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ABCs of Power Electronic Systems

ABCs of Power Electronic Systems

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ABCs of Power Electronic Systems

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  1. ABCs of Power Electronic Systems By Dr. Doug Hopkins & Dr. Ron Wunderlich DCHopkins & Associates Denal Way, m/s 408 Vestal, New York 13850-3035 dch@dchopkins-associates.com

  2. Our Professional Challenge “The illiterate of the 21st century will not be those who cannot read and write, but those who cannot learn, unlearn and relearn.” -- Alvin Toffler Dr. Toffler, Ph.D., is one of the world's preeminent futurists. As co-author of War and Anti-War, he sketches the emerging economy of the 21st century, presenting a new theory of war and revealing how changes in today's military parallel those in business.

  3. About the Course Authors? • Dr. Doug Hopkins • PhD. Virginia Tech, VA Power Electronics Center • GE-CR&D, Carrier Air Conditioning Company(UTC), University at Buffalo, and DCHopkins & Associates (President) • R&D for advanced power electronic systems • dch@dchopkins-associates.com • Dr. Ron Wunderlich • Ph.D. Binghamton University • IBM Power Systems, Celestica Power Systems, Transim Corp, and Innovative Design and Development (President) • Chief Engineer in design and development of power supplies for the computer and telecom industries. • raw@dchopkins-associates.com

  4. Course Topics 1. Overview of Power Electronics Technology 1a. Introduction to the power electronics system 2. Knowing your specifications 2a. Design for safety 3. Choosing the correct topologies 3b. Knowing where disaster can strike 4. Characterizing power components 4a. A safe operating area 4b. The dual faces of MOSFETS 4c. The circuit is a component 5. Design approaches and tools 5a. Simulating reality 5b. Input filtering 6. Design approaches and tools 6a. Design case study

  5. DCHopkins & Associates - Products Products designed by our Associates,photographed by our Associates. • 600W family of isolated DC/DC building blocks • Multi-output telecom power supply Pictures courtesy of Celestica, Incorporated

  6. DCHopkins & Associates - Products • 30A high efficiency, high-transient isolated power supply • Isolated power supply for high-end micro-processor Pictures courtesy of Celestica, Incorporated

  7. News Sources Where to go for news (other than suppliers)? • http://www.darnell.com (PowerPulse Daily) • http://www.poweronline.com (see electricnet) • http//www.electricnet.com (see poweronline) • http://www.powersystems.com • http://www.eedesign.com • http://www.psma.com • http://www.ejbloom.com (see attached catalog) • Conferences: • http://www.pels.org (the IEEE Power Electronics Society) • http://www.apec-conf.org • http://www.pesc06.org • http://www.intelec.org

  8. Introduction toThe System Source Load Power Processor

  9. Source Load Power Processor Conversion or Supply Motor drives • Linear • Rotational “Conversion” changes one energy form to another. Electrical Source Types of Loads Lighting • Fluorescent • HID • Halogen Pulsed power • Ignition • Flash lamp • Pulsed propulsion POWER CONVERSION

  10. Source Load Power Processor Conversion or Supply “Supply” changes only the attributes. Computer Applications • Desktops • Workstations • Servers • Mainframes Circuits: • CPU • Memory • Bus Terminators • Logic • Graphics LOAD Handheld Applications • PDA’s • Notebooks • Cell-phones Circuits: • RF Amps • CPU/Logic • Memory • Display • Audio Amps Telecom Applications • Routers • Tele. Switches Circuits: • Optical Amps • CPU • Memory • Switch Cards • Logic POWER SUPPLY

  11. Clean AC Utility Noisy AC Utility Power Processor Electronic Circuit Uninterruptible Power Supply Systems • Electronic Circuits are • Any electronic equipment that requires clean, reliable AC utility • Computers, Telecom equipment, Home appliances • Sources are • DC such as a battery or solar cells • AC utility that is of poor quality

  12. Source Load Power Processor The System - Source Characteristics SOURCE

  13. THE POWER PROCESSOR Converts an unregulated power source to a regulated output. Like CPU’s processing information - Power Supplies process energy. Linear Regulator Absorbs the energy difference Switch-mode Regulator Chops and averages energy packets The System - Source Characteristics Source Load Power Processor

