Power Electronics Laboratory User Manual
Contents
1. 1 3 8 PWM Signal Generation PWM signals required for the MOSFETs can be generated using the on board PWM controller UC3824 1 5 in Fig 1 2 There is also an option to supply PWM signals from an external source To use the onboard PWM Put switch 2 of the selector switch bank S30 E 5 in Fig 1 2 to its bottom position PWM INT To use external PWM e Put switch 2 of the selector switch bank S30 to its top position PWM Connect the external PWM signal to the terminal J68 G 6 in Fig 1 2 While using the onboard PWM for operation of the power pole open loop the duty ratio can be controlled using pot RV64 F 5 in Fig 1 2 The duty ratio can be varied from 4 to 98 The frequency of the PWM can be adjusted using the trim pot RV60 I 5 Fig 1 2 There is a provision for providing an external ramp to the UC3824 IC This is useful for peak current mode control For this remove jumper J61 H 5 in Fig 1 2 and use the RAMP pin on daughter board connector J60 14 1 3 9 Frequency Analysis Frequency analysis of any converter built using the power pole can be done by injecting a low voltage sinusoidal signal at jumper J64 G 5 in Fig 1 2 To do this Remove jumper J64 Connect the small signal sinusoidal source at the jumper terminal J64 Note J64 1s to be shorted in all other modes of operation 1 3 10 Power pole Board Feedback Control Mode The power pole board can be operated ei2. LOADOFH FOTENTIOMETER Figure 1 1 Block diagram of Power pole Board 1 r T Figure 1 2 Power Pole board 1 m tut ui quu LL M Table 1 1 Location of components Power Pole board Fig 1 2 6 Signal O O o 8 Signal supply 12Vfuse 9 SmmimplyLED DBS 10 Fault ed OvrwlaelED SD D OvwrammLED foa foe 10 Table 1 2 Test Point Details and Location Power pole Board No Test Point Description of Test Point Location in arem 1 2 V Terminal VI 217 44 Ss fest 14 CS2 Upper MOSFET source current D2 56 7 Lower diode or MOSFET source current D 4 7 CSS _ Outputcurrent 00 ac IH 9 CSLOAD2 Switched Load Voltage ve 15 10 ________ To observe the voltage across the lower MOSFET Connect an oscilloscope probe to the DRAIN and its ground to the SOURCE E 4 in Fig 1 2 of the lower MOSFET To observe the lower MOSFET source current Connect an oscilloscope probe to terminal CS3 and its ground to the SOURCE E 4 in Fig 1 2 of the lower MOSFET The current sense resistor value 15 0 05 Q The same test points also measure the lower diode current if that is included the circuit To observe the voltage across the upper diode Connect the positive and negative termin
3. 4 Powering the Circuit Switch ON the signal supply Check for green LED e Adjust the duty ratio to 50 Set the switching frequency of 100kHz Set RL 120 Apply input voltage Vd of 24 volts 20 DAIVE CIRCUIT INDUCTOR BOARD SWITCHED LOAD MAGNETICS BOARD 10 Hz 10 DUTY DRIVE SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER CONTROL SELECTION PWMTOTOP USEEXTERNAL sWircHED UNUSED MOSFET PWM SIGNAL LOAD ACTIVE HM m m DIN ON EXTERNAL INPUT AN OFF USEONBOARD SWITCHED DUTY CYCLE MOSFET PWM SIGNAL LOADOFF POTENTIOMETER Figure 3 1 Schematic of Buck Converter 21 3 5 Measurement and Waveforms 1 Observe and make a copy of the Anode Cathode diode voltage using a differential probe and the diode current using CS3 Adjust the time base to show the switching details during turn ON and turn OFF 2 Measure the forward voltage drop across the diode 3 Observe and make a copy of the Drain Source Mosfet voltage VDS using a differential probe and Mosfet current CS1 Adjust the time base to show the switching details during turn ON and turn OFF 4 Measure the voltage drop across the Mosfet during turn ON period and estimate the Of the Mosfet Note the differential probe might have an offset adjust your measurement based on this offset value 5 Measure the average load current Io and the duty cycle
4. copy of the output voltage V 2 6 8 Lab Report The lab report should have a brief abstract detailing what has been done in the experiment The remaining part of the report should consist of the information asked below along with any discussion you feel 1s necessary Attach the Bode magnitude and phase plot of the small signal transfer function 2 S from the results obtained 1n section 6 4 Obtain the following quantities from the Bode plot 5 and ZG s for a f crossover frequency of KHz Calculate the needed phase boost using the values obtained through PSpice above with a required phase margin of 60 degrees Calculate the controller gain at the crossover frequency given k 0 2 and Gowu S 0 556 Use the K factor method described chapter 4 of the book to design a type 3 voltage mode controller for the buck converter 1 e determine kc w and of the controller G s Determine the values of the resistors and capacitors used to implement the controller Fig 6 3 and substitute them in Table 6 1 34 7 The controller is implemented hardware using the values given in Table 6 1 column 3 Compare the responses of the output voltage for a step load change with and without closed loop control Attach the waveforms obtained steps 6 3 and 6 7 35 Experiment 7 Peak Current Mode Control 7 1 Objective In this experiment we will be using a plug in board to accomplish pe
5. hundred milliamps In order to minimize the potential hazards we will use dc power supplies that never exceed voltages above 40 50 and will have maximum current ratings of 5A or less However in spite of this precaution power electronics circuits on which the student will work may involve substantially larger voltages up to hundreds of volts due to the presence of large inductances in the circuits and the rapid switching on and off of amperes of current in the inductances For example a boost converter can have an output voltage that can theoretically go to infinite values if it is operating without load Moreover the currents in portions of some converter circuits may be many times larger than the currents supplied by the dc supplies powering the converter circuits A simple buck converter is an example of a power electronics circuit in which the output current may be much larger than the input dc supply current 2 Potential problems presented by Power Electronic circuits Electrical shock may take a life Exploding components especially electrolytic capacitors and arcing circuits can cause blindness and severe burns Burning components and arcing can lead to fire 3 Safety precautions to minimize these hazards 3 1 General Precautions Be calm and relaxed while working m Lab When working with voltages over 40V or with currents over 10A there must be at least two people in the lab at all times Keep the work area
