基于模糊系统的光伏系统最大功率点跟踪

1、Fuzzy System Based Maximum Power Point Tracking for PV System基于模糊系统的光伏系统最大功率点跟踪Bogdan M.Wilamowski and Xiangli LiUniversity of Idaho, Boise Graduate C and AbstractMaximum power point tracking for PV systems traditionally uses either perturbation and observation method

2、 or incremental conductance method. Both methods require modulation of the output voltage and this leads to significant power loss. In this paper, a method, which senses output circuit voltage and short circuit current and use the above two parameters for optimum control with a fuzzy controller, is

3、introduced. The short circuit current of PV cell represent illumination, and the output circuit voltage carry on information about the temperature. 摘要 光伏系统最大功率点跟踪通常使用扰动观察法或电导增量法，两种方式都需要调整输出电压这将导致显著的能量损失。在本文中提出一种方法，该方法测量输出电路的电压和短路电流并使用上述两个参数通过模糊控制器实现最优控制。光伏电池的短路电流反映光照，输出电路的电压代表温度信息。I. Introduction Wi

4、th the industrial development, the problem of energy shortage is more and more aggravating. The Photovoltaic (PV) system technologies are rapidly expanding and have increasing roles in electric power technology and regarded as the green energy of the new century1-2.I引言 随着工业的发展，能源短缺的问题越来越严重，作为新世纪的绿色能

5、源，光伏发电系统在电力技术方面迅速扩大和日渐作用1-2。 As the power supplied by solar arrays depends on the light illumination intensity, temperature and array voltage. It is necessary to track the maximum power of the solar arrays2. Some paper had proposed different maximum power point (MPPT) control methods in the past yea

6、rs. Two methods are proposed in this paper to track the maximum power point and use the fuzzy system to control the circuit to achieve the maximum power point and increase the efficiency of the PV system3-6. 由于太阳能电池板提供的功率决定于光照强度、温度和阵列电压，因此跟踪太阳能电池板的最大功率是非常有必要的。在过去的几年中，一些论文已经提出不同的最大功率点控制方式。本文提出了两种跟踪最大

7、功率点的方法，该方法应用模糊控制系统控制回路实现最大功率点从而增加光伏系统的效率。II. Operation Principle of Solar CellSolar array characteristic profoundly influences the converter and control system. A solar cell is a nonlinear device and can be represented as a current source model as shown in Fig.1.Fig.1 Simplified equivalent circuit o

8、f a solar cell （1） （2） （3） （4） （5）II 太阳能电池的工作原理太阳能电池的特点很大程度上影响变换器和控制系统，太阳能电池是一个非线性的装置，可以被看作是电流源模型，如图1所示。图1 太阳能电池的等效简化电路 （1） （2）（3） （4） （5） Whereis the light generated current, is the diode reverse saturation current, is the electronic charge,is the reference temperature,is the Boltzmann constant,is

9、the diode reversal current ,is the bad gap energy of the cell semiconductor,is the series resistance. 其中，为光照产生的电流，为二极管的反向饱和电流，为电荷，为基准温度，为波尔兹曼常数，为二极管的反向电流，为半导体单元的损坏能量，为串联电阻。The solar cell I-V characteristics are plotted in Fig.2 for different illumination levels. The P-V characteristics are plotted i

10、n Fig.3 under different illumination condition, and Fig.4 show the P-V characteristics for different temperature.Fig.2 I-V characteristics of PV system图2描绘了不同光照强度下太阳能电池的I-V特性曲线。图3描绘了不同光照强度下的P-V特性，图4给出了不同温度下P-V特性。图2 光伏系统的I-V特性Fig.3 P-V characteristics of PV system at different light intensityFrom Fig

11、.3, it is observed that the output characteristic of a solar cell is non-liner and affected by the light intensity, temperature and load condition. Each curve has a maximum power point condition (MPP), which is the optimal operation point for the efficient use of the solar array. As shown in Fig.3,

