MPPT&PWM Solar controller

1. What is the photovoltaic controller and the role of the photovoltaic controller?

Under the condition of illumination, solar street lights convert solar energy into electricity through solar panels and store it in the battery; When needed, the energy of the battery is converted into light energy to bring light to the night, and to achieve all this, you also need an insignificant but important configuration, that is, the photovoltaic controller.

The full name of the solar controller is photovoltaic charge and discharge controller, which is an automatic control device for controlling the solar cell array to charge the battery and the battery to power the solar inverter load in the photovoltaic power generation system.

It can set control conditions according to the charging and discharging characteristics of the battery, control the power output of the solar cell components and the battery to the load, stabilize the working state of the power station, and protect the battery, which can prevent the battery from overcharging, anti-reverse connection and anti-short circuit functions.

2. What are the categories of common photovoltaic controllers?

Photovoltaic charging controllers can be basically divided into five types: shunt photovoltaic controller, series photovoltaic controller, pulse width modulation photovoltaic controller (PWM), intelligent photovoltaic controller and maximum power tracking photovoltaic controller (MPPT). PWM and MPPT are commonly used.

3. What is PWM and MPPT?

PWM and MPPT are two different charging mode controllers for solar charging, which can be used to charge the battery with the current generated by the solar module. Both technologies are widely used in off-grid solar systems, and both work well to charge batteries efficiently. Choosing a PWM or MPPT controller is not purely based on which charging method is "better," but rather on which type of controller works best in your system.

PWM: Pulse-Width Modulation (PWM)

Pulse width modulation (PWM) refers to the digital output of the microprocessor to control the analog circuit, which is a method of digital coding the analog signal level. By controlling analog circuits digitally, the cost and power consumption of the system can be greatly reduced. Many microcontrollers include PWM controllers.

The early controller is generally this, the electrical structure is relatively simple, is composed of a power main switch, a capacitor, a drive and a protection circuit, actually equivalent to a switch, the component and the battery are connected together, the voltage of the component will be pulled down to close to the voltage of the battery pack. This controller adopts three stages of charging, namely, strong charge, balanced charge and floating charge.

① Strong charge: also called direct charging, that is, rapid charging, when the battery voltage is low, the battery is charged with high current and relatively high voltage.

Balanced charge: After the end of strong charge, the battery will stand for a period of time, until the voltage naturally falls to a certain value, it will enter the state of balanced charge, so that the battery end voltage is uniform and consistent.

③ After the end of the balanced charge, the battery will still be standing for a period of time, so that its end voltage naturally falls, when it falls to the "maintenance voltage" point, it will enter the floating charge condition, PWM (pulse width modulation) charging method, similar to "trickle charging", the battery voltage is low on the charge, one strand to avoid the battery temperature continues to rise, After adjusting the pulse width to reduce the battery charging current, so that the battery life is longer.

The controller of this charging mode can solve the problem of insufficient battery charging and ensure the service life of the battery. However, it should be noted that the charging efficiency of the PWM controller will be affected by temperature, and the charging efficiency is the best when the solar cell temperature is around 45~75 ° C.

MPPT: Maximum Power Point Tracking (MPPT)

To understand the difference between PWM and MPPT charging, let's first look at the power curve of photovoltaic panels. The power curve is important because it shows the expected power generation of the photovoltaic panel. The voltage (" V ") and current (" I ") generated by the photovoltaic panel. The voltage that generates the most power is called the "maximum power point". MPPT will dynamically track changes throughout the day, depending on the lighting conditions. P=U*I (P is the power generated by photovoltaic panels)

Power curve of photovoltaic panel

This controller is more complex, the cost is also a little higher, the price is usually several times or even tens of times the PWM controller, it can adjust the input voltage, so that it can get the maximum energy from the solar panel.

①MPPT current limiting charging: When the battery terminal voltage is very small, the MPPT charging method is used to pump the output power of the solar panel to the battery end, when the light intensity is strong, the output power of the solar panel is increased, the charging current reaches the threshold, and the MPPT charging is terminated and transferred to the constant current charging; When the light intensity is weak, it will be transferred to the MPPT charging mode.

2 Constant voltage equal charge: the battery in the MPPT charging mode and constant current charging mode free switch, cooperate with each other so that the battery voltage reaches the saturation voltage, it enters the constant voltage equal charge stage, with the battery charging current gradually decreases, to 0.01C, this charging stage terminates and enters the floating charge stage.

(3) Constant voltage floating charge: to float the battery with a voltage slightly less than the constant voltage charging, this stage is mainly used to supplement the kinetic energy consumed by the battery self-discharge.

4. Comparison between PWM and MPPT

The comparison between the two is simply made in a table

Compared with the PWM controller, the MPPT controller has the maximum power tracking function, before the battery does not reach the saturation state, during the charging period, to ensure that the solar panel is always at the maximum power output, will not be affected by temperature, from the charging efficiency, naturally is higher than PWM. In addition, the PWM controller can only be used with the relevant voltage, such as 12V system panel can only be used with 12V controller and battery, suitable for some small off-grid systems below 2kw, simple structure, convenient user connection, and relatively cheap price.

And MPPT controller use space to be larger, under normal circumstances, solar panel voltage between 12V~170V can be used, battery voltage 12~96V adjustable, applicability to be stronger, suitable for more than 2kw large off-grid system, high efficiency, component configuration is more flexible.