EE 8407 Power Converter Systems Topic 6 Graduate

EE 8407 Power Converter Systems Topic 6 Graduate Course EE 8407 Bin Wu Ph. D, PEng Professor ELCE Department Ryerson University Contact Info Office: ENG 328 Tel: (416) 979 -5000 ext: 6484 Email: bwu@ee. ryerson. ca http: //www. ee. ryerson. ca/~bwu/ Ryerson Campus Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 1

EE 8407 Topic 6 Multilevel Cascaded H-Bride (CHB) Inverters H-bride power cells CHB Inverter Fed Drive Source: Toshiba - General Electric Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 2

EE 8407 Multilevel CHB Inverters Topic 6 Lecture Topics • H-Bridge Inverter • CHB Inverter Topologies • Phase Shifted PWM • Level Shifted PWM • PWM Scheme Comparison Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 3

EE 8407 Multilevel CHB Inverters Topic 6 Why Use Multilevel Inverters? • To increase inverter operating voltage without devices in series • To minimize THD with low switching frequencies fsw • To reduce EMI due to lower voltage steps Switching frequency for high power converters: fsw = 60 Hz ~ 1000 Hz Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 4

EE 8407 Multilevel Inverter Topologies Topic 6 • Per-Phase Diagram Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 5

EE 8407 H-Bridge Inverter Topic 6 • H-bridge Power Cell Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 6

EE 8407 H-Bridge Inverter Topic 6 • Typical Industrial Applications Five-level CHB inverter H-bridge Power Cell Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 7

EE 8407 Topic 6 H-Bridge Inverter • Bipolar Modulation Bipolar PWM: v. AB from -Vd to +Vd or from +Vd to -Vd Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 8

EE 8407 H-Bridge Inverter Topic 6 • Bipolar Modulation (FFT) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 9

EE 8407 Topic 6 H-Bridge Inverter • Unipolar Modulation (1) • Two modulation waves vm and vm- • One carrier wave vcr • Unipolar PWM: v. AB from 0 to +Vd or from 0 to -Vd Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 10

EE 8407 H-Bridge Inverter Topic 6 • Unipolar Modulation (2) • One modulating wave: • Two carrier waves: vm vcr and vcr- Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 11

EE 8407 CHB Inverter Topologies Topic 6 • Five-Level CHB Inverter Complementary Switch pairs: S 11 and S 41; S 31 and S 21; S 12 and S 42; S 32 and S 22; Converters in cascade, but no switching devices in series. Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 12

EE 8407 CHB Inverter Topologies Topic 6 • Output Voltage and Switching Status (five-level) Waveform of v. AN is composed of five voltage levels: 2 E, E, 0, -E, and -2 E Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 13

EE 8407 CHB Inverter Topologies Topic 6 • Seven- and Nine-Level Inverters (Per phase diagram) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 14

EE 8407 CHB Inverter Topologies Topic 6 • Unequal dc Bus Voltages Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 15

EE 8407 CHB Inverter Topologies Topic 6 • Unequal dc Bus Voltages (Two-cell seven-level topology) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 16

EE 8407 Phase Shifted PWM Topic 6 • Carrier Based PWM – Phase Shifted • # of voltage levels: m = 7 • # of carriers: mc = m - 1 = 6 • Phase shift: 360° / mc = 60° Carriers for H 1 bridge: vcr 1 and vcr 1 Carriers for H 2 bridge: vcr 2 and vcr 2 Carriers for H 3 bridge: vcr 3 and vcr 3 m=7 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 17

EE 8407 Phase Shifted PWM Topic 6 • Inverter Waveforms (7 -level, phase shifted) • Switching occurs at different times • fsw(device) = 60 mf = 600 Hz • Inverter phase voltage levels: 7 • Low EMI • Line-to-line voltage levels: 13 • Close to a sinusoid • Low THD Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 18

EE 8407 Phase Shifted PWM Topic 6 • FFT (7 -level, phase shifted) • Lowest harmonics: around 2 mf • Lowest harmonics: around 6 mf • Containing triplen harmonics • No triplen harmonics • Equivalent fsw(inverter) = 60(6 mf ) = 3600 Hz Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 19

EE 8407 Phase Shifted PWM Topic 6 • Harmonic Content (7 -level, phase shifted) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 20

EE 8407 Level Shifted PWM • Carrier Based PWM – Level Shifted Topic 6 • # of voltage levels: m=5 IPD • # of carriers: mc = m - 1 = 4 APOD IPD provides the best harmonic profile. Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 21

EE 8407 Level Shifted PWM Topic 6 • Gating Arrangement (7 -level) • # of voltage levels: m =7 • # of carriers: mc = m - 1 = 6 • fsw(device): - not equal to fcr, and - not the same for all switches. • Device conduction angle: - not equal. • Necessary to swap switching pattern. Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 22

EE 8407 Level Shifted PWM Topic 6 • Inverter Output Voltages (seven-level) • m=7 • Switching occurs at different times • fsw(device) = fcr /mc = 600 Hz (avg) • v. AB close to a sinusoid • Low THD, low EMI • fsw(inv) = fc = 3600 Hz Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 23

EE 8407 Level Shifted PWM Topic 6 • Prototype at Ryerson (Seven-level CHB Inverter) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 24

EE 8407 Level Shifted PWM Topic 6 • Measured Waveforms (IPD, 7 -level) Inverter phase voltage v. AZ Line-to-line voltage Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 v. AB 25

EE 8407 PWM Scheme Comparison Topic 6 • PWM at Low ma • At ma = 0. 2: - Phase shifted PWM: THD = 96. 7% - Level shifted PWM: THD = 48. 8% Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 26

EE 8407 PWM Scheme Comparison Topic 6 • Total Harmonic Distortion (THD) Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 27

EE 8407 PWM Scheme Comparison Topic 6 • Summary Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 28

EE 8407 Topic 6 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 29