Hello,
In my simulink model, i need a model resistive load for DC, which should have constant voltage whatever the input voltage is.
I mean for example, the input have 300W power, 30 V voltage , 10 A current then the load will have 300 W power, 300 V and 1 A.
But, if the input have 150W, 30V and 5 A, the output should have 150W, 300 V and 0.5 A.
(There is a transformer for voltage step up and the input is not a problem. Also i could make it with changing the a single resistor value manually but i want this is done automatically.)
How can i model this type of load?
One of the popular methods to fix the DC voltage supplying the load is to use a suitable DC-DC converter; in your case a buck-boost converter can handle various situations. You will find the model of this converter in the library of the simpowersystems toolbox. You may refer to:
Article Reduced-order modelling of solar-PV generators for small-sig...
https://www.researchgate.net/publication/307926879_Dynamic_Security_of_Interconnected_Electric_Power_Systems_-_Volume_2_Dynamics_and_stability_of_conventional_and_renewable_energy_systems
A load with constant voltage is a constant voltage source connected back to back to the source. Physically it could be a battery in case of charging.
Best wishes
If you use DC DC power converter (buck, boost, buck-boost, etc..) you may need to design a feedback controller to obtained a fixed voltage across the resistance regardless the variation in the input voltage or the resistive load. You can use linear PI controller or even nonlinear feedback controllers such as sliding mode control, passivity-based control, etc...
I am using a PV module and push-pull converter and a PID controller. When the irradiance is 1000 w/m^2 everything is fine but when the irradiance drops 500 (or 800)w/m^2 the output voltage can not reach the same voltage unless i manuely change the resistor value.
Actually i want a costant voltage DC bus. The current can change as I=P/400V
Are you using MPPT? if you apply it , so you have to control the DC bus by another control loop (another controlled dc-dc converter) or by applying battery across the converter to fix the voltage.
I haven't implement the MPPT but i am finding the MPP with adjusting the duty cycle manually(of course while adjusting i am not using PID) . After finding the duty cycle for MPP, the output voltage is not at the desired level i think because of constant resistor. When i change the resistor value i am getting the voltage value and the current according to input power.
I used " Wye-Connected Variable Load" block as load to my system . It is for 3 phase but i connect the "+" terminal to the "a" input and "-" to the "n" input so it worked for DC system. The block changes the resistor according to external P(power) input and internal Rated Voltage parameter.
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