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1、无差拍控制在光伏并网发电系统中的应用张 超 何湘宁（浙江大学电力电子研究所 杭州 310027）摘要：光伏发电系统输出功率的大小和质量易受外部环境的影响，为了使系统能够最大限度的输出高质量的电能，就需要一种快速的电流控制方法控制逆变器工作。本文在分析了无差拍电流控制方法工作原理的基础上，给出参考电流的获取及占空比的计算过程，并将无差拍电流控制应用到两级式单相光伏并网发电系统逆变器的控制中。实验结果表明：该方法具有良好的稳态特性和动态特性。关键词：光伏；并网；电流控制；无差拍控制中图分类号：TM92 文献标识码：AImplementation of a deadbeat current cont
2、roller for Photovoltaic Grid-Connected InvertersZhang Chao， Wang Zhangquan，Jiang Yanjun， He Xiangning（Zhejiang University Hangzhou 310027 China）Abstract：To meet the requirement of the output power of photovoltaic grid-connected power generation system, the inverter should be controlled according to
3、the output power of PV arrays. In this paper, the deadbeat current control is analyzed in detail. The way how to get the reference current and the duty of converter is presented. Simulation and experimental results show the output power of PV inverter has good quality with the deadbeat current contr
4、ol.Key Words：photovoltaic; grid-connected; current control; deadbeat control1引言目前，光伏发电系统主要有独立运行模式和并网发电模式两种。光伏并网发电系统与独立发电系统相比具有造价低、输出电能稳定的优点，因此具有广阔的发展前景。根据控制方式的不同，可将逆变器的控制分为输出电压反馈控制和输出电流反馈控制两种。由于电网巨大的平衡作用，光伏并网发电系统中的逆变器再与电网并联工作时输出电压控制方法抗干扰能力较弱，且对外部环境变化响应的速度慢，因此光伏并网发电系统普遍采用逆变器输出电流控制的方法1, 2。在目前已有的电流控制方法
5、中，无差拍控制方法具有对外部干扰响应速度快、控制过程无过冲的特点。因此本文将其应用到两级式单相光伏并网发电系统逆变器的控制中，以提高逆变器抗干扰能力。仿真和实验结果表明，无差拍电流控制方法可在各种环境下稳定工作，提高了系统输出电能的质量。2无差拍控制在光伏逆变器中的应用2.1 无差拍工作原理无差拍控制是一种数字化PWM控制方法，它具有动态性能好、控制过程无过冲的特点。由于其具有非常快的暂态响应，因此非常适用于受外部多变环境影响的光伏发电系统逆变器的控制。无差拍控制的基本思想是根据含有滤波器的逆变系统的状态方程和输出的反馈信号推算出下一个采样周期逆变器的开关时间，即逆变器下一个周期开关器件的脉宽
6、控制量T（k1）是根据逆变器当前时刻的状态量和下一个采样时刻逆变器输出的参考电流计算出来。由以上分析可以得出：如果想得到K1时刻的脉宽控制量T（k1），必须得到时刻K时逆变器输出状态和下一个时刻逆变器的参考信号。2.2逆变器脉宽的计算假设逆变器工作时，逆变器输出参考电流为已知，逆变器输出的电感电流可以通过采样及时得到，且并网工作时图1中滤波器电容中电流与逆变器输出的电流相比可以忽略不计，那么可得到公式1：(1)式中各项参数定义如下：iL(k)：采样周期k时刻电感L的采样电流Ts：功率器件开关周期L：逆变器输出滤波器电感：采样周期k时刻逆变器输出电压平均值图1.光伏发电系统拓扑结构：采样周期k时
7、刻电网电压平均值RL：逆变器滤波器等效电阻：采样周期k时刻电感L平均电流由于逆变器输出滤波器等效电阻较小，因此RL可忽略不计，公式1可转换为：（2）经过移项，式2可变为：（3）由于逆变器与电网并连工作，因此可知逆变器的输出电压等于市电，有公式4存在：（4）在采样周期区间平均电压为：（5）综合上述公式可以得出：逆变器在k1时刻的输出平均电压可根据时刻k时电感电流iL(k)、电网电压及参考电流iL(k+1)计算得出。由于逆变器输出电压和直流母线电压Vd成比例关系，因此逆变器功率器件占空比为：（6）由式6即可得到逆变器下一个工作周期k1时刻的占空比D（k1），将该占空比控制逆变器开关器件就可以实现参
8、考电流iL(k+1)的输出，从而实现逆变器的无差拍控制3, 4。3.两级式单相光伏并网发电系统本文采用的光伏并网发电系统主电路由光伏器件、BOOST电路、全桥逆变器和升压变压器构成，如图1所示。光伏发电系统并网运行过程中，BOOST电路根据光伏器件的输出电压、输出电流调整BOOST电路的占空比，使系统在各种环境下输出最大功率。同时系统控制逆变器使其输出电流与电网保持频率和相位的一致，以免出现环流故障5。由于本文所用光伏系统升压比较小，因此逆变器输出电压还需通过升压变压器将其升压以满足并网工作的要求，同时满足电气隔离要求。光伏并网发电系统工作过程中，光伏器件输出功率是随外部环境变化而改变的，因此
9、必须根据光伏器件输出功率及时调整逆变器输出功率，以避免出现功率不平衡现象，影响系统的工作。通过上文对无差拍控制工作原理分析可知，为了获得逆变器下一个采样周期的脉宽控制宽度，就必须知道逆变器下一个周期的参考电流信号。无差拍电流控制所需要的参考电流计算方法如图2所示：图中UPV为光伏器件的输出电压、IPV为光伏器件的输出电流、Ugrid为电网电压的有效值。在系统运行过程中，光伏器件的输出功率PPV可由UPV、IPV得到，扣除电路中的损耗后既是逆变器理论输出功率Pout，Pout除以电网电压有效值Ugrid即得到逆变器参考控制电流有效值IREF，IREF再根据电网相位关系即可得到逆变器输出电流参考信
