Gate Drivers for Solar Inverter Application

Hi Rushi,

Thank you for your question. I have assigned the appropriate engineer to answer to your question.

A few questions : Are you still planning on operating the FETs between 15-20kHz if you use GaN?
GaN is used at higher switching frequencies while maintaining desired efficiencies for a wide range of input and output voltages.

Have you taken a look at SiC FETs? Here is a TI-design, TIDA-01606 for a solar string inverter using SiC.

regards,
Mateo

Hi Mateo,

Thanks for your reply.

Surely GaN would be used at 3 to 4 times the switching frequency compared to a normal IGBT.

Also, thanks for giving the reference to the SiC FETs. I had a look at it and I now I am more confused what to use.

I have structured all my doubts in the point form so that it becomes easy for you and your engineer to answer.

1. From my understanding based on what I have read - GaN FETs are better than SiC in terms of efficiency and possibility of higher switching speeds. Am I right or am I missing something?

2. My Solar Inverter is targeted for the Indian market where I would be competing with multiple companies who import solar inverters from China. They are less costly and that is the main reason it sells in the market. So, if I would be switching to GaN or SiC, will the cost increase or decrease. Though GaN and SiC are costly, I would be saving money on size of heat sink, packaging cost and magnetics cost. But, I am not sure how would the overall cost be affected. Maybe your experience will help me in getting some idea.

3. What technical difficulties I may face in switching to GaN or SiC based FETs. I believe one of them would be achieving the EMI standards as we are shifting to higher frequencies. Any other issue that I may face?

4. The integrated GaN power module available on TI is rated 600V 12A. For a 3.5kW solar inverter, I would have to use them in parallel to achieve the desired current (240V rms is the grid voltage and for power level of 3.5kW, I would need a peak current of 20.6A). OR are there any other GaN FETs available for the power levels that I want to achieve OR some other solution that you may suggest.

5. Lets say I stick to the silicon IGBTs with switching frequencies upto 20KHz. What would be the best gate drive solution? Is ISO5500 good enough or do you have a better suggestion for me.

6. I believe GaN and SiC have not been widely adopted. Am I right? If so, what is the reason? Or what do you think is the potential of GaN and SiC FETs.

7. Lastly, what according to you would be the best solution for a solar grid-tied inverter for a power level of 3.5 to 4 kW? (taking into account cost, ease of implementation, future scope of technology, etc)

I have tried my best to put forward my doubts clearly. I will wait for your answers.

Regards,
Rushi

I look forward to an answer for my queries. It will help me in designing a good inverter.

Hi Rushi, 

Please see the attached white papers on GaN to help you with your designs: 

http://www.ti.com/lit/wp/sszy017/sszy017.pdf

http://www.ti.com/lit/wp/slyy070/slyy070.pdf

regards,
Mateo

Hi Mateo,

I have already gone through these white papers. They do mention that GaN is at a pretty nascent stage for power applications.

Yet, they do not answer the questions that I have asked above. I am still confused and my queries above remain the same.

I hope you can answer them.

Looking forward to specific answers to my questions.

Thanks,
Rushi

Hi Masoud,

I have gone through the datasheet of LMG3410 and I understand that no external drivers are required. Is ISO7831x necessary for isolation if I am using a flyback converter to supply the isolated 12V supplies?