High Step-Up/Step-Down Soft-Switching Bidirectional DC-DC Converter with Coupled-Inductor and Voltage Matching Control for Energy Storage Systems

High Step-Up/Step-Down Soft-Switching Bidirectional DC-DC Converter with Coupled-Inductor and Voltage Matching Control for Energy Storage Systems

M. Muthukumaran1, M. Pandiselvi2, M. Jansirani3, K. Alagumeena4

Assistant Professor1, Final year Students2, 3, 4

Department of Electrical and Electronics Engineering, SreeSowdambika College of Engineering, Aruppukottai.

Abstract:- Novel series-resonant bidirectional DC-DC converter with fixed-frequency PWM control has been proposed and verified in this paper. Theoretical analysis and experimental verification indicates that high-efficiency bidirectional DC-DC power conversion and wide voltage range regulation are achieved with the proposed series- resonant bidirectional DC-DC converter. The normalized voltage gain of the converter is only determined by the duty cycle of primary-side switches and has nothing to do with the direction and amplitude of the transferred power, which makes the voltage regulation, power control, and design and implementation of the proposed resonant bidirectional converter very simple. The direction of power flow can be changed and regulated easily and smoothly. Furthermore, zero voltage switching of all the active switches has been achieved in a wide operation range. The experiments with the 1600W prototype have clearly demonstrated the claimed features. The analysis and experimental verifications indicate that the proposed converter is suitable for bidirectional energy storage applications. It can be used in sustainable energy power systems, micro-grids, electric-vehicles, uninterruptable power supplies, etc

Keywords:- Renewable energy sources, Main circuit, PIC Microcontroller, Driver circuit, Energy storage applications

III.INTRODUCTION

Renewable energy sources such as Solar, Wind Energy are available plenty on the whole with free of cost. Recently, Renewable energy sources such as the fuel cell stacks and photo-voltaic (PV) generation system are involving much in research fields. Because of using these resources result the possible solutions to the environmental problems. The characteristics of the PV panels, the output voltage from the PV panels various greatly due to different temperature, clouding effects, irradiation conditions, and shading. So, a dcdc converter with either step-up operation or step-down operation or even both step-up and step-down operation is needed. With the conventional converter, the technique interleaved method is implemented to improve power converter performance in terms of reduction in current stress and inductor size. The proposed system consists of the renewable energy source as the input source, buck- boost converter with interleaved technique for stepping up and stepping down operation of input voltage. The DC motor is connected with these components and the speed control of the motor is achieved by this proposed system.

1. HARDWARE ARCHITECTURE

   The proposed high step up/ step down soft switching bidirectional dc-dc converter with coupled inductor and voltage matching control for energy storage systemcontains three main hardware components. Main circuit, Peripheral Interface Controller, Driver circuit. The main circuit is used to step up/step down given voltage using soft switching bidirectional dc-dc converter (Buck Boost converter). The PIC sent PWM signals to the main circuit. The driver circuit used for Isolation and Amplification process.

   A.MAIN CIRCUIT

   One side of a BDC is connected to a storage battery, whose voltage is usually low and typically in the range 1248 V, while the other side of the BDC is connected to a high voltage bus up to 400 V or higher to satisfy the requirement of inverter and ac grid.

   Therefore, a BDC with high step-up/step-down voltage conversion ratio is desired for energy storage systems to connect the low-voltage battery with high-voltage dc bus.

   B.PIC Microcontroller

   PIC microcontrollers (Programmable Interface Controllers), are electronic circuits that can be programmed to carry out a vast range of tasks. They can be programmed to be timers or to control a production line and much more. They are found in most electronic devices such as alarm systems, computer control systems, phones, in fact almost

   any electronic device. Many types of PIC microcontrollers exist, although the best are probably found in the GENIE range of programmable microcontrollers. These are programmed and simulated by Circuit Wizard software

   .

   1. A/D Converters

      A/D converter is used to convert analog voltage values to digital voltage values. An A/D module in Peripheral Interface Controller comprises of 5-inputs for 28-pin devices & 8-inputs for 40-pin devices. The operation of the A/D converter is controlled by special registers like ADCON0 & ADCON1. The upper and lower bits of the converter are stored in registers like ADRESH and ADRESL. In this process, it needs 5V of an analog reference voltage.

   2. PWM Mode

   PWM is a technique that is used to reduce the overall harmonic distortion (THD) in a load current. It uses a pulse wave in rectangular/square form that results in a variable average waveform value f(t), after its pulse width has been modulated. The time period for modulation is given by T. Therefore, waveform average value is given by,

   y¯=1TT0f(t)dt

   1. Driver Board

      In this board five NPN & PNP transistors are used. The transistors output is connected to the main circuit. It is used for isolation and amplification purpose. 12 v supply given to this board.

