Week 4 Session 5

Q1) Explain the various applications of Power converters in an Electric vehicle. For Example. what type of converter will you use for Horn which requires DC and less than 10V. Likewise come up with different applications

Ans-In electrical vehicle mainly two types of convertor are used

1) DC to DC convertor

2) DC to AC Invertor

3) AC to AC convertor

4) AC to DC convertor

1) DC to DC convertor:- A DC to DC convertor a type of convertor is category of power convertor and it is an electric circuit which converts a source of direct current (DC) from one voltage level to another voltage level by shorting the input energy and then releasing that energy to the output at a different voltage.

DC to DC convertor can be designed to transfer power in only one direction from input to the output. However, almost all DC to DC convertor Can be made bi-directional. A bi-directional convertor can move power in either direction, which is useful in applications requiring regenerative breaking.

The amount of power flow between the input and the output can be controlled by adjusting the duty cycle (ratio of on/off time of the switch). Usually this is done to control to output voltage, the, the input current the output current or to maintain a constant power. Transformer based convertor may provide isolation between the input and the output. The main drawback of switching convertors include complexity, electronics noise and high cost for some topologies.

Types of DC to DC convertor

1. a) Non-isolated DC to DC convertor:-They are practically circuits that use power switches , inductors, diodes, and capacitors. Together, they transfer the energy and make output from the input. No matter if the user wants to achieve the buck, bust or invertor types, the parts can be arranged and step in more than one way. These are essentially the different types of convertors that you need to know about. Pay close attention to the next few subsections.

2) DC to AC convertor:- In the battery (HEV/EV) , the stored energy must be converted from DC to AC to drive AC motors using DC to Ac convertor. These convertor are called traction invertors, which usually transfer power in the range of tens of kilowatts up to 50kw. Usually , the semiconductor power switches used in these invertor topologies are insulated gate bipolar transistor (IGBTs). The typically voltage level for these power switched is 600-1200 v considering the high-power levels and voltage levels a three phase full-bridge invertor using six semiconductor power devices

Making of dc to ac convertor

The dc to dc convertor circuit using transistor is shown below. The basic function of an invertor circuit is to generate oscillations with the specified dc & apply these to the transformer’s primary winding by increasing the current. This main voltage is then step up high voltage based on the number of twist within main and minor coils.

3) AC to Ac convertor :- We require a particular voltage and particular frequency for operating some special devices or machines for speed control of induction motor , ac to ac convertors is used major for obtaining a desired ac power supply from the actual power supply . We need some convertors called ac to ac convertors.

Types of ac to ac convertor

1. i) Cycloconverters :- it is called as frequency changers that convert the ac power with one input frequency to ac power with a different output frequency and can be used for changing the magnitude of the ac power also. Cycloconverter are preferred for avoiding dc links and to avoid many stages like ac to dc to ac which is not economical and causes more losses . The cost of the dc link require will vary according to the ratings of the supply power being used.

Cycloconverter are divided into some types as

1. i) Blocking mode cycloconverter
2. ii) Circulating current mode cycloconverter
3. i) Blocking mode cycloconverter :- these converter does not need any limiting reactor as in this mode only one limb either positive or negative limb conducts at a time , and the other limb is blocked. Hence this is called as Blocking mode cycloconverters.
4. ii) Circulating current mode cycloconverter :- These cycloconverters need limiting reactor as both the positive limb rector and the negative limb conduct at a time, and hence a reactor is placed to limit the circulating current. As both the limbs conducting at the same time , there will be a circulating current in the system , and hence , it is called circulating current mode cycloconverter.

Classification of cycloconverter based on the number of phases of output voltage

1. i) Single Phase to single phase convertor Cycloconverters
2. ii) Three phase to single phase Cycloconverters

iii) Three phase to three phase cycloconverters

1. i) Single phase to single phase cycloconverter :- It consists of two full wave convertors that are linked back to back. If we have to get one fourth of input voltage , the positive convertor will operates and provides the current to the load and the input voltage gets rectifier . During the next two cycle the other convertor will operates , and provide the opposite direction . when one convertor is in operation , the other will be in the disable condition . Therefore , there is no circulating current between these convertors
2. II) Three phase to single phase cycloconverter :- this type of convertor can operate in four quadrants in two modes and in inverting modes positive convertor provides positive current and negative convertor provides negative current to the load. At a time , once converter will operate .

iii) Three phase to three cycloconverter :- These type of cycloconverter are formed by using three phase to single phase cycloconverter linked together to the load and is used in AC machine systems. Two basic configuration are wye and delta . Output of these convertors can be connected in wye and delta . The phase of output voltages are 120 degree shifted .

DC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels. Due to the automotive constraints, the power converter structure has to be reliable, lightweight, small volume, with high efficiency, low electromagnetic interference and low current/voltage ripple.