Isolated Soft Switching Current Fed Series LC Resonant DC-DC Convertor for Electrical Vehicle Application

The current fed series resonant converter for electrical vehicle application is offered in this paper. The converter is able to achieve ZVS for primary side semiconductor switches. In the overlap time of voltage and current at zero crossing series resonant tank circuit is gives short interval of resonant pulse. This resonant pulse provide natural voltage decrease for semiconductor switches and voltage pulse is zero earlier compare to current across switches and ZVS achieve for semiconductor switches. All devices turn off softly so dependency on snubber is decreased to clamp the voltage across the switches. Presented converter reduce the circulating current so switching losses is decreased and converter efficiency will improvise. The proposed converter is simulated in MATLAB Simulink environment to investigate and analyses the proposed converter.


Introduction
These days' solution for the environmental pollution and CO 2 emission through the conventional energy resources are major problem for the world is providing by the EV's and HEV's. Now day's scientists, government and industries pay more attention on renewable energy resources and electrical vehicles to reduce CO 2 emission and reduce the uses of fossil fuels uses [1]. Generally the battery uses in electrical vehicle are more half kW rating and isolated dc/dc convertor for power conversion is used [2].
Conventional dc-dc converters realize the main necessity of assimilating alternative energy sources into dc microgrids. The adaptable power supply voltage makes it difficult for semiconductor devices to switch in a considerable operating range, which greatly reduces the converter efficiency. If we can limits convertor process at high frequency subsequent In larger magnetics and immense system. The main key task is to be attain soft-switching for semiconductor devices when source voltage and load has wide dissimilarity. While achieving the soft switching has highly reliable, and volume, and cost is low of the converter [3].
In the works, assessment of soft switched voltage served convertor and current served convertor is presented. The current fed convertor has various advantages such as small input current wave and inherent short circuit current protection, high voltage gain, higher efficiency, wide soft switching range these advantages makes current-fed topology more popular for HV gain and low voltage high current use. With the current fed converter high voltage spikes through the semiconductor devices through turn-off is the main task with the current-fed converter, inactive sunbber take stress-free solution to defeat the device turn-off voltage point but with this convertor efficiency is compromise. Instead of use active clamping achieves and passive sunbber, ZVS of the semiconductor switches and result is enhanced effectiveness but its ads to the peak currents, and reduce boost capacity [4].
Various techniques and innovative topologies permitting soft-switching and removing the essential of outmoded snubber circuit has been stated in literature. The idea of sunbberless natural commutation and voltage clamping of semiconductor switches by applying secondary regulation in many current fed methods. Current operated resonant converter utilizing high frequency transformer and resonant tank and circuit parasitic to achieve soft switching for switches [5].
This paper investigate the zero voltage switching for front end switches for Converter. The battery side converter designated as a current fed full bridge boost converter to attain double voltage gain from primary to secondary transformer. Converter action and regulator is explained in section II. Detailed steady state investigation is explained in section III. Design steps exist presented in section IV. Simulation effects are explain in section V to validate the investigation. Conclusion are strained in section VI.

A. Proposed converter
The recommended series resonant converter is presented in fig. 1, presented converter has capability to offer high voltage output due to its interleaved boost connected to the primary of the HF transformer, and secondary side of the HF transformer connected with diode bridge rectifier. The resonant tank circuit is used to provide smooth sine wave at both secondary and primary verges of the high frequency transformer, which allows low conduction losses of switching devices. A resonant indictor L s and capacitor C s used as to realize ZVS for primary side of the switches. If the voltages of V H and V L are constant by DC source, the current be able to be controlled by current control loop, then voltages of V L or V H can be straight delimited by voltage control loop [6].

B. Modulation and Operating Principles
An easy PWM control technique is adopt to control the series resonant DC-DC converter. The SF of the convertor is static at the series resonant tank. The semiconductor switches are connected in the similar pare are operated opposite The 2 switching leg on the primary side function in an interleaving mode. The subsequent examination will designate that the voltage gain charterstics of the planned series resonant dc/dc is very like to the PWM converters, those voltage gain also controlled through the duty cycle of the switches, thus the moved power and the way of power movement can be controlled simply through modest PWM regulator.

