Vicor Corporation · NASDAQ:VICR
Vicor — Technical Presentation (2019)
31 slides from Vicor's technical presentation, Nov 20, 2019
Slide 1: AC-DC Front End Considerations
AC-DC Front End Considerations Author: Bob Pauplis, Principal Application Engineer Presenter: Massimo Gavioli, Senior Field Application Engineer ©2019 Vicor 1
Slide 2: INDEX: Design checklist
INDEX: Design checklist 1 Fully understand and characterize 7 Difference between a transient and a the source surge 2 Inrush current considerations at 8 Methodology of line disturbance turn on, hot restart, during surges arresting, shunt or series 3 Is power factor correction required? 9 Shunt distu
Slide 3: INDEX: Design checklist
INDEX: Design checklist 13 Stability considerations with 20 Fault currents available on DC bus downstream DC-DC Converters both positive and negative output 14 Resonance 21 Fusing 15 Damping at line frequencies, large 22 Operating temperature and filter components component selection 16 Damping at h
Slide 4: AC-DC front-end considerations: Understanding the System
AC-DC front-end considerations: Understanding the System 1 Design of AC front ends is relatively simple task if the operating conditions are fully understood Future designs may have new unknowns that must be considered Always perform a complete review using a checklist ©2019 Vicor 4
Slide 5: AC-DC front end considerations: Understanding the System
AC-DC front end considerations: Understanding the System 1 Entire operating range must be considered not only steady state One has to examine: – Turn-On, Turn-Off – Line Dropout – Line Surges – Transients – Conducted noise, such as a large inverter on the AC line – Aging effects of components su
Slide 6: Inrush current considerations
Inrush current considerations 2 Inrush current must be controlled as high peak current can trip breakers and cause line disturbances – High peak current may weld switch contacts An NTC thermistor may be used to limit inrush, however it does not work when a rapid restart occurs (e.g., during a li
Slide 7: Is Power factor correction required?
Is Power factor correction required? 3 PFC often required by governing agencies – review the standards that need to be met Not all designs require PFC – Omitted when System simplicity is the main goal Lowest possible initial cost required There are hidden costs when PFC is not used – Heati
Slide 8: No PFC, cause and negative effects
No PFC, cause and negative effects 4 Poor power factor of a Rectifier/Capacitor Causes overheating of iron-core front end is due to non-linear current flow transformers due to the high-frequency with respect content of the current impulses to time Causes overheating in Delta/Y transformers I
Slide 9: Passive PFC
Passive PFC 5A Passive: Inductance is added in series with the rectifier to slow the dI/dt Very simple solution, however heavy and bulky Limited PFC correction Creates a lagging PFC due to the inductance Very good solution for a pre-existing condition where the equipment cannot be modified
Slide 10: Active PFC
Active PFC 5B Uses a boost converter in series with the line and charges the hold-up capacitor to a voltage in excess of the peak of the line – By doing this the AC line cannot directly charge the capacitor, it can only be charged by increasing the amount of boost that the boost converter provides
Slide 11: Three-phase source considerations
Three-phase source considerations 6 3-phase power should be utilized whenever possible to create a DC supply – The rectified DC has no zero crossing – Unfiltered DC per cycle ranges from VPK to 0.866VPK – Minimal capacitance is required except for hold-up purposes and high-frequency bypass In in
Slide 12: Difference between a transient and a surge
Difference between a transient and a surge 7 To summarize, it is the relationship between the peak voltage and the time duration that the peak voltage is present Transients: Short-duration events and typically higher in peak voltage, higher source impedance – May be common mode or differential i
Slide 13: Methodology of line disturbance arresting
Methodology of line disturbance arresting 8 Transients: For attenuation of transients a shunt protection methodology is most often employed – Transient suppression stage most always will precede the surge protection stage to protect it from high-voltage transients – Transient clamp voltage setting
Slide 14: Shunt method of line disturbance arresting
Shunt method of line disturbance arresting 9 A transient arresting component Z1 is added directly across the AC line – Typically a Metal Oxide Varistor (MOV) or a bi-directional transient voltage suppressor (TVS) – Its voltage rating is always > VSURGE – Z1 MUST be safety agency approved device Z1
Slide 15: Series method of line disturbance arresting
Series method of line disturbance arresting 10 A pass element (Q1) is added in series with the DC bus after the bridge rectifier along with the associated control circuitry This element will drop the surge voltage across it and provide a fixed clamp voltage at the output terminals Surge-control
Slide 16: Front end supervisory circuitry
