New zv zcs full bridge dc-dc converter with fuzzy & pi control

Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30-31, December, 2014, Ernakulam, India
156
NEW ZV/ZCS FULL BRIDGE DC-DC CONVERTER WITH
FUZZY & PI CONTROL
ASWATHY HARIDAS1
, SARITHA K.S2
, AJITH K.A3
1
P G Scholar, Electrical & Electronics department,
Sree Narayana Gurukulam College of Engineering, Kolenchery, India
2
Associate Professor, Electrical & Electronics Department,
Sree Naryana Gurukulam College of Engineering, Kolenchery, India
3
Assistant 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
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
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Volume 5, Issue 12, December (2014), pp. 156-169
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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

158
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 .

161
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

162
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

163
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

164
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

165
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)
30-31, December, 2014,
166
6.1 CLOSED LOOP USING PI CONTROLLER
Fig.13. Closed loop control using PI controller
Fig.14. Control mechanism
Fig.15. Pulse generation
, December, 2014, Ernakulam, India

167
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 funct
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. It associates a weighting with each of the inputs
functional overlap between inputs, and ultimately determines an output response [3].
Fig.20
30-31, December, 2014,
168
blocks 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
variable (real number) into a linguistic 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
functional overlap between inputs, 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
cation. For a given crisp input, fuzzifier
The membership function is a graphical representation of the
input. It associates a weighting with each of the inputs that are processed, define

169
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,
2012, pp. 58 - 68, ISSN Print : 0976-6545, ISSN Online: 0976-6553.

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