Introduction to Electric Energy Systems Fall 2014 Mark Patterson TTh 4:30-5:45, KL-351G

Today’s Quote: Never go to sleep angry. “Fix your thoughts on what is true and honorable and right. Think about things that are pure and lovely and admirable. Think about things that are excellent and worthy of praise.” Philippians 4:8

3 Converters Electronic power converter is the term that is used to refer to a power electronic circuit that converts voltage and current from one form to another.  Rectifier converting an ac voltage to a dc voltage  Inverter converting a dc voltage to an ac voltage  Chopper or a switch-mode power supply that converts a dc voltage to another dc voltage  Cycloconverter and cycloinverter converting an ac voltage to another ac voltage.

4 Rectifiers Rectifiers may be classified as uncontrolled and controlled rectifiers. Controlled rectifiers can be further divided into semi-controlled and fully- controlled rectifiers. Uncontrolled rectifier circuits are built with diodes, and fully-controlled rectifier circuits are built with SCRs. Both diodes and SCRs are used in semi-controlled rectifier circuits.  Single-phase semi-controlled bridge rectifier  Single-phase fully-controlled bridge rectifier  Three-phase three-pulse, star-connected rectifier  Double three-phase, three-pulse star-connected rectifiers with inter-phase transformer (IPT)  Three-phase semi-controlled bridge rectifier  Three-phase fully-controlled bridge rectifier  Double three-phase fully-controlled bridge rectifiers with IPT.

5 AC to DC Conversion: Half-Wave Rectifier

6 Full Wave Rectifier

7 Figure 12.20, Three-Phase Diode Bridge Rectifier Waveforms and Conduction Times of Three-Phase Bridge Rectifier

Power electronics basics Rectifiers RectifierFilter tt t v v v

9 Controlled Rectifier Circuit Half-Wave Controlled Rectifier Waveforms Figure 12.25, 12.26

10 Figure 12.2 AC-DC Converter Circuit and Waveform

11 Figure 12.17, Rectifier Connected to an Inductive Load Operation of a Freewheeling Diode

AC-DC Power Supplies -Circuit Selection and Design Using Linear Regulators Using LDO Regulator Step-down Xfmer Regulator 120 V AC For low power (several watts or below) applications. Low efficiency, large size and weight (bulky step-down line transformer) Low cost

AC-DC Power Supplies -Circuit Selection and Design Using Switching-Mode High efficiency Small size and light weight For high power (density) applications

Specs, Performance and Protection Voltage ripple (+-50 mV, or 5%) Isolation (e.g., 1,500 V ac for 1 min.) Load regulation (e.g., 3%) Dynamic response (transients, wake-up time, etc.) Short circuit protection OC protection OV protection OT protection

Power Losses and Thermal Design For example, a 7815 linear regulator with input voltage of 20 V and output current of 1 A. The power loss is (20-15)Vx(1 A)=5 W. From the chip to the ambient,  T i can be calculated according to the thermal circuit using Ohm’s law (R=V/I), where R is the thermal resistance, V is the temperature and I is the power dissipation. Where: T case is case Temp. T ambient is ambient Temp. P dissipation is power loss P in is input power P out is output power  op is efficiency under given operating conditions

Power Losses and Thermal Design --A more detailed thermal circuit W : Device power loss Tj : Junction temperature of device Tc : Device case temperature Tf : Temperature of heatsink Ta : Ambient temperature Rth(j-c) : Thermal resistance between junction and case, specified in datasheet Rth(c-f) : Contact thermal resistance between case and heatsink, specified in datasheet Rth(f-a) : Thermal resistance between heatsink and ambient air, specified by the heatsink manufacturer

Power Losses and Thermal Design Tc=W×{Rth(c-f) + Rth(f-a)}+Ta Tj=W×Rth(j-c)+Tc

Example Tc=5×( )+25=127.5 °C Tj=5× =132.5 °C  Tj= =107.5°C Device : 7815 (Linear regulator) Vin=20V, Vo=15V, Io=1A W : (20-15)×1=5 watts Rth(j-c) : 5 °C/W Rth(c-f) : 0.5 °C/W, Greased surface Rth(f-a) :20 °C/W Ta=25 °C An assortment of 78XX series An assortment of heatsinks

Boost converter model and design (a) Continuous conduction mode (CCM) of boost converter. (b) Relevant waveforms thru’ resistor thru’ capacitor; ripple can be minimized thru’ proper choice of capacitor

Rectification, PFC and boost A bridge rectifier circuit. Current through load is in phase with voltage. However, for arbitrary loads this is not the case. Also, peak value of rectified voltage is capped at peak value of input voltage. By PWMing IGBT, current i L thru L d can be shaped to be similar to  v s , thus implementing power factor correction (PFC). Input current i s then is in phase w/v s. By using boost, rectified voltage V d can be made larger than v smax.

Control of PFCs Inner current loop for shape Outer voltage loop for ampl.