Cut-Off Solar Charge Controller as an alternative towards system efficiency optimization

Transcription

1 Cut-Off Solar Charge Controller as an alternative towards system efficiency optimization Abstract Based on the concept of optimizing the efficiency of the automated solar system in residential buildings application, this paper proposed a High efficiency solar Cut-Off charge controller as an alternative to the main solar charge controller in most conventional buildings solar system, the idea is to design an electronic circuit with low losses as a compared with the conventional charge controller to be a part of the integrated and automated building solar system, the design has an algorithm based on some environment parameters like sun Irradiance and weather temperature, this algorithm seems to be inversely calculated because its start from the value of full charge battery voltage. A Simulink Matlab simulator is attempted in the simulation phase of this research. The main difference between the method used in the proposed Cut-Off controller and other technique used in the past is that PV array output power is used directly through a bypass MOSFET to charge the battery bank when the voltage of the battery bank at lower level that its maximum while switching on another path when the batteries reaches its full charge value through another MOSFET to transfer this surplus power to what is called as an Auxiliary load,fans or auxiliary battery used for system ventilation or solar tracking to reduce the ambient temperature for the system components, so adding more improvements on system performance, this would reduce the complexity of the system on one hand and produce a competitive efficiency, low cost and can be easily modified on the other hand. Keywords component; PV solar analysis,solar cell parameters, Battery charge controller, power electronics, and MPPT. I. INTRODUCTION As an alternative friendly environment electric power, the photovoltaic solar energy is the best option as a natural power source that all the world looking for, but the conversion efficiency of the sun light to electrical power depends on many extrinsic factors, such as Insolation levels, temperature, and load conditions. There are three major approaches for maximizing power extraction in medium- and large-scale systems, the sun tracking system, maximum power point tracking (MPPT) or both. MPPT is popular for the small-scale systems based on economical reasons. Many techniques have been developed to provide maximum PV power [1] [10]. Enslin employed an integrated PV maximum-power-point tracker with soft switching to obtain the optimum efficiency [1]. Hiyama used a neural network to estimate maximum-power-point operating conditions [2], [3]. Some researchers control photovoltaic characteristics to match load conditions [4] [6]. Some systems use an online maximum power point tracking (MPPT) algorithm to obtain the maximum power point [7] [10]. An MPPT method often used is the perturbation and observation method [8], [9], because the method is easy to implement. However, oscillation is unavoidable. The incremental conductance method is used to avoid oscillation by comparing the incremental and instantaneous conductance of the PV array, but the implemented circuit is more complex [10]. II. PROJECT METHODOLOGY There are a sequence of steps would be carried out in this paper to achieve the goal it can be briefly described as a flowchart shown in Fig(1). Fig(1). Flowchart Start Inputs 1..The battery full charge voltage (Vbmax). 2..Temp. Range(Tmax,Tmin) 3..Irradiance Range(W/m2) Simulation Algorithm to find out the system parameters Output Cut-Off point of the battery charge controller (Vcutoff) and all solar panels parameters to be designed (Vmp, Isc,Voc...) End As mentioned earlier, this paper is a project portion proposed automated solar system using completely DC load matching technique with efficiency optimizing of the system, so the assumptions of some parameters like Vload or Vbmax. are based on previous components evaluation. So the case under study by this paper represented by the Cut-Off controller shown in Fig.(2) as a battery charger of the system. The maximum full charge battery voltage taken to be Vbmax.=162V, this value have been chosen based on the load DC operation voltage.

