A New Family of Soft-Switching DC-DC PWM Converters Using a True ZCZVT Commutation Cell Hélio L. Hey and Carlos M. de O. Stein Federal University of Santa Maria UFSM - CT - DELC 97105-900 - Santa Maria - RS - BRAZIL [email protected] Abstract – In this paper is introduced a new family of DC-DC II. A FAMILY OF DC-DC ZCZVT PWM CONVERTERS PWM converters using a true Zero Current and Zero Voltage Transition (ZCZVT) commutation cell. The soft-switching A. Common Equivalent Circuit of DC-DC PWM Converters technique utilized provides Zero Current Switching (ZCS) and An common equivalent circuit of DC-DC converters was Zero Voltage Switching (ZVS) simultaneously, at both turn-on proposed in [9] and it is shown in Fig. 1.a. It represents all and turn-off of the main switch and ZVS for the main diode. The types of non isolated DC-DC converters, which are obtained family of ZCZVT PWM converters is obtained from an common by connection of the input (Vi) and output (Vo) voltage equivalent circuit of ZCZVT PWM converters and the ZCZVT sources and the smoothing capacitor C, when it exists. The PWM boost converter is analyzed, simulated and implemented. connection scheme of these elements is shown in Fig. 1.b. In It is demonstrated the construction of state-plane diagram, which is obtained by using a proper state variable the case of buck, boost and buck-boost converters, where the transformation. Based on the commutation analysis and the c terminal is not connected, the L1 inductor can be suppress. relations between the most important circuit parameters, it is a a Components Connection presented a design guidelines and a design example. S Experimental results are presented, taken from a laboratory Vi Vo C prototype rated at 1 kW, input voltage of 155 V, output voltage L Buck a - d b - d 340 V and operating at 40 kHz. The measured efficiency at full b L1 Boost a - b a - d load was 97.9 %. c Buck-boost a - b b - d Cúk a - b c - d a - d D I. INTRODUCTION RL Sepic a - b c - d a - c Zeta a - b c - d b - d A wide variety of soft-switching techniques have been d d proposed to improve the energy conversion efficiency of the (a) (b) PWM converters. These techniques consist in to become Fig. 1. Equivalent circuit of DC-DC PWM converters. possible Zero Voltage Switching – ZVS and/or Zero Current (a) Circuit; (b) Components connection scheme Switching – ZCS on the power semiconductors devices [1-8]. B. ZCZVT PWM Commutation Cell The choice of the soft-switching technique, i.e., ZCS or The ZCZVT PWM commutation cell proposed in [10], is ZVS, it taken into account the technology of the shown in Fig. 2. It is composed by two resonant capacitors semiconductor device that will be used. For example, Power C and C , a resonant inductor L , a bi-directional auxiliary Mosfet presents a better performance when is commutated R1 R2 R switch SA-DA1 and two auxiliary diodes DS and DA2 form this under ZVS, since it exhibits turn-on capacitive losses when auxiliary circuit. operating in ZCS increasing the switching losses and EMI. On x the other hand, the IGBT presents better results when is a1 commutated under ZCS, which can avoid its lathup and the + D C C turn-off losses caused by its tail current. S R2 + R1 In [10] was proposed a ZCZVT commutation cell applied a SA LR PWM boost converter. This cell provides ZCS and ZVS a2 a3 DA2 simultaneously, at both turn-on and turn-off of the main DA1 switch and ZVS for the main diode. The shunt resonant Fig. 2. ZCZVT PWM Commutation Cell. network of the ZCZVT commutation cell is placed out the C. Equivalent Circuit of ZCZVT DC-DC PWM Converters power path and therefore, there is no voltage stresses on Figure 3 shows the equivalent circuit of ZCZVT DC-DC power semiconductor devices. Furthermore, it is activated PWM converters, which is achieved by incorporation of the during the main switch transitions only and is composed by ZCZVT commutation cell, shown in Fig. 2, in the equivalent fewer auxiliary devices, rated at small power. circuit of DC-DC PWM converters, shown in Fig. 1.a. The aim of this paper is to introduce a family of DC-DC a a PWM converters using the ZCZVT commutation cell + x DS CR2 ZCZVT proposed in [10]. The generation of this family is presented in SA CR1 commutation LR + section II. In section III is obtained the state plane diagram of S cell DA1 DA2 the ZCZVT boost converter, using