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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 - PowerPoint PPT Presentation
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An Electrically Isolated UPS System with Surge Protection
Presented by: Thusitha Mabotuwana Duleepa Thrimawithana
Supervisors : Mr. Nihal Kularatna Dr. Patrick Hu
Department of Electrical and Computer EngineeringDepartment of Electrical and Computer Engineering
Part IV ProjectPart IV Project
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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
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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.
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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.
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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)
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What is Transient Protection?
• Protection of user devices from whatever that happens at the primary power sources or in the environment.
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Current UPS SystemsFeature Offline Line-Interactive Online
Surge Protection Poor Poor Good
Protection Mechanism
Switches from main supply to battery during transients
Switches from main supply to battery during transients
Continuously regenerates clean AC using supply or battery
Weight Low Moderate High
Size Small Moderate Big
Cost Low Medium Very high
UsageHomes and small office environment
Medium scale operations
Power sensitive equipment, network protection systems
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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 surgeDiagrams reproduced from Kularatna, N. (1998) Power Electronics Handbook. Boston, Newnes.
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System Overview
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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
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New Concept for Surge Minimisation
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New Concept for Surge Minimisation (cntd..)(cntd..)
Energy PumpInverter and Load
Charge Transfer Unit
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Our System
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• Current controlled forward converter topology was used.
- Simple and economical design- Less number of exposed components to the
main supply- Provide electrical isolation
Energy Pump
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Energy Pump (cntd…)
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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.
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Charge Transfer Unit (cntd…)3rd bank (Discharging)
2nd bank (Standby)
1st bank (Charging)
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Charge Transfer Unit (cntd…)
• Charge transfer unit output waveforms:
2V ripple2V ripple1V ripple1V ripple
Charging logic
Discharging logic
Output waveform
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Charge Transfer Unit (cntd…)
• Load regulation characteristics when tested with the commercial inverter confirmed supercapacitors’ capability to transfer energy.
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Charge Transfer Unit (cntd…)
• Discharge time for a supercapacitor bank of 0.2F based on load variations:
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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.
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Inverter (cntd…)
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Inverter (cntd…)
• Inverter output characteristics with a 25W load:
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Inverter (cntd…)
• Load regulation characteristics:
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System Cost
ComponentCost (NZ$)Per unit price
Cost (NZ$)
Per 10000 units price
Transformers 120.00 40.00
Supercapacitors 120.00 30.00
Microcontroller 20.00 5.00
Other components (FETs, Opto-couplers
etc)120.00 55.00
Total Cost (approximately)
380.00 130.00
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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.
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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.
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Questions?