18 NEW ZV-ZCS FULL BRIDGE DC-DC CONVERTER WITH FUZZY … ZV-ZCS... · NEW ZV/ZCS FULL BRIDGE DC-DC...

Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)

156-169, December, 2014, Ernakulam, India

156

NEW ZV/ZCS FULL BRIDGE DC-DC CONVERTER WITH

FUZZY & PI CONTROL

ASWATHY HARIDAS1,

SARITHA K.S2, AJITH K.A

3

1P G Scholar, Electrical & Electronics department,

Sree Narayana Gurukulam College of Engineering, Kolenchery, India

2Associate Professor, Electrical & Electronics Department,

Sree Naryana Gurukulam College of Engineering, Kolenchery, India

3Assistant Professor, Electrical & Electronics Department,

Sree Naryana Gurukulam College of Engineering, Kolenchery, India

ABSTRACT

DC-DC conversion technology has been developing very rapidly and DC-DC converters have been widely used

in industrial applications. The main problem related to the conventional full bridge dc to dc converter is the large voltage

spikes across the output diodes. Lose of ZVS will increase the losses and EMI. In order to avoid these, here a new

ZVZCS full bridge converter is introduced. In this paper Conventional full bridge DC to DC converters and the proposed

converters are compared and simulation analysis also included. Moreover, closed loop control using different control

strategies is evaluated using the PI controller and fuzzy logic.

Keywords: Zero Voltage Zero Current Switching, Fuzzy Logic Controllers, Pi Controllers, Electro Magnetic

Interference

1. INTRODUCTION

DC-DC conversion technology has been developing very rapidly, and DC-DC converters have been widely used

in industrial applications such as DC motor drives, computer systems and communication equipments. In this paper, a

novel type of DC to DC full bridge converter which is having ZVZCS capability is presented. Conventional full bridge

DC to DC converter is having the problem of large voltage spikes across the output diodes due to leakage inductance of

the transformer. Since leakage inductor will act as a current source, it will lead to voltage spikes across the transformer

secondary, output voltage and the voltage across the output diodes. For example, for a 300V output DC supply a 1000V

voltage appears across the output diodes. As the switching frequency of the converter increases, the high frequency

voltage spikes are getting intensified at the output[1]. In the meantime EMI noise may arise. Thus the output diodes have

to withstand the voltage spikes and they get over rated. For high voltage high switching frequency applications,

MOSFET’s are mostly used. MOSFET should be switched under zero voltage for the reliable and robust operation.

Zero Voltage Switching (ZVS) topology, allows operation at a higher frequency and at higher input voltages

without sacrificing efficiency. Lose of ZVS will increase the losses and EMI increases, efficiency decreases. In order to

avoid these, here a new ZVZCS full bridge converter is introduced. The converter is operated under soft switching by

using an auxiliary circuit and the voltage across the output diode bridge is clamped. In this paper, the performance of the

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conventional full bridge converter with the novel ZVZCS full bridge converter. The controller is used to improve the

dynamic performance of DC-DC converter by achieving a robust output voltage against load disturbances. This paper

presents the performance of PI , Fuzzy controllers. Fuzzy controllers are well suited to nonlinear time-variant systems

and do not need an exact mathematical model for the system being controlled. The fuzzy logic controller determines the

operating condition from the measured values and selects the appropriate control actions using the rule base created from

the expert knowledge.

2. OVERVIEW

The ZVZCS full bridge DC to DC converter is implemented and operational principles are analyzed here. The

proposed full bridge converter is compared with the conventional full bridge DC to DC converter under the conditions of

identical supply DC voltage and frequency. Also different control strategies adopted for the closed loop control of the

converter is also implemented and analysed. Simulations are presented to verify the validities of the proposed inverter.

There are a number of simulation software available and the most efficient tool is the MATLAB. Hence, the Simulink

part of the MATLAB is employed. Various control strategies like fuzzy and PI control are also adopted and obtained the

simulation results.

2.1. CONVENTIONAL FULLBRIDGE CONVERTER

The full bridge inverter converts DC to AC and the output is a quasi-square wave voltage. Transformer step up

the output voltage of the full bridge inverter. The output rectifier rectifies the output obtained in the secondary side of the

transformer and we get a DC output.

