Exp 7 Familiarization with the ChopperInverter Control Unit.pdf

7/27/2019 Exp 7 Familiarization with the ChopperInverter Control Unit.pdf

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Universiti Sains MalaysiaElectrical Engineering DepartmentAdvanced Power Electronic Laboratory EEK471

Familiarization with the Chopper/InverterControl Unit (Chopper Modes)

OBJECTIVE

To learn how to use the Chopper/Inverter Control Unit in the various chopper modes.

INTRODUCTION

The Chopper/Inverter Control Unit

The chopper/Inverter Control Unit, whose front panel is shown in Figure 1, is a control elementwhich is especially designed to build two major types of power electronic circuits: choppers and

inverters. There are ten modes in which the chopper/Inverter control Unit can operate. Thesemodes are listed below.

OFF StandbyCHOP.PWM Pulse-width modulation (PWM) control chopperCHOP. STEPS Two-step control chopper3~ 120 120 modulation three-phase inverter3~ 180 180 modulation three-phase inverter3~ P1 Programmed-waveform 1 modulation three-phase inverter3~ P2 Programmed-waveform 2 modulation three-phase inverter3~ V/f Constant V/f ratio three-phase inverter2~ 180 180 modulation two-phase inverterAUX Auxiliary

In the OFF mode, the Chopper/Inverter Control Unit runs in a standby condition where itgenerates no control signals. Notice that the Chopper/Inverter Control unit also runs in thestandby condition in the AUX mode. This mode is kept available for future developments.

The Pulse-width Modulation (CHOP.PWM) and two-step control (CHOP.STEPS) modes of theChopper/Inverter Control Unit are used to build various types of choppers. These modes are dealtwith in this section.

Six other modes of the Chopper/Inverter Control Unit, that 3~ 120, 3~ 180, 3~ P1, 3~ P2, 3~ V/fand 2~ 180 are used to build various types of inverters. These modes will be dealt with in thenext section of this manual.

The front panel of the Chopper/Inverter Control Unit is divided into five sections which aredescribed in the following subsections.


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Figure 1: Front panel of the Chopper/Inverter Control Unit.

The two-step control chopper MODE (CHOP. STEPS)

In this mode, the Chopper/Inverter Control Unit acts as a controller for a two-step neutral-zonecontrol system, which is sometimes referred to as a bang-bang control system. A two-stepneutral-zone control system is a closed-loop control system. As in any closed-loop controlsystem, there is a reference signal, a feedback signal and an error signal. The controller in a two-step neutral-zone control system sends an on/off signal to the device which operates on thevariable under control, so that the value of this variable remains between two predefined values,which are often referred to as set points. Therefore, the error on the controlled variable remains ina certain range of values which is referred to as the neutral zone.

For example, a two-step neutral-zone controller, such as the Chopper/Inverter Control Unit usedin the CHOP, STEPS MODE, can be used to switch the transistor(s) in a chopper ON and OFFso that the instantaneous voltage, current, temperature etc., remains within two given set points.Figure 2 shows an example of the signals generated in such a circuit when the variable undercontrol is voltage. As can be seen, the control signals generated by the Chopper/Inverter ControlUnit change state when the instantaneous voltage reaches the lower and upper set points. Thismakes the error signal, that is the difference between the reference voltage (reference signal) andthe instantaneous voltage (feedback signal) remain in the neutral zone defined by the two setpoints. Notice that the control signals generated by the Chopper/Inverter Control Unit, which arenumbered 1, 2, 4, and 5, can be injected through isolators and amplifiers into the MOSFET gatesbearing the same number in the choppers circuit. These control signals are available on pins 1, 2,4, and 5 of the control outputs connector, respectively.


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Figure 2: Example of signals generated in a two-step neutral-zone control chopper.

