Based on the basic principle and control strategy of photovoltaic grid connected inverters, a structure of grid connected inverters was designed, which adopts a front and rear two-stage
structure with built-in high-frequency transformers, namely the front stage DC/DC high-frequency boost and the rear stage DC/AC power frequency inverter. This design mode has the
advantages of simple circuit, stable performance, and high conversion efficiency.

In today's increasingly tense energy situation, photovoltaic power generation technology is receiving increasing attention. The direct current generated by solar cells and wind turbines

needs to be inverted by inverters and meet the specified requirements before being connected to the grid. Therefore, the design of inverters is related to the reasonable, efficient, and
economical operation of photovoltaic systems.

The structure of photovoltaic grid connected inverters mainly consists of a front-end DC/DC converter and a back-end DC/AC inverter. The basic principle is to convert low-voltage direct
current into high-voltage direct current through high-frequency conversion technology, and then obtain 220V alternating current through a power frequency inverter circuit. This structure
has the advantages of simple circuit, low no-load loss of the inverter power supply, high output power, high inverter efficiency, good stability, and low distortion.

The control of the DC/DC module of the inverter main circuit uses the SG3525 chip. SG3525 is a dual output SPWM pulse width modulation chip that generates a PWM waveform with

variable duty cycle to drive the gate of the thyristor to control its on/off, thereby achieving the goal of controlling the output waveform.

As a key module of the grid connected inverter, the DC/AC module has higher control requirements. This design uses TI's TMS320F240 as the main control chip, which is used to collect
grid synchronization signals, AC input voltage signals, and adjust the pulse frequency of the IGBT gate drive circuit. Through software phase-locked loop control technology based on DSP
chips, the frequency and phase control of the grid connected current are completed, so that the output voltage meets the same frequency as the grid voltage In phase relationship.

The filtering adopts a second-order bandpass filter, which is a type of active filter used to transmit signals in useful frequency bands and suppress or attenuate signals in useless frequency
bands. It can effectively filter out the high-frequency interference waveform generated after inverter, so that the voltage waveform after inverter meets the requirements of grid connection.