ISSN Vol.03,Issue.06, August-2015, Pages:

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1 ISSN Vol.03,Issue.06, August-2015, Pages: V/20A Isolated Solar Charge Controller (MPPT Based) KASULA MAHESH 1, S. MALLIKARJUNAIAH 2 1 PG Scholar, Dept of EEE, CREC, Tirupati, AP, India, kasula.mahesh632@gmail.com. 2 Principal, Dept of EEE, CREC, Tirupati, AP, India, smalli_suluru@rediffmail.com. Abstract: The power generation of photo voltaic (PV) arrays are totally depends on the insolation and ambient temperature of the panel (Temperature of atmosphere). Both insolation and temperature are not stable, since the power generations by PV arrays are not stable. Therefore, the Maximum Power Point Tracking (MPPT) techniques are used to draw maximum power from photo voltaic panels at present insolation and supplies highest power to the load/battery. The MPPT technique is performed with a help of microcontroller and power electronics circuit and it overcomes the problem of mismatch between the PV panel and load/batteries. In this study, a microcontroller is employed to develop industrial grade 135V/20A isolated solar charge controller. Due to isolated charge controller, we achieved high power handling capability. We design a system with combination of microcontroller (FREESCALE microcontroller), a BUCK DC-DC converter, a transformer and a resistive load or load bank (200A). In this system MPPT algorithm, charge control patterns, reference signals are executed by an embedded program flashed in microcontroller. This solar charge controller was incorporated with Over Voltage (OV) protection, Under Voltage (UV) protection and high temperature protection, etc. Keywords: Solar, Charge, Controller, Converter, Load, Buck, Isolated, Insolation. I. INTRODUCTION In the present world of increasing demand for energy resources, it is crucial to come up with innovatory ideas to reduce and conserve usage of energy. The word Photovoltaic is a combination of the Greek word for Light and the name of the physicist Allesandro Volta. It identifies the direct conversion of sunlight into energy by means of solar cells [1]. Though the utilization of solar energy is little at present, even though it today this type of energy is not widely used as other available resources like thermal, wind, or hydroelectric. Solar power has many advantages over other non-renewable energy sources. It has even advantages over renewable energy sources like wind and water. However the drawback here is that it produces energy when there is sun presents. To overcome this problem, photovoltaic panels are usually coupled with a battery to store energy. This battery is connected to an inverter where the DC to AC conversion takes place. This AC power is utilized for our household applications or is send to the grid for distribution. The primary function of a charge controller in a stand-alone PV system is to maintain the battery at highest possible state of charge while protecting it from overcharge by the array and from over discharge by the loads. Although some PV systems can be effectively designed without the use of charge control, any system that has unpredictable loads, user intervention, optimized or undersized battery storage (to minimize initial cost) typically requires a battery charge controller. The algorithm or control strategy of a battery charge controller determines the effectiveness of battery charging and PV array utilization, and ultimately the ability of the system to meet the load demands. Additional features such as temperature compensation, alarms, meters, remote voltage sense loads and special algorithms can enhance the ability of a charge controller to maintain the health and extend the lifetime of a battery, as well as providing an indication of operational status to the system caretaker. Important functions of battery charge controllers and system controls are to. Prevent Battery Overcharge: to limit the energy supplied to the battery by the PV array when the battery becomes fully charged. Prevent Battery Over discharge: to disconnect the battery from electrical loads when the battery reaches low state of charge. Provide Load Control Functions: to automatically connect and disconnect an electrical load at a specified time, for example operating a lighting load from sunset to sunrise. A series charge controller or series regulator disables further current flow into batteries when they are full. A shunt charge controller or shunt regulator diverts excess electricity to an auxiliary or "shunt" load, such as an electric water heater, when batteries are full. Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. Pulse width modulation (PWM) and maximum power point tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery's level, to allow charging closer to 2015 IJIT. All rights reserved.