6. load resistance and observe the inductor current waveform Keep increasing the load resistance until the buck converter enters discontinuous current mode operation Note down the average inductor current value and make a copy of the inductor current waveform when the converter starts entering discontinuous current mode of operation 18 2 5 4 Determining Efficiency Determine the efficiency of the buck converter at frequencies of 40 kHz and 100 kHz Set duty ratio at 50 Set load resistance RL 10Q Measure the average output voltage V2 Measure the average output current 10 Measure the average input voltage Vd Measure the average input current Calculate the efficiency of the buck converter for the above two frequencies 2 6 Lab Report The lab report should have a brief abstract detailing what has been done in the experiment The remaining part of the report should consist of the information asked below along with any discussion you feel is necessary l Attach a graph output voltage V2 versus duty ratio using data obtained in section 2 5 1 Also plot the theoretically calculated results on the same graph Compare the two plots and comment about how the buck converter works as a variable dc step down transformer Enclose output voltage amp voltage across diode waveforms for duty ratio 50 Attach a copy of the inductor current CS5 and the capacitor current CS4 waveforms obtained in section 2 5 2 Explain the
7. neat and clean No paper lying on table or nearby circuits Always wear safety glasses when working with other than signal level power Use rubber door mats to Insulate yourself from ground when working in the Lab Be sure about the locations of fire extinguishers and first aid kits in lab A switch should be Included each supply circuit so that when opened these switches will de energize the entire setup Place these switches so that you can reach them quickly in case of emergency and without reaching across hot or high voltage components 3 2 Precautions to be taken when preparing a circuit Use only Isolated power sources etther Isolated power supplies or AC power through isolation power transformers This helps in using a grounded oscilloscope This reduces the possibility of risk of completing a circuit through your body This also reduces the possibility of destroying the test equipment 3 3 Precautions to be taken before powering the circuit Check for all the connections of the circuit and scope connections before powering the circuit to avoid shorting or any ground looping that may lead to electrical shocks or damage of equipment Check any connections for shorting two different voltage levels Check 1f you have connected load at the output This is very important in Boost and Buck Boost Converters and converters based on them Double check your wiring and circuit connections It 15 a
8. oM 9 09 00 Figure 7 5 Slope Compensation Jumper 7 3 2 Closed Loop Operation With Slope Compensation Ensure that the plug in board and the slope compensation jumper are plugged in Set the duty cycle pot to minimum Switch ON the main power supply and set it to 15 V Switch ON the signal power supply Observe the PWM and the inductor current waveforms Slowly increase the reference voltage by turning the duty cycle pot clockwise Observe the point where the inductor current starts displaying oscillatory behavior Record the corresponding duty cycle from the scope 7 3 3 Dynamic Performance of Closed Loop System Ensure that the plug in board and the slope compensation jumper are plugged in Set the duty cycle pot to minimum Switch on the main power supply and set it to 20 V Switch on the signal power supply Slowly increase the reference voltage to 12 V by turning the duty cycle pot clockwise Observe the output voltage V2 and the inductor current on the oscilloscope Store the waveform 39 7 4 Lab Report The lab report should have brief abstract detailing what has been done in the experiment The remaining part of the report should consist of the information asked below along with any discussion you feel 1s necessary Plot the output voltage Voand inductor current 1L obtained in step 7 2 What 15 the maximum duty ratio stable operation of the converter in step 7 3 1 Plot the inductor current waveform for
9. oy INPUT z PWMTOBOT USEONBOARD SWITCHED DUTY CYCLE hh 2i MOSFET PWMSIGNAL LOADOFF POTENTIOMETER Figure 4 1 Schematic of Boost Converter 24 4 5 Measurements Take the following measurements 4 5 1 Varying Duty Ratio e Vary the duty ratio from 10 to 60 in steps of 10 Measure the average DC load voltage V1 for the corresponding values of duty ratio e Calculate the theoretical average output voltage for the corresponding duty ratios Compare the observed average output voltage results with the calculated ones 4 5 2 Varying Switching Frequency Set the duty ratio to 50 switching frequency to 100kHz 200 e Observe and make copy of the input current CS5 ripple waveform 100kHz Measure the peak peak input current ripple Repeat the above procedure for different switching frequencies 40 kHz 60 kHz 80 kHz 4 5 3 Determining efficiency Set the duty ratio to 50 e Adjust the load resistance value to 200 Measure the efficiency at switching frequencies of 40kHz and 100 kHz 4 6 Lab Report The lab report should consist of the information asked below along with any discussion you feel is necessary 1 Attach a graph of duty ratio versus output voltage using the data obtained in section 4 5 1 Also plot the theoretically calculated results on the same graph Compare the two plots 2 Attach a copy of the inductor current CS5 waveform obtained in section 4 5 2 Plot the expe
