I–V curve simulation by multi-module simulator using I–V magnifier circuit

This paper presents an I–V curve simulation of PV array/modules using multi I–V magnifier circuits. The circuit magnifies an I–V output of a pn photo-sensor, which is regarded as a small solar cell, by analog technology. About 30 W I–V curve simulator circuits were made and their characteristics were evaluated. LED light irradiated into the photo-sensor works like irradiation of sun light on real PV modules. It has been confirmed that each voltage gain and current gain of the circuit is independently adjustable and the circuit magnifies an I–V output of the photo-sensor successfully. FF of the circuit can be modified by shunt register connected to the photo-sensor in parallel. The circuit showed enough response ability to apply the maximum power point tracker evaluation of PV inverters. Temperature dependence of module output can be simulated by temperature control of the photo-sensor. The result of output characteristics of series connection of the I–V magnifier circuits suggests that the simulator system composed of multi I–V magnifier circuit could simulate partial shading effect of PV array output.     

Artificial neural network-polar coordinated fuzzy controller based maximum power point tracking control under partially shaded conditions

The one of main causes of reducing energy yield of photovoltaic systems is partially shaded conditions. Although the conventional maximum power point tracking (MPPT) control algorithms operate well under uniform insolation, they do not operate well in non-uniform insolation. The non-uniform conditions cause multiple local maximum power points on the power?voltage curve. The conventional MPPT methods cannot distinguish between the global and local peaks. Since the global maximum power point (MPP) may change within a large voltage window and also its position depends on shading patterns, it is very difficult to recognise the global operating point under partially shaded conditions. In this paper, a novel MPPT system is proposed for partially shaded PV array using artificial neural network (ANN) and fuzzy logic with polar information controller. The ANN with three layer feed-forward is trained once for several partially shaded conditions to determine the global MPP voltage. The fuzzy logic with polar information controller uses the global MPP voltage as a reference voltage to generate the required control signal for the power converter. Another objective of this study is to determine the estimated maximum power and energy generation of PV system through the same ANN structure. The effectiveness of the proposed method is demonstrated under the experimental real-time simulation technique based dSPACE real-time interface system for different interconnected PV arrays such as series-parallel, bridge link and total cross tied configurations.     

Estimation of equivalent circuit parameters of PV module and its application to optimal operation of PV system

A method to estimate the equivalent circuit parameters of a PV (photovoltaic) module is presented. The parameters are calculated using a least-squares fitting of the equivalent model current–voltage characteristic with the measured one. For applications of the equivalent circuit model parameters, a quantitative diagnostic method of the PV modules by evaluating the parameters is introduced and examined by simulation. A new maximum peak power tracking (MPPT) method using the model parameters, a solar insolation, and a cell temperature is also shown. Its performance is compared with other MPPT control algorithms by simulations. The performance of the proposed method was better than other MPPT methods.     

光照不均匀情况下光伏阵列最大功率跟踪控制

当光伏阵列受到不均匀光照时,输出的功率电压曲线含有多个局域峰值。针对此光照不均匀情况,建立光伏阵列多峰数学模型,并提出一种最大功率跟踪控制方法。采用连续函数构建光照不均匀情况下光伏阵列输出功率电压曲线;依次从该曲线的两侧或中部迭代搜索各局部最大功率点,确保在各种光照情况下均获得全局最大功率;通过Matlab仿真实例验证了所提多峰数学模型和最大功率跟踪控制方法的正确性。     

Modeling and maximum power point tracking (MPPT) method for PV array under partial shade conditions

Influenced by partial shade, PV module aging or fault, there are multiple peaks on PV array's output power–voltage (P–V) characteristic curve. Conventional maximum power point tracking (MPPT) methods are effective for single peak P–V characteristic under uniform solar irradiation, but they may fail in global MPP tracking under multi-peak P–V characteristics. Existing methods in literature for this problem are still unsatisfactory in terms of effectiveness, complexity and speed. In this paper, we first analyze the mathematical model of PV array that is suitable for simulation of complex partial shade situation. Then an adaptive MPPT (AMPPT) method is proposed, which can find real global maximum power point (MPP) for different partial shade conditions. When output characteristic of PV array varies, AMPPT will adjust tracking strategies to search for global peak area (GPA). Then it is easy for conventional MPPT to track the global MPP in GPA. Simulation and experimental results verify that the proposed AMPPT method is able to find real global MPP accurately, quickly and smoothly for complex multi-peak P–V characteristics. Comparison analysis results demonstrate that AMPPT is more effective for most shade types.     

