Non-Isolated High Gain Quadratic Boost Converter

Abstract

A new non-isolated high gain quadratic boost converter is introduced in this paper. The concept of inductors asymmetric input voltage is adopted for developing this high gain converter. The proposed converter benefits from continuous input, positive output, common ground and high-power density features which makes it suitable for renewable energy applications, electric vehicles, dc microgrid applications etc. This converter has got many advantages when compared to the existing topologies in terms of component count, voltage gain, effectiveness index etc. This topology possesses a higher effectiveness index and lower switching device power rating. To validate the performance of the proposed converter, experiments are conducted on 6W laboratory prototype, and corresponding results are presented in this work.

Introduction

I. INTRODUCTION

For several years, switch-mode power converters are being used extensively in modern electronics technology across multiple sectors, including industrial, commercial, utility, and consumer markets.

For low power DC-DC applications, the conversion of power is accomplished  using three major types of power converters namely, buck, boost and buck-boost converters. However, certain specialized applications will require advanced combinations or enhanced variations of the conventional topologies. Several DC-DC converters are proposed in the past, but there is no one solution which is suitable for all the applications. In general, conversion techniques have found a wide variety of applications in industry, research and development, and   in our daily life.

DC-DC converters is an important aspect in the field of power electronics and energy drives as they are widely used in several industrial applications.

High voltage gain converters are used for  multiple applications, which includes radar systems, DC distribution systems, and also renewable       energy applications. Nowadays, the whole world is dependent on renewable energy sources for electric power generation due to climatic changes, pollution and mainly the depletion of fossil fuels. Therefore, high gain DC-DC converters are essential or crucial in case of renewable energy applications as it facilitates boosting of the voltage that makes it suitable for integration with the distribution system.

Usually, DC distribution offers a number of advantages including a  reduced number of conversion units, price, and improved power quality, which makes it a perfect  choice for a good range of applications. It is important to ensure that the design goals of power electronic converters, in general, vary from application to application. However, the most common criteria include maximizing performance and improving power density by reducing the overall cost. Also, the operating conditions need to be taken care of, which includes environmental considerations and operation at a suitable frequency where core losses and switching losses are minimal. Ripple reduction should also be taken care of for both voltage and current, along with heat dissipation and electromagnetic interference so that power density requirements can be fulfilled.

The DC-DC converter topologies employed for renewable energy applications need to draw continuous and smooth input current so that ripple reduction can be achieved. It should also be able to integrate with different types of power sources. Non-isolated interleaved high voltage gain topologies are typically used for interfacing renewables and microgrids.

To achieve high gain DC voltages, boost converters are used. Conventional boost converters use large switching duty cycles to obtain high output voltage. Due to this conduction losses and current stress is increased. Also, the efficiency is drastically reduced with parasitic resistors. The method of cascading proves to be unreliable due to complexity of design. Another method to obtain high output voltage is the inclusion of transformer or coupled inductor. The main disadvantage of this is production of voltage spike, and magnetic interference due to leakage  inductance. To overcome these drawbacks, we are introducing a new transformer less or non- isolated high gain quadratic boost converter. This topology introduces the concept of asymmetric  input voltage to derive a high voltage gain converter.

II. SYSTEM CONFIGURATION

Fig .1. Block Diagram of the system

The block diagram of the proposed high gain non-isolated quadratic boost converter is shown in above figure. The various blocks include; source, the proposed quadratic converter, load, a drive circuit and a control circuit. The input given to the converter is a DC source. The proposed converter consists of two converters in cascaded form; namely, the primary converter and the secondary converter. In between these converters a capacitor-diode cell is incorporated. It consists   of a drive circuit which is used to drive the switches and also to isolate the power circuit from the control circuit. The proposed converter consists of two active switches which are operated simultaneously. The control circuit is used to provide the PWM pulses to the synchronously operated active switches.

Fig. 2. Schematic diagram of the proposed converter system

The schematic diagram of the proposed converter is shown in figure 2. The proposed converter is derived utilizing diverse input voltage in the ON and OFF states of the secondary converter by integrating the diode-capacitor cell to the conventional quadratic converter.

Fig .3 Proposed high gain quadratic boost converter

The assumptions for circuit operation are, all the components used in the circuit are ideal, the capacitors are large enough to maintain output voltage constant, and the converter is operating  in continuous conduction mode (CCM). The proposed converter has two modes of operation as described below.

