Exp 12 Single Phase Inverter Part II

8/13/2019 Exp 12 Single Phase Inverter Part II

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Universiti Sains MalaysiaElectrical Engineering DepartmentAdvanced Power Electronic Laboratory EEK471

The MOSFET Single Phase Inverter Part II

OBJECTIVE

To learn the operation of a 180 modulation single-phase inverter.

INTRODUCTION

The PWM and 180 modulation single-phase inverters

Inverters are devices which convert dc power into ac power. This allows single phase, two-phaseand three-phase ac power networks with variable frequency and voltage to be obtained. Such acpower networks are widely used to build various ac motor drives.

Figure 1 shows a simplified diagram of a single-phase inverter. It consists of two semiconductorswitches (MOSFET Q1and Q4), two free-wheeling diodes (diodes D1and D4), and a SWITCHINGCONTROL SIGNAL GENERATOR. In this configuration, the single-phase inverter requires adual-polarity dc power supply (dc power supply E1, and capacitors C1and C2).

In the single-phase inverter, the duty cycles of the switching control signals are complementary toensure that when one MOSFET is on, the other MOSFET is off, and vice versa. A positive voltageis applied to the load when MOSFET Q1is on, whereas a negative voltage is applied to the loadwhen MOSFET Q4is on.

Figure 1: A single-phase inverter built with two MOSFETS and two free-wheeling diodes.


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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 8412-05 Lab-Volt DC Voltmeter/Ammeter EMS 8311 Variable Resistance

EMS 8325 Smoothing Inductor

EMS 9056-15 and EMS 9056-05 Voltage/Current Isolator

24V AC Power Switch

Textronic Oscilloscope

Connection Leads

Function Generator & BNC-connector cable

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). Please

take 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 IOperation of a PWM single-phase inverter built with two MOSFETs

1. In this part, you will set up the circuits shown in Figures 1a to observe the operation of aPWM single-phase inverter. You will vary the frequency and amplitude of the sine-wavesignal to observe the effects these have on the switching control signals as well as thewaveforms of the voltage and current at the output of the PWM single-phase inverter.You will compare the waveforms of the voltage and current at the output of the PWM

single-phase inverter to those obtained with the four-quadrant chopper. Set S1of powerMosfets to 0 (OFF) position. Connect the module as shown Figure 1a.

Figure 1a: A PWM single-phase inverter built with two MOSFETS.


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Figure 1b: L1= 6.4H

Table 1a: Parameters setting

C1(uF) C2(uF) e1(V) i1(A) E1(V) L1(H) R1()

13.9 13.9 600 0.5 300 6.4 4800

2. Using a BNC-connector cable, connect the SYNC. OUTPUT of the Function generator tothe external triggering input of the oscilloscope.

3. Make the following settings on the Function generator

FUNCTION Sine WaveRange1 HzFrequencyMid positionAmplitude Mid position

4. Make sure that the main power switch of the Power Supply is set to the 0 (OFF) position.Set the voltage control knob to 0.

5. Set the 24V ac power switch to the 1 (ON) position. The POWER ON LED on the PowerMOSFETS module should light up to indicate that the module is correctly powered.

6. Set the main power switch to 1 (ON) and slowly set the voltage control knob to 30%position. Measure and note the voltage across capacitor C1 (VC1) on the DC

Voltmeter/Ammeter.

VC1= ____________ V dc

7. Set the main power switch back to the O (OFF) position.

8. Disconnect only the lead going to the +ve terminal of the DC voltmeter from capacitor C1.Do not change the -ve terminal of the DC voltmeter. Then connect it so that the DCvoltmeter is connected across capacitor C2. Set the main power switch to the 1 (ON)position. Measure and note the voltage across capacitor C2, (VC2) on the DCVoltmeter/Ammeter.

VC2= ____________ V dc

Is the PWM single-phase inverter powered by a dual-polarity dc power supply? Explain.

9. The oscilloscope displays the waveforms of the current and voltage at the PWM single-phase inverter output. Note that the waveform of the current and voltage at PWM single-phase inverter output probably shifts towards left or right on the oscilloscope screen.Slightly readjust the Frequency control of the Function Generator so that thesewaveforms nearly cease to shift. Sketch the waveforms displayed on the oscilloscopescreen in Figure 1c. Compare these waveforms to those obtained using the four-quadrantChopper (See Figure 2c Lab 11).


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Figure 1c: Waveforms of the current and voltage at the PWM single-phase inverter output.

10. On the Function Generator, slowly vary the settings, first of the Frequency control andsecond the Amplitude control while observing the waveforms of the current and voltageon the oscilloscope screen. Describe what happens to the current and voltage at theoutput of the PWM single-phase inverter when these settings are varied. Briefly explain.

11. On the Power Supply, set the voltage control knob to the 0 position then set the mainpower switch and the 24 V ac power switch to the 0 position.

Experiment: Part IIOperation of a 180 PWM single-phase inverter built with two MOSFETs

1. In this exercise, you will set up the circuit shown in Figure 2a to observe the operation ofa 180 modulation single-phase inverter. You will vary the frequency of the switchingcontrol signals to observe the effect this has on the waveforms of the voltage and currentat the output of the 180 modulation single phase inverter. You will compare thewaveforms of the voltage and current at the output of the 180 modulation single-phaseinverter to those obtained with the PWM single-phase inverter.

2. Modify the connection so that the modules are connected as shown in Figure 2a. In this

figure, the Function Generator is replaced by DC SOURCE1, DC SOURCE 2 is removedand the connections on the oscilloscope are modified.

Figure 2a: A 180 modulation PWM single-phase inverter built with two MOSFETS.


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Table 2a: Parameters setting

C1(uF) C2(uF) e1(V) i1(A) E1(V) L1(H) R1()

13.9 13.9 600 0.5 300 6.4 4800

3. Make the following settings on the Chopper/Inverter Control Unit

DC SOURCE 1MaximumMODE 3 ~ 180

4. Set the 24V ac power switch to the 1 (ON) position. The POWER ON LED on the PowerMOSFETS module should light up to indicate that the module is correctly powered.

5. On the Power Supply, set the main power switch to the 1 (ON) position, then slowly setthe voltage control knob of the Power Supply to the 30%.

6. The oscilloscope now displays the waveforms of the switching control signals applied toMOSFETs Q1 and Q4 of the 180 modulation single phase inverter. Sketch thewaveforms of these signals in Figure 2b.

Figure 2b: Waveforms of the switching control signals in the 180 modulation

single-phase inverter.

Using the waveform sketched in Figure 2b, describe the switching sequence of theMOSFETs.

7. On the Chopper/Inverter Control Unit, slowly turn the DC SOURCE 1 control knob backand forth between the MAX position and the middle position while observing the signalson the oscilloscope screen, then set the control knob back to the MAX position. Describewhat happens to the switching control signals applied to the MOSFETs when the settingof the DC SOURCE 1 control knob is varied.

8. On the Power MOSFETs module, disconnect the leads connected to SWITCHINGCONTROL INPUTS 1 and 4, then connect them to the OUTPUTS of the Current Isolator

and Voltage Isolator, respectively. The oscilloscope now displays the waveforms of thecurrent and voltage at the output of the 180 modulation single-phase inverter. Sketchthese signals in Figure 2c


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Exp 12 Single Phase Inverter Part II

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