Solar Powered Battery Charger for Plug-in Electric Vehicle using Fourth Order Resonant Converter

With every passing year, the fossil fuel reserves are depleting rapidly, threatening the planet?s sustainability. Therefore, there exists a dire need to improvise the transportation sector by substituting conventional combustion engine vehicles with efficient electric vehicles. However, the major ba

Project Title

Solar Powered Battery Charger for Plug-in Electric Vehicle using Fourth Order Resonant Converter

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

With every passing year, the fossil fuel reserves are depleting rapidly, threatening the planet’s sustainability. Therefore, there exists a dire need to improvise the transportation sector by substituting conventional combustion engine vehicles with efficient electric vehicles. However, the major barrier in the widespread use of electric vehicles in developing countries such as Pakistan is the lack of charging infrastructure. Another key concern is that fossil fuels are the dominant source of electricity generation as 65% of energy is produced through coal, gas, and furnace oil in Pakistan which might nullify the effect of decarbonization by electric vehicles. Given the aforementioned issues, the proposed project focuses on the development of a solar-powered electric vehicle battery charger. In the past, different topologies of resonant power converters have been implemented in electric vehicle battery chargers. The most common topology is the LLC resonant power converter which offers higher efficiency and a wide soft-switching range however, its major drawback is low voltage regulation. In the proposed charger, the maximum power is to be extracted from the solar panels with variable output voltages highly dependent on solar irradiance. Moreover, depending on the battery state of charge, the charger is to be designed to work in different charging modes, such as constant voltage, constant current, and constant power. In view of these challenges, the need of the hour is to achieve extreme voltage regulation within the resonant converter. In this proposed charger, a fourth-order L3C resonant converter has been employed offering high voltage regulation capability which will not only enable maximum power point tracking but will also allow the incorporation of all the different charging modes of the lithium-ion battery. The proposed charger is divided into four parts; solar array, L3C resonant DC-DC converter, electric vehicle battery, and controller. The controller will receive feedback from the solar array and electric vehicle battery to send a controlling signal to the resonant converter. The First Harmonic Approximation technique is used to model the performance parameters of the resonant converter. The end product is expected to offer maximum efficiency, high power density, and required voltage regulation.

Project Objectives

• To develop a charging system for electric vehicle batteries that uses a renewable energy source and causes no adverse environmental impact. 
• To efficiently utilize fourth-order resonant converter to achieve zero voltage and zero current switching for all modes of Li-Ion battery charging.
• To track the maximum power generation from the solar panels to charge the electric vehicle battery. 
• To effectively control the switching frequencies of the resonant converter to set the required resonant tank gain.
• To build a complete prototype of a 500W solar-powered electric vehicle battery charger.

Project Implementation Method

The proposed project comprises four major parts. Firstly, the solar array which acts as the input voltage source for the electric vehicle battery charger. Secondly, the L3C resonant DC-DC converter which regulates the input voltage coming from the solar array. Thirdly, the electric vehicle battery which gets the regulated voltage. Lastly, the most important part of the charger is the Arduino controller. The Arduino controller monitors the input and output voltages and currents to send a controlling signal to the DC-DC converter. The schematic of the proposed project is shown in the figure below.

