Power conversion system and control device therefor

• US 5,566,061 A
• Filed: 11/09/1994
• Issued: 10/15/1996
• Est. Priority Date: 11/09/1993
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Uchino, Hiroshi
• Primary Examiner(s): Hecker, Stuart N.
• Application Number:
  US08/338,181
• Time in Patent Office: 706 Days
• Field of Search: 363/31, 363/71
• US Class Current: 363/71
• CPC Class Codes: H02M 1/0054 Transistor switching losses periodically suspending operation of switching converter in low power mode H02M1/0035
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control device for a power conversion system with a plurality of power converters, each of which is provided with a DC power source, a DC reactor and a unit converter composed of self-turn-off switching devices with DC terminals connected to the DC power source through the DC reactor, in which AC terminals of the plurality of unit converters are connected in common and is connected to an AC load. The control device includes a first unit for generating an instruction value vector for an AC output current of the power conversion system, a second unit for generating a set of actual value vectors showing all of the AC output currents that can be generated by the power conversion system, a third unit for selecting a closest actual value vector that is closest to the instruction value vector out of the set of the actual value vectors, and a fourth unit for controlling the self-turn-off switching devices in the unit converters in response to the closest actual value vector. The AC output current of the power conversion system is thereby controlled so as to track the instruction value vector.

Claims

1. A control device for a power conversion system with a plurality of power converters, each of which is provided with a DC power source, a DC reactor and a unit converter composed of self-turn-off switching devices with DC terminals connected to said DC power source through said DC reactor, in which AC terminals of said plurality of unit converters are connected in common and is connected to an AC load, said control device comprising:

first means for generating an instruction value vector for an AC output current of said power conversion system;

second means for generating a set of actual value vectors showing all of said AC output currents that can be generated by said power conversion system;

third means for selecting a closest actual value vector that is closest to said instruction value vector out of said set of said actual value vectors; and

fourth means for controlling said self-turn-off switching devices in said plurality of said unit converters in response to said closest actual value vector;

whereby said AC output current of said power conversion system being controlled so as to track said instruction value vector.

2. The control device according to claim 1, wherein:

said first means generates said instruction value vector within a prescribed range of electrical angle;

said second means generates said set of said actual value vectors within said prescribed range of said electrical angle;

said third means selects said closest actual value vector within said prescribed range of said electrical angle; and

said fourth means controls said self-turn-off switching devices in response to said closest actual value vector over all range of said electrical angle.

3. The control device according to claim 1, wherein said third means includes:

setting means for setting said set of regions, each of said regions being closest to one of said set of said actual value vectors, respectively;

selecting means for selecting a selected region out of said set of said regions in which said instruction value vector is; and

determining means for determining said actual value vector included in said selected region as said closest actual value vector.

4. The control device according to claim 1, wherein said third means includes:

detecting means fop detecting said set of deviations between said instruction value vector and one of said set of said actual value vectors, respectively; and

selecting means for selecting a smallest deviation that is smallest out of said set of said deviation; and

determining means for determining said actual value vector having said smallest deviation as said closest actual value vector.

5. A control device for a power conversion system with a plurality of power converters, each of which is provided with a DC power source, a DC reactor and a unit converter with DC terminals connected to said DC power source through said DC reactor, in which AC terminals of said plurality of unit converters are connected in common and is connected to an AC load, said control device comprising:

current instruction value generating means for generating three phase AC current instruction values for said power conversion system;

current phase detecting means for detecting a maximum phase during a predetermined time period in which one of absolute values of said three phase AC current instruction values in maximum, and for generating said maximum phase and a polarity of said AC current instruction value of said maximum phase;

conduction arm number calculating means for determining numbers of conduction arms in said plurality of unit converters in each of three phases, based on the ratios of said respective three phase AC current instruction values and DC current of said DC power source, respectively;

conduction arm calculating means connected to receive said maximum phase, said polarity and said numbers of said conduction arms for generating a conduction instruction to said plurality of said unit converter, including,

maximum phase current control means for generating a first conduction instruction for turning ON all arms of said unit converters decided by said maximum phase and said polarity,

AC current control means for generating a second conduction instruction for sequentially turning ON arms of said unit converters of one phase of the remaining two phases which are not said maximum phase, and sequentially turning OFF the arms of said unit converters of the other phase, and

bypass current control means for generating a third conduction instruction for turning ON an arm connected in series with said arm turned ON by said first conduction instruction in response to a sum of conducting arms of said remaining two phases in each of said unit converters,

said conduction instruction including said first, said second and said third conduction instruction;

whereby output currents of said power conversion system being controlled so as to track said three phase AC current instruction values.

6. The control device according to claim 5, wherein:

said unit converter includes a three-phase GTO converter; and

said conduction instruction is applied to GTO in said three-phase GTO converter to turn ON or turn OFF said GTO.

7. A power conversion system, comprising:

a first current source power converter including a first converter and a first inverter;

a second current source power converter including a second converter and a second inverter;

said second inverter being a self-commutated inverter;

an input of said first converter and an input of said second converter being connected to a power source;

a capacitor connected to an output of said first inverter and an output of said second inverter, and connected to one of a load and a power system;

current calculation means for detecting a distortion component of a current flowing into said one of said load and said power system and for calculating an output current reference of said second inverter such as to eliminate said distortion component; and

inverter control means for controlling said second inverter based on said output current reference.

8. The power conversion system according to claim 7, further comprising:

a first transformer connected between said power source and said input of said first converter; and

a second transformer connected between said power source and said input of said second converter.

9. The power conversion system according to claim 8, wherein:

said load includes a induction motor; and

said second inverter includes a GTO inverter.

10. A power conversion system, comprising:

a first current source power converter including a first converter and a first inverter;

a second current source power converter including a second converter and a second inverter;

said second converter being a self-commutated converter;

said second inverter being a self-commutated inverter;

a first capacitor connected to an AC input of said first converter and an AC input of said second converter, and connected to a first power source;

a second capacitor connected to an AC output of said first inverter and an AC output of second inverter, and connected to a second power source;

first current calculation means for detecting a first distortion component of a current flowing from a first power source for calculating an AC input current reference of said second converter such as to eliminate said first distortion component;

converter control means for controlling said second converter based on said AC input current reference;

second current calculation means for detecting a second distortion component of a current flowing into a second power source for calculating an AC output current reference of said second inverter such as to eliminate said second distortion component; and

inverter control means for controlling said second inverter based on said AC output current reference;

whereby exchanging power is both directions between said first and second power sources being capable.

11. The power conversion system according to claim 10, further comprising:

a first transformer connected between said first power source and said AC input of said first converter; and

a second transformer connected between said second power source and said AC output of said first inverter;

wherein;

a negative terminal of said first converter is connected to a positive terminal of said second converter;

a positive terminal of said first inverter is connected to a negative terminal of said second inverter;

said first capacitor is connected to said AC input of said first converter through said first transformer; and

said second capacitor is connected to said AC output of said first inverter through said second transformer.