In mode-I (0 < t < DT), the two active switches S1 and S2 will be turned on simultaneously, and   the three diodes D1, D2, and D0 will be reversed biased. In this mode, inductor L1 will be energized with the help of the input voltage source Vin and the inductor L2 will get energized with the total voltage supplied by the capacitor C1 and additional capacitor C2. The output capacitor is large enough to support the load current during this mode, and the corresponding power ?ow is shown in figure 4.

Fig 4. Circuit Structure of Operating Mode 1

Then,

????????1= ????????????                       ………………(1)

????????2= ????????1 + ????????2 …………….…(2)

????0= ????????0                                     ……….………(3)

In mode-II (D < t <T), the two active switches S1 and S2 will be turned off, and the three diodes D1, D2, and D0 will be in conduction as they are forward-biased. The inductors will be demagnetized, and capacitors will get charged in this mode, and the corresponding power ?ow is shown in Figure 5.

Then, the equations are obtained as;

 ????????1= ???????????? + ????????1

 ????????2= ???????????? + ????????

                           ????0= ???????????? + ????????1 + ????????2 ……………(4)

Therefore, equation 2 in 4;

                           ????0= ???????????? + ????????1 + ????????1 + ????????2

Fig .5. Circuit Structure of Operating Mode 2

Fig.6. The time-domain waveforms of the converter in CCM

III. PERFORMANCE ANALYSIS OF THE SYSTEM

The proposed non-isolated high gain quadratic boost converter is simulated using MATLAB- Simulink. Designing a converter usually consumes significant time as well as cost. Normally, the performance of the converter is generally determined after testing it at nominal operating points. Therefore, simulation can substantially reduce the development cost.

Fig.7. Simulation diagram of the proposed converter

The above figure shows the simulated diagram of the proposed converter. All the components of  the converters are selected from the Simulink tools and placed at the right position. Also, a closed loop system is implemented in order to maintain the output voltage constant even if there is any variations in the input voltage or load. Here, a PI controller is used so as to smoothen the output. That is, a PI control mechanism is used to reduce damping and overshoot. After simulating and compiling the converter, the output waveforms obtained are shown in fig 8.

Fig.8. Simulation Waveform

From the above simulated waveforms, we see that for an input voltage of 12V, we obtain 65V output for a load resistance of 100Ω. This shows that the proposed converter is capable to produce  an output which is almost five or six times that of the input voltage. Hence, we show that the proposed converter is a high gain converter.

IV. DESIGN OF THE SYSTEM

The below figure represents the schematic of hardware implementation of the control circuit. Here, the microcontroller used is dsPIC30F2010. This microcontroller is used to produce the PWM pulses for two synchronously operated active switches S1 and S2. The TLP250 driver circuit is used to drive the switches and to isolate the control circuit from the power circuit.

dsPIC30f2010 is a 28 pin IC. It requires a supply voltage of 5V which is provided using a regulator IC 7805. Supply is given to Vdd pin of the controller and Vss pin of the controller is grounded. A crystal oscillator pf of frequency 8Mhz is connected across the pins osc1 and osc2 of    the controller. Also, two capacitors are connected in parallel with the crystal oscillator.

Fig.9. Schematic of the hardware implementation

The circuit consists of two driver circuits as our converter has two switches S1 and S2. TLP250 driver circuits are used in the hardware implantation as shown in the above figure. TLP250 has 8 pins. Two PWM pin connections are taken from dsPIC30f2010 namely, PWM1 and PWM2. Anode pin of one of the TLP250 is connected to PWM1 and the anode of the other driver circuit is connected to PWM2 respectively. Pin 3 which is cathode of the driver circuit is grounded. Also, pin 5 of TLP250 is grounded. Pin 8 i.e., Vcc of TLP250 is given a supply voltage of 12V. Each TLP250 has two output pins which are pin 6 and 7. In one of the drive circuit, pin 7 is connected   to the gate terminal of the switch S1 while the pin7 of the other drive circuit is connected to the gate terminal of the switch S2 respectively.

