光伏发电逆变器并联技术研究摘要：文章主要是分析了三相逆变器控制技术，在此基础上讲解了逆变器并联控制技术，以及逆变器的并联控制，望可以为有关人员提供到一定的参考和帮助。
关键词：三相逆变器；环流；模糊控制1前言目前，我国电力电子技术快速发展，同时也推动了光伏发电技术的发展进程，三相逆变器是光伏发电系统中重要的组成部分，并有着十分重要的作用。
为此文章对三相逆变器控制技术展开了研究和探讨。
2三相逆变器控制技术从传统的集中供电到分布式供电的交流供电系统发展中，逆变器并联运行的控制技术是必不可少的关键技术。
传统的集中式电源采用集中式逆变器，由于成本高，体积大，安装难度大，运行可靠性差等原因，该方法的实用性越来越差。
只要出现故障点，整个系统就会瘫痪。
在研究并联系统的控制技术时，首先要研究各电源控制技术的模块化供应，模块化功率控制技术可以使系统具有更好的稳态性能和动态性能。
稳态性能主要体现在各个电源电压幅值和其稳定性、准确性上，第二阶段动态该模块的性能主要体现在输出电压、电流谐波含量（THD）和负载上突变。
2.1数字PID控制数字PID控制具有操作简单、参数调整方便等优点，在工程领域得到了广泛的应用。
早期的逆变器只能采用模拟PID控制，系统测试采用电压单环反馈控制，稳态和动态性能较差，非线性负载系统无法得到有效控制。
在反馈中引入滤波电感或滤波电容，无法有效控制系统，但使用模拟电路来实现这一功能会更加困难与复杂，数字信号处理芯片的出现很快解决了这一问题，使控制器的设计更加简单方便。
2.2重复控制重复控制是一种基于内模的控制方法理论。
原理是将作用于系统外部信号的动态模型嵌入控制器中，形成高精度的控制系统。
因此，只要使用预定频率的周期信号，系统就可以随时跟踪周期信号时间。
如果将其添加到控制器的前向通道中，可以反复控制和使用信号。
系统模型越精确，带有无差拍控制的逆变器的输出功率质量越高，总谐波含量越低，动态特性越好。
因此，在实际控制中，一旦受控对象的数学模型不准确，输出将变得不稳定。
英文资料原文来源: 出自JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA,VOL.7,NO.3, SEPTEMBER 2009Decoupling Control Strategy for Single Phase SPWM ParallelInvertersShun-Gang Xu,Jian-Ping Xu,and Tai-Qiang CaoAbstract: A decoupling control strategy of inverter parallel system is proposed based on the equivalent output impedance of single phase voltage source SPWM (sinusoidal pulse width modulation) inverter. The active power and reactive power are calculated in terms of output voltage and current of the inverter, and sent to the other inverters in the parallel system via controller area network(CAN)bus. By calculating and decoupling the circumfluence of the active power and reactive power, the inverters can share load current via the regulation of the reference-signal phase and amplitude.Experimental results of an 110V/2kV A inverter parallel system show the feasibility of the decoupling control strategy.Index Terms-CAN bus, current sharing, inverters, parallel operation.1. IntroductionParallel operation of inverters is an efficient way to enhance the capacity and reliability of inverter systems. The key issue of parallel operation is the distribution of the load current. In an inverter parallel system, the amplitudes and phases of output voltages of all inverters should strictly equal to each other to guarantee that each inverter shares the same load current. Otherwise, the current circumfluence and overload of some inverters in the inverter parallel system may exist. The current circumfluence may also decrease the efficiency and reliability of the inverter parallel system.There are various techniques for the control of inverter parallel operation. Among these techniques, central control and master-slave control are easy to implement and have good current-sharing performance. However, these two control strategies work at the cost ofsystem reliability because of conjunction operation among inverters.In instantaneous-current control of inverter parallel system, there is a current bus to share the current signal among inverters and the instantaneous circumfluence is used to regulate the output current, each inverter has good transient performance and the parallel system has good current sharing performance. However, its analog signal communication is easy to be disturbed and the signal isolation is complicated, which decrease the reliability of the parallel system.Independent control without interconnection droops the output voltage and frequency of inverters, the link among inverters is only via power lines. Thus fewer interconnections are needed and the reliability of inverter parallel systems is improved. Traditionally, this control strategy assumes the output impedance of inverters is mainly inductive due to high inductive