Control system for a power converter and method of controlling operation of a power converter

A system for providing AC power to an AC power network, the system intended for use with a first source that provides a reference AC voltage signal, a second source that provides a real current command signal and a third source that provides a reactive current command signal, the system comprising:

• a. a controlled current source including:
• i. a source of DC power;
• ii. a converter for converting said DC power to AC power having an output voltage;
• b. a current command unit for generating a resultant current command signal, wherein said current command unit is connected to said controlled current source and is connectable to said first and second sources, said current command unit including:
• i. an impedance current regulator that provides an impedance current signal;
• and
• ii. a summing unit for adding said impedance current to the real current command signal from the second source and the reactive current command signal from the third source so as to create said resultant current command signal.

An impedance current regulator for use in a power converter control system including a power converter providing an AC power output, a first source for a reference AC voltage signal, a second source for a real current command signal, a third source for a reactive current command signal, and a voltage signal device for generating a feedback voltage signal representing voltage of the AC power output from the power converter, the impedance current regulator comprising;

• a. a difference unit, connected to the device and to the first source, for determining a voltage difference between the reference AC voltage signal and a feedback voltage signal and generating a voltage difference signal representing said voltage difference;
• b. a gain unit connected to said difference unit for multiplying said voltage difference signal by a first gain so as to generate an impedance current signal;
• and
• c. a summing unit, connected to said gain unit, the second source, the third source and the controlled current source, that combines said impedance current signal with the real current command signal and the reactive current command signal to produce a resultant current signal usable for controlling the power converter.

An AC power system comprising:

• a. a power converter for converting a DC power input to an AC power output having an output voltage, said power converter having a rated output voltage and a rated output current;
• b. a first source for providing a reference AC voltage signal;
• c. a second source for providing a real current command signal;
• d. a third source for providing a reactive current command signal;
• e. an impedance current regulator including:
• i. a difference unit, connectable to said power converter and said first source, for determining the voltage difference between said output voltage from the power converter and said reference AC voltage and providing a voltage difference signal representing said voltage difference;
• ii. a gain unit, connected to the difference unit, for multiplying said voltage difference signal by a gain 1/R, where R is 2-20% of the rated output voltage divided by the rated output current, so as to generate an impedance current signal;
• iii. a summing unit, connected to said gain unit and connectable to said second source and said third source, for adding said impedance current signal to said real current command signal and said reactive current command signal to produce a resultant current command signal;
• and
• f. a voltage correction unit, connected to said summing unit and connectable to said power converter, for multiplying said resultant current command signal by a gain P to generate a correction voltage signal that is provided to said power converter.

A method of controlling the operation of a power converter connected to an AC power network that provides an AC power output, the method comprising the steps of:

• a. providing a reference AC voltage signal representing output voltage from the power converter;
• b. generating an impedance current command signal, wherein said impedance current command signal is generated based on said reference AC voltage signal;
• and
• c. generating a voltage command signal for controlling the operation of the power converter based on said impedance current command signal and providing said voltage command signal to the power converter.

A method of controlling the supply of AC power to at least one load comprising the steps of:

• a. connecting in parallel a plurality of power converters, each for converting DC input power from a corresponding respective DC power source into an AC output power having an output voltage;
• b. relative to each of said plurality of power converters, performing the steps of:
• i. providing a reference AC voltage signal representing output voltage from the power converter;
• ii. generating an impedance current command signal, wherein said impedance current command signal is generated based on said reference AC voltage signal;
• and
• iii. generating a voltage command signal for controlling the operation of the power converter based on said impedance current command signal and providing said voltage command signal to the power converter;
• iv. providing said AC output power from at least one of the power converters to said at least one load.

A distributed generation network, comprising:

• a. an AC power network for providing AC power;
• b. a DC power source for providing DC power;
• c. a power converter for converting said DC power into AC power, said power converter connected to said AC power network and said DC power source;
• and
• d. a control system connected to said power converter for providing a voltage command signal that controls the operation of said power converter, wherein said control system generates (i) a voltage feedback signal representing voltage in said AC power provided by said DC power source and (ii) an impedance current signal as a function of AC power provided by said DC power source, further wherein said control system generates said voltage command signal based on said voltage feedback signal and said impedance current signal.

An uninterruptible power supply, comprising:

• a. an AC power network for providing AC power;
• b. a DC power source for providing DC power, wherein said DC power source does not directly use fuel in developing said DC power;
• c. a power converter for converting said DC power into AC power, said power converter connected to said AC power network and said DC power source;
• and
• d. a control system connected to said power converter for providing a voltage command signal that controls the operation of said power converter, wherein said control system generates (i) a voltage feedback signal representing voltage in said AC power provided by said DC power source and (ii) an impedance current signal as a function of AC power provided by said DC power source, further wherein said control system generates said voltage command signal based on said voltage feedback signal and said impedance current signal.

A control system for a three-phase power converter for converting DC power into three-phase AC power, the converter having at least first and second output nodes for said AC power, said control system comprising:

• a. a first control system including:
• i. a voltage signal device, connectable to the power converter, for providing a voltage feedback signal representing voltage in the AC power output from the first output node as a first input to control the power converter;
• and
• ii. an impedance current regulator for generating an impedance current signal as a function of characteristics of the AC power output from the first output node of the power converter;
• and
• b. a second control system including:
• i. a voltage signal device, connectable to the power converter, for providing a voltage feedback signal representing voltage in the AC power output from the second output node as a second input to control the power converter;
• and
• ii. an impedance current regulator for generating an impedance current signal as a function of characteristics of the AC power output from the second output node of the power converter.