Three phase AC to DC power converter

• US 5,367,448 A
• Filed: 08/07/1992
• Issued: 11/22/1994
• Est. Priority Date: 08/07/1992
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Carroll, Lawrence B.
• Primary Examiner(s): RILEY, SHAWN
• Application Number:
  US07/926,988
• Time in Patent Office: 837 Days
• Field of Search: 323/207, 363/16, 363/17, 363/37, 363/39, 363/40, 363/41, 363/44, 363/45, 363/95, 363/97, 363/98, 363/79, 363/84, 363/87, 363/89, 363/131, 363/132, 363/127, 363/128
• US Class Current: 363/89
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 3/28 using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
• CPC Class Codes: H02M 5/4505 having a rectifier with controlled elements
• CPC Class Codes: H02M 7/1623 with control circuit

Abstract

A three phase AC to DC converter has an AC driven regulated current source, and it is provided with an unregulated current controller inverter. The zero crossing of the AC voltage input is monitored by a feedback control signal to a switching controller which is coupled to the current control switches of the regulated current source. In addition, the inverter is unregulated and current fed or controlled, and it is coupled to a high frequency current sensor in the preferred form of a current transformer, for sensing current flowing into the converter and which forms part of a control circuit for controlling the switching of the three phase AC regulated current source inputs for drawing currents. The unregulated current controlled inverter has an H bridge with series connected switches and a first diode (D1) and a second diode (D2) and a fifth switch (S12) in order not to dissipate energy. The first diode is series connected to the fifth switch and in series with the second diode, and the series combination is connected in parallel with the inverter legs. In addition, a recirculation inductor and the second diode are connected in parallel with the legs of the inverter, and the second diode is poled to permit circulating current in the recirculation inductor. A capacitor (C1), and the first diode are series connected, and the series combination connected in parallel with the first and second legs of the inverter. The diode (D1) is poled to provide current to the capacitor at the beginning of each inverter switching cycle. The fifth switch connected between the junction of the capacitor and the first diode and the junction between the second diode and second inductor permits discharging the capacitor without power dissipation during inverter operation.

Claims

1. A three phase AC-DC power converter for drawing sinusoidal input currents from a three phase power source comprising:

an input filter;

a three phase AC driven regulated current source coupled to said three phase power source through said input filter for drawing sinusoidal input currents, said regulated current source modulated according to the three phase line voltage of said three phase source to draw sinusoidal current;

an unregulated current controlled inverter having an "H" bridge configuration of two pairs of switches coupled to the output of said three phase AC driven regulated current source, said inverter having during operation one or the other of two pairs of switches or both pairs of switches conducting at any one time;

a transformer and output rectifier coupled to the output of the unregulated current controlled inverter for providing isolation and providing a DC output, conduction of one pair of said inverter switches providing current flow through said transformer in a first direction and conduction of the other pair of inverter switches providing current flow through said transformer in the opposite direction, said output rectifier comprising a plurality of output diodes, said unregulated inverter operated with overlap of conducting pairs of switches with the overlap time adjusted so that the opening pair of switches opens when the output diodes reverse recovery current reaches a peak.

2. A three phase AC-DC power converter according to claim 1 wherein the overlap time is adjusted so that the opening pair of inverter switches opens when the output diode reverse recovery current reaches its peak or on the first of the following ringing peaks, reducing inverter switch voltage stress.

3. A three phase AC-DC power converter according to claim 2 wherein the overlap time is approximately 0.5 to 2.5 times the reverse recovery time of the output diodes so that the opening pair of inverter switches opens when the output diode reverse recovery current reaches its peak or on the first of the following ringing peaks, reducing inverter switch voltage stress.

4. A three phase AC-DC power converter according to claim 1 wherein said unregulated current controlled inverter comprises:

a first leg having a first (S7) and second (S9) series connected switches and a second leg in parallel with the first leg having a third (S8) and a fourth (S10) series connected switches;

a first diode (D1) and a second diode (D2) and a fifth switch (S12), said first diode being series connected to said fifth switch and in series with said second diode, and the series combination connected in parallel with the inverter legs, said first and second diodes poled to carry current in opposite directions;

a capacitor (C10), said capacitor and first diode being series connected, with the series combination connected in parallel with said first and second legs of the inverter, said diode (D1) poled to provide current to said capacitor at the beginning of each inverter switching cycle; and

a recirculation inductor (L3), the recirculation inductor and second diode connected in series with said second diode (D2), the series combination connected in parallel with said first and second legs of the inverter, said second diode poled to permit circulating current in said recirculation inductor, said fifth switch connected between the junction of said capacitor and said first diode and the junction of said second diode and said second inductor for discharging the capacitor without power dissipation during inverter operation.

5. A three phase AC-DC power converter according to claim 1 wherein said three phase AC driven current source comprises:

a three phase switching bridge rectifier;

a freewheeling diode connected across the output of the three phase switching bridge rectifier; and

an inductor providing in series with the output of the three phase switching bridge rectifier for providing current to the unregulated inverter.

6. A three phase AC-DC power converter according to claim 5 wherein said three phase switching bridge rectifier and unregulated inverter have pairs of switches switched at the same fixed frequency.

7. A three phase AC-DC power converter according to claim 1 wherein said rectifier comprises a plurality of diodes forming a full wave rectifier and wherein the transformer has a secondary winding which provides energy to the full wave rectifier.

8. A three phase AC-DC power converter according to claim 1 wherein wherein a high frequency current sensor current sensor Tc is coupled to the primary of the of the inverter transformer T1.

9. A three phase AC-DC power converter according to claim 1 wherein wherein a high frequency current sensor current sensor Tc is coupled to the secondary of the of the inverter transformer T1.

10. A three phase AC-DC power converter according to claim 1 wherein wherein two ORed together current sensors Tc are coupled to sense the current passing from the inductor to the inverter to give the same signal results as a single transformer.