Do you know the different between MPPT and PWM? In inverter

In the solar off-grid system, the role of the photovoltaic controller is to convert the electricity from the photovoltaic components and store it in the battery. In addition, it also has the functions of protecting the battery and preventing the battery from overcharging. At present, the controller mainly has two technical routes: pulse width debugging (PWM) mode and maximum power point tracking (MPPT) mode. Each method has its advantages and disadvantages, which can be selected according to different scenarios.

1. PWM controller

The early photovoltaic controllers were all PWM. This kind of electrical structure is simple. The controller consists of a power main switch and capacitor as well as a drive and protection circuit. The output voltage is controlled by the PWM duty cycle of the switch tube.

The PWM controller connects the solar array and the solar panel with only one switch. As the battery is gradually charged and the battery voltage rises, the PWM controller will gradually reduce the amount of power provided to the battery, and the photovoltaic output will be output according to the maximum power. . The PWM controller has the function of battery charge and discharge management, which can prevent the battery from overcharging and over-discharging.

Because there is only one switch between the solar module and the battery of the PWM controller, there is no voltage divider device such as inductance in the middle, so in the design, the voltage of the module is about 1.2-2.0 times the voltage of the battery, such as a 24V battery, the module input The voltage is between 30-50V, each string can only be equipped with one module, 48V battery, the input voltage of the module is between 60-80V, and each string can only be equipped with two modules.

2. MPPT controller

The MPPT controller is the second-generation solar controller. Compared with the PWM controller, it has an additional inductor and power diode, so it has more powerful functions.

One is that it has a maximum power tracking function. During battery charging, solar modules can output at maximum power unless the battery reaches saturation; the other is that the voltage range of photovoltaic modules is wide, and there is a power switch tube and inductance circuit in the middle of the controller. The voltage of the module is 1.2-3.5 times the voltage of the battery. If it is a 24V battery, the input voltage of the module is between 30-80V. Each string can be equipped with one or two modules. If it is a 48V battery, the input voltage of the module is between Between 60-110V, each string can be equipped with two to three components.

How to choose PWM and MPPT controller

Both PWM and MPPT controllers have their own unique advantages and disadvantages. Which solution to choose depends on the design characteristics, cost, and external environment of the solar photovoltaic array. When we choose, we should focus on the following factors:

The PWM method has mature technology, simple and reliable circuit, and low price, but the utilization rate of components is low. The utilization rate of the module is about 80% or more; MPPT solar controller refers to the solar controller with the maximum power point tracking function. There is a BUCK step-down circuit between the module and the battery, and the utilization rate of the module is about 90% or more.

The main users of small off-grid systems below 2kW are poor areas without electricity, such as remote mountainous areas, and some poor countries in Africa. They mainly solve the needs of lighting. The users are very sensitive to prices. Therefore, it is recommended to use a PWM controller to correct the wave. Inverter, the controller, inverter and battery are integrated. This method has simple structure, high efficiency, convenient connection for users, and low price. There is no problem in driving light bulbs, small TVs, and small fans.

For off-grid systems above 2kW, it is recommended to use MPPT controllers, which have high component utilization, high overall machine efficiency and flexible component configuration. Generally speaking, no technology is the best, so for users, they should listen to the opinions of experts and ensure that they choose the correct controller to meet their needs.