Analysis of Switched Inductor Three-level DC/DC Converter

Transcription

1 Journal of peration and Automation ower Engeerg ol. 6, No., Jun. 08, ages: Analysis of Switched nductor Three-level C/C Converter E. Salary, M. R. Banaei, A. Ajami epartment of Electrical Engeerg, Azarbaijan Shahid Madani University, Tabriz, ran Abstract- A non-isolated C/C converter with high transfer ga is proposed this paper. The presented converter consists of the switched ductor and three-level converters. The C/C power converter is three-level boost converter to convert the output voltage of the C source to two voltage sources. The ma advantages of C/C converter are usg low voltage semiconductors and high ga voltage. The steady-state operation of the suggested converter is analyzed. A prototype is developed and tested to verify the performance of the proposed converter. To sum up, the MATLAB simulation results and the experimental results have transparently approved high efficiency of proposed converter as well as its feasibility. Keyword: renewable energy sources, -Battery system, non-isolated C/C converter, high ga C/C converter.. NTRUCTN Renewable energy sources such as photovoltaic () arrays, wd turbe, gas micro turbe and fuel cells have been creasg at a fast step distributed power systems. The obvious distctive of these sources is low voltage supply with wide range voltage drop and some cases generated energy depends on weather condition [- 4]. With regard to this characteristic, distributed power systems, have to employ a high step-up C/C converter [4]. n conventional C/C boost converter, practical cases, the duty ratio cannot tends to be the extreme value unity [4-6]. When the conventional C/C boost converter operates under the high duty ratio, the highfrequency EM issue and efficiency are unfavorable [8]. Typical solutions clude the use of high ga C/C boost converter to adjust the voltage ga. The use of high-frequency transformers is one solution to obta desired voltage ga. This may result an creased size and weight when compared with non-isolated C/C converters. For example, the ma drawbacks fullbridge C/C converter with high-frequency transformers are complexity and the need for four sets of active switches. Cascadg one or more conventional Received: 7 ct. 05 Revised: 0 Feb. 07 Accepted: 30 May 07 Correspondg author: m.banaei@azaruniv.edu (M. R. banaei) igital object identifier: 0.098/joape University of Mohaghegh Ardabili. All rights reserved. C/C converters is other way to obta high step-up power conversions. Switched-capacitor/ductor network provides another solution to achieve high stepup voltage ga. Several converters exist to achieve C/C voltage conversion. Each of these converters has its specific benefits and disadvantages, dependg on a number of operatg conditions and specifications [9-9]. The terleaved double dual boost converters are one type of high ga C/C converter [9-]. The ma drawback of these topologies are complex control and usg a large number of active switches. n [] a new topology is proposed with the objective of creatg a higher voltage ga comparison with the classical boost converter, i.e., the terleaved double dual boost converter. The presented topology [3], uses two termediary capacitors to double the output voltage when compared to the conventional boost converter. The new circuits, also named diode-assisted C/C converters [4], enhance the voltage boost/buck capability and avoid the extreme duty ratio. Some C/C buck boost converters are recently presented by usg the KY converters. KY converters are also used to construct high step-up converters like [5]. n [6], a new buck boost converter is proposed. The voltage ga of the proposed converter step-up mode is higher than the basic non-isolated buck boost converters. n [7] a two stage converter is proposed for AC-module photovoltaic () system. The proposed system consists of a high-voltage ga switched ductor boost verter. The switched ductor boost converter (SBC) has one switch operates like a contuous conduction mode. The

