MULTIPORT BIDIRECTIONALDUAL ACTIVE BRIDGE DC-DCCONVERTER FOR RENEWABLE

GENERATION SYSTEMS

S. Dimple Sathesh Kumar1

and Dr. V. Sivachidambaranathan2

1PG Student,Power Electronics ,Sathyabama university

sdimplesathesh@gmail.com,2HOD of EEE department,

Sathyabama Universitysivachidamabaram eee@yahoo.com

January 3, 2018

Abstract

An organized method for deriving multiport bidirectionaldc to dc converters from the full bridge (FB) converter(FBC) and bidirectional dcdc converters (BDCs) is designedin this paper using power semiconductor switches. By em-ploying the proposed method, families of full bridge (FB)and BDC-based multi-port converters (FB-BDC-MPCs), in-cluding some existing ones, are designed for renewable gen-eration systems with the merits of simple topology, reduceddevices, and one-stage power conversion. Voltage correc-tions between any two ports can be achieved by using pulsewidth modulation (PWM) and phase - angle shift controlscheme. Additionally, zero - voltage switching for all theswitches can be achieved in the proposed multi-port bidi-rectional dc to dc converter. A typical four - port converter

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designed by the proposed method, named buck-boost four-port converter, is analyzed in detail as an example in termsof operation principles, layout considerations, and controlstrategy.

Key Words : MPC (Multi-port Converters), Pulsewidth modulation, Zero voltage switching.

1 Introduction

Renewable sources are intermittent in nature. To smoothly supplyloads, storage elements, functioning as an energy buffer, are neededin a stand-alone renewable power system, where several separatedcdc converters are conventionally employed. These systems mayhave the drawbacks of high cost and low efficiency due to multiplestage conversion.

MPCs, which are capable of interfacing and controlling severalpower terminals synergistically and have the merits of low cost,high power density, high efficiency, and compact structure, haveattracted an increasing research interest latterly. An MPC can in-terface several renewable power sources, such as multichannel PVpanels, hybrid PV, and wind turbines, simultaneously. It can im-plement MPPT for each renewable source individually and helpto reduce the impacts of power mismatch among the renewablesources and maximize the output power of the system. Meanwhile,since energy storage systems are usually required to ensure the sys-tem stability and improve dynamics and steady-state performanceswhen utility grid is not available, a bidirectional interfacing is nec-essary for the MPC.

The main focus of this paper is to propose a systematic methodfor the derivation of MPC topologies from FBC and non-isolatedBDCs. The derived MPCs, including provide good candidates forthe applications of renewable power system, such as PV-suppliedaerospace power systems, hybrid energy storage systems, fuel celland battery systems, and thermoelectric generation systems withbattery backup. The bidirectional dc to dc converter along with en-ergy storage has become a promising option for many power relatedsystems, including hybrid vehicle, fuel-cell vehicle, solar and windenergy system and so forth. It not only minimizes the cost and im-

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proves efficiency, but also increase the performance of the system.The bidirectional dc to dc converter is mostly used to transfer thesolar energy to the capacitive energy source during the sunny time,although to deliver energy to the load when the dc bus voltage islow. The bidirectional dc-dc converter is controlled by the solararray photo-voltaic (PV) level, so it maintains a stable load busvoltage and make fully usage of the Photo-Voltaic(PV) array andthe storage battery.

In Section II, the theoretically explain about the topology andmode of operation also detailed. In Section III, simulation resultsare presented. The last section is the main conclusion of the study.

2 THEORY

In this section, the topology of proposed system is explained andcircuit diagram is presented.

A. HARDWARE

It consists of multiple sources such as PV panels and batterystorage system, Bidirectional buck-boost four port converter andcontrollers. Here bidirectional four port converters consist of fullbridge converter-1, high frequency transformer and full bridge converter-2. This four port converter is used to perform dc-dc conversionbetween various sources such as PV panels and battery to dc loadsand also used to perform bidirectional operation. Micro controllerand driver circuits are used to perform phase shift PWM for fourport converter.

