Single-phase Variable Frequency Switch Gear

Transcription

1 1 Single-phase Variable Frequency Switch Gear Department of Electrical and Computer Engineering Eric Motyl and Leslie Zeman Advisor: Professor Steven D. Gutschlag April 21, 2016

2 2 Outline Introduction Problem Background Problem Statement Design Constraints Design Approach System Block Diagram Subsystem Block Diagram Method of Solution and Progress Design Testing Results Summary and Conclusions

3 3 Outline Introduction Problem Background Problem Statement Constraints

4 4 Problem Background Variable frequency drive Controls the speed of a three-phase AC motor by varying the frequency and voltage supplied to the motor [1]

5 5 Problem Background Importance of variable frequency drives: Provides energy efficiency benefits to industries that consume large amounts of power operating AC machines [2] Matches the speed of motor driven equipment to load requirements Extends equipment life Smooth startup of AC motors reduces belt, gear, and bearing wear Reduces shaft fatigue

6 6 Problem Statement Design, build, and test single-phase variable frequency switch gear Accepts a user-selected input frequency between 1 and 60 Hz and generates an output voltage with a constant Volts/Hertz ratio

7 7 Constraints Single-phase variable frequency switch gear must: Provide output frequencies in the range of 1 to 60 Hz Use switching devices rated for a current of 1.5 A RMS Have a grounded neutral Be safe

8 8 Outline Design Approach System Block Diagram Subsystem Block Diagram

9 9 System Block Diagram +VDC User-selected Frequency Input Variable Frequency Switch Gear Single-phase, Variable Frequency Output with Constant V/Hz Ratio -VDC

10 10 Subsystem Block Diagram Gate Drive Circuitry + VDC User-selected Frequency Input PWM Generation Controller Upper half PWM Lower half PWM DC-to-AC Voltage Inverter VDC Single-phase, Variable Frequency Output with Constant V/Hz Ratio

11 11 Outline Method of Solution and Progress Design Testing Results

12 12 Subsystem Block Diagram Gate Drive Circuitry + VDC User-selected Frequency Input PWM Generation Controller Upper half PWM Lower half PWM DC-to-AC Voltage Inverter VDC Single-phase, Variable Frequency Output with Constant V/Hz Ratio

13 13 PWM Generation Controller Design Approach Testing Results

14 14 Design Approach for PWM Produce a PWM signal representative of a fully rectified sine wave PWM signal drives output bit 1 to control the low side power transistor gate driver on negative half cycles PWM signal drives output bit 2 to control the high side power transistor gate driver on positive half cycles A 1 µs delay is added between every half cycle to ensure both power transistors are not on simultaneously

15 15 Design Approach for PWM User selected sine wave frequency 1-60 [Hz] Constant triangle wave frequency 3 [khz] MATLAB Used to generate the values needed to represent each of the waves Atmel Studios Used to compare the waves and output a PWM signal

16 16 PWM Subsystem Block Diagram 3 khz Triangle Wave 1-60 Hz Sine Wave Comparator Switched PWM Switched PWM has a varying duty cycle representative of the fully rectified sine wave

17 17 PWM Subsystem Block Diagram Varying duty cycle representative of the sine wave

18 18 Testing Circuitry Triangle Wave Sine Wave PWM Generation Controller

19 19 Circuitry Digital-to-Analog Converter (DAC) DAC08-CN Provides a current output Op Amp LM741 Acts as a current-to-voltage amplifier

20 Amplitude (V) Triangle Wave Values generated in MATLAB are stored in lookup tables in the programmable memory space of the Atmel program Constant frequency of 3 [khz] 50 values per cycle DAC Triangle Wave Output Time (ms)

21 Amplitude (V) Fully Rectified Sine Wave Values generated in MATLAB were stored in lookup tables Max number of values used is 37,500 values per quarter cycle Program reads lookup table in ascending and descending DAC Sine Wave Output 1 Hz Time (sec)

22 22 PWM results Sine and Triangle compared each iteration

23 23 PWM results PWM representation of a sine waveform at 60 Hz

24 24 PWM results Selected sine frequency of 30Hz

25 25 PWM results PWM representation of a sine waveform at 30 Hz

26 26 Software Results PWM Generation controller produces a PWM signal that represents a sine wave The frequency of the sine wave can vary based on user input between 1 and 60 Hz Output bit 1 and output bit 2 are active during alternating half cycles

27 27 Subsystem Block Diagram Gate Drive Circuitry + VDC User-selected Frequency Input PWM Generation Controller Upper half PWM Lower half PWM DC-to-AC Voltage Inverter VDC Single-phase, Variable Frequency Output with Constant V/Hz Ratio

