* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Immunity-aware programming wikipedia , lookup
Power factor wikipedia , lookup
Audio power wikipedia , lookup
Stepper motor wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Control system wikipedia , lookup
Utility frequency wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Power engineering wikipedia , lookup
Electrical ballast wikipedia , lookup
History of electric power transmission wikipedia , lookup
Electrical substation wikipedia , lookup
Current source wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Power inverter wikipedia , lookup
Surge protector wikipedia , lookup
Stray voltage wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Distribution management system wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Integrating ADC wikipedia , lookup
Voltage regulator wikipedia , lookup
Schmitt trigger wikipedia , lookup
Three-phase electric power wikipedia , lookup
Alternating current wikipedia , lookup
Voltage optimisation wikipedia , lookup
Current mirror wikipedia , lookup
Mains electricity wikipedia , lookup
Buck converter wikipedia , lookup
Chapter 4 AC to AC Converters Outline 4.1 AC voltage controllers 4.2 Other AC controllers 4.3 Thyristor cycloconverters 4.4 Matrix converters 4.1.1 Single-phase AC voltage controller VT 1 VT2 u1 u1 io O uo t R uo O t io The phase shift range (operation range of phase delay angle): O u VT t 0 ≤α≤ π O t Resistive load, quantitative analysis RMS value of output voltage Uo 2U sint dt U 1 2 1 1 1 sin2 2 (4-1) RMS value of output current Uo R RMS value of thyristor current Io (4-2) 2 U1 1 1 2U 1 sin t sin 2 IT d t ( 1 ) 2 R R 2 2 (4-3) Power factor of the circuit P UoIo Uo S U1 I o U1 1 sin 2 2 (4-4) Inductive (Inductor- resistor) load , operation principle u1 VT 1 O io uG1 VT2 R u1 t uo L O uG2 O uo t O io t O t t The phase shift range: φ ≤α ≤ π uVT O t Inductive load, quantitative analysis Differential equation d io Ri o 2U 1 sin t dt i o t 0 (4-5) 140 /(°) Solution t 2U1 tg io sin(t ) sin( )e Z ã 90¡ = ¡ã 75 ¡ã 605¡ã 4 ¡ã 30 5¡ã 1 ¡ã 0 180 L t Considering io =0 when ωt= α+ θ We have sin( ) sin( )e (4-6) tg 100 60 20 0 (4-7) 20 60 100 /(°) 140 180 图4-3 The RMS value of output voltage, output current, and thyristor current can then be calculated. 4.1.2 Three-phase AC voltage controller Classification of three- phase circuits ia VT1 Ua0' a u a VT 3 n ub ia VT4 b VT5 uc ua n' VT6 c n Line- controlled Δ connection ia ua a a ia ub b b n ub uc ub uc Y connection n b c VT2 ua a uc c Branch-controlled Δ connection c Neutral-point controlled Δconnection 3- phase 3- wire Y connection AC voltage controller i a VT 1 ua VT3 n ub uc VT5 Ua0' a VT4 b n' VT6 c VT 2 For a time instant, there are 2 possible conduction states: –Each phase has a thyristor conducting. Load voltages are the same as the source voltages. –There are only 2 thyristors conducting, each from a phase. The load voltages of the two conducting phases are half of the corresponding line to line voltage, while the load voltage of the other phase is 0. 4.2 Other AC controllers 4.2.1 Integral cycle control—AC power controller VT1 VT2 u1 io Conduction uo angle = 2 U1 uo R O M 2 M 2N M u1 uo,io 3 M 4 M t Line period Control period = M *Line period = 2 Circuit topologies are the same as AC voltage controllers. Only the control method is different. Load voltage and current are both sinusoidal when thyristors are conducting. Spectrum of the current inAC power controller 0.6 There is NO harmonics in the ordinary sense. There is harmonics as to the control frequency. As to the line frequency, these components become fractional harmonics. 