  14. Knowing Your Specificationsand theUser’s Requirements

  15. Developing User Requirements Responsible Design is from Cradle to Grave • Typically, User Requirements are derived through a polling process. • This brings forward the highest-priority requirements, but are limited to personal experiences. • A comprehensive approach uses a matrix of Five Taxonomies and Three Characteristics

  16. MATRIXED Grouping User Requirements Characteristic Unspoken Expectations Articulated Needs Unexpected Features Taxonomy Financial Legal Social Environmental Technical

  17. Taxonomies in User Requirements • Financial requirements: represent cost and is base metric for other matrix entries. • Legal requirements: include intellectual property as a source of revenue, strategic positioning or enticement. • Social requirements: represent the corporate culture and image, global perceptions, and ethical conduct. • Environmental requirements: represent government regulations and broader global concerns. • Technical requirements: science based metrics related to ‘energy forms’ and provide the “SPECIFICATIONS.”

  18. Characteristics of User Requirements • Unspoken Expectations: • requirements for a product, process or service to be acceptable to all end users. Though labeled as unspoken, these may be new requirements that develop while a business has not been keeping up with the competition or market place, or basic requirements for entry into new markets. • Articulated Needs: • typical, open and printed “specifications. ” Discerns one user from another. There should be no question that these needs are requirements that must be met for each user. • Unexpected Features: • exciters that make the product, process or service unique and readily distinguishable from the competition. (This is what the sales force lives for.) Features are speculative requirements.

  19. Example User Requirements • Unspoken Environmental Expectation: the product is not lethally hazardous to shippers • Articulated Technical Need: the products will operate from -40°C to +100°C. • Unexpected Legal Feature: the product can have exclusive patent protection.

  20. Iin Iout Electric Magnetic Electromagnetic Thermal Mechanical Chemical Photonic Vin Power Supply Vout Defining Specifications Power electronic circuits condition and convert many energy forms! Technical User Requirements provide the SPECIFICATIONS for each Energy Form.

  21. Taxonomies Characteristics Framework leading to Specifications Responsible Design is from Cradle to Grave. Technical Characteristics • Energy Forms • Conditions • Start-up • Shut-down • Normal operation • Fault operation

  22. Electrical Specs Electrical Spec Input Output Controls Misc AC DC Vout, Iout PGood, On/Off Efficiency Vin, Iin Vin, Iin

  23. DC Input Spec Specifying Vin depends on the source voltage range. • Typical DC sources: • Car Battery  typical 12 volts with 11 to 14 volts variation • Solar Cell  0.5 to 1 volt per cell depending on sunlight • Telecom Bus  typical 48 volts with 36 to 72 volts variation • PC Internal 5V Bus  5 volts, +/- 10% • Example: A Telecom bus has a Vin operating range of 36 to 72 volts • If the input voltage drops below 36V, typically, a PS will shut down. • If the input voltage exceeds 72V, typically, a PS will be damaged by the excessive high voltage. • A PS can be designed so it can handle short duration of high input voltage such as line transients due to lightning. • This is known as a surge rating. • For example, this PS may have a surge rating of 100V for 100usec.

  24. DC Input Spec - Iin, Pout, Pin, • Pout (output power) = Vout x Iout • Pin (input power) = Vin x Iin •  (efficiency of the PS) = Pout / Pin • Typically between 0.5 to 0.98 • Substituting and solving for Iin Iin = (Vout x Iout) / (Vin x ) Iin is the current drawn by the PS and derived by Note: Worst case - Iin occurs at lowest value of Vin, e.g. for telecom PS most current is at Vin=36 volts.

  25. Irip Iin Time DC Input Spec Iin will have ripple current, Irip, from the switching stage within the PS. • Specified as peak-to-peak. • Occurs at usually < 10Mhz • Typically, < 10% of max Iin • E.g., if Iin max is 10A, Irip p-p should < 1A

  26. DC Input Spec • Iin will have switching noise that occurs at >10Mhz. • The noise is due to the internal capacitive coupling parasitics • Typically, the peak-to-peak noise is less than 1% of max Iin Iin will have switching noise.

