Inverter apparatus and uinterruptible power supply using the same

• US 5,446,645 A
• Filed: 02/18/1993
• Issued: 08/29/1995
• Est. Priority Date: 02/18/1992
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Kobayashi, Akira, Jifuku, Yorito, Mino, Tomoaki, Inukai, Satoru, Shimada, Keizo, Shirahama, Hidefumi, Yamato, Ikuo, Tokunaga, Norikazu, Sakurai, Yoshimi
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/019,642
• Time in Patent Office: 922 Days
• Field of Search: 363/71, 363/55, 363/72, 363/95, 363/65, 307/58, 307/64, 307/82
• US Class Current: 363/71
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel

Abstract

In a uninterruptible power supply in which a plurality of inverters are operated in parallel, a current control loop is provided which responds to the magnitude of an output current of each inverter brought into parallel running to change a command value for a voltage waveform control circuit associated with each inverter, and the gain of the current control loop is made to be variable, whereby currents shared by the inverters can be set desirably to effectively suppress a cross current flowing between the inverters upon establishment of parallel running.

Claims

1. An apparatus for controlling parallel running of inverters for use in an inverter system in which a plurality of inverters are connected at their output sides to a load common to said inverters and an output voltage of each inverter of said inverters is controlled in accordance with a duty command, said apparatus comprising:

a plurality of output current detection means each adapted to detect an output current of each inverter of said inverters;

a plurality of output voltage detection means each adapted to detect an output voltage of each said inverter;

a plurality of current difference calculation means each adapted to calculate a difference between said output current of respective said output current detection means and deliver a cross current signal equivalent to a current flowing between said inverters;

a plurality of cross current suppressing signal generation means each adapted to respond to said cross current signal delivered out of each said current difference calculation means to generate a cross current suppressing signal for suppressing said cross current signal to zero;

a plurality of voltage waveform command generation means each adapted to respond to said output voltage of each said output voltage detection means and said cross current suppressing signal generated from each said cross current suppressing signal generation means to generate a voltage waveform command for specifying amplitude and frequency of an output voltage of each said inverter;

a plurality of voltage difference calculation means each adapted to calculate and output as a calculation value, a difference between said voltage waveform command generated from each said voltage waveform command generation means and said output voltage of each said output voltage detection means;

a plurality of duty command generation means each adapted to generate from said calculation value of each said voltage difference calculation means a duty command for suppressing said calculation value to zero;

a plurality of duty command correction means each adapted to correct said duty command generated from each said duty command generation means with said cross current suppressing signal generated from each said cross current suppressing signal generation means; and

a plurality of inverter control means each adapted to control said output voltage of each said inverter in accordance with said duty command corrected by each said duty command correction means.

2. An apparatus for controlling parallel running of inverters for use in an inverter system in which a plurality of inverters are connected at their output sides to a load common to said inverters and an output voltage of each inverter of said inverters is controlled in accordance with a duty command, said apparatus comprising:

a plurality of output current detection means each adapted to detect an output current of each inverter of said inverters;

a plurality of output voltage detection means each adapted to detect an output voltage of each said inverter;

a plurality of current difference calculation means each adapted to calculate a difference between said output current of respective said output current detection means and deliver a cross current signal equivalent to a current flowing between said inverters;

a plurality of cross current suppressing signal generation means each adapted to respond to said cross current signal delivered out of each said current difference calculation means to generate a cross current suppressing signal for suppressing said cross current signal to zero;

a plurality of voltage waveform command generation means each adapted to respond to a voltage waveform command for specifying amplitude and frequency of said output voltage of each said inverter and said cross current signal calculated by each said current difference calculation means to generate a corrected voltage waveform command corrected by said cross current signal;

a plurality of voltage difference calculation means each adapted to calculate and output as a calculation value, a difference between said corrected voltage waveform command generated from each said voltage waveform command generation means and said output voltage of each output voltage detection means of said plurality of output voltage detection means;

a plurality of duty command generation means each adapted to generate from said calculation value of each said voltage difference calculation means a duty command for suppressing said calculation value to zero;

a plurality of duty command correction means each adapted to correct said duty command generated from each said duty command generation means with said cross current suppressing signal generated from each cross current suppressing signal generation means of said plurality of cross current Suppressing signal generation means; and

a plurality of inverter control means each adapted to control said output voltage of each said inverter in accordance with said duty command corrected by each said duty command correction means.

