Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-04-12
2001-11-06
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S799000, C318S798000, C318S800000, C318S801000, C318S807000, C318S805000
Reexamination Certificate
active
06313603
ABSTRACT:
The present invention relates to a method of regulating a rotary machine, in particular an asynchronous rotary machine. The invention also relates to power supply circuit for such a machine.
More precisely, the invention relates to a method of regulation that is capable of servo-controlling the electromagnetic torque of the machine, and incidentally the magnetic flux (rotor or stator flux) thereof, to corresponding reference values.
BACKGROUND OF THE INVENTION
The speed of an asynchronous machine is generally controlled by regulating the electromagnetic torque of the machine.
For this purpose, asynchronous rotary machines are generally provided with a regulator receiving as input a reference value for the electromagnetic torque, together with one or more sampled signals representing the electromagnetic torque of the machine and derived from a measurement of the stator current.
In order to servo-control the electromagnetic torque of the machine on the reference torque value, the regulator proceeds at each sampling instant with a prediction of the value of the torque at the following sampling instant, and it modifies the control voltage accordingly.
One of the main concerns in most industrial applications is to increase the dynamic performance of such regulators, and in particular to increase the dynamic range of the torque.
In order to enable such a system to have a good dynamic range for its torque, it is necessary for the chopper frequency of the inverter to be large compared with the dynamic range that it is desired to obtain, since otherwise compensation is poorly performed and performance suffers. In particular, the efficiency of the inverter and of the motor decrease so the losses to be dumped increase.
One solution to this problem consists in providing the system with low-loss electronic components. However that solution is unacceptable insofar as it contributes to increasing very considerably the cost of the power supply circuit of the machine.
OBJECT AND SUMMARY OF THE INVENTION
The object of the invention is to mitigate the above-mentioned drawbacks.
The invention thus provides a method of regulating a rotary machine powered by a voltage inverter receiving as an input a discrete control voltage delivered by a regulator for the purpose of servo-controlling the electromagnetic torque of the machine on a torque reference value, the regulator receiving as inputs, said reference value and at least one sampled signal representative of the electromagnetic torque of the machine, and proceeding at each sampling instant to predict the torque value at a following sampling instant and to modify accordingly the control voltage, wherein the servo-control of the electromagnetic torque comprises the following steps:
prior computation of a discrete model of the system comprising the machine and the inverter so as to establish the variation of electromagnetic torque between two sampling instants in the form of a first term corresponding to free variation of the system from a state corresponding to the sampling instant and in the absence of a control voltage, and a term corresponding to variation of the system under the action of the control signal; and
modification of the control voltage in such a manner as to cause the electromagnetic torque of the machine to vary from a value corresponding to free variation of the torque towards the torque reference value.
Thus, the improvement in dynamic performance is due to using an improved regulator, which is less expensive than providing higher-performance electrical components.
The regulation method of the invention may also include one or more of the following characteristics, taken in isolation or in any technically feasible combination:
during servo-control of the torque on the reference value, the magnetic flux of the machine is servo-controlled on a reference flux value received as input to the regulator, by acting on the control voltage in such a manner as to cause the magnetic flux to vary from a value corresponding to free variation of the magnetic flux to the reference flux value;
the control voltage is modified at each sampling instant in such a manner as to obtain the reference torque value and the reference flux value at the following sampling instant;
the step of modelling the system consists in rendering discrete the following state equations of the system:
{dot over (X)}=[A
(&ohgr;)]
X+[B]V
ref
,
and
Y=h
(
X
)
in which:
X and Y represent respectively the state vector and the output vector of the machine;
[A(&ohgr;)] represents a state matrix of the machine that varies as a function of the speed &ohgr; of the machine;
[B] represents an input matrix of the system;
h represents an output function of the system; and
V
ref
represents the control voltage; and
in generating characteristics &Dgr;C and &Dgr;&phgr; representative of the torque variation and the flux variation to be obtained between firstly free variation during the sampling period and secondly the following sampling instant, on the basis of the discrete model of the system as defined by the following equations;
Δ
C
=
(
Ψ
→
k
+
1
o
Λ
V
→
ref
)
-
(
ad
+
bc
)
&LeftDoubleBracketingBar;
V
→
ref
&RightDoubleBracketingBar;
2
and
Δ
φ
=
2
b
⟨
φ
→
k
+
1
o
,
V
→
ref
⟩
-
2
d
(
φ
→
k
+
1
o
Λ
V
→
ref
)
+
(
b
2
+
d
2
)
&LeftDoubleBracketingBar;
V
→
ref
&RightDoubleBracketingBar;
2
,
in
which
:
Ψ
→
k
+
1
o
=
[
a
-
c
+
c
a
]
φ
→
k
+
1
o
-
[
b
d
-
d
b
]
I
→
k
+
1
o
where a, b, c, and d represent coefficients of the discrete input matrix of the system,
I
→
k
+
1
o
designates the predicted free variation of the stator current vector during the sampling period,
Φ
→
k
+
1
o
designates the predicted free variation of the magnetic flux vector of the machine during the sampling period, and
&LeftDoubleBracketingBar;
V
→
ref
&RightDoubleBracketingBar;
2
designates the modulus squared of the control voltage; and
the regulator being implemented in such a manner as to determine the value of the control voltage to be applied to the input of the inverter so as to obtain the torque variation &Dgr;C and the flux variation &Dgr;&phgr;; and
the control voltage applied to the input of the inverter is constituted by the voltage corresponding to minimizing electrical power as selected from reference voltages that satisfy the equations defining said characteristics representative of torque variation and flux variation.
The invention also provides a power supply circuit for a rotary machine comprising a voltage inverter powered by a power supply voltage, a regulator receiving as input an electromagnetic torque reference value and at least one sampled signal representative of the electromagnetic torque of the machine and delivering to the inverter a control voltage suitable for servo-controlling the electromagnetic torque of the machine on the torque reference value, by predicting at each sampling instant the value of the electromagnetic torque at the following sampling instant and by modifying the control voltage accordingly, wherein the regulator includes, stored in memory, a discrete model of the system constituted by the machine and the inverter in the form of a term corresponding to free variation of the system in the absence of control voltage and a term corresponding to variation of the system under the action of the control signal, between two sampling instants, and the circuit further including means for generating a control voltage adapted to cause the electromagnetic torque to vary from a value corresponding to free variation of the torque to the reference torque value.
Advantageously, the regulator receives
Poullain Serge
Thomas Jean-Luc
Alstom
Masih Karen
Sughrue Mion Zinn Macpeak & Seas, PLLC
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