Analytical Power Loss Evaluation of 5 level H-Bridge with Coupled Inductor and Series Connected H-Bridge for PEBB Applications

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(1)PEDS2009. Analytical Power Loss Evaluation of 5 level H-Bridge with Coupled Inductor and Series Connected H-Bridge for PEBB Applications Huan H.Wang, Student Member, IEEE, Ashwin M. Khambadkone, Senior Member, IEEE Department of Electrical and Computer Engineering National University of Singapore Singapore 117576 Telephone: (65) 6516-5257 Email: [email protected]. I. ABSTRACT To realize the Power Electronics Building Blocks (PEBB) structural’s functional and spatial distribution partitioning, half bidge or H-Bridge converter are commonly used as the basic structure. Complicated converters for PEBB can be achieved by combinations of the basic building blocks. Single phase five level H-Bridge (5L-HB) with Coupled Inductor and Series Connected H-Bridge (5L-SCHB) are two important combinations of H-Bridge for PEBB applications. The aim of this paper is to evaluate the power loss of semiconductor devices in the single phase 5L-HB with Coupled Inductor and 5L-SCHB using analytical method. Conduction loss as well as switching loss are modeled based on semiconductor devices data sheet information, circuit current and voltage waveforms during all operating conditions. The modeling benefits the prediction and further investigation of the power loss distribution in other PEBB applications. The results can be used to justify the most suitable converter topology for PEBB applications according to the loss distribution. Index Terms—Power Loss Distribution, Power Electronics Building Blocks (PEBB), H-Bridge, Converter with Coupled Inductor.. II. I NTRODUCTION PEBB are a set of plug-and-play power electronics modules with both networking and stand-alone functionality. Aside from the reduction in production costs due to standardized components, the benefits to the end users are substantial, including reduced design and testing time [1]. The determination of the power loss dissipation in PEBB applications is a potential problem. This is because of power loss dissipation, heat is generated, which should be conducted away from the devices using some heat-sink. Heat-sink design is important for PEBB and the prior loss evaluation is thus critical. The evaluation of the power loss distribution would determine the best choice of the converter topology. No matter the optimal design goal is to minimize the size, the losses, or combination of them, the converter topology selection for PEBB applications would always rely on reliable actuate loss models for the system under a variety of operating conditions. Various publications in the literature provide methods for predicting the power losses in power electronic circuits. In. 458. case that both the operating current and applied DC bus voltage are constant, the loss calculation can be done according to the energy curve on the data sheet [2]. It is reported that the switching losses generated during one sine half-wave are about identical to the switching losses generated if an equivalent direct current is applied [3] [4] [5] and [6]. However, the method used for power loss calculation is not a complete and a general solution. This may not be suitable for loss determination for general PEBB, since the manufacturers offer the energy curves only in special cases. One possible solution to determine the distributed power losses is to measure the switching behavior of the converter circuit. But the solution needs complicated calculations, which is actually a verification process rather than a prediction of solution. From [7], the loss calculation considers the rated values specified in data sheet, neglecting the difference between the practical values and the rated values. In addition, only the IGBT power loss is evaluated excluding the diode. In this paper, an improved comprehensive analytical method to analyze the power loss of semiconductor devices for PEBB applications is proposed based on data sheet and dynamic characteristics of the semiconductor devices. The proposed method is useful for investigating the converter circuits and it is easy to observe the relationship between the losses and device parameters. The result can be used for selecting suitable converter topology for PEBB applications. III. P OWER LOSS MODELING OF SEMICONDUCTOR DEVICES DERIVED FROM H-B RIDGE The power losses of semiconductor devices, which are composed of conduction and switching losses are the dominating reason of the power dissipation in the converter design. In the PEBB applications, H-Bridge is always selected as the fundamental structure. The scheme of H-Bridge is described in Fig. 1(a). Different combinations of H-Bridge can be made to increase the number of voltage levels and thus decrease the THD of the output current. Thus in this section, the power loss distribution modeling is first analyzed in single phase H-bridge converter (3L-HB) as shown in Fig. 1(a). A. Basic ideas and assumptions of power loss modeling At first, for the following calculations, the semiconductor devices’ (IGBT and Diode) piecewise linearizing character-.

(2) PEDS2009. T1 VDC T3. T2 D1 R load Io D3. frequency, during each switching interval the current flowing through devices could be viewed as constant, which is equal to the instantaneous current through the load. Since both the conduction loss and switching loss are related to the semiconductor devices’ characteristics, the generic-switch switching characteristics of IGBT and Diode are investigated in Fig. 2. [8] [9]. D2. Vo. D4. T4. (a) three level H-Bridge (3L-HB). D7. L1. T2 D1 I RL o. L2. Vo. D3 T3. D2 D6. D4 T4. D8. D1 T 2. D2. T5. D5 T 6. VDC. D4. T7. D7 T 8. . . . . .

