OBJETIVO DEL ESTUDIO

Experimental tests that compare the abc- and synchronous-frame switching of the controllers are performed to further validate the proposed drive and its smooth hand-off transition. Switching between the IFOC controller and the V/f controller is applied, as a proof of concept. The experimental verification is carried out at different speed and load torque conditions, which are summarized in TABLE XIX.

TAB LE XIX. The Testing Conditions in Experimental Validation

Switching Type Speed (RPM) Load Torque (N·m)

1 IFOC to V/f 1800 3.08

2 V/f to IFOC 1800 1.05

3 IFOC to V/f 600 0.53

4 V/f to IFOC 600 0.53

The experimental setup is shown in Fig. 21. The IFOC and V/f controllers are built in Simulink and then loaded onto dSPACE 1104 platform. A virtual panel shown in Fig. 107 is created in dSPACE ControlDesk, which provides the speed command, switches between the controllers, and displays interested machine information in real time. A 1.5HP IM is loaded by a Kollmorgen servomotor which is used as a dynamometer, and can provide speed feedback. The current feedback are obtained from a three-phase inverter. The speed and current feedback are scoped to monitor the hand-off transients.

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Fig. 107. The virtual panel for experi mental validation of the proposed fault -tolerant control

The experimental results of the four testing conditions are shown in Fig. 108, Fig. 110, Fig. 112 and Fig. 113, respectively, while the zoom-in versions of Fig. 108 and Fig. 110 are also provided in Fig. 109 and Fig. 111 emphasizing the details at the hand-off transient. In each figure, channels 1 and 2 are the speed feedback and one phase of the current feedback, which are scaled by 1/270 and 1/6 of their real values, respectively. Channel 3 shows the signal that decides the executing controller: 0 represents the IFOC controller and 1 represents the V/f controller. Change of the level in channel 3 means a change of controller. It is clear in Fig. 108 to Fig. 113 that the proposed drive can achieve much smoother hand-off transients than the normal abc- frame switching in all of the conditions. Moreover, there is no sudden change of current magnitude at the switching instance using the synchronous-frame switching. On the other hand, the switching between the IFOC and V/f controllers at 1800RPM and rated TL using the

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synchronous-frame switching is shown in Fig. 114. Note that this operating condition is not available for the abc-frame switching, since the large current transient will trigger the over- current protection of the inverter and shutdown the setup. This figure indicates that the proposed drive can provide smooth hand-off transition all the way up to rated operating condition and can avoid immediate shutdown of the machine.

Fig. 108. Switching transients from IFOC to V/f controller at 1800 RPM: (a) switching in abc-

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Fig. 109. Zoom-in version of switching transients from IFOC to V/f controller at 1800 RPM: (a)

switching in abc-frame; (b) switching in the proposed synchronous frame

Fig. 110. Switching transients from V/f to IFOC controller at 1800 RPM: (a) switching in abc-

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Fig. 111. Zoo m-in version of switching transients from V/f to IFOC controller at 1800 RPM: (a)

switching in abc-frame; (b) switching in the proposed synchronous frame

Fig. 112. Switching transients from IFOC to V/f controller at 600 RPM: (a) switching in abc-

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Fig. 113. Switching transients from V/f to IFOC controller at 600 RPM: (a) switching in abc-

frame; (b) switching in the proposed synchronous frame

Fig. 114. Hand -off transients at 1800 RPM and rated torque using synchronous -frame switching:

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5.3 Summary

This chapter presents a model-based FDD method of IM faults. The presented method can be applied to all four major types of IM faults. The virtual modulating signals of model- based theoretical fault characteristic frequencies are applied to the current feedback, which can generate fault-indicative super low-frequency component if a fault exists. This method is simple and only requires multiplication processing and simple filters. It is also nonintrusive and does not affect main control loop. The accuracy and robustness of the proposed method are excellent.

This chapter also presents a model-based fault-tolerant control of IMs under sensor failures. The control is based on the proposed multi-controller drive which uses DTC, IFOC and V/f controllers as replacements of each other. The DTC and IFOC controllers are properly modified as voltage-type synchronous-frame controllers, which generate DC-type voltage commands in the synchronous frame and thus can be feasibly controlled using a Rate Limiter. The proposed drive can be equally used in sensor failure and sensor recovery conditions. The proposed drive with qd0-frame switching is compared with the conventional abc-frame switching in simulation and experiment. Significant reduction of hand-off transients when switching between controllers is observed using the proposed drive with qd0-frame switching. Since the hand-off transients could break power switches and/or trigger over-current protection of the drive, which will shut down the machine, the proposed drive and control can avoid these schemes and maintain the continuity of operation.

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CHAPTER 6

EFFICIENCY AND PERFORMANCE ENHANCEMENT OF THREE-PHASE INDUCTION MOTOR DRIVE SYSTEMS BY MATERIALS: ROTOR BAR AND

STATOR WINDING INSULATION

6.1 A Comparison of Rotor Bar Material of Squirrel-Cage IMs for Efficiency