      A driver circuit for an inverter includes a switching circuit formed of a first switching element and a second switching element connected in series, which are turned on and off in complementary with one another;

      a first DC power supply connected parallel to the switching circuit; a first driver circuit connected to the first switching element for driving the same; a second driver circuit connected to the second switching element for driving the same; a second DC power supply connected to the second driver circuit for supplying electric power to the second driver circuit; and a first capacitor connected to the first driver circuit and having a charge-up path communicating with the second DC power supply. During an ON-period of the second switching element, the first capacitor is charged up through the second DC power supply and supplies electric power to the first driver circuit. A series circuit formed of a PNP transistor and a diode and are disposed in the charge-up path, and a resistor is connected between a base of the PNP transistor and a negative terminal of the second DC power supply. The second DC power supply can rise smoothly.

2. CIRCUIT DIAGRAM:

3. WORKING OF PROPOSED SYSTEM

   Primary-side is an interleaved bidirectional Boost/Buck converter while the secondary-side is an active full-bridge circuit. The two sides of the SR BDC are linked by a series resonant tank, which is composed of Lr and Cr, and a high frequency transformer T. The resonant tank is used to produce a nearly sinusoidal current at both the primary and secondary sides of the transformer, which enables low switching losses of switching devices. An auxiliary inductor La is employed on the primary side to achieve ZVS for the primary side switches S1-S4, whereas the magnetizing inductance, Lm, of the transformer is used as another auxiliary inductor to realize ZVS for the secondary-side switches S5-S8. It should be noted that Lr only resonates with Cr, and La and Lm don't participate in the resonance, because the voltages applied on La and Lm ae always clamped by the active full-bridges on primary and secondary sides. Therefore, the proposed BDC is a SR converter. Vais the voltage on the clamping capacitor Ca. The converter operates in the forward mode when the low voltage Source VL, i.e. battery, delivers energy to the high voltage dc bus VH, while the backward mode means the battery is charged by VH. It should be noted that either the voltage or current of the VL and VH sides can be regulated by the SR BDC. If the voltages of VL and VH are fixed by DC sources, the current can be regulated by a current control loop, otherwise, voltage of VL or VH can be directly regulated using a voltage control loop. In this paper, only the voltage regulation is analyzed.

   High Switching Frequency Operation in Power Electronic Converters: The size of the energy storage components of a power electronic converter, such as inductors (L) and capacitors (C), accounts for much of the overall size of the converter. These components are needed to store and transfer energy from the input power supply to the output load in the converter. Their values depend on the frequency that the converter switch is turned on and off. As the switching frequency is increased, the values of the inductors and capacitors decrease and so do their physical size and weight; therefore the higher the converter switching frequency, the smaller is the converter size.

   Fig. Loss of power during hard switching

   Soft Switching: The problems of switching losses and EMI associated with hard-switching converter operation can be reduced by using soft-switching. The term "soft- switching" in power electronics refers to various techniques where the switching transitions are made to be more gradual to force either the voltage or current to be zero while the switching transition is being made. EMI is reduced by soft-switching because the switching transitions

   from on to off and vice versa are gradual and not sudden. Switching losses are reduced since the power dissipated in a switch while a switching transition made is proportional to the overlap of the voltage across the switch and the current flowing through it. Soft-switching forces either the voltage or the current to be zero during the time of transition; therefore there is no overlap between voltage and current and (ideally) no switching loss.

4. DC-DC CONVERTERS

   Boost Converters Dc-Dc converters convert an available unregulated dc input voltage into a regulated dc output voltage of a different magnitude and/or polarity as required by a particular load. Most Dc-Dc converters are switch- mode converters that operate with active semiconductor devices like MOSFETs and IGBTs, acting as on-off switches. These switches are required to undergo repetitive and periodic turn on and turn off. The two most basic types of Dc-Dc converters are the buck converter (output voltage is a stepped down value of the input voltage) and boost converter (output voltage is a stepped up value of the input voltage). Other types of Dc-Dc converters are buck-boost, Cuk, Sepic and Zeta etc.

   In steady state, after the switch is turned on, the whole input voltage is applied across the input inductor Lin and it stores energy. When the switches are turned off, a negative voltage equal to (Vin Vo) is applied across the inductor and the energy stored in the inductor is delivered to the output capacitance.

5. OUTPUT WAVE FORM

6. ADVANTAGES

   • Excellent soft switching performance

   • Less conduction losses

   • High-power density

7. APPLICATIONS

   • Energy power systems

   • Micro-grids

   • Electric-vehicles

   • Uninterruptable power supplies

   X.CONCLUSION

   In this paper the Bidirectional DC-DC converter using with soft switching has been proposed that uses auxiliary

   switches and auxiliary resonant circuit. The main switches were operated under zero voltage switching condition by employing the resonant circuit. The bidirectional transfer of power is ensured with less power loss as compared to conventional converters by the provision of soft switching elements. The step down mode as well as step up mode is well verified and the ripple content at the output of both stages is observed less than 0.05%. The high frequency transformer provides a galvanic isolation between low voltage and high voltage side. In order to reduce size of bidirectional DC-DC converter, conventional topologies using hard switching method operate with high frequency. As switching frequency is getting higher, switching loss is increased. The auxiliary circuit is implemented by using soft switching method in order to overcome this drawback.

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