【作者】 谭智力；

【导师】 陈坚； 段善旭；

【作者基本信息】 华中科技大学 ， 电气工程， 2007， 博士

【摘要】 统一电能质量调节器(UPQC)是一种电能质量综合调节装置。它以电力电子技术为基础,实现畸变波形的补偿、动态电压恢复,实现用户灵活供电,属于用户电力技术(Cuspow)重要内容之一。它改变了电能质量控制中传统电压或电流波形分别补偿方法,整体适应系统电流和电压的补偿要求,实现多种补偿功能,具有较远的发展前景和独特的研究价值。本文针对三相四线制的UPQC系统,进行了以下五个方面的研究工作。分析了三相四线UPQC的拓扑结构,介绍了在电源电压或负载电流出现不平衡或畸变时,三相四线UPQC的工作原理、功能以及达到的补偿效果;分析了三相四线UPQC的功率特性,推导出UPQC的有功与无功表达式,得到了潮流分布图。为获得控制方程的线性化模型,详细推导出其三相静止坐标下和d-q-0坐标中的低频模型以及d-q-0坐标中的小信号模型,获得了各电量的线性表达式;在此基础上,分析了直流侧电压与电源有功电流的线性关系,推导出了相关表达式,为后续章节的直流侧电压控制策略提供理论依据。探讨了在电源电压、负载电流出现不平衡和畸变时,补偿分量的提取方法。补偿分量的正确提取是实现UPQC补偿功能的前提条件。详细讨论了本文采用的两种方法。其一是基于同步坐标变换的补偿分量检测方法,即d-q-0坐标中的补偿信号的检测方法。分析了基于此种坐标变换的常规补偿分量提取方法在系统电压不平衡及畸变时,不能准确检测补偿信号的原因,进而提出了一种不需要常规锁相环来获得变换中需要的相角的新方法,给出了经过改进的,适合电源电压不平衡及畸变时,d-q-0坐标中的补偿信号的实际提取方法。其二是基于改进p-q-r理论的补偿分量实际检测方法。p-q-r理论是近年出现的一种新的坐标变换理论,但其变换复杂,现有的资料中大多用于补偿分量的检测而无法在p-q-r轴上实现控制。本文通过对这一理论进行推广及改进,减小了其变换的复杂性,使其能够用于实际的控制策略中,实现在p-q-r轴上的独立控制,提出了基于这一改进理论的p-q-r理论补偿分量的实际提取方法。仿真结果表明,改进后的两种补偿分量的实际提取方法能够准确的提取补偿分量。系统地分析了串并联补偿器协调控制两个方面的内容。首先以常见的两种控制策略为例,介绍了串并联补偿器在功能上的分工协作;接着分析了串并联补偿器由于外部电气联系造成的相互影响的原因,并提出了解决这一影响的基本措施,仿真结果证明,采用这种措施可以提高系统的控制精度,减少稳态误差。接着分析了在电源电压、负载电流不平衡、畸变时引起直流侧电压波动,进而造成串并联补偿器各自逆变器工作时相互影响的原因,通过分析得出结论,当电源电压或负载电流不平衡时,直流侧两个电容端电压的波动是不可避免的。提出了在直流电压波动时,实现与直流侧电压稳定时输出电压等效的两种方法。一种方法是通过对调制波乘以调节系数,另一种方法是利用冲量相等的原理,通过调整单个开关周期的开通时间来消除直流侧电压波动的影响。讨论了d-q-0坐标下的三相四线UPQC的间接控制策略。首先介绍了间接控制策略的原理,提出了一种直流侧电压调节器的设计新方法;分析了常规串联补偿的电压控制方案以及并联补偿的电流控制方案的局限性;为消除串并联侧存在相互影响,对串联补偿器,提出了一种带电压前馈的双闭环控制方案,对并联补偿器,提出了一种带状态解耦及负载电压(扰动量)前馈的控制方案。分析了当电源电压或负载电流不平衡或畸变时,在d、q、0轴上采用常规的直流PI调节器的控制方案无法消除稳态误差的原因,为解决这一问题,提高这种情况下的控制精度,实现零稳态误差控制,本文借助静止坐标下交流信号的零稳态误差调节器的原理,首次提出了交流等效PI调节器的概念,分析了其实现零稳态误差控制的原理,探讨了将其用于系统电压、负载电流不平衡及畸变时的串、并联补偿器的新型控制策略。最后给出了在各种电源电压、各种负载情况下的各种电压、电流仿真和实验波形。仿真和实验结果表明,采用的控制策略有效地实现了UPQC的补偿功能。详细讨论了在p-q-r坐标下的三相四线UPQC的直接控制策略。首先介绍了直接控制策略的原理,分别推导出在p、q、r轴上的串、并联补偿器的电流和电压的控制方程,详细分析了调节器参数的选取方法;针对电源电压或负载电流不平衡或畸变情况,为了消除直流侧电压波动的影响,在控制策略中加入直流电压调节系数,为消除并联补偿器对串联侧的影响,串联侧控制策略中加入了串联补偿电压(扰动)的前馈控制。为消除串联补偿器对并联侧的影响,并联侧控制策略中引入负载电流前馈控制;另外,为实现零稳态误差控制,对并联补偿器的电流环和电压环加入等效交流PI调节器,给出了详细的串、并联补偿器控制系统的框图,分析了在电源电压、负载单独或同时变化时,实际电源电流和负载电压的动态响应特性,最后给出了在各种电源电压、各种负载情况下的各种电压、电流仿真和实验波形。仿真和实验结果表明,采用上述控制策略,UPQC能保证输出电压、输入电流总谐波畸变率小于5%,输入功率因数接近于1,同时具有较好的动态响应特性。更多还原

【Abstract】 Unified Power Quality Conditioner (UPQC) is a kind of combined device for adjusting power quality. Based on power electronic technology, it can not only compensate distorted waveform ,but also restore dynamic voltage and implement flexible power supply. And it is one of the most important branches of customer power technology(Cuspow).It changes the traditional ways that compensating voltage waveform and current waveform respectively, and has capacity of simultaneously compensating both of them, which satisfying the compensating requires of current and voltage and realizing a great variety of function, so it must have a prospective future and characteristics attracting the eye ball of the researchers. Aiming at three-phase four-wire UPQC system, this paper works in the five areas as listed below.First of all,topology circuit of three-phase four-wire UPQC was carried on and its work principle ,function as well as compensating purpose was introduced under the condition that unbalance or distortion is included in source voltage. The power characteristic was then analyzed as well as the expressions of active power and reactive power were derived, based on which the power flow diagram gotten. On the purpose of obtaining