太阳能光伏系统MPPT控制算法的对比研究

根据光伏太阳电池板的内部结构和输出伏安特性建立光伏方阵的Matlab仿真模型,利用实测的气象光强数据对恒压跟踪法、爬山法、爬山改进法和INC法等4种光伏系统最大功率跟踪(MPPT)控制算法进行计算机仿真,评价每种算法在不同天气的光照变化条件下特别是光照强度迅速变化时的跟踪效果,得出各个算法的优缺点。仿真结果用于指导太阳能光伏系统最大功率跟踪器的设计及其控制算法的选择。     

Characterization of PV array output using a small number of measured parameters

The purpose of the present study was to develop a sufficiently good fit for the measured I–V curve of a PV module and array using only three easily measurable parameters: —the open-circuit voltage (V_oc); —the short-circuit current (I_sc); —the maximum power (P_m). With an additional three parameters ( ; ; ) it is possible to describe any I–V curve, taking into account cell temperature T and solar radiation Q. This method has been tested on various solar array panels as well as on a single 10 cm dia. solar cell. The difference between the real curve and the proposed fit was found to be less than 3 percent for a fixed temperature and radiation and about 6 percent for various combinations of temperature and radiation.     

Study on control method of the stand-alone direct-coupling photovoltaic – Water electrolyzer

Based on photovoltaic as an energy resource and hydrogen as an energy carrier, we propose control methods of a photovoltaic-water electrolyzer (PV-WE) system that efficiently generates hydrogen by controlling the number of WE cells. The advantage of this direct coupling between PV and WE is that the power loss due to the DC/DC converter is avoided. Here, several different methods to control the number of WE cells in a stand-alone PV-WE system that is isolated from the electrical grid according to the weather condition were investigated: IV estimation method, PV module temperature method and PV current method. In the IV estimation method, first the current–voltage (IV) characteristics of the PV are calculated based on the measured solar insolation and PV module temperature, and then the nonlinear equation of the IV characteristics of the PV is solved to determine the optimum number of WE cells. In the PV module temperature method, only the PV module temperature and PV output current are used for control. In the PV current method, only the PV output current is used, and thus this method is the easiest among these methods to actually implement. Neither the PV module temperature method nor the PV current method requires solving any nonlinear equation of the IV characteristics of the PV. Each of these three control methods experimentally achieved a high maximum power point tracking efficiency (MPPT efficiency = actual PV output/maximum PV output), which was 98% or higher. Furthermore, to compare each control method, simulations of the PV-WE system were carried out using measured insulation and PV module temperature data for a 1-year period. Each of these three control methods also achieved a high MPPT efficiency in the annual simulations.     

Dynamic evaluation of maximum power point tracking operation with PV array simulator

This paper presents an innovative method to measure the dynamic control ability of maximum power point tracking for PV inverters under the condition of irradiance fluctuation. The PV array I–V curve simulator is a kind of indoor testing facility and easy to be adopted by industries. Basic functions are given by a specially designed PV array I–V curve simulator composed of the active power load. Most of the parameters are controllable by sophisticated software with capability of treating a lot of 1-s data for a very long period of time. In this paper, detailed structure of the equipment is described and test examples are also given by using a commercial PV inverter.     

New algorithm using only one variable measurement applied to a maximum power point tracker

A novel algorithm for seeking the maximum power point of a photovoltaic (PV) array for any temperature and solar irradiation level, needing only the PV current value, is proposed. Satisfactory theoretical and experimental results are presented and were obtained when the algorithm was included on a 100 W 24 V PV buck converter prototype, using an inexpensive microcontroller. The load of the system used was a battery and a resistance. The main advantage of this new maximum power point tracking (MPPT), when is compared with others, is that it only uses the measurement of the photovoltaic current, I_PV.     

