AN4070 datasheet(29/53 Pages) STMICROELECTRONICS

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AN4070

STM32F103xx based current control for inverter grid connection

Doc ID 022934 Rev 1

29/53

STM32F103xx based current control for inverter grid

connection

The current control method is based on a d-q synchronous reference frame which provides

both the advantage of zero steady-state error, thanks to the use of PI controllers, and simple

implementation. This method has been implemented on a 32-bit, ARM based

microcontroller (STM32F103xx) and its performance was verified through simulations and

experimental results.

A block diagram showing the five feedback signals processed by the microcontroller for the

correct operation of the control algorithm is shown in Figure 18.

Figure 19.

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. The detection method used in this

implementation for a single-phase inverter is based on a synchronous reference frame PLL.

Single-phase inverters require a virtual bi-phase system. In fact, to create a rotating d-q

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 degrees. This is done via firmware. Knowing the

two voltage components Vβ and Vα, the transformation from the stationary reference frame

to the d-q rotating frame is given by the following equations:

Equation 39

where

θ is the angle between the d-q reference frame and the stationary reference frame

(Figure 27). The reverse transformation is given by:

⎥

⎦

⎤

⎢

⎣

⎡

⋅

⎥

⎦

⎤

⎢

⎣

⎡

−

⎥

⎦

⎤

⎢

⎣

⎡

cos

sin

cos

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