In the CHOP.STEPS MODE, CONTROL INPUTS 1 and 3 are used to inject the reference andfeedback signals, respectively into the Chopper/Inverter Control Unit. Voltages varying between

-10 and + 10 V can be applied to CONTROL INPUTS 1 and 3. CONTROL INPUT 2 allows therange of the neutral zone to be set. This range is equal to one half the absolute value of thevoltage applied to CONTROL INPUT 2. This voltage can be varied between 0 and 10 V.

Let us consider an example where the voltages applied to CONTROL INPUTS 1 and 2 are equalto +7 V and 3 V, respectively. This sets the reference signal to +7 V and the range of the neutralzone to 1.5 V (3V 2). Since the range of the neutral zone straddles the reference signal, theupper set point is at +7.75V (7V + 0.75V) and the lower set point is at + 6.25V (7V - 0.75V).

EQUIPMENTS

EMS 8821 Enclosure Power Supply

EMS 8840-0A PE Power Supply

EMS 8837-0A Power Mosfets Module

EMS 9029-00 Chopper/Inverter Control Unit

EMS 9034-00 PID Controller Unit

Textronic Oscilloscope

Connection Leads

BNC-connector cable


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WARNINGS

The voltages and currents that are used during this lab are larger and rated at 240VDCLine-to-Neutralwith current as high as 20 amps (or higher if circuits are improperly connected). Pleasetake the proper precautions and use your head before touching any circuitry. NEVERchange anycircuit connections while the power supply is turned on. Ask the demonstrator to check yourconnections before turning on the switches. And follow the rating of voltmeters and ammetersgiven to prevent equipments from damaged.

Experiment: Part IThe PWM-control chopper MODE (CHOP.PWM)

1. In this part, you will use the circuit shown in Figure 1a to observe the control signals theChopper/Inverter Control Unit generates in the CHOP.PWM.MODE. You will vary thevoltages applied to CONTROL INPUTS 1 and 2 while observing the PWM control signalsto verify the functions of these inputs. Connect the modules as shown in Figure 1a. Notethat the DC SOURCE 1 and 2 are part of the Chopper/Inverter Control Unit.

Figure 1a: Circuit for observing the operation of the Chopper/Inverter Control Unitin the CHOP.PWM.MODE.

2. Set the rocker switch of power supply to the 1 position. Make the following settings on the

Chopper/Inverter Control Unit

DC SOURCE 1 Mid positionDC SOURCE 2 MinimumMODE CHOP. PWM

3. Set the rocker switch of power supply to the 1 position. Use the oscilloscope to observecontrol signals 1, 2, 4, and 5 generated by the Chopper/Inverter Control Unit. Thesesignals are available on SWITCHING CONTROL INPUTS 1, 2, 4, and 5 of the PowerMOSFETS module, respectively. Sketch the waveforms of these signals in Figure 1b. Dothese signals resemble those shown in the discussion for this mode of operation of theChopper/Inverter Control Unit?

4. Connect channels 1 and 2 of the oscilloscope to SWITCHING CONTROL INPUTS 1 and4 of the Power MOSFETS module, respectively. On the Chopper/Inverter Control Unit,slowly turn the DC SOURCE 1 control knob in both directions while observing controlsignals 1 and 4 on the oscilloscope screen. Describe what happens. What is the functionof CONTROL INPUT 1 when the Chopper/Inverter Control Unit operates in theCHOP.PWM.MODE?


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Figure 1b: Waveforms of the control signals generated in the CHOP.PWM.MODE

5. On the Chopper/Inverter Control Unit, set the DC SOURCE 1 control knob to the middleposition. Slowly turn the DC SOURCE 2 control knob in both directions while observingcontrol signals 1 and 4 on the oscilloscope screen. Describe what happens. What is thefunction of CONTROL INPUT 2 when the Chopper/Inverter Control Unit operates in theCHOP.PWM.MODE?

