214 IEEE Proceedings of the 16th Euroean Conference on Power Electronics and Alications (EPE 214 - ECCE Euroe), Laeenranta, Finland, August 26-28, 214 Comarative Evaluation of Three-Phase Isolated Matrix-Tye PFC Rectifier Concets for High Efficiency 8V Sulies of Future Telco and Data Centers P. Cortes, D. Bortis, R. Pittini, J. W. Kolar This material is ublished in order to rovide access to research results of the Power Electronic Systems Laboratory / D-ITET / ETH Zurich. Internal or ersonal use of this material is ermitted. However, ermission to rerint/reublish this material for advertising or romotional uroses or for creating new collective works for resale or redistribution must be obtained from the coyright holder. By choosing to view this document, you agree to all rovisions of the coyright laws rotecting it.
Comarative Evaluation of Three-Phase Isolated Matrix-Tye PFC Rectifier Concets for High Efficiency 8V Sulies of Future Telco and Data Centers Patricio Cortes 1, Dominik Bortis 1, Riccardo Pittini 2 and Johann W. Kolar 1 1 Power Electronic Systems Laboratory, ETH Zurich Physikstrasse, 892 Zurich Switzerland Phone: +44 62 8 49 Email: cortes@lem.ee.ethz.ch URL: htt://www.es.ee.ethz.ch 2 Deartment of Electrical Engineering, Technical University of Denmark Kgs. Lyngby, Denmark Keywords << ower suly>>, <<Matrix converter>>, <<Power factor correction>>, <<Power suly>>, <<Efficiency>>. Abstract Due to the high energy consumtion in data and telco centers, the use of 8V or 4V facility-level distribution has been roosed as an alternative to the conventional AC distribution for a more efficient ower delivery structure. The voltage is owered from the three-hase mains by a PFC rectifier and in many cases a mains transformer is used to rovide galvanic isolation. In order to achieve a high efficiency in the voltage generation and to imlement the required isolation, a single-stage concet, such as a matrix-tye rectifier that enables PFC functionality and galvanic isolation in a single conversion, can be beneficial. In addition, due to the fact that with the matrix-tye rectifier the galvanic isolation is erformed with a high-frequency transformer, this results in a more comact rectifier system comared to conventional systems where the mains-frequency isolation transformer is located at the inut of the PFC rectifier. In this aer, an overview of isolated matrix-tye PFC rectifier toologies is given and a new converter circuit is roosed, analyzed and comaratively evaluated against another romising PFC rectifier concet, the hase-modular IMY-rectifier. 1 Introduction To imrove the energy efficiency in telco and data centers, the use of a ower distribution architecture (PDA) instead of an AC PDA has been roosed in the literature [1, 2]. The basic structures of a conventional AC PDA and a facility-level PDA are shown in Fig. 1. As can be noticed, the conventional AC PDA (cf. Fig. 1(a)) includes multile conversion stages, which lead to a strongly reduced overall ower distribution system efficiency. Tyically, at the AC distribution system s inut a double conversion Uninterrutible Power Suly (UPS) in combination with a bulky 5/6 Hz main transformer is utilized. The UPS rectifies the 4/48V AC into a voltage where an energy storage system, e.g. battery backu system, is connected. Then, the voltage is inverted back to 4/48V AC voltage that sulies the Power Distribution Unit (PDU). At the PDU, the voltage is steed down to a voltage suitable to the Power Suly Units (PSU), tyically between 9 and 264 V AC. In the PSU this AC voltage is then
4V (48V) -AC AC AC. 2V (28V) 1 -AC AC PSU 12V VR Fans loads (a) UPS PDU Rack (b) 4V (48V) -AC AC 8V. 8V UPS PDU Rack PSU 12V Fig. 1: Power distribution architectures (PDA) for data and telco centers, (a) conventional AC ower distribution and (b) 8V facility-level ower distribution. VR Fans loads 4V (48V) -AC AC 8V. 8V UPS PDU Rack PSU 12V Fig. 2: 8V facility-level PDA with an isolated three-hase buck-tye PFC rectifier that features PFC functionality and rovides galvanic isolation with a high-frequency transformer. VR Fans loads again converted to a voltage which is finally due to the large conversion ratio steed down by an isolated / converter to the 12V required by the different loads in the servers. Deending on the efficiency of the different comonents, the overall efficiency of such an AC PDA is between 5 % and 7 % [1]. In a facility-level PDA, however, several