2 its maximum capacity. Charge controllers may also monitor battery temperature to prevent overheating. Some charge controller systems also display data, transmit data to remote displays, and data logging to track electric flow over time KASULA MAHESH, S MALLIKARJUNAIAH buck and buck boost converters provide the opportunity to have either lower or higher output voltage compared with the input voltage respectively. II. HARDWARE IMPLEMENTATION Hardware of this system is combination of a solar panel module, a microcontroller (Free scale MC56F8025), PV panel, a buck type DC-DC converter, Transformer, a resistive load, Housekeeping supply, Results (scopes). These parts of system are presented in below, separately. A. Solar Panel Selection We are used WAAREE Aditya series WS-300 solar panel. The panel can produce 300wp power at maximum power voltage (Vmp) 35V and maximum power current (Imp) 8.57A. The open circuit voltage and currents are 43V and 9.3A respectively. These panels can connect in series upto maximum 1000V. B. Microcontroller This microcontroller is Digital Signal Processing controller from freescale [7]. It has a Efficient 16-bit 56800E family Digital Signal Controller (DSC) engine with dual Harvard Architecture. As many as 32 Million Instructions Per Second (MIPS) at 32MHz core frequency, Single-cycle bit parallel Multiplier-Accumulator (MAC), Four 36-bit accumulators, including extension bits, 32-bit arithmetic and logic multi-bit shifter, Parallel instruction set with unique DSP addressing modes, Hardware DO and REP loops, Three internal address buses. Four internal data buses, Instruction set supports both DSP and controller functions. Controllerstyle addressing modes and instructions for compact code, Efficient C compiler and local variable support. Software subroutine and interrupt stack with depth limited only by memory. TAG/Enhanced On-Chip Emulation (OnCE) for unobtrusive, processor speed-independent real-time debugging Fig2. Schematic of dc-dc converter. The fig2 shows the basic placement of dc-dc converter. We have two types of dc-dc converters, non-isolated and isolated type converters. In non-isolated type there is only electronic components are present and there is no separation between input and load. But in isolated by dc-dc converters, power transformer is presents along with power electronic components, due to the transformer we are providing separation between input and output(load). The fig shows the basic schematic diagram of a buck converter (step down converter). For the ideal buck converter, any output voltage from 0 V to VIN may be obtained. In actual DC/DC converter circuits, there are practical limitations. It has been shown that the output voltage is proportional to the duty cycle and input voltage. Given a particular input voltage, there are limitations that prevent the duty cycle from covering the entire range from 0 to 100%. Fig3. Schematic of Buck converter. Fig1. Freescale microcontroller (MC56F8025) C. DC-DC Converter It Operate as the main part of the MPPT. A dc/dc converter (step up/ step down) serves the purpose of transferring maximum power from the solar PV module to the load. A dc/dc converter acts as an interface between the load, when proposing an MPP tracker, the major job is to choose and design a highly efficient converter, which is supposed to operate as the main part of the MPPT. The efficiency of switch-mode dc dc converters is widely discussed in. Most switching-mode power supplies are well designed to function with high efficiency. Among all the topologies available, both The duty cycle may also be constrained at the upper end. In many converters, a dead time is required to charge the highside switching FET gate-drive circuit. Feedforward circuitry may also cause a flattening of the PWM ramp waveform as the slope of the PWM ramp is increased while the period remains constant.this will limit the maximumoutput Voltage with respect to VIN. Typically, if there is amaximum duty-cycle limit, it will be expressed as a percentage,and the maximum output voltage willbe [5] (1) Due to high power rating or power handling, full bridge configuration is selected to serve the present application. The full bridge configuration is shown in fig. In this full bridge (H-bridge) configuration four MOSFET s are used. And these switches are operated ant high switching frequency up to90khz.