10. relation between the two currents Comment on the ripple in the inductor current for the two frequencies Plot the peak peak ripple in the output voltage versus switching frequency using data obtained in section 2 5 2 Plot the theoretical results on the same graph Compare the two plots Comment on why you were asked to maintain the average output voltage constant Attach a copy of the inductor current waveforms obtained in section 2 5 3 Compare the theoretically calculated Rerit with the observed value Comment on the difference in efficiency results obtained for two switching frequencies 19 Experiment 3 Switching Characteristic of MOSFET and Diode using Power Pole Board 3 1 Objective The objective of this experiment is to study the switching characteristics of power MOSFETs and power diodes using a buck converter The circuit will be operated in open loop conditions no feedback Our main goal is to understand the switching behavior of these two power devices 3 2 Preparing the Setup Construct the buck converter circuit as shown in Fig 3 1 to use the upper MOSFET and lower diode Use the BB magnetics board The inductor is 100 uH e Use a variable load resistor as a load Connect 12V the signal supply to the DIN connector Signal supply switch S90 should be OFF 3 3 Checks Before Powering The Circuit Check the circuit connections as per the schematic have your circuit checked by your Lab Instructor 3
11. ripple in the flux A4 given the number of turns in the primary is 42 C Given the core area 93 9 what is the value of the peak flux density B 44 Experiment 9 Forward Converter 9 1 Objective The objective of this experiment is to study the characteristics of the forward converter The forward converter will be operated in open loop mode no feedback Our main goal is to compare the theoretical results with the experimental results 9 2 Preparing the Setup Make the connections on the power pole board as shown in Fig 9 1 to use the lower MOSFET Use the Forward magnetics board The turns ratio 1s 1 1 1 e Use a variable load resistor as a load e Connect the 12Vsignal supply to the DIN connector Signal supply switch S90 should be OFF 9 3 Checks before powering the circuit e Check the circuit connections as per Fig 9 1 Confirm that you have selected the lower MOSFET Have your circuit checked by your Lab Instructor 9 4 Powering the Circuit Switch ON the signal supply Check for green LED Set the switching to 100 kHz Set the duty ratio to its minimum Set RL 100 Apply input voltage Vd of 20 V at the terminals V1 and COM 45 DRIVE CIRCUIT Variable Power Resistor Wd SWITCHED LOAD COM MAGNETICS BOARD SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER CONTROL SELECTION PWMTOTOP USEEXTERNAL SWITCHED UNUSED MOSFET PWM SIGNAL LOAD ACTIVE 4
12. stable and unstable operation What 1s the maximum duty ratio stable operation of the converter in step 7 3 2 Plot the inductor current waveform for stable and unstable operation Explain how slope compensation affects the range of duty cycle obtainable in constant frequency peak current mode control Explain why in step 7 3 1 it is important to switch on the signal power supply after turning on the main power supply Plot the output voltage Vo waveforms and inductor current in closed loop operations with output voltage feedback step 7 3 3 Comment on the effect of peak current controller on the operation of converter 40 Experiment 8 Flyback Converter 8 1 Objective The objective of this experiment 1s to study the characteristics of the flyback converter using the power pole board open loop control mode Our main goal is to compare the theoretical results with the experimental results Note It is important that care must be taken while doing the Flyback converter experiment that the load is always connected to the output in the power pole board 8 2 Preparing the Setup Make the connections on the power pole board as shown in Fig 8 1 to use the lower MOSFET e Use the Flyback magnetics board The turns ratio N N2 2 e Use a variable load resistor as a load e Connect the 12Vsignal supply to the DIN connector Signal supply switch S90 should be OFF 8 3 Checks before Powering the Circuit Check the circuit con
13. the same waveform and compare Ignore the voltage ringing due to the leakage inductance of the transformer Attach the waveforms of input current and output current obtained in section 9 5 2 Also answer the following questions 47 Why 15 the input current negative for some interval b What is the minimum value of this negative current for all four operating conditions c Theoretically should the above value change with load Give reasons for your answer 4 Estimate the following Need to be calculated for all the four operating conditions RL 100 Fs 100 kHz RL 7 50 Fs 100 kHz RL 100 Fs 40 kHz and RL 7 50 Fs 40 kHz Output inductor value L b Core flux as given in Fig 8 6 in the book Number of turns in the primary is 16 and the magnetizing inductance Lj 15 0 2mH Hint Use the minimum value of the negative current seen at the input 48 APPENDIX The detailed circuit of the power pole is attached It consists of two sheets 49 02 THB eu on B LIE g ui Fla n 3 T Aa Waman 5 SH _ Len m E RAFF da 22 E H 8 7 gi aii TU Rif 1 Hi NURS DE E L3 E A S CUR 1H5B1H Power Pola Board Sm D merece _ Ere T H 0 F H ___ __ 1 DNS Luo TZ TuS To ds gt 1 i LUE ER
14. 112V EXTERNAL PWM INPUT 12V PWMTOBOT USEONBOARD SWITCHED DUTY CYCLE POTENTIOMETER MOSFET PWM SIGNAL LOAD OFF OFF Figure 9 1 Schematic of Forward Converter 46 9 5 Measurements Take following measurements 9 5 1 Varying Duty Ratio Vary duty ratio from minimum to 40 in steps of 10 Measure the average output voltage V2 for the corresponding values of duty ratio Calculate the theoretical average output voltage for the corresponding duty ratios Compare the observed average output voltage results with the calculated ones 9 5 2 Constant Duty Ratio with varying switching frequency and load Set the duty ratio to 40 switching frequency to 100 kHz and RL 10Q Observe and make a copy of the voltage across the switch Mosfet Observe and make a copy of the input current CS1 and output current CS5 in the same graph Repeat the above step make a copy of the current waveforms and not the voltage waveform for RL 7 50 Fs 100 kHz RL 100 Fs 40 kHz and RL 7 50 Fs 40 kHz 9 6 Lab Report The lab report should consist of the information asked below along with any discussion you feel is necessary 1 Attach a graph of duty ratio versus output voltage V2 using data obtained section 9 5 1 Also plot the theoretically estimated results on the same graph Compare the two plots Attach a copy of the voltage waveform across the switch obtained in section 9 5 2 Estimate theoretically
