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Objective

Validate the operation of the field-oriented control algorithm for the Festo 2 kW Doubly-Fed Induction Generation Research System using the OPAL-RT simulator and quadrature rotor currents of the WRIM (configured as a DFIG in Scherbius drive mode) will be controlled by the FOC scheme. The quadrature rotor current controls the real power either produced or consumed at stator terminals, while the direct rotor current controls the reactive power of the machine.

Model Overview

The RT-LAB model depicted in figure 1 consists of two subsystems:

• The “SM_OP5707” subsystem includes the model that runs on the real-time simulator

• The “SC_Offline_User_Interface” subsystem presents the user interface that runs on the host PC.

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Figure 1: RT-LAB model overview

The subsystem consists of five areas as shown in figure 2.

• The blue area (Operation mode configuration) configures the operation mode of the model which can be a simulation or experiment.

• The gray area (Signal Monitoring) is the block for receiving and monitoring data from the OPAL-RT simulator.

• The yellow area (GSC Control) consists of the grid-side converter control and the reference voltage.

• The green area (RSC Control) is dedicated to the WRIM control references.

• The orange area (INSTRUCTION) provides additional information and notes regarding the model application and its test procedure.

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Figure 2: Contents inside the SC_Offline_User_Interface subsystem

The SM_OP5707 subsystem also includes three main blocks highlighted by bold red titles, shown in figure 3.

• The “OP8662 and OP8219 IO Interface” block is used to interface the PWMs, voltages, current measurements, and encoder signals.

• The “GSC CONTROL (DC BUS REGULATION)” block is used to regulate the DC link.

• The “RSC CONTROL (WRIM’s FOC)” block is dedicated to controlling the WRIM.
  The other parts in the SM_OP5707 are considered for real-time simulation of the system, power calculations, reference signal selection, and communication with the “SC_Offline_User_Interface” subsystem.

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Figure 3: Contents inside the SM_OP5707 subsystem

 The structure of the “GSC CONTROL (DC BUS REGULATION)” and “RSC CONTROL (WRIM’s FOC)” blocks are shown in figure 4 and figure 5 respectively.

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Figure 4: Contents inside the GSC CONTROL (DC BUS REGULATION) subsystem

Connection Diagrams

• The connections of the OP5707 simulator to the OPAL-RT OP8662 and OPAL-RT OP8219 are demonstrated in figure 5. The encoder output (DB9F) of the dynamometer needs to be connected to the encoder input (DB9F) of OP8219 to measure the speed and position of the WRIM (DFIG).

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Figure 5: Block diagram of the test bench

• The connection diagram of the system is presented in figure 6. This schematic provides the details required to connect the equipment and measurements.

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Figure 6: Connections between OP8662 voltage and current channels and Festo hardware

• The encoder connections between OPAL-RT OP8219 and Festo 8540 dynamometer are illustrated in figure 7.

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Figure 7: Block diagram of the encoder connection to the OP8219

• The control connections (PWM) using the provided DB9 cables between OPAL-RT OP8219 and Festo 8857 inverters is presented in figure 8.

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Figure 8: Control connection (PWM) to the OP8219

• When coupling the 8505 WRIM with the 8540 dynamometer to run the demos of this guide, make sure that the end of the 8505 has the label “This end to 8540” is coupled to the dynamometer, as shown in figure 9 below.

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Figure 9: Coupling of the dynamometer with WRIM

• Make sure that the WRIM is physically connected (through its unique cable) to the back of the Festo test bench, as shown in the following figure.

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Figure 10: Physical connection of the WRIM to the Festo test bench

Test Procedure

• Make sure that all power source outputs are off (see figure 11).

• Connect the system power circuit and connection signals as shown in figures 5 to 10.

• Power on the OPAL-RT OP8662 (see figure 11).

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Figure 11: OP8662 power button

• Ensure that the power adaptor is connected to the OP8219.

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Figure 12: Power adaptor connector for OP8219

• Ensure that the Festo inverter modules 8857 are powered on using the 24 V AC voltage provided by the Festo power supply 8525.

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Figure 13: Festo 8857 power button

• Ensure that the jumpers are always installed on the OP8219 board. For all tests involved using OP8219, the jumpers need to be installed, unless otherwise stated.