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(6). . VDC. T1. . D5. D8. B. Conduction Losses. (c) 5L-SCHB converter Fig. 1: Schemes of Converter Topologies for PEBB Applications. istics is assumed. That means eq. (1) is available for the modeling. 0 , VCE < VCEO (1a) iC = VCE −VCEO , VCE ≥ VCEO . R on igbt 0 , VF < VF O iF = VF −VF O (1b) , VF ≥ VF O . Ron diode Where, Ron igbt , VCEO , VCE and iC are conduction resistance, threshold voltage, voltage and current through IGBT during conduction process respectively. Ron diode , VF O , VF and iF are all for diode and have the same meaning. Secondly, different PWM control will reflect the conduction time and thus the current flowing through the semiconductor devices, so they will cause different power loss dissipation. This paper only explores the power losses in converters under the typical sinusoidal modulation, and meanwhile working under continuous current mode (CCM). For the PWM control with this assumption, the modulation function can be described in (2). M (θ) = sin (θ + φ) , M (θ) ∈ [−1, 1] .. (2). Where, φ is the phase angle between the output current and voltage. If the modulation index is M , the duty cycle D of IGBT can be expressed as (3a). When the IGBT is turn off, the parallel diode will be turn on. Thus, the diode duty cycle is (1 − D) as shown in (3b). 1 [1 + M sin (θ + φ)] (3a) 2 1 (3b) 1 − D = [1 − M sin (θ + φ)] 2 An important assumption is that the switching frequency should be high. If the converter is operated under high D=. 459. The conduction loss is due to the semiconductor devices’ conduction characteristics and thus related to current through device and the device’s DC electrical characteristics, so it mainly depends on the modulation function. The conduction loss of IGBT Pcon igbt and diode Pcon diode can be calculated respectively following the processes in (4) and (5). Pcon. igbt. IC. ave. IC. Pcon. rms. diode. IF IF. = IC ave · VCEO + Ron π 1 = iC · D · dθ 2π 0 π 1 = i2 · D · dθ 2π 0 C. ave. rms. igbt. · IC2. = IF ave · VF O + Ron diode · IF2 π 1 = iF · (1 − D) · dθ 2π 0 π 1 = i2 · (1 − D) · dθ 2π 0 F. rms. (4a) (4b) (4c). rms. (5a) (5b) (5c). Where, IC ave and IC rms are the average and RMS current for IGBT respectively. IF ave and IF rms are for the diode. îo is the peak value of the output sinusoidal current. Four times the sum of Pcon igbt and Pcon diode gives the total conduction loss. C. Switching Losses From Fig. 2, the semiconductor devices’s switching loss consists of turning on loss, turning off losses, and reverse recovery losses. The switching loss is related to the switching frequency, the current through the device and the device’s dynamic characteristics, especially the switching time. In converter with high frequency, switching loss is main part of power losses, and therefore the switching losses need to be known in detail as below. Information of the practical curves and data values from semiconductor devices manufacture ’s data sheet are need to describe the different real current in.

