Integration PV panels with battery and generic load, how to choose capacitors and inductors?

Hello,

i would like to model a system composed by:

-dc common bus, 600 volts

-pv solar system (Voc=22V, Isc=3.76A, Vmp=17.2 Imp=3.49A) with perturb & observe mppt algorithm;

-battery energy storage system (Nominal Voltage 240V, Rated capacity 100Ah) and its control system;

-generic load;

The system should be similar to what attached.

1) Because of the variability of irradiance the duty cycle is not constant so how C and L values are to be chosen?

2) I model the generic load as a controlled current source block in order to obtain the known power absorbed (2 MW=600V*3333A), does this make sense?

3)Is the battery control system correct?

Thanks to who will help

Answer 1

[Riya]

Hello Andrea,

As per my understanding, you want to know how to choose capacitors and inductors.

Please note that to model a system with a PV array, battery storage, and a generic load, you'll need to consider the design of the DC-DC converter that will interface between these components and the common DC bus. The choice of capacitors and inductors is critical for the stability and performance of the converter. Here are a few pointers for your questions:

1. Choosing Capacitors (C) and Inductors (L):

• The values of capacitors and inductors in a DC-DC converter are chosen based on the desired ripple current and voltage, switching frequency, and the converter's power rating.
• For the inductor, use the following formula to start with an initial value:

\[ L = \frac{V_{out} \cdot (1 - D)}{f_{sw} \cdot \Delta I_L} \] 

Where \( V_{out} \) is the output voltage, \( D \) is the duty cycle, \( f_{sw} \) is the switching frequency, and \( \Delta I_L \) is the acceptable ripple current in the inductor.

• For the capacitor, the initial value can be estimated using:

\[ C = \frac{I_{out} \cdot D}{f_{sw} \cdot \Delta V_C} \] 

Where \( I_{out} \) is the output current, and \( \Delta V_C \) is the acceptable ripple voltage across the capacitor.

• Since the duty cycle will vary with the irradiance, you must design the converter to handle the worst-case scenario for the ripple specifications.

2. Modeling the Generic Load:

• Modeling the generic load as a controlled current source to represent a 2 MW load at 600V is reasonable. The current source should be set to deliver 3333A, as you've calculated, assuming the voltage remains constant at 600V.

For the MPPT control (Perturb & Observe algorithm), you will need to implement a control loop that adjusts the duty cycle of the DC-DC converter to maximize the power output from the PV panels. The MPPT algorithm will continuously perturb the operating point and observe the change in power to find the maximum power point as irradiance and temperature change.

You can refer the following articles for more information:

https://pcmp.springeropen.com/articles/10.1186/s41601-018-0099-8

https://en.wikipedia.org/wiki/Maximum_power_point_tracking

I hope it helps!