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Figure 14: Jumpers connections for the PWM signals

• Launch RT-LAB.

• Import model zip file in RT-LAB (see below).

• Build, load, and execute the model.

• The loaded model must have certain initial conditions as below:

  • The switches “Enable RSC” and “Enable GSC” are disabled (zero position)
    
    

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    Enable RSC
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    Enable GSC

  • “Ref_control” is set to “3” (Hardware based Rapid Control Prototyping)
    
    

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    Ref_control

  • “Idq_ref_sel” is set to “3” (manual)
    
    

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    Idq_ref_sel

  • “DClink_ref” is set to “110 V”
    
    

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    DClink_ref

  • “Idref” is set to “2” and “Iqref” reference is set to “0”
    
    

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    Idref” and “Iqref”

  • “theta_corr” is set to the proper value to align stator and rotor phases
    
    

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    theta_corr

• Turn on the Festo 8540 dynamometer and run it on “Speed mode” at 1200 rpm in the forward direction.

• Ensure the Festo power supply 8525 is power on and the voltmeter’s selection knob is set to AC 4-5.

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Figure 15: Festo 8525 power supply

• Adjust the variable voltage knob to establish an AC voltage level with the amplitude of 55 Vrms (Line-to-line voltage).

• Make sure that the phase voltages of the grid are properly connected to the corresponding input terminal of the inverter (A-to-A, B-to-B, and C-to-C).
  The phases can be distinguished using the oscilloscope.
  A mismatch between the sequence of the phases applied to the inverter leads to the trip of the inverter when the GSC controller is activated. 

• The PWM signals are enabled by the “Enable GSC.” The DC-link voltage starts tracking the reference voltage

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Figure 16: PWM enable switch

• The following start-up results are expected:

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Figure 17: Experimental performance of the GSC during its start-up

• Perform a DC-link voltage variation from 110 V to 150 V using “DClink_ref “ to check the dynamic performance of the GSC controller.

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Figure 18: The DC link reference

• The following experimental test results show that the controller can track the DC reference voltage.

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Figure 19: Experimental performance of the GSC
during the DC reference voltage variation from 110 V to 150 V

• Maintain the DC-link voltage at 150 V and then turn on the RSC by using the toggle switch “Enable RSC” from ‘0’ to ‘1’.
  Make sure that after a few seconds, I*rd=2 and I*qr=0 references have been reached (Check the “Monitor RSC (DFIG control))” in the “Signal Monitoring” area”.

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Figure 20: Setting d-axis and q-axis current references

• The corresponding measured voltages and currents can be verified through the following “displays” and “Scopes” in the “Signal Monitoring” area of the loaded model.

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Figure 21: Experimental results for the GSC and RSC during
the start-up of the RSC

• Set I*rd=4 first and then after about 20 seconds I*qr=2
  Observe the performance of the system through the “Signal Monitoring” area as well as the oscilloscope.
  The following experimental results captured by “OpWriteFile1” in the “SM-OP5707” are expected:

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Figure 22: Experimental results for the variations of id and iq from
start-up until stabilization after the step change of the references

• To stop the model:

  • First set I*rd=2 and I*qr=0

  • Reduce the DC-link voltage reference from 150 V to 110 V using “DClink_ref””

  • Switch the “Enable RSC” selector in the model to “0” for disabling the RSC

  • Switch the “Enable GSC” selector in the model to “0” for disabling the GSC

  • Turn the AC variable voltage knob to ‘0 V’

  • Reduce the speed to zero and stop the dynamometer

  • Since the DC link capacitors have no discharge path, enable the “Enable RSC” in the model to discharge the DC bus in the WRIM windings

  • Once the DC link voltage drops to zero, disable the “Enable RSC” in the model and turn off the converter’s power supply

  • Reset the model

  • Turn off the Festo 8525 and OPAL-RT OP8660

Conclusion

Based on the preceding tests, the hardware, and the software included in Festo Field Oriented Control (FOC) over a Wound-Rotor Induction Machine (WRIM) model are declared fully functional and compliant with OPAL-RT specifications.

Model (Zip File)