conversion stes can be avoided. As shown in Fig. 1(b), the /AC conversion in the UPS, the transformer in the PDU and the AC/ conversion in the PSU are eliminated, resulting in a higher efficiency of the ower distribution system, e.g. 72.7 % efficiency [1] (assuming 95. % efficiency of the AC/ converter). In the last years, the selection of the otimal voltage level for the facility-level PDA has been discussed in the literature and also several organizations are working on the standardization of low voltage grids, where mainly the use of 8V [2,, 4] or 4V [1] is roosed for a more efficient ower distribution architecture. However, a discussion about the otimal converter toology that sulies the facility-level ower distribution is still missing in the literature. Since the facility-level PDA is also owered from the three-hase 4V/48V mains, with the mentioned voltage selection of either 8V or 4V boost-tye PFC rectifiers are no more suitable because the outut voltage of boost-tye PFC rectifiers has to be at least above the eak value of the mains line-to-line voltage; thus, with a wide inut voltage range u to 48Vrms, the outut voltage is tyically selected to 7V to 8V. Consequently, a three-hase buck-tye PFC toology has to be selected which allows to directly ste down the varying inut voltage to the roosed 8-4V. In addition, the overall system volume can be strongly reduced by omitting the bulky mains-frequency transformer if the galvanic isolation is realized with a subsequent / conversion stage which contains a high-frequency isolation transformer (cf. Fig. 2). Furthermore, in order to achieve a high overall AC/ conversion efficiency, instead of this conventional two-stage conversion concet, a three-hase matrix-tye buck rectifier toology which rovides PFC functionality and galvanic isolation in a single conversion can be used; thus also no large -link caacitance for intermediate energy storage is required. In this aer, a review of different three-hase matrix-tye buck-tye isolated PFC rectifier toologies is resented in Section 2 and the most romising toology, regarding efficiency and realization effort, is
AC/AC AC/ /AC (a) (b) AC/ /AC AC/ /AC (c) (d) Fig. : Toologies of isolated matrix-tye three-hase AC/ converters, (a) direct matrix converter. (b) indirect matrix converter. (c) VIENNA rectifier III and (d) IMY-rectifier. further analyzed in Section, and is comared in Section 4 with a reviously analyzed hase-modular matrix-tye PFC rectifier system, the IMY-rectifier [5]. 2 Isolated Matrix-Tye PFC Rectifiers Tyically, the single-stage ower conversion can be realized with a direct matrix-tye PFC rectifier that directly converts the mains-frequency AC voltage into a high-frequency AC voltage which is sulied to a high-frequency isolation transformer and whose secondary voltage is then rectified to the desired outut voltage as roosed in [6] (cf. Fig. (a)). As can be noticed, in this toology for the direct AC/AC conversion a large number of semiconductor devices is needed, thus, also the control and modulation scheme comlexity are high. In order to strongly reduce the system comlexity and in most of the cases also the number of switches, the direct AC/AC conversion stage can be slit into an AC/ and a /AC conversion, which is then due to the still missing intermediate energy storage a so called indirect matrix-tye PFC rectifier. As roosed in [7, 8], e.g. a conventional buck-tye PFC rectifier in combination with a hase-shift / converter could be used (cf. Fig. (b)). In this case, however, the conventional buck-tye PFC rectifier suffers from high conduction losses in the high-frequency diodes which are needed in series to the switches [9]. Nevertheless, since with the indirect matrix-tye rectifier also other more efficient AC/ converter toologies can be combined, it offers a high flexibility and is attractive for the realization of the active front end of the PDA. Therefore, in order to fully utilize the otential of indirect matrix-tye isolated PFC rectifiers, in this aer it is roosed to substitute the conventional buck-tye PFC rectifier by a simle diode rectifier with an integrated active filter as resented in [1, 11], which in combination with