2 Journal of peration and Automation ower Engeerg, ol. 6, No., Jun SBC gives high ga by usg switched ductor circuit. A new power conversion system is explored [6] aimg wd turbes. The proposed configuration uses a C/C four-level boost converter as the termediate stage. A photovoltaic () system usg multilevel boost converter (MBC) and le commutated verter (LC), operatg both grid-connected mode and stand-alone mode has been analyzed [7]. The C/C converter [7] has one active switch but it uses a large number of diode and capacitors. The C/C converter can be used multilevel verters [-3]. n this paper, high ga C/C converter is proposed which is suitable for energy conversion applications. The proposed converter topology is the combation of threelevel converter and high ga switched ductor boost converter. The ga of voltage can be creases by addg switched ductor circuits. Analysis, simulation and experimental set-up are troduced to verify the proposed system performances.. C/C CNERTER n a classic C/C boost converter, the voltage stresses on switch and diode, which are equal to the output voltage, are high. n the three-level step-up C/C converter semiconductor device voltage ratg is only half of the output voltage [0-]. n these converter special modulation technique, offers lower put current ripple, too. The boost and voltage-doublers techniques are tegrated the three-level boost converter to achieve higher step-up voltage ga compared to conventional boost converter. The peak verse voltage of switches and diodes is half of output voltage. n this paper, a new C/C converter based on three-level C/C converter is analyzed. The proposed converter gives higher ga than conventional boost and three-level boost converters. The circuit configuration of the presented converter is shown Fig.. As shown Fig., the proposed converter consists of voltage-doublers circuit and switched ductor circuits. The switched ductor composed of two diodes and two ductors. Fig.. Configuration of the proposed converter... peratg prciples of the proposed converter n order to simplify the circuit analysis of the converter, all components are assumed ideal and the voltage of output capacitors of C/C converter is equal. Capacitors C, C and ductor are large enough. Thus, voltage of capacitors and current of ductors is considered as constant one switchg period. t is assumed that converter has one resistive load, too. The voltage of output capacitors is equal. C The output voltage is equal to sum of voltage of output capacitors. C () () Figure shows the topological stages of the proposed converter. The operatg modes are described as follows. Mode : Fig. (a) shows mode equivalent circuits. urg this mode T and T are turned on. The C-source energy is transferred to L and L. n this mode ductors are series. The voltage of ductors has positive value. n this mode, are turned on and 3, o and o are turned off. Energy of output capacitors is given to load and capacitors put on discharge mode. L uration of mode is equal as: t T. f (3) (4) (5), T and f are the duty cycle switchg period and switchg frequency respectively. Mode : T is turned on and T is turned off. n this mode 3, o are turned on and, and o are turned off. The voltage of ductors has negative value and energy is pumped to C while energy of C is given to load. The currents of ductors decrease. Figure (b) shows mode equivalent circuit. urg mode, the voltage across the ductors is: L C uration of mode is equal as: t ( ). T (6) (7) Mode 3: T is turned off and T is turned on. n this mode 3, o are turned on and, and o are turned off. The energy is pumped to C through T, and o, so currents of ductor is decreased. Figure (c) shows mode

3 E. Salary, M. R. Banaei, A. Ajami: Analysis of Switched nductor Three-level C/C Converter 8 3 equivalent circuit. urg mode 3, the voltage across the ductor is: i L n this study value of L is equal to L so: L i L uration of mode 3 is equal as: t 3 ( ). T (8) (9) (0) () The ductor average voltage over one cycle is zero [6]. 0. ( ) ( ) ( ( ) ) () Figure 3 shows the voltage ga for different duty ratio. Fig. 3. oltage ga for different duty ratio. (a) (b) (c) Fig.. Topological stages of the proposed converter (a) mode (b) mode and (c) mode 3. The current of capacitor is: ( ) ( i ) ( ) T (3) The capacitor average current over one cycle is zero [6]. i c 0. ( ) ( L ( ) ( ) ) 0 (4) f C is equal to C then the voltage ripple of output capacitors are shown as: C ( ) fc (5) The root mean square current of capacitors can be calculated as follows C ( ) ( ) (6) Figure 4 shows the signal gates and voltage of semiconductors, ductors and capacitors. The charge

4 Journal of peration and Automation ower Engeerg, ol. 6, No., Jun and discharge of L is the same as L. The frequency of ductor voltage is double of switchg frequency. The ripple of ductor current is half of ripple of ductor current classic boost C/C converter. This is one advantage of three-level converters [0-]. Figure 5 shows voltage and current of one ductor CM condition. By equatg the average value of this v L waveform to zero, one obtas: 0 ( ( ) ) (0) i o The dc component of the o, i o K K L T o o R, is: () By sertg Eq. (0) to Eq. (), and rearrangg terms, one obtas the followg quadratic equation: TK ( o o ) R o RK L T 0 Suppose that is defed as: () L RT (3) Fig. 4. The signal gates and voltage of components. Based on Eq. (), the put current can be expressed as: ( ) ( ) (7) Where, is the output current. n addition, the current ripple of i and i L denoted by i L and i L, respectively. The current ripple of ductors can be expressed to be i i i L. T L ( ) 3iL 3. T 4L (8) (9) Fig. 5. oltage and current of one ductor. Then, the voltage boostg ga of the proposed converter CM condition is found as o 4K (4)

5 E. Salary, M. R. Banaei, A. Ajami: Analysis of Switched nductor Three-level C/C Converter 30.. oltage ratgs of semiconductors An important problem power electronic converters is the ratgs of semiconductors. n other word, voltage and current ratgs of the semiconductors a converter play important roles on the cost and realization. The voltage stresses on semiconductor are given as: T T 3 o ( ) o.3. ower loss calculation ( ) ( ) (5) (6) (37) Generally, power electronic converters have losses. ifferent elements proposed converter such as ductors, capacitors and semiconductor generate power loss [7]. Fig. 6 shows an equivalent circuit of the proposed converter with parasitic resistances. The passive components, capacitors and ductors have ternal resistant. The conduction losses of ductors L and L are R RL R R L L 4R ( ) 4R ( ) L (48) (59) as R The conduction losses of the diodes can be calculated Ro R Ro R F ave R o o 4R ( ) F ( ) Ro ( ) o o Fo oave Fo R3 R 3 3 4R3 ( ) 3 F33ave F3 (3) (33) (34) (35) (36) (37) Where R and F are the diode resistance and threshold voltage. The conduction loss of the power switch is RT RT R TT (7 ) RT ( ) (38) Where R T is switch on-resistance. The switchg losses are due to non-ideal operation of switches [0]. ( E swt swt on Eoff ) f (39) Where E on and E off are turn on and off energy losses switch..4. Extended topology The proposed topology gives high transfer ratio. To obta bigger ga, switched ductor circuits can be added to ma structure as shown Fig. 7. n this state, the voltage ga is deduced the followg equation ( n) ( ) Where n is the number of switched ductor cells. (40) Fig. 6. Equivalent circuit of the proposed converter with parasitic resistances. R The power losses capacitors C and C are R R( ) ( ) (30) 3. CMARSN STUY Figure 8 shows cascaded boost converter. For comparison study between cascaded boost converter and presented topology, Tables is presented. RC R C C RC ( ) ( ) (3)

6 Journal of peration and Automation ower Engeerg, ol. 6, No., Jun Fig. 7. resented topology with additional switched ductor cells. As can be seen Tables, comparison has been performed between the proposed converter and conventional cascaded boost converter ideal case. t is obvious that the ga of the proposed converter is higher than the conventional boost converter and cascaded boost converter. The number of components presented topology is higher than cascaded converter while the voltage stress of elements is lower than cascaded converter. The cost of semiconductor has direct relation to voltage stress. Table. comparison between the proposed converter and cascaded boost converter resented Cascaded boost ( ) ( ) (5 4) ( ) T o T ( ) Sum of voltage stress of semiconductor ( 4 ) voltage stress of semiconductor ( ) o C ( ) Capacitor voltage T T 3 4 Co ( ) The nomal load is 400 Ω, which results an output current of 0.34 A, and an output power of 47W. The selected operatg switchg frequency is 5800 Hz. Fig. 0 shows gate pulse of C/C converter. n any time one or two switch is on. The voltage and current of L is shown Fig.. 3. Experimental Results A switched ductor three-level converter usg a one switched ductor circuit was built the laboratory. Fig. 9. Circuit of C/C converter. Fig. 8. Cascaded boost topology. The simulation and experimental results show operation of presented converter. Figure 9 shows circuit of C/C converter. The values used the prototype are shown Table. The output voltage is 37. C source L, L C, C Switchg frequency R MSFET driver MSFET iode Controller Table. arameters 4 500µH 000 µf 5800 Hz 400 ohm 0.5 TL50 RF460 U560 STMS30F8335

7 E. Salary, M. R. Banaei, A. Ajami: Analysis of Switched nductor Three-level C/C Converter 3 Fig. 0. Gate pulses of C/C converter. Fig.. oltage of and 3. (a) The voltage of L is the same as L. Figure shows voltage of and 3. The voltage of is the same as. The turng on and off of and is reverse of 3. n Fig. channel 3 shows voltage of 3 and channel 4 shows voltage of. The voltage of output diodes ( o and o) are shown Fig. 3. t is clear that both output diodes don t on simultaneously. Figure 4 shows put current and output voltage of C/C converter. (b) Fig.. oltage and Current of L (a) voltage and (b) current. Fig. 3. oltage of output diodes.

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