《单相AC-AC变换器补偿电压骤降和骤升-电气工程及其自动化外文文献翻译》由会员分享，可在线阅读，更多相关《单相AC-AC变换器补偿电压骤降和骤升-电气工程及其自动化外文文献翻译（29页珍藏版）》请在金锄头文库上搜索。
1、外文文献翻译专业电气工程及其自动化学生姓名班级BD电气071学号指导教师电气工程学院Compensation of Voltage Sags and Swells usinga Single-Phase AC-AC ConverterAbstract-In this paper, a topology to compensate voltage sags and swells simultaneously in critical loads is proposed. It consists in a single-phase AC-AC converter in a matrix arrang
2、ement, which keeps a continuous regulation in the output voltage. The proposed scheme has the capability to compensate up to 25% voltage sags and 50% voltage swells.Energy storage devices are not required by the AC-AC converter and it is connected between the AC mains and the load by using a series
3、transformer. One of the advantages of this topology is that taps for the coupling transformer are no necessary to change the polarity of the compensation voltage. A four step switching technique is used to drive the AC-AC converter switches, executing snubber-less operation. The reference signal is
4、generated using single-phase d-q theory, obtaining a fast response time and high regulation.Simulation and experimental results of a 5kW capacity, 127V, 60Hz equipment are presented.I.INTRODUCTIONThe quality of the AC mains has been affected by the use of new semiconductor-devices technologies. Nowa
5、days, it is common to find disturbances in the amplitude or waveform shape of current and voltage in the electric systems. These conditions could produce fails in the equipments, raising the possibility of an energy interruption. The voltage fast variations that appear in the AC mains during 10 seco
6、nds or less are commonly known as voltage sags and swells. These variations are produced by normal operation of high power loads as well as theirs connection and disconnection; the voltage fast variation effects are function of the amplitude and the duration of the event. Some studies show that 92%
7、of all disturbances in the electrical power distribution systems are produced by voltage sags 1.It is important to eliminate the voltage fast variations because they are the most frequently cause of disrupted operations for many industrial processes, particularly those using modern electronic equipm
8、ent, which are highly sensitive to short duration source variations 2.Dynamic Voltage Restorer(DVR) and Uninterrupted Power Supply (UPS) systems had been researched and developed along the last decades and they are capable to compensate voltage sags and swells. Nevertheless, they depend on devices t
9、o store energy, like large capacitors or batteries bank. The nominal power operation is a function of size and capacity of those devices; if the power is increased, the size of the devices will increase. In spite of the above, the UPS systems are capable to support energy interruptions.Other option
10、developed, which is able to compensate voltage sags is based on PWM AC-AC converter3,4.This solution uses an autotransformer composed by one primary side and two secondary windings presenting a good performance. The system compensates until 50% voltage sags and swells and can continuously shape the
11、output voltage to be sinusoidal (with low THD). Nevertheless, the autotransformer drives all the load power due to it is connected between the load and the AC mains.In this paper a PWM AC-AC converter is presented, in order to compensate voltage sags and swells simultaneously in critical loads, and
12、to maintain a continuous regulation in the output voltage. The system consists in a single-phase AC-AC converter in a matrix arrangement, and energy storage devices are not required. A four step switching technique is used to drive AC-AC converter switches, executing snubber-less operations. The ref
13、erence signal is generated using single-phase d-q theory, obtaining a fast response time and continue regulation, with a high efficiency.One of the advantages in this structure is that the taps of the coupling transformer are not required to change the polarity of the compensation voltage, and the c
14、onverter drives only a percent of the load power.Design, construction and performance are detailed, and several simulations and experimental results obtained with a laboratory prototype are showed to validate the approach. II.CONVERTER ANALYSISThe structure of the proposed approach is shown in Fig.
15、1.Fig.l Conceptual design of the proposed approach Its principal objective consists in supply a compensation voltage in order to keep always the nominal value of the AC mains. When voltage sag occurs, the converter supplies the necessary voltage to maintain regulation in the output voltage. In the s
16、ame way, when voltage swell occurs, the converter reproduces the necessary voltage to cancel out theovervoltage.The topology of the single-phase AC-AC converter is shown in Fig. 2.Fig.2 Single-Phase AC-AC converter The converter has the following elements: Four current and voltage bi-directional swi
17、tching devices connected to the AC mains 5,6,7. Two low-pass filters to reduce the high frequency associated to switching in input current and output voltage8. The AC-AC converter generates a PWM AC voltage to cancel the variations in the AC mains and to compensate the voltage sags and swells.S1,S2,
18、S3 and S4 are used to generate the PWM voltage with the polarityrequired. The adequate operation of the switches allows producing anoutput voltage Vout on phase or 180phase-shifted with respect to Vin. When the utility voltage is at normal level, the switches S3 andS4 are closed (or S1 and S2) and t
19、he output voltage is equal to zero. Whenthere is a voltage sag, the switch S4 is closed, and S1 and S3 are operatedwith a duty cycle D, generating a Vout, for compensation. When there isa voltage swell, the switch S3 is closed, and S2 and S3 generate a Vout,with a polarity inverted for compensation.
