University of Saskatchewan Department of Electrical and Computer Engineering EE 343.3 Power Electronics Lab Exercise 4 Instructor: N. Chowdhury Lab instructors: Jason Pannel and Indra Karmacharya ===================================================================== Title: Buck and boost choppers Objective: The purpose of this lab is to study the voltage, current relationship and input/output voltage waveforms of buck and boost choppers. The student will examine how the output voltage and current wave shapes are affected by the duty cycle of the thyristor. High voltages are present in this laboratory exercise. Do not make or modify any banana jack connections with the power on unless otherwise specified. Ask your instructor to verify your circuit before turning the power supply on. Buck (Type A) Chopper 1. Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply. Connect the Low Power Input of the IGBT Chopper/Inverter to the Power Input of the Data Acquisition and Control Interface. Turn the 24 V ac power supply on. 2. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer. Connect the USB port of the Four-Quadrant Dynamometer/Power Supply to a USB port of the host computer. 3. Make sure that the main power switch of the Four-Quadrant Dynamometer/ Power Supply is set to O (off), then connect the Power Input to an ac power outlet. Set the Operating Mode switch of the Four-Quadrant Dynamometer/Power Supply to Power Supply. This connects the internal power supply of the module to the Power Supply terminals on the front panel. Turn the Four-Quadrant Dynamometer/Power Supply on by setting the main power switch to I (on). 4. Connect the Digital Outputs of the Data Acquisition and Control Interface (DACI) to the Switching Control Inputs of the IGBT Chopper/Inverter using a DB9 connector cable.
Connect Switching Control Input 1 of the IGBT Chopper/Inverter to Analog Input 1 of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the common (white) terminal of the Switching Control Inputs on the IGBT Chopper/Inverter to one of the two analog common (white) terminals on the Data Acquisition and Control Interface using a miniature banana plug lead. 5. Turn the host computer on, then start the LVDAC-EMS software. In the LVDAC-EMS Start-Up window, make sure that the Data Acquisition and Control Interface and the Four-Quadrant Dynamometer/Power Supply are detected. Make sure that the Computer-Based Instrumentation and Chopper/Inverter Control functions for the Data Acquisition and Control Interface are available, as well as the Standard Functions (C.B. control) for the Four-Quadrant Dynamometer/Power Supply. Select the network voltage and frequency that correspond to the voltage and frequency of your local ac power network, then click the OK button to close the LVDAC-EMS Start- Up window. 6. Set up the circuit shown in Figure 1. Notice the presence of capacitor CBUS and diode D4 in the Chopper/Inverter. Capacitor CBUS is used to filter the dc voltage at the buck chopper input. 7. Connect R (57 W) in series with L (57 W) to form the load. 8. In LVDAC-EMS, open the Four-Quadrant Dynamometer/Power Supply window and make the following settings: Voltage Source () function. to 50 V.
Chopper Q 1 I2 DC 50 V E1 C BUS D 4 R L E2 Switching control signals from digital outputs on DACI Figure 1: Buck chopper 9. In LVDAC-EMS, open the Chopper/Inverter Control window and make the following settings: - Make sure that the Function parameter is set to Buck Chopper (highside switching). This setting allows the Data Acquisition and Control Interface to generate the switching control signal required by a buck chopper implemented with an electronic switch located on the high voltage side of the power supply. - Set the Switching Frequency parameter to 1000 Hz. This sets the frequency of the switching control signal to 1000 Hz. - Set the Duty Cycle Control parameter to Knob. - Set the Duty Cycle parameter to 50%. This sets the duty cycle of the switching control signal to 50 %. - Set the Acceleration Time parameter to 0 s. - Set the Deceleration Time parameter to 0 s. - Make sure that the Q 1 parameter is set to PWM. - Notice that the Status parameter is set to Stopped. This indicates that the buck chopper is disabled. 10. In the Chopper/Inverter Control window, start the buck chopper by clicking on the Start/Stop button (or by setting the Status parameter to Started). 11. In LVDAC-EMS, open the Oscilloscope window and display the following parameters: voltage (input E1) at the buck chopper input, switching control signal (AI-
1), average output voltage measured across series RL ( E2), and the output current flowing through the load (I2). Select the Continuous Refresh mode, then set the time base to display at least two complete cycles, and set the trigger controls so that the Oscilloscope triggers when the rising edge of the switching control signal (AI-1) reaches 2 V. Select convenient vertical scale and position settings in the Oscilloscope to facilitate observation. 12. Measure average output voltage, EO for duty cycles 0%, 20%, 40%, 60%, 80% and 100%. Compare the observed values with calculated values. 13. In the Chopper/Inverter Control window, set the duty cycle to 50%. This sets the average output voltage EO of the buck chopper to about 25 V. Measure the average output voltage, EO for switching frequencies 200 Hz, 500 Hz, 1000 Hz, 2000 Hz and 5000 Hz. Boost chopper 1. Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply. Connect the Low Power Input of the IGBT Chopper/Inverter to the Power Input of the Data Acquisition and Control Interface. Turn the 24 V ac power supply on. 2. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer. Connect the USB port of the Four-Quadrant Dynamometer/Power Supply to a USB port of the host computer. 3. Make sure that the main power switch of the Four-Quadrant Dynamometer/ Power Supply is set to O (off), then connect the Power Input to an ac power outlet. Set the Operating Mode switch of the Four-Quadrant Dynamometer/Power Supply to Power Supply. This connects the internal power supply of the module to the Power Supply terminals on the front panel. Turn the Four-Quadrant Dynamometer/Power Supply on by setting the main power switch to I (on). 4. Connect the Digital Outputs of the Data Acquisition and Control Interface (DACI) to the Switching Control Inputs of the IGBT Chopper/Inverter using a DB9 connector cable. Connect Switching Control Input 4 of the IGBT Chopper/Inverter to Analog Input 1 of the Data Acquisition and Control Interface using a miniature banana plug lead.