0.5 0.4 IO/I0m 0.3 0.2 0.1 2 0 4 6 8 10 12 14 Harmonic order as to control frequency 0 1 2 3 4 Harmonic order as to line frequency 5 4.2.2 Electronic AC switch Circuit topologies are the same as AC voltage controllers. But the back- to- back thyristors are just used like a switch to turn the equipment on or off. Application—Thyristor-switched capacitor (TSC) I U TSC waveforms when the capacitor is switched in/out uVT 1 uC iC C VT2 t uC VT1 us us t uVT 1 t VT1 iC t VT2 t1 t2 The voltage across the thyristor must be nearly zero when switching in the capacitor, and the current of the thyristor must be zero when switching out the capacitor. TSC with the electronic switch realized by a thyristor and an antiparallel diode uVT uC iC VT us C VD us t uC t uVT t VD iC VT t t 1 t2 t 3 t 4 The capacitor voltage will be always charged up to the peak of source voltage. The response to switching- out command could be a little slower (maximum delay is one line-cycle). 4.2.3 Chopping control—AC chopper AC chopper Modes of operation VD 1 V1 i1 u1 V2 VD 2 V3 VD 3 VD 4 uo V4 u>0, io >0: V1 charging, V3 freewheeling 图4-7 u>0, io <0: V4 charging, V2 freewheeling u<0, io >0: V3 charging, V1 freewheeling u<0, io <0: V2 charging, V4 freewheeling R L 4.3 Thyristor cycloconverters 4.3.1 Single- phase thyristor-cycloconverter Circuit configuration and operation principle P N Z uo ap= π 2 Output voltage Average ap=0 output voltage ap = π 2 t Single- phase thyristor-cycloconverter Modes of operation uo u o,io O t1 iP uP uo t2 t4 t3 t5 t O iN uN t uo uP io io uN t uo O iP P N O iN t O t Rectifi Inver cation sion blocking blocking Rectifi Inver cation sion Typical waveforms uo t O io O t 1 3 2 4 6 5 Modulation methods for firing delay angle Calculation method – For the rectifier circuit u o U d0 cos (4-15) u2 u3 u4 u5 u6 u1 ωt –For the cycloconverter ap3 ap4 output uo U om sinot (4-16) –Equating (4- 15) and (4-16) U om cos sin o t sin o t U d0 –therefore (4-17) cos 1 ( sin o t ) (4-18) us2 us3 us4 us5 us6 us1 uo ωt Principle of cosine wave-crossing method Output voltage ratio (Modulation factor) 150 Uom 120 (0 1) Ud 0 /( º ) 90 60 30 0 γ γ 3 2 t 2 2 Output voltage phase angle 4.3.2 Three- phase thyristor-cyclo converter The configuration with common input line 图4-24 The configuration with star-connected output Typical waveforms Output voltage 200 t/ms Input current with Single-phase output Input current with 3-phase output 200 t/ms 200 t/ms Input and output characteristics The maximum output frequency and the harmonics in the output voltage are the same as in single-phase circuit. Input power factor is a little higher than single-phase circuit. Harmonics in the input current is a little lower thanthe single- phase circuit due to the cancellation of some harmonics among the 3 phases. To improve the input power factor: –Use DC bias or 3k order component bias on each of the 3 output phase voltages Features and applications Features: –Direct frequency conversion—high efficiency –Bidirectional energy flow, easy to realize 4- quadrant operation –Very complicated—too many power semiconductor devices –Low output frequency –Low input power factor and bad input current waveform Applications: –High power low speed AC motor drive 4.4 Matrix converter Circuit configuration input b a c u S1 S1 S1 1 2 3 S2 S2 S2 1 2 3 S ij v output w S3 S3 S3 1 2 3 a) b) Usable input voltage Features Direct frequency conversion—high efficiency can realize good input and output waveforms, low harmonics, and nearly unity displacement factor Bidirectional energy flow, easy to realize 4- quadrant operation Output frequency is not limited by input frequency No need for bulk capacitor (as compared to indirect frequency converter) Very complicated—too many power semiconductor devices Output voltage magnitude is a little lower as compared to indirect frequency converter.