Closed Loop Power Conversion Efficiency Improvement of AC-DC Boost Converter using1:1Transformer

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Closed Loop Power Conversion Efficiency Improvement of AC-DC Boost Converter using1:1Transformer

Nirmal Kumar, Gayathri Ramanathan, Satheeswari Ponraj, Manikandan Manivel, Ashokraj Veerakumar

Department of Electrical and Electronics Engineering, Indra Ganesan College of Engineering,

Trichy, India.

Abstract- This paper proposes a circuit structure that can improve the power conversion efficiency of an AC-DC boost converter with closed loop control technique. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, a diode, a MOSFET, a PIC microcontroller ,a voltage sensor and a PI controller. This project describes the new type of ac dc boost converter with high voltage conversion ratio. The transformer forces the converter to operate in continuous conduction mode for input current, and there by reduces input ripple, power loss due to turn-ON of switch and reverse recovery of diode is minimized. This proposed converter improve the voltage gain with reduced stages when compared with conventional converter. The proposed converter has high e over a wide range of ac input voltage Vac: e = 92.9% at Vac = 85 V and e = 97.4% at Vac = 264 V, when the converter was operated at dc output voltage of 400 V and output power of 500W.

Key words: AC-DC power conversion, closed loop technique, coupled inductor, MOSFET, PI controller.

  1. INTRODUCTION

    The ac-dc boost converter is simple in structure and can improve the power factor (PF) by shaping the input current waveform [1,2]. The conventional ac-dc boost converter (Fig. 1(a)) can be operated in continuous conduction mode (CCM) or critical conduction mode (CrM). The input current iin does not fall to zero during CCM operation but does fall to zero during CrM operation. The inductor Lb for CCM operation has high inductance to reduce the slope of iin. The ripple and peak of iin obtained by CCM operation are smaller than those obtained by CrM operation at the same average value of iin [3]. However, CCM operation produces a power loss from hard switching and reverse recovery of diode DO [4,5]. Several passive snubbers [6-10] have been proposed to overcome the problem of CCM operation.

    Fig. 1. Structure of open loop ac-dc boost converter

    The current products that are commercially available mainly focus on one type of power conversion (e.g. AC/DC, DC/AC, DC/DC, or AC/AC) and do not allow for much flexibility and user control in terms of input and output. The conventional ac-dc boost converter can be operated in continuous conduction mode ( CCM ) and DCM .It provides a high voltage gain, a reduced voltage stress on transistors and limited input current ripples. Two winding and three winding coupling inductor has been implemented in the booster circuit fig1. It have high voltage stress and reverse recovery problem. The boost diode is turned off at zero voltage switching (ZVS) condition, so the reverse recovery current is minimized.

    For CrM operation, a current sensor detects the time point at which iin = 0, then this signal is used to turn- ON switch SW. Therefore, iin of the converter in CrM reaches 0 at the end of each switching period, and in this way reduces turn-ON switching loss [11]-[13]. One drawback of CrM operation is that the peak of iin is twice the average input, so iin ripple and the size of the input filter increase [14]-[16].

    A circuit structure of ac-dc boost converter that operates in CCM for the input current and in CrM for the inductor current iLb. The proposed circuit increases the power conversion efficiency e by reducing both turn-ON switching loss and reverse recovery current of diode. Also, it reduces input current ripple and current stress on the switch. The existing system II ,circuit structure and principle of operation are given in Section III, experimental results are given in Section IV, and a conclusion is given in Section V.

  2. EXISTING SYSTEM

    A .Block diagram of Existing system

    In Existing system open loop coupled inductor based ac -dc boost converter has been implemented. Two winding and three winding coupling inductor has been implemented in existing work. It has high voltage stress and reverse recovery problem. In existing model this system designed in open loop. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn-on of switch and reverse recovery of diode is minimized.

    Fig.2.Block diagram of ac- dc boost converter with open loop

    The existing system has implements a circuit structure of ac-dc boost converter that operates in CCM for the input current and in CrM for the inductor current iLb. The proposed circuit increases the power conversion efficiency by reducing both turn-ON switching loss and reverse recovery current of diode. Also, it reduces input current ripple and current stress on the switch.

  3. CIRCUIT STRUCTURE AND PRINCIPLE OF OPERATION

    A. coupled inductor

    First, this analysis is applicable to coupled inductors with directly or inversely coupling. The inversely coupled inductor is more suitable for miniaturization than the directly coupled inductor because the cancelation of the DC flux is obtained [1],[2], [7]. Therefore, in this analysis, we perform an operating analysis of the inversely coupled inductor is the input voltage , v rec is the rectified input voltage, Vo is the output voltage, L1 and L2 are the self-inductance of each winding, and M is the mutual inductance.

    1. Block diagram of proposed system

      Fig.3.Block diagram of ac – dc boost converter with closed loop control technique

      In the proposed circuit include the closed loop control technique by using PIC microcontroller and PI controller .The proposed converter controls the output dc voltage using a pulse width modulation (PWM) at a variable switching frequency

      The ac input voltage is converted into dc voltage by using rectifier circuit. The rectifier circuit consists of four diodes to convert the dc voltage. The dc voltage is applied to the 1:1 boost converter to boost the dc voltage at 1:4 ratio. When the output voltage is controlled by measuring the digital signal

      from output dc voltage. The measured digital signal is applied through the pi controller to compare the signal in constant value. In pi controller produce the error signal and its applied to the pic microcontroller. The microcontroller creates the gate pulse signal and its applied to the gate supply at MOSFET switch. Using a single core coupled inductor also named as 1:1 transformer.