the isolated / converter rovides galvanic isolation and a highly efficient PFC functionality (cf. Fig. 4, [12]). As an alternative, the indirect matrix-tye converter in Fig. (b) could be modified in such a way that one bridge-leg of the / converter is again integrated into the inut rectifier stage, thus results in the VIENNA rectifier III [1] which could be seen as hybrid combination of a direct and an indirect matrix-tye rectifier (cf. Fig. (c)). However, even if the system comlexity and the number of switches are further reduced only five instead of ten switches are needed the large number of diodes leads to high conduction losses. Consequently, this toology is not further considered in this aer. Utilizing the indirect matrix-tye rectifier concet, a different aroach is to use hase-modular converters, e.g. the isolated matrix-tye Y-rectifier (IMY-rectifier) as roosed in [5, 14], where the three-hase indirect matrix-tye converter is slit into three searated single-hase indirect matrix-tye converters (cf. Fig. (d)). Besides the advantage of modularity, since to each of the single-hase converters only the single-hase voltage is alied, 6V instead of 12V semiconductor devices can be used, which feature a lower on-state resistance and imroved switching behavior. In addition, the converter can be controlled with a simle modulation scheme that enables soft-switching for each switching transition. Hence, due to the low system comlexity and the exected high efficiency, the hase-modular IMY-rectifier is another suitable otion to suly the PDA. Therefore, in the next section the roosed three-hase Isolated Integrated Active Filter Matrix-tye (I 2 AFM) PFC rectifier is resented and will be evaluated in comarison to the hase-modular IMY-rectifier. Isolated Integrated Active Filter Matrix-tye PFC Rectifier.1 Oerating Princile As shown in Fig. 4, the rectifier stage of the roosed I 2 AFM PFC rectifier consists of a simle three-hase diode bridge rectifier with an additional injection circuit, the integrated active filter (IAF), comrising a high-frequency bridge-leg with the switches S 1 and S 2, the inductance L and the low-frequency bidirectional switches S a, S b and S c. As can be noticed, as long as the injection circuit is not enabled, that means S 1 and S 2 are not switched, the inut stage of the I 2 AFM rectifier is working as a simle three-hase diode bridge rectifier and a highly distorted inut current is flowing through the two diodes connected to the highest and lowest inut voltage (cf. Fig. 5(c) for t < 4 ms). However, in order to achieve sinusoidal inut currents drawn from the mains, the switches S 1 and S 2 of the injection circuit can be controlled in such a way that always a third harmonic current is imressed into the hase with the smallest inut absolute voltage, i.e. the inut hase which would not conduct current at that time (cf. Fig. 5(d) for t > 4 ms). Since in the three-hase mains every 6 of the mains eriod the smallest absolute inut voltage (v a, v b or v c ) alternates between the inut hases a, b and c, the roer hase has to be selected by turning on one of the switches S a, S b or S c (cf. Fig. 5(b) for t > 4 ms). As analytically described in [1, 11], if during each 6 interval the injected current is roortional to the smallest inut voltage, i.e. a 6 -ortion of a sine wave, and a constant outut ower is delivered by the / converter stage, with this modulation scheme all inut currents will show a sinusoidal shae (cf. Fig. 5(c) for t > 4 ms). The major advantages of the IAF rectifier are the relatively low imlementation effort with the low comonent count, the simle modulation scheme and the high exected efficiency, since on the one hand for the bridge rectifier slow switching rectifier diodes with a low on-state voltage dro can be used and on the other hand in the injection circuit always only the hase current with the lowest instantaneous value has to be rocessed. However, assuming a certain needed intermediate caacitance C dc in order to kee the inductance in the commutation ath of the injection circuit and the / converter low, the outut voltage v dc will not be constant but will vary with a sixfold mains-frequency (cf. Fig. 5(e)). In fact, the outut voltage is always equal to the maximum hase-to-hase inut voltage since it is now defined by the diode rectifier and thus the average outut voltage can also vary with the ossible wide inut voltage range of the local mains. Therefore, in order to eliminate the sixfold mains-frequency and to avoid large outut voltage variations, the highly romising IAF rectifier has to be combined with a subsequent / converter that rovides an isolated and constant outut voltage. In the / stage, both half-bridges are modulated with a 5 % duty cycle, whereas the outut voltage is controlled by the hase shift between the two half-bridge voltages. As already mentioned, since the instantaneous inut voltage is varying
