Fabrication of multi-modular Input Series Output Series Isolated DC-DC converters with control scheme

Project Title

Fabrication of multi-modular Input Series Output Series Isolated DC-DC converters with control scheme

Project Area of Specialization RoboticsProject Summary

DC-DC converters are used to vary DC voltages to achieve desired value of DC voltage. A single converter works just fine but in order to achieve better continuity and stability of high DC voltages multiple converters are connected in different configurations.  The converters can be connected in four different configurations: Parallel-Input Parallel-Output, Series-Input Parallel-Output, Parallel-Input Series-Output and Series-input Series-output. This project focuses on making a modular Series-input Series-output configuration for boost converters. For example, three boost converters are connected in series and each converter is supplied a voltage of 12volts at the input terminals. Thus the input voltage as whole will be 36volts. The output of each converter is estimated to be about 24volts at the output terminals and the net result is 72volts. So what is ultimately achieved is equal voltage sharing and power balance among the three boost converters.

               The control scheme for this configuration is designed such that in the case of a fault at any one converter the other two converters provide the same output of 72volts. Under faulty conditions the converter on which the fault occurs would draw zero volts and the other two converters would draw 18volts each on the input terminals. And both the unfaulty converters would have an output of 36volts each.  Hence, the load connected at the output would still receive the required voltage without any interruption even under faulty conditions. Also, as the circuit is designed to be modular the input and output configurations could be changed either to Parallel-Input Parallel-Output, Series-Input Parallel-Output, Parallel-Input Series-Output.

Project Objectives

As load to ISOS Multi-modular DC-DC converter is changed, voltage and current sharing to modular is changed this causes loss of stability. The main aim of this research work is to achieve proper distribution of input voltage to modules. If input voltage to modules is properly distributed than because of nonlinearity of transformer the output voltage will automatically be properly distributed. Taking into account the problems associated with ISOS Multi-modular DC-DC converter the main objectives of this research are mentioned below:

1. To understand basic difference between conventional converters and modular converters

2. To become well-aware of basic PWM switching techniques

3. To understand the need of using transformers in DC-DC converters

4. Simulation analysis of multi-modular DC-DC boost converter

5. Hardware model of multi-modular converters controlled by proposed control scheme

6. Validation of results

Project Implementation Method

PV SYSTEM:
Renewable energy systems offer economic and environmental benefits in providing clean and sustainable energy rather than conventional fossil fuels . Renewable energy sources such as solar energy has received tremendous demands since it is pollution-free from any poisonous byproducts that can pollute the environment. DC-DC converters are widely used in renewable energy generation systems such as solar photovoltaic (PV) system for correct energy conversions. The solar photovoltaic power generation system is extensively used in grid-connected and off-grid applications.A combination of PV cells will form a PV module and a combination of PV modules will form a PV array to supply the specified loads.These solar PV modules will be connected in series to increase the PV output voltage due to the nature of solar PV energy that can only generate low DC output voltage in the range between 12V to 75V. Thus, the power converter such as DC-DC converter is a compulsory interface to convert the low DC output voltage from solar PV system to the required voltage rating needed by the utility grid or any utilization voltage. The low DC output voltage from the solar PV system can be used locally through indirect connection before supplying the excessive energy to the utility grid. These PV modules or arrays can charge the rechargeable batteries by using PV battery charger for various applications such as the solar PV off-grid systems ,solar vehicles, base transceiver stations as well as building interated PV systems where the solar energy can be stored for winter or rainy seasons, during nighttime and others. However, direct charging from solar PV modules or arrays will damage the batteries and reduce its lifespan due to the unregulated charging voltage and current. So, the DC-DC converter will regulate the charging voltage/current from the solar PV modules or arrays.

