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Controller

2021-09-29 17:25:19

The controller is an important part of the solar lamp system, and its performance directly affects the service life of the system, especially the service life of the battery. The system realizes the main functions of system working state management, battery residual capacity management, battery MPR (maximum photovoltaic power tracking) charging control, switching control of main power supply and standby power supply, and battery temperature compensation through the controller. The controller uses industrial MCU (microcontroller) as the main controller. Through the measurement of ambient temperature, the detection and judgment of voltage, current and other parameters of battery and solar cell module, it controls the opening and closing of MOSFET devices (metal oxide semiconductor effect transistor), achieves various control and protection functions, and plays the role of overcharge protection and over discharge protection for battery. In places with large temperature difference, the qualified controller shall also have the function of temperature compensation. Other additional functions such as optical control switch and time control switch shall be auxiliary functions of the controller. The controller is the key component to act as the manager in the whole street lamp system. 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 overcharge point, discharge point, recovery connection point, etc. When selecting the street lamp controller, it is particularly necessary to pay attention to the parameters of the recovery connection point of the controller. Due to the voltage self recovery characteristics of the battery, when the battery is in the over discharge state, the controller cuts off the load and then the battery voltage recovers. If the parameter points of the controller are not set properly at this time, the lamp may flicker and shorten the service life of the battery and light source.

 

Control system

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 whole system, which controls the normal operation of the whole solar street lamp system. The microcomputer main control circuit has the measurement function. Through the detection and judgment of solar panel voltage, battery voltage and other parameters, it controls the opening or closing of the corresponding circuit to realize various control and protection functions. The charging drive line is composed of MOSFET drive module and MOSFET. MOSFET drive module adopts high-speed optocoupler isolation, emitter output, short-circuit protection and slow shutdown functions. The selected MOSFET is a special IC for isolated and energy-saving single chip microcomputer switching power supply. The full voltage input range of driving LED is 150 ~ 200V and the output current is 8 ~ 9A. Wide input voltage range, good voltage regulation rate and load regulation rate, strong anti-interference ability and low power consumption. The system completes the charging of the solar battery pack to the battery through the charging driving line, and the corresponding protection measures are also provided in the circuit. The lighting driving circuit is composed of IGBT driving module (insulated gate bipolar transistor) and MOSFET to adjust and control the brightness of lamps.

 

The lighting system can be flexibly controlled by programming, and the switching control can be realized by PWM (pulse width modulation) in any time period. For example, the street lamp controls the brightness of the first and second midnight, and the control proportion 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 make the optimal design according to the local geographical location, meteorological conditions and load conditions. However, due to seasonal factors, the solar radiation in winter is less than that in summer, and the power generated by the solar cell array in winter is less than that in summer, but the power required for lighting in winter is more than that in summer, so that the power generation and power demand of the lighting system are in contrast, It is still difficult to balance the monthly power generation surplus and power consumption loss. In order to improve the utilization rate of the power generation of the lighting system and overcome the shortcomings caused by the lack of power in the system, in the development of solar lighting system, people constantly analyze the common control modes of the lighting system and design various practical and feasible working modes. At the same time, the light source technology is also constantly updating, The charging mode of battery is also under constant research and exploration, and the effective utilization rate is getting higher and higher.

 

According to the characteristics of solar photovoltaic system, the influence of battery residual capacity should be considered in operation. When the system is normally turned on, the current battery capacity is obtained by using the battery residual capacity detection method, and the power supply time to be maintained by the battery is obtained after query, and then the existing power of the battery is used evenly. At the same time, the lighting mode of the system street lamp is flexibly controlled according to the available power of the battery that night, and the existing power of the battery is used reasonably.

