AN3095 datasheet(39/55 Pages) STMICROELECTRONICS

39 / 55 page

AN3095

STM32F103xx-based current control strategy for inverter grid connection

Doc ID 16555 Rev 3

39/55

For these reasons, this method was implemented on a 32-bit ARM-based STM32F103xx

microcontroller and its performance was verified through simulations and experimental

results on the grid connected inverter.

A block diagram of the implemented control algorithm is shown in Figure 24.

Figure 24.

Block diagram of the implemented control

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. The detection method used in this implementation for a single-phase

inverter is based on a synchronous reference frame PLL. While in three-phase inverters the

use of DQ based PLL is quite common, for single-phase inverters, the necessity of a virtual

bi-phase system arises. In fact, to create a rotating DQ reference, starting from a stationary

frame, at least two independent phases are required. This problem is overcome with the

creation of a virtual voltage, Vβ, phase-shifted with respect to the real grid voltage, Vα, of

90°. This task may be easily accomplished with firmware. If the two voltage components Vα

and Vβ are available, the transformation from the stationary reference frame to the DQ

rotating frame is given by:

Equation 54

where

θ is the angle between the DQ reference frame and the stationary reference frame

(Figure 25). The reverse transformation is given by:

Equation 55

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