Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2000-10-10
2001-07-17
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C323S207000
Reexamination Certificate
active
06262904
ABSTRACT:
The invention concerns a method and a device for controlling a static converter designed to make it possible to adjust an electrical, and/or magnetic and/or mechanical control value of a current source supplied by this static converter.
Right from the start, one of the principal applications for static converters of electrical power has been the supply of variable frequency electrical machines, making it possible in this way to obtain good performances on systems for regulating velocity and position.
The triphase voltage inverter is a static converter particularly dedicated to the supply of alternating current machines for systems which demand good drive quality (precision, linearity, transient response, stability) in a wide range of variation of speed and load regime.
Traditionally, the structure of the voltage inverter used is composed of a single switching cell per phase, delivering an output voltage with a degree of harmonic distortion of which the limits are known. However, this inverter, a so-called two-level inverter, comes up against technological limits associated with its operating principle.
A new structure for a voltage inverter has been developed, making it possible to modulate the amplitude of the pulses. This multicellular structure, with interleaving cells, has a modular character, permitting a notable improvement in the quality of the voltage delivered which increases with the number of cells.
These multi-level series inverters may be considered as high-powered numerical/analogue converters.
In addition, present numerical signal processors are sufficiently rapid and precise for direct torque control (DTC) of the alternating current machine to be used. This control strategy consists of acting directly on the state of the inverter, from data on the instantaneous values of the torque and flux of the machine.
This control strategy rapidly has appeared as a major innovation making it possible to improve very appreciably the response time of the control of the torque of alternating current machines. Moreover, the basic principle remains very simple since it consists of “directly” choosing the inverter configuration as a function of the sign of the error of the torque and of the sign of the error of the flux which does not, in particular, require the presence of a speed or position sensor.
However, the performances, which are exceptional by certain aspects of this strategy, have not been sufficient to ignore the defects associated with the variable frequency operation which it imposes
an increase in losses by switching or by hysteresis and the putting in danger of semiconductors during high-frequency operations,
acoustic disturbances during low frequency operations,
excitation of mechanical and/or electrical resonances due to scanning of the frequency.
The object of the present invention is to overcome these disadvantages and its principal object is to provide a method and a device for controlling a static converter preserving the dynamics of direct control methods such as described above, while leading to a choice of switching frequency as an independent parameter.
To this end, the object of the invention is first of all a method for controlling a static converter associated with a polyphase current source and a direct voltage source, the said method being designed to make it possible to adjust an electrical and/or magnetic and/or mechanical value of the current source, a so-called control value, wherein:
synchronization instants t(i) are generated, defined by a periodic clock T,
at least one electrical, magnetic or mechanical value is measured, representative of the state of the current source,
at least one control value c(t) and its derivative {dot over (c)}(t) are calculated from the measured values, and the value cp(t(i)+T) which each control value would have at the following synchronization instant t(i)+T, for the configuration Cc of the static converter at the instant t(i),
each control value cp(t(i)+T) is compared with a preselected reference value, a so-called set value and, as a function of the result from the comparison and the configuration of the static converter at each synchronization instant t(i), the configuration of the said static converter is determined which is able to minimize the difference between the control value and the corresponding set value at the following synchronization instant t(i)+T,
the derivative at the instant t(i)+T is calculated of a control value, a so-called preferred value, corresponding to the configuration Cc(t(i)+T) at the instant t(i)+T,
the switching instant t(i)+tcom is determined between these instants t(i) and t(i)+T making it possible to minimize the difference at the instant t(i)+T between the preferred control value and the corresponding set value,
and switching of the static converter is controlled at the instant t(i)+tcom.
According to the invention, the control principle is divided into three steps:
choice of the configuration of the static converter at an instant t(i)+T as a function of the configuration of this converter at an instant t(i) and measured values representing the state of the current source,
computation of the switching instant t(i)+tcom between the present and future configurations, for a preferred control value of which it is desired to control the switching frequency,
control of the switching of the static converter at the instant t(i)+tcom.
This control method accordingly leads to:
controlling a single switching of the static converter between two sampling instants t(i), t(i)+T,
fixing, between these two instants, and by means of computing derivatives, the switching instant so as to minimize the difference between the preferred control value and the corresponding preselected set value.
Such a control method thus makes it possible to assign the control value(s) delivered by the current source in a highly dynamic way, while selecting the switching frequency of the static converter as an independent parameter and while no longer treating it as a consequence of the operating conditions.
According to the application, it will then be possible to choose to assign a fixed frequency (for example in order to enable electrical or mechanical filtering to take place with the aid of a very selective band eliminator circuit) or to vary the cut-off frequency according to the load conditions, (for example to keep the temperature of semiconductors constant and to reduce thermal cycling).
According to a first application designed to control an N-level inverter, with N≧2, associated with a triphase asynchronous machine, the stator flux &phgr;s and the electromagnetic torque Cem of the said machine are preferably selected as the control value, and the electromagnetic torque Cem as the preferred control value.
In addition, and advantageously, with a view to calculating the control values &phgr;s and Cem, measurements are taken of the line currents I
1
, I
2
, I
3
and the estimated or measured stator voltages V
1
, V
2
, V
3
at the output from the inverter.
In addition, according to this application, the derivatives &phgr;s and Cem of the control values &phgr;s and Cem are preferably calculated from the following formulae:
φ
.
s
=
ⅆ
φ
s
ⅆ
t
=
2
3
φs
(
φ
s
α
V
s
α
+
φ
s
β
V
s
β
-
Rs
(
φ
s
α
I
s
α
+
φ
s
β
I
s
β
)
)
and
C
.
em
=
ⅆ
Cem
ⅆ
t
=
P
(
V
s
α
K
s
β
-
V
s
β
K
s
α
-
k1
)
with:
K
s
α
=
I
s
α
-
φ
s
α
σ
Ls
;
K
s
β
=
I
s
β
-
φ
s
β
σ
Ls
k1
=
Rs
′
&
Martins Carlos de Almeida
Meynard Thierry
Roboam Xavier
Berhane Adolf Deneke
Centre National de la Recherche Scientifique (C.N.R.S.)
Young & Thompson
LandOfFree
Method and device for controlling a static converter... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for controlling a static converter..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for controlling a static converter... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2539780