A Simple Design and Simulation of Full Bridge LLC Resonant DC-DC Converter for Pv Applications

Transcription

1 Middle-East Journal of Scientific Research 23 (2): , 25 ISSN IDOSI Publications, 25 DOI:.5829/idosi.mejsr A Simple Design and Simulation of Full Bridge LLC Resonant DC-DC Converter for Pv Applications 2 M. Shanthi and R. Seyezhai Department of ECE, University College of Engineering, Ramanathapuram , Tamil Nadu, India 2 Department of EEE, SSN College of Engineering, Rajiv Gandhi Sallai, Kalavakkam-63, Tamil Nadu, India Abstract: This paper deals with the design and simulation of full bridge LLC resonant converter suitable for photovoltaic applications. LLC converter has several desired features such as high efficiency, low electromagnetic interference (EMI) and high power density. This paper provides a detailed practical design aspect of full bridge LLC resonant converter. The LLC converter is implemented with a full-bridge on the primary side and a full-bridge rectifier on the secondary side. It includes designing the transformer turns ratio and selecting the components such as resonant inductor, resonant capacitor and magnetizing inductor. Also performance parameters such as voltage gain and output voltage ripple are calculated. Simulation of LLC resonant converter is carried out using MATLAB / SIMULINK and the results are verified. Key words: LLC resonant converter Output voltage ripple Voltage gain INTRODUCTION The conventional Pulse Width Modulation (PWM) technique developed power by adjusting the duty cycle and Interfering the power flow. Most the switching devices are hard-switched with sudden changes of currents and voltages, which results in more than a few Fig. : LLC resonant tank circuit switching losses and noises.in order to resolve the limitations of the conventional converters, the LLC for photovoltaic applications. Beginning with a brief resonant converter has been proposed.basically the operation of basic full bridge LLC resonant converter is resonant technique process power in a sinusoid form and presented in Section II. Next, a method for defining the switching devices are softly commutated [-3]. parameter values is describedin the form of flow chart and Therefore the switching losses and noise can be also to demonstrate how a design is created; a step-bytheoretically reduced. Hence resonant converters have step procedure is presented for a converter with 5W of drawn a lot of attention in various applications [4]. It output power in Section III [5]. Simulation studies are consists of two inductors and one capacitor and the carried out using MATLAB/SIMULINK. Finally converter can regulate the output voltage in contradiction performance parameters such as voltage gain and output of line and load variation over a wide range. The tank voltage ripples are calculated. circuit of LLC Resonant Converter as shown in Fig.. In LLC arrangement, the uncoupled inductor can be Operation of Full Bridge LLC Resonant DC-DC interchanged by a coupled one so that the size of the Converter: Fig. 2 shows a typical topology of a full-bridge converter can be compact. This paper emphasis on the LLC resonant converter. The converter arrangement design features for the full bridge LLC resonant converter has three main parts. Such as switching bridge, LLC tank, Corresponding Author: R. Seyezhai, Department of EEE, SSN College of Engineering, Rajiv Gandhi Sallai, Kalavakkam-63, Tamil Nadu, India. 285

2 Middle-East J. Sci. Res., 23 (2): , 25 Fig. 2: Typical topology of full bridge LLC resonant converter transformer and rectifier. Power switches Q, Q2, Q3, Q4, i.e. at resonance, below resonance and above resonance. which are generally MOSFETs, are arranged to form a Each of the modes pointed out may hold one or both of square wave generator. This generator yields a bipolar these operations [7]. square-wave voltage (Vsw) by driving switches Q and Q3 & Q2 and Q4, with alternating 5% duty cycles for Power distribution operation happens twice in a each switch. A small dead time is needed between the switching cycle; first, when the resonant tank is successive transitions, both to avoid the possibility of Motivated with a positive voltage, current resonates cross conduction and to allow time for zero voltage in the positive way in the first half of the Switching switching (ZVS) to be attained. The resonant tank, also cycle and second event is when the resonant tank is called a resonant network, consists of the resonant motivated with negative voltage, current resonates in capacitance (Cr) and two inductances series resonant the negative direction in the second half of the inductance (Lr) and the transformer s magnetizing switching cycle, for the duration of the power inductance (Lm). The transformer turns ratio is n. distribution operations, the magnetizing inductor The resonant network circulates the electric current and voltage is the positive/negative reflected output as a result, the energy is circulated and delivered to the voltage and the magnetizing current is load through the transformer. The transformer s primary charging/discharging correspondingly. The winding accepts a bipolar square wave voltage. difference between the resonant current and the This voltage is transmitted to the secondary side, with the magnetizing current permits through the transformer transformer given that both electrical isolation and the and rectifier to the secondary side and power is turn s ratio to distribute the required voltage level to the distributed to the load. output. On the converter s secondary side, establish a Freewheeling operation happens following the power full-bridge rectifier to convert AC input to DC output and delivery operation only if the resonant Current supply the load R. The output capacitor smooth s the extents the transformer magnetizing current, this only rectified voltage and current [6]. occurs when fess<fro, producing the transformer For this configuration, there are two resonant secondary current to reach zero and the secondary frequencies. Resonant frequency one is determined by the side rectifier to disconnect. Therefore the resonant components Lr and Cr. The other one is magnetizing inductor will be free to arrive the determined by magnetizing inductance Lm, Cr and load resonance with the resonant inductor and resonant condition. As load receiving heavier, the resonant capacitor, the frequency of this second resonance is frequency will shift to greater frequency. The two smaller than the original resonant frequency fro, resonant frequencies are shown in equation & 2. particularly at high values of m where Lm>>Lr, thus the primary current during the freewheeling operation fr = /2 LC () will only changes lightly and can be estimated to be r r unchanged for simplicity. fr2 = /2 Lm + LC (2) r r Design of LLC Resonant Converter: Fig. 3 shows a The converter can function in three modes design flow chart that reviews the design methodology of depending on Input voltage and load current conditions LLC resonant converter [8]. Initially the terminal voltages 286

