Studies have shown the efficiency benefits of DC dis- tribution systems are largely due to the superior performance of DC/DC converters. Nonetheless, these studies are often based on product data that differs widely in manufacturer and operating voltage. This work develops a rigorous loss model to theoretically compare the efficiency of a DC/DC and an AC/DC PFC boost converter. It ensures each converter has the same components and equivalent operating voltages. The results show AC boost converters below 500 W to have 2.9 to 4.2 times the loss of DC

Gerber, Daniel

Musavi, Fariborz

English

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AC vs. DC Boost Converters: A Detailed Conduction Loss Comparison

eScholarship - University of California

Lawrence Berkeley National LaboratoryLBL PublicationsTitleAC vs. DC Boost Converters: A Detailed Conduction Loss ComparisonPermalinkhttps://escholarship.org/uc/item/97v3035xAuthorsGerber, DanielMusavi, FariborzPublication Date2019-05-20 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaAC vs. DC Boost Converters: A Detailed Conduction Loss Comparison Daniel Gerber (dgerb@lbl.gov), Fariborz Musavi (fariborz.musavi@wsu.edu)MotivationBackground• DC power distribution has the potential for efficiency savings, improved power quality, ease of islanding, reduced costs, and combined data/power• US Department of Energy focuses on quantifiable efficiency comparison• Numerous studies compare efficiency of AC and DC buildings• Most loss occurs at the load input convertersGaps in Prior Research• In all prior research, converter efficiency is based on product data. It is hard to compare AC and DC converters using product data because:- Requires a lot of data, which is often unavailable- Products only use standard inputs such as 120 V AC or 48 V DC.  High-voltage converters are often more efficient regardless of AC or DC- Different products use different components with different parasiticsProject Goal• Develop a detailed loss model of a boost converter• Compare AC/DC PFC boost and DC/DC boost converter with the same voltage and same componentsDeriving the Conduction Loss ModelComponent CurrentsSimulation, Experiment, and ResultsVOUTQCLD LoadVIN B+~_~iL(θ,t)iref(θ)0 π θ Ipk ΔiL,pp(π/2)π/2 T0BAADT DTiL(θ,t)iref(θ)tΔiL,pp(θ)δQ(θ)TiQ(θ,t) iD(θ,t)δD(θ)TTABLE I: Simple model of component currentsParameter AC/DC PFC DC/DC min(PLoss,AC/PLoss,DC)IL,rmsIB,rmsp2PoVpkPoVpk2IB,avg 4⇡PoVpk     IQ,rmsPopVoVpkq2Vo   163⇡VpkPopVoVpkpVo   Vpk 2ID,rms 4p3⇡PopVoVpkPopVoVpk163⇡ ⇡ 1.70ID,avgPoVoPoVo1IC,rmsPoVopVpkq163⇡Vo   VpkPoVopVpkpVo   Vpk 163⇡ ⇡ 1.70TABLE II: Model of component currents with rippleParameter AC/DC PFC DC/DCIL,rmsIB,rmsr576⇡L2P2o V2o +12⇡T2V 2o V4pk 64T2VoV 5pk+9⇡T2V 6pk12LVoVpkp2⇡r12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk2LVoVpkp3IB,avg4Po⇡Vpk  IQ,rmsvuuut2880⇡L2P2o V3o  7680L2P2o V2o Vpk+60⇡T2V 3o V4pk... 480T2V 2o V5pk+135⇡T2VoV6pk 128T2V 7pk12LVpkq10⇡V 3or⇣Vo Vpk⌘⇣12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk⌘2LVpkq3V 3oID,rmsr3840L2P2o V2o +80T2V 2o V4pk 45⇡T2VoV 5pk+64T2V 6pk12Lq5⇡V 3o Vpkr12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk2Lq3V 3o VpkID,avgPoVoPoVoIC,rmsr3840L2P2o V2o  720⇡L2P2o VoVpk+80T2V 2o V4pk 45⇡T2VoV 5pk+64T2V 6pk12Lq5⇡V 3o Vpkr⇣Vo Vpk⌘⇣12L2P2o Vo+T2VoV4pk T2V 5pk⌘2Lq3V 3o VpkG. Summary of Model CurrentsFinal expressions of all the component currents are given inTables I and II for the simple and ripple models, respectively.In Table I, the leftmost column shows the ratio of losspower