Saint Lucia PV grid-connected inverter

Every algorithm for grid-connected inverter operation is based on the estimation or direct measurement of grid-voltage frequency and phase angle. Both parameters are fundamental for correct operation and special care must be taken in their detection to avoid the influence of any external noise.

As PV systems need an electronic interface to be connected to the grid or standalone loads, the PV market has started appealing to many power electronics manufacturers. Improvements in design, technology and manufacturing of PV inverters, as well as cost reduction and high efficiency, are always the main objectives, [see References 1, 2].

A single-phase grid-connected inverter, with unipolar pulse-width modulation, operates from a DC voltage source and is characterized by four modes of operation or states. Two modes take place during the positive load current period and two modes in the negative load current period, as shown in Table 6. Table 6.

Table 1. The dual-stage inverter for grid-connected applications includes a DC-DC converter to amplify the voltage and a DC-AC inverter to control the current injected into the grid. Figure 3. The DC-DC converter is depicted in Figure 3 together with the DC-AC converter and LCL filter.

The inverter current is transformed, using Park equations, in the two components referred to the rotating DQ reference frame of the grid voltage. These components, Id and Iq, are proportional to active and reactive generated power, respectively.

For this reason, the power converter, based on a dual-stage topology, has been investigated and experimentally evaluated for photovoltaic applications. The converter performs MPPT and grid connection by means of an ARM Cortex M3-based STM32F103xx microcontroller, which is proven to be well suited for such an application.