20、 Switches S1-S3 and S2-S4never should be closed at the same time in order to avoid a short-circuitin the AC mains side. The switches are driven using a signal pattern which incorporate afour-step switching strategy, reducing the switching losses andeliminating the use of snubbers circuits. III.MODUL
21、ATION TECHNIQUEThe function of the single-phase AC-AC converter is to reproduce avoltage with a peak amplitude lower or equal than the AC mains value. To achieve this, the voltage of the AC mains is modulated by using a switching pattern. The amplitude of the fundamental voltage will depend on themo
22、dulation index of the switching pattern. Fig.3 shows the scheme used to obtain a pulsed pattern. In thiscase, it is used a Digital Signal Processor(DSP) to generate the duty cycle D and to control the PWM of the switching devices. The operation mode of the scheme consists in to obtain a referencesig
23、nal that represents the compensation voltage Vc. In this case, it isused the d-q theory to transform the AC mains voltage in a DC signal. Thed component is compared with the nominal peak voltage of the AC mainsVnom, to obtain the Vc. (The d-q theory is explained in section IV).Fig.3 Scheme to genera
24、te the control pulsesThe C(s)controller calculates the duty cycle D from Vc and the Control logic determines which of the AC-AC converter switches will be turned on and which be turned off(S1,S2,S3 or S4).The switching pattern is obtained when D and a saw-tooth signal generated by the DSP are compar
25、ed.A. Switching pattern analysisIt is possible to determine the harmonic content of the converteroutput voltage Vpwm from the analysis of the switching pattern. The sampling process theory is used to know the amplitude and frequency of each harmonic generated in the converter output. The representat
26、ion of the switching pattern in Fourier series is given by (1): (1)Expressing (1)in complex form: (2)The Fourier complex coefficients of the switching pattern are calculated using equation (3). (3)Considering that the switching pattern has an amplitude Vx and that the pulse width is x: (4) Equation
27、(5) permits to know the amplitude and frequency of the harmonics and therefore, to propose the cut-off frequency of the low-pass filters. In this case, it is just necessary to multiply the magnitude of (4) by the amplitude of the AC mains. (5)where:Ah = Harmonics magnitude.A = AC mains voltage ampli
28、tude.Vx = Commutation pattern amplitude.x = Pulse width.T = Commutation pattern period.m = 0,1,2,3,.ws = Switching frequency.Once calculated the amplitude and frequency of the harmonics, the cut-off frequency of the low-pass filters is selected. It is noted that the output voltage in the AC-AC conve
29、rter depends on the average duty cycle D: (6) In the same form, D is related with the compensation and regulation of the load voltage: (7)The duty cycle is affected by the relation of transformation n of the coupling transformer selected. In this case, it is chosen a buck transformer, such that curr
