Monostage High Powerfactor AC-DC Converter

Monostage High Powerfactor AC-DC Converter

Monostage High Powerfactor AC-DC Converter

Arun kumar.V

Electrical and Electronics Engineering Department (P.G) Sri Ramakrishna Engineering College

Coimbatore, India

Prof. D. Prakash Asst. Professor (SR.G) Electrical and Electronics

Engineering Department(U.G) Sri Ramakrishna Engineering College

Coimbatore, India

DR.R.Mahalakshmi, Professor &Head Electrical and Electronics Engineering,

Sri Krishna College of Technology, Coimbatore, India

Abstract This paper describes a single stage AC- DC converter with high power factor. The diode- capacitor type of rectifier cause low power factor because of its nonlinearity. PFC serves to smooth out power drawn and regulates the output voltage. High power factor at the input is assured by operating the buck-boost converter at discontinuous conduction mode of operation. With same operation on both cycle and detailed designed circuit parameter, zero- voltage switching on all the active switches of the converter can be retained to achieve good efficiency. This gives soft switching condition which increases the efficiency of the system and reduces the switching power losses. The buck boost converter and the filter circuit are used to re-shape the input current waveform so as to be in phase with input voltage waveform. The design, analysis, simulation and hardware realization of the AC-DC converter with soft switching.

Keywords-Buck-boost converter, full-bridge resonant converter, power factor correction (PFC), zero-voltage switching(ZVS).

1. INTRODUCTION

   Power factor (PF) is the cosine of the angular difference between voltage and current. It is calculated as PF = cos = cos (Vs^Is). It can vary between zero and one depending on the type of load. If the supply voltage and current are in-phase with each other, then the power factor of the circuit (cos) is

   unity. The power electronic switching devices introduce distortion into the system. As a result, the power factor gets lowered.

   The diode bridge rectifier with capacitive filter is used as the fundamental block of many power electronics converters. Due to its non-linear nature, non-sinusoidal current is drawn from the utility and harmonics are injected into the utility lines. The injected current has lower order of harmonics and causes voltage distortion and poor power factor at input AC mains. This causes slow varying ripples at DC output load resulting in lower efficiency and larger size of AC and DC filters [2]. These converters are required to operate with high switching frequencies due to demand for small filter size and high power density. High-switching frequency operation results in higher switching losses, increased electromagnetic interference (EMI), noise and reduced converter efficiency [3]. To overcome these drawbacks, the switches of buck-boost converter are operated with zero voltage and zero current switching. High-switching frequency with SS provides low switching stress and losses, high-power density, less volume and lowered ratings for the components, high reliability and efficiency.

   To improve the efficiency, a large number of soft switching technique including resonant circuits have been proposed [4]-[7]. But these converters increase the number of switches and stages in power conversion circuit thus complicating the sequence of switching operation, excessive voltage and current stresses, and also narrower line and load ranges[8],[9].

   This paper describes a single stage AC-DC converter with high power factor. For high power application power handling capacity is increased so full bridge resonant converter is adopted which is combined with two Buck-boost type PFC circuits. Two active power switches act as a PFC circuits Therefore, power handing capacity increased. A high power factor at the input line is achieved by operating the PFCs at discontinuous conduction mode. The output voltage is regulated by controlling the

   ON/OFF time of switches present in buck-boost converter. The higher order harmonics are eliminated by using low pass filter, which reduce the size of filter and increases the power factor. Here soft switching can be obtained by using a new partial resonant converter. The higher order harmonics are eliminated by using low pass filter, which reduce the size of filter and increases the power factor. Here soft switching can be obtained by using a full bridge resonant converter. The proposed system has the advantage of less components and less switching losses.

2. PROPOSED CIRCUIT CONFIGURATION

   A single stage ac-dc converter is integrated with PFCs as shown in the figure 1.The diodes (D9-D12) represents the intrinsic body diodes of the MOSFETs. A series resonant circuit and a transformer T1 form

   conducting switches. Each modes are explained below.

