In the independent operation of photovoltaic power generation system and solar street light, energy storage battery must be equipped. The battery plays the role of storing and regulating electric energy. When there is excess electric energy generated by sufficient sunshine or strong wind, the battery stores the excess electric energy; on the contrary, when the power generation of the system is insufficient or the power consumption of the load is large, the battery supplements the power to the load and keeps the power supply voltage stable. (Click to enter some recommended good quality lithium ups battery product pages)
Batteries, especially lead-acid batteries, require control during charging and discharging. Frequent overcharge and overdischarge will affect the service life of the battery. Overcharging will cause a large amount of gas (electrolyzed water) from the battery, resulting in the loss of water and the shedding of active substances; overdischarge will easily accelerate the commercial corrosion and irreversible sulfation of the grid. In order to protect the battery from being damaged by overcharge and overdischarge, it is necessary to have a control system to prevent overcharge and overdischarge of the battery, which is called a charge and discharge controller. The controller judges whether the battery has reached the overcharge point or overdischarge point by detecting the voltage or state of charge of the battery, and issues instructions to continue charging, discharging or terminating charging and discharging according to the detection result.
With the popularization and widespread use of photovoltaic power generation systems and solar street lights, designers and users have higher and higher requirements for the rationality of the system’s operating state and operating mode, and the safety of the system is more prominent and important. Therefore, in recent years, designers have endowed the controller with more protection and monitoring functions, so that the early battery charge controller has developed into today’s more complex system controller. In addition, the controller has also been greatly developed and improved in terms of the control principle and the components used. At present, the advanced system controller has used a microprocessor to realize software programming and intelligent control.
The main functions of the charge and discharge controller in the photovoltaic power generation system are as follows.
(1) High voltage (HVD) disconnection and recovery function, the controller shall have the function of input high voltage disconnection and recovery connection.
For a 48V on/off controller, the voltage setting for high voltage disconnect and restore connection, HVD is 56.5V; restore is 52V.
(2) Under-voltage (LVG) alarm and recovery function, when the battery voltage drops to the under-voltage alarm point of 44V, the controller should automatically send out an audible and visual alarm signal; the recovery point is 49V.
(3) Low voltage (LVD) disconnection and recovery function. This function prevents the battery from over-discharging. Connect the load through a relay or electronic switch, which can automatically cut off the load at a given low voltage point. When the voltage rises to the safe operating range, the load will be automatically reconnected or manually reconnected.
(4) Protection function, circuit protection to prevent any load short circuit; circuit protection to prevent internal short circuit of the charge controller; protection to prevent reverse discharge of batteries through solar cell components at night; circuit protection to prevent reverse polarity of loads, solar cell modules or batteries; line lightning protection to prevent induction lightning.
(5) Temperature compensation function (only applicable to the full voltage of the battery), when the temperature of the battery is lower than 25 ℃, the full voltage of the battery should be appropriately increased; on the contrary, when it is away from this temperature, the threshold of the full voltage of the battery should be appropriately reduced. Usually the temperature compensation coefficient of the battery is -(3~5)mV/(℃·Cell),
(6) The solar street light controller also has the functions of light control switch and timing work.