3 Middle-East J. Sci. Res., 23 (2): , 25 Vinmin Np / Ns =. Mnom Vout (3) Here Mnom = Determine Mg_min and Mg_max Mg_min And Mg_max can be determined by Equation 4 & 5 Mg Mg max min Vin _ nom =. Mnom Vin _ max Vin _ nom =. Mnom Vin _ max (4) (5) Select m and Q e Moderate Q value of around.5 seems to be e satisfying the voltage gain requirement. Select Q max moderately Q e=.4 Lower value of m can achieve higher boost gain, in addition to narrow range of frequency modulation. Fig. 3: Design flow chart of LLC resonant converter Reasonable initial value for m=6.3 Vin_ min, Vin_ max& Vin_ nom must be taken from the converter Specifications. After that the transformer turns ratio (N) If the values m=6.3 and Q e =.4 are selected, the can be obtained from Equation 3 then the Mg_ min and corresponding K_max=.974, which is greater than Mg_ max calculated using Equation 4 & 5. By selecting M g_max=.833. No need for tuning the m value. Any K_ max proper values for m and Q e the corresponding K_ max value values above this line are greater than M g_max. So the calculated. If it satisfies the desired condition then the designed converter should operate in the inductive designed converter should operate in the inductive region. Which satisfies the design requirement? region. Finally the resonant component values such as Cr, or and Lm are calculated using Equation 7, 8, 9 Calculating resonant component values respectively. The reflected load resistance at full load is calculated The specifications for the design are: by Equation 6. Input voltage range: 8V 36V (33V in_nom) Output voltage: 27V (6) Maximum load: 45? Next we solve the Equations 7, 8, 9 to obtain the The design equations for turns ratio, resonant resonant tank component values. inductor, resonant capacitor, magnetizing inductor are as follows [9-]. Lr (7) Qmax =.4 = Cr Determine Transformer Turns Ratio (n) Rac min The transformer turns ratio is determined by fr = KHz = (8) Equation 3. 2 LrCr 287

4 Middle-East J. Sci. Res., 23 (2): , 25 Table : Design Equations Normalized Gain Resonant Frequency Quality Factor Normalized Frequency Inductor Ratio ( V in nom M = ) M nom Vin min f r = Lr 2 LrCr Q Cr max = Rac min f = f /f n s r Lr + L m = m L r Table 2: Voltageand Current Specification Parameter Value Input Voltage Vin 33V Output Voltage Vo 27V Output Current Io.85A Output Power P 5W Lr + Lm m = 6.3 = Lr o Table 3: Design Parameters Component Designator Value Magnetic Inductor Lm 5.95µH Resonant Inductor Or.238µH Resonant Capacitor Cr 2.25µH Duty Ratio D.5 Switching Frequency fs 48.9Khz Turns Ratio N :2.2 Resonant Frequency fro Khz Reflected load resistance Race-min.763 Lr =..238µH, Lm = 5.95µH, Cr = 2.25µH Specifications of the 5W LLC resonant converter are as follows: (9) Table, 2 and 3 are the specifications and key components of the 5W LLC converter, respectively. RESULTS Simulation studies are carried out using MATLAB/SIMULINK and the simulation circuit of full bridge LLC Resonant DC-DC Converter for an input of 33V is shown in Fig. 4. The driving pulse of MOSFET Q&Q3 with phase delay of and duty ratio of.5 is obtained. Driving pulse of MOSFET Q&Q3, current and voltage waveforms are as shown in Fig. 5. The driving pulse of MOSFET Q2&Q4 with phase delay of 8 and duty ratio of.5 is obtained. Driving pulse of MOSFET Q2&Q4, current and voltage waveforms are as shown in Fig. 6. Output voltage of inverter and Current through Resonant components is as shown in Fig. 7 (a) & (b) Fig. 8 (a) & (b) shows the simulated voltage waveforms resultant to the primary side & secondary side of the transformer which are achieved by experiments of the 5W converter under normal load Condition. Fig. 4: Simulink diagram of full bridge LLC resonant converter 288

5 Middle-East J. Sci. Res., 23 (2): , 25 Voltage (V) Current (A) Voltage (V) Driving pulse of Q & Q x -4 MOSFET current x -4 MOSFET voltage x -4 Fig. 5: Driving pulse of MOSFET Q&Q3, current and voltage waveforms Voltage (V) Current (A) Voltage (V) Driving pulse of Q2 & Q time (S) x -4 MOSFET current time (s) x -4 MOSFET voltage time (s) x -4 Fig. 6: Driving pulse of MOSFET Q2&Q4, current and voltage waveforms 4 output voltage of the inverter 3 2 Voltage (v) (a) x -4 Current through Resonant Components 5 Current (A) (b) Time(S) Fig. 7: Output voltage of inverter & current through resonant components 289

6 Middle-East J. Sci. Res., 23 (2): , 25 4 Primary voltage oftransformer 3 2 Voltage (V) (a) T ime(s) 3 Secondary voltage ofthe transformer 2 Voltage (V) - -2 (b) Time(S) Fig. 8: Transformer primary and secondary voltages 2 Output current ofllc resonant Converter.5 Current(A).5 (a) T ime(s) 3 Output voltage ofllc Resonant Converter 25 Voltage(V) (b) T ime(s) Output power ofllc resonant converter 4 power(w) 3 2 (c) T ime(s) Fig. 9: Output current, output voltage and output power of LLC resonant converter 29

7 Middle-East J. Sci. Res., 23 (2): , Output ripple voltage of LLC Resonant Converter voltage(v) Fig. : Output ripple voltage waveform Table 4: Performance Parameters Parameters Full bridge LLC resonant converter Voltage gain.833 Output voltage ripple.3 Fig. 9 (a), (b), (c) shows the simulation results of output current, output voltage and output power of LLC converter under normal load conditions. It is observed that soft-commutation of both output diodes and power MOSFET s are achieved. So that simulated output power is near to the estimated value with the input voltage of 33V. Evaluation of Performance Parametersfor LLC Converter: The performance of full bridge LLC resonant converter is examined by calculating the voltage gain and output voltage ripple by using the equation,. V ( in nom Mmax = ) Mnom Vin min The Ripple in the output voltage is calculated as. V Vripple = V vavg max min () () where V as the average value of maximum and minimum arg voltage from voltage ripple waveform [2]. The output voltage ripple waveform as shown in Fig. and it is around.3. Table 4 shows performance parameter of LLC resonant converter. CONCLUSION The design procedure of Full Bridge LLC Resonant Converter is presented for photovoltaic application. Theoretical values of resonant component values are calculated using the design equations. Simulation results are provided for LLC Resonant converter for an input voltage of 33V. The voltage gain and output voltage ripple of LLC resonant converter is calculated which shows that the ripple is less in the proposed converter. ACKNOWLEDGMENT The authors thank the Management, Principal & EEE Department of SSN College of Engineering and Dean of University College of Engineering for giving the necessary facilities to carry out this work. REFERENCES. Abramovitz, A. and S. Bronshtein, 2. A design methodology ofresonant LLC DC-DC converter Power Electronics and Applications (EPE2), Proceedings of the European Conference, pp: Bing Lu, Wenduo Liu, Yan Liang, F.C. Lee and J.D. Van Wyk, 26.Optimal design methodology for LLC resonant converter, Applied Power Electronics Conference and Exposition. Twenty-First Annual IEEE, 6: Choi, H.S., 27. Design consideration of half bridge LLC resonant converter, Journal of Power Electronics, 7(): Gopiyani, A. and V. Patel, 2. A closed-loop control of high power LLC Resonant Converter for DC-DC applications, Nirma University International Conference, pp: Senthamil, L.S., P. Ponvasanth and V. Rajasekaran, 22. Design and implementation of LLC resonant half bridge converter Advances in Engineering, Science and Management (ICAESM), International Conference, pp:

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