Fig.1. Conventional full-bridge converter

The main problem related to the conventional full-bridge DC/DC converter is the voltage spikes across the

output diodes due to the transformer leakage inductance. Basically, the leakage inductance of the transformer acts as a

current source and this will leads to the voltage spikes across the output diodes. Theses spikes get intensified as the

switching frequency of the converter is increased. Thus, the diodes should be designed overrated in order to withstand

these voltage spikes. And also, these spikes significantly increase the EMI noise of the converter. This fact makes the

topology not very practical for high frequency, high voltage applications. In battery charger applications, after the battery

is fully charged, the load is zero. So, the converter might be operating at absolutely no-load for a long period of time and

the converter should be able to safely operate under the zero load condition. In case of conventional full-bridge PWM

converters, the ZVS is achieved by utilizing the energy stored in the leakage inductance and this is used to discharge the

output capacitance of the MOSFETs. So, the range of the ZVS operation will highly depend on the load and the

transformer leakage inductance. Thus, the conventional converter is not able to operate under ZVS condition for a wide

range of load variations. The loss of zero voltage switching will lead to extremely high switching losses at high switching

frequencies and very high EMI due to the high di/dt and can also cause a very noisy control circuit, which leads to shoot-

through and loss of the semiconductor switches. The ZVS range can be extended by increasing the series inductance, but



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having a large series inductance will limit the power transfer capability of the converter and it will reduce the effective

duty ratio of the converter.

2.2. PROPOSED ZV/ZCS FULLBRIDGE DC/DC CONVERTER

The proposed converter rectifies the voltage stress problems related to the conventional full-bridge DC/DC

converter. The proposed ZVZCS full bridge DC to DC converter topology provides zero current switching (ZCS) for the

output rectifiers, and zero voltage switching (ZVS) for the full bridge inverter.

Fig.2. Proposed ZVZCS full-bridge converter

Output diode rectifiers are turned on when the current zero in the transformer leakage inductance. In the

proposed ZVZCS converter, an auxiliary circuit is used to produce the reactive current for the full bridge switches and

this ensures the ZVS. This auxiliary circuit will be working independently of the system operating conditions and is able

to guarantee ZVS at all operating conditions. The role of the auxiliary circuit is to provide reactive current for the full-

bridge semiconductor switches, which guarantees zero voltage switching for the semiconductor switches.

3. MODES OF OPERATION



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Fig.3. Modes of operation (i) Mode 1 (ii) Mode 2 (iii) Mode 3 (iv) Mode 4(v) Mode 5

(vi) Mode 6 (vii) Mode 7

3.1 Mode 1: (t0≤ t ≤ t1) In mode1, S1 is discharging and S2 is charging in this mode.VAB is nearly zero. is is not sufficient to forward

bias the secondary diodes. (i) shows the active components during this mode of operation .



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3.2 Mode 2: (t1≤ t ≤ t2

In this mode, the output diodes get forward biased. The active components during this mode is shown in (ii).

Capacitor of S1 is still discharging to finally reach zero and that of S2 is charging up to Vdc. At the end of this mode,

voltage across this capacitor becomes zero.

3.3 Mode 3: (t2≤ t ≤ t3)

MOSFET of the output capacitors have been charged and discharged completely. Now the gate voltage is

applied to S3 and is turned ON. (iii) shows the active components during this mode. The series current ramps up to its

peak value.

3.4 Mode 4: (t3≤ t ≤ t4)

The active circuit during this mode is shown in (iv).The output capacitor of S3 is discharging and that of S4 is

charging up to Vdc.. At the end of the mode 4, VAB is 0(t4) .

3.5 Mode5: (t4 ≤ t≤ t5)

The active components during this mode of operation is shown in (v). Once this voltage VAB will become zero,

this mode starts. During this mode, the output voltage of the inverter is zero and the output diodes will clamp the

secondary voltage to the output voltage. Thus, a net negative voltage is seen across the series inductor, which is the

reflected output voltage at the transformer primary side. Thus current is ramps down.

3.6 Mode 6: (t5 ≤ t ≤ t6 ) Mode 6 starts when the gate pulse is applied to S3 . The active components in this mode are shown in (vi). The

series inductor current is still ramping down and reaches zero at the end of this mode. Switch S1 turns off under near zero

current switching at the end of this mode. At the end of this mode, the current through the series inductor reaches zero

and the output diodes D2 and D3 naturally turns off with zero current.

3.7 Mode 7: (t6 ≤ t≤ t7)

The active components during this mode of operation is shown in (vii). The current through output diodes

reaches zero and the diodes naturally turn off in this mode. The output capacitor Cf feeds the output load with its stored

energy while there is no current on the transformer primary side. In one switching cycle, the proposed circuit has 14

modes during steady-state operation. The remaining 7 modes have the symmetrical structure as the previous 7 modes.

