Thursday, 23 February 2012

Introduction report

I officially started this MPhil 8th February and so far I have met my supervisors and I have been told this is a partnership with Nottingham and some companies as well. Just to start off with I had to do a report and presentation within 4 weeks on:
  1. What is power electronics?
  2. How is it different to Microelectronics?
  3. How do we predict reliability of power electronics modules?(classify each technique)
  4. How can finite element analysis be used to predict reliability?
  5. What is meant by the term "Prognostic" and "Health Management"
  6. How are power electronic modules used in:
    1. Wind Power
    2. Solar Power
    3. Traction and drive
    4. Electric veichles
    5. Airbus 380
So far this is what I have got:

What is power electronics?

Power electronics deals with the control and flow of electricity so it is involved in converting from AC to DC current. Also involved in converting the voltage up and down. It can also be used in delivering power gradually. . “Power electronics uses semiconductor technology to convert and control electrical power.” From Hua Lu, Chris Bailey, Chunyan Yin on the paper “Design for reliability of power electronics modules”

How is it different to Microelectronics?

Microelectronics relates to the study and manufacture of microelectronic designs and components. Components found in normal electric design are found in microelectronics e.g. transistors, capacitors, inductors, resistors, diodes and of course insulators and conductors. Another definition is Microelectronics carries communication and data.

How do we predict reliability of power electronics modules?

Reliability is to do with the lifetime prediction of the product. There are several predictions methods available many can be found from Reli Soft or you could look at their lists:

MIL-HDBK-217 Predictive Method

This consists of two parts:
  1. One part is called “parts count” where it assumes typical operating conditions like temperature, electrical stresses etc. These are called Reference conditions. The failure rate for a part under the reference conditions is calculated as (see diagram). Yref is the failure rate under reference conditions and i is the number of parts.
  2. The other part is called “parts stress”. Since the real operating conditions will be different to the parts count part stress needs the specific part complexity.

How can finite element analysis be used to predict reliability?

Finite element analysis is used to solve partial differentiable equations (PDEs). Finite element analysis is needed to perform a stress analysis of the component that will be used to predict reliability. We need to know what components of a model need to be accelerated in order to work out to test it’s lifespan.

What is meant by the term "Prognostic" and "Health Management"

Prognostic is the discipline in predicting the time in which a component can no longer perform its function. Health management has a couple of meanings, one is it the field of administrating, leadership and management of hospitals. The other definition is concerning itself with the different effects on health like physical, social, nutrition, housing etc.
The definition of "Integrated systems health management" include fault detection, fault diagnosis (fault isolation) and fault prognosis.

How are power electronic modules used in:

Wind Power

Power electronics enables the variable speed operation in variable speed wind turbines. Whereas fixed speed wind turbines can’t follow optimal aerodynamic efficiency point. (source). I know I'm not meant to talk about it but some bright spark may have eliminated power electronics from wind power. Artemis hydraulic system eliminates the gearbox and power electronics from wind turbines, making them lighter, cheaper and more robust. (source)

Solar Power

Power electronics is used in 2 different ways:
To interconnect the individual solar panels – two solar panels cannot be identical hence a dc-dc converter interfacing the two will help maintain the required current and voltage, and with regulation improve the overall efficiency. Several non-isolated dc-dc converters have been employed for this purpose. Buck, buck-boost, boost, and Cuk topologies with suitable modifications can be employed for this purpose.
To interface the dc output of the photovoltaic system to the grid or the load - This includes the previously discussed topics of dc-dc-ac and dc-ac-ac conversion. The topologies considered for fuel-cell system grid interconnection correlates to the grid interconnection of photovoltaic based system as well including the usage of the Z-source inverter. Source

Traction and drive

From Wikipedia I believe power electronics helps trains/trams to stop from slipping and a smooth acceleration. “As the DC motor starts to turn, the magnetic fields inside start to join together. They create an internal voltage. This electromagnetic force (EMF) works against the voltage sent to the motor. The EMF controls the current flow in the motor. As the motor speeds up, the EMF falls. Less current flows into the motor, and it makes less torque. The motor will stop increasing its speed when the torque matches (is the same as) the drag on the train. To accelerate the train, more voltage must be sent to the motor. One or more resistors are removed to increase the voltage. This will increase the current. The torque will increase, and so will the speed of the train. When no resistors are left in the circuit, full line voltage is applied directly to the motor.”

Electric vehicles

From Tesla website it talks about the power electronic module converting AC to DC when charging and converts DC to AC when driving. When in drive mode it gathers information about how much pressure on the gas pedal, motor speed sensor, ABS speed sensors and other sensors. It can detect if the car is slipping, then produce torque by directing current from the batteries to the motor terminals. Where it can go from 0 to 60 mph in 3.7 seconds.

Airbus 380

"The Airbus A380 first introduced electrical control actuators in civil service to back up the primary hydraulic systems" from p26 of Power electronics: A strategy for success. Areas in which power electronics can be used for A380 are:
  • Motor drives for flight control actuators
  • Electrical starter generator
  • Environmental cooling system
  • Power conversion (e.g. DC/DC, DC/AC converter)