component of the line impedance and the large inductor filter. Thus active power-frequency droop and reactive power-voltage droop schemes are adopted. However, this is not always true as the closed-loop output impedance also depends on the control strategy, and the line impedance is predominantly resistive for low voltage cabling. Thus, there is coupling relationship between output active/reactive power and frequency/amplitude of the output voltage. Traditional independence control may lead to instability of inverter parallel systems.In this paper, a decoupling control strategy for inverter parallel systems is proposed. The active power and reactive power of inverters in a parallel system are calculate by their corresponding output voltage and output current, and the output power information is shared by controller area network(CAN)bus communication. Then the active and reactive power circumfluence of each inverter is calculated and applied to regulate its corresponding output voltage and output frequency by decoupling of the power circumfluence, respectively. Thus, the proposed decoupling control strategy overcomes the disadvantages of inverter parallel systems controlled by independence control without intercommunication and instantaneous-current control. The inverter parallel system implemented by this strategy can achieve better current-sharing performance, good stability, and good reliability.2. Analysis of Single Phase PWM InverterDual closed-loop feedback control is usually adopted to control single phase inverters.Fig.1 shows a dual closed-loop feedback control scheme with an inductor-current inner loop and a capacitor voltage outer loop. The capacitor-voltage outer loop adopts proportion-integral control to regulate output voltage, where Pv k and Iv k are proportionalcoefficient and integral coefficient, respectively. The inductor-current inner loop uses proportional control to enhance the transient response of the inverter, Pi k is a proportionalcoefficient.In Fig.1,the power stage includes a full-bridge configuration and an L-C filter,in V is DC link voltage, 1s to 4s are power switches, L and C are filter inductor and capacitor,ref v is a sinusoidal reference voltage signal of the inverter,L r is the sum of inductor equivalent series resistance, switch on-resistance, and connection-line resistance. According to nonlinear control and feedback linearization theory, open-loop averaged output voltage can be characterized by2000002L L in d v d v d i LC r C v L r i V u dt dt dt〈〉〈〉〈〉++〈〉++〈〉=〈〉 (1) where x 〈〉means the average value of x over one switching cycle and u is the control variable, which can take the values 1,0,or-1,depending on the state of switches 1S ,2S ,3S and 4S .For the dual closed-loop feedback control inverter shown in Fig.1,the controller can be characterized by()()000Pv Iv in ref Pi k s k V u v v i Cs v k s +⎛⎫〈〉=-〈〉-〈〉-〈〉 ⎪⎝⎭(2) From (1) and (2) ,the dynamic characteristics of the closed-loop output voltage can be expressed in Laplace domain as()()()()()032203211Pv Pi Pi Iv ref L Pi Pv Pi Pi Iv L Pi L Pi Pv Pi Pi Iv k k s k k v v LCs r C k C s k k s k k Ls r k s i LCs r C k C s k k s k k +=+++++++-+++++ (3)The single phase dual closed-loop inverter can be modeled by two terminal equivalent circuits as00()()ref v G s v Z s i =- (4)()()32()1Pv Pi Pi Iv L Pi Pv Pi Pi Ivk k s k k G s LCs r C k C s k k s k k +=+++++ (5) ()()()232()1L Pi L Pi Pv Pi Pi IvLs r k s Z s LCs r C k C s k k s k k ++=+++++ (6)Fig.1.Block diagram of Single phase dual closed-loop inverter.Frequency (rad/sec)(a)Frequency (rad/sec)(b)Fig.2.Bode diagram of the voltage