L out v a L F v b v c i a i b i c S a S b S c L S 1 i L N 1 : N 2 C D,out out v dc v v out C dc C F S 2 Injection circuit } AC/ } / Fig. 4: Proosed Isolated Integrated Active Filter Matrix-tye (I 2 AFM) PFC rectifier. (a) (b) (c) (d) Inut voltages [V] Switching signals Inut currents [A] IAF current [A] 4 2 2 25 5 4 45 5 55 6 1 S a 1 S b 1 S c 1 S 1 2 25 5 4 45 5 55 6 2 2 25 5 4 45 5 55 6 2 _ i L i L v a v b v c i a i b i c 2 25 5 4 45 5 55 6 time [ms] (e) (f) (g) (h) voltage [V] Duty cycles Outut voltage [V] Outut voltage [V] 6 4 2 2 25 5 4 45 5 55 6 1..5 2 25 5 4 45 5 55 6 6 4 2 2 25 5 4 45 5 55 6 6 4 2 2 25 5 4 45 5 55 6 time [ms] v dc d A,B v out v D,out Fig. 5: Simulated waveforms of the I 2 AFM PFC rectifier, where the IAF rectifier is turned on at time t = 4 ms, while the / stage is already in steady-state oeration at t = ms, (a) hase inut voltages, (b) switching signals of the IAF rectifier, (c) hase inut currents, (d) inductor current in the injection circuit, (e) intermediate -link voltage, (f) duty cycle of the / converter, i.e. the hase shift between the half-bridge voltages, (g) rectified outut voltage of the transformer and (h) controlled outut voltage. over time, the hase shift between the two half-bridge, i.e. the duty cycle, has to be roerly adated in order to obtain a constant outut voltage (cf. Fig. 5(f)-(h)). In addition, it is assumed that the leakage inductance of the isolation transformer is large enough and thus enables soft-switching for each switching transition. This almost eliminates all switching losses and only slightly increases the conduction losses in the switches, thus results in high overall system efficiency.
Table I: Current stresses in the semiconductor devices of the I 2 AFM PFC rectifier. (Î in denotes the mains hase current amlitude and I dc is the outut current). Comonent Average current RMS current Inut diodes Î in 2 Injection circuit switches S a,s b,s c Half-bridge switches S 1,S 2 Antiarallel diodes of switches S 1,S 2 - converter switches - converter outut diodes Î in 1 Î in Î in N 2 I dc N 1 2 I dc 2 2 2 ln( ) 2 ln 1 + 1 2 1 2 q 1 Î in 6 + q 8 1 Î in Î in r Î in r N 2 2 I dc N 1 2 I dc 12 8 2 8 6 + 2 ln 2 6 2 ln 2.2 Converter Design For the design and otimization of the roosed I 2 AFM PFC rectifier, first the current stresses in the different comonents have to be calculated, which for the IAF PFC rectifier was already done in [11]. A summary of the current stresses in the semiconductor devices of the I 2 AFM PFC rectifier is shown in Table I. There, a large outut inductor of the / stage is assumed, whereby the switching frequency rile of the outut current can be neglected. In order to enable a fair comarison of the roosed I 2 AFM PFC rectifier and the IMY-rectifier, the design of the I 2 AFM PFC rectifier is erformed for the same oerating conditions as described in [5] which are listed again in Table II. Since in the I 2 AFM PFC rectifier the voltage stress of all semiconductor devices is defined by the eak hase-to-hase inut voltage of the three-hase mains, 12V instead of 6V semiconductor devices have to be used. A major art of the losses in the IAF PFC rectifier result due to the conduction losses in the inut bridge rectifier, which rectifies the low frequency inut voltage. Therefore, silicon diodes with low forward voltage dro have to be selected, in order to kee the efficiency high. Based on the secification given in Table II, with the selected 12V/45A diodes (DSP45-12A) the conduction losses in the inut rectifier are 2.6 W. For the bidirectional switches S a, S b and S c of the injection circuit which also switch at low switching frequency two times the mains frequency the switching losses are negligible and therefore can be imlemented with two standard IGBTs connected in anti-series that feature a low forward voltage dro. Alternatively, it would be also ossible to use reverse blocking IGBTs in antiarallel connection, which would reduce the conduction losses from 6.6 W to 5 W. However, due to the limited availability of RB-IGBT, 12V/4A standard IGBTs (IHW4T12) with integrated antiarallel diodes are used. In contrast to the bidirectional switches S a, S b and S c, for the switches S 1 and S 2 of the high-frequency