2 Fig(2). Showing the location of Cut-Off controller Now, based on the application geographic location and system components operation conditions, we can specify the range variation of the irradiance values and environment temperatures, so the well-know VP curves of the solar panel array like the one in Fig.(3) can be obtained as it would be described in the next paragraph, these curves would be attained as a result of an algorithm process proposed in this paper and would be illustrated in the next paragraphs. the de-facto standard in various engineering disciplines. An important contribution of this work is the incorporation of a two-diode model as the main engine of the simulator. This model is known to have better accuracy, especially at low irradiance levels. As a result, its application allows for a more accurate prediction of PV system performance especially during partial shading conditions. However, previous researchers have avoided the use of this model in their PV simulators. This is probably due to the significant increased in computational time. Another possible reason why this model has not been used is the insufficient information on certain semiconductor parameters that characterize a specific module. So the model that attempts in this work can be represented in the circuit shown in Fig.(4). A. Solar-Induced Current IV.. SOLAR MODELLING: The block represents a single solar cell as a resistance R s that is connected in series with a parallel combination of the following elements: Current source Two exponential diodes Parallel resistor R p The following illustration shows the equivalent circuit diagram: Fig(3). VP curves of system solar panels at range of different temperature and Irradiance variations. III. SOLAR PANELS PARAMETERS EVALUATION After specify the max. voltage of the load ( )V which is subsequently Battery full charge voltage let us see the solar panels to find out the power cut-off for our system point. PV power generation, due to the high cost of modules, optimal utilization of the available solar energy has to be ensured. The most important component that affects the accuracy of a simulation is the PV cell modelling, which primarily involves the estimation of the non-linear I-V and P-V characteristics curves. There are so many researches in this field to analyse the Solar cell and panels and investigate the system parameters. The more accurate representation one illustrated in [11]. In this paper a fast and accurate PV system simulator based on the MATLAB-Simulink environment is described. The availability of the simulator in the MATLAB platform is seen as an advantage from the perspective of researchers and practitioners alike because this software has almost become Fig(4). Two Diode representation of the solar cell The output current I is: where: I ph is the solar-induced current: where: I r is the irradiance (light intensity) in W/m 2 falling on the cell. I ph0 is the measured solar-generated current for the irradiance I r0. I s is the saturation current of the first diode.

3 I s2 is the saturation current of the second diode. V t is the thermal voltage, kt/q, where: k is the Boltzmann constant. T is the Device simulation temperature parameter value. q is the elementary charge on an electron. N is the quality factor (diode emission coefficient) of the first diode. N 2 is the quality factor (diode emission coefficient) of the second diode. where TRP1 is the Temperature exponent for Rp, TRP1 parameter value. V. SOLAR POWER CUT-OFF POINT after specifying the maximum voltage of the load, (162)V, which is subsequently Battery full charge voltage, let us find out the power cut-off point for our system : The following figure, Fig(5), shows the solar cells arrays for small power type of the proposed system design to find out the cut-off region, point, to be attempted in the design of the cutoff circuit that illustrated in fig(3). V is the voltage across the solar cell electrical ports. The quality factor varies for amorphous cells, and is typically 2 for polycrystalline cells. The block lets you choose between two models: An 8-parameter model where the preceding equation describes the output current A 5-parameter model that applies the following simplifying assumptions to the preceding equation: The saturation current of the second diode is zero. The impedance of the parallel resistor is infinite. B. Temperature Dependence Several solar cell parameters depend on temperature. The solar cell temperature is specified by the Device simulation temperature parameter value. The block provides the following relationship between the solar-induced