Figure 1-3 shows a typical block diagram of micro inverter. There are two power stages in the micro inverter. The first power stage is DC/DC converter that converts the variable PV panels output voltage to a regulated high-voltage DC link suitable for the DC/AC inverter stage, and the first power stage also achieves the MPPT function. Commonly a micro inverter has 1, 2, or 4 DC/DC blocks allowing connected to 1, 2, or 4 PV panels, accordingly. Examples in Figure 1-2 show micro inverter with DC/DC blocks. The second power stage is the inverter that converts the high-voltage DC link to the grid ac voltage. It can be single phase or three phases inverter based on the targeted system configuration.

Figure 1-3 Block Diagram of Micro Inverter

Besides the two power stages, there are other function blocks, such as DSP control, gate driver, PV voltage and current sensing, inverter or grid voltage and current sensing, PV current OCP, grid voltage zero-crossing and Insulation detection, wire/wireless communication and temperature sensing, and importantly the bias supply which is critical for the entire system to function.

Generally, the DSP control system and related signal acquisition circuits operates in low voltage referenced to the DC side ground, which is also the PV panel return node. So, no isolation is required for these circuit. However, circuits in the DC/AC side, such as the inverter gate driver, need isolation. This requires the auxiliary bias supply, which takes power from the PV panel, to be able to produce both the non-isolated low voltage bias voltages for the DSP and signal acquisition circuit, and the isolate bias voltages for the inverter gate drivers' use.