US 2004/0057262 A1Published application

Three-level neutral point clamping pwn inverter and neutral point voltage controller

AssigneeKabushiki Kaisha Yaskawa Denki

InventorsYoshiyuki Tanaka, Katsutoshi Yamanaka, Eiji Watanabe

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Abstract

On the basis of: a first calculated value ic which is a product of a calculated value of a time of three-phase output voltages in a state where a positive bus, a negative bus, and a neutral line are connected respectively to three-phase phase output terminals, and a predicted neutral current value in the state; and second and third calculated values icx and icy which are products of a calculated value of a time of the three-phase output voltages that can take state 1 where two of the three-phase phase output terminals are connected to the positive bus or the neutral line, and a remaining one terminal is connected to the neutral line or the negative bus, and state 2 opposite to the state, and predicted neutral current values in states 1 and 2, a time ratio of state 1 and 2 during a PWM period is determined so as to make a current flowing through the neutral line close to zero, or a potential of the neutral line of the three-phase output voltages close to a voltage which is exactly the middle between voltages of the positive and negative busses.

Claims11

Dependent claims

A three-phase neutral-point-clamped PWM inverter apparatus which has a positive bus, a negative bus, and a neutral line, and in which neutral-point-clamped PWM inverters for three phases are disposed, each of said neutral-point-clamped PWM inverters being configured by:

connecting in series first and second switch elements, and third and fourth switch elements between said positive bus and a phase voltage output terminal, and said negative bus and a phase output terminal, respectively;
and connecting a node between said first and second switch elements, and a node between said third and fourth switch elements to said neutral point via respective clamp elements, characterized in that said apparatus comprises:
means for obtaining a first calculated value which is a product of:
a calculated value of a time of three-phase output voltages in a state where said positive bus, said negative bus, and said neutral line are connected respectively to said three-phase phase output terminals during a PWM period;
and a value of a current which is predicted to flow through said neutral point in said state;
means for obtaining a second calculated value which is a products of:
a calculated value of a time of three-phase output voltages that can take a second state where two of said three-phase phase output terminals are connected to said positive bus, and one of said three-phase phase output terminals is connected to said neutral line, or a third state where two of said three-phase phase output terminals are connected to said neutral line, and one of said three-phase phase output terminals is connected to said negative bus;
and a value of a current which is predicted to flow through said neutral line in said state;
means for obtaining a third calculated value which is a products of:
a calculated value of a time of three-phase output voltages that can take a fourth state where one of said three-phase phase output terminals is connected to said positive bus, and two of said three-phase phase output terminals are connected to said neutral line, or a fifth state where one of said three-phase phase output terminals is connected to said neutral line, and two of said three-phase phase output terminals are connected to said negative bus;
and a value of a current which is predicted to flow through said neutral line in said state;
and
ratio determining means for determining ratios of said second and third states, and said fourth and fifth states during a PWM period so as to, on the basis of said first, second, and third calculated values, make a current flowing through said neutral line close to zero, or a potential of said neutral line close to a potential which is exactly a middle between potentials of said positive and negative busses.

10 more elements

A neutral voltage controller which controls a neutral voltage that is a voltage between a neutral point of two capacitors connected in series between positive and negative busses of a three-level inverter apparatus, and said negative bus, characterized in that said neutral voltage controller comprises:

subtracting means for outputting a value which is obtained by subtracting a first reference voltage value from a value of said neutral voltage, said first reference voltage value being one half of a voltage between said positive and negative busses;
a comparator which outputs a 2-bit digital signal having different values in cases where said value output from said subtracting means is smaller than a second reference voltage value which is a negative value, where said value output from said subtracting means is larger than a third reference voltage value which is a positive value, and where said value output from said subtracting means is equal to or larger than said second reference voltage value and equal to or smaller than said third reference voltage value;
insulating means for outputting said digital signal in an insulative manner;
and
storage means for previously storing a table of sets of a value of said digital signal and a neutral voltage control command which is to be output at said value, obtaining a neutral voltage control command which corresponds to said digital signal supplied from said insulating means, from said table, and outputting said neutral voltage control command.

2 more elements

Dependencies are inferred from the claim text.