6. Set the main power switch to the 0 position and turn OFF the power supply. Remove allleads, cables and probes.


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Experiment: Part IIThe two-step control chopper MODE (CHOP.PWM) [open loop operation]

1. In this part, you will use the circuit shown in Figure 2a to understand the operation of theChopper/Inverter Control Unit in the CHOP.STEPS.MODE (operation as a two-stepneutral-zone controller). In this circuit, the voltage applied to CONTROL INPUT 1 is thereference signal and the voltage applied to CONTROL INPUT 2 sets the range of theneutral zone. The voltage applied to CONTROL INPUT 3 is the feedback signal. As youcan see the feedback loop is opened in this circuit. You will determine the upper andlower voltage set points from the voltages applied to CONTROL INPUTS 1 and 2. Youwill vary the feedback voltage using DC SOURCE 2 while observing the control signalproduced by the Chopper/Inverter Control Unit. Connect the modules as shown in Figure2a. Note that the DC SOURCE 1 and 2 are part of the Chopper/Inverter Control Unit.

Figure 2a: Circuit for observing the operation of the Chopper/Inverter Control Unitin the CHOP.PWM.MODE (open loop operation).

2. Set the rocker switch of power supply to the 1 position. Make the following settings on theChopper/Inverter Control Unit

DC SOURCE 1 Mid positionDC SOURCE 2 Mid positionMODE CHOP. STEPS

3. On the Chopper/Inverter Control Unit, set the DC SOURCE 1 control knob so that thevoltage applied to CONTROL INPUTS 2 (channel 1 on the oscilloscope) is equal to +4 Vdc. From the dc voltages applied to CONTROL INPUTS 1 and 2 of the Chopper/InverterControl Unit, determine the values of the reference voltage and the voltage range of theneutral zone.

Reference voltage: __________ VNeutral zone range: __________ V

From the reference voltage and the voltage range of the neutral zone. Determine theupper and lower voltage set points of the two-step neutral zone controller.

Upper voltage set point (calculated): __________ VLower voltage set point (calculated): __________ V


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4. Disconnect the oscilloscope probe connected to CONTROL INPUT 2 of theChopper/Inverter Control Unit then connect it to CONTROL INPUT 3 of the same module.The oscilloscope now displays the feedback signal (on channel 1) and the control signalproduced by the two-step neutral zone controller (on channel 2). On the Chopper/InverterControl Unit, slowly vary the setting of the DC SOURCE 2 control knob so that thevoltage at CONTROL INPUT 3 (feedback signal) varies between 0 and +8 V whileobserving the control signal produced by the two-step neutral-zone controller. Describewhat happens.

5. On the Chopper/Inverter Control Unit, vary the setting of the DC SOURCE 2 control knobto slowly vary the voltage at CONTROL INPUT 3. While doing this, observe the controlsignal produced by the two-step neutral-zone controller to determine the feedbackvoltages at which the level of the control signal changes. Note these voltages in thespaces provided below. These voltages correspond to the upper and lower voltage setpoints of the two-step neutral-zone controller.

Upper voltage set point (measured): __________ V

Lower voltage set point (measured): __________ V

Are the calculated and measured voltage set points nearly equal? Briefly explain theoperation of the two-step neutral-zone controller.



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Experiment: Part IIIThe two-step control chopper MODE (CHOP.PWM) [close loop operation]

1. In this part, you will use the circuit shown in Figure 3a to control signal produced by thetwo-step neutral-zone controller (available on SWITCHING CONTROL INPUT 4 of thePower MOSFETS module) is fed back to CONTROL INPUT 3 of the Chopper/InverterControl Unit through LOW PASS FILTER 2 in the P.I.D. Controller. LOW PASS FILTER 2acts as a simple RC circuit which integrates the control signal produced by the two-stepneutral-zone controller. You will determine the upper and lower voltage set points fromthe voltages applied to CONTROL INPUTS 1 and 2. You will vary the voltages atCONTROL INPUTS 1 and 2 while observing the effect on the control signal and thefeedback signal. Connect the modules as shown in Figure 3a. Note that the DC SOURCE1 and 2 are part of the Chopper/Inverter Control Unit.

Figure 3a: Circuit for observing the operation of the Chopper/Inverter Control Unitin the CHOP.PWM.MODE (closed loop operation).