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16. EM DAVE CIRCUIT Cm i 27 Variable Power Resistor SWITCHED LOAD MAGNETICS BOARD SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER DIN ON PWMTOTOP USEEXTERNAL SWITCHED UNUSED E MOSFET PWM SIGNAL LOAD EMITE m EXTERNAL PWM INPUT PWMTOBOT USEONBOARD SWITCHED DUTY CYCLE MOSFET PWM SIGNAL LOAD OFF Figure 2 1 Schematic of Buck Converter 17 2 5 Measurement and Waveforms Take the following measurements 2 5 1 Varying Duty Ratio Set the duty ratio at 50 switching frequency at 100 kHz and RL 10Q Observe and make a copy of the output voltage and voltage across the diode Vary the duty ratio from 10 to 90 in steps of 10 Measure the average output voltage for the corresponding duty ratio Calculate the theoretical average output voltage for the corresponding duty ratios 2 5 2 Varying Switching Frequency Set the duty ratio to 50 Measure the peak peak output ripple voltage and the peak peak ripple in inductor current Repeat the above procedure for different switching frequencies 40 kHz 60 kHz 80 kHz Make sure that output voltage V2 is maintained at 12V Observe and make a copy of the inductor current CS5 and capacitor current CS4 waveforms at 40kHz and at 100kHz 2 5 3 Varying Load Set the switching frequency at 100kHz and duty ratio at 50 Set the load resistance RL 10Q Increase the
17. HING FREQUENCY ADJUSTMENT POTENTIOMETER puri CONTROL SELECTION PWMTOTOP USEEXTERNAL SWITCHED UNUSED LOAD ACTIVE EXTERNAL PWM INPUT MOSFET PWM SIGNAL DUTY CYCLE USEONBOARD SWITCHED MOSFET PWM SIGNAL LOAD OFF Figure 6 1 Buck Converter using Power pole board 31 1 Obtain the Bode plots for the transfer function as shown in Fig 4 10 of S textbook for the values given in this simulation 2 Obtain the gain and the phase of the transfer function part at frequency of 5 kHz which will be chosen as the crossover of the open loop transfer function G s Ideal trans CCM2 L1 a CPI COPE VO PARAMETERS IL Vin 3 Vin 30V D V VofVin ID gt RLoad PARAMETERS ___ V1 L 100uH vin di m C 697uF Rc 0 1 0hms 1 PARAMETERS duty cycle R 6 667ohms buck_conv_avg sch PWM TO USE EXTERNAL SWITCHED UNUSED MOSFET PWM SIGNAL LOAD ACTIVE PWM USE ONBOARD SWITCHED MOSFET PWM SIGNAL LOAD OFF Figure 6 2 Selector switch position for switched load 6 5 Type 3 Voltage Controller 32 Once you get the transfer function or the Bode plot of the buck converter you can design a Type 3 voltage controller The Type 3 voltage control board has the schematic as shown in Fig 6 3 The values of the resist
18. NUSED MOSFET PWM SIGNAL LOAD ACTIVE m PWMTOBOT USEONBOARD SWITCHED MOSFET PWM SIGNAL LOAD OFF DUTY CYCLE POTENTIOMETER 2 Variable Power Resistor SWITCHED LOAD 10 Hz 10 DUTY DRIVE SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER PWM IC CONTROL SELECTION EXTERNAL PWM INPUT Figure 7 1 Peak Current mode controller schematic 37 PWM TO USE EXTERNAL SWITCHED UNUSED MOSFET PWM SIGNAL LOAD ACTIVE PWM USE ONBOARD SWITCHED MOSFET PWM SIGNAL LOAD OFF Figure 7 2 Switch positions for switched load EXTERNAL OPEN CONTROL O LOOP Figure 7 3 Switch Position for Closed Loop Operation 150pF 482k 820pF IN 9 10 0k 13 QUT VREF 6 11 o W 2 0k Figure 7 4 Type 2 Controller Change the switch positions of the switch bank as shown in Fig 7 1 Switch ON the signal power supply Ensure that main power supply is ON before signal power supply is switched ON Observe the PWM and the inductor current waveforms Slowly increase the reference voltage by turning the duty cycle pot clockwise Observe the point where the inductor current starts displaying oscillatory behavior Record the corresponding duty cycle from the scope 38 Plug in the slope compensation jumper on to 761 slope compensation jumper circuit is shown in Fig 7 5 Observe how the inclusion of slope compensation affects the stability of the converter
19. Power Electronics Laboratory User Manual Department of Electrical and Computer Engineering University of Minnesota Revised September 8 2011 Rev E SAFETY WARNING Before using this laboratory read understand and follow the Safety Precautions mentioned inside this manual This is an educational laboratory where high voltage terminals and large current carrying components and circuits are exposed for ease of measurements Therefore regardless of the voltage and current levels these should be treated as high voltages and high currents and the safety precautions mentioned in the manual must be followed Contents Title Safety Precautions Laboratory Power pole Board Familiarization Buck Converter Switching Characteristic of MOSFET and Diode Boost Converter Buck Boost Converter Voltage Mode Control Peak Current Mode Control Flyback Converter Forward Converter Appendix 16 20 23 26 30 36 41 45 49 SAFETY PRECAUTIONS 1 Why is safety important Attention and adherence to safety considerations is even more important a power electronics laboratory than 1s required any other undergraduate electrical engineering laboratories Power electronic circuits can involve voltages of several hundred volts and currents of several tens of amperes By comparison the voltages in many teaching laboratories rarely exceed 20V and the currents hardly ever exceed a few
