Charge and discharge controller for photovoltaic power system

The charge and discharge controller is also called a photovoltaic controller, and the low-power photovoltaic controller panel is shown in Figure 1. Photovoltaic controller is an indispensable part of an independent photovoltaic power generation system. It is the most basic control circuit, which is mainly composed of electronic devices, meters, relays and switches. Any independent photovoltaic power generation system, as large as hundreds of kilowatts of photovoltaic systems, as small as a lawn lamp and flashlight, must use a charge and discharge controller. Although the size of the system is different, the control principle of the charge and discharge controller is the same. The complexity of hardware and software are not the same.
Photovoltaic controllers should have the following functions: ①Prevent battery overcharging and overdischarge, and prolong battery life; ②Prevent solar panels or photovoltaic arrays, and battery polarities from being reversed; ③Prevent loads, controllers, inverters and other equipment Short circuit; ④With lightning breakdown protection; ⑤With temperature compensation function; ⑥Display various working status of photovoltaic power generation system, including battery (group) voltage, load status, photovoltaic array working status, auxiliary power supply status, environment Temperature status and fault alarm, etc.

Charge and discharge controller for photovoltaic power system
Figure 1 Low-power photovoltaic controller panel

Figure 1 Low-power photovoltaic controller panel
(1) The role of photovoltaic controller
In a small photovoltaic system, the photovoltaic controller is generally used to protect the battery, prevent it from overcharging and overdischarging, and prolong the service life of the battery.
In large and medium-sized systems, the photovoltaic controller plays a role in balancing the energy of the photovoltaic system, protecting the battery and the normal operation of the entire system.

(2) Classification of photovoltaic controllers
Photovoltaic controllers are divided into parallel type, series type, pulse width modulation (PWM) type, multi-channel control type, two-stage dual voltage control type and maximum power point tracking type according to the different circuit modes.
According to the different input power and load power of solar cell components, it can be divided into low power type, medium power type, high power type and special controller.
There is also a controller with automatic data acquisition, data display and remote communication functions called intelligent controllers.

(3) Circuit principle of photovoltaic controller
Figure 2 shows the basic principle diagram of a most basic photovoltaic controller. The circuit is mainly composed of solar cell components, control circuits, control switches, batteries and loads.

Charge and discharge controller for photovoltaic power system
Figure 2 Basic schematic diagram of photovoltaic controller

(4) Introduction of several common charge and discharge controllers
①The battery charger UC3906 with UCG3906 as its dedicated chip is used as a dedicated chip for charging sealed lead-acid batteries. It has all the control and detection functions required to achieve the best charging of sealed lead-acid batteries. More importantly, it can make the charger’s various conversion voltages change with the change of the battery voltage temperature coefficient, so that the sealed lead-acid battery can reach the best state of charge in a wide temperature range.
②Solar lawn lamp controller The solar lawn lamp is an independent photovoltaic power generation system, so the lawn lamp controller is the same as other controllers. In addition to controlling the normal operation of the lamp, it should also have anti-overcharge, anti-overdischarge and anti-reverse And other protection functions.

(5) The control principle of the controller
The control principle of the photovoltaic controller is usually expressed in the form of the charge and discharge protection mode of the controller. The photovoltaic controller must have the following charge and discharge protection modes:
(1) Direct charge protection point voltage
(2) Voltage of equalization control point
(3) Floating charge control point voltage
(4) Over-discharge protection point voltage

(6) Selection of controller
At present, there are no national or industry production standards and model identification technical regulations for charge and discharge controllers. There are many types of controllers on the market, so the selection design here refers to the determination of the technical parameters of the product. The following technical parameters are usually given:
(1) System voltage
(2) The maximum charging current of the controller
(3) Allowable input channels of the controller
(4) Loss of circuit itself
(5) Battery overcharge protection voltage
(6) Over-discharge protection voltage of battery
(7) Battery charging float voltage
(8) Temperature compensation
(9) Working environment temperature controller