Power converter

Claim 2

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage control means connected to receive said first voltage and said second voltage for comparing said first voltage with said second voltage to generate a voltage difference and for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices based on said voltage control output signal; whereby to suppress the fluctuation of said neutral potential of said three-level DC power source.

Claim 3

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a first reactor connected in the forward direction between a positive potential point and a neutral point of said three-level DC power source, a first diode connected in the reverse direction between a connecting point of said first switching device and said first reactor and a negative potential point of said three-level DC power source, a series circuit of a second switching device and a second reactor connected in the forward direction between said negative potential point and said neutral point of said three-level DC power source, a second diode connected in the reverse direction between a connecting point of said second switching device and said second reactor and said positive potential point of said three-level DC power source, said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage control means connected to receive said first voltage and said second voltage for comparing said first voltage with said second voltage to generate a voltage difference and for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices based on said voltage control output signal; whereby to suppress the fluctuation of said neutral potential of said three-level DC power source.

Claim 4

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a first reactor connected in the forward direction between a positive potential point and a neutral point of said three-level DC power source, a first diode connected in the reverse direction between a connecting point of said first switching device and said first reactor and a negative potential point of said three-level DC power source, a series circuit of a second switching device and a second reactor connected in the forward direction between said negative potential point and said neutral point of said three-level DC power source, a second diode connected in the reverse direction between a connecting point of said second switching device and said second reactor and said positive potential point of said three-level DC power source, said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage control means connected to receive said first voltage and said second voltage for comparing said first voltage with said second voltage to generate a voltage difference and for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices based on said voltage control output signal; whereby to suppress the fluctuation of said neutral potential of said three-level DC power source.

Claim 5

The power converter according to claim 1 or 2, wherein: said control means includes pulse width modulation control means for turning ON one of said first and second switching devices determined by the polarity of said voltage difference of said voltage control output signal at a pulse width corresponding to said voltage difference of said voltage control output signal.

Claim 6

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first arm and a second arm connected between a positive side potential point and a negative side potential point of said three-level DC voltage source, each of said first and second arms composed of a series circuit of a first switching device and a second switching device, a first diode connected in antiparallel with said first switching device, and a second diode connected in antiparallel with said second switching device, a third diode connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices in said first arm, a fourth diode connected between said neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices in said second arm, and a reactor connected between said neutral potential point of said three-level DC voltage source and a connecting point of said first and second arms, an anode of said first switching device of said first arm being connected to said positive side potential point of said three-level DC voltage source, a cathode of said second switching device of said first arm being connected to an anode of said first switching device of said second arm, a cathode of said second switching device of said second arm being connected to said negative side potential point of said three-level DC voltage source; said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage control means connected to receive said first voltage and said second voltage for comparing said first voltage with said second voltage to generate a voltage difference and for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices in said first and second arms based on said voltage control output signal, such that one arm of said first and second arms is turned ON based on said voltage control output signal and a current is flown through said reactor from one of said capacitors, then said switching device of said three-level DC voltage source side is turned OFF and said current flowing through said reactor is circulated and stored through one of said third and fourth diodes, and then said switching device of the other side is turned OFF and said current stored in said reactor is discharged through the other of said capacitors and the other arm; whereby to suppress the fluctuation of said neutral potential of said three-level DC power source.

Claim 7

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first arm and a second arm connected between a positive side potential point and a negative side potential point of said three-level DC voltage source, each of said first and second arms composed of a series circuit of a first switching device and a second switching device, a first diode connected in antiparallel with said first switching device, and a second diode connected in antiparallel with said second switching device, a third diode connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices in said first arm, a fourth diode connected between said neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices in said second arm, and a reactor connected between said neutral potential point of said three-level DC voltage source and a connecting point of said first and second arms, an anode of said first switching device of said first arm being connected to said positive side potential point of said three-level DC voltage source, a cathode of said second switching device of said first arm being connected to an anode of said first switching device of said second arm, a cathode of said second switching device of said second arm being connected to said negative side potential point of said three-level DC voltage source; said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage control means connected to receive said first voltage and said second voltage for comparing said first voltage with said second voltage to generate a voltage difference and for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices in said first and second arms based on said voltage control output signal, such that one arm of said first and second arms is turned ON based on said voltage control output signal and a current is flown through said reactor from one of said capacitors, then said switching device of said three-level DC voltage source side is turned OFF and said current flowing through said reactor is circulated and stored through one of said third and fourth diodes, and then said switching device of the other side is turned OFF and said current stored in said reactor is discharged through the other of said capacitors and the other arm; whereby to suppress the fluctuation of said neutral potential of said three-level DC power source.

