250W wind power grid-connected inverter

The inverter is interfaced to the grid via an LCL filter. A relay is used to connect and disconnect the inverter from the grid whenever required by the application. The schematic in Figure 11 shows the filtering and relay schematic section.

This application note describes the implementation of a 250 W grid connected DC-AC system suitable for operation with standard photovoltaic (PV) modules. The design is associated to the STEVAL-ISV003V1 demonstration board which demonstrates the possibility of implementing a full microinverter solution (MIC) using STMicroelectronics products.

Every algorithm for grid-connected inverter operation is based on the estimation or direct measurement of grid voltage frequency and phase angle. The detection method used in this implementation for a single-phase inverter is based on a synchronous reference frame PLL.

Figure 38. Figure 39. This application note describes the design and performance of a dual stage 250 W microinverter characterized by maximum power point tracking and active and reactive power control capability. This is the main reason why the power conversion is based on a dual stage topology rather than the more common single-stage one.

The control algorithm has been developed to allow system operation both with 230 V AC, 50 Hz grids and with 240 V AC, 60 Hz without any hardware modifications. The connection to a 120 V AC, 50/60 Hz grid requires few hardware modifications to ensure the best system performance.

In these operating conditions the current THD is 2.8%. When operating in grid connection, the current THD is higher and equal to 4.8% at full load while the power factor is equal to 0.92. Figure 30 shows the current and voltage waveforms during grid connected operation.