# Reactive power compensation through grid connected inverter

I recently designed a bidirectional DC-DC charger for an Electric Vehicle (EV) battery.

I would like to focus on the inverter control. In this application, I designed the inverter to have unitary power factor (cosφ=1 , Q=0, S=P). I have read that in an application like this, it is possible to make use of the capacitors in order to offer voltage regulation to the grid. In other words, we can offer reactive power to the grid.

So, let's say that I redesign the topology: S=P/coφ in order to have the ability to transfer reactive power as well. So, the maximum power that we can offer to the grid is :

So, in case there is no active power transferred (P=0), the maximum reactive power is Qmax=P. I would like to ask if something like this is realistic. Are there any undesired consequences in the system? Should I take into consideration some parameters (for instance, the capacitor size) during the design methodology?

Also, almost the same topology is used in order to connect photovoltaic panels to the grid. In this case, it is also possible to use the capacitor to offer reactive power. However, in the most cases, I noticed that unitary power factor is desired. I would like to ask why is this happening since topologies like that seem like good solutions for local voltage regulation.

• I would really appreciate if you have an article/paper to propose to me, related to this topic. Commented Sep 16, 2018 at 19:26

You can do this and it is known as STATCOM. There are several topologies, and one possibility is to have an inverter with a capacitor at DC link. You have to design the capacitor for the rms current in this operation. You typically put a STATCOM plant close to a consumer of large reactive power.

For more details see e.g. section 9 in this document

I would suggest zones for GTI's needed to generate real power are not always close to zones where active PFC correction is needed, so unless there is a smart grid to regulate the GTI remotely from the utility as the owner, then unity PF generates the maximum real power to the grid and PF correction is done by other remote means, but this is guesswork from seeing a few MW GTI PV farms using Huawei GTI's. Other farms added to the grid did cause harmonic ingress and increase the rate of 60A 600V fuses blows from external harmonic farms while the outgoing fundamental was only 45A. So the customer installed bigger fuses.

The injected current power must be regulated by comparing an ideal sine wave PLL synced to the grid to generate a reference current waveform for RMS current according to the remote set parameters and safety trigger circuits.

The phase of the current could be offset by remote settings dynamically if active PFC was needed. This would offset the reference sine wave inside to be compared with the current waveform being generated.

I suppose high pulse energy loads could be supplied by customers with a solar farm in order to reduce their peak power demands from the grid. But often cap banks might be more suitable with the right transformer impedance to their needs. e.g. arc furnaces and smelters.

If you want to learn how to become a well-informed Engineer, you must learn how to search the web yourself. The answers are most likely already researched and published in Google Scholar or Microsft Academic Research sites.