12、if the real operating point differs from the optimum operating point, then power loss should be caused in that circuit. It is necessary that maximum power always would be extracted at any condition in order to eliminate this power loss4. 图3 不同光照强度下光伏系统的P-V特性 从图3可以看到，光伏电池的输出特性是非线性的并且受光照强度、温度以及负载情况的影响

13、。每条曲线都有最大功率点的状态，这是有效利用太阳能阵列的理想操作点。如图3所示，如果实际操作点与理想的操作点不同，那么在电路中就会引起能量损耗。因此为了消除功率损耗在任何条件下取的最大功率是必须的。Fig.4 P-V characteristics of PV system at different temperatureFrom Fig.3, it is observed that when the light intensity increases, the output power will also increase. From Fig.4, it is observed that w

14、ith the temperature increasing, the open circuit voltage and maximum power will fall.图4 光伏系统在不同温度下的P-V特性曲线 如图3所示，当光照强度增加时，输出功率增加。如图4所示，随温度的增加开路电压和最大功率降低。III Current Methods to Tracking Maximum Power Point In order to extract the maximum power from the solar array, it is necessary to operate the sola

15、r array at the maximum power point (MPP). Many methods for tracking maximum power point have been proposed. So far, two algorithms often used to achieve the MPPT are: (1) Perturbation and observation method; (2) Incremental conductance method.2,5,6III 当前实现最大功率跟踪的方法 为了得到太阳能电池的最大功率，需要操作太阳能电池阵列工作在最大功率点

16、。而且已经提出了许多跟踪最大功率的方法。到目前为止，实现MPPT的经常使用的两种方法是：(1) 扰动观察法；(2) 电导增量法。2,5,6A. Perturbation and observation methodPerturbation and observation (P&O) method 5 has a simple feedback structure and fewer measured parameters. It operates by periodically perturbing (incrementing or decreasing) the array output v

17、oltage V(k) and comparing the PV output power P(k) with that of the previous perturbation cycle P(k-1). (6) (7)And Fig.5 shows how the perturbation and observation method works.Fig.5 Perturbation and observation diagramA 扰动观察法扰动观察法(P&O)5有一个简单的反馈结构和较少的测量参数。它是通过周期性扰动(递增或递减)阵列的输出电压V(k)和比较PV输出功率P(k)与前一个

18、扰动周期P(k-1)控制的。 (6) (7)图5给出了扰动观察法的工作方式。图5 扰动观察法图解 Fig.5(A) illustrates that the system is working above the optimum power point under the condition thatandhave different phases. To make the PV system work at the maximum power point, the duty time should be adjust to reduce the output voltage, namely,

19、 to increase the PV system output power. Fig.5 (B) shows the PV system works at the maximum power point when. Ifandhave the same phase, shown in Fig.5 (C), the PV system works below the maximum power condition. In order to reach the maximum power point, the duty time should be adjusted to increase t

20、he output voltage, namelyto increase the output power. In this manner, the peak power tracker continuously seeks the peak power condition. 图5(A)表明，系统在和不同相的条件下工作于理想功率点。为了使光伏发电系统工作于最大功率点，需要调节占空比降低输出电压，即增加光伏发电系统输出功率。图5(B)给出当时，光伏发电系统工作于最大功率点。如果和同相，如图5(C)所示，光伏发电系统在最大功率以下。为了达到最大功率点，需要调节占空比增加输出电压，即增加输出功率。以

21、这种方式，峰值功率跟踪器连续的寻找峰值功率条件。Fig.6 shows the control loop of the perturbation and observation method.Fig.6 Perturbation and observation control loops图6所示为扰动观察法的控制回路。图6 扰动观察法控制回路B. Incremental conductance method The incremental conductance method6 uses the source incremental conductance method as its MPP

22、search algorithm. It is more efficient than perturbation and observation method and independent on device physics. The output voltage and the current from the source are monitored by what the MPPT controller relies on to calculate the ratio ofand incremental conductance, and to make its decision (to

