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Figure 7: Speed voltage regions.

Figure 7 Speed voltage regions.

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A block diagram of a DTC system for an induction ma- chine is shown in Figure. 1[2]. DTC scheme uses a station- ary d-q reference frame. Torque and flux are controlled by the stator voltage space vector defined in this reference frame. Figure. 1: Direct torque control of induction machine
A block diagram of a DTC system for an induction ma- chine is shown in Figure. 1[2]. DTC scheme uses a station- ary d-q reference frame. Torque and flux are controlled by the stator voltage space vector defined in this reference frame. Figure. 1: Direct torque control of induction machine
Sa=1 means top switch closed, bottom switch opened. Figure. 2: Inverter output voltage vectors The operation may be described by the following manner:
Sa=1 means top switch closed, bottom switch opened. Figure. 2: Inverter output voltage vectors The operation may be described by the following manner:
The electromagnetic torque value resulting from the previous stage is then compared with the electromagnetic torque reference, using the three level hysteresis comparator, represented in figure 3. In this manner, the result may be increase, decrease or maintain the torque, depending on the comparator output [3]. Figure 3. Three level hysteresis comparator: t =1=> increase torque; t =0=> maintain torque; t = -1=> decrease torque.
The electromagnetic torque value resulting from the previous stage is then compared with the electromagnetic torque reference, using the three level hysteresis comparator, represented in figure 3. In this manner, the result may be increase, decrease or maintain the torque, depending on the comparator output [3]. Figure 3. Three level hysteresis comparator: t =1=> increase torque; t =0=> maintain torque; t = -1=> decrease torque.
Figure 5: DSVM-DTC control scheme. The main idea the DSVM-DTC control strategy is to force the torque and stator flux to approach their reference by applying in one sampling period several voltage vectors instead of only one voltage vector as in basic DTC.[7]
Figure 5: DSVM-DTC control scheme. The main idea the DSVM-DTC control strategy is to force the torque and stator flux to approach their reference by applying in one sampling period several voltage vectors instead of only one voltage vector as in basic DTC.[7]
Figure.6 voltage vector obtained by using DSVM with three equal time interval This control algorithm uses prefixed time intervals within a cycle period and in this way a higher number of voltage space vectors can be synthesized with respect to those used in basic DTC technique The increased number of voltage vectors allows the definition of switching tables according to the rotor speed the flux and torque errors. With DSVM- DTC strategy, 19 voltage vectors can be selected for each sector, according to the rotor speed, the flux and the torque errors range as is represented in Figure.6 and TABLE 2. The switching period is divided into three equal time intervals and one voltage vector is applied at each time interval.
Figure.6 voltage vector obtained by using DSVM with three equal time interval This control algorithm uses prefixed time intervals within a cycle period and in this way a higher number of voltage space vectors can be synthesized with respect to those used in basic DTC technique The increased number of voltage vectors allows the definition of switching tables according to the rotor speed the flux and torque errors. With DSVM- DTC strategy, 19 voltage vectors can be selected for each sector, according to the rotor speed, the flux and the torque errors range as is represented in Figure.6 and TABLE 2. The switching period is divided into three equal time intervals and one voltage vector is applied at each time interval.
4-high speed voltage (-1sector)
4-high speed voltage (-1sector)
1-low speed voltage 2-medium speed voltage
1-low speed voltage 2-medium speed voltage
The DSVM can produce more voltage vectors which if properly applied produce less ripple. To achieve this, the orque hysteresis has 5 levels instead of two. Figure8. If orque error is small hysteresis is in state 0. In this case a voltage vector is chosen trying to maintain torque at its ac- ual level. If hysteresis is in state +/- 1, a vector just as big as to push torque into the small region is chosen. When hysteresis is in state +/- 2, a vector compensating for the error as fast as possible is chosen, i.e. the same vectors used in the classical DTC [1]. Figure .9: 5-level hysteresis comparator
The DSVM can produce more voltage vectors which if properly applied produce less ripple. To achieve this, the orque hysteresis has 5 levels instead of two. Figure8. If orque error is small hysteresis is in state 0. In this case a voltage vector is chosen trying to maintain torque at its ac- ual level. If hysteresis is in state +/- 1, a vector just as big as to push torque into the small region is chosen. When hysteresis is in state +/- 2, a vector compensating for the error as fast as possible is chosen, i.e. the same vectors used in the classical DTC [1]. Figure .9: 5-level hysteresis comparator
Figure.11b .torque response in DSVM-DTC
Figure.11b .torque response in DSVM-DTC
International Journal of Scientific & Engineering Research, Volume 4, Issue 10, October-2013 ISSN 2229-5518
International Journal of Scientific & Engineering Research, Volume 4, Issue 10, October-2013 ISSN 2229-5518
Related topics:
Computer ScienceSpace vector modulation
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