Recently, people are considering solar mobile phone chargers for including a broader range of consumer electronics applications. Solar panels provide power is highly dependent on the working environment. This includes such optical density, time and location of such factors. Therefore, the battery is often used as energy storage unit. When more than electricity from solar panels when you can charge the battery; when the solar panels provide enough power, the battery that can power the system.
Currently on the market range of solar panels, solar panels, according to the different materials used can be divided into:
① silicon solar cells;
② the inorganic III-V compounds such as gallium arsenide, cadmium sulfide, copper indium selenium compounds such as multi-material solar cells;
③ functional polymer materials (organic semiconductor) solar cells prepared large;
④ nano-crystalline solar cells. We use a silicon solar cell.
2.1 Processor
Processor 51 series 89C51. Internal microcontroller has two timers, two external interrupts and a serial port interrupt, three eight-way I / O port, using a 12MHz crystal. SCM is the task of real-time collection by sampling circuit the solar panel output voltage and current, and battery charging status, the decision by calculating how the maximum output power of solar panels for charging batteries to find and identify the charge state.
2.2 Sampling part
If the current in the system to be tested on, you must first current signal is converted to voltage signal before the A / D conversion. The conversion method is commonly used to add precision resistors in the circuit, which the current signal into voltage signal. This method has the advantage of easy measurement, but this method when the current is very small, affect the measurement accuracy, making it difficult to choose a suitable resistance; Secondly, the current detection signal obtained after amplification to enter only through the circuit comparator, thus increasing the circuit complexity of debugging. Therefore, we can use current and voltage conversion chip MAX472, to overcome the existing conventional method of measuring the current measurement range is small, measurement error and other shortcomings, can improve the measurement accuracy, and can be used for precise control of the microcontroller.
Voltage and current samples using a serial A / D converter TLC0834, 8-bit resolution, and easy to use microprocessor interface or stand-alone work or full-scale reference voltage with 5V logic multiplexer address strobe of a single 4 or 8 input channels 5V power supply, input range 0 - 5V.
2.3 PWM control circuit
Controller uses pulse width modulation (PWM) control of the supply current.
By the microcontroller PWM generator PWM wave output circuit by controlling the main controller and interrupt the way it used to communicate, control the increase or decrease the pulse width. PWM signal back through the optical coupler drive the main road MOSFET.
Switch, diode, LC circuits switching power supply. By PWM control of switching power supply can reduce power consumption while allowing for digital control, but the bus ripple is relatively large.
Principle 3 Rechargeable Battery
Lithium-ion battery during charging or discharging the event of overcharge, over discharge or over-current, it will cause damage or reduce the life of the battery, lithium battery charge in Figure 3 for the curve is divided into three phases: pre-charge state, constant current charging and constant voltage charging phase.
Battery with 800mAh capacity, for example, charge termination voltage of 4.2V. With 1/10C (about 80mA) for constant current pre-charge the battery when the battery terminal voltage reaches the low voltage threshold V (min), with its 800mA (charge rate of 1C) constant current charging, the battery voltage to the start of a larger slope step, when the battery voltage approaches 4.2V, 4.2V constant voltage into the current gradually decreased and little change in voltage, charge current is reduced to 1/10C (about 80mA) when that close to full, you can terminate the charge.
4 Find the maximum output power point of solar
Looking for maximum power point, we use comparative methods to achieve specific approach is: first, collecting solar panel output voltage and current, calculate the power at this time, and continue collecting. Shown in Figure 4. In Figure 4, C-point and B point of comparison, such as large than or equal to point B, give a positive sign of power and position; such as hours than point B, give the right to place a negative sign. The point A than point B, such as large or equal, give the right to place a negative sign; point A than point B, such as hours, give a positive sign of power and position. When a relatively complete after three o'clock, if two positive numbers is a positive slope is the right place, should increase the output voltage and improve power output; if two negative numbers is negative then the slope of power and position, should reduce the output voltage, increase Output power; such as power and position to zero is a positive and negative peak that, without any changes. In A, B, C three-point power value of borrowing from point B to get the first foothold of power, then the first read point C power, and then from point C back to read A point power. Detection of three consecutive power values and to compare its size and then calculate the right bit value by the value of power and position to determine the starting point to move to point C, A point moves, or does not move. Although this method of computing time than the traditional slow disturbance observation maximum power point and the rapid changes in the amount of sunlight the maximum power point can not be reached, but can reduce the traditional observation of disturbance of unknown interference and to determine the error caused by power loss , the effect on the control are acceptable.
touch screen interface， lcd drive module
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