(7) PEDS2009. the switching process. The IGBT’s switching characteristics in Fig. 2 is described as follows,. loss is derived in (18).. During the turning on process with quite small rising time tr , the current flowing through IGBT can be linearized as a function (6). The voltage during this interval will keep the value as shown in (7). The rising time mainly depends on the actual current through the device and is thus related to the output current io . Two reasonable parameters a and b are selected to describe the relation between the rated curve in data sheet and practical curve. They will work to improve the model performance. An approximation function could be given in (8). With the switching frequency of fs , the IGBT turning on power loss Pon igbt could be derived via (9). io (t − t1 ) t 2 − t1 Vr = VDC îo sin θ tr = trN a + b ICN π t2 fs Vr ir tr dθ ight = 2π 0 t1 ir =. Pon. , t ∈ [t1 , t2 ]. (6). , t ∈ [t1 , t2 ]. (7) (8). , t ∈ [t1 , t2 ]. (9). 2) Reverse recovery interval t ∈ [t2 , t4 ]: The current keeps increasing after the time t2 , and the value finally arrives at t3 with a peak value larger than the output current by IRR as shown in (10), which is indicated as the reverse recovery current and depends on rated value IrrN and output current. From t3 to t4 , the current decreases to output current value and keep the value during the following conduction process. The reverse recovery current Irr is approximated in (11). îo sin θ (10) IRR = IrrN g + h ICN IRR , t ∈ [t2 , t3 ] −t2 (t − t1 ) irr = tI3RR (11) (IRR +Io ) (t − t ) , t ∈ [t3 , t4 ] 3 t4 −t3 With the same reason as above, parameters g, h, l and k are selected to approximate the relationships between the rated values and practical values. For easy calculation, the voltage is roughly considered to be a constant value in (12). Equation (13) is to describe the practical reverse recovery time trr . The reverse recovery losses Prr igbt is derived in (14). Vrr = VDC. l+k. trr = trrN Prr. ight. =. fs 2π. 0. π. . îo sin θ ICN. . t4. Vrr irr trr dθ. , t ∈ [t2 , t4 ]. (12) (13). , t ∈ [t2 , t4 ]. (14). t2. Where, trrN are rated reverse recovery time. 3)Turning off interval t ∈ [t8 , t9 ]: With similar analyzing as previous, the switching off current if , voltage Vf , and falling time tf are linearized in (15), (16) and (17) respectively. The final switching off power. 460. io (t − t9 ) t 9 − t8 Vf = VDC îo sin θ t f = tf N c + d ICN π t9 fs Vf if tf dθ ight = 2π 0 t8 if =. 1) Turning on interval t ∈ [t1 , t2 ] :. Pof f. , t ∈ [t8 , t9 ]. (15). , t ∈ [t8 , t9 ]. (16) (17). , t ∈ [t8 , t9 ]. (18). Finally, the distributed switching power losses of IGBT in 3L-HB as shown in Fig. 1(a) are in (19), (20) and (21). b ˆ2 aˆ (19) Pon igbt = VDC trN fs io io + 2π 8ICN d ˆ2 cˆ Pof f igbt = VDC tf N fs (20) i io + 2π 8ICN o (lh + gk) IrrN îo lgIrrN Prr igbt = VDC trrN fs + 4 2πICN (hk + 2kICN ) î2o (21) + 2 8ICN Where, a, b, c, d, l, h, g and k are parameters to describe the differences between the practical values and rated values. tf N , IrrN , and ICN are all rated values, which can be found from semiconductor manufactures’ data sheet. îo is the peak current through the load. cos φ is the power factor and fs is the switching frequency. Similar derivations can be also done for diode. Equations (19), (20) and (21) are all the type of function y = A + Bio + Ci2o ,. (22). which is indicated in [2]. The simplified function (22) is used for rough evaluation of energy dissipation of semiconductor devices for industry application. The modelings in [7] [9] are very special case of the above modeling derived. In case with accuracy requirement, the improved modeling derived is an available effective solution. D. Total Power Losses Distribution The improved calculation derived above is carried out to investigate the behavior of semiconductor losses. The distribution of the power losses for the 3L-HB can be found in Fig. 3. From the derived equations, it can be also found that the power losses distribution has complex dependencies between the losses, device parameters and operating conditions. The complex relationships are visualized in Fig. 4. The conduction loss of the converter is related to both the modulation factor and the current flowing through the semiconductor device. The switching loss is mainly reflected by the switching frequency and the current flowing through the semiconductor device. IV. P OWER LOSSES DISTRIBUTION OF SINGLE PHASE 5L-HB WITH C OUPLED I NDUCTOR AND 5L-SCHB In PEBB applications, though many factors need to be balanced, power losses evaluation is quite critical to decide.

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(14) . A. Converter Descriptions The 5L-SCHB shown in Fig. 1(c) consists of a series connection of one standardized H-Bridge, and one dc link capacitor. The expense for the replacement of a failed power cell is comparable to the basic H-Bridge in PEBB applications. Using the typical PWM control, the basic switching states of the semiconductor devices including IGBT and Diode are described in Table I(a) and I(b). The commutations between. .

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(22) . TABLE I: Basic Switching States in 5L-SCHB (a) Switching States of IGBTs. .

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(25) 120. . T2. T3. T4. T5. T6. T7. T8. 1. on. off. off. on. on. off. off. on. 2. off. on. on. off. off. on. on. off. (b) Switching States of Diodes. . . States. D1. D2. D3. D4. D5. D6. D7. D8. 1. off. on. on. off. off. on. on. off. 2. on. off. off. on. on. off. off. on. the states determine the distribution of the power losses. All commutations take place between four controlled switches (IGBT) and four diodes. Even if more than eight devices turn on or off, only the IGBTs or Diodes experience essential power losses. Assuming the converter are working under specification listed in Table II..

(26) ,- .#"/%. (a) Relation between conduction Loss, modulation index and output peak current. 6 3"#$%. T1. (d) Reverse Recovery Loss. Fig. 3: Power Losses Distribution in 3L-HB. . States. TABLE II: Specifications for Converter Design. . Variable. . Symbol (Unit). Value. . switching frequency. fs (kHz). 10. . modulation index. M. 0.8. power factor output peak current. cos φ îo (A). 200. DC side voltage. VDC (V). 400. . "#45%. . .