a proper state variable L b transformation. The commutation analysis is presented in L1 section IV. Design guidelines and a design example are c presented in section V. In section VI are presented the DRL simulation and experimental results, taken from a laboratory prototype rated at 1 kW, input voltage of 155 V, output d d voltage 340 V and operating at 40 kHz. The measured Fig. 3. Equivalent circuit of DC-DC ZCZVT PWM converters efficiency at full load was 97.9 %. The family of ZCZVT PWM converters is obtained using 0-7803-4503-7/98/$10.00 1988 IEEE 1030 the connection scheme shown in Fig. 1.b. The x terminal can = LR , = LR be connected in the input voltage source, in the output voltage Zx Stages Z1 Z2 CR CR source or in the common point between them. The operation Z1 1, 2, 3, 7, 8, 9 and 10 1 2 Z 4, 5, 6, 12 and 14 of these configurations differs only by the voltage across the 2 L C C Z 11 and 13 = R , = R1 R2 resonant capacitor C . Figure 4 shows the configuration of e Ze Ce R1 C C + C ZCZVT DC-DC PWM converters obtained by the connection e R1 R2 of the x terminal in the input voltage source. To illustrate the procedure used for the obtainment of the D +C C + state variable transformation, normalization and equations for S R2 + R1 DS CR2 CR1 S SA LR SA L + S R Vi each circuit stage, will be utilized the stage 4 (t , t ). L 3 4 V DA1 DA2 DA1 L DA2 i Vo A. State Variable Transformation and Normalization of the D V RL o DRL Initial Conditions: i ()t (a) (b) ()= LR 3 = Iin = in t3 1 ( 5 ) + + I I DS CR2 CR1 DS CR2 CR1 in in SA L + SA L + S R Vi S R Vi ()− () L L vC t3 vC t3 − DA1 DA2 DA1 DA2 R2 R1 Vo Vi ′ L v ()t = = =V ( 6 ) 1 C n 3 n3 DRL Vo Iin Z x Iin Z 2 DRL Vo where V ′ is the normalized voltage in the instant t3 and Z2 is n3 (c) (d) the characteristic impedance of the stage 4. D +C C D +C C B. Current normalization. S R2 S + R1 S R2 S + R1 S A LR Vi S A LR Vi C The equation (7) defines the resonant inductor current DA1 L DA2 DA1 L DA2 L1 L1 during the stage 4 and is given by: di ()t v ()t − v ()t C LR CR2 CR1 D V D V = ( 7 ) RL o RL o dt L R (e) (f) Fig. 4. DC-DC ZCZVT PWM converters L Iin DRL (a) Buck; (b) Boost; (c) Buck-boost; (d) Cúk; (e) Sepic; (f) Zeta D SA A2 LR III. CONSTRUCTION OF THE STATE PLANE + DIAGRAM + DA1 S CR2 Vi C Vo To analyze the operation of the proposed ZCZVT DC-DC R1 DS PWM converters was selected the ZCZVT PWM boost converter. Figure 5 shows the ZCZVT PWM boost converter Fig. 5. ZCZVT PWM boost converter. represented in the conventional topological form. It differs I I I from the boost converter presented in Fig. 4.b only by the in in in SA LR DA2 SA LR components placement. The operation stages are represented DRL Vi in Fig. 6. A complete analysis of the operation principles of + DRL DRL Vo Vi CR1 Vi this converter was presented in [10] and will be suppressed in Vo s Vo stage 1 - t0, t1 this paper. tage 2 - t1, t2 stage 3 - t2, t3 Since the ZCZVT commutation cell contains three reactive Iin Iin Iin components (CR1, CR2 and LR), during one switching cycle D SA LR D SA LR D SA LR there are three resonant frequencies and third order equations A2 A2 A2 + [10]. Therefore, the state plane analysis of these converters by Vi CR2 Vi DS Vi S conventional techniques are difficult and so that, the state s stage 4 - t , t stage 6 - t , t plane will be obtained using a proper state variable 3 4 tage 5 - t4, t5 5 6 transformation. A similar analysis applied to a multi-resonant Iin Iin Iin converters was reported in [11]. DA1 LR SA LR Vi S The state variable transformation is done considering as the + + Vi CR1 S Vi CR1 S state variables, the inductor resonant current and the s difference between the voltage of the resonant capacitors as stage 7 - t6, t7 tage 8 - t7, t8 stage 9 - t8, t9 follows: Iin Iin Iin ()= () i t iL t ( 1 ) R SA LR SA LR DA2 SA LR ()=− () () e vt vC t vC t ( 2 ) + + + + R21R Vi CR1 DS Vi CR1 CR2 Vi CR2 The normalization is done with base in the input current Iin s stage 10 - t9, t10 tage 11 - t10, t11 stage 12 - t11, t12 and the generic characteristic impedance Zx as follows: () Iin Iin it() itL ()==R ( 3 ) itn DA1 LR I I + in in Vi C + + R2 ()− () Vi CR1 CR2 vt() vtvtC C ()==R21R ( 4 ) s vtn stage 13 - t12, t13 tage 14 - t13, t0 IZin x IZin x The value of the generic characteristic impedance Zx depends on the reactive components enveloped in each stage.