How to set and varry Short Circuit Ratio (SCR) in Grid Tied Inverter System

Hi there,

I am facing trouble regarding the settiing of Short Circuit Ratio (SCR) for grid-tied inverter simulation to measure the strength of the grid against SCR variations. Could you please guide me regarding this? For your information, I am attaching a photo with my request. I would like to produce such grid voltage waveforms in Simulink with different SCRs. Thanks in advance.

Answer 1

[MULI]

Hi Shuvra,

I understand you want to change the Short circuit ratio to measure grid strength.

By changing the grid source parameters, the SCR values can be changed. When the required SCR is known, the values of source reactance (Xs) can be calculated using the function below:

function Xs = SCRtoImpedance(SCR, PVpower) 

    Vbg = 4.16e3; % Base Voltage at Point of Interconnection (POI) in volts 

    MVAb = PVpower; % Base MVA is PV plant Peak MW capacity in MVA 

    zbg = (Vbg)^2 / (MVAb * 1e6); % Base impedance in ohms 

    zg_pu = 1 / SCR; % Per-unit impedance of the grid 

    zg = zg_pu * zbg; % System impedance in ohms 

    % Assuming the impedance is purely inductive 

    Xs = zg * ((24.9/4.16)^2); % Adjust for the transformer ratio and convert to ohms 

end 

Connect the impedances in parallel to the main source and enable them using circuit breaker as attached in the screenshot.

In this way one value of Xs is connected for 5 sec and for another value of Xs for 5 to 10 sec. This results in variation of SCR in the network.

Hope this answers your query!