the linearization model of UPQC,the Low Frequency model in the three phase stationary and d-q-0 coordinates as well as small-signal model in d-q-0 coordinates were deduced, and the linearization expresses of voltage and current of UPQC were deveried. Based on that, the linear relationship between source active current and voltage on DC side is discussed, the related expression is deduced at the same time, which supplying the theory gist for the dc voltage control strategy discussed subsequently.Secondly, the method of extracting of compensation component when supply voltage or load current is unbalance and distort was discussed. Correct extraction of compensation component is the prior condition for UPQC to realize its function. Two methods adopting in this thesis was studied in detail. One was based on synchronous coordinate transform- ation, namely the measure method in d-q-0 coordinate, the conventional measure methods on which can not accurately get the value of compensation signals when supply voltage was unbalance and/or distort .After analyzing the reasons of nonpreciseness, a new sort of method having no use for conventional PLL to get the phase angle needed in the transform was put forward. Based on that, an improved and practical method of extraction of compen- sation signals in d-q-0 coordinate was then presented, which worked well even when supply voltage was unbalance and/or distort. The other method was based on p-q-r theory, a new coordinate transformation theory it was presented recent years. Although it had many advantages, its transformation is so sophisticate that it was only used to the measuring compensation component according the available reference, the control strategy on p-q-r axle can not achieve. By promoting and improving this theory, complexity of the transform- ation decreased, so the improved p-q-r theory can be used for actual control strategy, which brings independent control at p-q-r axis into effect. The simulation result shows that the two improved actual method can abstract the compensation component precisely.And then,two aspect of coordinated-control of series-parallel compensator were discussed systematically. The cooperation of function of series-parallel compensator was introduced, with the two usual control strategy as example,meanwhile,the reasons of the interaction between series and parallel compensator on account of external electric connection were analyzed in detail, based on that, basic undertakings to cancel the interaction were presented. Simulation result showed that, this method could increase control accuracy and decrease steady-state error. The voltage on the dc side might fluctuate when source voltage and load current are unbalanced and distort, which in turn effect on the inverters of the series and parallel compensator respectivly.It was concluded that, under this condition, voltage fluctuation of the two capacitance on the dc side is inevitable. Two ways were brought into effect to assure the equivalence of the output wave of the two invert when dc voltage fluctuating and stabilization. One was that the modulation wave in SPWM was multiplied by a regulation factor, the other is adjusting the switch time in particularity switching cycle according to the impulse equal theory, so that the effect of voltage fluctuation on dc side can be eliminated.Next, the indirect control strategy