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TIDM-SOLAR-DCDC: Large current spikes in boost converter when analog comparator with CBC trip used

Damith Pavithra
Expert 1125 points
Part Number: TIDM-SOLAR-DCDC

Hi all

I referred the above mentioned project to build a MPPT boost converter. It used analog comparator output to limit the output voltage of the boost converter  by feeding it to the pwm output with CBC trip option. 
Voltage is limited as expected. But input current shows very large current spikes when the comparator limit engaged. PWM output is switch on off according to comparator output. 
When pwm output turns on. large currents draws from input which is cause the failure of the converter. 
Please provide a solution to this. 


Input voltage=30V
Limit voltage=50V
Max duty=0.6
voltage at max duty if comparator limit is not used =75V
PWM Frequency=100k
Inductance=300uH
Output capacitance= 2mH

This converter intended to use at 200V vin and 400V vout at 5kW load. 
Hence the high output capacitance. I started testing the above low voltages to ensure the proper operation without any large transient conditions. 

Regards

  • 0
    TI__Intellectual 1200 points

    Hi Damith,

    Could you do a simulation of your implemented method to see if the spike is as expected? My take is that since it has a MPPT loop, it will always try to output power. When you use CBC function, the boost converter input side will take the power and have the current spike.

    Thanks,

    Qing

  • 0 in reply to Qing Ye
    Expert 1125 points

    Hi Qing

    Yes you are right. MPPT tries to push all the power hence its output Duty cycle is alwys tried to increase . But in this test case, even though i indented to use this with MPPT, in this stage, i didn't used the MPPT algorithm. I just gave a PWM value to the register and observed how the inputs and outputs works. No problem before the Internal comparator fires. When the set point of the ADC comparator block was exceeded by the output voltage, it starts CBC operation and then the output voltage wont rise above the setpoint but, the High current spikes happens. 
    Again, this is not with any algorithm running. Just the hard coded PWM reference value and the internal comparator block was in operation. 



    Damith
    Regards

  • 0 in reply to Damith Pavithra
    TI__Intellectual 1200 points

    If that is the case, could you do a simulation to see if the circuit behavior is as expected ? Meanwhile. on the hardware, could you take the waveform of the PWM signals, inductor current, VIn and Vo?

    By comparing them. it should unveil the mystery.

    Thanks,