pwm inverter filter inductor design

[FvM]

It seems like you forgot to consider load current magnetization in your inductor design. In a short, the AC peak current of about 1.6 A has to be considered like a DC magnetizing current, producing H of about 650 A/m for an ungapped 44916 core, in other words full saturation.

 

[dreamsys]

It seems like you forgot to consider load current magnetization in your inductor design. In a short, the AC peak current of about 1.6 A has to be considered like a DC magnetizing current, producing H of about 650 A/m for an ungapped 44916 core, in other words full saturation.

Hi , thanks for the reply.
So if I changed my Load current from 1.5A to 1.6A to account for magnetizing current I can still use the design. Or should I changed the design to one using gapped ferrite while using a slightly higher current to account for load current magnetization.

Note: Please, is my design procedure for the inductor the correct one?
regards.

 

[FvM]

Maybe I overlooked something, but I didn't find a calculation of saturation current in your design. As asked in your previous post, the filter choke design is in fact similar to a DC/DC buck converter design, with peak load current in place of the DC output current. When using standard power ferrites, the core must be gapped. Iron powder cores could be used without air gap.

 

[dreamsys]

Hi FvM,
I think that is the heart of my problem and thanks for your replies at least with this I can feel like I am getting closer to understanding how to design inductor.
None of the books I study (Switching power supply Design - Abraham Pressman,Switchmode power supply Handbook - Keith Billings, High Frequency Switching power supplies Theories and Design- George Chryssis, Power Supply Cookbook - Marty Brown etc.) specifically design a filter inductor for SPWM inverter and the choke filter inductor designs used as examples in these books did not mention saturation current: but what they did mention in the design procedure is to add the AC ripple current to the Dc output current to get the peak inductor current used in calculating for the required Core parameters while Average output current was used to calculate for the required inductance for output filter inductor of the DC-DC converter.
Please, can you suggest a book that describe inductor core-selection using saturation current as part of the design parameter.
Regards.

 

[FvM]

Exceeding the inductor's saturation current is just the extreme condition, depending on the designed core losses, you'll possibly want to limit the magnetization to lower values.

I presume, the topic is discussed in text books, but I don't remember a particular reference. In my view, it's an obvious conclusion from general inductor design methods.

 

[dreamsys]

Exceeding the inductor's saturation current is just the extreme condition, depending on the designed core losses, you'll possibly want to limit the magnetization to lower values.

I presume, the topic is discussed in text books, but I don't remember a particular reference. In my view, it's an obvious conclusion from general inductor design methods.

Thanks, Please, I have another question, is it possible to find a blocking capacitor that can withstand about 100Amps current to be inserted in series with the primary of my Transfomer for H-Bridge converter configuration.
Also, can I contact your privately if I have other questions?

 

[goldsmith]

Hi goldsmith, please check out the design I attached to this reply.

1. I used a constraint of total harmonic distortion of less than 3% of out put voltage and design for inductor that is non-saturate but thermally limited
Design parameters
a. PWM technique is SPWM
b. output voltage sinusoidal with THD<3% of output voltage
c. Output voltage RMS value =220V
d. Output power = 250Watts
e. Constraint condition for the inductor's inductive impedance is I(load)*2*PI*L <0.03*Vrms

Hi again
Just a simple rule : Zout should be normalized as 0.5sqrt(L/C)
Best Wishes
Goldsmith

 

[dreamsys]

Hi again
Just a simple rule : Zout should be normalized as 0.5sqrt(L/C)
Best Wishes
Goldsmith

Hi goldsmith, thanks for the reply.
So, my design calculation and method in the attached doc is okay? also is it okay for me to select and design for the core of the inductor using the selection method for the design of output choke of a DC-DC converter. This is my main problem that I am not to sure of. Please Advice.
Regards.
Dreamsys

 

[FvM]

is it possible to find a blocking capacitor that can withstand about 100Amps current to be inserted in series with the primary of my Transfomer for H-Bridge converter configuration.

Why do you want a series capacitor for the H-bridge? I would try without it, if ever possible. For large capacitance values, multiple low ESR electrolytic capacitors are needed, siimilar to the bypasxs capacitors in the CPU DC/DC converter of a recent PC. For higer frequencies than 50 kHz, ceramic can be an option.

 

[dreamsys]

Why do you want a series capacitor for the H-bridge? I would try without it, if ever possible. For large capacitance values, multiple low ESR electrolytic capacitors are needed, siimilar to the bypasxs capacitors in the CPU DC/DC converter of a recent PC. For higer frequencies than 50 kHz, ceramic can be an option.

I need it as one of the possbile correction for volt-seconds imbalance in the HF transformer as I can't get my hand of a Current mode PWM controller for the DC-DC section of my inverter, so together with a gap in the centre leg of my HF transformer and usage of MOSFETs as the power switch I intend to add the series blocking capacitor as an additional guarantee that my transformer will not walk into stair-case saturation due to Volt-sec imbalance.
Regards
Dreamsys