bridge-leg, that controls the current over the IAF inductor L, the switching losses have to be considered. Due to the needed blocking voltage of 12V silicon MOSFETs are not alicable, thus the selection of the roer switch technology is limited to either IGBTs which are otimized for fast switching alications (e.g. 12V, 4A, IGW4N12H) or Silicon Carbide (SiC) MOSFETs (12V, 8 mw, C2M812D). Although the conduction losses in both cases are low (4.6 W with IGBTs and 1.6 W with SiC-MOSFETs), Table II: Electrical secifications used for the comarative evaluation of the I 2 AFM PFC rectifier and the IMYrectifier. Parameter Value Nominal ower P 7.5 kw Outut voltage V out 8 V Inut voltage V N 4 V h h,rms Switching frequency f sw 48 khz
Table III: Main comonents of the I 2 AFM PFC rectifier rototye. Comonent Value/details Inut diodes 12 V/45 A rectifier diodes (DSP45-12A) Inj. circuit switches S a,s b,s c 12 V/4 A IGBTs (IHW4T12) Half-bridge switches S 1,S 2 12 V/1.6 A SiC MOSFETs (C2M812D) / converter switches 12 V/1.6 A SiC MOSFETs (C2M812D) / converter outut diodes 12 V/54 A SiC diodes (C4D412D) IAF inductor L 8 µh, 1 air E55 N87 cores, x1.4 mm air ga, 6 turns of 2 mm,.1 mm/175 strands litz wire Isolation transformers Stack of two E55 N87 cores, N 1 /N 2 = 16/16, 4 µm/27 strands litz wire (4 in arallel) Filter inductor L out 2x497 µh, E55 N87 cores, x.8 mm air ga, 4 turns of 2.5 mm solid coer wire the switching losses in the IGBTs (6 W) are five times higher than for the SiC-MOSFETs (6.7 W) assuming a switching frequency of 48 khz. Consequently, the switches S 1 and S 2 of the injection circuit as well as the switches of the / converter s full-bridge are realized with SiC-MOSFETs, even if the full-bridge can be oerated in softswitching at nominal outut ower. However, namely at low load conditions, where the current in the leakage inductance is no more sufficient to charge/discharge the outut caacitances of the switches, soft-switching is lost resulting in high switching losses. The conduction losses in the / converter s full-bridge are calculated to 44.9 W at nominal outut ower. Due to the high switching frequency and the hard commutation of the outut rectifier, which would lead to high reverse recovery losses if silicon diodes would be used, the outut diode bridge is realized with 12V SiC Schottky diodes (C4D412D). Even if the reverse recovery losses can be neglected in this case, the conduction losses in the outut rectifier of 8 W (together with the conduction losses of the full-bridge) are dominating the achievable efficiency of the / stage, since the forward voltage dro of SiC Schottky diodes comared to silicon diodes is relatively high. In order to kee the inut filter effort low and due to reasons of system controllability, the inductor L of the IAF rectifier s injection circuit is designed with resect to a maximum current rile which has to be below 5 % of the eak inut current. Based on this assumtion, an inductor otimization considering different core tyes and wires (solid and litz wire) is erformed, and the inductor design offering the best comromise between losses and volume is selected. The same otimization rocedure of the magnetic comonents was also alied for the design of the outut inductor L out, however with a lower current rile of 2.5A (25 %), as well as for the isolation transformer. The turns ratio of the isolation transformer was selected to N 1 /N 2 = 1, which still allows a 15 % voltage margin for the outut voltage control at minimum inut voltage. Details concerning the design of the magnetic comonents and a list of the selected semiconductor devices are summarized in Table III. The corresonding D CAD model of the designed laboratory rototye is visualized in Fig. 6(b). In order to show the lacement of the described ower comonents, the to board containing the EMI filter, control board and outut caacitors has been omitted. Based on this design, a total volume of 4.68 dm and/or a ower density of 1.6 kw/dm is achieved. For the sake of comleteness, it has to be mentioned that the / stage of the laboratory rototye is advantageously realized with two arallel / converters (cf. Fig. 6(a)). Consequently, on the one hand the efficiency can be further increased, esecially in art load below 5 % where e.g. one / converter can be turned off, and on the other hand the current rile in the outut caacitor can be reduced by interleaving the switching signals of two arallel / converters.
L out IAF inductor Power board Inut caacitors a b c Sa Sb Sc S1 L il C dc N1: N2 C out v out inductor Isolation transformer S2 CF L out N1: N2 Heatsink Outut rectifier board inductor Isolation transformer (a) (b) Fig. 6: I 2 AFM PFC rectifier 7.5 kw laboratory rototye, (a) circuit diagram with two arallel interleaved / converters, (b) D CAD model of the converter without the to PCB. 4 Comarative Evaluation of Three-Phase Isolated Matrix-Tye PFC Rectifiers Based on the secifications given in Table II, now the erformance of the roosed and designed I 2 AFM PFC rectifier is comared to the also romising hase-modular IMY-rectifier resented in [5] (cf. Fig. (d)). Two alternative imlementations for each PFC rectifier toology are considered for the comarative evaluation: I 2 AFM PFC rectifier with a / stage consisting of only one / converter; I 2 AFM PFC rectifier with a / stage consisting of two arallel / converters; IMY-rectifier where each switch of the full-bridge is imlemented with only a single MOSFET of the CFD-CoolMOS series from Infineon (IPW65R41CFD); IMY-rectifier where each switch of the full-bridge is imlemented with two arallel MOSFETs of the CFD-CoolMOS series (IPW65R41CFD). For the efficiency calculations of the two considered imlementations of the I 2 AFM PFC rectifier, the analytical equations for the current ratings given in Table I and the devices listed in Table III are used. The efficiency of the hase-modular IMY-rectifier is calculated according to the design resented in [5]. In addition, for both PFC rectifier toologies it is considered that in the full-bridges soft-switching is only achieved above a certain minimum outut ower and thus in low load oeration the switching losses have to be taken into account. The calculated efficiencies of the different imlementations as a function of the load ower are shown in Fig. 7(a). At nominal load, with the I 2 AFM PFC rectifier and a / stage consisting of only one / converter an overall efficiency of 97 % can be achieved, which can be increased to 97.6 % if a second / converter is connected in arallel. The maximum efficiency of 97.7 % is achieved at 25 % of the nominal load, whereas 2.8 % (12.1W) of the losses are generated in the AC/ stage and 79.2 % (45.9W) in the / stage. As already mentioned, in order to imrove the low load behavior of the I 2 AFM PFC rectifier, the second / stage is turned off when the load current is below a certain limit and therefore the efficiencies of both imlementations, with either one or two / converters, are the same (cf. Fig. 7(a)). In contrast, the achievable efficiency of the IMY-rectifier is considerably lower, which is 95. % if only one MOSFET is used er switch and 96 % if two arallel MOSFETs are used er switch [5] (cf. Fig. 7(a)). The main reasons for the difference in efficiency can be found in the conduction losses of the inut diode rectifier, the full-bridge and the transformer, which in the IMY-rectifier are almost twice to three times higher than those of the I 2 AFM PFC rectifier (cf. Fig. 7(b)). In all three cases this can rincially be
Efficiency, % 1 98 96 94 92 I 2 AFM PFC rectifier (1-/) I 2 AFM PFC rectifier (2-/) IMY-rectifier (1 switch) IMY-rectifier (2 switches) Losses,W 14 12 1 8 6 4 2 I 2 AFM IMY 9 2 4 6 8 1 Load, % EMI filter Inut diodes Injection circuit S a,b,c Half-bridge switches S 1,2 / full-bridge Outut diodes Transformer inductor (a) (b) Efficiency, % (c) 98 97.5 97 96.5 96 I 2 AFM PFC rectifier (1-/) I 2 AFM PFC rectifier (2-/) IMY-rectifier (2 switches) 95.5 IMY-rectifier (1 switch) 95.8.9 1. 1.1 1.2 1. 1.4 1.5 1.6 Normalized converter cost Fig. 7: Comarative evaluation of the I 2 AFM PFC rectifier and the IMY-rectifier, (a) achievable efficiency at different load conditions, (b) calculated loss distribution at nominal load of 7.5 kw and (c) resulting efficiencies at nominal load of 7.5 kw with resect to the normalized converter costs considering the ower semiconductors and main assive comonents. exlained by the higher number of comonents which are needed in the IMY-rectifier comared to the I 2 AFM PFC rectifier; 12 instead of 6 inut diodes, 12 instead of 4 switches in the full-bridge and transformers instead of 1 transformer. In addition, each inut diode of the IMY-rectifier is conducting the inut current during one half-cycle of the mains voltage, while in the I 2 AFM PFC rectifier an inut diode is only conducting during one third of the mains eriod. Hence, due to the same inut current amlitude in both converter toologies, for