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Inverters_102913

# 8 06 04 vpwm v 02 0 02 04 06 08 1 0 2 4 6 8 t

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Unformatted text preview: erter regulates an AC output voltage –  Converts DC power to AC power –  Particularly useful for motor drives Basic Inverter Make a Square Wave and Filter Basic Inverter Make a Square Wave and Filter But Filtering a 60Hz Square Wave is Hard Spectrum of a 60Hz Square Wave 1400 1200 1000 Mag 800 600 400 200 0 0 100 200 300 400 500 f (Hz) 600 700 800 900 1000 Make a PWM Sine Wave and Filter PWM Waveform 1 0.8 0.6 0.4 VPWM (V) 0.2 0 −0.2 −0.4 −0.6 −0.8 −1 0 2 4 6 8 t (ms) 10 12 14 16 PWM Synthesis V AC ,V Saw (V) 1.5 1 x = sine > saw y = -sine > saw 0.5 0 −0.5 −1 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 1 0 V PWM (V) 0.5 −0.5 −1 1.5 V Out (V) 1 0.5 0 −0.5 −1 −1.5 1 L I (A) 0.5 0 −0.5 −1 t (ms) Digitally generate sine with quarterwave table 100kHz PWM, 60Hz Sine (1667:1) VAC, VSaw (V) 1.5 1 0.5 0 2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 VPWM (V) 1 0.5 0 −0.5 −1 0.76 VOut (V) 0.74 0.72 0.7 0.68 0.9 IL (A) 0.8 0.7 0.6 0.5 t (ms) Spectrum of 100kHz PWM Signal 5 9 x 10 8 7 6 Mag 5 4 3 2 1 0 1 10 2 10 3 4 10 10 f (Hz) 5 10 6 10 Circuit Simulation SPICE Waveforms Close Up of 2 PWM Cycles Inverter Details •  Can operate independently or drive the grid. –  Grid connected inverters use the AC line as a “sine-wave” reference. •  This gives the proper phase •  It also compensates for distortion of the sine wave •  Current-mode control often used –  To give close to unity power factor into AC line –  This is the same as a PFC circuit but the current is flowing the other way Anti-Islanding •  Grid-connected inverters need to turn off when the grid goes down. •  Safety issue for firemen, linemen, etc… •  How do you detect when the grid goes down? Anti-Islanding •  Line monitoring –  Voltage limits, frequency limits. –  Rate of change of frequency –  Rapid phase shift •  Active detection –  Impedance measurement –  Forced phase shift/frequency shift Inverters Summary •  Convert a DC Voltage to an AC Voltage •  AC is just slowly changing DC •  Use a full-bridge to generate a PWM Sine Wave –  Pulse width proportional to sin(x) •  LC Filter to reject high frequencies Questions? In Upcoming Lectures •  Batteries •  Experimental Technique •  Guest Lectures from Tesla and Enphase...
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