10、号iREF，该电流即为无差拍控制中所需的参考电流iL(k+1)。得到逆变器下一个k1时刻参考电流iL(k+1)后，即可利用上述公式得到逆变器下一个开关周期的脉宽时间。图2. 光伏发电系统参考电流获取原理图4仿真与实验根据上述分析，将无差拍电流控制方法对光伏发电系统逆变器的控制进行仿真研究和实验验证。仿真和实验所用光伏器件的最大输出功率200W，开路电压60V，系统所用电路如图1所示。无差拍电流控制基于TI公司TMS320F2407A DSP控制芯片实现，系统对光伏器件的输出电压、输出电流、逆变器输出电感电流及电网电压采样，通过上述公式计算得到逆变器功率器件k1时刻占空比，如图3系统控制框图所示
11、。图3 无差拍控制原理框图图4是日照稳定情况光伏系统并网工作时逆变器输出电压和输出电流的仿真波形。从图中可以看出逆变器输出电流与输出电压同相位，输出功率因数为1。图5是日照变化情况下光伏器件输出电压和电流的波形，由于光伏器件重新工作在最大输出功率需要一定的时间，因此逆变器输出电流随光伏器件输出功率增加而增加。图6为逆变器与电网并联工作投放过程中逆变器的输出电压与输出电流波形。该波形表示逆变器在与电网并网工作前后输出电压变化不大，基本无环流。图7是外部环境稳定情况下逆变器输出电流和电网电压的波形，从图中可以看出电流波形基本稳定，且保持和电网电压的同步。上述仿真和实验表明：在无差拍电流反馈控制下，
12、光伏并网发电系统逆变器能可靠的实现与电网的并联工作，它可以在日照变化频繁的情况下仍能保证光伏发电系统输出电能的质量。图4. 日照稳定情况下逆变器仿真输出波形图5.日照变化情况下逆变器仿真输出波形图6. 并网过程逆变器电压、电流波形图7. 逆变器输出电压、电流波形（稳定环境）图8. 逆变器输出电压、电流波形（日照上升）5结论在光伏并网发电系统中，由于外部环境的变化会影响到输出电能的质量，因此需要控制逆变器使其输出功率始终随光伏器件的输入功率而变化。无差拍电流控制方法利用光伏发电系统已有的数据通过计算得到逆变器下一个工作周期开关信号的控制量，因此能根据外部环境变化及时调整逆变器的输出功率。实验表明
13、，该方法具有良好的稳态性能和动态响应，能够有效提高了系统抗干扰的能力，使输出电能质量稳定。参考文献1汪海宁. 光伏并网功率调节系统及其控制的研究：博士学位论文 .合肥工业大学, 20052Malesani L, Tomasin P. PWM current control techniques of voltage source converters-a survey. Industrial Electronics, Control, and Instrumentation, 1993. Proceedings of the IECON 93., International Conferenc
14、e on, 1993, 1993:67067523Hung G K, Chang C C, Chen C L. Analysis and implementation of a delay-compensated deadbeat current controller for solar inverters. Circuits, Devices and Systems, IEE Proceedings, 2001,148(5):2792864Hua C, Hoft R G. High performance deadbeat controlled PWM inverter using a cu
15、rrent source compensator and nonlinear loads. Power Electronics Specialists Conference, 1992. PESC 92 Record., 23rd Annual IEEE, 1992, 1992:44345015王飞, 余世杰, 苏建徽等. 采用最大功率点跟踪的光伏并网逆变器研究. 电力电子技术, 2004, 38(5):45作者简介：张超（1973-），男，江苏人，博士生，研究方向为光伏并网发电及相关技术研究通讯方式：浙江杭州浙江大学玉泉校区电机工程楼402室 张超（收） 310027电话：0571.8795
16、2416Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through
17、 the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky,
18、 and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot t
19、apping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of s
20、pace - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straigh
21、t line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that
22、 same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry clea
23、ning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission contro
24、l as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited
25、cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial air
26、liners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll b
27、ack the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like divi
28、ng into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the mo
29、re dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main
30、chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgart
31、ner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