  27. DC Input Spec • Surge current, Isurge, is due to charging of internal capacitors • Usually Isurge is less than 5 times max Iin • This can cause problems with fusing. Iin will have a surge during start-up.

  28. AC Input Spec Specifying Vin depends on the source voltage range • Typical AC sources for the home • Doorbell, heating systems  24Vrms +/- 30% • Household wiring  Typically 110Vrms with 90 to 130 range • Electric stoves  Typically 220Vrms with 180 to 260 range • Actually, 220Vrms with a center-tap is delivered to the home. 110Vrms is derived from the center-tap • Typical AC sources for business (single phase derived from three phase) • Office wiring  Typically 120Vrms with 90 to 140 range • Industrial/Computer  Typically 208Vrms with 180 to 260 • Smaller businesses will use the household AC utility • Europe and some other countries are wired with either 208Vrms or 220Vrms

  29. AC Input Spec • Vin for typical products • Desktop PC sold in the US, 90Vrms – 140Vrms • Desktop PC sold Worldwide, 180Vrms – 260Vrms • High-end servers sold worldwide, 180Vrms – 260Vrms • Desktop PC with “universal” PS, 90Vrms – 260Vrms • Why not use a “universal” PS in all desktop PC’s ? • “Universal” PS are more expensive and difficult to design • Operating frequency for Vin is specified as • USA - 60Hz; Europe and other countries - 50Hz, range is +/-3Hz • A “universal” PS operates from 47Hz to 63Hz • This is not a cost or a design problem

  30. Iin Iout Vpk Vin Power Supply Vout AC Input Spec - Vin-rms Vin is from the wall outlet or a UPS for “Off-Line”converters • AC sources are: • Single Phase • Three Phase (>5kW, not covered) • Vin is understood to be Vin-rms; • Vin-rms = Vpk / 1.4142 * • RMS makes calculations easier • For DC, Pin = Vin x Iin • For AC, Pin = Vin-rms x Iin-rms • For single frequency sine wave

  31. AC Input Spec - sags, surges, and transients • AC voltage will have transients and surges • 2000V spikes are not uncommon • Florida is the worst US state • Due to lightning, industrial equipment and solar flares • The “front-end” PS circuitry must be able to shunt this energyThe PS cannot have direct connection between input and output. Hence, isolation is required. This is a safety requirement. • AC supply has brown outs, sags, or drop outs in power • This occurs when • The utility transformer in a sub-station goes bad • The grid becomes overloaded from air-conditioners, etc. • Solar flares induce too much voltage and “pop” the breakers • These occur quite often • More than 99% of the drop outs are less than 20ms in length

  32. AC Input Spec - Hold-up Time When AC momentarily is interrupted • For non-mission-critical devices • e.g., televisions, radios, VCRs • PS can shut down temporarily • For mission-critical devices • e.g., high-end servers • PS shall maintain operation for a loss of AC up to 20ms • After 20ms it can shut downThis is known as hold-up time • This is accomplished by a large energy storage device such as a capacitor in the input (PFC). • Typical specifications for hold-up is 20ms.

  33. AC Input Spec - Power Factor Ideally, Iin should follow Vin emulating a resistor • A bridge rectifier with a large capacitance is usually at the PS input. • Iin, with respect to Vin, will be distorted. • Iin-rms is now significantly higher than for a resistor inputto have the same usable energy flow. • The distortion adds frequency harmonics.

  34. AC Input Spec - Power Factor (con’d) • Apparent power is Pa = Vin-rms x Iin-rms • Real power is the average Pr = Vin x Iin • Power Factor, PFPF = Real Power / Apparent Power • The lower the PF, the higher the Iin-rms for the given power • The problems with lower PF are • Wire sizes must be increased to handle the higher Iin-rms current • Power Loss increases by the square of current! • This is extra power for which the feeders and fuses must be size • Iin is rich in harmonics which adds noise and circulating currents in 3-phase systems

  35. AC Input Spec - Inrush Current • Usually, peak Iin is specified to be <5X the steady- state Iin-rms. • Another factor to consider is fusing and circuit breakers. • If the inrush current is too high or can occur throughout the day, fuses and circuit breakers can be weakened, damaged, or open up. Like DC, Iin has inrush issues with AC applications.