B. CIRCUIT DIAGRAM

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Fig1: Circuit diagram of proposed system

C. MODES OF OPERATION

The Proposed converter contains three modes of operations,

Mode I: In this mode the above circuit acts as boost con-verter. Photo-Voltaic array converts sunlight to electrical energyusing Photo-Voltaic effect. The electrical energy produced fromPV array energizes the battery as well as supplies power to theload. Boost converter increase the voltage obtained from PV ar-ray, it energizes the battery. In this mode bidirectional dc to dcDAB converter acts as inverter-rectifier combination from sourceside. Finally the rectifier output is given to the dc load.

Fig2: Two PV panels operate in MPPT state and battery charging

Mode II: This mode represents night time operation, the sun-light is absent. The charged battery supplies power to the load.Dual active bridge converter consists of two power converters in-verter and rectifier. The inverter converts dc from battery into

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ac power. High frequency transformer steps-up ac voltage. Thenthe rectifier converts ac into dc power. Finally capacitor filters theripple in the dc power. Power semiconductor switches S5 and S8are turned ON in inverter side and S9 and S12 are turned ON inrectifier side.

Fig3: Battery discharging mode

Mode III: During this mode the circuit acts as buck converter.This mode represents regenerative braking. Bidirectional dc to dcDAB converter helps to replace the braking energy into useful en-ergy. During this mode DAB converter acts as inverter-rectifiercombination from load side and it charges the battery. Power semi-conductor switches S10 and S11 are turned ON in the inverter sideand S6 and S7 are turned ON in the rectifier side.

Fig4: Regenerative braking mode

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3 EXPERIMENTAL RESULTS

The simulation for this paper was done using Matlab/Simulink.Switching frequency of the power semiconductor switches used inthe paper is 20 KHz, the total simulation time is 0.5 seconds. ThePhoto-Voltaic array is designed in the simulation using electricalcharacteristics of solar cell. Solar cells are connected in series andparallel to add the voltage and current respectively. PI controller isused to generate pulse signal for the power semiconductor switchesused in the dual active bridge converter depends on the batteryvoltage. Here the 24V battery is used with seventy five percentageinitial state of charging Powergui block is used to run simpowersystem elements. Scope is used to show the output in graphicalview.

Pulses are given to the gate terminals using pulse generator.Here the dc machine acts as load. X-axis and Y-axis of the belowinput and output waveform represents time duration and amplituderespectively.

Fig5: Simulation diagram of the proposed system

4a. Input voltage from PV

Photo-Voltaic panel absorb sunlight in the panel surface so thecovalent bond get broken and free electrons excited so the flowof free electrons create photo-voltaic current. Here the PV arrayproduces 28V during MPPT state and it produce 14V during non-MPPT state.

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Fig6: Voltage obtained from solar

4b. Battery state of charging

Fig7: Voltage and current obtained from battery and super-capacitor

The above graph represents the state of charging of the battery.Battery gets discharging for half time period and gets charging foranother half time.

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4c. Buck-Boost converter output voltage

Fig8: Output voltage of buck-boost converter

4d. Output voltage of high-frequency transformer

Fig9: HF transformer output voltage

The high-frequency transformer steps-up the 24V ac to 48V ac.The above graph shows the 48V square wave ac output voltage.

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4e. Output voltage

Fig10: Output voltage across dc machine

The ac power obtained from high frequency transformer is con-verted into dc power using rectifier. Here we obtain 50V dc voltageacross dc machine. Permanent magnet dc machine (PMDC) is usedin the simulation. The mechanical input for this machine is torque.Armature resistance and inductance of the machine is 0.6 and 0.012respectively.

4 CONCLUSION

This paper proposed a Bidirectional buck boost dc to dc converter.So we achieved the bidirectional power flow input and dc machine.Regenerative braking energy was converted into useful energy withthe help of bidirectional power flow. High frequency transformerhelps to achieve step-up the ac voltage. Bidirectional dc to dcconverter helps to connect many input sources like PV panels andbattery and allow bidirectional power flow so efficiency of this wasimproved.

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