ELECTRIC VEHICLES
HEV and EV applications are a growing interest, related to the need to reduce both the polluting emissions and fuel consumption of land transportation vehicles with Internal Combustion Engines (ICE) by replacing or reducing the use of ICEs with electric propulsion. Currently in HEVs and EVs, a high voltage battery pack supplies energy for cruising to the electric traction system. The conventional 12V system still exists to feed the usual car loads (an auxiliary battery supplies all the electric loads such as head and tail lights, heating fans, audio systems and so on), while the high voltage bus feeds the traction inverter and motor.A DC/AC (Traction Inverter Module) converter is also used for traction and designed for tens or hundreds of kilowatts, while the DC/DC auxiliary power converter is designed for hundreds or thousands of watts. The traction battery can be charged by the hybrid system control and/or the AC/DC converter from the Mains, while the 12V battery is charged from the traction battery via the DC/DC converter.

Benefits of the Project

In ISOS Multi-modular DC-DC converters modules of low voltage ratings are connected in series so choice can easily be made due to less voltage stress on each device. MOSFETs of lower voltage ratings are used and high switching frequency which lead to high conversion efficiency. As switching frequency of devices is very high on several tens of kilo hertz. So, size and cost of transformer is reduced. Standardized and easily available components are connected in series combination so any required voltage rating and power rating can be achieved without manufacturing a whole new device. Utilization of components which are standardized both time and cost of converter are reduced. If proper distribution of voltages is achieved both reliability and stability of the system is improved. Hence the expected benefit can be the reliability and stability of any system.

Technical Details of Final Deliverable

In this project, 3 full-bridge Dc-to-Dc boost converters are connected in series-input-series-output (ISOS) configuration. To achieve desired results a controller is used. The technical description is divided into following parts:

Operation of an individual Module: A basic FBC has 4 main circuit elements: power switches, transformer, rectifier diode and LC filter. The power switches, either a transistor or MOSFET, used to control flow of energy. A transformer is placed to provide DC isolation between input and output and also perform stepping up operation of input voltage. The rectifier diode and LC filter form energy transfer mechanism to supply energy for maintaining voltage and current at required level at load side. The diagonally opposite switches (Q1 and Q2, or, Q3 and Q4) are turned on and off simultaneously in portion of each half cycle of switching frequency (for time interval D*T). When all four switches are turned off, the load current freewheels through the rectifier diode (for time interval (0.5-D)*T). The PWM pulse generator has input of duty cycle (D) and will produce appropriate pulses and sends them to switches.

     Operation of control scheme: The control scheme consists of current mode input voltage sharing (IVS) control with three control loops to ensure input and output voltage sharing. Current reference to the inner current loop is provided by the output voltage loop that is common to all the three converter modules. GVo is the compensator for the outer voltage loop and GIo is the compensator for individual inner current loops. In this control scheme two voltage control loops and one current control loop is used to control ISOS DC-DC converter. The outer voltage loop changes the reference to the inner current (I’ref). I’ref to the input voltage loop is taken as the average of the input voltage of each converter module. A proportional controller K is used to regulate the input voltage control loops in accordance with conditions such as input voltage change due to changes in irradiation condition and is chosen according to the mismatches between input and output voltage regulation loops. A common duty ratio is given to all the converter modules. Gvo is the common output voltage compensator, while GIo1, GIo2, GIo3 are individual current compensators for inner current loops. G1id, G2i , G3id are the transfer functions of the three modules respectively.

Final Deliverable of the Project Hardware SystemType of Industry Energy , Transportation , Telecommunication Technologies Wearables and ImplantablesSustainable Development Goals Affordable and Clean Energy, Industry, Innovation and Infrastructure, Responsible Consumption and ProductionRequired Resources

Item Name	Type	No. of Units	Per Unit Cost (in Rs)	Total (in Rs)
			Total in (Rs)	70696
Isolated DC DC converter	Equipment	3	15000	45000
Portable Oscilloscope	Miscellaneous	1	7000	7000
Clamp meter	Miscellaneous	1	2500	2500
Resistor, Capacitor, Inductor etc	Equipment	30	100	3000
PCB design	Equipment	4	1300	5200
Aurdino	Equipment	4	1999	7996