current I ph and the solar cell temperature T: where: TIPH1 is the First order temperature coefficient for Iph, TIPH1 parameter value. T meas is the Measurement temperature parameter value.the block provides the following relationship between the series resistance R s and the solar cell temperature T: where TRS1 is the Temperature exponent for Rs, TRS1 parameter value. The block provides the following relationship between the parallel resistance R p and the solar cell temperature T: Fig(5). PV and VI curves From the block diagram in Fig(5) and software algorithm, we can find out the value of the cut-off point which controls the charging current between the solar array and battery bank, this cut-off point selected based on the following parameters:- 1- The variation range for each of Sun Irradiance and weather temperature in the site environment all over the year. 2- Battery bank full charge voltage which is equal to the maximum system DC load voltage. 3- The application (home or accommodation), Battery bank one of the main component. Based on the above three points and the algorithm that analyses the parameter and taking the peak value of the VP

4 curve at the maximum temperature and minimum irradiance, the voltage at that peak power point should be taken to be equal to battery voltage at full charge as shown in Fig.(3), then:- Vbmax=Vload=Vcut_off=Vmp...(1) Voc=1.25*Vmp...(2) Vmp= at 0.6KW/m² If Vmp= at 1KW/m² Voc=216...at 1KW/m². Where: Vbmax is the full charge battery voltage. Vload: is the maximum load voltage. Vcut_off: is the voltage value at the peak of power curve. Vmp; is the solar voltage at maximum power. So the peak point of the PV-curve of that of the maximum environment temperature and less sun irradiance which is volt that apposite to 1093 watt. Although that the peak value of the power is about 1200 watt at 1KW/m² irradiance, but this selection to design the cut-off circuit is more efficient and more reliable and the electronic switching component of the circuit is working only after this region to change the direction of the charging current towards the auxiliary system load. It is worth mentioning that there is a no loss in this circuit takes place at time when there is an irradiance produce more than the chosen power value( )watt, this paper propose an effective solution to use this extra power to supply auxiliary load, like system fans for ventilation, to enhance the system performance at that time in which the system components has relatively high embedded temperature. There is very important point to mention that the designer should remember that the value of this point already selected earlier, this point is Vmp= solar array voltage at maximum power (at max. Temp. And min. Sun Irradiance), then conversely returned to extract the rest of the solar array parameters, like( Isc, Voc, Pmax... etc.) As mentioned earlier Vbmax has been taken to be the voltage at maximum power and to be at maximum mean temperature and minimum mean irradiance, in this case at 50C temp. and 600 W/m². After the Cut-off region, the difference, like ( ) is used to energize the auxiliary load of the system, so that means the auxiliary load voltage range between 0-Voc. Fig(6) Block diagram of Cut-Off circuit VII. SCHEMATIC DIAGRAM. Schematic Diagram of this circuit simulated in Matlab 2013 is shown in Fig.(7), in this circuit, not only the circuit components but also the battery and load with the solar panel array to show the effects of irradiance variation on its performance. Fig(8) illustrate the curves of the main output voltages to charge the battery bank and the auxiliary one to supply the system ventilation components or can be used for another purposes. VI. CUT-OFF CONTROLLER DIAGRAM A traditional PWM power converter has a non-ideal switching process. The resonant power converter using the capacitor parallel to the power switch can be employed to overcome the above mentioned disadvantages. The voltage is a sinusoidal waveform during the instant when the power switch switches and resonance occurs, thereby decreasing the area of overlap between voltage and current, and reducing switching losses [12]-[15]. The primary advantage of the resonant converter is that it reduces voltage or current on the power switch to zero, decreases switching loss from the power switch and effectively protect against electromagnetic interference. This paper proposed a Mosfet transistor switching circuit that satisfy the use of all possible power of the solar panels without components complexity, Fig(6) represents the block diagram of this circuit, where :- Vbmax, the full charge voltage of the battery bank, this value should be used as the first step of our algorithm calculations. Fig.(7). Schematic Diagram of the Cut-Off circuit