Claim 8

The power converter according to claim 4, wherein: said control means includes pulse width modulation control means for generating a first switching signal to turn ON one of said first and second arms determined by the polarity of said voltage difference of said voltage control output signal at a pulse width corresponding to said voltage difference of said voltage control output signal, and for generating a second switching signal for generating an ON command at the same time when said first switching signal generates an ON command and for generating an OFF command at a predetermined time after said first switching signal generates an OFF command; and said first switching signal is applied to one of said first and second switching device at said three-level DC voltage source side, and said second switching signal is applied to the other of said first and second switching devices.

Claim 9

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said inverter neutral current with said chopper current to generate a current difference therebetween, current control means connected to receive said current difference for generating a current control output signal so that said current difference becomes zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal.

Claim 10

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said inverter neutral current with said chopper current to generate a current difference therebetween, current control means connected to receive said current difference for generating a current control output signal so that said current difference becomes zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal.

Claim 11

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, inverter neutral current computing means for computing an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said computed inverter neutral current with said chopper current to generate a current difference therebetween, current control means connected to receive said current difference for generating a current control output signal so that said current difference becomes zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal.

Claim 12

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, inverter neutral current computing means for computing an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said computed inverter neutral current with said chopper current to generate a current difference therebetween, current control means connected to receive said current difference for generating a current control output signal so that said current difference becomes zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal.

Claim 13

The power converter according to claim 7: wherein said chopper control means further includes second current detecting means for detecting three-phase currents flowing between said three-level NPC inverter and a load of said three-level NPC inverter; and wherein said inverter neutral current computing means receives said three-phase currents from said second current detecting means and an information for controlling said three-level NPC inverter from an inverter control circuit for controlling said three-level NPC inverter and computes said inverter neutral current based on said three-phase currents and said information.

Claim 14

The power converter according to claim 7: wherein said inverter neutral current computing means receives an information for controlling said three-level NPC inverter from an inverter control circuit for controlling said three-level NPC inverter and computes said inverter neutral current based on said information.

Claim 15

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, inverter neutral current computing means for computing an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, first comparator means for comparing said computed inverter neutral current with said chopper current to generate a first current difference therebetween, second comparator means for comparing said detected inverter neutral current with said chopper current to generate a second current difference therebetween, current control means connected to receive said first and second current differences for generating a current control output signal so that said first and second current differences become zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal, said current control means including a proportional compensator connected to receive said first current difference for proportional control, an integral compensator connected to receive said second current difference for integral control and an adder for adding an output of said proportional compensator and an output of said integral compensator to generate said current control output signal so that said first and second current differences become zero.

Claim 16

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, inverter neutral current computing means for computing an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, first comparator means for comparing said computed inverter neutral current with said chopper current to generate a first current difference therebetween, second comparator means for comparing said detected inverter neutral current with said chopper current to generate a second current difference therebetween, current control means connected to receive said first and second current differences for generating a current control output signal so that said first and second current differences become zero, and control means connected to receive said current control output signal for driving said first and second switching devices based on said current control output signal, said current control means including a proportional compensator connected to receive said first current difference for proportional control, an integral compensator connected to receive said second current difference for integral control and an adder for adding an output of said proportional compensator and an output of said integral compensator to generate said current control output signal so that said first and second current differences become zero.

Claim 17

The power converter according to any one of claims 6-10: wherein said chopper control means further includes, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage comparator means for comparing said first voltage with said second voltage to generate a voltage difference, voltage compensation means connected to receive said voltage difference for generating a voltage control output signal so that said voltage difference becomes zero, and adder means for adding said current control output signal from said current control means and said voltage control output signal from said voltage compensation means; and wherein said control means receives an output signal of said adder means instead of said current control output signal and drives said first and second switching devices based on said output signal of said adder means.

Claim 18

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage comparator means for comparing said first voltage with said second voltage to generate a voltage difference, voltage control means connected to receive said voltage difference for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices based on said voltage control output signal.

Claim 19

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first voltage detecting means for detecting a first voltage between one of said capacitors, second voltage detecting means for detecting a second voltage between the other of said capacitors, voltage comparator means for comparing said first voltage with said second voltage to generate a voltage difference, voltage control means connected to receive said voltage difference for generating a voltage control output signal so that said voltage difference becomes zero, and control means connected to receive said voltage control output signal for driving said first and second switching devices based on said voltage control output signal.

Claim 20

The power converter according to claim 12: wherein said chopper control means further includes, first current detecting means for detecting a chopper current flowing through said reactor, a stabilizing compensator connected to receive said chopper current for proportional control, and subtractor means for subtracting an output signal of said stabilizing compensator from said voltage control output signal of said voltage control means; and wherein said control means receives an output signal of said subtractor means instead of said voltage control output signal and drives said first and second switching devices based on said output signal of said subtractor means.

