A Tranformerless Grid-Connected Photovoltaic(2)

这些都是光伏发电系统吧比较经典的论文,希望可以帮到大家。大概都是零八年以后的IEEE论文,有些方法运用比较经典。

II. SYSTEM CONFIGURATION AND CONTROL

Figure 2 shows a schematic diagram of a transformerless type grid-connected PV system. The DC/DC converter is connected between the PV array and DC link capacitor, and controlled so as to track the maximum power point of the PV array.

The PWM inverter is synchronized and connected to the grid. The inverter current (Iinv) should be controlled not only to compensate the reactive current of the grid depending on the load, but also to produce its active current corresponding to the PV output power.

be obtained.

Figure 3 shows the proposed control block diagram. The DC/DC converter performs the maximum power point tracking (MPPT) to extract the maximum possible power from the PV array. The DC-link voltage controller is used to control the voltage loop to produce the dc reference current command (IVdc). The load current and the grid voltage are used in the PQC block to generate the active current component of the load current. Using (2), the required grid current amplitude can be calculated. The load current and required grid current amplitude which is multiplied by sin* t are used to produce the inverter reference current command I*inv. Then, the PWM inverter decides the PWM switching pattern via the PI current controller which have the reference current (I*inv) and the real output current (Iinv) of the inverter as the inputs.

Fig. 2. Schematic diagram of transformerless type grid-connected PV system.

The system currents can be expressed as (1);

ILoad=Iinv±Ig (1) where, '-' means Ppv > PLoad and '+' means Ppv < PLoad. Ppv and PLoad are the active power of the PV arrays and load, respectively.

In sunny mode, the proposed system supplies the active and reactive power to the grid or loads. For unity power factor of the grid, the grid current should be controlled to ensure that it includes only the active current. The active current is defined as the sinusoidal current in phase with the grid voltage. Hence the required grid current amplitude can be expressed as (2).

P

(2)Ig*=Re[ILoad] IVdc=Load IVdc

VgWhere, Re[ILoad] is the active current component of the load

current and IVdc is the output current of the dc-link voltage

controller.

Parameter Value Parameter Value

FsFsw_invFilter capacitor 4.7uF

Boost input

Boost inductor 3.4mH 340uF

capacitor

Fsw_con1KVA Where, Fs is the fundamental frequency, Fsw_con is the switching frequency of Filter inductor

3mH

The required grid current amplitude can be to ensure that the DC/DC converter and Fsw_inv is the switching frequency of inverter.

grid current includes only the active current is as follows. The operation characteristics were analyzed into two modes:

(3) the sunny mode, the night mode. Where Vg is the voltage Iinv*=ILoad Ig*×sin*ωt

waveform of the grid, and Ig, Iinv and Iload are current waveforms

Where, sin* t is an unity sinusoidal waveform in phase with

of the grid, inverter and load, respectively. Also Pg, Ppv and Pload

the grid voltage by phase-lock-loop (PLL).

are the active power waveforms of the grid, PV arrays and load,

respectively. In night mode, the grid active current can be calculated by

Figure 4 shows the simulation results of the conventional

IVdc=0 (equation (2)). Also, if the grid active current is applied to

system in sunny mode where the load changes from no load to

the equation (3), the reference current of the inverter (I*inv) can

1kVA nonlinear load at 0.5sec.