Tasks of Power Electronics

Transcription

1 Power Electronic Sytem Power electronic refer to control and converion of electrical power by power emiconductor device wherein thee device operate a witche. Advent of ilicon-controlled rectifier, abbreviated a SCR, led to the development of a new field of application called the power electronic. Before SCR, mercury-arc rectifier were ued for controlling electrical power, but uch rectifier circuit were part of indutrial electronic and the cope for application of mercury-arc rectifier wa limited. The application pread to many field uch a drive, power upplie, aviation electronic, high frequency inverter and power electronic Tak of Power Electronic Rectification referring to converion of ac voltage to dc voltage DC-to-AC converion DC-to DC converion AC-to-AC converion 1

2 Converter Electronic power converter i the term that i ued to refer to a power electronic circuit that convert voltage and current from one form to another. Rectifier converting an ac voltage to a dc voltage Inverter converting a dc voltage to an ac voltage Chopper or a witch-mode power upply that convert a dc voltage to another dc voltage Cycloconverter and cycloinverter converting an ac voltage to another ac voltage.

3 Rectifier Rectifier may be claified a uncontrolled and controlled rectifier. Controlled rectifier can be further divided into emi-controlled and fully-controlled rectifier. Uncontrolled rectifier circuit are built with diode, and fully-controlled rectifier circuit are built with SCR. Both diode and SCR are ued in emi-controlled rectifier circuit. Single-phae emi-controlled bridge rectifier Single-phae fully-controlled bridge rectifier Three-phae three-pule, tar-connected rectifier Double three-phae, three-pule tar-connected rectifier with inter-phae tranformer (IPT) Three-phae emi-controlled bridge rectifier Three-phae fully-controlled bridge rectifier Double three-phae fully-controlled bridge rectifier with IPT. 3

4 DC to AC Converion The converter that change a DC to AC i called an inverter. Earlier inverter were built with SCR. Since the circuitry required to turn the SCR off tend to be complex, other power emiconductor device uch a bipolar junction tranitor, power MOSFET, inulated gate bipolar tranitor (IGBT) and MOS-controlled thyritor (MCT) are ued nowaday. Currently only the inverter with a high power rating, uch a 500 kw or higher. Emergency lighting ytem AC variable peed drive Uninterrupted power upplie Frequency converter. 4

5 DC to DC Converion When the SCR came into ue, a dc-to-dc converter circuit wa called a chopper. Nowaday, an SCR i rarely ued in a dc-to-dc converter. Either a power BJT or a power MOSFET i normally ued in uch a converter and thi converter i called a witch-mode power upply. Step-down witch-mode power upply Step-up chopper Fly-back converter Reonant converter. 5

6 AC to AC Converter A cycloconverter or a cycloinverter convert an ac voltage, uch a the main upply, to another ac voltage. The amplitude and the frequency of input voltage to a cycloconverter tend to be fixed value, wherea both the amplitude and the frequency of output voltage of a cycloconverter tend to be variable. Tthe circuit that convert an ac voltage to another ac voltage at the ame frequency i known a an AC-chopper. A typical application of a cycloconverter i to ue it for controlling the peed of an ac traction motor and mot of thee cycloconverter have a high power output, of the order a few megawatt and SCR are ued in thee circuit. In contrat, low cot, low power cycloconverter for low power ac motor are alo in ue and many of thee circuit tend to ue TRIACS in place of SCR. Unlike an SCR which conduct in only one direction, a TRIACS i capable of conducting in either direction and like an SCR, it i alo a three terminal device. It may be noted that the ue of a cycloconverter i not a common a that of an inverter and a cycloinverter i rarely ued. 6

7 Application of Power Electronic In a conventional car, power electronic application are a major area of future expanion. Look inide the audio ytem, for example; the amplifier in today car tereo are uually capable of delivering 40 W or more. But a 1 V upply applied to an 8 Ohm peaker produce 18 W output at bet. To olve thi power upply problem, deigner ue a boot converter (DC to DC Converter) to provide higher voltage power to the amplifier circuit. Thi allow car amplifier to generate the ame audio output power a home tereo. 7

8 Automobile Ignition Sytem Another univeral power electronic application i the automobile ignition ytem. Thouand of volt are required to ignite the fuel-air mixture inide a cylinder o that internal combution can occur. Today car employ all-electronic ignition ytem, which have replaced the traditional park plug with boot converter coupled to tranformer. 8

9 Hybrid Car We are curiou about new electric and hybrid car, in which the primary electrical ytem i dominated by power electronic. Electric car offer high performance, zero tailpipe emiion, and low cot, but are till limited in range by the need for batterie. Hybrid car deign ue variou trategie to combine both an engine and electrical element to gain advantage of each. Inverter and DC-DC converter rated for many kilowatt erve a primary energy control block. See 9

10 Diode 10

11 Zener Diode 11

12 Semiconductor Switche Four-Level Diode Thyritor SCR Gate-Turnoff Thyritor (GTO) BJT Power Tranitor 1

13 Semiconductor Switche 13

14 Silicon Controlled Rectifier The baic purpoe of the SCR i to function a a witch that can turn on or off mall or large amount of power. It perform thi function with no moving part that wear out and no point that require replacing. There can be a tremendou power gain in the SCR; in ome unit a very mall triggering current i able to witch everal hundred ampere without exceeding it rated abilitie. The SCR can often replace much lower and larger mechanical witche. 14

