Study of the transitory regime performances of an electromechanic drive with asynchronous motor.
Ruja, Ioan ; Bizau, Viorel ; Marta, Constantin 等
1. INTRODUCTION
The electric drives automated by means of asynchronous motors are
rapid adjustment systems. The reduction of the delay time constant of
the adjustment system constitutes an issue of interest for both
specialists and users. We shall present several technical elements
related to the possibility of reducing the duration of the insertion
process for the adjustment system meant for the asynchronous motor
rotative speed / number of revolutions in the case of certain rapid
processes, taking place under difficult conditions (high temperatures,
dust, vibrations, etc.). The research refers to the execution element of
the adjustment system (Ruja et al., 2003).
2. THEORETICAL CONSIDERATIONS
The structural diagram of the automatic system is shown in Figure 1
(Grimble, 2002; Wai & Lee, 2008).
[FIGURE 1 OMITTED]
Input parameter is:
[n.sub.ref] (s) = 1/s (1)
The transfer function of the fixed part of the system is:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)
[H.sub.f] (s) = [H.sub.F] (s) x [H.sub.CF] (s) x [H.sub.MA](s) x
[H.sub.C] (s) x [H.sub.ML] (s) (3)
where: [H.sub.F](s) is the transfer function of the low-passage
philtre, [H.sub.CF](s) is the transfer function of the frequency static
converter, [H.sub.MA](s) is the transfer function of the asynchronous
motor, [H.sub.C](s) is the transfer function of the coupling and
mechanical / power brake, whereas [H.sub.ML](s) is the transfer function
of the working machine.
The execution element is made of: the indirect frequency static
converter, the asynchronous motor with the rotor in short-circuit and
the mechanical / power brake. In order to increase the rapidity of the
adjustment system and to raise the operation safety, we propose a
mechanical / power brake with conical coupling and elastic elements
which does not require an electrohydraulic lifting device. Figures 2 and
3 show the mechanical / power brake.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
The transfer function of the mechanical brake is:
[H.sub.c] (s) = [k.sub.2]/1 + [T.sub.2]s (4)
and the transfer functions of the system elements containing
parasite time constants are:
[H.sub.F](s) = [k.sub.1]/1 + [T.sub.1]s (5)
[H.sub.CF](s) = [k.sub.3] x [e.sup.-[tau]s]/1 + [T.sub.3]s (6)
[H.sub.TR](s) = [k.sub.4]/1 + [T.sub.4]s (7)
Consequently, the sum of the parasite time constants is:
[T.sub.[summation]] = [T.sub.1] + [tau] + [T.sub.2] + [T.sub.3] +
[T.sub.4] (8)
where: the [T.sub.2] time constant depends of the constructive
shape, the steel characteristics and the elastic elements of the
coupling. The duration of the transitory regime is:
[t.sub.t] = 4,72/[[omega].sub.n] (9)
The own oscillation frequency is:
[[omega].sub.n] = 1/[square root of 2 x [T.sub.[summation]]] (10)
The super-adjustment is:
[sigma] = e - [xi] x [pi]/[square root of 1 - [[xi].sup.2]] (11)
Output parameter is:
n(t) = [t.sup.2]/2! - [t.sup.3]/3! + [t.sup.5]/5! - [t.sup.6]/6! +
[t.sup.8]/8! - [t.sup.9]/9! + ... (12)
3. EXPERIMENTAL RESULTS
The determination of the insertion process performances of the
system was done on an experimental stand having as charge a rotative
speed / number of revolutions reducing gear(Ruja et al., 2001).The
measurements were performed with a digital laser tachometer, model
DT-209X. The registration of the index response of the system, in
rotative speed / number of revolutions, for different frequencies, is
shown in Figures 4,5 and 6 (Chakraborty & Hori, 2003) .
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
4. CONCLUSION
The present paper aims to achieve a fast electromechanical system
of adjusment and to withstant to high temperature, over 800[degrees]C
degrees. The use of the mechanical / power brake proposed to become part
of the execution element contributes to the reduction of the mechanical
coupling defects, especially when the mechanism is used in
high-temperature environments. We remarked a duration of the transitory
system, [t.sub.t] = 0.5 s, smaller than that obtained when using the
brake with electrohydraulic lifting device (0,6 s).The other insertion
process performances, such as: increase time [t.sub.c] = 0,25 s,
super-adjustment [sigma] = 6% are also small. The operation safety of
the system is also high.
5. REFERENCES
Chakraborty, C.; Hori, Y. (2003). Fast Efficiency Optimization
Techniques for the Indirect Vector-Controlled Induction Motor Drives,
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Grimble, M.J. (2002). Restricted structure controller tuning and
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Ruja, I.; Szabo, S. (2003). Low cost frequency converter for AC
motor supply, Proceedings 4th of the International Conference on
Electromechanical and Power Systems SIELMEN, September 2003, Chisinau
Ruja, I.; Piroi, I.; Szabo, S. (2001). Study of the behaviour of
the adjustment system of the rotative speed / number of revolutions of
an asynchronous motor fed from a static converter, The 3rd International
Conference of Electromechanical and Energetic Systems, ISBN:
9975-9638-8-9, September 2001, Chisinau
Wai R.-J. ; Lee J.-D. (2008). Comparison of Voltage-source Resonant
Driving Schemes for a Linear Piezoelectric Ceramic Motor, IEEE
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ISSN 0278-0046
