Ch.8 INVERTER 8.1 Introduction 8.2 The Full-Bridge Converter 8.3 The Square-Wave Inverter 8.4 Fourier Series Analysis 8.5 Total Harmonic Distortion 8.6 PSpice Simulation of Square-Wave Inverters 8.7 Amplitude & Harmonic Control 8.8 The Half-Bridge Inverter 8.9 Multilevel Inverters 1
Ch.8 INVERTER 8.10 PWM Output 8.11 PWM Definitions & Considerations 8.12 PWM Harmonics 8.13 Class D Audio Amplifiers 8.14 Simulation of PWM Inverters 8.15 3 Phase Inverters 8.16 PSpice Simulation of 3 phase Inverters 8.17 Induction Motor-Speed Control 8.18 Summary 2
8.1 Introduction Inverter : Converting dc to ac Applications : AC motor speed control, UPS (Uninterruptible Power System), DVR (Dynamic Voltage Restorer) Discharge Lamp Control, Solar/Wind Generation Induction Heating 3
(1) Fig.8-1 : Full-Bridge Inverter 8.2 Full-Bridge Converter Switches Closed S 1 and S 2 S 3 and S 4 Output Voltage, v o +V dc -V dc S 1 and S 3 0 S 2 and S 4 0 (2) Switch transition time : dead time 4
8.3 Square Wave Inverter (1) from Fig.8-1 : Full-Bridge Inverter for R-L load, 5
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(3) Fig.8-3 : Full-Bridge Inverter with R-L load. 7
8.4 Fourier Series Analysis (1) set voltage & current as follow (2) power in load (3) for square function 8
8.5 Total Harmonic Distortion 8-17 9
8.7 Amplitude & Harmonic Control (1) Switching Pattern Control : 출력파의크기와고조파제어. (2) From Fig. 8-5a (3) Fourier series form 10
(5) Fig. 8-5 : Specific Harmonic Elimination (n=3 & 5) Fourier coefficient Fig. 8.6 Specific Harmonic Elimination (n=3 & 5) 11
8.8 Half Bridge Inverter (1) Fig. 8-8 : Half Bridge Inverter 2 Capacitor source 12
8.9 Multilevel Inverters (1) Purpose of multilevel inverter is to be more sine-like in quality Fig. 8-9 Multilevel Inverters Independent dc Sources Fig. 8-10 output of multilevel inverters 13
(2) from Fig. 8-10 (4) Delay 각을적절히조절하면고조파제거가능 14
(5) Fig. 8-11 shows 5-source cascade multilevel converter Fig. 8-11 5-source cascade multilevel converter Fig. 8-12 voltages of Fig. 8-11 15
Fig. 8-12 voltages of Fig. 8-11 16
(7) Pattern swapping 의평균전력의 equalizing : Fig. 8-9 & 8-13 Fig. 8-9 Multilevel Inverters Independent dc Sources Fig. 8-13 Pattern swapping 17
(8) Diode-Clamped Multilevel Inverter : 1- dc source 사용 18
8.10 PWM Output (1) In load current, to suppress THD : PWM (switching) + Filter (output) (2) Reference (modulation or control) signal + Carrier signal - using sinusoid & triangular wave - Bipolar & Unipolar switching technique 19
(3) In Fig. 8-17, PWM with bipolar switching Fig. 8-17 PULSE-WIDTH-MODULATED OUTPUT Bipolar Switching 20
(4) In Fig. 8-18, PWM with unipolar switching 21
(5) In Fig. 8-19, PWM with unipolar switching with high- and low- frequency 22
8.11 PWM Definition & Considerations 1. Frequency Modulation Ratio : 8-35 2. Amplitude Modulation Ratio : 3. Switch : 1) feedback diode is needed to carry current in either direction 2) considering switching time 4. Reference Voltage : generating reference signal 23
8.12 PWM Harmonics (1) Bipolar Switching Fourier Series of PWM Output in Fig. 8-17 from Fig. 8-20 24
(2) Spectrum of PWM (Bipolar Switching) Table 8-3. Normalized Fourier Coefficients V n /V dc for Bipolar PWM m a =1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 n = 1 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 n = m f 0.60 0.71 0.82 0.92 1.01 1.08 1.15 1.20 1.24 1.27 n = m f ± 2 0.32 0.27 0.22 0.17 0.13 0.09 0.06 0.03 0.02 0.00 Fig. 8-21 Spectrum at bipolar switching ( )
(3) Spectrum of PWM (Unipolar Switching) Table 8-5. Normalized Fourier Coefficients V n /V dc for Unipolar PWM m a =1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 n = 1 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 n = 2m f ± 1 0.18 0.25 0.31 0.35 0.37 0.36 0.33 0.27 0.19 0.10 n =2m f ±3 0.21 0.18 0.14 0.10 0.07 0.04 0.02 0.01 0.00 0.00 Fig. 8-22 Spectrum at unipolar switching ( )
8.14 Class D Audio Amplifier (1) Conventional Analog audio amplifier : Class A, B, AB or Push-Pull (2) Digital D class audio amplifier : Efficiency, High Power, size etc. 1) Using PWM techniques 2) Sampling frequency : 250 [KHz] 3) Low pass filter for output 27
8.15 3φ Inverter (1) 6- step Inverters 28
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- frequency : depend on switch frequency - Amplitude : depend on input 30
(3) PWM 3 Phase Inverters 2) PWM generation 31
(4) Multi level 3 Phase Inverters Fig. 8-30 MULTILEVEL THREE-PHASE INVERTERS 32
8.15 Induction Motor Speed Control (1) Induction motor control 1) Torque vs. Slip characteristics : 2 Pgap 3R E TD = = [ N w sw S S r BR 2 2 [( R / s) + X ] r BR m] 2) Slip Frequency Control 33
8.15 Induction Motor Speed Control (1) Induction motor control 1) Slip Frequency Control 34
Keywords in Ch. 8 Inverter, Frequency Changer, Full Bride Inverter, Square wave inverter, Fourier Series in Inverter, Total Harmonic Distortion, Harmonic elimination, Special Harmonic Elimination, Half Bridge Inverter, PWM, Bipolar switching, Unipolar Switching, Modulation Factor, Amplitude Modulation, PWM Harmonics, 3 Phase Inverter, Speed Control of Induction Motor. Homework Examples Problems : 8-1, 8-2, 8-3, 8-6 Problems : 8-1, 8-2, 8-8 35