3. An apparatus for controlling parallel running of inverters for use in an inverter system in which a plurality of inverters are connected at their output sides to a load common to said inverters and an output voltage of each inverter of said plurality of inverters is controlled in accordance with a duty command, said apparatus comprising;

a plurality of output current detection means each adapted to detect an output current of each inverter of said plurality of inverters;

a plurality of output voltage detection means each adapted to detect an output voltage of each said inverter;

a plurality of current difference calculation means each adapted to calculate a difference between said output current of respective said output current detection means and deliver a cross current signal equivalent to a current flowing between said inverters;

a plurality of cross current suppressing signal generation means each adapted to respond to said cross current signal delivered out of each said current difference calculation means to generate a cross current suppressing signal for suppressing said cross current signal to zero;

a plurality of output voltage difference calculation means each adapted to calculate and output as a first calculation value, a difference between said output voltage of respective said output voltage detection means;

a plurality of voltage waveform command generation means each adapted to respond to a voltage waveform command for specifying amplitude and frequency of said output voltage of each said inverter, said cross current signal calculated by each said current difference calculation means and said first calculation value of each said output voltage difference calculation means to generate a corrected voltage waveform command corrected by said cross current signal and said first calculation value of each said output voltage difference calculation means;

a plurality of voltage difference calculation means each adapted to calculate and output as a second calculation value, a difference between said corrected voltage waveform command generated from each said voltage waveform command generation means and said output voltage of each said output voltage detection means;

a plurality of duty command generation means each adapted to generate from said second calculation value of each said voltage difference calculation means, a duty command for suppressing said calculation value to zero;

a plurality of duty command correction means each adapted to correct said duty command generated from each said duty command generation means with said cross current suppressing signal generated from each said cross current suppressing signal generation means; and

a plurality of inverter control means each adapted to control said output voltage of each said inverter in accordance with said duty command corrected by each said duty command correction means.

4. An apparatus for controlling parallel running of inverters for use in an inverter system in which a plurality of inverters are connected at their output sides to a load common to said inverters and an output voltage of each inverter of said plurality of inverters is controlled in accordance with a duty command, said apparatus comprising:

a plurality of output current detection means each adapted to detect an output current of each inverter of said plurality of inverters;

a plurality of output voltage detection means each adapted to detect an output voltage of each said inverter;

an average value calculation means for calculating an average value of said output current of respective said output current detection means;

a plurality of current difference calculation means each adapted to calculate and output as a cross current signal, a difference between said average value of said average value calculation means and said output current of each said output current detection means;

a plurality of cross current suppressing signal generation means each adapted to respond to said cross current signal delivered out of each said current difference calculation means to generate a cross current suppressing signal for suppressing said cross current signal to zero;

a plurality of voltage waveform command generation means each adapted to respond to a voltage waveform command for specifying amplitude and frequency of said output voltage of each said inverter and said cross current signal calculated by each said current difference calculation means to generate a corrected voltage waveform command corrected with said cross current signal;

a plurality of voltage difference calculation means each adapted to calculate and output as a calculation value, a difference between said corrected voltage waveform command generated from each said voltage waveform command generation means and said output voltage of each output voltage detection means of said plurality of output voltage detection means;

a plurality of duty command generation means each adapted to generate from said calculation value of each said voltage difference calculation means, a duty command for suppressing said calculation value to zero;

a plurality of duty command correction means each adapted to correct said duty command generated from each said duty command generation means with said cross current suppressing signal generated from each said cross current suppressing signal generation means; and

a plurality of inverter control means each adapted to control said output voltage of each said inverter in accordance with said duty command corrected by each said duty command correction means.