The DS200DCFBG1BLC inverter system, as the core of photovoltaic power generation, currently operates independently or in grid connection. If the two are effectively combined, the application scope of the system can be further expanded, the structure can be simplified, and investment can be reduced. This proposes an independent/grid connected duplex mode inverter system. The system uses an isolated full bridge DC/DC converter to construct the front stage, uses a high-frequency transformer to reduce the system volume, and uses a phase-shifting PWM ZVS control method to reduce switching losses; By using a full bridge DC/AC inverter to construct the rear stage and adopting a unipolar frequency doubling SPWM method, the elimination and suppression of harmonics are strengthened to improve system efficiency. On this basis, the control methods of each part were analyzed, and improvements were made to the inverter control methods under the two working modes. Finally, a novel circuit switching method is proposed to achieve the conversion of operating modes.

The working process of DS200DCFBG1BLC is divided into two steps:

(1) The front stage isolated full bridge DC/DC converter increases the variable low-voltage DC input to a stable high-voltage DC output of 400 V.

On the one hand, this section utilizes switch junction capacitors and transformer leakage inductance to achieve circuit ZVS, thereby reducing switch losses and improving system efficiency; On the other hand, increasing the DC isolation capacitor can solve the problem of magnetic bias caused by the inconsistent characteristics of switching tubes, which leads to the generation of DC components in the transformer primary.

(2) The rear full bridge inverter converts a stable high-voltage DC input of 400 V into a sinusoidal AC output of 220 V/50Hz.

This section achieves twice the equivalent switching frequency at a lower switching frequency through unipolar frequency doubling SPWM, thereby reducing switching losses and helping to eliminate harmonics and improve the quality of electrical energy output. When the grid connection switch is turned on, the system operates independently and supplies power to the load; When the switch is closed, the system is connected to the grid for operation, and the output is fed into the grid.