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# Research on Control Strategy of New Type Solar Grid-connected Inverter

Nov 13, 2020

Research on Control Strategy of New Type Solar Grid-connected Inverter

In the 21st century, solar grid-connected inverter technology has been continuously developed. This article introduces a new type of inverter, which is different from traditional inverters and can improve the quality of inverter output current.

1. System composition

1.1 Main circuit structure

It is a voltage-type active inverter with output current control. The system adopts a full bridge structure composed of intelligent power modules. It can be seen that the energy output by the solar array is first passed through a full-bridge inverter and inductive filtering, and then merged into the grid in the form of a controlled current source. The control process is: compare the reference current given value of the same frequency and phase with the grid voltage with the actual instantaneous feedback value of grid-connected current. After the difference is processed by the PI regulator, it is compared with the actual instantaneous feedback value of the grid voltage. After triangular wave modulation, a sine wave pulse width modulation signal is output, which is amplified by the drive circuit to drive the power switching device, thereby generating a sine wave current with the same frequency and phase as the grid voltage.

1.2 Mathematical model of system inverter link

Take the current iL flowing through the filter inductor L as the state variable. Available:

uab=unet+L(di/dt)+ir

From equation (1) after Laplas transformation, i(s) can be solved:

i(s)=[1/(sL+r)][uab(s)-unet(s)]

Where: uab is the unfiltered inverter output voltage; r is the equivalent resistance of the line.

When the switching frequency of the inverter is high, ignoring the effects of switching devices and dead zone characteristics, the bridge inverter under the SPWM control mode can be approximated as an equivalent amplification factor of K, namely:

G(s)=K (3)

2 System control strategy

In order to make the inverter output a good grid-connected current waveform, the output grid-connected current of the inverter must be closed-loop controlled. The existence of dead zone, asymmetry factors inside the inverter, DC side voltage and grid disturbances will cause the grid-connected current waveform output by the inverter to be distorted. However, when the traditional PI control is used to track a given sinusoidal signal, the system's static-free tracking cannot be achieved.