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MEP 1523 ELECTRICAL DRIVES

MEP 1523 ELECTRICAL DRIVES. Current ripple in unipolar and bipolar switching schemes. Current ripple. Current ripple – unavoidable in power electronic converter systems:. Undesirable because:. Zero average – increase machine heating. Ripple in torque – can be reflected in speed response.

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MEP 1523 ELECTRICAL DRIVES

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  1. MEP 1523 ELECTRICAL DRIVES Current ripple in unipolar and bipolar switching schemes

  2. Current ripple Current ripple – unavoidable in power electronic converter systems: Undesirable because: • Zero average – increase machine heating • Ripple in torque – can be reflected in speed response • Ratings of devices must consider ripple - higher rating of peak current

  3. Current ripple H-bridge dc-dc converter with dc machine as load

  4. Current ripple H-bridge dc-dc converter with dc machine as load Approximate dc machine with RL load

  5. Vdc Vdc Vave Vave Vdc Current ripple • Load is linear • Principle of Superposition can be applied Unipolar Bipolar

  6. Unipolar Vdc Vave Current ripple

  7. Unipolar Vdc Vave Vave Vdc Vave Current ripple v(t) = Vave + vripple i(t) = Iave + iripple +

  8. Iave iripple i(t) Current ripple - unipolar Switching frequency is high - Impedance of AC component dominated by L i(t) = Iave + iripple - Ripple is calculated based on v-i relation of L - L appear as short circuit in DC = +

  9. iripple Current ripple - unipolar

  10. vL iripple Vdc Vdc-Vave i t Ttri iripple T Current ripple - unipolar + vL  TdAB

  11. Current ripple - unipolar but Vave = dabVdc , maximum when dab= 0.5

  12. It can be shown that for bipolar scheme, Max current ripple in bipolar scheme is four times that of unipolar scheme

  13. Vdc VdcVave Vave Vave Current ripple - bipolar Bipolar v(t) = Vave + vripple i(t) = Iave + iripple -Vdc +

  14. vL iripple 2Vdc Vdc-Vave i t Ttri iripple Current ripple- bipolar + vL  TtridAB

  15. Current ripple- bipolar but Vave = (2dab1)Vdc , maximum when dab= 0.5

  16. Max ripple for bipolar Max ripple for unipolar Current ripple- bipolar

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