power electronics lecture 1

what is studied in power electronics

the application of electronic devices and circuits to the conversion and control of energy.

what do power electronic circuits handle

These circuits handle energy flow at levels much higher than individual device ratings.

how is energy converted from dc to ac

the only option was electrical to mechanical to electrical conversion: a motor driving a generator.

how is energy converted from ac to dc

have the transformer, which at least can adjust voltage levels.

what type of process is energy conversion

nonlinear process: The form we want differs in basic ways from the form we start with.

what are examples of power electronics

every computer, almost every appliance or new electrical product.

how much energy can modern devices manage

1W to 1000MW

what are challenges for power electronics (example is PC)

Power supply is the largest part. Significant cost, reliability impact, system issues.

where is a converter located in a circuit

Converter sits between source and load.

what happens to energy consumed during conversion

Any energy consumed in conversion is lost to the system.

what happens when the converter fails

Any failure in the converter results in failure of the system.

what is the efficiency target of lossless methods

100%

what is the reliability target of simple systems

100%

define a switch

a simple lossless element

what is the voltage and power of an on switch

0

what is the current and power of a switch when off

0

what are important variables when designing a circuit

Average power at a specified location. Peak values of voltages and currents. Average values of voltages and currents. RMS voltages and currents. Waveforms

when does energy balance work

Energy balance works if we can identify a specific element.

how does energy balance work (method)

The element is analyzed as a one-port network. if the element is lossless, input and output energy must balance.

characteristics of the one-port model

The input power is defined as (v)(i), positive with current and voltage polarities as shown. This means the output power is -(v)(i). For lossless balance, we can either take P(in) = P(out), or we can take a total P(in) of zero.

characteristics of polarity reverser

With left switch on, input power is Pin = (Vin)(iL ). With right switch on, input power is Pin = (Vout)(iL ).

what are the functions of converters

Provide a very tightly fixed dc output from an uncertain input voltage source. Provide polarity reversal. Step a dc voltage up or down. Rectify, invert, and otherwise facilitate energy flow between ac and dc circuits, or between ac circuits operating at different frequencies.

what is the switch matrix

If a converter has m input lines and n output lines, an m X n matrix allows all possible interconnections.

what are the 2 types of power electronic circuits

Direct switch matrix circuits, Indirect switch matrix circuits

what is a Direct switch matrix circuits

storage elements connected to the matrix only at the input and output terminals. (matrix converters)

what is a Indirect switch matrix circuits

storage elements connected within the matrix structure (embedded converters)

what does a switch matrix provide

Provides a clear way to organize devices for a given application.

what are the three areas of switch matrix

hardware problem. software problem. interface problem.

what is the hardware problem

build a switch matrix

what is the software problem

operate the matrix to achieve the desired conversion.

what is the interface problem

add energy storage elements to provide the filters or intermediate storage necessary to meet the application requirements.

what happens If a fixed voltage is applied to an inductor

current rises without limit.

what happens If a fixed current is applied to a capacitor

charge rises without limit.

what property is key to circuit analysis

an inductor carries no average voltage; a capacitor carries no average current.

can capacitor sustain dc current over extended times.

NO

what can switch matrix NOT be used for

We cannot use a switch matrix for direct connection of voltage sources or of current sources.

what are the conditions for a useful converter

must mix voltage and current sources. “Voltage converts to current,” “Current converts to voltage.”

how is a switching function defined

Define a switching function, q(t) as 1 when a device is on, 0 when off. each physical switch is associated with a simple discrete function.

what is a switch state matrix, Q(t).

The matrix Q has elements that correspond to each individual switch. The element at row i and column j represents switch ij and function q_ij(t).

characteristics of an ideal switch

On, v = 0. Off, i = 0. Any polarity of v or I, and no limits. Can turn on or off at any time. Acts instantly.