Front end supervisory circuitry 11 Adding intelligent control and Monitored parameters may include: monitoring of the front end will protect – UV Lockout: Undervoltage lockout keeps the it from a wide variety of operating front end off any time the input voltage is below the specified value, it
Slide 17: Front end supervisory circuitry
Front end supervisory circuitry 12 Monitored parameters may include: – Restart timer: will prevent the front end from turning back on until fault conditions have cleared for a predetermined length of time, particularly useful if the AC power drops out and recovers rapidly. The timer will prevent f
Slide 18: Front end stability with DC-DC converter loads
Front end stability with DC-DC converter loads 13 In general the output impedance of the front end should be no greater than 1/10 of the connected load impedance The frequency range that needs to be considered is from DC to 2X the corner frequency of the connected DC-DC converter load The self
Slide 19: Resonance
Resonance 14 The front end must be very well damped – Avoid using high-Q components unless absolutely necessary; the exception being active power processing components The front end can resonate at its natural frequency and can be excited from multiple sources – There is typically more than one
Slide 20: Damping at line frequency
Damping at line frequency 15 When selecting power handling components in the front end, choose components that have relatively low loss at the line frequency, however ensure they are well damped to prevent resonance Under-damped filters and line reactors can cause large voltage excursion during
Slide 21: Damping at frequencies higher than line
Damping at frequencies higher than line 16 Front ends may exhibit resonances at frequencies at other than the AC line ripple or the switching frequency of the connected DC-DC converter loads – This resonance will negatively impact conducted emission performance The resonance on the peak of the r
Slide 22: AC leakage currents
AC leakage currents 17 Front ends and the connected loads often have EMI suppression capacitors connected between the AC line and earth ground (e.g., C2, C3, C4 and C5 below) The magnitude of the AC current to earth ground is dependent on: 1. The applied voltage 2. Total capacitance to earth gro
Slide 23: Front end common-mode voltage at output of DC bus
Front end common-mode voltage at output of DC bus 18 In addition to the differential DC voltage at the output of the front end there is an AC common-mode component AC common-mode voltage is non-sinusoidal and very low impedance It is the reason that a front ends DC output must not be earth-ref
Slide 24: AC voltages on DC bus with differing source configurations
AC voltages on DC bus with differing source configurations 19 Example of common source configurations with voltages at output, however there are more… ©2019 Vicor 24
Slide 25: Fault current available at output of the front end
Fault current available at output of the front end 20 The front end most The DC bus has significant Fault current capability of the commonly has three fault current capability as it is AC line alone are in the range low-impedance sources the impedance of the AC line of 3 – 5kA for residential
Slide 26: Fusing
Fusing 21 Choosing the correct fuse is critical for life Considerations: and property safety Fuse voltage rating must exceed the applied voltage The component or equipment manufacturers The interrupt current rating of the fuse must exceed the recommendations for fusing must be followed “bolt
Slide 27: Operating temperature and component selection
Operating temperature and component selection 22 The selection of components is critical for maximum life of the product Operation of components near maximum temperature shortens the life of the components Components such as electrolytic capacitors degrade rapidly at high temperature and have
Slide 28: Safety and general considerations
Safety and general considerations 23 With the diversity of applications Examples: Aggressive environments, high humidity, salt air, water, high and the endless possible Grounding requirements, loss altitude or high pressure designs to meet these needs, of ground or line connections (sea bottom
Slide 29: Telemetry and crossing the safety barrier
Telemetry and crossing the safety barrier 24 For applications that require the highest system availability remote monitoring should be designed into the system Both limit and trend analysis of the data may be used to determine system health – Parameters such as DC output voltage, current, AC lin
Slide 30: Hipot considerations
Hipot considerations 25 Hipot test voltage is NOT the working voltage Hipot test is a time-limited application of high test voltage to prove that the electrical insulation is functional – Time duration of the applied voltage is typically 1 minute Test proves that the insulation is intact and a
Slide 31: Thank you
Thank you Questions? The information contained herein and presented by Vicor is for general informational purposes only. Vicor assumes no responsibility for inaccuracies, errors or omissions in this presentation. Users of power supply products remain responsible for the design, testing and operation