Week 4 Session 5

Answer:

1) DC - DC converter:

• A DC to DC converter is a category of power converters and it is an electric circuit which converts a source of direct current (DC) from one voltage level to another, by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors).
• DC/DC converters can be designed to transfer power in only one direction, from the input to the output. However, almost all DC/DC converter topologies can be made bi-directional. A bi-directional converter can move power in either direction, which is useful in applications requiring regenerative braking.
• In case of interfacing the Fuel Cell, the DC/DC converter is used to boost the Fuel Cell voltage and to regulate the DC-link voltage. However, a reversible DC/DC converter is needed to interface the SCs module.
• The non-isolated converters type is generally used where the voltage needs to be stepped up or down by a relatively small ratio (less than 4:1). And when there is no problem with the output and input having no dielectric isolation. There are five main types of converter in this non-isolated group, usually called the buck, boost, buck-boost, Cuk and charge-pump converters. The buck converter is used for voltage step-down, while the boost converter is used for voltage step-up. The buck-boost and Cuk converters can be used for either step-down or step-up. The charge-pump converter is used for either voltage step-up or voltage inversion, but only in relatively low power applications.
• In the applications where the output needs to be completely isolated from the input, an isolated converter is necessary. There are many types of converters in this group such as Half-Bridge, Full-Bridge, Fly-back, Forward and Push-Pull DC/DC converters. All of these converters can be used as bi-directional converters and the ratio of stepping down or stepping up the voltage is high.

2) DC - AC converters(inverter):

• An inverter is a device that converts DC power from the battery to AC power in an electric vehicle motor. The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current.
• The use of inverters can increase or decrease the power or torque of the motor by adjusting the amplitude of the signal.
• It plays a significant role in capturing energy from regenerative braking and feeding it back to the battery. The key component is that it has a direct impact on on-road performance, driving range, and reliability of the vehicle also as a consequence of their weight and size.
• The output voltage waveform of ideal inverters should be sinusoidal. However, the waveform of practical inverters is non-sinusoidal and contains certain harmonics.

3) AC - DC converter:

• AC-DC converter takes a harmonic AC input and converts it to a DC output.
• These concerters are also known as rectifiers.
• Inverters are used in Ev/Hev mainly for the on-board charging purpose. Since the charging stations use AC power to charge the vehicle and the battery stores DC power, rectifiers are used to convert AC-DC.