5 Fig(8). Main Battery and auxiliary outputs voltages of the cut-off circuit at different irradiance values. VIII. CONCLUSIONS This project developed a novel battery charger with a zero volt switching circuit and auxiliary branch for decreasing switching loss and using the potential extra portion of power to supply some of system components to improve its performance and enhances charging efficiency. Matlab 2013 simulation results obtained by charging a lead-acid battery demonstrate the effectiveness of the proposed approach, indicating that the two switch branches in the proposed battery charger are operated at minimum losses and its frequency depends on the comparator threshold value or deviation range, small components and small circuit volumes can be achieved. An expected significant decrease in the working temperature of switches, significant decrease in heat loss and markedly increase in charging efficiency were attained by changing the extra solar charging current to the direct auxiliary system load to be used in ventilation process or other application that could improve the system performance. The charging voltage curve shows that the mean battery voltage remain at the set value at 162V and the tolerance depends on the comparator threshold setting, if the power accedes the setting, at high level of insolation, auxiliary branch switched on to use this power to enhance the performance of the system components. Practical experiment result will be performed in the next few months to satisfy the above idea, because this work is a part of a PhD Research that illustrate the applications of intelligent solar building on completely DC load and calculates the losses that could attain through performing this technique. [3], Evaluation of neural network based maximum power tracking controller for PV system, IEEE Trans. Energy Conversion, vol. 10, pp , Sept [4] J. Applebaum, The quality of load matching in a direct-coupling photovoltaic system, IEEE Trans. Energy Conversion, vol. EC-2, pp , Dec [5] S. M. Alghuwainem, Matching of a DC motor to a photovoltaic generator using a step-up converter with a current locked loop, IEEE Trans. Energy Conversion, vol. 9, pp , Mar [6] M. M. Saied, A. A. Hanafy, M. A. El-Gabaly, and A. M. Sharaf, Optimal design parameter for a PV array coupled to a DC motor via a DC DC transformer, IEEE Trans. Energy Conversion, vol. 6, pp , Dec [7] I. H. Altas and A. M. Sharaf, A novel on-line MPP search algorithm for PV arrays, IEEE Trans. Energy Conversion, vol. 11, pp , Dec [8] B. K. Bose, P. M. Szczeny, and R. L. Steigerwald, Microcomputer control of a residential photovoltaic power conditioning system, IEEE Trans. Ind. Applicat., vol. IA-21, pp , Sept./Oct [9] C. Hua, J. Lin, and C. Shen, Implementation of a DSP-controlled photovoltaic system with peak power tracking, IEEE Trans. Ind. Electron., vol. 45, pp , Feb [10] K. H. Hussein, I. Muta, T. Hoshino, and M. Osakada, Maximum photovoltaic power tracking: An algorithm for rapidly changing atmospheric conditions, Proc. IEE Generation, Transmission, Distribution, vol. 142, no. 1, pp , Jan [11]. Accurate MATLAB Simulink PV System Simulator Based on a Two- Diode Model. Kashif Ishaque, Zainal Salam, and Hamed Taheri. Dept. of Energy Conversion, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia [12] Ned Mohan, Tore M. Undeland, William P. Robbins, Power Electronics Converters, Applications and Design, Second edition, John Wiley & Sons, Inc, [13] L. C. defreitas and P. R, C. Gomes, A ZVT Buck Converter Using a Feedback Resonant Circuit, Fifth European Conference on Power Electronics and Applications, Vol. 3, Sep. 1993, pp [14] Guichao Hua, Soft-Switching Techniques for Pulse-Width-Modulated Converters, Ph. D. Dissertation, Virginia Polytechnic Institute and State University, [15]. Implementation of High-Efficiency Battery Charger with a Zero- Voltage-Transition Pulse-Width-Modulated Boost Converter Yu-Lung Ke, Senior Member, IEEE, Ying-Chun Chuang, and Mu-Shi Chen Department of Electrical Engineering Kun Shan University Tainan, Taiwan, R.O.C REFERENCES [1] J. H. R. Enslin, M. S.Wolf, D. B. Snyman, andw. Sweigers, Integrated photovoltaic maximum power point tracking converter, IEEE Trans. Ind. Electron., vol. 44, pp , Dec [2] T. Hiyama, S. Kouzuma, and T. Imakubo, Identification of optimal operation point of PV modules using neural network for real time maximum power tracking control, IEEE Trans. Energy Conversion, vol. 10, pp , June 1995.