Presentation Transcript

1. Uninterruptible Power Supply The Utilization of Thyristor-SCR Drives to Protect Data Center-Based Products. Kevin Oresick; Matt Logue EE 435 – Introduction to Power Electronics West Virginia University
2. Contents Introduction Background on Devices Protection of the Devices PSPICE Simulation of SCR Devices Simulink Simulation of SCR Devices Conclusions West Virginia University 2
3. Introduction Over the past few decades, there has been considerable research and advancement in uninterruptible power supplies. More importantly, with the advancements in modern power electronic devices, engineers have been able to utilize different drive technologies to enhance overall system security. This specific project is based primarily off of these advancements and is inspired by the ever increasing usage of server-based products, storage of large amounts of data, and the havoc that can be caused on a business and their clients by an outage/emergency. West Virginia University 3
4. Introduction An uninterruptible power supply (UPS) is essentially an electrical device that will provide power to a load when the input source fails, usually during an emergency. This particular design encourages the use of thyristors to create a converter that stores energy in order to supply a base of servers during the unfortunate occasion of a blackout, power outage, inclement weather, or other unpredictable disasters that can potentially cost businesses a fortune. Make note that a UPS differs significantly from that of a standby generator or a back-up emergency source due to the design parameters. While both supply power during an outage, only a UPS will provide near-instantaneous protection from any interruptions of the source, in which energy is supplied from battery or flywheel storage. Because a UPS is supplying energy to a large load, the UPS is only capable of supplying to the respective load for a brief period of time. West Virginia University 4
5. Background on Devices AC Power Supplies Thyristor SCR Devices Teccor brand Thyristor Fast-Acting Semiconductor Fuses (LittleFuse, Inc.) West Virginia University 5
6. AC Power Supplies AC power supplies are commonly used as standby sources for critical loads and in applications where normal AC power supplies are not available. These standby sources are not only reliable, but the conversion (or switch) happens almost instantaneously. There is ideally no need for breaking the supply if there is a failure. Something to consider is the type of battery material utilized, however that is particularly out of the general scope of this project. The main focus is to choose appropriate switching devices and their respective parameters. West Virginia University 6
7. Thyristor SCR Devices Since the first thyristor silicon-controlled rectifier (SCR) was developed, many advances have been accomplished in power semiconductor devices. A thyristor has three terminals; an anode, a cathode, and a gate. When a small current is passed through the gate terminal to cathode, the device conducts. There are many types of thyristors and each type has their own specific characteristics and usages. Once a thyristor is in a conduction mode, the gate circuit has no control and the device will continue to conduct. Also, the forward voltage drop is very small, often between 0.5V and 2V. A functioning thyristor can be turned off by making the potential of the anode equal to or less than the cathode potential. The UPS design incorporates standard phase-controlled SCRs that are triggered with few milliamps of current at less than 1.5V of potential [Littlefuse, Inc 2010]. West Virginia University 7
8. Teccor brand Thyristor The Teccor SCR is an excellent unidirectional switch optimized for phase-controlled applications. The typical applications are AC solid-state switching, industrial power tools, exercise equipment, white goods and commercial appliances. The SCR of choice for the UPS was a thyristor designed by Teccor. The device is a Sxx20x and Sxx25x Series thyristor and can be purchased from LittleFuse Incorporated. Figure 1. Teccorthyristor. West Virginia University 8
9. Teccor brand Thyristor West Virginia University 9
10. Teccor brand Thyristor Note: Device Sxx25L West Virginia University 10
11. Fast-Acting Semiconductor Fuses Fast-Acting Semiconductor Fuses (LittleFuse, Inc.) Model #: LA100P25-1 West Virginia University 11
12. Fast-Acting Semiconductor Fuses Device LA100P25-1 applications include but are not limited to protection of UPS systems, AC/DC drives, reduced voltage motor starters and other 1000V or less semiconductor devices. West Virginia University 12
13. Protection of Devices Types of Device Protection Which Device for Which Application? Thermal Protection Cooling/Heat Sink Overcurrent Protection Fusing Devices West Virginia University 13
14. Types of Device Protection Due to the reverse recovery process of power devices and switching actions in the presence of circuit inductances, voltage transients occur in converter circuits. Even thoroughly designed circuits can have short-circuit fault conditions, resulting in excessive current flow through the devices. The heat produced by losses in a semiconductor device must have the appropriate apparatus to dissipate sufficiently to ensure that the device can operate efficiently within the specific device temperature limitations. In practical terms, power devices are designed to be protected from thermal runaway by heat sinks, high changes in currents and voltages by snubber circuitry, reverse recovery transients, and supply/load-side transients, and lastly, fault conditions by fuses. For sake of the UPS design, thermal cooling and fuse protection will be discussed. West Virginia University 14
15. Heat Sinks and Cooling Devices Due to on-state and switching losses, heat is generated within the power device. Inevitably, this heat must be transferred from the device to a cooling unit to maintain a proficient operating environment. There are many ways to accomplish the heat transfer, however this design explicitly uses convection cooling or the installment of a heat sink. Heat must flow from a device, to the case, and then to a heat sink in the cooling medium. To appropriately add a heat sink to a system, one must calculate the junction temperature of the device . This temperature can be found by the following equation: where = thermal resistance from junction to case, = thermal resistance from case to sink, = thermal resistance from sink to ambient, = ambient temperature. West Virginia University 15
16. Heat Sinks and Cooling Devices Figure 7.Thermal resistance characteristics of heat sink apparatus [Rashid, 2003]. There are further assessments for cooling devices, and more options are available (discussed in oversight). West Virginia University 16
