# LC filter design calculation for Inverter to be connected to single phase Grid

#### gurramjanu

Joined Jun 29, 2016
12
Dear all,
I am designing a single phase SPWM inverter , which is to be connected to single phase Grid . I need Filter design calculations , What should be the Land C calculation that well suits for my inverter.
Though I have referred good no.of papers which talk about filter design, many of them talk about frequency response more on . Actually I am looking for L and C calculations (formule)

Janardhan

#### MisterBill2

Joined Jan 23, 2018
9,288
You are reading totally the wrong filter reference papers.
The sole purpose of an inverter filter is to assure that the output is a good sine wave, free of harmonics and other disturbances. The simple way to do that is with an L-C tuned circuit.
My guess is that the inverter output is from a transformer. What I know is that we have no information about the power or frequency of the inverter, nor about the intended voltage.
A resonant filter will tend to have a sine wave output when driven at the resonant frequency. Given the information supplied that is what I can tell you and know that it is correct.

#### Papabravo

Joined Feb 24, 2006
16,814
It is considered bad form to ask the same question multiple threads. I'll say this again in simple words. We need more information in order to guide you. You are not going to get a pure sine wave, but you can get close. How close you need to be is where the art of specification comes in. Among the things that would be helpful are the driving impedance, the load impedance, and the carrier frequency of the PWM. Again, no matter what kind of filter you design, it may require unavailable components.

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#### MisterBill2

Joined Jan 23, 2018
9,288
Some "true sine wave" inverters are actually power amplifiers driven by low distortion amplifiers. Unfortunately they are much less efficient and generate a lot more heat. So there is a serious trade-off with that variety of inverter.
So just like stated in posts #2 and #3, a lot more information is needed so that the responses are better than guesses as to the best choice.

#### gurramjanu

Joined Jun 29, 2016
12
Dear all,
I am designing a single phase SPWM inverter , which is to be connected to single phase Grid . I need Filter design calculations , What should be the Land C calculation that well suits for my inverter.
Though I have referred good no.of papers which talk about filter design, many of them talk about frequency response more on . Actually I am looking for L and C calculations (formule)

Janardhan

PWM frequency=2400Hz
Fundamental Frequency =50Hz
Vrms= 230
Is some thing more needed ?

#### Sensacell

Joined Jun 19, 2012
2,891

#### gurramjanu

Joined Jun 29, 2016
12
Dear Sensacell ,
PWM Freq=2400Hz, Fundamental Freq=50Hz, Rms output Voltage 230 ( Same as single phase grid voltage )
The Dc bus voltage 330V H bridge Unipolar SPWM (inside Box), I need Lf, Cf to be designed(so that current is sinusoidal) , My motive is to feed current to the grid so that I expect inverter output current need to be sinusoidal as we cant feed harmonics into grid.
Thanks
Janardhan

#### Sensacell

Joined Jun 19, 2012
2,891
Schematic of what's inside the "H4" box, please.

#### gurramjanu

Joined Jun 29, 2016
12
Schematic of what's inside the "H4" box, please.
Hi sir Here is the schematic

#### MisterBill2

Joined Jan 23, 2018
9,288
The problem has two parts, first is that the filter shown is simply a low pass filter, not a resonant filter. This means that it will not do an adequate job of turning that high frequency string of variable width pulses into a sine wave. A resonant transformer across the output, with at least the primary tuned to the desired frequency, is what is needed. Tune the primary because it is a higher voltage and thus more turns and higher inductance, needing a lower capacitance.
And there is still not one word about the power level that the inverter would be delivering.

So I am also going to suggest seeking service schematic information about a solar power system designed to be able to feed the electrical grid. At least some of those are able to meet the power company requirements for harmonic content. Quite often it is useful to see how those who are succeeding are doing something. "Copy a winner", we might say.