Stady State Analysis
This part of the article describe about the steady state process and examination of the series resonant dc/dc current fed converter. Designed for abridging the convertor investigation, the subsequent assumption are complete a) A higher significance of the boost inductor is selected to transfer a inflexible dc current. b) Completely semiconductor switches are idyllic and loss free.
c) The output filter capacitor value is sufficient to provide the continuous output voltage.
d) Capacitor C s and inductor L s of the high frequency transformer constitute for resonant tank parameter.

=
(1) When both M 2 and M 4 are ON, the current of inductor L 1 and L 2 are changed by V L .
Here L 1 and L 2 =L. in addition, L s and C s and in the resonant tank stores energy is served to the HV side. The subsequent equation is obtained.
The current of Ls and voltage on Cs at t0 and V0, respectively, the solutions if i Ls (t) and V cs (t) can be stated as follows: After t 6 a same process the whole thing in the next cycle of the switching period.

Convertor Design
A 1000 W converter design to operate at 110 kHz switching frequency is taken to identify the main parameter design. The parameters are follow V L =100V-180V, V H = 250 V resonant frequency f r = 90 kHz.

A. Turns Ratio of the Transformer
The turn's proportion of the transformer would be intended to mark indisputable that the power and voltage can be controlled with in the complete range of low to high voltage. This can be identified effortlessly since the regularized the voltage improvement of the converter can be widely controlled. In the case of a larger duty cycle D, a lower voltage strain can be obtained on the primary side switch. With the new point of view for the resonant period, the main duty cycle of the resonant energy stored in the resonant tank is not affected by the smallest value of D and 1-D. with respect to increase the capacity of resonant tank circuit, the duty cycle should be taken 0.45. Taking these factors into account, it is suggested to select the transformer's turn's ratio. When setting duty cycle is 0.45 the voltage at center of the complete voltage range [7].
Established on these consideration, the turns ratio of the transformer is calculated at n=1 so that duty cycle D=0.5 after the battery voltage is at center 140V.

B. Resonant Tank
The main concern for the specification of the resonant tank (that is, L r and C r ) is to make the resonant frequency equivalent to the SF of the converter. In edict to decrease the current stress and conduction loss linked to circulating current, the worth of the resonance tank must be larger. But, the peak voltage on the resonant capacitor is equivalent to the impedance Z r . However, a larger resonant inductance will damage the capacity and power thickness of the converter. The value of Z r is recommended to be in the range of 15 to 30.
For the scheme example, seeing that the actual worth of C r is 50nf, select C r . Then, given the resonant frequency, the resonant inductor L r is 44.54uH.

C. Filter Inductors L1 and L2
The Boost converter on the primary side function in the interleaved method. For the assumed duty cycle L 1 =L 2 =L, the current ripple and the total current wave ΔI L on the battery side can be designed as: Considering the current ripple and the soft switching performance of the primary side switch, L 1 and L 2 are designed to be 250uH.

D. Clamping Capacitor Ca
Ca is designed based on the wave on the capacitor, which is the similar as the scheme of filter capacitors in maximum power converters. In a scheme example, a 10uF capacitor is used for Ca .

Simulation Results
The Isolated Soft Switching Current Fed Series LC Resonant DC-DC Converter is simulated by using MATLAB SIMULINK to authenticate the theoretic notions of DC-DC convertor.  Fig.4 shows an input side interleaved inductor current waveforms. It is vibrant that the simulated waveforms contest with the theoretic examination.
In Fig.5 displays that zero voltage switching at key switches M 1 to M 4. Where it is seen soft switching attained for all switches.

Conclusion
Isolated Current Fed Series LC Resonant DC-DC Converter takes occurred offered and substantiated in this article. Theoretic examination of simulated confirmation specifies that zero voltage switching achieved for primary side of semiconductor switches and conduction losses in minimized and efficiency of the converter improvised. The investigation and simulated verification designate that offered convertor is suitable for electrical vehicle charging. It can be used in maintainable energy power system uninterruptable power supplies, micro grids etc.