PWM or MPPT? Distinguish the advantages and disadvantages


the choice of solar street light controller is no longer difficult

PWM or MPPT Under light conditions, solar street lights convert solar energy into electric energy through solar panels and store it in a battery. When needed, it converts the battery’s electric energy into light energy to bring light to the night and save it all. To achieve it, another inconspicuous but very important configuration is needed, and that is the photovoltaic controller.

Only with it can the electric energy generated by the solar panel be stored in the storage battery after transformation. In addition, it can also protect the storage battery and prevent the storage battery from overcharging. At present, there are two popular ones on the market. , PWM and MPPT controllers, two have their own advantages and disadvantages, and the adaptation scenarios are also different. Let’s take a look at it in detail below.

1. PWM controller (pulse width debugging method)

Early controllers were generally of this kind. The electrical structure was relatively simple. It consisted of a power main switch, a capacitor, a driver, and a protection circuit. It was actually equivalent to a switch that connected the component and the battery together. The voltage of the component will be pulled down to be close to the voltage of the battery pack.

This kind of controller uses a three-stage charging method: strong charge, balanced charge, and floating charge.

  • Strong charge: also called direct charge, which means rapid charging. When the battery voltage is low, the battery is charged with a high current and relatively high voltage.
  • Equalized charge: After the strong charge is over, the battery will stand for a period of time, and when the voltage naturally drops to a certain value, it will enter the state of equalized charge, so that the battery terminal voltage has a uniform consistency.
  • Floating charge: After the equalization charge is over, the battery will also stand for a period of time. When the voltage naturally drops to the “maintenance voltage” point, it is the floating charge stage, so that the battery can be kept in a satisfactory state of charge without overcharging.

The controller of this charging method can solve the problem of battery dissatisfaction and guarantee the service life of the battery. But it should be noted that the charging efficiency of the PWM controller will be affected by temperature. When the solar cell temperature is around 45~75℃, the charging efficiency is the best

2. MPPT controller (maximum power point tracking method)

This kind of controller is more complicated, and the cost is a little higher. The price is usually several times or even dozens of times that of the PWM controller. It can adjust the input voltage in order to obtain the maximum energy from the solar panel.

After that, the voltage is transformed into the charging voltage required by the battery, which cuts off the direct link between the solar panel and the battery, allowing the high-voltage solar panel to charge the low-voltage battery. It is divided into MPPT current limiting charging and constant voltage equalizing charging. And constant voltage float charge three-stage mode.

  • MPPT current-limiting charging: When the battery terminal voltage is very small, the MPPT charging method is used to draw the output power of the solar panel to the battery terminal. When the light intensity is strong, the output power of the solar panel increases, and the charging current reaches the threshold, then it is terminated MPPT charging will switch to constant current charging; when the light intensity becomes weak, it will switch to MPPT charging mode.
  • Constant voltage equalization charging: the battery can switch freely between MPPT charging mode and constant current charging mode. When the battery voltage reaches the saturation voltage, it enters the constant voltage equalization stage. As the battery charging current gradually decreases, it reaches 0.01C. At this time, the charging phase is terminated and enters the floating charging phase.
  • Constant voltage floating charge: Float the battery with a voltage slightly lower than that of constant voltage charging. This stage is mainly used to supplement the energy consumed by the self-discharge of the battery.

Compared with the PWM controller, the MPPT controller has a maximum power tracking function. Before the battery reaches the saturation state, during the charging period, it can ensure that the solar panel always outputs the maximum power without being affected by the temperature. From the charging efficiency, In other words, it is naturally higher than PWM or MPPT.

In addition, the PWM controller can only be used with related voltages. For example, the 12V system battery board can only be used with the 12V controller and battery. It is suitable for some small off-grid systems below 2kw. The structure is simple, the user wiring is convenient, and the price is relatively cheap.

The MPPT controller uses a larger space. Generally, the solar panel voltage can be used between 12V and 170V, and the battery voltage is adjustable from 12 to 96V. The applicability is stronger, and it is suitable for large-scale off-grid systems above 2kw. , High efficiency, and flexible component configuration.

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