AC-AC converter using switches in a DC link

• US 4,894,763 A
• Filed: 12/05/1988
• Issued: 01/16/1990
• Est. Priority Date: 12/05/1988
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Ngo, Khai D. T.
• Primary Examiner(s): Wong, Peter S.
• Application Number:
  US07/279,636
• Time in Patent Office: 407 Days
• Field of Search: 363/35, 363/37, 363/51, 363/124, 318/376, 318/767, 318/800, 318/801, 318/802, 318/803
• US Class Current: 363/35
• CPC Class Codes: H02J 3/36 Arrangements for transfer of electric power between ac networks via a high-tension dc link
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: Y02E 60/60 Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

A power conversion system for converting polyphase AC power at a first frequency and voltage to AC power at a second frequency and voltage includes an input rectifier circuit and an output inverter circuit coupled by a DC link or interface comprising solid state devices. The interface includes a reversely-poled diodes connected between selected terminals of the rectifier and inverter circuits for carrying current in a forward direction. Controllable switches interconnect the same terminals for carrying current in a reverse direction to the inverter circuit. A controller responds to instantaneous current at the inverter terminals and to instantaneous input line voltages for selectively energizing the interface switches.

Claims

1. Apparatus for converting polyphase AC electric power at a first frequency and voltage to AC electric power at a second frequency and voltage, comprising:

a polyphase rectifier having input terminals for connection to a source of polyphase electric power and having a first and a second output terminal for providing rectified electric power;

a polyphase inverter having first and second input terminals for connection to a source of rectified electric power and having plural output terminals for connection to a load;

a first unidirectional current-carrying device connected between said first output terminal of said rectifier and said first input terminal of said inverter;

a second unidirectional current-carrying device connected between said second input terminal of said inverter and said second output terminal of said rectifier, said first and second unidirectional current-carrying devices being poled oppositely to each other;

first controllable switch means connected between said first output terminal of said rectifier and said second input terminal of said inverter;

second controllable switch means connected between said first input terminal of said inverter and said second output terminal of said rectifier; and

control means responsive to instantaneous polarity of current at one of said first and second input terminals of said inverter and to instantaneous polarity of the input line voltages for selectively gating said first and second controllable switch means substantially in synchronism into and out of conduction such that current at said rectifier output terminals is unidirectional regardless of current direction at said inverter input terminals and such that the rectified voltage at said inverter input terminals is maintained unipolar.

2. The apparatus of claim 1 wherein each of said unidirectional current-carrying devices comprises a solid state diode.

3. The apparatus of claim 1 wherein each of said controllable switch means comprises a field effect transistor having a gate terminal connected to said control means for receiving gating signals.

4. In a power conversion system having a rectifier circuit for converting input AC electric power to rectified electric power and having an inverter circuit for converting rectified electric power to output AC electric power, the combination comprising:

a DC link for coupling the rectifier circuit to the inverter circuit, said DC link comprising a pair of synchronously-operable controllable switching means for coupling rectified electric power between the rectifier circuit and the inverter circuit; and

control means responsive to instantaneous direction of current at the inverter circuit and to instantaneous polarity of input line voltages for rendering said switching means conductive or nonconductive substantially in synchronism so as to enable said switching means to maintain unidirectional current from the rectifier circuit and unipolar voltage at the input of the inverter circuit.

5. The power conversion system of claim 4, further including a current monitor coupled to an input terminal of said inverter circuit for providing an indication of instantaneous inverter input current direction, and a voltage monitor for sensing the power conversion system input line voltage polarities.

6. The power conversion system of claim 4 wherein the DC link includes first and second oppositely-poled diodes for interconnecting corresponding terminals of the rectifier and inverter circuits.

7. The power conversion system of claim 6 wherein said switching means are arranged to cross-couple said corresponding terminals of the inverter and rectifier circuits.

8. The power coversion system of claim 7 wherein said switching means comprises first and second field effect transistors having source and drain terminals interconnecting selected output terminals of the rectifier circuit to selected input terminals of the inverter circuit.