Analysis and Simulation of Full-Bridge Boost Converter using Matlab

Improvement of high power and high performance applications causes attention to the DC-DC converter topologies. In this paper we analyze and simulate full-bridge boost converter, an isolated DC-DC converter. The advantages of isolated DC-DC converters include high efficiency, low manufacturing cost, safety, electrical isolation using transformer. The transformer is used to produce a higher voltage in secondary voltage side. Matlab Simulink is used for simulation of this converter. Nominal input voltage in this simulation is 30V and the output voltage is 55V. Also other parameters are given in this paper.


I. INTRODUCTION
OWADAYS isolated DC-DC converters are very popular and used in different sections and applications.These converters have some advantages compared to the non-isolated converters, like high efficiency, low manufacturing cost, electrical isolation using transformer [1][2][3].In many of the applications, we need to have isolation between input and output.Isolation can be done by simply connecting a transformer at the converter input.When we need a large stepup or step-down conversion ratio the transformer can improve the performance of the converter [2].By choosing the appropriate ratio, the voltage or current stresses on the transistors and diodes can be reduced [1].There are different topologies for the isolated converters.In this paper we will describe the isolated full-bridge boost converter topology.This topology is very useful in high power applications.Also A variety of circuit topologies can be used for the full-bridge boost converter.In this paper we analyze a topology in Fig. 1.Isolated full bridge boost converters can be obtained by inversion of the source and load of isolated full bridge buck converters.The circuit performance of this converter in the first and second subinterval is equivalent to basic non-isolated boost converter.By placing the ratio of 1:1 for the transformer, output and induction current waveforms are the same waveforms for non-isolated boost converter.
Omid Alavi is with the Department of Electrical Engineering, K.N.Toosi University of Technology, Tehran, Iran (e-mail: alavi.omid@mail.com)Soheil Dolatabadi is with the Department of Electrical Engineering, Tabriz University, Tabriz, Iran (e-mail: sl.dolatabadi@gmail.com).
This paper outlines the design and analysis of a full-bridge boost converter with considering losses [1].
In the first stage of designing of the full bridge power converter, we estimate the required parameters according to the known data of the converter.In this simulation, in regular simulation method with respect to voltage input range (18-40 volt) and fixed voltage output (55 volt).We can do this simulation with the appropriate input voltage value (30 volt) for the converter.For this simulation we used Matlab Simulink and we will explain simulation steps in order in this paper.For this converter, the high peak input voltage and wide input voltage range are items that will be challenging to meet.Since the converter has only one main control variable, duty-cycle, then in order to maintain a constant output voltage in the presence of a wide input voltage range, the duty-cycle will also have a wide operating range.However, it is important to keep in mind that the duty-cycle control range for practical reasons, should be in range of duty-cycle maximum and minimum [1,4].

II. CONVERTER TOPOLOGY
The various arrangements of the components, and their operation, will dictate the converter characteristics which give rise to many different topologies, such as buck, Fly-back and bridge converters.It is the strategic placing of the components that will expose them to certain electrical and thermal stress which translates to volume, weight and cost of the overall system.In an effort to minimize the key drivers of volume weight and cost, the designer is forced to find a balance between converter performance and customer satisfaction.Some selected topologies and their inherit capabilities are listed in Table II  Justification of an isolation transformer for this design is given for two reasons, safety and step-down capability.Although the output voltage of 55V is in the "safe range".
The input voltage is well beyond anything that you would want to come in contact with.Therefore, galvanic isolation provided by a transformer would be appreciated.Additionally, the transformer allows one to set a turns-ratio to assist with large difference between input and output voltages, as is the case in this design.
The electrical block diagram from the converter is given in Figure 1 [1]: This schematic is for ideal mode.To consider the losses, we need to add an inductor parallel with transformer in primary side of transformer.The electrical block diagram from the converter with transformer equivalent circuit is given in Figure 2: Equation 24 shows boost Conversion ratio M (D) with turns ratio n.

A. Turns Ratio Selection
The turns ratio is determined by assuming that the nominal voltage for this converter is exactly in the middle of the input voltage range, 30V.Then the duty-cycle, being limited to 45% is chosen to be exactly in the range [1].In this manor, the duty cycle can be adjusted higher or lower in equal quantities to accommodate the input voltage range of 18V to 40V.Since the output of our converter is 55V, and given the voltage transfer function derived in past equation, we can now select the appropriate turns-ratio as follows: With this equation we can find n and correct D value, With 1:1 turns ratio, inductor current i(t) and output current io(t) waveforms are identical to non-isolated boost converter regularly maximum value of duty-cycle is 0.45, so primary duty-cycle is chosen to be exactly in the middle of its range or 22.5%, but in full-bridge maximum duty-cycle is (2×Dmax):  In this simulation we used C=25 µF.
V. SIMULATION VALIDATION The models derived in the previous sections were simulated using Simulink; the circuit diagram is shown in Figure 8: ) × 100% for pulse width.For Q1 and Q4 we set phase delay to 0, for Q2 and Q3 we set phase delay to TS.For considering losses we set Lm, Rm to transformer configurations.
The simulated results are provided in Figure10.

Fig. 7 .
Fig. 7.The voltage and current waveforms of Full-bridge boost converter IV.CONVERTER PARAMETERS ANALYSIS (2 * 0.225)) =  ⇒  = 1 (26) So we set n in range of 1-1.4: n=1.2 Next step is checking of duty-cycle: ) = 1.2 ⇒ 0.345 ≤ 0.45 (27) B. Select L, C and R:In Converter Specification table (Table.I), we have Power of load in range of 10-150w, with Equation 28 we can find R range: The minimum value of the output capacitor can be determined from this equation[6]:

Fig. 8 .
Fig. 8. Matlab simulation scheme construction of Full-bridge boost converter

Fig. 10 .
Fig. 10.The Full-bridge boost converter output voltage and current waveforms Zoom in on the output voltage and current ripple:

Fig. 11 .
Fig. 11.Zoom in on the Full-bridge boost converter output voltage and current Primary and secondary sides of transformer voltages in simulation: