Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 1 Power Converter Systems Graduate Course EE8407 Ryerson Campus Bin Wu PhD, PEng Professor ELCE Department Ryerson University Contact Info Office:ENG328 Tel: (416) ext:

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 2 CHB Inverter Fed Drive Source: Toshiba - General Electric H-bride power cells Topic 6 Multilevel Cascaded H-Bride (CHB) Inverters

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 3 Lecture Topics H-Bridge Inverter CHB Inverter Topologies Phase Shifted PWM Level Shifted PWM PWM Scheme Comparison Multilevel CHB Inverters

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 4 To increase inverter operating voltage without devices in series To minimize THD with low switching frequencies f sw To reduce EMI due to lower voltage steps Why Use Multilevel Inverters? Switching frequency for high power converters: f sw = 60Hz ~ 1000Hz Multilevel CHB Inverters

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 5 Per-Phase Diagram Multilevel Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 6 H-bridge Power Cell H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 7 H-bridge Power Cell Typical Industrial Applications Five-level CHB inverter H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 8 Bipolar Modulation Bipolar PWM: v AB from -V d to +V d or from +V d to -V d H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 9 Bipolar Modulation (FFT) H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 10 Unipolar Modulation (1) Two modulation waves v m and v m - One carrier wave v cr Unipolar PWM: v AB from 0 to +V d or from 0 to -V d H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 11 One modulating wave: v m Two carrier waves: v cr and v cr - Unipolar Modulation (2) H-Bridge Inverter

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 12 Five-Level CHB Inverter Converters in cascade, but no switching devices in series. Complementary Switch pairs: S 11 and S 41 ; S 31 and S 21 ; S 12 and S 42 ; S 32 and S 22 ; CHB Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 13 Output Voltage and Switching Status (five-level) Waveform of v AN is composed of five voltage levels: 2E, E, 0, -E, and -2E CHB Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 14 Seven- and Nine-Level Inverters (Per phase diagram) CHB Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 15 Unequal dc Bus Voltages CHB Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 16 Unequal dc Bus Voltages (Two-cell seven-level topology) CHB Inverter Topologies

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 17 Carrier Based PWM – Phase Shifted # of voltage levels: m = 7 # of carriers: m c = m - 1 = 6 Phase shift: 360° / m c = 60° Carriers for H1 bridge: v cr1 and v cr1- Carriers for H2 bridge: v cr2 and v cr2- Carriers for H3 bridge: v cr3 and v cr3- m = 7 Phase Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 18 Inverter Waveforms (7-level, phase shifted) Switching occurs at different times f sw(device) = 60 m f = 600Hz Inverter phase voltage levels: 7 Low EMI Line-to-line voltage levels: 13 Close to a sinusoid Low THD Phase Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 19 FFT (7-level, phase shifted) Lowest harmonics: around 2m f Lowest harmonics: around 6m f Containing triplen harmonics No triplen harmonics Equivalent f sw(inverter) = 60(6m f ) = 3600Hz Phase Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 20 Harmonic Content (7-level, phase shifted) Phase Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 21 Carrier Based PWM – Level Shifted # of voltage levels: m = 5 # of carriers: m c = m - 1 = 4 IPD provides the best harmonic profile. IPD APOD POD Level Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 22 # of voltage levels: m = 7 # of carriers: m c = m - 1 = 6 f sw(device) : - not equal to f cr, and - not the same for all switches. Device conduction angle: - not equal. Necessary to swap switching pattern. Gating Arrangement (7-level) Level Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 23 Inverter Output Voltages (seven-level) m = 7 v AB close to a sinusoid Low THD, low EMI f sw(inv) = f c = 3600Hz Switching occurs at different times f sw(device) = f cr /m c = 600Hz (avg) Level Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 24 Prototype at Ryerson (Seven-level CHB Inverter) Level Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 25 Measured Waveforms (IPD, 7-level) Inverter phase voltage v AZ Line-to-line voltage v AB Level Shifted PWM

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 26 PWM at Low m a - Phase shifted PWM: THD = 96.7% - Level shifted PWM: THD = 48.8% At m a = 0.2: PWM Scheme Comparison

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 27 Total Harmonic Distortion (THD) PWM Scheme Comparison

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 28 Summary PWM Scheme Comparison

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006 EE8407 Topic 6 29