BRIDGELESS PFC IMPLEMENTATION USING ONE CYCLE CONTROL TECHNIQUE PDF

In this paper, One Cycle Control technique is implemented in the bridgeless PFC. By using one cycle control both the voltage sensing and current sensing. rectifier and power factor correction circuit to a single circuit, the output of which is double the voltage implementation of One Cycle Control required a better controller. . The figure shows a typical buck converter using PWM technique. PWM switching technique is used here as implementation of One Cycle Power Factor Correction, Bridgeless voltage Doubler, Buck Converter, One Cycle Control This problem can be solved by using bridgeless converters to reduce the.

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Analysis and design of a voltage doubler bridgeless buck converter is performed during the course of project and hardware implementation of a prototype was done during this period. Voltage doubler bridgeless buck converters can be used in switched mode power supplies as rectification as well as power factor correction circuit. Conventional switched mode power supplies contains a bridge rectifier followed by power factor correction circuit and second stage dc to bridgelfss converters for generating the required dc voltage.

Fechnique voltage doubler circuit combines both the rectifier and power factor correction circuit to a single circuit, the output of which is double the voltage produced by a single buck converter [3] used as pfc circuit.

This circuit consists of two buck converters connected in parallel in series out manner. The total output obtained is the sum of voltage across each capacitor of the buck converters which are operating during positive and negative half respectively. MOSFET is used as the switching device of implementatiob buck implemeentation Usually pulse width modulation technique is used for switching operation and clamped current mode control is used for controlling the buck converter.

In this paper ,a new control method called One Cycle Control is used for controlling the buck converter during both half of supply voltage. This method is a non linear control technique to control the conrol ratio of the switch in real time such that in each half cycle the average value of the chopped waveform is made equal to the reference value. This twchnique provides greater response and rejects input voltage perturbations. A prototype of voltage doubler buck converter generating a dc voltage of 12V operating at a switching frequency of 65kHz is developed.

PWM switching technique is used here as implementation of One Cycle Control required a better controller. The results obtained are also presented in pfx paper. Related article at PubmedScholar Google. Switch mode power supplies without power factor correction will introduce harmonic content to the input current waveform which will ultimately results in a low power factor and hence lower efficiency.

A bridge diode rectifier followed by a power factor correction circuit which is either a buck or boost frontend is commonly implejentation for all switched mode power supplies. This drop of efficiency at low line can cause increased input current that produces higher losses in semiconductors and input EMI filter components. Also it has relatively output voltage, typically in the V range. At lower power levels the drawbacks of the universal-line boost PFC front-end may be overcome by implementing the PFC front-end with the buck topology [7].

Conventional ac-dc converters has a diode bridge rectifier followed by power factor correction circuit.

One Cycle Control of Bridgeless Buck Converter

But this circuit suffers from significant conduction and switching losses due to larger number of semiconducting devices. This problem can be solved by using bridgeless converters to reduce the conduction losses and component count.

A bridgeless buck PFC rectifier[3] combines both rectification and power factor correction using a single circuit. This circuit also act as a voltage doubler circuit whose output voltage is greater than a single buck converter.

Usually the switching operation is controlled by pulse width modulation technique using clamped mode current control of a buck converter. This paper explains a new control method called One Cycle Control [6] which is a non linear control technique and produce faster response than the later implemebtation.

Each converter is operating during positive and negative half cycle respectively. This PFC rectifier employs two back-to-back connected buck converters that operate techniuqe alternative halves of the line-voltage cycle. The buck converter operating during positive half-cycles of line voltage Vac consists of a unidirectional switch comprising of diode Da in series with switch S1 freewheeling diode D1filter inductor L1 and output capacitor C1.

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Similarly, the buck converter consisting of the unidirectional switch implemented by diode Db in series with switch S2freewheeling imllementation D2filter inductor L2and output capacitor C2 operates only during negative cobtrol of line voltage Vac.

The input current flows through only one diode during the conduction of a switch, implsmentation. Efficiency is further cgcle by eliminating input bridge diodes in which two diodes carry the input current.

An additional advantage of the proposed circuit is its inrush current control capability. Since the switches are located between the input and the output capacitors, switches S1 and S2 can actively control the input inrush current during start-up.

In pulse width modulation PWM control, the duty ratio is linearly modulated in a direction so as to reduces the error.

Any change in the input voltage must be sensed as an output voltage change and error produced in the output voltage is used to change the duty ratio to keep the output voltage constant. This means that it has slow dynamic performance in regulating the output in response to the change in input voltage.

A large number of switching cycles are also required to attain the steady state. In PWM control, the duty ratio pulses are produced by comparing control reference signal with a saw-tooth signal. As a result the control reference is linearly modulated into the duty ratio signal.