Connect the common (white) terminal of the Switching Control Inputs on the IGBT Chopper/Inverter to one of the two analog common (white) terminals on the Data Acquisition and Control Interface using a miniature banana plug lead. 5. Turn the host computer on, then start the LVDAC-EMS software. In the LVDAC-EMS Start-Up window, make sure that the Data Acquisition and Control Interface and the Four-Quadrant Dynamometer/Power Supply are detected. Make sure that the Computer-Based Instrumentation and Chopper/Inverter Control functions for the Data Acquisition and Control Interface are available, as well as the Standard Functions (C.B. control) for the Four-Quadrant Dynamometer/Power Supply. Select the network voltage and frequency that correspond to the voltage and frequency of your local ac power network, then click the OK button to close the LVDAC-EMS Start- Up window. 6. Set up the circuit shown in Figure 2. Use the 50 mh inductor in the filtering Inductors/Capacitors module to implement L1. Chopper I1 L 1 50 mh D 1 I2 EI DC 20 V E1 E3 300 W R 1 E2 Q C BUS 4 Switching control signals from digital outputs on DACI Figure 2: Boost chopper 7. Make the necessary connections and switch settings on the Resistive Load in order to obtain the resistance value required. 8. In LVDAC-EMS, open the Four-Quadrant Dynamometer/Power Supply window and make the following settings: Select the Voltage Source () function. Set the voltage to 20 V.
Start the voltage source. 9. In LVDAC-EMS, open the Chopper/Inverter Control window and make the following settings: Select the Boost Chopper function. Set the switching frequency to 400 Hz. Set the Duty Cycle Control to Knob. Set the duty cycle to 20%. Make sure that the acceleration time is set to 0.0 s. Make sure that the deceleration time is set to 0.0 s. Make sure that the Q4 parameter is set to PWM. Start the boost chopper 10. For each duty cycle of 20%, 40%, 60% and 80%, calculate the theoretical dc output voltage EO when the dc voltage EI at the boost chopper input is 20 V. 11. In LVDAC-EMS, open the Oscilloscope window and display the voltage and current (inputs E1 and I1) at the boost chopper input, the switching control signal (AI-1), the dc voltage across electronic switch Q (input E3), the dc output voltage (input E2), and the dc output current (input I2). Select the Continuous Refresh mode, set the time base to display at least two complete cycles, and set the trigger controls so that the Oscilloscope triggers when the rising edge of the switching control signal (AI-1) reaches 2 V. Select convenient vertical scale and position settings in the Oscilloscope to facilitate observation of the waveforms. 12. Successively set the duty cycle to 20%, 40%, 60% and 80%. For each value, measure the dc voltage EI (input E1) at the boost chopper input, the dc voltage across electronic switch Q (input E3), and the dc output voltage EO (input E2) across the resistive load R1. Record your results. 13. In the Chopper/Inverter Control window, set the duty cycle to 50%. Make sure that the source voltage is still set to 20 V in the Four-Quadrant Dynamometer/Power Supply. In the Chopper/Inverter Control window, successively set the switching frequency to each of the values of 500, 1000, 1500, 2000 and 5000 Hz. For each value, measure the dc voltage at the output of the boost chopper using the Oscilloscope and record your results.
14. In the Chopper/Inverter Control window, set the switching frequency to 500 Hz and the duty cycle to 80%. In Four-Quadrant Dynamometer/Power Supply window, make sure that the source voltage is still equal to 20 V. In the Oscilloscope window, display the value of power P1 and power P2. Power P1 is the power in watts determined from the voltage and current measured using inputs E1 and I1, and power P2 is the power in watts determined from the voltage and current measured using inputs E2 and I2. Since inputs E1 and I1 measure the input voltage and current of the boost chopper, power P1 corresponds to the input power. Similarly, since inputs E2 and I2 measure the output voltage and current of the boost chopper, power P2 corresponds to the output power of the boost chopper. Record the input power PI and the output power PO. Determine the power efficiency of the boost chopper using your measured powers. THE END