This is a power electronics DC DC converter question:

What is the function of the capacitor and resistor connected between two series inductors?

enter image description here

This is part of the schematic from a photovoltaic inverter. I coudn't understand the function of the components in the red circle. Sure they do not participate in buck or boost feature. There is no heavy filtering required on PV side (IMO.) So what is the function of these components?

Specifically, the 10uF film capacitor and 100Ohm/5W resistor connected between the inductors.


Inductors block high frequencies, so it's my guess that they are to keep the switching current from the inverter seen by the photovoltaic module/cell near DC. It would be a bad thing to have the voltage drop on a photovoltaic system, because it would not be operating at the Maximum Peak Power Tracking point.

It would also prevent the PV system from turning into an antenna and creating interference with other devices.


It doesn't look like the resistor actually accomplishes anything for filtering (but might if you plug the PV system in).

The filters look like they have a pole to keep 100kHz away from the solar cells. I am also unsure if the inductors are in a choke but it looks like they are separate distinct inductors.

enter image description here

  • \$\begingroup\$ I slightly agree but also i feel if that was the true function why they used two inductors ? what are those C & R doing there \$\endgroup\$ – Busy_Life Jul 30 at 18:38
  • \$\begingroup\$ I think it would have to do with inrush current, it does nothing for the filter to have two inductors. \$\endgroup\$ – Voltage Spike Jul 30 at 19:22
  • \$\begingroup\$ It's a d/dt limiter to mitigate long harness \$\endgroup\$ – JonRB Jul 30 at 21:49
  • \$\begingroup\$ @JonRB Is the limiter for inrush current or a changing load on the solar cells (like when the inverter turns on)? The circuit should be operating mostly at DC at that point. \$\endgroup\$ – Voltage Spike Jul 30 at 22:09
  • \$\begingroup\$ Not that kind of inrush, remember there is a switching element. I'll write a reply \$\endgroup\$ – JonRB Jul 30 at 22:24

The goal of every MPT regulator is to have a conjugate matched impedance. The minimum R-value is at maximum power and this rises many orders of magnitude with no solar input where it doesn't matter.

Just looking at the PV at MPT, ΔV/ΔI = R [ Ω] in parallel with some capacitance of the array that depends on the size and thus the power of the array inverse to its impedance.

The analysis is not intended to be the final one since there are no PV specs. Rather it was to show those interested how to do Network Analysis with scatter plots in simulation.

The reactor shunt R only adds dampens the peak resonances (lower Q) for the 2.5kHz and this R value may be close the PV R at max power, but nevertheless I chose a smaller R to amplify the series resonance peaks.

In my Models I had to assume some values for PV PMT impedance , R=V^2/P since it not a high impedance current source at MPT.

So I decided to do scattering parameter simulations with some guestimated Source R and load R for s11,s21,s12.

I wanted to see the impedance of the PV load (s11) from the MPT filters to their switched regulator. Although the PWM switch will alter the Resistance of open to close, creating dynamic Q changes, the SRF and PRF resonances should not shift significantly.

The addition of the 30uF adds another peak but more important creates a value so that the switching regulator does not shunt load the input PV current with load pulse currents reducing the voltage. You want the DC response to be matched impedance and not have the switched battery load of many thousand Farads (almost AC short) with the switched inductors to allow current pulses to flow in CCM mode but not lower impedance and pump down the Vmpt voltage with all the pulses.

enter image description here


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.