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Original question:

TIDA-010054: peak current mode control of DAB converter

TIDA-010054: Peak Current Mode Control/DC Blocking Capacitors

Neal Malackowski
Prodigy 20 points
Part Number: TIDA-010054
Other Parts Discussed in Thread: TIDM-02000

Tool/software:

In reference to the TIDA-010054 Dual Active Bridge design...

It's my understanding that as of roughly 4 years ago, Peak Current Mode Control had not yet been implemented, hence the need for the DC blocking capacitors in the design. Is this still the case or has this control been implemented? If it has, is there a reference that exists to understand its implementation? In the design guide TIDM-02000, PCMC is implemented for a PSFB converter, is this applicable to a DAB converter as well?

Further, in a high power Dual Active Bridge design with a large voltage conversion ratio, the secondary transformer RMS currents are significant enough that the implementation of the DC blocking capacitors becomes challenging. Are there intricacies involved with PCMC that preclude it from being used in such a design? If so, are DC blocking capacitors the only effective way of preventing transformer saturation? 

Thanks

  • 0
    TI__Expert 4290 points

    Hi,
    Thanks for reaching out.
    We did not implement peak current control yet. We went on and implemented extended-phase-shift control to improve performance over a wider output voltage range.
    I do not think that this is compatible with PCMC.|

    DC Blocking capacitors are not the only way to prevent core saturation. It is an option to sense the transformer current and do active  flux balancing, by adjusting the duty cycle on primary and secondary side if a DC offset is measured. This is also not yet implemented at the moment. The challenge here is to get a accurate measurement of the DC content iof the transformer current.

    Best regards,
    Andreas

  • 0 in reply to Andreas Lechner
    Prodigy 20 points

    Andreas,

    Thanks a lot for your response. Is it required that both primary and secondary transformer current be sensed to implement active flux balancing or could this be achieved while only sensing the "low-current" side of the transformer? Further, do you have any references that you could share that implement this? 

    Thanks,

    Neal

  • +1 in reply to Neal Malackowski
    TI__Expert 4290 points

    Hi Neal,

    There are different approaches to flux balancing, some only measure current on one side but most measure current on both sides.
    Here are some IEEE papers about this topic:

    Y. Panov, M. M. Jovanović and B. T. Irving, "Novel transformer-flux-balancing control of dual-active-bridge bidirectional converters," 2015 IEEE Applied Power Electronics Conference and Exposition (APEC), Charlotte, NC, USA, 2015, pp. 42-49, doi: 10.1109/APEC.2015.7104330.
    keywords: {Saturation magnetization;Circuit faults;Magnetic flux;Bandwidth;Magnetic separation;Bridge circuits;Modulation},

    Z. Gao, P. Yao, H. Li and F. Wang, "A Flux Balancing Strategy for 10-kV SiC-Based Dual-Active-Bridge Converter," 2022 IEEE 9th Workshop on Wide Bandgap Power Devices & Applications (WiPDA), Redondo Beach, CA, USA, 2022, pp. 148-153, doi: 10.1109/WiPDA56483.2022.9955288.
    keywords: {Ferrites;Magnetic flux;Modulation;Medium voltage;Transformer cores;Harmonic analysis;Circuit faults;Dual-active-bridge converters;flux balancing;medium voltage},

    Best regards,

    Andreas

  • 0 in reply to Andreas Lechner
    Prodigy 20 points

    Thank you, Andreas, I'll look into this. I appreciate your quick responses and suggestions!

  • 0 in reply to Andreas Lechner
    Prodigy 20 points

    Andreas,

    Just a quick follow up question... The method proposed in "Novel transformer-flux-balancing control of dual-active-bridge bidirectional converters" seems promising, however I was just curious if you've heard of it (or something similar) being implemented in a production design? Essentially, do you have any thoughts on the practicality of the solution?

    Thanks.

  • 0 in reply to Neal Malackowski
    TI__Expert 4290 points

    Hi Neal,

    There are two points which need to be considered I think:

    1. Saturation behavior of the transformer. Before implementing something to prevent saturation, the behavior needs to be analyzed. How much DC content for how long does it really need to see saturation effects. Are there options to prevent this without any flux balancing techniques?
    2. If we find out we really need flux balancing the question is if the measurement of the DC content can be accurate enough in the noisy environment of a converter to effectively prevent saturation.

    Best regards,

    Andreas