12-04-2011, 02:49 PM
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CASCADED MULTILEVEL INVERTER FOR
HYBRID ELECTRIC VEHICLES
OBJECTIVE
• HEV are used for increase fuel efficiency and to tackle pollution problems.
• To make a transformer less multilevel inverter for high voltage and high current HEV.
• The cascaded inverter is IGBT based and it is fired in a sequence.
• The simulation has been done in PSIM and MATLAB and its responses match the theoretical concept of multilevel inverter.
INTRODUCTION
HEV
ARCHITECTURE
ENGINE EFFICIENCY
INCREASE FUEL EMISSIONS
POWER ELECTRONICS
MEET HIGH POWER DEMANDS using BATTERIES.
Multilevel inverters
HIGH VOLTAGES AND HIGH POWER
NO TRANSFORMERS
A STAIRCASE OUTPUT (similar to sinusoidal output waveform )
LOW HARMONIC DISTORTION
INCREASE IN VOLTAGE LEVELS
HYBRID ELECTRIC VEHICLES
• Series : Single path to power the wheels. Two energy sources. The fuel tank feeds engine coupled to generator to charge battery which provides electrical energy to motor/generator to power the wheels. Motor/generator also used to recharge the battery during deceleration and braking.
• Parallel : Two parallel paths - engine path and electrical path to power the wheels. The transmission couples motor or generator and engine, allowing either/ both to power the wheels. Controlling is complex.
• Series-parallel: Both Series and Parallel energy paths. A system of motors and/or generators that sometimes includes a gearing or power split device couples allows engine to recharge battery. Variations on this configuration can be very complex or simple, depending on the number of motors/generators and how they are used. Configuration classified as Complex hybrids (Toyota Prius and Ford Escape Hybrids), Split-Parallel hybrids, or Power-Split hybrids.
DIODE CLAMPED
Proposed by Nabea,Takahasi and Akagi in 1981. Switches are switched in such manner that it will give stair case output. Here for each step four switches are ON and capacitor have equal charge(Vdc/4) .
There are m capacitors and 2(m-1) switches and (m-1)*(m-2)diode per phase.
Advantages
All of the phase share a common DC bus, which minimizes the capacitance requirement of the converter.
The capacitor can be pre-charged as a group.
Efficiency is high for fundamental frequency switching.
Disadvantages
Real power flow is difficult as the intermediate DC levels will tend to overcharge or discharge without precise monitoring and control.
The number of clamping diodes required is quadratic related to levels which is cumbersome with units of high number of levels.