# How to Generate the Optimal Inner and Outer Phase Shifts for Extended Phase Shift Modulation in a Series Partial-Power Dual Active Bridge Converter?

**URL:** <https://forum.plexim.com/t/how-to-generate-the-optimal-inner-and-outer-phase-shifts-for-extended-phase-shift-modulation-in-a-series-partial-power-dual-active-bridge-converter/3256>\
**Category:** General\
**Created:** [August 5, 2026, 4:39am UTC](https://forum.plexim.com/t/how-to-generate-the-optimal-inner-and-outer-phase-shifts-for-extended-phase-shift-modulation-in-a-series-partial-power-dual-active-bridge-converter/3256 "2026-08-05T04:39:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Arnob](https://avatars.discourse-cdn.com/v4/letter/a/ec9cab/32.png) [@Arnob](https://forum.plexim.com/u/Arnob)\
**Post date:** [August 5, 2026, 4:39am UTC](https://forum.plexim.com/t/how-to-generate-the-optimal-inner-and-outer-phase-shifts-for-extended-phase-shift-modulation-in-a-series-partial-power-dual-active-bridge-converter/3256/1 "2026-08-05T04:39:23Z")

</div>

Hi everyone,

I am working on a **series partial-power DAB converter** and would like to implement **Extended Phase Shift (EPS)** modulation.

My goal is **not just to transfer the required power** , but to generate the **optimal inner and outer phase shifts** that minimize:

- Backward (circulating/reactive) power
- RMS current
- Peak current (if possible)

while maintaining the desired transmitted power.

### Converter specifications

- Series partial-power DAB
- Forward boost operation (300 V → 400 V)
- Transformer turns ratio: 2.5:1
- Leakage inductance: 8.94 µH
- Switching frequency: 100 kHz

### My question

Suppose I know:

- Input voltage
- Output voltage
- Transformer turns ratio
- Leakage inductance
- Switching frequency
- Desired transferred power

**How do I determine the optimal inner phase shift and outer phase shift for EPS?**

In particular:

- Is there a closed-form method to calculate them?
- Is numerical optimization (grid search, `fmincon`, etc.) the usual approach?
- How do you ensure that the selected phase shifts minimize circulating/backflow power and RMS current rather than simply satisfying the power equation?
- Are there practical constraints that should be enforced during the optimization?

I’m interested in understanding the **design methodology** rather than just obtaining one operating point.

If anyone has implemented an EPS optimizer or can explain the workflow used in practice, I would really appreciate the guidance.

Thank you!

 ![Screenshot 2026-08-05 003859](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/7/7d42b717a9e0e3e92678b9ed15560dcdebf54b37.png)