gain and the equivalent outputimpedance of the dual closed-loop inverter:(a)magnitude vs. frequency and(b)phase vs.frequency.Fig.3.Inverter equivalent circuit.where ()G s is the voltage gain and ()Z s is the equivalent output impedance. The bode diagram of ()G s and ()Z s are shown in Fig.2.From (6), we can know that the equivalent output impedance is closely related to the parameters of the output filter and the feedback control parameters. Let R be the resistive component and X the inductive component of equivalent impedance Z(s).The inverter equivalent circuit can be shown as Fig.3.When 500L H μ=, 10C F μ=, and 0.1L r =Ω,the relations between the impedance ratio R X and the control parameters Pv k ,Pi k , and Iv k are shown in Fig.4.Fig.4.Relations between the impedance ratio R/X and control parameters:(a)R/X vs.Pv k ,(b)R/X vs.Pi k ,and(c)R/X vs.Iv k .From Fig.4, the equivalent output impedance trends to be resistive when PI control parameter Pv k and Pi k are increasing, and trends to be inductive when PI control parameter Iv k is increasing. In the design of dual closed-loop single phase inverter, the PI control parameters must be chosen carefully as they affect both the transient characteristics of the inverter and the current sharing performance of the inverter parallel system.3. Analysis of Inverter Parallel SystemBased on above discussion, the equivalent circuit of inverter parallel system of two inverter modular can be given as Fig.5, where 0E ∠is load voltage, 1111()ref E G s v δ∠=and 111()R jX Z s +=are the output voltage and equivalent output impedance of inverter 1,2222()ref E G s v δ∠=and 222()R jX Z s +=are the output voltage and equivalent output impedance of inverter 2.In the inverter parallel system, the active output power and the reactive output power of the inverter 1 can be expressed as:()()0111101111221101111111012211cos sin cos sin E R E R E X E P R X E X E R E X E Q R X δδδδ-+=+--=+ (7)Due to small difference the phase of output voltage between individual inverters, we can assume that sin ,cos 1i i i δδδ≈≈,12R R R ==and 12X X X ==.Therefore, we have21010101222101010122RE E E E X RE P R X XE E E E R RE Q R X δδ+-=+--=+ (8) Similarly for the inverter 2, we have22020202222202020222RE E E E X RE P R X XE E E E R RE Q R X δδ+-=+--=+ (9)Fig.5.The equivalent circuit of the parallel system of two inverter modular.Fig.6.Structure of parallel operation system.From above analysis we can know that the active/reactive power is related to the amplitude and phase of voltage, and the influence of output voltage amplitude and phase on active and reactive power is closely related to the inductive component and resistive component of the output impedance of the inverter. When resistive component is dominating, active power is mainly depended on the amplitude of output voltage, and reactive power is mainly depended on the phase of the output voltage, and vice versa.4. Control DesignFig.6 shows the structure of inverter parallel system. The digital signal processor TMS320F2812 is adopted in the proposed parallel system; the inverters decouple the active power and the reactive power circumfluence to regulate the amplitude and the phase of the sinusoidal reference voltage signal. Each inverter adopts instantaneous voltage and instantaneous current dual closed-loop feedback control. The inverters can operate not only independently but also in parallel. The CAN bus transfers information of the active power and the reactive power among the inverters.Fig.7.Decoupling control strategy.Fig.8.Experiment wave of inverter parallel system: (a)steady current