3 135V/20A Isolated Solar Charge Controller (MPPT Based) voltage & Input current).the flow chart we used is show in below fig. Fig4. Full bridge (H-bridge) buck converter. D. Design of Transformer: The transformer is designed in such a way that it can with stand for input voltage up to 175V. The core used in this transformer is TDK make and model number E70/33/32 B66371 core [8]. This is E-shape core. It can withstand up to 100A of primary and secondary current. Fig6. Flow chart of P&O method. Fig5. Transformer (E-Type core). F. Housekeeping Supply This is one of the main section in this project, because the microcontroller works with 3.3V of input voltage and that voltage must be constant. In this section we are using flyback tropology, primary input dc is converted into 3.3V and supply to the microcontroller constantly. In fig it is clear that F44A is the flyback transformer and combination of one switch (MOSFET) is connected in series with the primary winding of the transformer. The number of turns in primary and secondary are selected by using eq. The transformer turns ratio is 1, it is chosen in such a way that it works as an impedance matching transformer and satisfies the isolation purpose in converter. E. MPPT Technique There are so many techniques to draw maximum power from the solar panel are, P&O Method. Incremental cond. Method. Hill climbing Method Fuzzy logic Method. Neural networks Method. Perturb & Observe Method is the medium efficiency method to track maximum power point tracking from solar panel. This method requires only two sensing input (Input Fig7. Housekeeping supply. III. RESULTS We tested this module at 4Amp of load and different waveforms are taken and shown below. The fig voltage demand (Vdem) signal generated by the microcontroller. The frequency of this vdem signal is 23KHz.

4 KASULA MAHESH, S MALLIKARJUNAIAH Fig8. Vdem signal generated by microcontroller. The fig represents the switching pulses for H-bridge converter. These pulses are generated with help of analog pulse width modulation (PWM) generator. In this waveform channel 1 represents pulses for switch1 (S1) and channel 2 for switch2 (S2). That means both witches are in conduction mode at same time and off mode at same time. Fig10. Output voltage & current. IV. CONCLUSION In this paper, the industrial grade 135V/20A isolated solar charge controller is designed and tested with different load conditions. The charge controller is operating with 92% efficiency at 4A load condition. The charge controller is operates at 87%-92% depends on input insolation. Fig9a. Gate pulses to the MOSFETS. In this waveform channel 1 represents pulses for switch1 (S1) and channel 2 for switch2 (S3). That means if one switch is in ON then another switch is in off. This is switching is to avoid short circuit in the system. Fig9b. Gate pulses to the MOSFETS. The fig shows the output voltage and output current waveform. Chanel 1 represent the output voltage. V. REFERENCES [1] On the Design of an Intelligent Battery Charge Controller for PV Panels- S. M. Çınar and E.Akarslan- Received 26 August 2012; Revised 24 September 2012; Accepted 12 October [2] Photovoltaic Battery Charging System Based on PIC16F877A Microcontroller- Zaki Majeed AbduAllah, Omar Talal Mahmood, Ahmed M.T. Ibraheem AL-Naib- ISSN: , Volume-3, Issue-4, April [3] Design and development of advanced micro controller based solar battery charger and solar tracking system-maruti Pammar, Santosh Chavan-Volume: 03 Special Issue: 03 May-2014 NCRIET eissn: pissn: [4] A Cost Effective Solar Charge Controller-Md. Atiqur Rahaman,M. A. Matin, Apurba Sarker,Md. Rubaiat Uddin. Volume: 04 Issue: 03 Mar-2015 eissn: pissn: [5] Understanding output voltage limitations of DC/DC buck converters- John Tucker. [6] controller. [7] 025.pdf. [8] Author s Profile: Kasula Mahesh was born in 1991 in tirupati ap state India.He completed his graduation from siddharth institute of engg and technology puttur in the year Presently he pursing his masters of technology in power electronics and drives in Chadalawada Ramanamma Engineering College in Tirupati, AP, India. kasula.mahesh632@gmail.com.

5 135V/20A Isolated Solar Charge Controller (MPPT Based) Dr. S.Mallikarjunaiah was born in Chittoor, Andhra pradesh, India in the year He was awarded B.Tech EEE degree in the year 1998 from S.V.U. College of Engg and M.Tech in Power System Engineering from S.V.U. College of Engg. Ph.D obtained from S.V.University, Tirupati in Presently working Principal & Professor of EEE Dept. in CREC, Tirupati, and Andhra Pradesh, India. 2