4. NEW CONVERTER-WAVEFORMS

Fig 4. Waveforms



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All the four required gate pulses are shown in fig 4. The modes of operation can be understood easily from the

waveforms shown above. The transformer secondary voltage, auxiliary inductor current, series inductor current, diode

current, the voltage across A & B points are also shown. We may get a clear idea about what happens in each and every

mode from this.

5. DESIGN

The system should be designed well to obtain the required output. Auxiliary inductors are designed based on the

amount of reactive power required to guarantee ZVS for the MOSFETs. The auxiliary inductor acts as a constant current

source, which discharges the capacitor across S1 and charges the capacitor across S2.

Auxilliary inductor current:

I PA = Vdc/(8Lauxfs) (1)

Auxiliary inductance is find out using the following equation:

Laux = 1/(128Csofs2)

(2)

Time delay should be adjusted to ensure zero voltage switching. The dead-time td , should be adjusted to allow the output

capacitors of the MOSFETs to fully charge and discharge and is given by :

td =0.125/fs (3)

The sequential inductance:

Lseq = Ls + Lleak (4)

This series inductance Lseq plays an important role in the energy transfer from the primary to the secondary side

of the transformer.

6. SIMULATION RESULTS & ANALYSIS

There are number of simulation software available and the most efficient is the MATLAB. Hence, the simulink

part of the MATLAB is employed. Simulation of conventional and the proposed full bridge converter is performed using

MATLAB. The output waveforms of the conventional full bridge converter and proposed ZVZCS full bridge converter

are given. All input DC sources are equal. MATLAB 8.1.0(R2013a) is used for simulation part of the project. Simulation

of conventional full bridge converter, proposed full bridge converter , closed loop control using PI & Fuzzy controller are

evaluated in this paper.

TABLE 1: Design specifications of the proposed converter

SYMBOL PARAMETER VALUE

Laux1,2 Auxiliary inductor 0.1662µH

Ls Series inductor 0.03125mH

Cf Filter capacitor 100µF

Lf Filter inductor 80µH

Cs Split capacitor 0.47µF



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Fig.5. Output voltage and output current of conventional converter for 190V input

The output voltage and current waveforms are shown above. But the spikes are observed in the MATLAB

simulation. So our main aim is to mitigate these spikes and to obtain a spike free output. Input voltage is chosen as 20V.

Fig 6 shows simulation of new converter also design specifications are given in table 1.Fig 7 shows the pulse generation

in MATLAB.

Fig.6. Simulation of new converter



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Fig.7. Pulse generation

Zero voltage switching across switch 1 is shown in fig 10. Switching pulses are provided only when the voltage

across the switch reaches a zero value. Fig.11 shows the converter output without any spikes in the output. The secondary

of the transformer will be spike free. Thus overrating of diodes can be avoided. Here choosing the transformer turns ratio

as 1:3, 46V is obtained as output while doing simulation.

Fig.8. Pulses obtained

Fig 9. Inverter output



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Fig 10. Zero voltage switching

Fig 11. Converter output voltage and current waveforms

6. CLOSED LOOP CONTROL & SIMULATION

Closed loop control systems are those that provide feedback on actual state of the system and compare it to the

desired state of the system in order to adjust the system.

Fig.12. Closed loop control

A closed-loop control system is one in which an input forcing function is determined in part by the system

response. The measured response of a physical system is compared with a desired response. The difference between

these two responses initiates actions that will result in the actual response of the system to approach the desired response.

This in turn drives the difference signal toward zero. In this configuration shown in fig.12, a feedback component is

applied together with the input R. The difference between the input and feedback signals is applied to the controller. In

responding to this difference, the controller acts on the process forcing C to change in the direction that will reduce the

difference between the input signal and the feedback component. This, in turn, will reduce the input to the process and

result in a smaller change in C. This chain of events continues until a time is reached when C approximately equals R.

We may use any sort of controllers. It can be a PI controller or a Fuzzy logic controller. Study and simulation of both PI

and fuzzy logic controllers are done.