wave,(b)current wave with a sudden increasing load, and (c)current wave with a sudden decreasing load.In the parallel operation system, the differences between the output active power and reactive power of individual inverter lead to the asymmetry of output current among the inverters. The relation between the active/reactive power and output voltage amplitude/phase is given by (8).In the single phase SPWM inverter which adopts dual closed-loop feedback control, output voltage tracks the amplitude and phase of the sinusoidal reference voltage signal. Thus, the output active and reactive power of the inverter can be controlled by the amplitude and phase of the reference voltage signal. If output active and reactive power equal to each other in the parallel system, the inverters can share the load current well.In the inverter, the output voltage and output current are sampled by digital signalprocessor (DSP) for the calculation of output active and reactive power. All of the inverters share the active and reactive power by the CAN bus, each inverter calculates its corresponding active power circumfluence P∆.These∆and reactive power circumfluence Q circumfluence signals are decoupled to regulate the amplitude and the phase of reference voltage signal as shown in Fig.7.Therefore, each inverter outputs the same active power and reactive power, and the inverters can share the load current in the system.5. Experiment ResultsTwo 2 KV A inverters are used in our experiment. In the parallel system, the output filter inductance is 500μH,the filter capacitance is 10μF,the DC input voltage is 200 V DC, and the AC output voltage is 110 V with 50 Hz. 6N137 is used to isolate the signal between the inverters and the CAN bus, the baud rate of CAN bus is set to 1 Mbps. The closed-loop control, decoupling arithmetic and the SPWM control signal are realized by TMS320F2812 digital signal processor. Experiment results of the inverter parallel system are shown in Fig.8.In the steady state, the two inverters share the current very well and during transient under sudden load variation, the inverter parallel system still can work well. This indicates that excellent load sharing is achieved between these two inverters. 6. ConclusionsThis paper proposes a decoupling control strategy for inverter parallel systems. Theoretical analysis and experimental results verify the feasibility of the proposed control strategy. This control strategy has the following characteristics:1)inverters can work independently or in parallel;2)CAN bus is used for the inverter parallel system; 3)the inverter parallel system supports hot-s operation and has good reliability and expansibility. 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第一章绪论1.1 光伏发电背景与意义作为一种重要的可再生能源发电技术，近年来，太阳能光伏(Photovoltaie，PV)发电取得了巨大的发展，光伏并网发电已经成为人类利用太阳能的主要方式之一。
目前，我国已成为世界最大的太阳能电池和光伏组件生产国，年产量已达到100万千瓦。
但我国光伏市场发展依然缓慢，截至2007年底，光伏系统累计安装100MWp，约占世界累计安装量的1％，产业和市场之间发展极不平衡。
为了推动我国光伏市场的发展，国家出台了一系列的政策法规，如《中华人民共和国可再生能源法》、《可再生能源中长期发展规划》、《可再生能源十一五发展规划》等。
这些政策和法规明确了太阳能发电发展的重点目标领域。
《可再生能源中长期发展规划》还明确规定了大型电力公司和电网公司必须投资可再生能源，到2020年，大电网覆盖地区非水电可再生能源发电在电网总发电量中的比例要达到3％以上。
对于这一目标的实现，光伏发电无疑会起到非常关键的作用。
当下，我国地方和企业正积极共建兆瓦级以上光伏并网电站，全国已建和在建的兆瓦级并网光伏电站共11个（2008年5月前估计），典型的如甘肃敦煌10MW 并网光伏特许权示范项目，青海柴达木盆地的1000MW大型荒漠太阳能并网电站示范工程，云南石林166MW并网光伏实验示范电站。
可以预见，在接下来的几年里，光伏并网发电市场将会为我国摆脱目前的金融危机提供强大的动力，光伏产业依然会持续以往的高增长率，光伏市场的前景仍然令人期待。
光伏并网发电系统是利用电力电子设备和装置，将太阳电池发出的直流电转变为与电网电压同频、同相的交流电，从而既向负载供电，又向电网馈电的有源逆变系统。
按照系统功能的不同，光伏并网发电系统可分为两类：一种是带有蓄电池的可调度式光伏并网发电系统；一种是不带蓄电池的不可调度式光伏并网发电系统。
典型的不可调度式光伏并网发电系统如图1-1所示。
图1-1 不可调度式光伏并网发电系统从图1-1中可知，整个并网发电系统由光伏组件、光伏并网逆变器、连接组件、计量装置等组成，对于可调度式光伏并网发电系统还包括储能用的蓄电池组。