20. ak current mode control for a buck boost converter First the aspects of constant frequency peak current mode control will be explored Then the plugin board will be used to achieve feedback voltage control of the converter The goal is to understand how to design a peak current mode controller with voltage feedback 7 2 Preparing setup for Open Loop Operation e Reconstruct the buck boost converter used in Expt 3 as in Fig 7 1 Turn on the signal power supply and set the switching frequency to 100 kHz and duty cycle such that output voltage Vo 12 V Change the switch positions of the switch bank as shown in Fig 7 2 Set Vd to 20 V and the variable power resistor to 20 7 2 Measurements Observe the output voltage V2 and inductor current on the oscilloscope Store the waveform 7 3 Preparing setup for closed loop operation and measurements 7 3 1 Closed Loop Operation Without Slope Compensation Setup the control selection as in Fig 7 3 e Remove shorting link from 161 and insert the Type 2 Controller plug in board whose circuit 15 shown in Fig 7 4 into the terminal strip J60 The pin numbers shown in the figure correspond to pin numbers on the terminal strip This board will add the voltage feedback to the control Set the duty cycle pot to minimum Switch ON the main power supply and set it to 25 V 36 Vi INDUCTOR BOARD MAGNETICS BOARD PWMTOTOP USEEXTERNAL SWITCHED U
21. als of a differential probe to terminal CATH and ANODE E 2 in Fig 1 2 of the upper diode To observe the voltage across the lower diode Connect an oscilloscope probe to CATHLOW and its ground to the ANODE of the lower diode D 4 in Fig 1 2 11 1 3 2 Magnetics Boards To build various converters using the Power pole Board three plug in boards are provided 1 BB Board Fig 1 3 a For buck boost and buck boost converters 2 Flyback Board Fig 1 3 b For flyback converter 3 Forward Board Fig 1 3 c For forward converter How to use these boards will be described in the subsequent experiments a BB Board b Flyback Board c Forward Board Figure 1 3 Magnetics boards 1 3 3 Signal Supply 12 volts signal supply is required for the MOSFET drive circuits and also the measurement and protection circuits This is obtained from a wall mounted isolated power supply which plugs into the DIN connector J90 A 5 in Fig 1 2 Switch S90 B 6 in Fig 1 2 controls the signal power to the board Each time a fault occurs turn off and turn on this switch to reset the board The green LED D99 B 5 Fig 1 2 indicates if the 12 V signal supply 15 available to the board Fuses F90 B 5 in Fig 1 2 and F95 B 6 in Fig 1 2 provide protection for the 12 V and 2 V supplies respectively 1 3 4 Load Any external load is to be connected across terminals V2 and L 1 and L 6 in Fig 1 2 An onboard switched loa
22. basic block diagram of the Power pole Board 15 shown in Fig 1 1 and the actual board 1s shown in Fig 1 2 Please note that the locations of the various components on the board are indicated in Table 1 1 1 3 1 Power pole power pole consists of MOSFETs 010 015 and diodes D10 and D15 The source of the upper MOSFET and the drain of the lower MOSFET are connected to screw terminals for external connection and so are the anode of upper diode and the cathode of the lower diode The voltage and current waveforms at the terminals of the MOSFETs and diodes can be observed Table 1 2 shows the locations of test points on the power pole board Note Take care whenever you are using oscilloscope probes to measure voltage If the measurement reference potential is different to the oscilloscope reference potential you must use differential probe To observe the voltage across the upper MOSFET Connect the positive and negative terminals of a differential probe to the DRAIN and SOURCE of upper MOSFET To observe the upper MOSFET source current Connect the positive and negative terminals of a differential probe to terminals CS2 and SOURCE D 2 in Fig 1 2 of upper MOSFET The current sense resistor value 15 0 05 Q OFF PAT TOP USE EXTERNAL UNUSED MOSFET PUM SIONAL LOAD ACTIVE EXTERNAL PM INPUT SUITONED DUTY CYCLE MOSFET PVNESIONAL
23. circuit checked by your Lab Instructor 5 4 Powering the Circuit Switch ON the signal supply Check for green LED e Set the duty ratio to its minimum Set RL 200 e Adjust the switching frequency to 100 kHz Apply input voltage Vd of 10 volts at the terminals V1 and V2 26 DRIVE CIRCUIT Vi ps COM DIN ON PWMTOTOP USEEXTERNAL SWITCHED UNUSED MOSFET PWMSIGNAL LOAD m m PWMTOBOT USEONBOARD SWITCHED MOSFET PWM SIGNAL LOAD OFF Figure 5 1 Schematic of Buck Boost Converter MAGNETICS BOARD DUTY CYCLE POTENTIOMETER LEM SWITCHED LOAD SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER CONTROL SELECTION EXTERNAL OPEN CONTROL LOOP Variable Rigaistor 27 5 5 Measurements Take the following measurements 5 5 1 Varying Duty Ratio e Vary the duty ratio from 10 to 70 in steps of 10 Measure the average DC load voltage V2 for the corresponding values of duty ratio e Calculate the average theoretical DC output voltage for the corresponding duty ratios Compare the observed average output voltage results with the calculated ones 5 5 2 Varying Switching Frequency Set the duty ratio to 60 switching frequency to 100kHz RL 150 Observe and make the copy of the inductor current CS5 ripple waveform 2100 7 Measure peak peak inductor current ripple e Repeat the above procedure for different switching frequ
24. d is provided to facilitate the observation of the transient response of any converter built using the power pole Thus it 1s possible to periodically switch 1n and out a 20 Q load K 4 to K 6 in Fig 1 2 The frequency and duty ratio of this load is fixed at 10 Hz and 10 To select the switched load 12 Put switch 3 of selector switch bank S30 E 5 in Fig 1 2 to the top position Load SW ON In order to observe the switched load current Connect the positive and negative terminals of a differential probe to CSLOADI and CSLOADJ2 L 5 in Fig 1 2 This measures the voltage across the 20 Q resistor Switched load current is the measured voltage divided by 20 1 3 5 Input Output Voltage Measurement Test points for input output voltage measurements are provided on the Power pole Board For input voltage measurement e Connect the oscilloscope probe to test point V1 C 1 in Fig 1 2 and its ground to COM D 1 in Fig 1 2 For output voltage measurement Connect the oscilloscope probe to test point V2 K 1 in Fig 1 2 and its ground to COM L 1 1n Fig 1 2 1 3 6 Current Measurement LEM current sensors B 1 K 2 in Fig 1 2 are provided to measure the input and output currents The input current sensor 15 located after the input filter capacitor and the output current sensor 15 located before the output filter capacitor Calibration of the current sensors 1s such that for 1A current flowing through each the
