Solar photovoltaic grid-connected control inverter working principle and control method

RF cable can be customized for other specifications

description:

This paper mainly introduces the system components of the grid-connected photovoltaic power generation system and the working principle of the main components. The basic principle of maximum power tracking is given, and the main circuit topology and control method of photovoltaic inverter are analyzed. As a sunrise technology that has the potential to revolutionize people's lives, solar photovoltaic technology has a bright future. Let us hope that photovoltaic technology will make greater contributions to mankind tomorrow.

Figure 1 shows the structure of a grid-connected photovoltaic system. Grid-connected photovoltaic systems consist of two major components: one, solar modules. The light energy that transmits the sun to the earth is converted into DC power; second, the solar-controlled inverter and the grid-connected equipment are responsible for converting the output DC power of the panel into the AC energy acceptable to the grid. Depending on the power, the output form of the solar inverter can be single-phase or three-phase; it can be equipped with an isolation transformer or an isolation transformer.

The solar control inverter and the grid-connected complete equipment mainly comprise a controller, an inverter and a monitoring and protection unit. The controller mainly realizes the maximum power tracking of the solar panel. The inverter is mainly responsible for converting the DC power outputted by the controller into a regulated and stable frequency AC power feeding grid. The monitoring and protection unit is mainly responsible for the safety related problems of the power generation system such as the islanding effect. Protection, and timely communication with the host computer to transfer energy transmission information.

Figure 2 shows the ideal circuit model for a silicon-type photovoltaic panel. Among them, Iph is a photo-generated current, and the Iph value is related to the area of ​​the photovoltaic cell, the irradiance of the incident light, and the ambient temperature. The ID is dark current. In the absence of sunlight, the basic external characteristics of silicon solar panels are similar to ordinary diodes. Dark current refers to the unidirectional current flowing through the PN junction under the external voltage of the photovoltaic cell in the absence of illumination. v is the open circuit voltage, RS is a series resistance generally less than 1 ohm, and RSH is a bypass resistance of several tens of kilo ohms.

In the high output voltage region, the solar panel has low internal resistance and can be regarded as a series of different voltage sources. In the low output voltage region, the power supply has high internal resistance characteristics and can be regarded as different current sources. The intersection of the voltage source and the current source is the maximum output power of the panel under the corresponding conditions. When the temperature of the panel remains the same, this maximum power value will change with the change of the light intensity. The maximum power tracking requirement can automatically track the condition that the panel works at an extremely high output power. The circuit topology of the solar controller is, in principle, a step-up chopper, which adjusts the duty cycle of the switching device S to adjust the equivalent load impedance of the panel to achieve maximum power tracking of the panel. The maximum power tracking technology has two technical routes: one is CVT technology, which controls the battery component port voltage to approximate the maximum power tracking. This method is simple but the tracking accuracy is not enough. The second is MTTP technology to detect the PV array output power in real time. Maximum power tracking is achieved by adjusting the impedance. At present, the MPPT technology widely used by solar inverter manufacturers.