the IMY-rectifier this results in higher average and RMS currents and consequently in higher conduction losses. Furthermore, even if in the IMY-rectifier 65V-CoolMOS devices with a suerior low on-state resistance can be used, the three times larger number of switches results in more than twice the conduction losses in the full-bridge comared to the I 2 AFM PFC rectifier. Desite the fact that additional losses are generated in the injection circuit (cf. Fig. 7(b)), the IMY-rectifier can t comete in efficiency, since the losses in the injection circuit are moderate comared to the overall I 2 AFM PFC rectifier losses (cf. Fig. 7(b)). Besides the achievable efficiency the comarative evaluation also considers another asect, namely the resulting material costs of each PFC rectifier toology. In Fig. 7(c) a normalized cost comarison considering the costs of the ower comonents is shown, where the rices for the semiconductor devices and assive comonents have been extracted from distributor s data, i.e. the rice for 1 ieces. It can be noticed that for both PFC rectifier toologies the costs are very similar (difference of only 8 %) if in the IMY-rectifier only one MOSFET er switch and in the I 2 AFM PFC rectifier only one / converter is used (Fig. 7(c)). Imroving the efficiency of both rectifier toologies by aroximately.6 % (45W), by either adding a second MOSFET er switch in the IMY-rectifier or a / converter in the I 2 AFM PFC rectifier, increases the corresonding costs by % and 28 %, resectively. This relatively strong increase in costs clearly shows that the exensive semiconductor devices account for the largest share of the overall costs.
5 Conclusions This aer gives an overview of isolated matrix-tye PFC rectifier toologies suitable for facility-level PDA for more efficient telco and data centers. In the comarative evaluation of isolated threehase PFC rectifier systems it is shown that matrix-tye PFC rectifier toologies offer the advantage of erforming PFC functionality and galvanic isolation in a conversion single-stage. On the one hand, this otentially enables higher system efficiency comared to two-stage concets and on the other hand, the bulky mains transformer, which is tyically used in existing ower distribution systems, can be omitted. Furthermore, in this aer a new isolated matrix-tye PFC rectifier toology is roosed, the I 2 AFM PFC rectifier. The I 2 AFM PFC rectifier features an indirect matrix converter structure which basically is a combination of an AC/ stage and a subsequent / stage without intermediate energy storage elements. The rectification with PFC functionality is erformed with a simle three-hase diode rectifier circuit with an additional injection circuit, the IAF-rectifier. The major advantages of the IAF-rectifier are the relatively low imlementation effort with the low comonent count, the simle modulation scheme and its high efficiency. The erformance of the designed I 2 AFM PFC rectifier is evaluated in comarison with the hase-modular IMY-rectifier, which is also a romising solution for the realization of the active front end of the PDA. It is shown that with the roosed I 2 AFM PFC rectifier an almost 2 % higher efficiency can be achieved comared to the IMY-rectifier, even if the material costs are aroximately the same. With a single / outut stage of the I 2 AFM system the achievable efficiency at nominal load is 97 %, and can be imroved u to 97.6 % if a second / converter is used in arallel. Future work includes the realization of a 7.5 kw laboratory rototye to exerimentally verify the resented converter erformance. References [1] A. Pratt, P. Kumar, and T. Aldridge, Evaluation of 4v dc distribution in telco and data centers to imrove energy efficiency, in Proc. of 29th International Telecommunications Energy Conference (INTELEC), 27,. 2 9. [2] E. Waffenschmidt and U. Boeke, Low voltage dc grids, in Proc. of 5th International Telecommunications Energy Conference (INTELEC), 21,. 1 6. [] M. Noritake, T. Ushirokawa, K. Hirose, and M. Mino, Verification of 8V dc distribution system availability based on demonstration tests, in Proc. of rd International Telecommunications Energy Conference (INTELEC), 211,. 1 6. [4] M. Salato, A. Zolj, D. Becker, and B. J. Sonnenberg, Power system architectures for 8V dc distribution in telecom datacenters, in Proc. of 4th International Telecommunications Energy Conference (INTELEC), 212,. 1 7. [5] P. Cortes, L. Fässler, D. Bortis, M. 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