Step-up maximum power point tracker for photovoltaic arrays

This paper discusses a new maximum power point tracker (MPPT), which has been devised and tested at the laboratory. This MPPT is a high-frequency set-up dc-to-dc power conditioning unit. Simple and inexpensive analog circuitry is used to continually maximize the true PV array output power rather than maximizing the current or voltage at either the PV array or load. The control circuit is designed such that the actual current and voltage are sensed directly from the PV array. These two signals are then multiplied by a single-chip multiplier.The multiplier output charges or discharges two separate RC circuits of different time constants. These two RC signals are then mixed to set the duty cycle of a pulse width modulated signal to continually track the array maximum power point.This MPPT is simple and inexpensive; and it continuously tracks the true PV array maximum power point regardless of the load type.     

基于电压预估法的光伏发电系统MPPT算法

光伏发电系统处于复杂光照条件下时,光伏电池阵列的输出特性呈多峰现象,致使传统的MPPT算法追踪结果可能停留在次优点。针对此问题,提出一种基于电压预估法的光伏发电系统MPPT算法,采用DMPPT电路结构的光伏阵列,通过研究其输出特性,得到复杂光照条件下光伏阵列最大功率点对应的工作电压最佳区域,并以该预估到的电压值为基础,设计了一种新型的MPPT控制算法。仿真结果表明,所提算法能有效避免光伏系统工作在次优点,提高了光伏发电的出力。     

Monitoring current–voltage characteristics and energy output of silicon photovoltaic modules

Photovoltaic (PV) system designers use performance data of PV modules to improve system design and make systems more cost effective. The collection of this valuable data is often not done due to the high costs associated with data acquisition systems. In this paper, we report on the design of a low-cost current–voltage (I–V) measuring system used to monitor the I–V characteristics of PV modules. Results obtained from monitoring seven crystalline silicon modules between October 2001 and November 2002 are presented and discussed. Results obtained also show the value of being able to continuously monitor the current–voltage characteristics of PV modules.     

Simulation of I–V characteristics of a PV module with shaded PV cells

The authors are studying a diagnostic method of a PV power generating system. We consider that the change of I–V characteristics can be utilized for the diagnosis. However, the report on the change of I–V characteristics is very little. In this paper, we investigate the relation between the output lowering due to shaded PV cells and the change of I–V characteristics, utilizing the computer simulation. It was proven from the simulation that I–V characteristics are changed by the condition of the shadow, which covered the module. The change of I–V characteristics of a PV module with shaded PV cells is discussed by the shift of the avalanche breakdown voltage of shaded PV cells.     

A maximum power point tracking for photovoltaic-SPE system using a maximum current controller

Processes to produce hydrogen from solar photovoltaic (PV)-powered water electrolysis using solid polymer electrolysis (SPE) are reported. An alternative control of maximum power point tracking (MPPT) in the PV-SPE system based on the maximum current searching methods has been designed and implemented.Based on the characteristics of voltage–current and theoretical analysis of SPE, it can be shown that the tracking of the maximum current output of DC–DC converter in SPE side will track the MPPT of photovoltaic panel simultaneously.This method uses a proportional integrator controller to control the duty factor of DC–DC converter with pulse-width modulator (PWM).The MPPT performance and hydrogen production performance of this method have been evaluated and discussed based on the results of the experiment.     

A Novel Auto-Scaling MPPT Algorithm based on Perturb and Observe Method for Photovoltaic Modules under Partial Shading Conditions

Maximum Power Point Tracking (MPPT) controller is required in a solar photovoltaic (PV) system to deliver the maximum power to load from PV module. This paper proposes a novel stepped MPPT method to realize a simple MPPT controller, which can track the real maximum power point (RMPP) even under partial shading conditions. The proposed algorithm is started by scanning the characteristic curve of the PV modules to detect the global maximum power point and then the algorithm will be switched to the conventional P&O algorithm to track the true maximum power point. The obtained simulation results, using Power electronic simulation software (PSIM), are compared with those found using the P&O method to confirm the performance of our proposed MPPT method even under non-uniform solar irradiation.     

