DSP Implementation of an Improved DTC Technique for Induction ...

stator d-axis flux (Wb)
stator d-axis current (A)
(a) Proposed Method (b) Conventional Method
Figure 4 Phase Current and d-axis Stator Flux (ωr =20 rad/s and TL=1.2 Nm).
0.5
-0.5
(a) Proposed Method (b) Conventional Method
Figure 5 Stator Flux Trajectories of Induction Motor (ωr =20 rad/s and TL=1.2 Nm).
Experimental Results
1
0
-1
0.5
0
-0.5
0.1 0.2 0.3
time (sec.)
0.4
0.1 0.2 0.3
time (sec.)
0.4 0.5
q-axis stator flux (Wb)
1
0
-1
-1 -0.5 0 0.5 1
d-axis stator flux (Wb)
Experimental tests were carried out on a 0.37kW squirrel-cage induction motor using a TMS320C31 floating point
Digital Signal Processor (DSP) as the controller. The basic TMS320C31 DSP has been modified by the addition
of 64k-words of memory, an 8-channel Analogue to Digital Converter (ADC) and 4-channel Digital to Analogue
Converter (DAC). The communication between the external board and the DSP board is performed by “built-in”
control signals and external user ports.
The modified DTC method is compared with conventional DTC under the same operating conditions. The torque
and speed responses of both schemes are shown in Figure 6. It can be observed that there is no significant
difference between the responses under each of the schemes. Figure 8 illustrates the stator current waveforms
obtained using both the proposed DTC method and conventional DTC. Figure 7(a) shows that the current
waveform is more sinusoidal under the proposed DTC scheme. The experimental results for stator flux locus are
shown in Figure 8. It can be seen from Figure 8(a) that the stator flux trajectory is more circular than that under
the conventional DTC scheme.
1V=2.35rad/s
1V=0.25Nm
q-axis stator flux (Wb)
4
stator d-axis flux (Wb)
1
0.5
0
-0.5
stator d-axis current (A)
2
1
0
-1
-2
0.05 0.1 0.15 0.2 0.25 0.3 0.35
time (sec.)
0.5
0
-0.5
0.05 0.1 0.15 0.2 0.25 0.3 0.35
time (sec.)
-1
-1 -0.5 0 0.5 1
d-axis stator flux (Wb)
1V=2.35rad/s
1V=0.25Nm
(a) Proposed Method (b) Conventional Method
Figure 6 Torque and Speed Responses of Induction Motor (ωref =20 rad/s and TL=1.2 Nm).