17. Fusing Devices A thyristor requires a minimum time to spread the current conduction uniformly throughout the junctions. If the rate of rise of anode current is fast compared with the spreading velocity of a turn-on process, excessive heating may occur due to high current density and the device may possibly fail as a result of excessive temperatures [Rashid, 2003]. The chosen semiconductor device (thyristor SCR) may be protected by carefully choosing the locations of the fuses. As a safety measure, most manufacturers strongly suggest placing a fuse in series with each device. This provides individual protection that permits better coordination between a device and its fuse, allows conforming utilization of the device, and obviously protects from shorting faults. Not all fuses are identical, and choosing the right fuse can be a daunting task. However, by knowing a few parameters, the correct fuse can be obtained. West Virginia University 17
18. Fusing Devices In selecting a fuse, it is necessary to estimate the fault current and then to satisfy the following requirements: 1) The fuse must carry continuously the device rated current. 2) The i2t let-through value of the fuse before the fault current is cleared must be less than the rated i2t of the device to be protected. 3) The fuse must be able to withstand the voltage, after the arc extinction. 4) The peak arc voltage must be less than the peak voltage rating of the device. Some things to note are the following: the i2t value is termed as the let-through energy which is responsible for melting the fuse. For the UPS operation, a fast-acting fuse is needed. A general rule of thumb is that a fast-acting fuse with an RMS current rating equal or less than the average current rating of the thyristor normally can provide adequate protection under fault conditions [Rashid, 2003]. West Virginia University 18
19. PSPICE Simulations The following section includes all preliminary data simulated, schematic design of the SCR drives, and output waveforms of the RMS voltage no load/full load, the system current at full load, the SCR current at no load/full load, and the SCR gate voltage pulsed 180 degrees apart. NOTE: Tables are excerpt from design documentation. West Virginia University
20. PSPICE Simulations The following figure is the circuit schematic of the SCR designed specifically for utilization within the UPS system. Although the following diagram is the design of a thyristor rectifier, the device design requires eight thyristors total (four thyristor rectifiers and four thyristor inverters). Figure 8: Thyristor –SCR rectifier design schematic. West Virginia University
21. PSPICE Simulations Figure 9: RMS Voltage waveform at No Load. West Virginia University
22. PSPICE Simulations Figure 9: RMS Voltage waveform at Full Load West Virginia University
23. PSPICE Simulations Figure 10: Current waveform at Full Load West Virginia University
24. PSPICE Simulations Figure 11: SCR Current waveforms at Full Load West Virginia University
25. PSPICE Simulations Figure 12: SCR Current waveforms at No Load West Virginia University
26. PSPICE Simulations Figure 13: SCR Gate Voltages when fired 180 degrees apart. West Virginia University
27. PSPICE Simulations Heat Sink – Fuse –Power Calculations Figure 14: Desired heat sink and appropriate parameters West Virginia University
28. PSPICE Simulations Heat Sink – Fuse –Power Calculations Figure 15: Fuse selection parameters. NOTE: Power loss based on all thyristors in system West Virginia University
29. Simulink - An Alternative Approach Figure 16: Simulink design of functional UPS system. Figure 17: UPS Layout container. West Virginia University
30. Simulink - An Alternative Approach Figure 18: Simulink design of thyristor rectifier. West Virginia University
31. Simulink - An Alternative Approach Figure 19: Simulink design of thyristor inverter. West Virginia University
32. Simulink - An Alternative Approach Figure 20: Simulink scope of current output at UPS activation. West Virginia University
33. Simulink - An Alternative Approach Figure 21: Simulink scope of RMS voltage output at UPS activation. West Virginia University
34. Closing Remarks Future Design Consideration Electromagnetic Interference (EMI) High-Power Application Cooling Oversight? Overall Design Conclusion West Virginia University 34
35. Future Design Considerations Electromagnetic Interference Power electronic circuits switch on and off large amounts of current at high voltages and thus can generate unwanted electrical signals which affect other electronic systems. These unwanted signals occur at higher frequencies and give rise to EMI, also known as radio frequency interference (RFI). Numerous sources of EMI (atmospheric noise, lightning, radar, radio, television, etc). Any power converter is a primary source of EMI. In the future, we will research appropriate approaches to minimize EMI generation within a desired system. Shielding, advanced control techniques for minimizing input/output harmonics, operating at unity input power factor, soft switching, and lower total harmonic distribution (THD). West Virginia University 35
36. Future Design Considerations High-Power Application Cooling Techniques Devices are more effectively cooled by liquids, normally oil or water. Water cooling is very efficient and approximately three times more effective than oil cooling. However, it is necessary to use distilled water to minimize corrosion to some applications and antifreeze to obviously avoid freezing. Oil cooling, which may be restricted to some applications, provides good insulation and eliminates the problems of corrosion and freezing (However, oil is flammable). Heat pipes and liquid-cooled heat sinks are commercially available. These are just some alternatives to the conventional heat sink design. West Virginia University 36
37. Conclusive Thoughts Overall Design Conclusion The UPS system will function appropriately for approximately 15 minutes. This is an adequate amount of time to activate alternative sources or shut down data centers, servers, etc. The main purpose of the UPS system is to ensure that a load is continuously powered during the rise of a emergency or outage. Not designed to operate for long periods of time. Only long enough to activate a secondary back-up generator or alternative source. Ultimately, the UPS proves to be a reliable system that can save companies multitudes of data and valuable hardware. More importantly, this fail-safe makes clients feel confident that data is safe. West Virginia University 37
38. Conclusive Thoughts Questions? West Virginia University 38