25. en while doing the boost converter experiment that the load is always connected to the power pole board The input and output terminals in the case of the boost converter are interchanged as compared to that of the buck converter V2 amp COM is the input and V1 amp COM is the output 4 2 Preparing the Setup Make the connections of the power pole board as shown in Fig 4 1 to use the lower MOSFET and the upper diode Use the BB magnetics board for the boost circuit The inductor 15 100 uH Use a variable load resistor as a load Connect the 12 signal supply to the DIN connector Signal supply switch S90 should be OFF 4 3 Checks before powering the circuit e Check the circuit connections as per the schematics e Confirm that you have connected the input and output terminals correctly to source and load as shown in Fig 4 1 Have your circuit checked by your Lab Instructor 4 4 Powering the Circuit Switch ON the signal supply Check for green LED Set duty ratio to its minimum 10 and RL 20Q e Adjust the switching frequency to 100kHz Apply input voltage Vd of 10 volts at terminals V2 and COM 23 Variable 5 Power Resistor INDUCTOR BOARD COM COM SWITCHED LOAD P DRIVE J MAGNETICS BOARD Zx GRGUIT SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER e PWMTOTOP USEEXTERNAL SWITCHED UNUSED MOSFET SIGNAL LOAD iiid SELECTION 121
26. encies 40 kHz 60 kHz 80 kHz 5 5 3 Determining Efficiency Set the duty ratio to 60 Adjust the load resistance to RL 15Q Measure the efficiency at switching frequencies of 40 kHz and 100 kHz 5 5 4 Varying Load Set the duty ratio to 40 RL 200 and switching frequency to 40 kHz Keep increasing the load resistance until the converter enters into the discontinuous conduction mode and note the value of load resistance 28 5 6 Lab Report The lab report should consist of the information asked below along with any discussion you feel is necessary 1 Attach a graph of duty ratio versus output voltage CS5 using the data obtained in section 5 5 1 Also plot the theoretically calculated results on the same graph Compare the two plots 2 Attach a copy of the inductor current CS5 waveform obtained in section 5 5 2 Plot the experimental and theoretically estimated ripple current waveforms on the same graph Compare the two graphs and comment 3 Plot the efficiency versus frequency using the data obtained section 5 5 3 Comment on the results you obtain 4 Calculate the critical value of load resistance ReritBuck Boost at Which the converter is in the border of Continuous Discontinuous and compare with that obtained section 5 5 4 29 Experiment 6 Voltage Mode Control 6 1 Objective The objective of this experiment is to design a controller to operate the buck converter voltage control mode Fo
27. good idea to use a point to point wiring diagram to review when making these checks 3 4 Precautions while switching ON the circuit Apply low voltages or low power to check proper functionality of circuits Once functionality 15 proven increase voltages or power stopping at frequent levels to check for proper functioning of circuit or for any components 1s hot or for any electrical noise that can affect the circuit s operation 3 5 Precautions while switching on or shutting down the circuit Reduce the voltage or power slowly till 1t comes to zero Switch of all the power supplies and remove the power supply connections Let the load be connected at the output for some time so that it helps to discharge capacitor or inductor if any completely 3 6 Precautions while modifying the circuit Switch on the circuit as per the steps In section 3 5 Modify the connections as per your requirement Again check the circuit as per steps In section 3 3 and switch ON as per steps in section 3 4 3 7 Other Precautions No loose wires or metal pieces should be lying on table or near the circuit to cause shorts and sparking Avoid using long wires that may get in your way while making adjustments or changing leads Keep high voltage parts and connections out of the way from accidental touching and from any contacts to test equipment or any parts connected to other voltage levels When working with ind
28. ing oscilloscope data via RS232 port Note The lab instructor will demonstrate how to use the software to capture oscilloscope waveforms Students should bring floppy disks or flash drives to download the captured waveforms data for use in their lab reports This equipment will be used to set up the circuits and to perform most measurements The laboratory will also have several miscellaneous components including power resistors magnetics boards hookup wire etc as needed for specific experiments 1 3 Power pole Board Familiarization The main feature of the Power pole Board 1s the reconfigurable power pole consisting of two MOSFETS and two diodes The drive circuits for the MOSFETS are incorporated on the board and so are the various protection circuits for over current and over voltage PWM signals to control the MOSFETs can be generated onboard or supplied from an external source The power pole can be configured to work in various topologies using three magnetics boards BB board for buck boost and buck boost converters Flyback board for flyback converter and Forward board for forward converter which plug into the Power pole Board In addition there is an option of doing frequency analysis of each topology by injecting a small signal sinusoidal control voltage The board can also be operated in voltage current feedback mode using an external control circuit mounted on a daughter board which plugs into the Power pole Board The