  36. AC Input Spec - THD Total Harmonic Distortion, THD - the same for your stereo as for the power supply • Any waveform can be broken down into a sum of sine waves with different amplitudes • If there is any distortion, then • I = 1.414 x [I1sin(2ft)+I2sin(4ft)+I2sin(6ft)+…] • I1 is the rms of the “fundamental” current waveform • I2 is the second-order harmonic, I3 is third, etc. • The Total Harmonic Distortion is thenTHD = {sqrt[ (I2)^2 + (I3)^2 + (I4)^2 + …] / (I1)} x 100% • A good value for THD < 5%

  37. AC Input Spec - Noise • Conducted noise current is measured on the line cord. • The frequency is less than 30Mhz • A “LISN” box is connected to the cord to filter out the 50/60hz • A frequency-spectrum analyzer then displays the noise spectrum • Federal specifications must be met • If the frequency is > 30Mhz, this is known as radiated • This is measured with an antennae usually 10 meters away • At these frequencies, line cords and cables become very effective antennae • Federal specifications that must be met Conducted versus Radiated Noise

  38. Vout Specs Line, Load & Temperature Static Regulation Load Step Dynamic Regulation VOUT Noise Ripple & HF Noise Drift Long Term Stability

  39. Static Regulation • Line Regulation • % change in output voltage versus input voltage at a given load • Typically 1-2% • Load Regulation • % change in output voltage versus load at a given input voltage • Typically 0.1-3% • Vout Temperature Effect • % change in output voltage versus temperature for given input and load • Typically 0.2-1%

  40. Static Regulation • Cross-Regulation (multi-output converters) • Change in output voltage of channel 2 for a change in load on channel 1 at a given input voltage • Typically 0.1-10%

  41. Dynamic Regulation Change in output voltage is due to the dynamic behavior of the power supply • The output voltage initially changes because of the I step x ESR of the output cap (5A x 0.3ohms) • The second part is due to the loop response of the converter • The change in output voltage is measured from the nominal output voltage • 5% for this example

  42. Dynamic Regulation • This is due to inductance of • Output capacitor • Connector • Bus distribution • This is not always included in the spec. • Could typically be < 5% Another effect shows up as L x (di/dt)

  43. Ripple and Noise • Ripple • Triangular-shaped current at the switch frequency • Due to inductor current x ESR of output cap • High Frequency Noise • Noise > 10 x fSW • Either random or the excitation of high-frequency parasitics. • Typically 0.2-3% Vrip Vout Time

  44. Drift • Drift is due to • Aging • Soldering • Package compression • Typically < 0.2% Over time, a reference voltage can change.

  45. Question - How can you improve the transient response of the converter without… changing the components or changing the switching frequency?

  46. Answer • Use adaptive control (positioning) • At no load, start at +X1% above nominal Vout • At full load, change Vout to be X2% below nominal Vout • In the previous example, dynamic regulation was 5% • This can be changed to 3% dynamic regulation by modifying VREF for the control loop scheme • Common in IC’s

  47. Maximum current Over current trip point di/dt rate Iout I step Minimum current Time Iout Specs • Below is a typical Iout load behaviour

  48. Question What happens to current in COUT if IOUT’s frequency >> than the bandwidth of the converter ?

  49. Answer • Normally, the ripple current in Cout is the same as the inductor current • If the load is switching faster than the bandwidth of the converter • the ripple current in Cout is due to Iout (load shift). • the converter will not respond to the load changes so the current it delivers will be the average of Iout • The ripple current in Cout due to Iout may be significantly higher than that due to the inductor current • This condition occurs with most modern micro-processors when executing certain software • Local decoupling caps help solve this problem

  50. Design For Safety Standards, Certificates & Regulations