per component between equivalent AC and DC boostconverters. For IQ,rms and IC,rms, this ratio is minimized atvery high Vo. RMS and average currents correspond to resistiveand diode losses, respectively.IV. MODEL VALIDATIONThis work validates the boost converter loss model througha transient PSIM 11.1.5 simulation over a 120 Hz period. Thesimulated boost converter is ideal, with either an AC/DC PFCor a DC/DC control loop. As shown in Tables III and IV, thesimulation results closely match the model.This work also validates the model with the experimentalprototype in Figure 3. The prototype is designed for an outputpower Po = 250 W, output voltage Vo = 350 V, and inputvoltage Vpk = 170 V. Its components, shown in Table V, arethe same between AC and DC boost experiments. Tables IIIand IV show the experiment to be somewhat consistent withthe model and simulation. As previously mentioned in Sec-tion II, the model only holds for prototypes with relativelyhigh efficiency (>90%).TABLE III: AC/DC PFC Boost Model Validation Currents (A):Po = 250 W, Vo = 350 V, and Vpk = 170 VParameter Model(simple)Model(ripple) Simulation ExperimentIL,rmsIB,rms2.153 2.161 2.162 2.356IB,avg 1.938 1.938 1.938 2.105IQ,rms 1.655 1.662 1.662 1.723ID,rms 1.376 1.381 1.382 1.323ID,avg 0.733 0.733 0.733 0.781IC,rms 1.165 1.171 1.171   V. AC VS DC EFFICIENCY COMPARISONThis section presents a direct comparison between ACand DC boost converters using the loss models developed inSections II and III. The analysis combines the componentcurrents from Table II with real component parasitics inTable V. The overall loss is the sum of the component lossesdetermined in Equations (1) and (2).Future Work1. Derive a switching loss model, which will curve at low power2. Extend the model to an inverter and flyback. These should cover most types of converters in a building3. Redo boost experiment with a PCB4. Perform experimental validation for the inverter and flybackOutput Power (W)Efficiency (%)Efficiency Curve ModelsJust Conduction LossConduction and Switching LossBoost Converter Circuit Model (AC)Inductor Current(AC timescale)Component Currents (switching time scale)Triangle Current AnalysisHow to find converter loss?• Determine steady state currents in each component• For resistive loss elements:!"#$$,& = (& ∗ *+,$-• For diode loss elements: !./00,1 = 21 ∗ *345 + (1 ∗ *7802• (& , (: , and 2: from component datasheetResistive loss element currents• Inductor (L): *",+,$• Switch (Q): *H,+,$• Capacitor (C): *I,+,$Diode loss element currents• Bridge Diode (B): *J,+,$, *J,KLM• Boost Diode (D): *:,+,$, *:,KLMModel assumptions• Continuous conduction mode • Unity power factor• No output voltage ripple• 100% efficiency for determining currents• No switching and gate-drive losses... for nowHow to find component currents?• Take RMS or AVG for two timescales:• Switching frequency (i.e. 65 kHz)• AC 60 Hz time scale (not necessary for DC-DC boost)• On the switching timescale, every current can be represented by either:• A bilateral triangle (inductor, bridge)• An elevated right triangle (switch, boostdiode, capacitor)• Use orthogonality to combine waveforms of different frequency: *.,780 = *75N,7802 + Δ*.,7802• Component current expressions for simple model (without ripple).  