Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-03-30
2001-06-26
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S810000, C318S811000, C318S812000
Reexamination Certificate
active
06252372
ABSTRACT:
The present invention relates to a process for the variation and regulation of the speed of a motor. It also relates to a system for the practice of this process. It is more particularly concerned with monophase AC motors such as universal motors.
Present processes for the regulation of the speed of a motor is either a direct measurement of the speed, or an estimation of the speed from observation and measurement of the physical parameters such as a difference of potential proportional to the speed, or the current intensity drawn by the motor. In this latter case, it is a matter of measuring at the terminals of a shunt placed in series with the motor, a difference of potential proportional to the drawn current. The signal is then integrated and then compared with a reference voltage. The result of this comparison leads to a slowing of triggering of the triac which permits compensating variations of speed resulting from an overload or a loss of load of the motor. This regulation process is widely used and particularly in integrated circuits that are specialized or dedicated to speed regulation.
The object of the present invention is to provide a new process for the regulation of speed which offers a greater flexibility of use than the present processes, whilst costing less.
This object is achieved with a process to cause to vary and to regulate the speed of a motor supplied from an AC source via switch means controlled to apply to this motor a voltage of variable waveform, comprising an adjustment of the periodical instance of triggering said controlled switches.
According to the invention, this process comprises moreover at least one time per period of the alternating voltage, the following steps:
a surface quantity is calculated corresponding to the current drawn in a time window defined between an instant of establishing the current and a following instant of extinguishing this current;
a duration of the next time for blocking the control switch means is computed,
and the triggering of said switch means is controlled at the end of this blocking time.
There is thus obtained with the process according to the invention a better reliability of taking account of the physical parameter which constitutes the current intensity drawn by the motor. This process moreover offers the possibility of controlling a keyboard, a display, or any other safety function or member. There can thus be provided the possibility of adjusting the speed by use of a keyboard.
Speeds or sequences of operation can be preprogrammed. The regulation process according to the invention can be used for low speeds. There can moreover be provided a limitation of the maximum load current and the detection of the condition of the triac (in short circuit or in open circuit). It is to be noted that the regulation of the speed obtained by the process according to the invention will be more effective than that obtained with the present regulation processes.
The computation of the surface quantity is preferably carried out in the following manner:
a plurality of samples are taken of the current intensity drawn by the motor, in a time window comprised between an instant of establishing the current and an instant of extinguishing this current;
the elements of surface are computed from these taken samples; and
the summation of the surface elements is carried out to determine a quantity of surface corresponding to the current drawn by the motor during a conductive phase of the controlled switch means.
In one preferred embodiment of the process according to the invention, there is calculated a preliminary duration t′ of the next time of blocking the control switch means by applying the following relationship:
t
′
=
T
v
2
-
k
v
·
P
I
in which
T
v
is the period of alternating supply voltage,
k
v
is a proportionality factor related to the type of motor and to the desired speed, and
P
I
is a parameter associated with calculated quantity of surface.
For operating regimes in which there is no linear relation between the parameters of quantity of surface and blocking time, the parameter P
I
is then preferably used as a pointer for a memory zone containing values of blocking time t′ corresponding to values of the surface quantity.
When this linearity is substantially verified, there is then taken for the parameter PI the surface quantity S
I
.
For transitional regimes in which the motor requires an energy supplement, the process according to the invention comprises moreover preferably a correction of the duration of each next blocking time corresponding to a difference between the next blocking time t
+
and the last applied blocking time t
−
limited to a predetermined fraction f of the difference between the new computed blocking time t′ and the last applied blocking time t
−
.
Moreover, a computation of the coefficient of energy correction C is carried out by applying the relationship:
C
=
2
(
1
,
5
-
sin
(
2
·
π
·
t
+
T
V
)
)
and then the predetermined fraction f is divided by this energy correction coefficient C.
On the contrary, for transitional regimes corresponding to a decrease of the conduction time of the controlled switch means, there can be directly applied the new computed blocking time.
The surface quantity S
i
can be computed by applying the following relation:
S
i
=
(
I
1
+
I
n
2
+
∑
j
=
2
j
=
(
n
-
1
)
I
j
)
in which
I
1
, I
j
, . . . I
n
represents samplings of the drawn current intensity.
According to another aspect of the invention, there is provided a system to regulate the speed of a motor supplied from a source of alternating voltage via controlled switch means to apply to this motor a voltage of variable waveform, for practicing the process according to the invention, this system comprising:
means to predetermine the periodic instants of triggering said controlled switch means,
means to supply control signals for triggering said controlled switch means, and
means to measure the current drawn by the motor.
According to the invention, this system comprises moreover control and processing means arranged to:
compute a quantity of surface corresponding to the current drawn in a time window defined between an instant of establishing the current and a following instant of extinguishing this current;
computing a duration of the next time of blocking the controlled switch means, and
controlling the triggering of said switch means at the end of this blockage time.
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Arroubi Mustapha
Leroy Jean-Luc Alain Henri
Leykin Rita
Moulinex (S.A.)
Nappi Robert E.
Young & Thompson
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