   A. MODE I

   This mode begins at when turning off the MOSFETs (M2 and M3), since the load current ir is negative at the switching off time. The diodes (D9 and D12) are forced to freewheel ir.The drain to sources voltage (Vds2 and Vds3) of M2 and M3 are combined to -0.7 v. The voltage across the resonant circuit is equal to dc-link voltage Vdc3 and Vdc4.After some time gating signal are given to MOSFETs (M1 and M4) but there are still in off condition. The voltage in the reactive component L1 is equal to the line voltage. The inductor current Ip1 increases linearly from zero. Then M1 is turned on at zero voltage.

   D3 L2

   D1

   the load resonant circuits. (PFC1 and PFC2) to make

   the sine wave sinusoidal and in phase with the input line voltage. PFC1 and PFC2 operating simultaneously at both positive half cycle and negative half cycle of the input line. A small low pass filter is used to remove the high frequency component at the input.

   D3 L2

   Pulse

   genertor

   L1

   AC C1

   Pulse

   D2 genertor

   L3

   D4

   M1 D9

   L4 C2

   T

   M2 D10

   D5 D6

   M3 D11 C3

   C4

   M4 D12

   D1 Pulse

   genertor M1

   L1

   D9

   L4 C2

   M3 D11 C3

   D7 C5 D8

   LOAD

   AC C1

   T

   C4 B. MODE II

   Pulse

   D2 genertor M2

   L3

   D10

   M4 D12 D3

   L2

   D4

   D1

   Pulse

   D11

   D5 D6

   C5

   Genertor

   L1

   M1 D9

   M3 C3

   D7 D8

   L4 C2

   LOAD

   AC

   Figure 1: Single stage high power factor converter

3. CIRCUIT OPERATION

   There are four switches, namely M1., M2,M3,and M4 are controlled by four gating signals,namely,Vgs1,Vgs2,Vgs3, and Vgs4 respectively.

   C1

   Pulse genertor

   D2

   L3

   D4

   T

   M2 D10

   D5 D6

   C5

   C4

   M4 D12

   Gating signal Vgs1and Vgs4 and gating signals Vgs2 and Vgs3 forms two voltage waveforms. The gated signals have equal and same waveform. M1 and M4 is turned on, M2 and M3 is turned off simultaneously and vice versa, each gated signals has a duty ratio of 0.5.

   Since the circuit operates equally, the operation of the negative half cycle of the line voltage are equal to positive half cycle, except for inductor and power factor correction circuit .Hence the circuit is analyzed for positive half cycle only. The circuit operation divided into seven modes of operation with respect to

   D7 D8

   LOAD

   During this mode, ir is still negative.small part of IP1 flow through M1, but it is equal to ir which flows to D12. This mode will end at when Ir passes zero and becomes positive,then M4 turned on approximately at zero voltage

   C. MODE III

   D3 L2

   E. MODE V

   3 L2

   D1

   Pulse genertor

   M1 D9

   D11

   D1

   D1

   M3 C3

   L1

   L4 C2

   Pulse

   genertor

   L1

   M1 D9

   M3 D11 C3

   AC C1

   T

   C4 AC C1

   L4 C2

   T

   Pulse

   D2 genertor

   L3

   M2 D10

   M4 D12

   Pulse

   D2genertor

   M2 D10

   C4

   M4 D12

   D4 L3

   D5 D6

   D7 C5 D8

   LOAD

   D4

   D5 D6

   D7 C5 D8

   During this mode, M1 and M4 are kept at ON state. Since the line voltage keeps applying on inductor L1, ip1 increases continuously and flows through switch M1, current ir is positive and flows through switches M1 and M4.

   D. MODE IV

   D3 L2

   D1

   LOAD

   When the rectified input voltage is at high level, the peak value of ip1 is high. On this condition, ir declines to zero before ip1 does. When ir resonates to pass zero, the circuit operation enters mode 5. At this instant, D2 and D 3 turn off naturally ,and M2 and M3 are turned on at nearly zero voltage to carry ir.

