Solar photovoltaic controller function
1. Battery overcharge and overdischarge protection;
2. Automatic recovery of discharge function;
3. Prevent the reverse connection between the battery and the solar cell.
(1) High voltage (HVD) disconnect and recovery function: The controller should have the function of input high voltage disconnection and recovery connection.
(2) Undervoltage (LVG) alarm and recovery function: When the battery voltage drops to the undervoltage alarm point, the controller should be able to automatically emit an audible and visual alarm signal.
(3) Low voltage (LVD) disconnect and recovery function: This function prevents overdischarge of the battery. The load is automatically disconnected at a given low pressure point by a relay or electronic switch that connects the load. When the voltage rises to a safe operating range, the load will automatically re-access or require manual re-access. Sometimes, a low pressure alarm is used instead of an automatic cut.
(4) Protection function:
1 Circuit protection against any load short circuit.
2 Circuit protection against internal short circuit of the charge controller.
3 Prevent night battery from being reverse-discharge protected by solar cell components.
4 Circuit protection against load, solar cell component or battery polarity reversal.
5 Prevent breakdown protection due to lightning strikes in the minefields.
(5) Temperature compensation function: When the battery temperature is lower than 25 °C, the battery should require a higher charging voltage in order to complete the charging process. Conversely, batteries above this temperature require a lower charging voltage. Usually, the lead-acid battery has a temperature compensation factor of -5mv/C/CELL.
Classification of solar photovoltaic controllers
Photovoltaic charging controllers can be basically divided into five types: parallel photovoltaic controllers, series photovoltaic controllers, pulse width modulation photovoltaic controllers, smart photovoltaic controllers, and maximum power tracking photovoltaic controllers.
1. Parallel photovoltaic controller. When the battery is full, the output of the photovoltaic array is shunted to the internal shunt resistor or power module using electronic components and then consumed as heat. Parallel photovoltaic controllers are typically used in small, low power systems such as voltages up to 12V, 20A, and systems. These controllers are reliable and do not have mechanical components such as relays.
2. Series photovoltaic controller. The mechanical relay is used to control the charging process and the photovoltaic array is switched off at night. It is typically used in higher power systems where the capacity of the relay determines the power level of the charge controller. It is easier to manufacture a series-type photovoltaic controller with a continuous energizing current of 45A or more.
3. Pulse width modulation type photovoltaic controller. It switches the input of the PV array in PWM pulses. When the battery tends to be full, the frequency and time of the pulse is shortened. According to research conducted by the National Laboratory of Sandia, this charging process forms a relatively complete state of charge, which can increase the total cycle life of the battery in the photovoltaic system.
4. Smart PV controller. Based on MCU (such as Intel's MCS51 series or Microchip's PIC series), the operating parameters of the photovoltaic power system are collected at high speed, and the single or multi-channel photovoltaic arrays are cut off and connected by software programs according to certain control rules. control. For medium and large-scale photovoltaic power systems, distance control can also be performed through the MCU's RS232 interface with the MODEM modem.
5. Maximum power tracking controller. The solar cell voltage V and the current I are multiplied to obtain the power P, and then it is judged whether the output power of the solar cell reaches the maximum at this time. If the power is not running at the maximum power point, the pulse width is just adjusted, the output duty ratio D is modulated, and the charging is changed. The current is again sampled in real time, and a determination is made whether or not to change the duty cycle. Through such a optimization process, the solar cell can always be operated at the maximum to fully utilize the output energy of the solar cell array. At the same time, the PWN modulation method is adopted to make the charging current become a pulse current to reduce the polarization of the battery and improve the charging efficiency.