【作者】 胡晓磊；

【导师】 邹云屏；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2008， 硕士

【摘要】 随着现代技术的发展,生产和生活中的电力设备不断增加,对现有电网的容量和扩容速度产生了巨大的冲击和考验。在用电的高峰和低谷时,电压波动,即瞬时电压跌落(Voltage Sag)、电压浪涌(Voltage Surge)发生的比较频繁,导致许多敏感性电气设备不能正常工作。保护负载不受瞬时电压跌落影响最常用的设备是动态电压恢复器(DVR)。目前动态电压恢复器(DVR)主要存在补偿电压时间有限,不能补偿电网电压浪涌,及检测电网电压波动并实时补偿电压等问题。针对动态电压恢复器存在的问题,本文给出了由一个串联PWM变换器及一个PWM整流器构成的DVR系统。串联变换器借鉴了电流周期平均模型(PAM)的概念,采用通过控制串联变压器二次侧电流,在变压器内部磁势平衡约束下,控制负载电流的方法。在负载电流达到额定值时,负载的端电压就是负载的额定电压。串联变压器的励磁电流会使负载电压有稳态误差,本文给出了负载电流有效值反馈补偿法、励磁电流完全补偿法两种励磁电流补偿方法,以提高负载电压的控制精度。本文使用PWM整流器为DVR提供直流电压。PWM整流器能工作在单位功率因数,实现能量回馈,可以很好地解决传统DVR不能补偿电压浪涌的问题。当DVR补偿电压跌落时,PWM整流器从电网吸收能量,当DVR补偿电压浪涌时,PWM整流器将能量回馈至电网,保证了直流侧的电压稳定。为了使DVR系统对电网不造成新的污染,应使之尽量工作在单位功率因数,所以在负载端并联有源电力滤波器(APF),专门为负载提供无功电流及谐波电流。因此,在设计变压器时只需考虑负载的有功电流,有效地减小了变压器的容量和体积,同样也降低了开关器件的功率等级。本文所述DVR补偿效果依赖于并联APF的补偿效果及实时运算出的负载电流给定值的速度及精度。因此本文采用了自适应谐波电流检测方法,从负载电流中分离出有功电流、无功电流及谐波电流分别作为指令信号送至DVR和APF。本文介绍了自适应谐波电流检测原理,并介绍了自适应滤波的模拟实现法及LMS算法,在此基础上比较了两种方法的效果。并提出了规一化的LMS算法。本文所作工作也是统一电能质量调节器(UPQC)的前期工作,在本文所述的DVR基础上,将PWM整流器从并联在电网侧改到并联至负载端,由本文所述的自适应滤波谐波电流检测方法给PWM整流器无功及谐波电流指令,使其起到APF的作用,并由其直流电压环给出有功电流指令,起到稳定直流侧电压的作用。就构成了单相统一电能质量调节器(UPQC)。更多还原

【Abstract】 Electric power device used in industry and personal living has been increased when new technique is developing. It impacts and charges the capacity and the velocity of the capacity increasing of the grid. Voltage surge and sag, especially voltage sag happens continually, makes some sensitive electric device working abnormally. Dynamic voltage restorer (DVR) is a common device to protect sensitive electric device inflected by voltage sagging or surging.Now, the problems of existed DVR are that the compensation time is limited, can’t compensate voltage surge and detect voltage change and compensate the change by real time.This paper discusses a DVR system consists by a series PWM converter and a PWM rectifier. Serried PWM converter uses the concept of current average model. At the restrictions of the transformer’s internal magnetic field balance, via controlling the secondary current of series transformer to meet the invariableness of the load current. When load current is meeting, the load voltage is the rated value. As series transformer needs magnetizing current, which make load voltage has state error, this paper designs tow methods of magnetizing current compensation. One of the magnetizing current compensation methods is based on the LMS value feedback of the load current, the other one is transformer magnetizing current complete compensation.This paper uses PWM rectifier to provide the DC voltage for DVR. PWM rectifier can work on unit power factor condition, and could returns energy back to grid. Using PWM rectifier could solve the problem that traditional DVR couldn’t compensates the voltage surge. When DVR compensates voltage surge, PWM rectifier returns energy back to grid, while DVR compensates voltage sag, PWM rectifier get energy from grid. This keeps the DC voltage steady.Make DVR working at unit power factor condition to avoid make new pollution to grid. This paper has a parallel Active Power Filter connecting to the load, providing the reactive power current and harmonic current. Only active power current needs to be considered when design the transformer. This cuts the capacity and volume of the transformer efficiently, so as the power level of the power electric device. The compensation result depends on the parallel APF, the velocity and precision of the real-time calculated load current setting value. This paper uses adaptive filter to detect harmonic current. This filter can divide fundamental active power current, fundamental reactive current and harmonic current, then send to DVR and APF as setting signal. This paper introduces the concept, traditional realizing method in analog current and LMS realizing method using digital signal processing of adaptive filter. Based on the cooperation of tow adaptive filter realizing method, this paper designs a new LMS method that converter all signal to unit.The work of this paper is also the preparing work of Unified Power Quality Conditioner (UPQC). Based on DVR discussed in this paper, connects the PWM rectifier to the load form grid. Using the fundamental reactive current and harmonic current from adaptive filter as the setting value, PWM rectifier could work as APF besides keeping the DC voltage by the active power current given by DC voltage loop. The PWM rectifier and series PWM converter make up a Unified Power Quality Conditioner.更多还原