   1. MODE VI

      When the rectified input voltage is at low level, the

      Pulse genertor

      L1

      D9 D11

      M1 M3 C3

      L4 C2

      peak of ip1 is small and declines to zero before ir resonates to zero. The circuit operation will enter

      AC C1

      T

      Pulse

      mode 6 when ip1 decreases to zero. In this mode ends D3 is off and ir keep flowing through D10 and D11. This mode ends at the time when ir resonates to zero.

      D2genertor

      L3

      M2 D10

      M4 D12

      Then,M2 andM4 are turned at zero voltage to carry ir

      C4

      C4

      .

      D4 D3

      D5 D6 L2

      D7 C5 D8

      LOAD

      D1

      Pulse

      genertor

      L1

      D9

      M1 M3 C3

      This mode begins when M1

      and M4

      are turned off.

      L4 C2

      At the switching off instant ,ip1 reaches its peak and irAC

      is positive. Current ir will freewheel through D10 and D11 to charge the capacitor. Then diode D5 is reverse biased and ip1 will flow through diode D7 to charge

      C1

      Pulse

      D2 genertor

      T

      C4

      M2 D10 M4 D12

      the capacitor. The voltage across L1 is Vdc1, therefore,ip1 starts to decrease linearly.

      Since the peak of ip1 is proportional to the rectifier input voltage, the duration for ip1.

      L3

      D4

      D5 D6

      D7 C5 D8

      LOAD

   2. MODE VII

      VOLTAGE(V)

      VOLTAGE(V)

      D3 1

      L2

      D1

      Pulse

      genertor

      D9

      M1 M3

      D11 C3

      L1

      AC C1

      Pulse

      L4 C2

      T

      D10

      0.5

      C4 0

      0 1 2 3 4 5

      D2 genertor

      L3

      M2 M4 D12

      Time(S)

      Fig. 3 Gate pulses for switches M2 & M3

      x 10-4

      D4

      D5 D6

      output voltage (v)

      output voltage (v)

      D7 C5 D8

      LOAD

      400

      During this mode,ir

      is negative and flows through

      300

      M2 and M3. The capacitor supply energy to the load resonant circuit, then both the switching devices are turned off.

4. RESULTS

   The simulation result of proposed converter was analysed by MATLAB/Simulink Software. Fig. 1 shows the input voltage and current waveform of the proposed converter

   Voltage and Current waveform

   Voltage and Current waveform

   400

   200

   0

   -200

   -400

   0 0.01 0.02 0.03 0.04 0.05

   Time(s)

   Fig. 1 Input voltage and current waveform

   VOLTAGE (V)

   VOLTAGE (V)

   1

   0.5

   0

   0 1 2 3 4 5

   200

   100

   0

   0 5 10 15

   Time(s)

   Fig. 4 output voltage of the proposed converter

   Output Current(A)

   Output Current(A)

   1.5

   1

   0.5

   0

   -0.5

   0 5 10 15

   Time(s)

   Fig. 5 Output current of the proposed converter

   Fig. 1 shows the input voltage is sinusoidal and the input current is also in phase with each other and the power factor the proposed circuit is 0.99 for the given inductive load.

   Fig. 2 and Fig. 3 shows the gate pulses for the switches whenever the gate pulses is given switches will in the on condition whenever the gate pulses is not given the switches will in the off condition.

   Fig 4 shows the output voltage of the proposed converter. The output voltage of the proposed converter is 300V for the given switching sequence.

   Time (S)

   x 10-4

   The output voltage waveform stabilizes after 10

   Fig. 2 Gate pulses for switches M1 & M4

   seconds

   Fig 5 shows the output current of the proposed converter.The output current of the proposed converter is 1A the output current waveform stabilizes after 10 seconds.

5. CONCLUSION

   The power factor of the AC-DC converter has been improved by using power factor correction circuit and filter. In this project, comparative results of voltage regulation of AC-DC converter with load conditions and the power factor correction also realized in MATLAB environment. The switching power losses and stresses has been minimized due to soft switching technique.

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