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An Electrically Isolated UPS System with Surge Protection

Department of Electrical and Computer Engineering Part IV Project. An Electrically Isolated UPS System with Surge Protection. Presented by: Thusitha Mabotuwana Duleepa Thrimawithana Supervisors : Mr. Nihal Kularatna Dr. Patrick Hu. Presentation Outline. Project background

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An Electrically Isolated UPS System with Surge Protection

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  1. Department of Electrical and Computer Engineering Part IV Project An Electrically Isolated UPS System with Surge Protection Presented by: Thusitha Mabotuwana Duleepa Thrimawithana Supervisors : Mr. Nihal Kularatna Dr. Patrick Hu

  2. Presentation Outline • Project background • Transients and transient protection • Current protection mechanisms and drawbacks • A new transient minimisation scheme • Supercapacitors as energy storage devices • System we have implemented • Power stage design and control • Results • Future developments • Conclusions

  3. Project Background • Immense damage caused to electronic equipment by heavy lightning. • Current low cost UPS systems have limited protection. • Systems with good protection schemes are very costly and bulky – not suitable for domestic use.

  4. Project Goals • Design and develop a new UPS topology with complete isolation between supply and load. • Investigate possibilities of using supercapacitors for energy storage in UPS.

  5. What are Transients? • Forms of transients • Spikes (in excess of 6000V in less than 200µs) • Surges (about 20% over nominal line voltage. Lasts for about 15-500ms) • Sags (similar to surges. But under-voltage condition) • Electrical impulse noise (high frequency interference) • Blackouts and brownouts (total or short-duration power loss)

  6. What is Transient Protection? • Protection of user devices from whatever that happens at the primary power sources or in the environment.

  7. Current UPS Systems

  8. Our Tasks and Specifications • Investigate possibilities of using supercapacitors for power transfer while maintaining complete isolation. • Design a UPS with the following specifications: • Input voltage – 230VAC at 50/60Hz • Output voltage – 230VAC at 50Hz • Output regulation – ±5% • Output power – 100W • Common and differential mode isolation Common mode surge Differential mode surge Diagrams reproduced from Kularatna, N. (1998) Power Electronics Handbook. Boston, Newnes.

  9. System Overview

  10. Why Supercapacitors? • Properties of supercapacitors • Very high capacitance (even 1000F) • High power density • Virtually unlimited number of charge-discharge cycles • No toxic substances like in conventional batteries • Low energy density • High ESR Extracted from Prophet, G. (2003). EDN. Supercaps for Supercaches, January, 53-58

  11. New Concept for Surge Minimisation

  12. New Concept for Surge Minimisation (cntd..) Energy Pump Inverter and Load Charge Transfer Unit

  13. Our System

  14. Energy Pump • Current controlled forward converter topology was used. • Simple and economical design • Less number of exposed components to the main supply • Provide electrical isolation

  15. Energy Pump (cntd…)

  16. Charge Transfer Unit • Transfers power to the inverter while maintaining isolation. • Banks are switched so that the discharging bank is not connected to the input. • Supercapacitor banks cycle through charging-standby-discharging cycles.

  17. Charge Transfer Unit (cntd…) 3rd bank (Discharging) 2nd bank (Standby) 1st bank (Charging)

  18. Charge Transfer Unit (cntd…) • Charge transfer unit output waveforms: Output waveform Charging logic Discharging logic 1V ripple 2V ripple

  19. Charge Transfer Unit (cntd…) • Load regulation characteristics when tested with the commercial inverter confirmed supercapacitors’ capability to transfer energy.

  20. Charge Transfer Unit (cntd…) • Discharge time for a supercapacitor bank of 0.2F based on load variations:

  21. Inverter • Needed a single stage sine wave inverter. • Some techniques we looked at: • PWM • PAM • Square wave • Resonant • Decided to implement a single stage PWM push-pull scheme.

  22. Inverter (cntd…)

  23. Inverter (cntd…) • Inverter output characteristics with a 25W load:

  24. Inverter (cntd…) • Load regulation characteristics:

  25. System Cost

  26. Future Developments • Develop a commercial prototype • Consider use of cheaper supercapacitors with higher capacitance. • Optimise inverter and energy pump modules. • Consider a compact FPGA or DSP implementation strategy.

  27. Conclusions • A method of energy transfer using supercapacitors has successfully been implemented. • Complete supply-load isolation has been achieved using three supercapacitor banks with dynamic transfer. • Sine wave inverter based on a 1kHz PWM has been implemented. • Charger has been implemented using a forward converter with current mode control.

  28. Questions?

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