Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2001-04-03
2003-01-14
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S089000, C307S105000
Reexamination Certificate
active
06507505
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power conversion device that converts AC power into DC power or DC power into AC power and more particularly relates to a power conversion device of small size wherein resonance of the AC filter for harmonic current suppression can be suppressed without using a damping resistance for resonance suppression.
2. Description of the Related Art
Power conversion devices constituted by PWM (Pulse Width Modulation) converter devices (hereinbelow simply called converter devices) in which for example AC power is converted to DC power have previously become well known in which self-turn-off switching devices are employed.
FIG. 1
is a block circuit diagram showing an example of the construction of a conventional converter device of this type.
As shown in
FIG. 1
, the converter device comprises reactors
2
a,
2
b,
capacitor
2
c,
AC filter
2
for suppression of harmonic current comprising a damping resistance
2
d,
and a PWM converter (hereinbelow simply called a converter)
3
constituting a power conversion circuit that converts AC power to DC power and is connected to AC power source
1
through this AC filter
2
.
The AC currents iu and iw of converter
3
detected by converter output current detector
4
a
are decomposed into the current component (active component) parallel with the voltage vector of the AC voltage and the current component (reactive component) orthogonal thereto by voltage reference calculation circuit
5
and a vector control calculation is then made; thus, the voltage reference corresponding to the voltage to be output by the converter circuit is calculated as the voltage component Eq parallel with the voltage vector of the AC voltage and the voltage component Ed orthogonal thereto.
This calculated voltage reference is converted to a 3-phase AC voltage reference by a 2-phase/3-phase conversion circuit
11
and controls the AC output voltage of converter
3
by performing PWM control by being input to the PWM control circuit
6
.
The frequency component of the carrier wave that is employed in the PWM control circuit
6
in the converter device flows to AC power source
1
as harmonic current.
Accordingly, in order to suppress this, an AC filter
2
comprising reactors
2
a
and
2
b
and a capacitor
2
c
is connected between AC power source
1
and converter
3
.
However, this AC filter
2
has a self-resonance frequency, and if the harmonic current created by PWM control switching coincides with this self-resonance frequency, resonance occurs, distorting the AC current.
Accordingly, conventionally, in order to suppress this resonance phenomenon, a damping resistance
2
d
was connected in series with capacitor
2
c.
The details of voltage reference calculation circuit
5
and 2-phase/3-phase conversion circuit
11
are prior art disclosed in for example Early Japanese Patent Publication No. H. 10-105261; a detailed description thereof is therefore omitted.
However, although, in a prior art converter device constituting a power conversion device constructed in such a way having an AC filter
2
and a damping resistance
2
d
for resonance suppression, resonance of the AC filter
2
can be suppressed, there are the problems that the effectiveness of capacitor
2
c
which is inserted in order to bypass the harmonic current is lowered by the insertion of damping resistance
2
d,
with the result that the harmonic current flowing in AC power source
1
is increased and the device becomes large in size due to the insertion of damping resistance
2
d.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a novel power conversion device of small size capable of suppressing resonance of the AC filter for harmonic current suppression, without employing a damping resistance for resonance suppression.
In order to achieve the above object, according to the present invention, in a power conversion device comprising an AC filter for harmonic current suppression comprising a combination of at least some of a reactor, capacitor and resistance and a power conversion circuit that converts AC power into DC power or DC power into AC power and is connected to an AC power source through the AC filter, there are provided: voltage reference calculation means (unit) that calculates and outputs a voltage reference corresponding to the voltage that is to be output by the power conversion device main unit; current detection means (unit) that detects and outputs current flowing through a prescribed location between the AC power source and the power conversion circuit; and voltage reference correction means (unit) that uses the output from the current detection means (unit) as a voltage reference correction signal to correct the voltage reference that is output from the voltage reference calculation means (unit).
Consequently, in a power conversion device according to the present invention, by detecting the current flowing through a prescribed location between the AC power source and the power conversion circuit, and using this as a voltage reference correction signal to correct the voltage reference, the power conversion circuit being controlled using this corrected new voltage reference, the resonance current of the AC filter can be damped in the same way as if a damping resistance were connected.
Also according to the present invention, in the power conversion device, as the current detection means (unit), the current flowing through a capacitor of the AC filter is detected; and as the voltage reference correction means (unit), a quantity responsive to the output from the current detection means (unit) is used as a voltage reference correction signal, which is added to the voltage reference which is output from the voltage reference calculation means (unit) to constitute a new voltage reference.
Consequently, in a power conversion device according to the present invention, by detecting the current flowing in a capacitor of the AC filter and using this as a voltage reference correction signal to correct the voltage reference, and controlling the power conversion circuit using this corrected new voltage reference, the resonance current of the AC filter can be damped in the same way as if a damping resistance were connected.
Further, according to the present invention, in the power conversion device, as the current detection means (unit), the current flowing between the AC filter and the power conversion circuit is detected; and as the voltage reference correction means (unit), a quantity responsive to the output from a bandpass filter that passes the self-resonance frequency band of the AC filter and is connected on the output side of the current detection means (unit) is used as a voltage reference correction signal which is added to the voltage reference constituting the output from the voltage reference calculation means (unit) to constitute a new voltage reference.
Consequently, in a power conversion device according to the present invention, the current flowing between the AC filter and the power conversion device is detected, and, using a quantity responsive to the output obtained by passing this through a bandpass filter that passes the self-resonance frequency band of the AC filter as a voltage reference correction signal to correct the voltage reference, the power conversion circuit is controlled using this corrected new voltage reference; damping of the resonance current of the AC filter can thereby be achieved in the same way as if a damping resistance were connected.
Further, according to the present invention, in the power conversion device, as the current detection means (unit), the current flowing between the AC power source and the AC filter is detected; and as the voltage reference correction means (unit), a quantity responsive to the output from a bandpass filter that passes the self-resonance frequency band of the AC filter and is connected on the output side of the current detection means (unit) is used as a voltage reference correction signa
Kawakami Kazuto
Oka Toshiaki
Foley & Lardner
Kabushiki Kaisha Toshiba
Laxton Gary L.
Sterrett Jeffrey
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