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Solar Energy Controller Based on PWM Technology
- May 24, 2018 -

Solar power generation system uses solar panels (PV panels) to absorb the sun's light energy into electricity, charging the battery to store energy, and then output low voltage DC power (usually a small system is 12V or 24V), or through the inverter to become 220V Conventional utility power, such as to achieve the use of the sun's energy to use electrical appliances environmental protection and energy saving programs.




The solar power core device is a solar controller. Its performance and design level directly affect the system's efficiency and cost performance, and even the working life and maintenance costs, especially the battery life.




Solar garden lights consists of solar panels, controllers, batteries, and 12V light sources to form parts for electrical appliances, plus a combination of hardware accessories such as lamp posts, lampshades, lamp holders, and solar panel supports. The battery is a large proportion of the investment cost in the system, and the control must be done under no circumstances to allow the battery to overcharge or overdischarge, otherwise it will greatly shorten its life.




At present, solar panels have a high efficiency of about 23%. The battery can be overcharged over-discharge protection. This is the main task of the solar controller.




I. Solar Garden Light Solar Controller Function




Battery reverse polarity protection is "+", "-" pole reverse protection; solar battery reverse connection protection; load over-current and short circuit, surge protection; open battery protection such as open battery, controller cut off load to ensure that the load is not Damage; overcharge, overvoltage protection; battery type can choose ordinary lead-acid or colloidal lead acid; battery over-discharge protection; soft output start, to prevent the battery voltage suddenly dropped when the load access false protection; line lightning protection, to prevent lightning From the solar panels and leads into the burning controller; light control, time control or light / time mixing switch, programmable selection; a variety of state display that is charging, charging state, load state; PWM charging method, floating charge function is superior; Anti-reverse discharge protection at night; PWM ambient temperature compensation; Full electronic switch, effectively extending controller life and reducing operating current losses.




Second, the technical parameters (according to the ambient temperature 25 °C)


Third, solar controller types




The use of a single-chip microcomputer can make the charging work simple and efficient. Line selection is not selected in parallel, as a short-circuit on the PV panel output will affect the service life of the PV panel when fully charged. Therefore, it is advisable to use tandem type. The single-chip microcomputer PWM system has the photovoltaic maximum power point tracking capability, and the utilization of photovoltaic cells is high. When PWM makes the battery tend to be full, the pulse frequency and time are shortened, and the average charging current during charging is more in line with the state of charge of the battery. 0 to 100% charge work.


Solar PV panels charge the battery into three stages: direct charge, float charge, and trickle charge. When designing a circuit, temperature compensation must be performed on the battery's charge and discharge voltage setpoints, that is, the voltage setpoints for each charge and discharge phase are automatically adjusted as the temperature changes. The temperature compensation should meet the technical conditions of the battery, and the single section should take 4mV/°C as the reference value.




Most battery manufacturers recommend that batteries (colloidal batteries are not needed) need to be overcharged occasionally. This requires a balanced charge every two months. After the normal charge is completed for one hour, it is directly charged. The maximum voltage is 16V, and then the charge is stopped for one hour. The charge is then equalized, and the equalization charging process is repeated 2 to 3 times.


Fourth, the controller




This controller is used for solar garden lights, and the load is less than 50W. 5A current is enough for system design. The controller consists of a charging circuit, a discharge circuit, a status indication circuit, and a temperature compensation circuit.




The battery BTl is a fully sealed 12V34Ah battery and is the main power source for the controller. Capacitors C1, C3, and C4 are high-frequency filter capacitors that remove unwanted high-frequency clutter from the PV board and load, reducing interference with the microcontroller and system. The varistor RVl absorbs lightning pressure from the lightning through the PV panel and leads into the controller. Components such as T4 and D6 stabilize the voltage at the input of the 12V battery by about 10V to prevent the effects of battery voltage changes on the system. T2, D4 regulator 5V supply microcontroller and individual components. D1, D3 are MOSFET gate protection elements. R1, R2, R12, R28, and D5 form a solar PV panel voltage detection circuit, and various statuses of the PV board are input to the single-chip microcomputer by U1's 3 pins, and the courtyard lights are automatically switched on and off. R19, R24, C6 form a battery voltage detection circuit, from the battery voltage across the battery to reflect the state of the battery, and then processed by the microcontroller software, to make the appropriate charge for each stage of control. One foot of the one-chip computer U1 is the positive power foot, 10 foot is the control ground wire, namely the negative end of the battery. Pin 4 is a lead-acid liquid battery and colloidal battery selection function pin. It is determined by the closure of the S4 switch that the battery is a colloidal structure. T3 is the transistor that controls the output of the load. When it is turned on, the MOS output control transistor T turns off, so that the load RL has no power and the output protection LED1 is on.