Maximum power extraction from photo-voltaic power generator with adaptive MPP tracker

Power generation with the help of Photovoltaic (PV) arrays is emphasized increasingly and regarded as an important resource of power energy in the coming years. As the power supplied by PV arrays depends upon the insolation, temperature and array voltage, it is necessary to control the operating point to extract the maximum power from the PV arrays. A number of methods for Maximum Power Point Tracking (MPPT) has been reported in the literature. This paper discusses an adaptive method as well as compares with the conventional fixed step size method, effectively improves the MPPT speed and accuracy simultaneously. An adaptive algorithm and two phase dc-dc Converter is exercised as a MPP tracker. Ripple reduction is possible at input and output side of the converter. Mathematical models of converter are developed using state space averaging technique. The tracking responses of the system operating at the solar array MPP are evaluated. A theoretical analysis of the new algorithm in connection with dc-dc converter is provided and its feasibility is also verified by simulation results.     

Near-maximum-power-point-operation (nMPPO) design of photovoltaic power generation system

The present study proposes a PV system design, called “near-maximum power-point-operation” (nMPPO) that can maintain the performance very close to PV system with MPPT (maximum-power-point tracking) but eliminate hardware of the MPPT. The concept of nMPPO is to match the design of battery bank voltage V_set with the MPP (maximum-power point) of the PV module based on an analysis using meteorological data. Three design methods are used in the present study to determine the optimal V_set. The analytical results show that nMPPO is feasible and the optimal V_set falls in the range 13.2–15.0 V for MSX60 PV module. The long-term performance simulation shows that the overall nMPPO efficiency η_nMPPO is higher than 94%. Two outdoor field tests were carried out in the present study to verify the design of nMPPO. The test results for a single PV module (60Wp) indicate that the nMPPO efficiency η_nMPPO is mostly higher than 93% at various PV temperature T_pv. Another long-term field test of 1 kWp PV array using nMPPO shows that the power generation using nMPPO is almost identical with MPPT at various weather conditions and T_pv variation from 24 °C to 70 °C.     

A novel two-mode MPPT control algorithm based on comparative study of existing algorithms

In this paper, the effectiveness of these three different control algorithms is thoroughly investigated via simulation and a proposed efficiency evaluation method of experimentation. Both the steady-state and transient characteristics of each control algorithms along with its measured efficiency are analyzed. Finally, a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Finally, a novel two-mode MPPT control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Experimental results show that the proposed two-mode MPPT control provides excellent performance at less than 30% insolation intensity, covering the whole insolation area without additional hardware circuitry.     

Experimental results of controlled PV module for building integrated PV systems

Last issues about Building Integrated Photovoltaic Systems (BIPV) still show average Performance Ratio (PR) values in the range of 0.75–0.80. The main causes well known: partial shadows, temperature effects, PV inverter losses, thermal losses, etc. and mismatching losses. Ideally, all the modules work in the same conditions, but differences between modules really exist due to differences in the working temperature, the inclination or orientation angles, differences in the I–V characteristic coming from the manufacturing process, etc. The effect is that the output power of the complete PV system is lower than the addition of the power of each PV module.These mismatching losses can be decreased by means of suitable electronics. This paper presents the experimental results obtained over PV systems equipped with controlled PV modules, PV modules with low cost and high efficiency DC–DC converters, including MPPT algorithm and other functions, such as power control and Power Line Communications (PLC).Tests have been divided into two great categories: tests on the electronic performance of the DC–DC converter and tests on grid-connected PV systems with multiple DC–DC converters. Many of these tests have been carried out taking advantage of the PV System Test Platform, a powerful tool especially designed by Robotiker to evaluate all kind of PV systems, especially systems with differences between modules. Aspects of the DC–DC converter performance have been detailed and among the most important experiments, the paper analyses different situations such as partial shadows, different inclined planes, PV systems with different PV modules, and finally a comparison between a conventional system and a system composed by controlled PV modules have been described. To sum up, the importance of a good system dimensioning is analysed, with very interesting results.