AN3095 datasheet(38/55 Pages) STMICROELECTRONICS

38 / 55 page

STM32F103xx-based current control strategy for inverter grid connection

AN3095

38/55

Doc ID 16555 Rev 3

STM32F103xx-based current control strategy for

inverter grid connection

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.

The switching patterns are defined by a control algorithm which generates the desired

outputs starting from the information provided by the feedback signals. For example,

algorithms for the grid connection are based on the use of current controllers, consisting of a

single loop or multiple loops according to the desired level of dynamics and accuracy.

Multiple-loop controllers are generally preferred, thanks both to their superior performance

and the relative ease of implementation in modern microcontrollers. With single-voltage loop

control methods, the inverter output voltage is compared with a sinusoidal reference,

proportional to the grid voltage and the generated error is then sent to the input of a current

regulator to create a sinusoidal reference for the PWM modulator. Despite its simple

implementation, this approach does not provide good regulation under non-linear loads and

is characterized by steady-state error. For these reasons, both output voltage and current

are used in control algorithms to provide better dynamic response and damping of the

resonant peak caused by the output LC or LCL filter. However, the time varying nature of the

controlled variables prevents an optimal regulation of output voltage and current. To

overcome such problems, a predictive current controller or deadbeat controller may be

implemented. The first approach, based on the assumption that a precise model of the

controlled system is available, predicts the inverter voltages required to force the measured

current to follow the reference current, but has the disadvantage of being difficult to

implement. The second method, while providing really fast dynamic response, is very

sensitive to system noise and is dependent on system parameters, [see References 12, 13,

, 15, 16].

Recently, new methods such as the PR (proportional resonant) current control method have

been adopted to control the PV inverters with zero steady-state error and the possibility of

selective harmonic compensation with low computational effort. However, implementations

in low cost fixed-point microcontrollers have been proven to be difficult due to limited

computational capability and restricted numerical representation.

Another possible current-control method uses DQ synchronous reference frames and

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

and simple implementation.

Table 6.

Operating modes of grid-connected voltage source inverter

Mode

Vout

Iout

OnOff

Off

OnOff

Off

Vbus

Off

-Vbus

Off

AN3095 bảng dữ liệu(PDF) 38 Page - STMicroelectronics

AN3095 bảng dữ liệu(HTML) 38 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

bảng dữ liệu tải về

Link URL