Once, the switches S1 and S2 are provided with the gate pulses, the converter operates and  produces output. This output voltage is then scaled down using two resistors as shown in the figure   which acts like a voltage divider. Then, this output is fedback to analog pin (AN05) of the controller. It then compares Vref and Vout to produce the corresponding PWM.

A. Design of Passive Components

              Input voltage, Vin  = 12V

Output voltage, Vout  = 72V

Switching frequency, fsw  = 40kHz

Load resistance, RL  = 1000 Ω

Output power, Pout  = 6W

Efficiency, η = 90%

Then, the input power is,

Pin  = Poutη  =60.9  = 6.67W

P= VI

    Input current, Iin  = PinVin  = 6.6712  = 0.56A

Also, Iin  = IL1

Voltage gain of the converter is,

                       MCCM  = VoutVin  = 7212  = 6

Duty cycle of S1 & S2 is,

                                 D = 1+2MCCM- (1+8MCCM) 2MCCM

                                      = 1+26-√(1+8(6))2(6)  = 0.5

Therefore, D = 0.5

Now,

                                   L1  = Vin DΔiL1 fs  

ΔiL1  is 30% of IL1

ΔiL1  = 0.56 ×  0.3 = 0.168A

Then,  L1  = 12 ×0.50.168 ×40 ×103  = 893µH

L1≅900 µH

              L2  = 2Vin ΔiL2 fs  D1-D

             IL2  ≅  Iout1-D

            Iout  = PoutVout  = 672  = 0.0834A

            IL2  = 0.08341-0.5  = 0.167A

ΔiL1  is 40% of IL2

ΔiL1 = 0.4×0.167=0.0668A

               L2  = 2 ×120.0668 ×40 ×103 0.51-0.5  = 8mH

               L2  ≅6mH

Now,  VC1  = VC2  = Vin1-D  = 121-0.5  = 24V

i.e.,  VC1  = VC2  = 24V

Δvc1 is 5% of VC1

Δvc1 =  24 ×0.05 =1.2 V

Then, C1  = Vout Δvc1 R fs  D1-D

          C1  = 721.2 ×1000 ×40 ×103 0.51-0.5  

          C1  = 1.5µF

Similarly, C2  = Vout Δvc2 R fs  D1-D  = 1.5µF

C0  = Vout  DΔvc0 R fs

Δvc0  is 1% of VC0

VC0  ≅ Vout

Δvc0  = 0.01 ×72=0.72V

           C0  = 72 ×0.50.72 ×1000 ×40 × 103  = 1.25µF

Therefore, the values of all the passive elements are found. The corresponding experimental specifications are shown in the table below.

Table .1. Experimental Specifications

Fig.10. Prototype Testing

To validate the performance of the proposed high gain quadratic boost converter, experiments are conducted on the 6W laboratory prototype as shown in fig. 10. Also, fig. 11 shows the output voltage waveform and fig.12 shows the gate signals of switches S1 and S2 respectively when connected to 1000Ω resistive load.

Fig.11. Output voltage waveform                  Fig.12. Gate signals of S1 and S2

Conclusion

Nowadays, the whole world is dependent on renewable power generation and electric vehicles due to varying climatic conditions, pollution and depletion of fossil fuels. A high gain DC-DC converter with continuous input is required to meet the dc bus voltage and loads due to low voltage at renewable power sources. A new high gain non-isolated quadratic boost converter is proposed in this paper. The concept of inductors asymmetric input voltage is adopted for developing this high gain converter. To get the quadratic boost gain, usually two conventional boost converters are connected in cascaded nature, where one converter output is fed to another converter. In this we use an additional capacitor-diode cell in between the two converters to obtain the diverse input voltage in the ON and OFF state of secondary converter. This converter consists of two synchronously operated active switches. It has two modes of operation in continuous conduction mode (i.e., when the switches are in ON and OFF states). The proposed converter has continuous input, provides positive output and common ground. Also, this converter has got many advantages when compared to the existing topologies in terms of component count, voltage gain, effectiveness index etc. This topology possesses a higher effectiveness index and lower switching device power rating. This converter is well suited for renewable energy generation, electric vehicles, avionics and dc microgrid applications. Detailed theoretical models for these converters were derived and practically verified. This methodology can be further investigated to derive new high gain DC- DC converters.

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Copyright © 2025 Shefni ., Rasnas P, Aneesrahman T. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.