Performance Analysis of Bidirectional DC to DC Converters for Electric Vehicles

A large number of automobiles in use around the world has caused and continues to cause serious problems of the environment. Electric Vehicles (EVs) & Hybrid Electric Vehicles (HEVs) have been typically proposed to replace conventional vehicles in the near future. The use of a bi-directio

Project Title

Performance Analysis of Bidirectional DC to DC Converters for Electric Vehicles

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

A large number of automobiles in use around the world has caused and continues to cause serious problems of the environment. Electric Vehicles (EVs) & Hybrid Electric Vehicles (HEVs) have been typically proposed to replace conventional vehicles in the near future.

The use of a bi-directional dc-dc converter in motor drives devoted to EVs allows a suitable control of both motoring and regenerative braking operations. In the regenerative braking system, the motor; which drives an electric vehicle, also performs the function of braking. The system consists of an electric motor with dual function. It works as a motor, in one direction and also as a generator, in the opposite direction. When it runs as a motor, it converts electrical energy into mechanical energy and drives the wheels. However, while braking; it runs in the opposite direction and becomes an electric generator. Applying the brakes of an electric or hybrid vehicle causes the electric motor to run in reverse direction i.e. in generator mode, thereby; slowing down the wheels.

In this final year project, we will do the performance analysis and comparison of two types of bidirectional DC-DC converters - Cascaded Buck-Boost-Capacitor in the middle (CBB-CIM) and Cascaded Buck-Boost-Inductor in the middle (CBB-IIM) for use in plug-in electric and hybrid electric vehicles. The comparison of the two converters will be based on device requirements, rating of switches and components, control strategy and performance. Each of the converter topologies will have some advantages over the other in certain aspects. Efficiency analysis will be carried out for specific scenarios in-vehicle applications.

Project Objectives

The objectives of this project are to:

1. Develop a bi-directional DC-DC Converter in order to improve the range and efficiency of electric vehicles.
2. Analyze two types of bidirectional DC-DC converters Cascaded Buck-Boost-Capacitor in the middle (CBB-CIM) and Cascaded Buck-Boost-Inductor in the middle (CBB-IIM) on the basis of device requirements, rating of switches and components, control strategy and performance.

Project Implementation Method

Two different converters of interest will be developed, the conventional Cascaded Buck-Boost Inductor in the middle (CBB-IIM) having an interfacing inductor between the input and output sides and the Cascaded Buck-Boost Capacitor in the middle (CBB-CIM) topology where the two half-bridge converters are cascaded together with a common dc bus capacitor. 

Comparisons of the two converter topologies are done for the following aspects: 

Switching mechanism:

Both the converters basically require only one switch to be switched at a particular frequency to operate either as buck or boost converter. The other switch is required to be in the ON mode for the full switching period for current conduction.

Stresses on switches and diodes:

Stresses on switches and diodes are one of the major concerns when going for final implementation of the converters. Equipment size, weight and cost are largely dependent on the ratings of the switches.

Ratings & size of the passive components: 

CBB-IIM requires only one inductor whereas CBB-CIM requires two. For the final selection, inductor ratings and sizes will be calculated. In both circuits, the required inductor rating depends on the operating condition. Both the converters have the same expression for the minimum required capacitance. The required values are calculated considering certainly allowed voltage ripple across the capacitor.

Multi-input, output capability: 

DC-DC converter with multi-input and multi-output capability is useful for EV/HEVs that use multiple input sources or require multiple auxiliary outputs. Multiple input options are needed to connect two sources such as an ultra-capacitor and a battery pack combination.

Efficiency: 

Efficiency analysis will be carried out for different load conditions for both converter topologies using LTspice circuit simulator. Inductor loss, conductor loss and switching loss will be considered in the analysis.

Benefits of the Project

Some advantages of using bidirectional DC-DC converter in EV are as follows:

• lower consumption of fossil fuels
• High efficiency  
• low power consumptions
• Compact size and less bulky.
• Lower EMI (electromagnetic interference).
• Lower input and output current ripple.
• Instead of input voltage variation controlled power flow.

Technical Details of Final Deliverable

Two bidirectional DC-DC converters - Cascaded Buck-Boost-Capacitor in the middle (CBB-CIM) and Cascaded Buck-Boost-Inductor in the middle (CBB-IIM) will be developed and The comparison of the two converters will be done based on device requirements, rating of switches and components, control strategy and performance. Each of the converter topologies has some advantages over the other in certain aspects. Efficiency analysis will be carried out for specific scenarios for in-vehicle applications.

Final Deliverable of the Project

HW/SW integrated system

Core Industry

Energy

Other Industries

Core Technology

Clean Tech

Other Technologies

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

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