Claim 21

The power converter according to claim 12: wherein said chopper control means further includes, a false differentiator connected to receive said voltage difference for false differentiating said voltage difference, a stabilizing compensator connected to receive an output signal of said false differentiator for proportional control, and subtractor means for subtracting an output signal of said stabilizing compensator from said voltage control output signal of said voltage control means; and wherein said control means receives an output signal of said subtractor means instead of said voltage control output signal and drives said first and second switching devices based on said output signal of said subtractor means.

Claim 22

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said inverter neutral current with said chopper current to generate a current difference, integrating means connected to receive said current difference for integrating said current difference, voltage control means connected to receive an output signal of said integrating means for generating a voltage control output signal so that said output signal of said integrating means becomes zero, a stabilizing compensator connected to receive said chopper current detected by said first current detecting means for proportional control, and subtractor means for subtracting an output signal of said stabilizing compensator from said voltage control output signal of said voltage control means, and control means connected to receive an output signal of said subtractor means for driving said first and second switching devices based on said output signal of said subtractor means.

Claim 23

A power converter, comprising: a converter; a three-level DC voltage source, composed of a series connected capacitors connected between outputs of said converter, to generate a positive potential, a neutral potential and a negative potential; a three-level NPC inverter connected to said three-level DC voltage source; a chopper circuit; and chopper control means for controlling said chopper circuit; said chopper circuit including, a series circuit of a first switching device and a second switching device connected between a positive potential point and a negative potential point of said three-level DC voltage source, a first diode connected in antiparallel with said first switching device, a second diode connected in antiparallel with said second switching device, and a reactor, an anode of said first switching device being connected to said positive side potential point of said three-level DC voltage source, a cathode of said first switching device being connected to an anode of said second switching device, a cathode of said second switching device being connected to said negative side potential point of said three-level DC voltage source, said reactor being connected between a neutral potential point of said three-level DC voltage source and a connecting point of said first and second switching devices; said chopper control means including, first current detecting means for detecting a chopper current flowing through said reactor, second current detecting means for detecting an inverter neutral current flowing between said neutral potential point of said three-level DC voltage source and a neutral potential point of said three-level NPC inverter, comparator means for comparing said inverter neutral current with said chopper current to generate a current difference, integrating means connected to receive said current difference for integrating said current difference, voltage control means connected to receive an output signal of said integrating means for generating a voltage control output signal so that said output signal of said integrating means becomes zero, a stabilizing compensator connected to receive said chopper current detected by said first current detecting means for proportional control, and subtractor means for subtracting an output signal of said stabilizing compensator from said voltage control output signal of said voltage control means, and control means connected to receive an output signal of said subtractor means for driving said first and second switching devices based on said output signal of said subtractor means.

Claim 24

The power converter according to any one of claims 6-10: wherein said converter includes a three-level NPC converter; wherein said neutral potential point of said three-level Dc power source is connected to a neutral potential point of said three-level NPC converter; wherein said chopper control means includes, at least one of converter neutral current detecting means for detecting a converter neutral current flowing between said neutral potential point of said three-level DC power source and said neutral potential point of said three-level NPC converter, and converter neutral current computing means for computing a converter neutral current flowing between said neutral potential point of said three-level DC power source and said neutral potential point of said three-level NPC converter, and at least one of first adder means for adding said detected inverter neutral current and said detected converter neutral current, and second adder means for adding said computed inverter neutral current and said computed converter neutral current; and wherein in said chopper control means, at least one of outputs of said first and second adder means is used instead of at least one of said detected inverter neutral current and said computed inverter neutral current in the following control stage.

Claim 25

The power converter according to any one of claims 6-10: wherein said converter includes a series connected two-level NPC converters; wherein said neutral potential point of said three-level Dc power source is connected to a connecting point of said series connected two-level NPC converters; wherein said chopper control means includes, at least one of converter neutral current detecting means for detecting a converter neutral current flowing between said neutral potential point of said three-level DC power source and said connecting point of said two-level NPC converters, and converter neutral current computing means for computing a converter neutral current flowing between said neutral potential point of said three-level DC power source and said connecting point of said two-level NPC converters, and at least one of first adder means for adding said detected inverter neutral current and said detected converter neutral current, and second adder means for adding said computed inverter neutral current and said computed converter neutral current; and wherein in said chopper control means, at least one of outputs of said first and second adder means is used instead of at least one of said detected inverter neutral current and said computed inverter neutral current in the following control stage.