of three-phase wire UPQC in d-q-0 coordinates was discussed in detail. The theory of indirect control strategy was firstly introduced and a new method to design the voltage conditioner on dc side was then presented. After that, the limitations of the conventional voltage control scheme for series compensator as well as current control scheme for parallel compensator were discussed. In order to eliminate the interaction existing in series and parallel side, a two-closed-loop with voltage feedforward control scheme was presented for series compensator and a load voltage feedforward with state discoupling control strategy for shunt compensator. When source voltage or load current are unbalance or distort, ordinary DC proportional-intergral controller on the d-q-0 axis can not eliminate steady-state error, the reason of that was analized.For the purpose to solve this question, enhance the control accuracy and achieve zero steady-state error control, an AC equivalent proportional-intergral controller in d-q-0 axis, referring to the zero steady-state error regulator of AC signal in stationary coordinates, was proposed. Its principle of eliminating steady-state error to zero was analyzed and a new control strategy by using of it was presented under the condition that system voltage and/or load current are unbalance and/or distort. Then the simulation and experiment waveforms of different voltage and current under different electric network and loading condition were gave out. The simulation and experiment result shows that UPQC efficiently carry out its compensation function while adopting the proposed control strategy. Finally, the direct control strategy of three-phase four-wire UPQC in p-q-r coordinates was discussed in detail. The principle of direct control strategy was firstly introduced. The control equation of current and voltage of series and shunt compensator were deduced on the p-q-r branches as well as the process to calculate the regulator parameter was discussed. Considering the unbalance or distortion of source voltage and load current, for the sake of eliminating voltage fluctuation on dc side, a direct current voltage regulation coefficient was added into the adopting control strategy, meanwhile, in order to eliminate the effect of shunt compensator on series compensator, a series compensation voltage feedforward control was joined into the control strategy on series side. In order to cancel the effect of series compensator on parallel compensator, load current feedforward control was led into the control strategy on parallel side. In addition, the equivalent proportional-intergral controller was added into current and voltage loop of control strategy of shunt compensator for the sake of decreasing steady-state error, the schematic diagram of control system for shunt and series compensator were gave out as well. Dynamic response of source current and load voltage were discussed on the condition that source voltage and load both or one of them changed. Finally, simulation and experiment waveform of voltage and current under different electric network and loading condition were given out. The simulation and experiment result manifested that, adopting forementioned control strategy; UPQC can ensure the THD of its output voltage and input current less than 5%, input power factor in proximity to 1 and with good dynamic response.更多还原