23、 increase or decrease duty radio output).B 电导增量法电导增量法使用源电导增量法作为其MPP的搜索算法。该方法比扰动观察法更有效并且是独立的物理装置。依靠MPPT控制器测量输出电压和电流源计算的比率和电导增量，作出决策（增加或降低输出的占空比）。From equation (5), it is trivial to derive equation (8) that can be used to demonstrate the algorithm. (8)Define the source incremental conductance: (9)In g

24、eneral, the output voltage from a source is positive. Equation (8) explains that the operating voltage is below the voltage at the maximum power point if the ratio of is larger than the incremental conductance, and vise versa. The job of this algorithm is therefore to search the voltage operating po

25、int at which the ratio is equal to the incremental conductance. The ideas are expressed by equation (10), and graphically show in Fig.7. (10)Fig.7 Incremental conductance algorithm P-V characteristics公式(5)源于公式(8),可以用来证明该算法。 (8)定义源的电导增量： (9)通常，电压源的输出电压为正。公式(8)表明工作电压低于最大功率点的电压如果的比率大于电导增量，反之亦然。该算法的任务是搜

26、寻比率等于电导增量的电压工作点。该想法被表达成公式(10)，并且生动地描绘为图7. (10)图7 电导增量算法的P-V特性In both algorithm perturbation and observation method and the incremental conductance method, the AC component must be added to the DC one. In this paper, two methods for maximum power point tracking are proposed. 扰动观察法和电导增量法两种算法，交流分量必须加到直

27、流分量上。本文提出了两种最大功率跟踪的方法。IV Proposed Methods for Maximum Power Point TrackingIV MPPT试行方法A. The Current Control Maximum Power Point TrackingIn order to determine the operating points corresponding to maximum power for different illumination levels, from equation (4) and (5), the partial derivative of po

28、wer is computed as the following: (11)The solution of equation (11) represents the currents corresponding to the maximum poweras a function of illumination current of PV system. (12)A 电流控制MPPT为了确定在不同光照强度下操作点和最大功率一致，由式(4)和(5)，功率的偏导数计算如下：(11)方程(11)的解代表最大功率时对应电流，它作为光伏系统光照电流函数。 (12)Fig.8 shows optimum l

29、oad to illumination current ratio at different temperature and different illumination levels. This means that, at a given temperature and illumination level, the current corresponding to maximum power is the function of illumination current. From Fig.8 it can be observed that at a given temperature,

30、 with the light illumination increasing the ratio will increase accordingly; and at a given light intensity level, with temperature increasing the ratio will drop. At a given temperature, if the illumination current value is measured, then from the Fig.8, it is not different to know the optimum curr

31、ent the PV system should work on.Fig.8 Optimal load to illumination current ratio under different temperature图8给出了在不同温度和不同照度级的条件下理想负载的光照电流。即在给定的温度和光照水平下，对应于最大功率的电流是光照电流的函数。如图8所示，在给定的温度下，随着光照强度的增加比率也会相应地增加；在给定的光照强度水平下，随着温度的增加比率将会降低。在给定的温度下，如果测得光照电流的值，然后由图8 不难知道光伏发电系统工作的最优电流。图8 不同温度下理想负载光照电流比率Fig.9 sh

32、ows the diagram to measure the illumination current. In this diagram, the operational amplifier is used to control the circuit operation and measure the illumination current indirectly, which will reduce the impact of the measurement circuit to the PV system and increase the measurement accuracy.Fig

33、.9 Illumination current measurement diagram图9给出了测量光照电流的图解。如图所示，运算放大器用来控制电路工作和间接测量光照电流，这样可以降低测量电路对光伏发电系统的影响和增加测量的精度。图9光照电流测量图解BThe Voltage Control Maximum Power Point TrackingSimilar to the current control maximum power point tracking method, the voltage control method7 can also be used. From equatio