 

Battery charge and discharge control

Battery charge and discharge control is an important function of the whole system. It not only affects the operation efficiency of the whole solar street lamp system, but also prevents over charging and over discharging of the battery pack. Overcharge or over discharge of battery has a serious impact on its performance and service life. The charge discharge control function can be divided into switch control (including single channel and multi-channel switch control) type and pulse width modulation (PWMD) control (including maximum power tracking control) type according to the control mode. The switching device in the switch control type can be relay or MOS (semiconductor metal oxide) transistor. Pulse width modulation (PWM) For the control type, only MOS transistors can be selected as its switching devices. In sunny days, the corresponding duty cycle mode is selected to charge the battery according to the remaining capacity of the battery, so as to strive for efficient charging; at night, the lamp brightness is adjusted by adjusting the duty cycle mode according to the remaining capacity of the battery and future weather conditions, so as to ensure balanced and rational use of the battery. In addition The system also has the function of protecting the battery from overcharge, that is, when the charging voltage is higher than the protection voltage, the charging voltage of the battery will be automatically reduced; after that, when the voltage falls to the maintenance voltage, the battery will enter the floating charge state. When it is lower than the maintenance voltage, the floating charge will be closed and enter the equalizing charge state. When the battery voltage is lower than the protection voltage, the controller will automatically close the load switch to protect the battery No damage. Charging by PWM can not only maximize the efficiency of solar panels, but also improve the charging efficiency of the system.

 

Any independent photovoltaic system must have a method to prevent reverse current from flowing from the battery to the array. If the controller does not have this function, blocking diodes are used. Blocking diodes can be on each parallel branch and on the main road between the array and the controller. However, when multiple branches are connected together to form a large system, blocking diodes should be used on each branch The diode is used to prevent the current from flowing from the strong current branch to the weak current branch due to branch failure or shielding. In addition, if several batteries are shaded, they will not generate current and will become reverse bias, which means that the shielded battery consumes power and generates heat. Over time, it will form a fault, so the bypass diode is added for protection.

In most photovoltaic systems, the controller is used to protect the battery from overcharge or over discharge. Overcharge may vaporize the electrolyte in the battery and cause failure, and over discharge of the battery will cause premature failure of the battery. Overcharge and over discharge may damage the load, so the controller is an important component in the photovoltaic system. The function of the controller depends on the state of charge (SOC) of the battery To control the system. When the battery is about to be full, the controller will disconnect part or all of the array; when the battery discharge is lower than the preset level, all or part of the load will be disconnected (at this time, the controller includes low-voltage circuit breaking function).

 

The controller has two action set points to protect the battery. Each control point has an action compensation set point. For example, for a 12V battery, the array open circuit voltage of the controller is usually set at 14V. In this way, when the battery voltage reaches this value, the controller will disconnect the array. Generally, the battery voltage will quickly drop to 13V; the array reconnection voltage of the controller is usually set at 1 2.8V. In this way, when the battery voltage drops to 128, the controller acts to connect the array to the battery and continue to charge the battery. Similarly, when the voltage reaches 11.5V, the load is disconnected and can not be connected until the voltage reaches 12.4V. These on-off voltages of some controllers are adjustable within a certain range. This performance is very useful and can monitor the use of the battery The controller voltage must be consistent with the nominal voltage of the system and must be able to control the maximum current generated by the photovoltaic array.

 

Other characteristic parameters of the controller include: efficiency, temperature compensation, reverse current protection, display table or status light, adjustable set point (high voltage open circuit, high voltage on, low voltage open circuit, low voltage on), low voltage alarm, maximum power tracking, etc.

 

Type of controller

There are two basic types of controllers in photovoltaic systems. One is shunt controller, which is used to change or shunt battery charging current. These controllers have a large radiator to dissipate the heat generated by the excess current. Most shunt controllers are designed for systems with currents below 30A. The other is the series controller, which disconnects the charging current by disconnecting the photovoltaic array. Shunt controller and series controller can also be divided into many categories, but in general, these two types of controllers can be designed into single-stage or multi-stage working mode. The single-stage controller disconnects the array when the voltage reaches the highest level; The multi-stage controller allows different current charging when the battery is close to full charging, which is an effective charging method. When the battery is close to the full charge state, its internal resistance increases and is charged with a small current, which can reduce the energy loss.

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