Singlephase halfbridge inverter ECE 442 Power Electronics 1

Single-phase half-bridge inverter ECE 442 Power Electronics 1

Operational Details 3 -wire DC source • • Consists of 2 choppers, 3 -wire DC source Transistors switched on and off alternately Need to isolate the gate signal for Q 1 (upper device) Each provides opposite polarity of Vs/2 across the load ECE 442 Power Electronics 2

Q 1 on, Q 2 off, vo = Vs/2 Peak Reverse Voltage of Q 2 = Vs ECE 442 Power Electronics 3

Q 1 off, Q 2 on, vo = -Vs/2 ECE 442 Power Electronics 4

Waveforms with resistive load ECE 442 Power Electronics 5

Look at the output voltage rms value of the output voltage, Vo ECE 442 Power Electronics 6

Fourier Series of the instantaneous output voltage ECE 442 Power Electronics 7

rms value of the fundamental component ECE 442 Power Electronics 8

When the load is highly inductive ECE 442 Power Electronics 9

Turn off Q 1 at t = To/2 Current falls to 0 via D 2, L, Vs/2 lower + Vs/2 - ECE 442 Power Electronics 10

Turn off Q 2 at t = To Current falls to 0 via D 1, L, Vs/2 upper + Vs/2 - ECE 442 Power Electronics 11

Load Current for a highly inductive load Transistors are only switched on for a quarter-cycle, or 90 ECE 442 Power Electronics 12

Fourier Series of the output current for an RL load ECE 442 Power Electronics 13

Fundamental Output Power In most cases, the useful power ECE 442 Power Electronics 14

DC Supply Current • If the inverter is lossless, average power absorbed by the load equals the average power supplied by the dc source. • For an inductive load, the current is approximately sinusoidal and the fundamental component of the output voltage supplies the power to the load. Also, the dc supply voltage remains essentially at Vs. ECE 442 Power Electronics 15

DC Supply Current (continued) ECE 442 Power Electronics 16

Performance Parameters • Harmonic factor of the nth harmonic (HFn) for n>1 Von = rms value of the nth harmonic component V 01 = rms value of the fundamental component ECE 442 Power Electronics 17

Performance Parameters (continued) • Total Harmonic Distortion (THD) • Measures the “closeness” in shape between a waveform and its fundamental component ECE 442 Power Electronics 18

Performance Parameters (continued) • Distortion Factor (DF) • Indicates the amount of HD that remains in a particular waveform after the harmonics have been subjected to second-order attenuation. for n>1 ECE 442 Power Electronics 19

Performance Parameters (continued) • Lowest order harmonic (LOH) • The harmonic component whose frequency is closest to the fundamental, and its amplitude is greater than or equal to 3% of the amplitude of the fundamental component. ECE 442 Power Electronics 20

Single-phase full-bridge inverter ECE 442 Power Electronics 21

Operational Details • • Consists of 4 choppers and a 3 -wire DC source Q 1 -Q 2 and Q 3 -Q 4 switched on and off alternately Need to isolate the gate signal for Q 1 and Q 3 (upper) Each pair provide opposite polarity of Vsacross the load ECE 442 Power Electronics 22

Q 1 -Q 2 on, Q 3 -Q 4 off, vo = Vs + Vs - ECE 442 Power Electronics 23

Q 3 -Q 4 on, Q 1 -Q 2 off, vo = -Vs - Vs + ECE 442 Power Electronics 24

When the load is highly inductive Turn Q 1 -Q 2 off – Q 3 -Q 4 off ECE 442 Power Electronics 25

Turn Q 3 -Q 4 off – Q 1 -Q 2 off ECE 442 Power Electronics 26

Load current for a highly inductive load ECE 442 Power Electronics 27

Example 6. 3 – Multi. Sim 7 ECE 442 Power Electronics 28

Example 6. 3 using the scope ECE 442 Power Electronics 29

Fourier Analysis of load current ECE 442 Power Electronics 30