An important part of the solar lighting system is the controller, whose performance directly affects the life of the system, especially the life of the battery. The system realizes the main functions of the management of the system working status, the management of the remaining capacity of the battery, the MPPT (Maximum Photovoltaic Power Tracking) charging control of the battery, the switching control of the main power supply and the backup power supply, and the temperature compensation of the battery through the controller. The controller uses an industrial-grade MCU (microcontroller) as the main controller. Through the measurement of the ambient temperature, the detection and judgment of the voltage and current of the battery and solar cell components, it controls the turn-on and turn-off of the MOSFET device (metal oxide semiconductor effect tube), to achieve various control and protection functions, and play the role of overcharge protection and overdischarge protection for the battery. In places with large temperature differences, a qualified controller should also have the function of temperature compensation. Other additional functions such as light-controlled switches and time-controlled switches should be auxiliary functions of the controller. The controller is the key component of the entire street light system as a manager, and its biggest function is to comprehensively manage the battery. A good controller should set various key parameter points according to the characteristics of the battery, such as the battery’s overcharge point, overdischarge point, and recovery connection point. When choosing a street light controller, you need to pay special attention to the controller’s recovery of connection point parameters. Because the battery has voltage self-recovery characteristics, when the battery is in an over-discharged state, the controller cuts off the load, and then the battery voltage is restored. If the parameter points of the controller are not set properly at this time, the lamps may flicker and shorten the life of the battery and light source.
The control system includes: microcomputer main control circuit, charging drive circuit and lighting drive circuit. The microcomputer main control circuit is the control core of the entire system, which controls the normal operation of the entire solar street light system. The main control circuit of the microcomputer has a measurement function. Through the detection and judgment of the solar panel voltage, battery voltage and other parameters, it can control the opening or closing of the corresponding circuit to realize various control and protection functions. The charging drive circuit is composed of a MOSFET drive module and a MOSFET. The MOSFET drive module adopts high-speed optocoupler isolation, emitter output, short circuit protection and slow shutdown functions. The selected MOSFET is an isolated energy-saving single-chip microcomputer switching power supply dedicated IC to drive the LED. The full voltage input range is 150~200V, the output current is 8~9A, and the input voltage range is wide, with good voltage regulation and load regulation, strong anti-interference ability and low power consumption. The system completes the charging of the solar battery pack to the storage battery through the charging drive circuit, and corresponding protection measures are also provided in the circuit. The lighting drive circuit is composed of IGBT drive module (insulated gate bipolar body tube) and MOSFET to realize the adjustment and control of the brightness of the lamp.
The lighting system can be controlled flexibly through programming, and the switch can be controlled by PWM (Pulse Width Modulation) in any period of time. For example, street lights control the brightness of the first half of the night and the second half of the night, and the control ratio depends on the situation; turn on the unilateral street lights or turn on the lights in the first half of the night, and turn off the lights in the second half of the night. The control system can be optimally designed according to the local geographic location, meteorological conditions and load conditions. However, due to seasonal factors, the solar radiation is less in winter than in summer, and the solar cell array generates less electricity in winter than in summer, while the electricity required for lighting in winter is more than in summer, which makes the power generation of the lighting system contrast with the electricity demand, which is still difficult to balance the monthly power generation surplus and the power consumption loss. In order to improve the utilization of the power generation of the lighting system and overcome the shortcomings caused by the lack of power, in the development of solar lighting systems, people continue to analyze the commonly used control modes of the lighting system and design various practical and feasible working modes. At the same time, the light source technology is constantly being updated, and the effective utilization rate of the battery charging mode is also getting higher and higher in the continuous research and exploration.
According to the characteristics of the solar photovoltaic system, the operation must take into account the influence of the remaining capacity of the battery. When the system is turned on normally, the current battery capacity is obtained using the battery remaining capacity detection method, and the power supply time that the battery will maintain after the query is obtained, and then the existing battery power is used on average. At the same time, the street lights of the system can be flexibly controlled according to the amount of storage pool that can be used that night, and the existing power of the battery can be used reasonably.
There are two basic types of controllers in photovoltaic systems. One is the shunt controller, which is used to change or shunt the battery charging current. These controllers have a large heat sink to dissipate the heat generated by the excess current. Most shunt controllers are designed for systems with currents below 30A. The other is a series controller, which disconnects the charging current by disconnecting the photovoltaic array. Shunt controllers and series controllers can also be divided into many types, but in general, both types of controllers can be designed as single-stage or multi-stage operation. The single-stage controller disconnects the array when the voltage reaches the highest level; while the multi-stage controller allows charging with different currents when the battery is nearly fully charged, which is an effective charging method. When the battery is close to the fully charged state, its internal resistance increases and it is charged with a small current, which can reduce energy loss.