Introduction

Solar energy is an alternative and renewable power source, and has been proposed by many as a great source of energy. Conversion of energy into electrical power is a complex process. Energy/power conversion for the implemented system will be of two forms: Direct current and alternating current. Maintaining optimal power delivery of solar power energy requires careful monitoring and adjustment of voltages and current to a load.

Pelco has proposed the project concept of building a device that will collect solar power, convert the power to AC/DC regulated electrical energy, and provide cooling to a temperature-based operating crystal oscillator. This project will require the following specifications: Collection and conversion of solar energy to provide regulated electric power, providing a combined 40W of 24VAC (RMS) and 12VDC power, and storing of at least 5 Watt-Hours of energy to allow an orderly shut-down at night. A control loop will be implemented to regulate and monitor the internal temperature of the crystal oscillator to ensure accurate performance. An Ethernet debug port for remote monitoring and limited control from a central location and two polarized conductor connectors for both 24VAC and 12VDC outputs.

Due to financial and time restraints the Project was rescoped to exclude the cooling system and the oscillator analysis. The main focus was then shifted to the design and implemantation of a solar power station with a focus on maximizing efficiency.

General statement of the problem

The harvest of solar energy and its transformation into regulated electrical energy is required for a design application at Schneider Electric Company.

Project Objectives

• Using a Maximum Power Point Tracker, maximize the output power of the Solar Panel.
• Regulate the Solar Panel Output Power to charge a battery.
• Maintain a Battery Voltage in accordance to irradiation levels.

Scope of the Study

Through the courses offered in CSU Fresno’s Lyles College of Engineering ECE Department, we as a team have all the tools required to solve the problems presented in this project.

In the Solar Energy Collection stage, knowledge of maximizing the output power must be used to insure a good percentage of the power from the solar panel is utilized.

 In the DC-DC conversion stage, circuit analysis methods must be used to anticipate the current passing through the voltage regulator. From there a control system is designed to regulate voltage using a negative feedback loop, a compensator and pulse width modulation to control a Power MOSFET switch which then controls the output charge of the battery. The charging circuit consists of a series of microcontroller-controlled switches allowing current to flow into the battery, the load, or both.

Technologies Applied: Boost Converter, Buck Converter, Voltage Controller, Charge Controller, Digital Power PIC, Power MOSFET Driver, and Lead Acid Battery.

Theories Applied: Maximum Power Point Tracking, Pulse Width Modulation, Negative Feedback Control, Compensation, and Battery Charge Design.

Statement of the Hypotheses

If the Solar Charge system absorbs maximum power during the day, then the Lead Gel Acid Battery will not only be fully charged but also provide a voltage to the load and/or outputs.

Definition of Terms

MPPT: Maximum Power Point Tracking is a system-efficiency improving technique used to get the maximum possible power from a solar panel. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency demonstrated by its characteristic I-V curve. It is the purpose of the MPPT system to sample and compare the output power of the solar cells and apply the proper resistance (load) to obtain maximum power for any given environmental conditions.

Pulse Width Modulation: A technique in which the data of a signal is placed within the duty cycle of a pulse wave. Pulse-width modulation (PWM), as it applies to a switching transistor (MOSFET), is a way of controlling the gate voltage through delivering energy through a succession of pulses rather than a continuously varying (analog) signal.

Microcontroller: A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general-purpose applications.

Negative Feedback: Negative feedback occurs when a differential occurs between the actual value and a desired value of a system parameter, and is used to reduce the difference. Changes that move a value away from the reference value are attenuated. If a system has overall a high degree of negative feedback, then the system will tend to be stable.

Compensator: A device that stabilizes and optimizes the response of the system. It also removes or fixes unwanted results in the output of the system. In addition, compensation prevents positive feedback and increases the overall stability of the system.

Buck Converter: A DC-DC converter that outputs a voltage at a desired level lower (step-down) than that at the input voltage terminals. The simplest way to reduce the voltage of a DC supply is to use a linear regulator (such as a 7805), but linear regulators waste energy as they operate by dissipating excess power as heat. Buck converters can be significantly efficient (95% or higher for integrated circuits), indicating uses for tasks such as converting the 12–24 V typical battery voltage in a laptop down to the few volts needed by the processor.

Voltage Regulator: A voltage regulator is an electrical regulator designed to automatically maintain a constant desired voltage level. A voltage regulator may be a feed-forward design or may include negative feedback control loops. It can use an electromechanical mechanism, or alternatively, electronic components.

Charge Controller: A charge controller limits the rate at which electric current is added to or drawn from electric batteries.  It prevents overcharging and may prevent against overvoltage, which can reduce battery performance or lifespan, and pose a potential safety hazard. It may also prevent completely draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life. The terms "charge controller" or "charge regulator" may refer to either a stand-alone device, or to control circuitry integrated within a battery pack, battery-powered device, or battery recharger.