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TIDA-010210: TIDA-010210

Harish Kumar Basude
Prodigy 30 points
Part Number: TIDA-010210

Tool/software:

I am designing LCL filter for ANPC converter for 300 kHz switching frequency. The LCL design formulae provided in the documentation is working fine up to 100kHz. Beyond 100 kHz, the converter is failing to operate correctly in rectifier mode. However, in inverter mode, it is working well. Can you please guide me to design LCL filter for 300 kHz switching frequency, Also, please guide me on how to choose attenuation factor, percentage of reactive power. My LCL filter should meet THD requirement of below 5% in both modes. 

  • 0
    TI__Intellectual 2800 points

    my suggestion is that you run pspice simulation of the equivalent filter in differential mode and common mode by having the right filter values.

    So you will need to put even the value of leakage inductance, or parasitic capacitance between the winding etc. By doing this, you will be able to observe all the resonance happening in the system.

    For the reactive power, the converter must be able always to provide on nominal operation a power factor that it is unitary. Of course, if you have solar converter then in case of weird conditioon of the grid you will need to provide reactive power too. By saying you need cosphi one, it does not mean that you cannot use capacitors as filter, it just means that the capacitor corrent needs to be compensated by the DCAC converter.

    On the other hand, one condition you need to consider is when you have a converter tied to the grid and it is off. Of course, in this condition the converter cannot drain any reactive current so cosphi will be really bad. This can be a limiting factor on selecting the right value of Cx capacitor.

    For THD requirements, sometimes it is hard to tell from a formula itself. It can depend by different factors: DC bus voltage, load, how it is going the control, current sensing technology etc.