29. nections as per the schematic Check that the lower MOSFET has been selected Have your circuit checked by your Lab Instructor 8 4 Powering the Circuit Switch ON the signal supply Check for green LED Set the switching frequency to 100kHz and the duty ratio to 50 Set RL 100 e Apply input voltage Vd of 15V at terminal 1 and COM 8 5 Measurements Take the following measurement 8 5 1 Varying Duty Ratio Vary the duty ratio from 0 to 50 in steps of 10 41 DRIVE 1 N CIRCUIT c Variable Power Md Resistor COUPLED INDUCTOR SWITCHED LOAD DRIVE MAGNETICS BOAAD 7 SWITCHING FREQUENCY ADJUSTMENT POTENTIOMETER m PWMTOTOP USEEXTERNAL SWITCHED UNUSED MOSFET PWMSIGNAL LOAD dli 12V 12V PWM CONTROL LOOP OFF PWMTOBOT USEONSOARD SWITCHED DUTY CYCLE MOSFET PWM SIGNAL LOAD OFF Figure 8 1 Schematic of Flyback Converter 42 Measure the average output voltage V2 for the corresponding values of duty ratios Calculate the theoretical average output voltage value for the corresponding duty ratios Compare the observed average output voltage results with the calculated ones 8 5 2 Constant Duty Ratio with varying switching frequency and load Set the duty ratio to 40 switching frequency to 100 kHz and RL 10Q Observe and make a copy of the voltage across the secondary side of the coupli
30. ng inductor Observe and make a copy of the input current CS1 and output current CS5 in the same graph Repeat the above step make a copy of the current waveforms and not the voltage waveform for RL 7 50 Fs 100 kHz RL 100 Fs 40 kHz and RL 7 50 Fs 40 kHz 8 6 Lab Report The lab report should consist of the information asked below along with any discussion you feel is necessary le Attach a graph of duty ratio versus output voltage V2 using data obtained section 8 5 1 Also plot the theoretically calculated results on the same graph Compare the two plots Attach the copy of the voltage waveform obtained in section 8 5 2 Construct the voltage across the primary side of the coupled inductor Label the waveform both voltage and time axis appropriately Note Ignore the ringing in the waveform Using the voltage waveform obtained in section 8 5 2 construct the voltage across the primary side switch Label the waveform both voltage and time axis appropriately You can verify your calculation by observing the waveform on the board Note Ignore ringing and voltage when snubber circuit 1s on 43 4 Attach the waveforms obtained in section 8 5 2 and estimate the following Need to be calculated for all the four operating conditions RL 10Q Fs 100 kHz RL 7 52 Fs 100 kHz 100 Fs 40 kHz 7 50 Fs 40 kHz a Inductance as seen from the primary side Lym b Peak peak
31. of operation 3 6 Exercises 1 Attach the waveforms for turn ON and turn OFF of the diode showing the switching details by expanding the time base 2 Calculate the conduction loss of the diode using eqn 2 1 in the book and the measurements from step 2 of section 3 5 3 Attach the waveforms for turn ON and turn OFF the Mosfet showing the switching details by expanding the time base 4 Estimate the rayon of Mosfet from step 4 of section 3 5 and compare with the datasheet of Mosfet IRF640N 5 Calculate the conduction loss of the Mosfet using eqn 2 3 in the book and the measurements from step 4 of section 3 5 6 Using the values of conduction losses of the Mosfet and the Diode obtained through measurements and switching losses of the Mosfet obtained through simulation Refer to Experiment No 2 in the PSpice based Power Electronics Laboratory User Manual estimate the efficiency of the converter Compare the estimated efficiency with the efficiency obtained for the buck converter in the Buck Converter Experiment 27 Experiment 4 Boost Converter 4 1 Objective The objective of this experiment is to study the characteristics of a boost converter The circuit will be operated under CCM and openloop condition Our main goal is to compare the theoretical results with the experimental results For PSpice Simulation refer Exp No 5 PSpice based power electronics lab manual Note It is important that care must be tak
32. ors and capacitors of the voltage control board are given in Table 6 1 Reference value VREF can be set using the duty ratio pot e Reference value VREF can t be set below 10V e For the pin details of terminal strip J60 please refer the schematic of the power pole board The op amp in the dotted region is a part of the IC UC3824 which is designated asU60 on the power pole board The numbers 9 12 and 13 are pins of J60 port out on the board Vier IS generated through a potential divider on the board Figure 6 3 Voltage controller plug in board Table 6 1 Voltage control board component values p mo __________ a 1 3 22 EXTERNAL O DPEN 163 CONTROL 46 L Figure 6 4 Control selection for Voltage Mode Control plug in board 6 6 Preparing the Setup for Voltage Mode Control Operation Set the control selection jumpers J62 and J63 as shown in Fig 6 4 Insert the Voltage Mode Control plug in board the terminal strip 60 33 Keep RL 100 Switch ON the switched load to the active position using the selector switch bank as shown Fig 6 2 e Turn ON 12Vsignal supply and check for green LED Have your circuit checked by your Lab Instructor Set Vd to 30V e Use the duty cycle pot RV64 to set V2 to 15V 6 7 Measurements in Voltage Mode Control Operation Observe and make a
33. output is 0 5 V These signals are amplified by a factor of 2 and are brought out to the daughter board connector J60 for use in feedback current control Currents through the MOSFETs and output capacitor are measured using current sense resistors Refer to Table 1 2 for details of the various current measurement test points To measure input current Connect oscilloscope probe to CS1 B 1 in Fig 1 2 and its ground to COM D 1 in Fig 2 To measure output current Connect oscilloscope probe to CS5 K 4 in Fig 1 2 and its ground to COM L 1 in Fig 13 measure output capacitor ripple current Connect oscilloscope probe to CS4 K 3 in Fig 1 2 and its ground to COM The current sense resistor value 1s 0 1 1 3 7 MOSFET Drive Circuit The power pole MOSFETs are driven by high side drivers IR2127 These drivers have in built overcurrent protection using a current sense resistor for each MOSFET see locations C 3 and C 5 in Fig 1 2 The voltage across these sense resistors can be observed using test points provided on the board To see the upper MOSFET current Connect the positive and negative terminals of a differential probe to CS2 and SOURCE of upper MOSFET To see the lower MOSFET current Connect an oscilloscope probe to CS3 and its ground to SOURCE of lower MOSFET Note The lower diode current can also be observed using test point CS3 However the upper diode current cannot be observed
