Presented by R.SARAVANAN

16111100162nd yr M.Tech(PED)

A Novel Pulse Shift Modulation Technique For Controlling Dc-

Dc Converter

Pulse Width Modulation Technique (PWM) and Pulse frequency Modulation Technique(PFM) are commonly used techniques to generate pulses to control switches in DC-DC converters.

The conduction losses and output voltage ripples are dominant in PWM at High loads, and Switching losses are dominant in PFM at low loads.

In proposed a Phase Shift modulation technique, which dynamically changes the duty cycle and frequency of the control pulse to control the switches in DC-DC converters.

This techniques reduces the conduction losses and ripple voltage inherent in PWM and switching losses inherent in PFM .

Abstract:

The Load condition in these Portable devices changes extreme from standby mode to the operating mode.

PWM technique changes the duty cycle of the control pulse without altering the frequency.

PFM technique changes the frequency of the control pulse without altering the duty cycle.

This inefficiency is due to conduction losses, switching losses and output voltage ripples.

PFM technique due to the high switching frequency.

Introduction:

A Pulse Shift Modulation Technique that increases the efficiency of the DC-DC converters at Wide load ranges.

This technique dynamically manipulates the switching frequency and the duty cycle of the control pulse to maintain a constant output and reduce the losses to both PWM and PFM techniques.

At Low load values the switching frequency is manipulated along with the duty cycle in the PWM technique.

To Minimize the ripple output voltages and the losses in the PWM technique.

At High load values, the duty cycle is manipulated along with the switching frequency in the PFM technique.

Lower the switching losses inherent in the PFM technique.

Cond…..

Control Pulse Generation through PSM technique:

The triangular pulse (Vtp) of varying duty cycle and switching frequency changes dynamically with the change in the load value.

At each clock cycle, this triangular pulse (Vtp) is compared to an error voltage (Verr) which corresponds to the difference between the output voltage (Vout) of the DC-DC converter and a reference voltage (Vref).

If Verr is higher than Vtp, the control pulse Vcon is driven high (3.3V); otherwise it is driven low (<0.8V).

One can see that the control pulse Vcon in the PSM technique has a variable duty cycle ,switching frequency in contrast to the constant switching frequency in the PWM technique and the constant duty cycle in the PFM technique.

Description:

Flow Chart:

Circuit Diagram of Buck Converter:

The output voltage at the load is sensed and converted to a digital signal by an Analog/Digital converter.

The duty cycle and frequency are determined to transfer the appropriate amount of power to the load such that the output voltage remains constant.

Description:

FPGA-based hardware implementation of the PSM controlled:

Waveform for Duty Cycle:

The duty cycle dynamically changes with the change in the load condition whereas it is constant in PFM technique and goes below the minimum value (20%) in PWM.

This duty cycle is smoothly increased with the increase of the load value to avoid that the circuit enters in the discontinuous mode,which corresponds to duty cycles under 20%.

Description of duty cycle at differential load values:

Waveform for Frequency:

The frequency in the proposed technique changes with the change of the load conditions.

As can be seen, this frequency is kept higher compared to the constant frequency in the PWM mode and smaller compared to the switching frequency in the PFM mode of operation.

Description Of Frequency at Differential Load Values:

These conduction losses (inductive and capacitive losses) dominate in the PWM technique.

Therefore,these losses are calculated for the proposed technique and compared to those of PWM technique at different load values.The inductive and capacitive losses are given as

Conduction Losses :

Waveform for Inductive Losses:

Waveform for Capacitive Losses:

The Switching Losses are Equation as given as,

. Where is the resistive losses in the switch, is the switching losses, is the output current, is the output voltage, is the input voltage, F is the switching frequency, and is the capacitance of the switch.

Switching Losses:

Contd…..

Switching losses with the Proposed technique, the switching frequency of the control pulse is high, Which result in High switching losses .

In this Proposed technique the duty cycle as well as the switching frequency is Manipulated,which results in lower Switching frequency is lower switching losses.

This ripple voltage is due to the switching behavior of the converter.

In the feedback loop for the converters, this voltage corrupts the input supply voltage, and hence, reduces the stability of the system.

Appropriate values of LC combination can be used to minimize this ripple voltage. For a given LC combination, the ripple voltage increases rapidly with the decrease in the duty cycle and switching frequency.

These ripple voltages are dominant in the PWM technique. Therefore, the ripple voltages with the proposed technique are calculated and compared to those of the PWM technique at different load values.

Voltage Ripple:

The ripple voltage is given as

Where V/V is the ripple voltage, D is the duty cycle, F is the switching frequency, L is the inductance, and C is the capacitance.

The ripple voltage is significantly reduced with the proposed technique compared to the ripple voltage with the PWM technique.

This reduction leads to a more stable DC-DC conversion process.

Contd…

Waveform of Voltage Ripple:

This paper discusses an FPGA-based technique to control DC-DC converters. This technique dynamically manipulates

The duty cycle and the switching frequency of the control Pulse.

The results indicate that the proposed technique has lower conduction losses and ripple voltage compared to the losses and ripple voltages inherent in the PWM technique.

Furthermore, it also significantly reduces the switching losses compared to those of the PFM technique. Thus, a converter based on the proposed technique results in higher efficiency under a wide range of load conditions.

Conclusion:

Thank

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