(27) ,- .#"/%. (b) Relation between switching Loss, switching frequency and output peak current Fig. 4: Relations between Losses Distribution & Converter Variables. the most suitable topology. Different combinations of HBridge are available that satisfy complex requirements and achieve high performance. Series connecting of H-Bridge is one conventional solution, e.g. 5L-SCHB as shown in Fig. 1(c). The objective can be also realized by using a splitwound coupled inductor within each inverter-leg and using interleaved PWM switching of the upper and lower switches, e.g. 5L-HB with coupled inductor as shown in Fig. 1(b). This topology differs from the conventional scheme because coupled inductors are included inside the standard modules using interleaved PWM rather than adding switching modules and AC side inductors. [10] In this section, power losses distribution of the single phase 5L-HB with Coupled Inductor and 5L-SCHB are investigated using the above losses modeling derived.. 461. 0.8. Then, the output waveforms of current and voltage of the converter are shown in Fig. 5. The 5L-HB with coupled inductor has a unique feature is the insertion of a symmetrical split-wound coupled inductor between the upper and lower switches in the inverter-legs. Their coupling direction as indicated by the dots in Fig. 1(b). In this converter topology, the switching states of the power semiconductor switches are listed in Table III(a) and III(b). With the same converter design specifications in Table II, the output voltage and current waveforms of 5L-HB with coupled inductor are shown in Fig. 6(a) and 6(b). B. Final Power Losses Distribution Analysis Infineon EUPEC standard series IGBT module FF200R12KE3 is selected as the switching devices for 3L-HB, 5L-SCHB, and 5L-HB with coupled inductor respectively. The semiconductor devices’ specifications are listed in Table IV..

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(30) '"/%. . . . . . "%. . . "%. (a) Output Current. (a) Output Current '" %. . '" %. . . . . . . . "%. . . . "%. . (b) Output Voltage. (b) Output Voltage. Fig. 5: Output Current and Voltage of 5L-SCHB. Fig. 6: Output Current and Voltage of 5L-HB with coupled inductor . (a) Switching States of IGBTs. . States. T1. T2. T3. T4. 1. on. off. off. on. 2. off. on. on. off. !"$%. TABLE III: Basic Switching States in 5L-HB with coupled inductor. . 6: 6: . .! ;#$. .! ;#$. .! ;#$ . (b) Switching States of Diodes. States. D1. D2. D3. D4. D5. D6. D7. D8. 1. off. on. on. off. off. on. on. off. 2. on. off. off. on. on. off. off. on. 34926:2 '-! 2 '. 349. 37849. Fig. 7: Comparison of Power Loss Distribution among the three Different Topologies. TABLE IV: Power Semiconductor Devices’ Specifications TABLE V: Efficiency Comparison. Variable. Symbol (Unit). Value. rated current of IGBT. ICN (A). 200. threshold voltage of IGBT. VCEO (V). 0.5. voltage @ICN of IGBT. VCEN (V). 2.15. 5L-HB Efficiency η=. P total P out. 3L-HB. with coupled inductor. 5L-SCHB. 96.72%. 97.89%. 86.87%. threshold voltage of Diode. VF O (V). 0.6. rated current of Diode. IF N (A). 200. voltage @IF N of Diode. VF N (V). 1.7. level H-Bridge (5L-HB) with coupled inductor is the best topology.. rising time. trN (μs). 0.1. V. C ONCLUSION. falling time. tf N (μs). 0.18. reverse recovery time. trrN (μs). 0.18. The proposed comprehensive analytical power loss modeling is helpful to observe the power loss distribution in PEBB converters. It is effective to select best topology for PEBB applications. In future, experimental analysis will be carried out to verify the prediction of proposed work.. The comparison of the total power losses distribution among the three converters is shown in Fig. 7. With the coupled inductor, the H-Bridge converter ’s level is increased to five levels with lower THD. While the power loss is increased about 28.6%. The total power loss 5L-HB with coupled inductor is 2.7kW and is lower than 5L-SCHB by nearly 35.7%. Furthermore, the switching loss of the five level H-bridge with coupled inductor is much smaller than the switching loss in the 5L-SCHB. The efficiency comparison of the three available converters is demonstrated in Table V. Thus, from the aspect of power loss distribution, the five. 462. ACKNOWLEDGMENT The work is financially supported by Research Fund R − 263 − 000 − 507 − 305. R EFERENCES [1] T.Ericsen, N.Hingorani, and Y.Schugart, “Pebb-power electronics building blocks, from concept to reality,” IEEE IAS Annu. Meeting, pp. 1–7, Oct. 2006. [2] MitsubishiElectric, “Igbt application notes,” pp. 56–72, Dec. 2007. [3] D. Krug, S.Bernet, and S.Fazel, “Comparison of 2.3kv medium voltage multilevel converters for industrial medium-voltage drives,” IEEE Tran.Ind. Electron., vol. 54, pp. 2979–2992, Dec. 2007..

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