Grid-Tied Inverter

This project has a bit of an experimental character and essentially consists of two parts:

• A DC to DC converter that brings the battery voltage from nominal 48V (the batteries are charged by PV modules) to 350V.
• An inverter that generates 230V AC (50Hz) from 350V DC.

The DC-to-DC converter is of course protected against all adverse reactions (undervoltage, overvoltage, overcurrent, overtemperature,..) and is designed for high efficiency.

The output voltage (nominal 350V DC) is galvanically isolated from the input voltage and can be adjusted in the range of 280V to 380V. This is necessary to feed energy into an existing 230V grid in conjunction with the inverter.

The inverter generates a short-circuit-proof, 230V sine AC voltage from the nominal 350V DC, previously with the DC DC converter.

 

To be flexible, the control voltages for the IGPTs come from a small extra board attached:

 

I have chosen two development steps here: First, to generate only the 230V AC (not synchronized). Here the control signals are generated with an ASIC.

In the second step, the generated 230 V AC is synchronized with the external mains voltage. The energy is supplied by means of PLL, current control and slight phase shift. An STM32L475 or STM32G474 (STM32CubeIDE) make the PLL and controls and regulates the H-bridge.

Attached is an image demonstrating how the PLL works. The mains voltage is blue, and the voltage generated and synchronized by the inverter is yellow. Using MCU PLL -> This requires a bit of mathematics (Inverse Park and Clarke Transformation, Proportional Resonant Controller, ...).