1. In the circuit of Figure 3a, SWITCHING CONTROL INPUT 4 of the Power MOSFETSmodule is used as an output. It delivers control signal 4 coming from the Chopper/InverterControl Unit. Set the rocker switch of power supply to the 1 position. Make the followingsettings on the Chopper/Inverter Control Unit.

DC SOURCE 1 Mid positionDC SOURCE 2 Mid positionMODE CHOP. STEPS

2. On the Chopper/Inverter Control Unit, set the DC SOURCE 1 and DC SOURCE 2 control

knobs so that the voltages applied to CONTROL INPUTS 1 and 2 are equal to +2 V dc.From the dc voltages applied to CONTROL INPUTS 1 and 2 of the Chopper/InverterControl Unit, determine the values of the reference voltage, the voltage range of theneutral zone, the upper and lower voltage set points.

Reference voltage: __________ VNeutral zone range: __________ VUpper voltage set point (calculated): __________ VLower voltage set point (calculated): __________ V


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3. Disconnect the oscilloscope probe connected to CONTROL INPUT 1 and 2 of theChopper/Inverter Control Unit then connect them to the LOW PASS FILTER 2 INPUT ofthe P.I.D. Controller and CONTROL INPUT 3 of the Chopper/Inverter Control Unitrespectively.

On the oscilloscope, set the channel 1 sensitivity to 2 V/DIV. The oscilloscope nowdisplays the control signal produced by the two-step neutral-zone controller (on channel1) and the feedback signal applied to CONTROL INPUT 3 (on channel 2). Sketch thewaveforms of these signals in Figure 3b.

Figure 3b: Waveforms of the signals generated in the CHOP.STEPS MODE(+2 V applied to CONTROL INPUTS 1 and 2).

4. Determine the maximum and minimum voltages the feedback signal reaches. Does thevoltage of the feedback signal remains between the upper and lower voltage set pointscalculated in the previous steps?

Maximum feedback voltage: __________ VMinimum feedback voltage: __________ V

5. On the Chopper/Inverter Control Unit, slowly turn the DC SOURCE 2 control knob in bothdirections to vary the voltage applied to CONTROL INPUT 2 of the Chopper/InverterControl Unit. While doing this, observe the feedback signal on the oscilloscope.

Describe what happens. Briefly describe the function of CONTROL INPUT 2 when theChopper/Inverter Control Unit operates in the CHOP.STEPS MODE

6. On Chopper/Inverter Control Unit, set the DC SOURCE 2 control knob so that thefeedback signal resembles again the feedback signal sketched in Figure 3b.

On the Chopper/Inverter Control Unit, slowly turn the DC SOURCE 1 control knob in bothdirections to vary the voltage applied to CONTROL INPUT 1 of the Chopper/InverterControl Unit. While doing this, observe the control signal produced by the two-step

neutral-zone controller and the feedback signal on the oscilloscope.

Describe what happens. Briefly describe the function of CONTROL INPUT 1 when theChopper/Inverter Control Unit operates in the CHOP.STEPS MODE.



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REVIEW QUESTIONS

1. Briefly describe the operation of the Chopper/Inverter Control Unit in the CHOP. PWMMODE.

2. What are CONTROL INPUTS 1, 2, and 3 of the Chopper/Inverter Control Unit used for inthe CHOP.STEPS MODE?

3. Briefly describe the operation of the Chopper/Inverter Control Unit in the CHOP.STEPSMODE.

4. Determine the reference voltage, the voltage range of the neutral zone and the upper andlower voltage set points when voltages of 6 V and + 2 V are applied to CONTROLINPUTS 1 and 2, respectively of a Chopper/Inverter Control Unit operating in theCHOP.STEPS MODE.

5. What are the duty cycle and frequency ranges of the control signals generated in theCHOP.PWM MODE of the Chopper/Inverter Control Unit?

Exp 7 Familiarization with the ChopperInverter Control Unit.pdf

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