Soft-switching, high performance single-phase AC-DC converter
View Patent ↗A soft-switching, high-performance single-phase alternating current (AC)-direct current (DC) converter is provided. The AC-DC converter described herein provides a new circuit topology for single-stage, single-phase or multi-phase AC-DC power conversion with power factor correction (PFC) and galvanic isolation using a high-frequency isolation transformer. The AC-DC converter improves power conversion efficiency and power density—two of the most important metrics for a power converter. It achieves soft switching for high frequency switches in the circuit, leading to higher efficiency and lower electromagnetic interference (EMI).
1. An alternating current (AC)-direct current (DC) converter, comprising:
an AC input/output (I/O) comprising a first AC I/O node and a second AC I/O node;
a DC I/O comprising a first DC I/O node and a second DC I/O node;
an isolation transformer, comprising:
a first coil comprising a first terminal coupled to the first AC I/O node and a second terminal; and
a second coil magnetically coupled to the first coil and comprising a third terminal coupled to the first DC I/O node and a fourth terminal coupled to the second DC I/O node;
a first switch coupled between the first AC I/O node and a common top node;
a second switch coupled between the first AC I/O node and a common bottom node;
a first capacitor coupled across the first switch and the second switch;
a third switch connected between the common top node and the second AC I/O node; and
a fourth switch connected between the second AC I/O node and the second terminal of the first coil of the isolation transformer;
wherein:
the third switch and the fourth switch are configured to switch at a line frequency; and
the first switch and the second switch are configured to switch at a higher switching frequency than the line frequency.
2. The AC-DC converter of claim 1 , wherein the second terminal of the first coil is connected to the common bottom node.
3. The AC-DC converter of claim 1 , wherein the second terminal of the first coil is connected to the second AC I/O node.
4. The AC-DC converter of claim 1 , wherein the second terminal of the first coil is connected to the common top node.
5. The AC-DC converter of claim 1 , further comprising an inductor connected between the first AC I/O node and an intermediate high-frequency node; wherein:
the first switch is connected between the intermediate high-frequency node and the common top node; and
the second switch is connected between the intermediate high-frequency node and the common bottom node.
6. The AC-DC converter of claim 5 , further comprising a second capacitor connected between the intermediate high-frequency node and the first terminal of the first coil of the isolation transformer.
7. The AC-DC converter of claim 1 , wherein the line frequency is between 20 Hz and 1000 Hz.
8. The AC-DC converter of claim 1 , wherein the first switch and the second switch are controlled such that they become closed when a voltage across a respective switch is zero.
9. The AC-DC converter of claim 1 , wherein the first switch, the second switch, the third switch, and the fourth switch are controlled such that a current from the AC I/O is sinusoidal and at unity power factor.
10. The AC-DC converter of claim 1 , wherein each of the third switch and the fourth switch comprises a diode.
11. The AC-DC converter of claim 1 , further comprising a rectifier coupled between the second coil and the DC I/O.
12. The AC-DC converter of claim 11 , wherein the fourth terminal of the second coil is a center-tap terminal and the rectifier comprises:
a fifth switch connected between the third terminal of the second coil of the isolation transformer and the first DC I/O node; and
a sixth switch connected between a fifth terminal of the second coil of the isolation transformer and the first DC I/O node.
13. The AC-DC converter of claim 12 , wherein the rectifier is a full-wave rectifier.
14. The AC-DC converter of claim 12 , further comprising a DC I/O capacitor connected between the first DC I/O node and the second DC I/O node.
15. A circuit, comprising:
an isolation transformer, comprising:
a primary coil; and
a secondary coil;
a direct current (DC) circuit coupled to the isolation transformer; and
an alternating current (AC) circuit coupled to the isolation transformer and galvanically isolated from the DC circuit, the AC circuit comprising:
a bridgeless single-stage power factor correction circuit isolated from the DC circuit;
a first zero-voltage switch (ZVS) connected in shunt to a first node between an AC source or load and a first terminal of the primary coil; and
a second ZVS connected in shunt to the first node.
16. The circuit of claim 15 , wherein the AC circuit further comprises:
a first line frequency switch connected to the first ZVS; and
a second line frequency switch connected in series with the first line frequency switch.
17. The circuit of claim 16 , wherein the DC circuit comprises:
a first rectifier switch coupled between a second terminal of the secondary coil and a DC source or load; and
a second rectifier switch coupled between a third terminal of the secondary coil and the DC source or load.
18. An alternating current (AC)-direct current (DC) converter, comprising:
an AC input/output (I/O) comprising a first AC I/O node and a second AC I/O node;
a DC I/O comprising a first DC I/O node and a second DC I/O node;
an isolation transformer, comprising:
a first coil comprising a first terminal coupled to the first AC I/O node and a second terminal; and
a second coil magnetically coupled to the first coil and comprising a third terminal coupled to the first DC I/O node and a fourth terminal coupled to the second DC I/O node;
an inductor connected between the first AC I/O node and an intermediate high-frequency node;
a first switch coupled between the intermediate high-frequency node and a common top node;
a second switch coupled between the intermediate high-frequency node and a common bottom node;
a first capacitor coupled across the first switch and the second switch;
a third switch connected between the common top node and the second AC I/O node; and
a fourth switch connected between the second AC I/O node and the second terminal of the first coil of the isolation transformer.
19. The AC-DC converter of claim 18 , further comprising a second capacitor connected between the intermediate high-frequency node and the first terminal of the first coil of the isolation transformer.
20. The AC-DC converter of claim 18 , further comprising a rectifier coupled between the second coil and the DC I/O, the rectifier comprising:
a fifth switch connected between the third terminal of the second coil of the isolation transformer and the first DC I/O node; and
a sixth switch connected between a fifth terminal of the second coil of the isolation transformer and the first DC I/O node.