The solar photovoltaic controller is the core component of the off-grid photovoltaic power generation system and the main component of the balance system. In small systems, the controller is mainly used to protect the battery. In large and medium-sized systems, the controller is responsible for balancing the energy of the photovoltaic system, protecting the battery and the normal operation of the entire system, and displaying the working status of the system. The controller can be used alone or integrated with the inverter. The appearance of a common photovoltaic controller is shown in Figure 1.
The photovoltaic controller should have the following functions: ①Prevent the battery from overcharging and overdischarging, and prolong the battery life; ②Prevent the battery components or the photovoltaic array and the battery from being connected in reverse polarity; ③Prevent the internal short circuit of the load, controller, inverter and other equipment; ④With the breakdown protection caused by lightning strike; ⑤With the function of temperature compensation; ⑥Display various working states of the photovoltaic power generation system, including battery (group) voltage, load state, photovoltaic square array working state, auxiliary power supply state, ambient temperature state, fault alarm, etc.
Photovoltaic controllers are divided into parallel type, series type, pulse width modulation type, multi-channel control type, two-stage dual voltage control type and maximum power tracking type according to the different circuit modes; according to the different input power and load power of battery components, it can be divided into low-power type, medium-power type, high-power type and dedicated controller (such as lawn lamp controller), etc.; according to the different control methods of the discharge process, it can be divided into the conventional over-discharge control type and the remaining power (SOC) discharge full-process control type. For the application of the microprocessor circuit, the realization of software programming and intelligent control, and the controller with automatic data acquisition, data display and remote communication functions, it is called an intelligent controller.
According to different photovoltaic systems, although the complexity of the controller control circuit is different, the basic principle is the same. Figure 2 is a block diagram of the most basic photovoltaic controller circuit. The circuit is composed of battery components, controller, storage battery and load. Switch 1 and switch 2 are respectively a charge control switch and a discharge control switch. When the switch 1 is closed, the battery module charges the battery through the controller; when the battery is overcharged, the switch 1 can cut off the charging circuit in time to stop the photovoltaic module from supplying power to the battery; the switch 1 can also automatically resume charging the battery according to a preset protection mode. When the switch 2 is closed, the battery supplies power to the load; when the battery is over-discharged, the switch 2 can cut off the discharge circuit in time, and the battery stops supplying power to the load; when the storage battery is recharged and reaches the preset recovery charging point, the switch 2 can automatically resume power supply. The switch 1 and the switch 2 can be composed of various switching elements, such as electronic switches such as various transistors, thyristors, solid state relays, power switching devices, and mechanical switches such as ordinary relays. The following articles respectively introduce the circuit principles and characteristics of various commonly used controllers according to the different circuit modes.