6.1 CLOSED LOOP USING PI CONTROLLER

Fig.13. Closed loop control using PI controller

International Conference on Emerging Trends in Engineering and Management (ICETEM14)


166

CONTROLLER

Fig.13. Closed loop control using PI controller

Fig.14. Control mechanism

Fig.15. Pulse generation


, December, 2014, Ernakulam, India



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Fig.16. Triangular wave and pulses generated

Fig.17. Counter output

Fig.18. Output using PI controller

6.2 FUZZY LOGIC

Fuzzy control is applied to control DC–DC converters because of its simplicity, ease of design and ease of

implementation. Fuzzy controllers are well suited to nonlinear time-variant systems and do not need an exact

mathematical model for the system being controlled. The fuzzy logic controller determines the operating condition from

the measured values and selects the appropriate control actions using the rule base created from the expert knowledge

[2]. Other advantages of FLC are: 1) It can work with less precise inputs 2) It doesn’t need fast processors 3) It needs less

data storage in the form of membership functions and rules than conventional look up table for nonlinear controllers; and

4) It is more robust than other nonlinear controllers [5]. Fuzzy is not point to point, but range to point control. The FLC


has three functional blocks for calculation and two databases. The functional

and defuzzifier. Fuzzy logic uses linguistic variables instead

variable (real number) into a linguistic variable

finds the degree of membership in every

magnitude of participation of each input.

functional overlap between inputs, and ultimately determines an output response [3].

Fig.20



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locks for calculation and two databases. The functional blocks in FLC are: Fuzzifier, rule evaluator

defuzzifier. Fuzzy logic uses linguistic variables instead of numerical variables. The process of converting a

nguistic variable (fuzzy number) is called fuzzification. For a given crisp

finds the degree of membership in every linguistic variable. The membership function is a graphical

input. It associates a weighting with each of the inputs that

and ultimately determines an output response [3].

Fig.19. Fuzzy control

Fig.20. Control using fuzzy logic-simulation block

Fig.21. Obtained fuzzy output


, December, 2014, Ernakulam, India

blocks in FLC are: Fuzzifier, rule evaluator

process of converting a numeric

(fuzzy number) is called fuzzification. For a given crisp input, fuzzifier

The membership function is a graphical representation of the

inputs that are processed, define



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7. CONCLUSION

A new closed loop full bridge dc-dc converter is implemented which is having zero voltage and zero current

switching capability. Mitigation of voltage spikes is possible by making use of soft switching. Closed loop control is

done using both PI controller and fuzzy logic controller. Control can be made easily using them and the reference will be

obtained as output. Response of the system using both controllers is analysed using simulation. By varying the reference

input, the output is observed and is found to be desired values.

REFERENCES

[1] Praveen K. Jain, Fellow, IEEE, Josef Drobnik, Senior Member, IEEE, Majid Pahlevaninezhad, Student Member,

IEEE, and Alireza Bakhshai, Senior Member, IEEE “A Novel ZVZCS Full-Bridge DC/DC Converter Used for

Electric Vehicles” IEEE Transactions on Power Electronics, Vol. 27, No. 6, June 2012.

[2] E. H. Mamdani, “Twenty years of fuzzy control: Experiences gained and lessons learnt,” IEEE, 1993.

[3] Takahiro Yasukawa and Michio Sugeno; “A fuzzy logic based approach in qualitative modelling” IEEE

transactions on fuzzy systems, vol.1, no.1. February 1993.

[4] A. Bakhshai ,M. Pahlevaninezhad, J.Drobnik and P. Jain, “A load adaptive control approach for a zero voltage

switching DC/DC converter used for electric vehicles,” IEEE Trans. Ind. Electron., vol. 59, no. 2, pp. 920–

933,Feb. 2012.

[5] Lalit Mohan Saini, Sudha Bansal and Dheeraj Joshi, “Design of PI and Fuzzy Controller for High-Efficiency

and Tightly Regulated Full Bridge DC-DC Converter”. International Journal of Electrical, Robotics, Electronics

and Communications Engineering Vol:7 No:4, 2013

[6] Ms.Nisha S.Singh and Prof.C.S.Khandelwal, “DSPIC Based Digitized Feedback Loop For DC-DC Converter”

International journal of Electronics and Communication Engineering &Technology (IJECET), Volume 5, Issue

5, 2014, pp 105 - 110, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

[7] P. Hari Krishna Prasad, Dr. M. Venu Gopal Rao, KL University, A.P., India, “DC-DC Converters For Telecom

Power Supply Applications” International Journal of Electrical Engineering & Technology (IJEET), Volume 3,

Issue 1, 2012, pp. 156 - 166, ISSN Print : 0976-6545, ISSN Online: 0976-6553.

[8] Vandana Jha, Dr. Pankaj Rai, Dibya Bharti, “Modelling and Analysis of DC-DC Converter Using Simulink For

Dc Motor Control” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 2,

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