The L3C resonant converter in the proposed converter consists of three major parts; a controlled switching network(inverter), a resonant tank, and a rectifier circuit. The output voltage from the solar array act as input for the controlled switching network of the resonant converter. The controlled switching network consists of four MOSFET switches(S1-S4). The gain of the converter is regulated by controlling the switching frequency of the switches. After passing through the switching network the DC voltage is converted into a square wave AC which is fed to the resonant tank. The L3C resonant tank contains three inductors and a capacitor. The first inductor (L1) is connected in series on the primary side of the transformer and the second inductor(L2) is connected in series on the secondary side of the transformer. Whereas, the third inductor(L3) is connected in parallel on the primary side of the transformer. The capacitor(C1) is connected parallel with the load on the secondary side of the transformer. The transformer in the resonant converter not only provides voltage gain but also acts as galvanic isolation between the solar array and the electric vehicle battery. There are two different implementation techniques of the L3C resonant converter tank; a discrete solution and an integrated solution. In the discrete solution, the inductances are located outside the isolation transformer separately. Whereas in the proposed project, an integrated solution is implemented for the L3C resonant converter and all the three inductances of the resonant converter tank are incorporated in the high-frequency isolation transformer as the primary, secondary, and magnetizing inductance. The integrated solution not only increases the power density of the transformer but also reduces the overall battery charger cost. The transformer is followed by a rectifier circuit and a filter capacitor(Cf) that coverts the AC volage back into regulated DC voltage which can then be supplied to the electric vehicle battery.

Benefits of the Project

• The solar energy and the electric vehicle battery are DC in nature which reduces additional conversion losses and increases the power density of the charger.
• Solar energy is readily available and can be easily installed on roofs of offices or in solar car parking areas where electric vehicles will be parked for longer periods of time. The solar panels that are integrated with the charger will not only provide power to the electric vehicle batteries but also act as a shade for the vehicle.
• In traditional solar systems, there is a need for batteries for the storage of generated energy. In the case of solar-powered electric vehicle battery charging, the electric vehicle batteries serve as the energy storage device.
• The energy demand on the grid will be reduced due to the use of the proposed charger as the electric vehicle batteries will be charged from locally generated renewable energy. 
• Solar energy is a sustainable form of energy that is almost maintenance-free and causes no noise and air pollution.
• The proposed charger can be used in rural or far away areas where the electricity supply is not available. 
• Electric vehicles are playing an important role in the transition of the world towards green energy and combining it with renewable charging sources will further facilitate this transition. 

Technical Details of Final Deliverable

• Solar array                                                                                                         

The solar array in the proposed project consists of three 160W solar panels connected in series. The maximum input power generated by the solar panels in case of optimum solar irradiance is 480W. The solar panels in the array will be generating an approximate maximum voltage of 18V each. The combined voltage output of the array at nominal condition will be 54V with a variation of +/-10V due to a change in working temperatures. The maximum current that the solar can provide also ranges between 6-7A.

• Electric vehicle battery charger

The battery charger consists of the L3C resonant converter and controller. The DC input of the solar array is converted to square wave high-frequency AC after passing through the controlled switching network of the resonant converter. The frequency of the AC ranges from 25KHz to 100KHz depending on the voltage gain requirement. The resonant tank of the L3C converter implements an integrated technique and comprises a high-frequency transformer and a parallel capacitor at the secondary of the transformer. The transformer uses a ferrite core with a core rating of around 300W. In order to reduce skin-effect, the transformer uses multiple wire conductors for the primary and secondary. The rectifier of the converter uses high-frequency Schottky diodes for full-wave rectification. The controller used to control the switching frequency of the inverter is an Arduino Uno. The maximum power point tracking and PID error correction algorithms are implemented on the controller. The controller gets voltage and current feedbacks from the solar array and the electric vehicle battery using current sensing modules ACS712.

• Prototype electric vehicle battery

Electric vehicle batteries usually possess high nominal voltages ranging from 100V to 450V. Keeping this design into consideration, the proposed project integrates a 103V 4.2Ah lithium-ion battery pack. The battery pack will be comprised of 28 18650 lithium-ion cells in series. Two 14s BMS’s will be connected to the battery pack that will ensure the cell balancing and will provide feedback of important parameters to the controller such as battery voltage, current, and state of charge (SOC).

Final Deliverable of the Project

Hardware System

Core Industry

Transportation

Other Industries

Core Technology

Clean Tech

Other Technologies

Sustainable Development Goals

Affordable and Clean Energy, Industry, Innovation and Infrastructure, Sustainable Cities and Communities

Required Resources

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