    2. Proposed Circuit Diagram

    The proposed circuit consists of a boost capacitor C1, a 1:1 transformer, and a diode D1, in addition to the components Lb, DO, CO, and SW which are required for the conventional ac-dc boost converter. The transformer is represented with a magnetizing inductance Lm . The transformer between input and output decreases the slope of iin when SW is turned OFF; this prevents iin from reaching 0 A while allowing inductor current iLb to reach 0A and reduces the input current ripple. Lm and Lb control the turn-ON slope of switch current isw, that reduces the turn-ON switching loss and the current stresses of SW.

    Fig:4 Structure of the proposed ac- dc boost converter with closed loop technique

    C1 is located between two windings of transformer, creates a freewheeling path for iLb when SW is turned OFF, and acts as a charge pump capacitor to increase the voltage gain. C1 is charged when SW is turned OFF, and it is discharged when SW is turned ON. D1 provides a current path for iLb when SW is turned OFF. A pickp coil was wound on Lb to detect the zero- crossing point of iLb.

    Modes of Operation:

    The proposed converter controls the output dc voltage Vo using a controller called PID controller at a variable switching frequency fs= 1/Ts. The switch ON time DTs of the converter is fixed for a given sinusoidal input voltage. This forces the peak of iin to follow Vin because the slope of iin is proportional to Vin, so a high PF is achieved. The zero-crossing point of iLb determines Ts, so CrM operation of iLb is guaranteed. The voltage conversion ratio VO/Vin is controlled by adjusting D, where Vin is the peak input voltage.

    The first operation (Mode 1) starts at t= t0 by turning ON SW. During this operation, DO stays ON and D1 stays OFF. Because = ( + 1 )/2 and = ( + 1 )/2 , iLb and im are given by

    + 1 1

    () = ( ) +

    ( )

    4

    2 2 2

    The converter operates in CCM for iin because the transformer decreases the slope of iin(t). A freewheeling current path is formed by Lb, D1, and C1, so vLb, and iLb is given by

    () =

    1

    () = ( ) +

    ( )

    1

    2 2

    Fig.5.1 Operation of Mode 1(t0 < t < t1)

    Because SW is turned ON at iLb= 0 A, the boost inductor Lb is operated in CrM, so the power loss caused by turn-ON of SW and from the reverse recovery of D1 is reduced. Because(2) = (2)

    () =

    + 1

    () = ( )

    and () = () during this mode, iC1 is obtained

    2 0

    using previous equation.

    + 1

    () = ( ) +

    ( )

    1() = () ()

    2

    0

    + 1

    1 1

    io and iin are obtained using

    () =

    () + () and

    =

    4

    ( 2) 2 (2) +

    ( 2)

    () = () + ()as

    + 1 ()

    () = ( ) +

    4

    0

    + 1 4

    2

    ( 0)

    + 1 ()

    () = ( ) +

    4

    0

    + 1 4

    2

    ( 0)

    Mode 1 ends when io decreases to 0 A.

    The second operation (Mode 2) starts at t = t1 when DO turns OFF. During Mode 2, SW stays ON and D1 stays OFF. iin can flow only through SW because DO is OFF, so

    () = () = ()

    Fig.5.3 Operation of Mode 3 (t2 < t < t3)

    1Flows in the direction to charge C1 when1() < 0 for t2 < t < t2 + kTs, and it flows in the direction to discharge C1 when1() > 0 for the other periods. The value of k is obtained using (5),1(2 + ) = 0, and(2) = 1(1 )/ as

    =

    +

    ( 1) + (1)

    =

    1 2

    + 1

    (1 ) ( +

    4

    1 1

    )

    Fig.5.2 Operation of Mode 2(t1 < t < t2)

    Mode 2 ends when SW is turned OFF.

    The last operation (Mode 3) starts at t = t2 when SW is turned OFF. D1 and DO turn ON during this mode. Because = ( + 1 )/2, im is given by

    Mode 3 ends when SW is turned ON for next switching period.

  4. EXPERIMENTAL RESULTS

Fig.6.Simulation diagram of ac- dc boost converter

+ 1

() = ( ) +

( )

2

2 2

iin is obtained using() = () and () =

() + ()as

Fig.6.1.simulation waveform for 85v

Fig.6.2.simulation waveform for 264V V.CONCLUTION

This paper proposes an ac-dc converter that can operate over a wide range of input voltage. The proposed converter reduces the ripple of input current by using a 1:1 transformer, and decreases the switching loss by operating the switch in a critical conduction mode. Experimental results at 85 Vac 264 V, VO = 400 V, and 100 PO 500 W show that the proposed converter had higher power conversion efficiency than the other previous ac-dc converters.

REFERENCES

  1. L. Huber, B. T. Irving, and M. M. Jovanovic, Open-loop control methods for interleaved DCM/CCM boundary boost PFC converters, IEEE Trans. Power Electron. , vol. 23, no. 4, pp. 16491657, Jul. 2008.

  2. Y. Itoh, F. Hattori, S. Kimura and J. Imaoka, "Design method considering magnetic saturation issue of coupled inductor in interleaved CCM boost PFC converter," in IEEE Energy Conversion Congress and Exposition (ECCE), Montreal, QC, 2015.

  3. X. Yang, Y. Ying, and W. Chen, A novel interleaving control scheme for boost converters operating in critical conduction mode, J. Power Electron., vol. 10, no. 2, pp. 132137, Mar. 2010.

  4. F. Yang, X. Ruan, Q. Ji, and Z. Ye, Input differential- mode EMI of CRM boost PFC converter, IEEE Trans. Power Electron., vol. 28, no. 3, pp. 11771188, Mar. 2013.

  5. F. Yang, X. Ruan, Y. Yang, and Z. Ye, Interleaved critical current mode boost PFC converter with coupled inductor, IEEE Trans. Power Electron., vol. 26, no. 9, pp. 24042413, Sep. 2011.

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