| dc.description.abstract | Induction machine, the work horse of the industry, has been widely used in industrial
drives. The most common and efficient way to control the speed of induction machine is
with variable frequency drives. The variable frequency drive schemes can be classiffied as
scalar and vector control methods. Scalar control, which is based on the steady state ma-
chine model, is a simpler and cost-effective way to control the speed of induction machine.
Using scalar control, the amplitude and frequency of stator voltage are controlled with-
out phase control, resulting in its poor dynamic response. This limits the usage of scalar
control to the applications that do not require faster response. The advantage of scalar
control is that it is not sensitive to the variation in machine parameters. In contrast to
this, vector control that is based on the dynamic machine model, allows the independent
control of torque and ux. The amplitude, frequency and phase of the stator voltage
are controlled in vector control. The torque response in vector control is much faster
when compared to that of scalar control techniques. However, vector control techniques
are sensitive to the variation in machine parameters. Slip estimated in vector control
scheme depends on the rotor resistance, rotor leakage and mutual inductances. Thus,
either inaccurate estimation or variation in these parameters can lead to the incorrect
estimation of slip, that results in the incorrect value of synchronous speed. This can lead
to the degradation in the performance of vector control.
A novel speed control scheme, that includes the advantageous features of both scalar
and vector control schemes, is proposed. The proposed scheme provides good transient
performance, while retaining the robustness aspects of scalar control. Scalar control acts
as steady state platform in the proposed method. The transient response is improved by
employing phase control of stator voltage as well. This is achieved through the addition
of transient vector estimator to the scalar control. Slip in the proposed method is taken
from the scalar control portion. Thus, the problems that arise due to the inaccurate
estimation of slip can be overcome with the proposed method.
Self commissioning is an important feature in the modern day electric drives. This
allows the auto tuning of controllers, when high dynamic performance control schemes
are employed. Performing no load and blocked rotor tests, is the conventional way for pa-
rameter identification in induction machines. However, these tests require the mechanical
blocking of rotor and thus it becomes more difficult to automatise these tests. Besides,
the results obtained from these tests are not accurate. The self commissioning schemes
reported in the literature assume a relation between stator and rotor leakage inductances.
A self commissioning scheme that identifies all the six electrical parameters (stator
resistance, rotor resistance, core loss resistance, stator leakage inductance, rotor leakage
inductance and mutual inductance) is proposed. The estimation is done using Kalman
filter algorithm, which is a recursive least squares algorithm. Pseudo random binary
sequence (PRBS) signals are commonly used as input excitation in parameter estimation
methods, as these very well meet the conditions of persistency of excitation. In the
proposed method, sine triangle pulse width modulation (SPWM) signals are used as
input excitation. This advantages is that, SPWM signals can be easily generated with
voltage source inverters, when compared to that of PRBS signal generation. Generalised
expression to evaluate core loss resistance at any given fundamental frequency, is also
presented as a part of the proposed self commissioning scheme.
Finally, the proposed speed control strategy and self commissioning schemes are
practically implemented on open source electric vehicle platform. | en_US |