15 AC to DC Converion: Half-Wave Rectifier 15

16 Full Wave Rectifier 16

17 Claification of Power Electronic Device The following i taken from Principle and Application of Electrical Engineering by G. Rizzoni, McGraw Hill Figure

18 Power Electric Circuit Table

19 AC-DC Converter Circuit and Waveform Figure 1. 19

20 AC-AC Converter Circuit and Waveform Figure 1.3 0

21 DC-DC Converter Circuit and Waveform Figure 1.4 1

22 Rectifier Connected to an Inductive Load Operation of a Freewheeling Diode Figure 1.17, 1.18

23 Three-Phae Diode Bridge Rectifier Waveform and Conduction Time of Three-Phae Bridge Rectifier Figure 1.0, 1.1 3

24 Half-Wave Controlled Rectifier Waveform Controlled Rectifier Circuit Figure 1.5, 1.6 4

25 DC Motor Step-Down Chopper (Buck Converter) Figure 1.34, 1.35 E I T w a a m m 5

26 Half-Bridge Voltage Source Inverter Half-Bridge Voltage Source Inverter Waveform Figure 1.41, 1.4 6

27 PID Controller PID tand for Proportional, Integral, Derivative. One form of controller widely ued in indutrial proce i called a three term, or PID controller. Thi controller ha a tranfer function: A proportional controller ( p ) will have the effect of reducing the rie time and will reduce, but never eliminate, the teady tate error. An integral control ( I ) will have the effect of eliminating the teady-tate error, but it may make the tranient repone wore. A derivative control ( D ) will have the effect of increaing the tability of the ytem, reducing the overhoot, and improving the tranient repone. I GC ( t) p + + D The controller provide a proportional term, an integration term, and a u( t) p e( t) + I e( t) dt + D de( t) dt derivative term 7

28 8 Proportional-Integral-Derivative (PID) Controller k p k i / k i e(t) u(t) E U G E U t y t r t e t e t e t e t u I P D PID D I p D I P D I p ) ( ) ( ) ( ) ( ) ( ) ( repectively. and derivative feedback gain, integral, are the proportional, and,, and the ytem output; the error between the reference ignal i ) ( ) ( ) ( ) ( ) ( ) ( ) (

29 Time- and -domain block diagram of cloed loop ytem r(t) e(t) u(t) PID R() + E() Controller U() - Sytem y(t) Y() G( ) Y ( ) R( ) G y 1+ G ( ) G y PID ( ) G PID ( ) ( ) 9

30 PID and Operational Amplifier A large number of tranfer function may be implemented uing operational amplifier and paive element in the input and feedback path. Operational amplifier are widely ued in control ytem to implement PID-type control algorithm needed. 30

31 Inverting amplifier V o ( t) R V S ( t) R 1 Figur e

32 Op-amp Integrator Z ( ) Z 1( ) G( ) V V ( ) Z ( ) out 1 ( ) Z1( ) RSCF Figure

33 Op-amp Differentiator The operational differentiator perform the differentiation of the input ignal. The current through the input capacitor i CS d v (t)/dt. That i the output voltage i proportional to the derivative of the input voltage with repect to time, and V o (t) _R F C S dv (t)/dt Z ( ) G( ) V V o S ( ) ( ) Z Z 1 ( ) ( ) _ R F C Figure 8.35 S Z 1 ( ) 33

34 Linear PID Controller Z () C 1 C R R 1 Z 1 () v (t) v o (t) V G( ) V G PID o S ( ) ( ) ( ) D ( R C + 1)( R C + 1) 1 + P 1 R C 1 + I R R1C 1 + R ; P R C 1 C 1 C R1C 1 + R + R C ; I 1 1 C 1 R C + ; 1 R C D 1 R C 1 34

35 Tip for Deigning a PID Controller When you are deigning a PID controller for a given ytem, follow the following tep in order to obtain a deired repone. Obtain an open-loop repone and determine what need to be improved Add a proportional control to improve the rie time Add a derivative control to improve the overhoot Add an integral control to eliminate the teady-tate error Adjut each of p, I, and D until you obtain a deired overall repone. It i not neceary to implement all three controller (proportional, derivative, and integral) into a ingle ytem, if not needed. For example, if a PI controller give a good enough repone, then you do not need to implement derivative controller to the ytem. 35

36 36 The popularity of PID controller may be attributed partly to their robut performance in a wide range of operation condition and partly to their functional implicity, which allow engineer to operate them in a imple manner. ( ) ( )( ) - plane - hand located anywhere in the left that can be tranfer function with one pole at the origin and two zero a Accordingly the PID introduce. / and ; / Where ) ( b a z z b a t G C

37 Deign of Robut PID-Controlled Sytem The election of the three coefficient of PID controller i baically a earch problem in a three-dimenional pace. Point in the earch pace correpond to different election of a PID controller three parameter. By chooing different point of the parameter pace, we can produce different tep repone for a tep input. The firt deign method ue the ITAE performance index in Section 5.9 and the optimum coefficient of Table 5.6 for a tep input or Table 5.7 for a ramp input. Hence we elect the three PID coefficient to minimize the ITAE performance index, which produce an excellent tranient repone to a tep. The deign procedure conit of the following three tep. 37