34、n (12) and equation (4), the optimal voltage corresponding to the maximum power can be drawn, represent as the following: (13)At the open circuit condition () it gives: (14)B电压控制最大功率点跟踪如同电流控制最大功率点跟踪，电压控制同样可以使用。由公式（12）和（4）可得，与最大功率的一致的最优电压可以被描绘出，如下： (13)在开路条件()下为： (14)Therefore, the voltage correspond

35、ing to maximum power can be expressed as a function of cell open circuit voltage, namely (15)Fig.10 shows the optimum output voltage to the open circuit voltage ratio at different temperature and different light intensity levels, and Fig.11 shows the optimal output voltage to open circuit ratio at d

36、ifferent temperature.Fig.10 Optimal output voltage to open circuit ratio at different temperature and different light intensityFig.11 Optimal voltage to open circuit ratio at different temperature因此，电压与最大功率相一致可以表示为电池开路电压的函数，即 (15)图10给出了不同温度和不同光照强度水平下的最佳输出电压的开路电压比，图11给出了不同温度下最佳输出电压的电压比。图10 不同温度和不同光照强

37、度水平下的最佳输出电压的开路电压比图11 不同温度下最佳输出电压的电压比From Fig.10 and Fig.11, it can be observed that at a given light intensity level, with the temperature raising, the voltage corresponding to maximum power point to the open circuit ratio will decrease; and at a given temperature, with the light intensity improving

38、, the ratio will also increase. 从图10和图11可以观察到，在给定的光照强度下，随着温度的升高，与最大功率点一致的开路电压比降低；在给定的温度下，随着光照强度的增加电压比也增加。Fig.12 shows the open circuit measurement diagram. The operational amplifier can also be introduced to control the measurement circuit.Fig.12 Open circuit measurement diagram图12 给出了开路测量的电路图，该运算放大

39、器也可以用来控制测量电路。图12 开路测量的电路V Fuzzy System Based Maximum Power Point TrackingFuzzy controllers are used to provide solutions to control problems that cannot be described by complex mathematical models. Fuzzy systems are relatively easy to design and produce reasonable results. In this paper, the fuzzy s

40、ystem is used to control the PV system to make the PV system work at the maximum power point. In the current approach the fuzzy system was implemented by the using Motorola HC11 micro-controller 8. Fuzzy system provides nonlinear mapping of the function shown in Fig.13.Fig.13 Optimal current to shor

41、t circuit ratio at different open circuit voltageFig.14 Fuzzy system based current control MPPT diagramV 基于模糊控制的最大功率点跟踪模糊控制器用来提出复杂数学模型控制问题的解决方法。模糊控制系统设计相对简单产生结果合理。在本论文中，模糊控制系统用来控制光伏系统使光伏系统工作在最大功率点。目前采用模糊控制的方法是采用摩托罗拉公司的HC11微控制器。模糊系统提供了函数的非线性图形，如图13.图13 不同开路电压条件下的最佳短路电流比图14 基于模糊系统的电流控制的MPPT结构图 The blo

42、ck diagram, for identifying the optimal operating point and also the maximum power output of the PV system, is shown on Fig.14. 图14的框图确定出最优工作点和光伏系统的最大功率输出。VI Conclusion A method for maximum power tracking was developed. In contrast to the existing methods there is no need for modulation of the outpu

43、t voltage. The proposed method senses output circuit voltage and short circuit current and uses these two parameters for optimum control using a fuzzy controller. The short circuit current of PV cell represents illumination, and the output circuit voltage carries on information about the temperature

44、.VI 总结 开发了一种最大功率跟踪的方法。与现存的方法相比他不需要调整输出电压。该方法测量输出电路电压和短路电流并且运用这两个参数通过模糊控制器实现最优控制。输出电流反应当前光伏电池的光照强度，输出电压反应温度信息。Acknowledgment This work was supported in part by NASA-Idaho PSCOR and NASA-EPSCOR grant.致谢 该研究得到NASA-Idaho EPSCOR 和 ASA-EPSCOR的支持VII Reference1 Takashi Hiyama, Shinichi Kouzuma, Tomofumi Ima

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