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Unformatted text preview: ELEC387 — Power electronics Jonathan Goldwasser 1 Power electronics systems pp. 3–15 Main task: process and control flow of electric energy by supplying voltage and current in a form that is optimally suited for user loads. In the year 2000: 50% of the electrical load supplied through power electronics. Linear electronics: low efficiency because transistor are used as resistors. Switch mode: efficient because fully off or fully on. @ high frequency: transformers and filters are small. Selection of f s : compromise between switching power dissipation (increases with f s ) and cost of transformer (decreases with f s ). Outputs (2): dc (regulated or adjustable) and ac (constant frequency, adjustable magnitude or adjustable frequency and magnitude). Categories (4): ac to dc, dc to ac, dc to dc, ac to ac. Converter: generic term. Rectifier: Power from ac to dc. Inverter: Power from dc to ac. Line frequency converter: naturally commutated (50 or 60Hz). Switching converter: f s >> . Resonant and quasi-resonant converter: switching @ v = 0 and/or i = 0 . 2 Overview of power semiconductor switches pp. 16–32 Diodes: on and off states controlled by the power circuit. Reverse-recovery time t rr required to block negative polarity voltage. Schottky , fast-recovery, line- frequency. Thyristors: on state controlled by gate pulse, off state controlled by the power circuit. Turn-off time interval t q during which a reverse voltage must be applied. Phase-control thyristors, inverter-grade thyristors, light-activated thyristors. Ideal switches: block arbitrarily large forward and reverse voltages with zero current flow when off, conduct arbitrarily large currents with zero voltage drop when on, switch from on to off and vice versa instantaneously, vanishingly small power required to trigger the switch. P T = 1 2 V d I o f s ( t c (on) + t c (off) ) bracehtipupleft bracehtipdownrightbracehtipdownleft bracehtipupright P s + V on I o t on T s bracehtipupleft bracehtipdownrightbracehtipdownleft bracehtipupright P on 1 Figure 1: Overview of devices capabilities 3 Review of basic electrical and magnetic circuit concepts pp. 33–60 Steady-state: reached when the circuit waveforms repeat with a time period T . % THD i = 100 I dis I s 1 = 100 radicalbig I 2 s − I 2 s 1 I s 1 = 100 radicaltp radicalvertex radicalvertex radicalbt summationdisplay h negationslash =1 parenleftbigg I sh I s 1 parenrightbigg 2 Crest factor = I s, peak I s PF = I s 1 I s cos φ 1 = I s 1 I s DPF = 1 radicalBig 1 + THD 2 i DPF Inductor: current cannot change instantaneously, net change of flux over T is zero, areas in volt-second must be equal. Capacitor: current cannot change instantaneously, net change of charge over T is zero, areas in ampere-second must be equal....
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This note was uploaded on 08/22/2011 for the course EEE 230 taught by Professor Subramanian during the Spring '07 term at Berkeley.
- Spring '07