AN4070 Datasheet, PDF (29/53 Pages) STMicroelectronics – 250 W grid connected microinverter

AN4070
STM32F103xx based current control for inverter grid connection
4
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
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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, V_β, phase shifted with
respect to the real grid voltage, V_α, of 90 degrees. This is done via firmware. Knowing the
two voltage components V_β and V_α, the transformation from the stationary reference frame
to the d-q rotating frame is given by the following equations:
Equation 39
⎡V_d
⎢⎣_Vq
⎤
⎥
⎦
=
⎡ cos θ
⎢⎣− _{sin θ}
sin θ ⎤
cos θ⎥⎦
⋅
⎡
⎢
⎣
V_β
V_α
⎤
⎥
⎦
where θ is the angle between the d-q reference frame and the stationary reference frame
(Figure 27). The reverse transformation is given by:
Doc ID 022934 Rev 1
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