltage protection by ZnO2 arrester and specially designing the series transformer in term of magnetic saturation characteristics. The main circuit diagram and its electrical control circuit of the series hybrid active power filter with FMFC are given. The magnetizing impedance choosing criterion of the series transformer and condition on how to use the magnetic saturation principle are explained. The dynamic switching process of the system, active part and passive part is explained in detail. Finally, static response question and the other key questions in the practical application are analyzed in the paper. 7) There are two kinds of realizing methods in the secondary winding when a transformer is used in many known FACTS equipments: injecting a current source and energizing a voltage source. The Generalized principle and relations of two kinds of realizing methods are originally addressed. The principle of a few FACTS equipments is explained in term of the generalized principle. These FACTS equipments include three kinds of realizing methods of injecting a current source and four kinds of realizing methods of energizing a voltage source.更多还原