34. r this experiment a plug in daughter board will be used to accomplish the control objective The small signal transfer function 7 s d s d is a small signal perturbation in the duty cycle and is the corresponding variation in the output voltage must first be obtained for the buck converter The plug in daughter board 1s used to implement the voltage mode control feedback with the required open loop gain 6 2 Preparing the Setup and Open Loop Mode Construct the buck converter circuit as shown in Fig 6 1 using the BB magnetics board Connect and turn on the 12vsignal supply and check for green LED e Adjust the duty ratio to 50 e Adjust the switching frequency to 100kHz Switch ON the switched load to active position using selector switch bank as shown in Fig 6 2 e Adjust the variable load resistance to 100 Have your circuit checked by your Lab Instructor Apply DC supply voltage Vd to 30V 6 3 Measurements in Open Loop Operation Observe and make a copy of the output voltage waveform V2 Adjust the time base to show the details of the switching transients as the load 1s switched 6 4 Using PSpice to find 2 9 d s Using the schematic file buck avg sch Refer to Exp 10 in PSpice based power electronics lab manual perform the following experiment 30 c Variable 4 Power Resistor Vi INDUCTOR BOARD COM SWITCHED LOAD MAGNETICS BOARD SWITC
35. rimental and theoretically estimated input ripple current on the same graph Compare the two graphs and comment 3 Plot efficiency versus frequency using the data obtained in section 4 5 3 Comment on the results you obtain 25 Experiment 5 Buck Boost Converter 5 1 Objective The objective of the experiment is to study the characteristics of the buck boost converter The circuit will be operated under CCM and openloop conditions Our main goal 15 to compare the theoretical results with the experimental results For PSpice Simulation refer Exp No 6 in PSpice based power electronics lab manual Note It is important that care must be taken while doing the buck boost converter experiment that the load is always connected to the power pole board The input and output terminals in the case of the buck boost converter are different as compared to that of the buck or boost converters 5 2 Preparing the Setup Make the connections for the power pole board as shown in Fig 5 1 Use the BB magnetics board for the buck boost converter circuit The inductor value is 100 uH Use a variable load resistor as a load Connect the 12 signal supply to the DIN connector Signal supply switch S90 should be OFF 5 3 Checks before powering the circuit Check the circuit connections as shown in Fig 5 1 Confirm that you have connected the input and output terminals correctly to source load as shown in Fig 5 1 Have your
36. ther open or closed loop and 15 selected by jumpers J62 and J63 J 5 1n Fig 1 2 For open loop operation Keep 162 and J63 in the righthand positions Closed loop operation will be described in the relevant experiment 15 Experiment 2 Buck Converter 2 1 Objective The objective of this experiment is to study the characteristics of a buck converter The circuit will be operated under continuous current mode CCM and open loop conditions no feedback Our main goal will be to compare the theoretical results with the experimental results Simulation results can be obtained by performing Experiment No 4 in PSpice based Power Electronics Laboratory User Manual 2 2 Preparing the Setup Make the connections on the power pole board as shown in Fig 2 1 to use the upper MOSFET and the lower diode e Use the magnetics board BB board for the buck converter circuit The inductor is 100 uH e Use a variable load resistor RL as a load Use onboard PWM signals Connect the 12 signal supply at the DIN connector Signal supply switch S90 should be OFF 2 3 Checks before powering the circuit e Check the circuit connections as per the schematics Have your circuit checked by your Lab Instructor 2 4 Powering the Circuit e Switch ON the signal supply Check for green LED e Adjust the duty ratio to 50 Adjust the switching frequency to 100kHz e Apply input voltage Vd of 24 volts at terminals V1 and COM 16 L
37. uctive circuits reduce voltages or currents to near zero before switching open the circuits AWARE of bracelets rings metal watch bands and loose necklace if you are wearing any of them they conduct electricity and can cause burns Do not wear them near an energized circuit Learn CPR and keep up to date You can save a life When working with energized circuits while operating switches adjusting controls adjusting test equipment use only one hand while keeping the rest of your body away from conducting surfaces Experiment 1 Laboratory and Power pole Board Familiarization 1 1 Introduction The power electronics laboratory is built around a reconfigurable circuit board termed the Power pole board along with accessory daughterboards The details of the Power pole board are discussed in later sections of this experiment This first experiment will familiarize you with the laboratory equipment and Power pole circuit board 1 2 Laboratory Equipment Each experiment station has the following equipment e Digital Oscilloscope with RS232 interface e Function generator DC power supply 0 60 V 2 A max 12 V Signal Power Supply with DIN connector output e Differential voltage probe e Power Pole circuit board and associated plug in boards with magnetic components and daughterboards with onboard components for implementing closed loop control e Digital Multimeter e Desktop computer with software for captur
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