If the power supply voltage is changed, for example by a large step up, the duty ratio control does not see the change instantaneously since the error signal must change first. Therefore, the output voltage jumps up and the typical output voltage transient overshoot will be observed at the output voltage. Then the error produced in the output voltage is amplified and compared with the saw tooth signal to control the duty ratio pulses.

A large number of switching cycles is required before the steady-state is reached. The output is always influenced by the input voltage perturbation.

The figure shows a typical buck converter using PWM technique. The voltage output Vo is compared with Vref to generate an error signal and it is amplified.

usong The error signal thus obtainedand saw tooth waveform is given as input to the comparator where it is compared is compared to generate the PWM signal for the switch. Since the error generated is used to vary the duty ratio to keep the voltage constant ,this method usinh a slow response.

One Cycle Control is a new nonlinear techbique technique implemented to control the duty ratio of the switch in real cyle such that in each cycle the average value input waveform at the switch rectifier output diode is exactly equal to the control reference.

One-Cycle Control method [2] reject input voltage perturbations in only one switching cycle and follow the control reference very quickly. This new control method is very general and directly applicable to all switching converters.

Switching converters are pulsed and nonlinear dynamic systems. This technique takes advantage of the pulsed and nonlinear nature of switching converters and achieves instantaneous control of the average techniqud of the chopped voltage or current.

This technique provides fast dynamic response and good input-perturbation rejection. Figure shows a typical buck converter employing One Cycle control. The one-cycle controller implementatioon comprised of an integrator with reset, a comparator, a flip-flop, a clock and an adder. The clock triggers the RS flip-flop to turn ON the transistor with a constant frequency. When the switch is turned on by a fixed frequency clock pulse, voltage available controp the diode is being integrated.

The output of the integrator is compared with the control reference in real time using a comparator. When the integrated value of the diode-voltage becomes equal to the control reference, the transistor is turned OFF and the integration is immediately reset to zero to prepare for the next cycle. In each cycle, the diode-voltage waveform may be different. As long as the area under the diode-voltage waveform in each cycle is the same as the control reference signal, instantaneous control of the diode-voltage is achieved.

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Since the usijg variable always follows the control reference the output voltage is independent of all input voltage variations. The clock triggers the RS flip-flop to turn ON the transistor with a constant frequency. Figue shows an OCC controller [2] for controlling a bridgeless buckconverter. Here Vo is the output voltage obtained across the two capacitors C1and C2. Bricgeless output obtained is amplified and is fed to implemetnation integrator with reset.

At each instant the integral value is being compared with a reference Vref. When integral value Vint reaches the control reference,Vref comparator changes its state and turns the switch transistor off and the integrator is reset to zero at the same time.

Since the reset signal is a pulse with very short width, the reset time is very short, and the integration is activated immediately after the resetting. The operation of an OCC trchnique is explained by means of the following waveforms. Here Ts is the time period of one switching cycle. The operation is explained for positive half cycle during which switch Q1 is operating and Q2 is off ,Vref techhnique the reference voltage. The integrator is also activated during the start of each switching cycle.

When the integral value of Vo reaches the Vref ,the comparator changes its state from low to high which is indicated by a short pulse uisng shown in the graph. When this condition is reached the switch is turned off till the starting of the next switching cycle implemengation this process repeats for both positive and negative half. By increasing the switching frequency almost constant output voltage can be obtained by this control method. This also eliminates any variation of the input supply voltage and provides a dynamic performance.

The simulink model of the bridgeless buck converter is shown below. The values of inductors and capacitor is designed to obtain an output of 12 V DC. G1 and G2 shows the gating signals generated by the one cycle controller which is used to control the switching operation of S1 and S2.

The simulation is done at a switching frequency of 65kHz. The voltage available at the output is double the voltage across each capacitor.

The two inductor topology can be also replaced by using a single inductor at the middle so that same inductor can be made common to both the buck converters operating at positive and negative half. The simulink model of OCC controller is shown below. The output voltage V0 is fed to the integrator. The output of the integrator is compared with the reference techniuqe the comparator and the output of the comparator is used to set and resets the D flip flop.

The output of the flip flop is implemenyation required gating pulse for the switches. The buck converter is generating an output voltage of 12V using One Cycle Control method. The gating signals bridgeles to the switches during the positive and negative half cycle, input and the output waveforms obtained during the simulation are shown below.

Bridgeless PFC Implementation Using One CycleControl Technique

When switching pulses are given to one of the ipmlementation the other switch will be off. Thus it is important to identify whether the incoming waveform is from the positive half or from the negative half. The hardware setup of the circuit is designed and implemented.

The bridgeless buck converter was designed for an output voltage of 12V dc. The prototype of a typical converter is shown below. BYQ28E is used as the diode rectifier.

Constant Power supply required for the microcontroller and the driver is provided using separate DC source. Supply required for the operation of other semiconductor devices is being supplied by the power supply unit being implemented within the circuit.