Expressions for model with inductor current ipple are in the paper• Currents are all in terms of output power !P , output voltage 2P , and peak input voltage 2QR (= 2ST for DC/DC)• min(PLoss,AC/PLoss,DC) is the theoretical smallest possible ratio of component loss between the AC/DC boost and DC/DC boostTABLE I: Simple model of component currentsParameter AC/DC PFC DC/DC min(PLoss,AC/PLoss,DC)IL,rmsIB,rmsp2PoVpkPoVpk2IB,avg 4⇡PoVpk     IQ,rmsPopVoVpkq2Vo   163⇡VpkPopVoVpkpVo   Vpk 2ID,rms 4p3⇡PopVoVpkPopVoVpk163⇡ ⇡ 1.70ID,avgPoVoPoVo1IC,rmsPoVopVpkq163⇡Vo   VpkPoVopVpkpVo   Vpk 163⇡ ⇡ 1.70TABLE II: Model of component currents with rippleParameter AC/DC PFC DC/DCIL,rmsIB,rmsr576⇡L2P2o V2o +12⇡T2V 2o V4pk 64T2VoV 5pk+9⇡T2V 6pk12LVoVpkp2⇡r12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk2LVoVpkp3IB,avg4Po⇡Vpk  IQ,rmsvuuut2880⇡L2P2o V3o  7680L2P2o V2o Vpk+60⇡T2V 3o V4pk... 480T2V 2o V5pk+135⇡T2VoV6pk 128T2V 7pk12LVpkq10⇡V 3or⇣Vo Vpk⌘⇣12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk⌘2LVpkq3V 3oID,rmsr3840L2P2o V2o +80T2V 2o V4pk 45⇡T2VoV 5pk+64T2V 6pk12Lq5⇡V 3o Vpkr12L2P2o V2o +T2V 2o V4pk 2T2VoV 5pk+T2V 6pk2Lq3V 3o VpkID,avgPoVoPoVoIC,rmsr3840L2P2o V2o  720⇡L2P2o VoVpk+80T2V 2o V4pk 45⇡T2VoV 5pk+64T2V 6pk12Lq5⇡V 3o Vpkr⇣Vo Vpk⌘⇣12L2P2o Vo+T2VoV4pk T2V 5pk⌘2Lq3V 3o VpkG. Summary of Model CurrentsFinal expressions of all the component currents are given inTables I and II for the simple and ripple models, respectively.In Table I, the leftmost column shows the ratio of losspower per component between equivalent AC and DC boostconverters. For IQ,rms and IC,rms, this ratio is minimized atvery high Vo. RMS and average currents correspond to resistiveand diode losses, respectively.IV. MODEL VALIDATIONThis work validates the boost converter loss model througha transient PSIM 11.1.5 simulation over a 120 Hz period. Thsimulated boost converter is ideal, with either an AC/DC PFCor a DC/DC control loop. As shown in Tables III and IV, thesimulation results closely match the model.This work also validates the model with the experimentalprototype in Figure 3. The prototype is designed for an outputpower Po = 250 W, output voltage Vo = 350 V, and inputvoltage Vpk = 170 V. Its components, shown in Table V, arethe same between AC and DC boost experiments. Tables IIIand IV show the experiment to be somewhat consistent withthe model and simulation. As previously mentioned in Sec-tion II, the model only holds for prototypes with relativelyhigh efficiency (>90%).TABLE III: AC/DC PFC Boost Model Validation Currents (A):Po = 250 W, Vo = 350 V, and Vpk = 170 VParameter Model(simple)Model(ripple) Simulation ExperimentIL,rmsIB,rms2.153 2.161 2.162 2.356IB,avg 1.938 1.938 1.938 2.105IQ,rms 1.655 1.662 1.662 1.723ID,rms 1.376 1.381 1.382 1.323ID,avg 0.733 0.733 0.733 0.781IC,rms 1.165 1.171 1.171   V. AC VS DC EFFICIENCY OMPARISONThis section presents a direct comparison between ACand DC boost converters using the loss models developed inSections II and III. The analysis combines the componentcurrents from Table II with real component parasitics inTable V. The overall loss is the sum of the component lossesdetermined in Equations (1) and (2).Validation of AC/DC PFC BoostPO = 250 W, VO = 50 V, Vpk = 170 V Experimental Validation Setup• Model is validated through PSIM simulation and experi ent• Experiment has parasitic wire runs that cause oscillations and increase inp t current; this will be i proved in future work• Paramet ic model runs wit  VO = 200-400 V and PO = 100-500 W• In this range, AC/DC boost has 2.9 to 4.2 times the loss of DC/DC• Loss analysis shown for Vpk = 170 V and VO = 400 V

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AC vs. DC Boost Converters: A Detailed Conduction Loss Comparison

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