28 28 Gate Drive Circuitry Two 8-pin Avago HCPL-3120 chips High and low side drivers 18 V supply +V DC Gate Drive Circuitry Upper Half PWM High Side Driver Lower Half PWM Low Side Driver Load -V DC

29 29 Initial Testing of Gate Drive Circuitry 5 V 18 V R D 1 HCPL V o TTL Open Collector

30 30 Initial Testing of Low Side Driver Computed value of R D I D R D + V D _ + V Qsat _ 5 V V Qsat I D R D + 5 = 0 R D = 5 V Q sat V D I D

31 31 Initial Testing of Gate Drive Circuitry 5 V 18 V R D 1 HCPL V o TTL Open Collector

32 32 Results of Initial Testing of Gate Drive Circuitry Output of HPCL-3120 TTL Input

33 33 DC-to-AC Voltage Inverter Two power MOSFETs +V DC and -V DC voltage rails +VDC Upper Half PWM Load Lower Half PWM - VDC

34 34 Initial Testing of Low Side Driver 18 V 5 V 18 V R Load R D 1 HCPL Rg IRF640 TTL Open Collector

35 35 Initial Testing of Low Side Driver Computed value of R g R g must be high enough to limit the current through pins 6 and 7 of the HCPL-3120 to 2 A R g = V i Power dissipation for R g P Rg = i 2 R g = = 32 W P Rg = N sw iv GS N sw = cycles = 6000 cycles μsec cycle = sec P Rg = N sw iv GS = = 0.18 W

36 36 Initial Testing of Low Side Driver Computed value of R Load 18 V I Load R Load IFR640 + V DS _ R Load = 18 V DS I Load P Load = I Load V DS

37 37 Initial Testing of Low Side Driver 18 V 5 V 18 V R Load R D 1 HCPL Rg IRF640 TTL Open Collector

38 38 Results of Initial Testing of Low Side Driver Output of HCPL-3120 Output of IRF640 TTL Input

39 39 Low Side Driver with Snubber Capacitor Circuit 18 V R Load 5 V 18 V R S R D 1 HCPL Rg IRF640 C S TTL Open Collector

40 Low Side Driver with Snubber Capacitor Circuit 40 Computed value of C S Computed value of R S

41 41 Low Side Driver with Snubber Capacitor Circuit 18 V R Load 5 V 18 V R S R D 1 HCPL Rg IRF640 C S TTL Open Collector

42 42 Low Side Driver with Snubber Capacitor Circuit Output of HCPL-3120 Output of IRF640 TTL Input

43 43 High Side and Low Side Drivers with Bootstrap Capacitor Arrangement 25 V 5 V R R D 1 HCPL Rg TTL Open Collector C BS R 5 V R D 1 HCPL R S 2 7 Rg C S TTL C BS -25 V

44 44 High Side and Low Side Driver with Bootstrap Capacitor Arrangement Computed value of R HCPL-3120 draws 5 ma current Computed value of C BS

45 45 High Side and Low Side Drivers with Bootstrap Capacitor Arrangement 25 V 5 V R R D 1 HCPL Rg TTL Open Collector C BS R 5 V R D 1 HCPL R S 2 7 Rg C S TTL C BS -25 V

46 46 Low Side Driver with Bootstrap Capacitor Arrangement Gate Voltage Load Voltage

47 47 High Side and Low Side Drivers with Bootstrap Capacitor Arrangement 25 V 5 V R R D 1 HCPL Rg TTL Open Collector C BS R 5 V R D 1 HCPL R S 2 7 Rg C S TTL C BS -25 V

48 48 High Side Driver with Bootstrap Capacitor Arrangement Gate Voltage Load Voltage

49 49 Results Gate drive circuitry and DC-to-AC voltage inverter tested independently at ±V DC = 25 V The high and low side drivers switch as desired Next steps: Use the output of the PWM generation controller as an input to gate drive circuitry and test the high and low side drivers together

50 50 Summary and Conclusions A switched PWM was generated through software Hardware for gate drive circuitry and a DC-to- AC voltage inverter have been built and tested Future work Test the full system using the output of the PWM generation controller Test the full system at ±120 V RMS

51 51 Single-phase Variable Frequency Switch Gear Department of Electrical and Computer Engineering Eric Motyl and Leslie Zeman Advisor: Professor Steven D. Gutschlag April 21, 2016

52 52 References 1. Introduction to AC Drives, [Online]. Available: /ITACDS-D.PDF 2. C. Hartman. (2014). What is a Variable Frequency Drive, [Online]. Available: 3. K. Lemke and M. Pasternak. (2014). Variable Frequency AC Source, [Online]. Available: Proposal.pdf 4. K. Lemke and M. Pasternak, Variable Frequency AC Source (VFACS) Project Report, Bradley Univ., Peoria, IL, Variable Frequency Drive (VFD) [Online]. Available: n%20guide.pdf