A Variable-Speed, Sensorless, Induction Motor Drive
Using DC Link Measurements
ABSTRACT:
This paper presents a new control strategy for three-phase
induction motor which includes independent speed & torque control loops and
the current regulation thereby overcoming the limitation (i.e. sluggish
response) of volts per hertz controlled industrial drives. For close-loop
control, the feedback signals including the rotor speed, flux and torque are
not measured directly but are estimated by means of an algorithm. The inputs to
this algorithm are the reconstructed waveforms of stator currents and voltages
obtained from the dc link and not measured directly on stator side. The
proposed drive thus requires only one sensor in the dc link to implement the close-loop
speed and torque control of a three-phase induction motor. The simulation
results on a 2.2 kW induction motor drive in Matlab/Simulink software show fast
dynamic response and good agreement between the actual values and the estimated
values of torque and speed. Replacement of the open-loop control strategy of
existing v/f drive by the proposed close-loop strategy appears to be possible
without requiring any additional power components and sensors.
KEYWORDS:
1. Speed-sensorless
2. Estimation
3. Dc link
4. Band-pass filter
5. Reconstruction
6.Three-phase induction motor
7.Space-vector.
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure
1. Block diagram of the proposed scheme.
CONCLUSION:
In this paper, a new control strategy for
induction motor drive is proposed. The drive is operated under torque control
with an outer speed loop and is very similar to open-loop v/f drive in terms of
power components and sensors required. Due to the inclusion of torque control
loop, the drive response is fast and stable. Simulation results confirm the
effectiveness of the proposed scheme. The technique uses only dc link voltage
and dc link current measurements to generate the estimates of the dc link
voltage is assumed as constant, only one current sensor in the dc link is
sufficient to give the estimates of all required feedback variables. Moreover,
the same current sensor that is already available in the dc link of an
open-loop v/f drive for protection purpose can be used. Thus the open loop control
strategy in an existing v/f drive can be replaced by the proposed close-loop
control strategy without requiring any additional power components or the
physical sensors. The proposed strategy appears to be a good compromise between
the high-cost, high-performance field-oriented drives and the low-cost,
low-performance v/f drives. Practical implementation of the proposed scheme on
a 16 bits floating point arithmetic Texas Instrument TMS320C31 processor are
the subject of future follow-up research work.
REFERENCES:
[1]
B. K. Bose, Power Electronics and Motor Drives, Delhi, India, Pearson
Education, Inc., 2003.
[2]
M. Rodic and K. Jezernik, “Speed-sensorless sliding-mode torque control of
induction motor,” IEEE Trans. Ind. Electron., vol. 49, no. 1, pp.
87-95, Feb. 2002.
[3]
L. Harnefors, M. Jansson, R. Ottersten, and K. Pietilainen, “Unified sensorless
vector control of synchronous and induction motors,” IEEE Trans. Ind.
Electron., vol. 50, no. 1, pp. 153-160, Feb. 2003.
