Reduced capacitance AC/DC/AC power converter

• US 20040095784A1
• Filed: 11/19/2002
• Published: 05/20/2004
• Est. Priority Date: 11/19/2002
• Status: Active Grant

• Current Assignee: Wicon Incorporated
• Original Assignee: Wicon Incorporated
• Inventors: Zhou, Dongsheng
• Granted Patent: US 6,804,127 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 5/458 using semiconductor devices only

Abstract

An AC/DC/AC power converter is constructed without using any electrolytic capacitor, such that it is more compact, durable and reliable. This converter only required a small capacitance for its DC link and this capacitor can be easily obtainable with other types of capacitors such as film or ceramic type. The system further includes means to disconnect both input and output to this DC bus capacitor. A controller capable of fast monitoring the DC bus voltage is also able of quickly disconnecting the capacitor out of either input or output energy path to prevent the capacitor from being charged to over-voltage. The controller also possesses capability of re-connecting the disrupted energy path once the DC bus voltage returns to normal.

Claims

1. An AC/DC/AC power converter, comprising:

A rectifier having diodes, anode of one said diode connected to cathode of another said diode to form a phase leg, the middle node of said diode leg serves to accepts one input power line, the free cathode end of all said diode legs are tied as a positive terminal and free anodes of all legs are similarly tied together to serve as the negative terminal;

An inverter having switching semiconductors, with a free-wheeling diode connected across each said switching semiconductor to form a be-directional current carrying switch-diode module, two said modules to form a leg, the middle node of said leg serves as an output terminal, free nodes of all legs with diode cathode to tie together to accept DC positive bus, free nodes of all legs with diode anode to tie together as negative terminal;

A DC link section with an inductor, a capacitor and a precharge means in series, said capacitor is constructed with film or ceramic materials, said capacitor terminals serve as DC output for said inverter;

A control means supplying signals engaging or disengaging said capacitor to input and output of said converter.

Whereby said capacitance in said DC link section is reduced and capacitor construction is simplified for compactness, endurance and reliability of said converter. The over-voltage transient is protected by fast reaction of said control means.

2. The rectifier and inverter of claim 1, are either three-phase or single phase circuits.

3. The DC link section of claim 1, wherein said inductor comprises two parts, one part on the positive bus and another on the negative bus, said inductor possesses differential and common mode inductances.

4. The DC link section of claim 1, wherein the precharge means further comprises a precharge resistor and a DC relay in parallel.

5. The DC link section of claim 1, wherein the precharge means further comprises a precharge resistor and a semiconductor power switch in parallel.

6. The DC link section of claim 1, wherein the location of the precharge means can be either before the inductor, between the inductor and the capacitor, on either positive or negative bus.

7. The control means of claim 1, wherein it does fast sensing of said DC link capacitor voltage, disengages the capacitor from input source when said voltage is lower than a under-voltage threshold, from output load when said voltage is higher than an over-voltage threshold and returns said capacitor to normal operation when said voltage is in its normal range.

8. An AC/DC/AC power converter, comprising:

An AC section connecting an input power source to a rectifier;

A rectifier having diodes, anode of one said diode connected to cathode of another said diode to form a phase leg, the middle node of said diode leg serves to accepts one input power line, the free cathode end of all said diode legs are tied as a positive terminal and free anodes of all legs are similarly tied together to serve as the negative terminal;

An inverter having switching semiconductors, with a free-wheeling diode connected across each said switching semiconductor to form a be-directional current carrying switch-diode module, two said modules to form a leg, the middle node of said leg serves as an output terminal, free nodes of all legs with diode cathode to tie together to accept DC positive bus, free nodes of all legs with diode anode to tie together as negative terminal;

A DC link section with at least a capacitor, said capacitor is constructed with film or ceramic materials;

A control means supplying signals engaging or disengaging said capacitor to input and output of said converter.

Whereby said capacitance in said DC link section is reduced and capacitor construction is simplified for compactness, endurance and reliability of said converter. The over-voltage transient is protected by fast reaction and regulation of said control means.

9. The AC section of claim 8, wherein it further comprises at least one of an AC precharge means and an AC inductor. Said AC precharge means and AC inductor are in series.

10. The AC precharge means of claim 8, wherein it further comprises a resistor in parallel to each said AC contact. The AC contact can be constructed by either an AC contactor or semiconductor power switch. Said contact is opened during low DC bus voltage and closed when said DC bus voltage is high and in normal range, via said control means of claim 8.

11. The AC inductor of claim 8, wherein its location can be either between the input power source and precharge means or between said precharge means and said rectifier.

12. The AC section, rectifier and inverter of claim 8, wherein they can be either three-phase or single phase circuits.

13. The DC link section of claim 8, wherein it can further comprises of either a DC inductor or a DC precharge means, respectively said AC inductor or AC precharge means in said AC section is no longer needed and can be removed.

14. The control means of claim 8, wherein it does fast sensing of said DC link capacitor voltage, disengages the capacitor from input source when said voltage is lower than a under-voltage threshold, from output load when said voltage is higher than an over-voltage threshold and returns said capacitor to normal operation when said voltage is in its normal range.