Hybrid switch for resonant power converters
View Patent ↗A hybrid switch comprising two semiconductor switches connected in parallel but having different voltage drop characteristics as a function of current facilitates attainment of zero voltage switching and reduces conduction losses to complement reduction of switching losses achieved through zero voltage switching in power converters such as high-current inverters.
1. A soft switching power converter including two series connected hybrid switches, each said hybrid switch comprising
an insulated gate bipolar transistor (IGBT), and
a power MOSFET, wherein
conduction terminals of said IGBT and said power MOSFET are connected in parallel, and wherein
a control terminal of said IGBT is responsive to a control signal, and
a delay circuit connected to a control terminal of said power MOSFET whereby said power MOSFET is responsive to said control signal to turn on after a delay; said hybrid switch diverting current through said IGBT during said delay, said power converter further comprising
an auxiliary resonant current source connected to a node connecting said two series connected hybrid switches which does not deliver load current.
2. The power converter as recited in claim 1 further including
a delay circuit for delaying application of said control signal to said MOSFET such that turn-off of said MOSFET is delayed relative to turn-off of said IGBT.
3. The power converter as recited in claim 1 , wherein said power converter is an inverter.
4. The power converter as recited in claim 3 , wherein said inverter is a phase leg circuit.
5. The power converter as recited in claim 4 , wherein said power converter includes multiple phases.
6. The power converter as recited in claim 3 , wherein said inverter is a half bridge circuit.
7. The power converter as recited in claim 3 , wherein said inverter is a full bridge circuit.
8. The power converter as recited in claim 3 , wherein said inverter comprises a three-phase bridge circuit.
9. The power converter as recited in claim 1 , wherein said resonant current source comprises
a first transistor,
a second transistor connected in series with said first transistor, and
an inductor connected in series with at least one of said first transistor and said second transistor.
10. The power converter as recited in claim 9 , further comprising
a capacitor connected in parallel with each said hybrid switch.
11. The power converter as recited in claim 9 , wherein said inductor comprises two inductor windings that are electrically connected and magnetically coupled to each other.
12. The power converter as recited in claim 9 , further including two additional hybrid switches connected to said two hybrid switches in a full bridge circuit.
13. The power converter as recited in claim 9 , wherein said resonant circuit is also connected to a node at the mid-point of a capacitive voltage divider.
14. A method of reducing conduction losses in a high current switching circuit comprising steps of
controlling two hybrid switches to conduct alternately, wherein each of said hybrid switches comprise two switches which are controlled to conduct concurrently, wherein one of said two switches exhibits a substantially resistive voltage drop as a function of current and another of said two switches exhibits a substantially constant voltage drop plus a reduced resistive voltage drop characteristic as a function of current compared to said resistive voltage drop as a function of current compared to said one of said switches, wherein conduction current is shared between said two switches in accordance with respective voltage drop characteristics of said two switches during a period said switches are controlled to conduct concurrently,
delaying turn-on of said one of said switches that exhibits said substantially resistive voltage drop as a function of current for a delay period relative to turn-on of said another of said switches that exhibits said substantially constant voltage drop plus a reduced voltage drop compared to said one of said switches, whereby current is diverted through said another of said switches during said delay period, and
applying a resonant current to a node connecting said two hybrid switches in series.
15. The method as recited in claim 14 , wherein said two hybrid switches form a half-bridge circuit.
16. The method as recited in claim 14 , wherein two additional hybrid switches are controlled to conduct alternately in a full bridge circuit.
17. The method as recited in claim 14 , wherein said two hybrid switches form a phase leg of a multi-phase power converter.