30、ent of the AC-AC converter will be lower than current flowing through the AC mains. The equation that determines D valuein open loop is as follows: (8)Where Vnom is the peak of reference voltage and VdDQ is the peak voltage related to the single-phase d-q transformation of Vin. Equation(8) shows tha
31、t VnomVdDQ for a voltage sag and Vnom VdDQ及电压膨胀Vnom VdDQ。这允许D保持在1 y-1。B、四步切换技术四步切换技术提供了从一个双向开关电流安全过渡的感性负载，并确保安全的PWM操作。这种技术独立控制开关装置内的每个双向开关元件上的输入，而确定电压和负载电流的极性。在交流-交流转换器，S1的运行状态情况下，S2和S3和S4将取决于输入电压的极性，实现的补偿（骤降或骤升）和开关器件的控制信号。电压骤降的操作序列图如图4所示。为了补偿骤升它需要改变S3的 S1和S2的S4。尽可能多模式切换为骤升骤降轮流两种形式交替开关设备来提供一个安全的电感性负
32、载电流，即过渡，S3和S4被用于第一个脉冲控制下和S1和S2被用于第二个脉冲控制下。上述保证开关转换和传导松动是平衡的。图4 电压骤降状态机表示 图5显示了交流- 交流转换器的单相操作顺序。 图5 交流-交流转换器的单相操作顺序现场可编程门阵列（FPGA）被用于确定状态机，并产生一个死区时间在转身之间为双向关闭开关。FPGA允许减少数字信号处理器的处理时间。在这种情况下，DSP仅仅产生电压参考和开关模式。四、参考发电单相d-q理论是用来实现补偿处理，并选择占空比。d- q理论转化为直流基频信号组件，允许快速的瞬态响应补偿电压骤降和骤升。为了实现单相d-q变换，一个虚正交系统的概念被引入。该主要
33、思路是虚构的正交变换保持完全一样的系统组件和参数，始终保持实际组件9的90相移。在本文中，它是采用假想概念的建议10，正交电路中有一个90滞后。图 6显示了真实和虚构的正交变换用于确定来自交流电源的d-q变换。图6 实部和虚变量从实部和虚电路矩阵变换为d- q旋转框架为： (9)其中：Vd = 实际电路的电压Vq = 假象的电压该d-q变换提供了有关活性成分补偿的信息。作为一个例子，正弦信号Vpsin（wt）（无谐波含量）的Vd和Vq的组件是“Vp”和“0”。 五、耦合变压器设计 在图1中，补偿电压测量了负载：Vo = Vin + Vcon (10)使用电器系统方程和考虑的一个因素，就是当电压
34、骤降或膨胀时，会呈现以百分比幅度的速度递增或递减： （11）图7显示了方程（11）所得的a和n的不同值。人们注意到，每个n有两个a值；此值可能产生最高补偿的百分比来获得转换器。图7 不同值a和n用来设计耦合变压器表1.最高补偿百分比取决于变换关系六、闭回路分析一个闭环方案被使用，以减少参考电压和转换器产生的电压之间的差异。在这种情况下，交流电源瞬时振幅是时变直流信号。鉴于以上原因，必须要有一个良好的电压调节，建议用一个比例-积分控制器，改善了单相交流- 交流变换器的动态响应。图8给出了单相交流- 交流变换器的闭环框图。 图8 单相交流- 交流变换器的闭环框图PI控制器的传递函数为： （12）七
35、、模拟结果为了验证单相交流 交流转换器的运行，转换器的几个模拟开环和闭环被运行。这些模拟被用于一个5KW负荷带有127 VRMS。60Hz的额定电压。换向频率等于20 kHz时，输出低通滤波器的918 Hz和截止频率选定的转换关系为3:1，被使用的电动方案在图1中被显示。图9显示了开环仿真结果当电压骤升发生时。波形（b）是交流电源的电压。当产生的电压保持其标称值时，该转换器输出电压Vout=0。在时间P，当有振幅干扰时，（对应电压膨胀）转换器再现了必要组成部分，以补偿负载电压。该系统快速响应速度如下。图9 模拟结果的AC - AC变换器（从180至220 高峰变化）。（a）占空比D，（b）交流
36、电源，（c）转换器产生的补偿电压，（d）负载电压。在这种情况下，干扰P造成的短暂T的持续时间是最低限度的。在交流电源出现骤升和骤降时，图 10显示了开环模拟结果。图10 交流 交流变换器的仿真结果（从220到150高峰变化）。（a）占空比D，（b）交流电源，（c）转换器产生的补偿电压，（d）负载电压闭环仿真结果如下。当出现电压骤升时，转换器的反应时间如同11所示。可以看出，转换器补偿大约在两个周期。图11闭环仿真结果（交流电源的变化从180至220高峰）。（a）交流电源，（b）转换器产生的补偿电压，（d）负载电压。考虑到交流电源谐波含量的闭环仿真如图12所示。图12 闭环仿真结果（交流电源的变
37、化从220 至150高峰）。（a）交流电源，（b）转换器产生的补偿电压，（c）负载电压。交流 交流转换器能够重现必要的电压，以补偿负载电压，即提出了一种交流电源的谐波失真。八、实验结果补偿电压骤降和骤升的原型被实施以验证分析表示。原型是一个单相设备，5KW容量，127V，60Hz。它能够弥补高达25的电压骤降和50的电压骤升。图13显示了交流- 交流变换器的PWM电压。在这种情况下，交流电源的VRMS等于100V和需要补偿。图13 交流-交流变换器的实验结果（a）交流电源，（b）交流-交流PWM电压值得注意的是单相交流- 交流变换器再现脉冲电压VPWM，而四步调制技术为输入和输出电流提供一个安
38、全过渡。参考电压，转换器的过滤输出电压和开环交流电源电流如图14所示。一个1kVA的电阻负载和单相交流-交流变换器的输出连接。图14 交流-交流变换器的实验结果(a)交流电源，（b）转换器的过滤输出电压，（c）交流电源电流图15显示了稳定的结构补偿,交流电源中存在15的电压骤降。波形（a）是交流电源的电压，（b）是转换器产生的补偿电压，（c）是输出电压。 在补偿期间，单相交流-交流转换器再现了所需的电压，以维持负载电压。图15 稳态补偿结果（a）交流电源，（b）转换器产生的补偿电压，（c）输出电压图16显示由DSP产生的控制信号S1A和S1B以补偿电压骤降。在双向开关的打开和关闭之间产生由FPGA产生的死区时间，该时间等于1us。图16 DSP产生的控制信号(a)占空比，（b）交流电源极性，（c）S1A开关装置，（d）S1B开关装置九、结论本文提出了一种拓扑结构以补偿电压骤降和电压骤升，同时建议在关键负载保持输出电压的连续调节。该方案采用矩阵安排中的单相交流- 交流转换器，它的优点是能源存储设备不是必需的。四步切换技术被用来驱动交流-交流转换器开关来执行无缓冲操作。仿真和实验结果证实了单相交流-交流转换器的良好性能和显示了补偿的快速响应。
