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
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