Introduction to Power Electronics Lecture Notes PDF

Alexandria University Lecture 1: Introduction to Power Electronics Dr. Abdelrahman Farghly Department of Electrical Engineering Faculty of Engineering Introduction to Power Electronics ...

Alexandria University Lecture 1: Introduction to Power Electronics Dr. Abdelrahman Farghly Department of Electrical Engineering Faculty of Engineering Introduction to Power Electronics Alexandria University Alexandria University Mark Analysis Course Work 10 Marks Midterm 30 Marks Final 60 Marks References Power Electronics: Devices, Drivers, Applications, and Passive Components" by Barry W. Williams Power Electronics: Circuits, Devices & Applications. Power Electronics: Converters, Applications, and Design" by Ned Mohan, Tore M. Undeland, and William P. Robbins pdf Fundamentals of Power Electronics" by Robert W. Erickson and Dragan Maksimovic Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Simulation Program Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Outlines Introduction to Power Electronics Classification of Power converters Classification of Power Electronics Devices Uncontrolled device — Power Diode Uncontrolled rectifiers: half wave and full wave Controlled device — Power Thyristors Controlled rectifiers: half wave and full wave Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University What is Power Electronics? Definition is the electronics applied to conversion and control of electric power. A more exact explanation The primary task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads. Range of power scale: ❖ Watts(W) ❖ Kilowatts(kW) ❖ Megawatts(MW ❖ Gigawatts(GW) Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Conversion of electric power Changeable properties in Types of Electric Power conversion DC (Direct Current) Magnitude Frequency, Magnitude, AC (Alternating Current) Number of phases Other names for electric power converter: -Converter -Power converter -Power electronic circuit -Power electronic converter Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Classification of Power Converters DC AC AC to AC converter (Fixed frequency : AC controller AC AC to DC converter Variable frequency: Cycloconverter (Rectifier) or frequency converter) DC to DC converter DC (Chopper) DC to AC converter (Inverter) Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Applications of Power Electronics Industrial: Motor drives, Welding, Arc…etc. Transportation: Trains Subways, Electric vehicles. Utility systems: High-voltage dc transmission(HVDC), wind, photovoltaic, fuel cells…etc. Residential and home appliances: Lighting, Heating, Air conditioning…etc. Other Applications. Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Classification of P.E. devices Uncontrolled device: Diode has only two terminals and can not be controlled by control signal. The on and off states of the device are determined by the power circuit. Half-controlled device: Thyristor is turned-on by a control signal and turned-off by the power circuit Fully-controlled device: Power MOSFET, IGBT. The on and off states of the device are controlled by control signals. Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University P.E. Devices: The Diode The pn junction is basically a Diode, which is a device that allows current in only one direction. Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Forward Bias and Reverse Bias Forward Bias : Connect positive of the Diode to positive of supply…negative of Diode to negative of supply Reverse Bias: Connect positive of the Diode to negative of supply…negative of diode to positive of supply. Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University P.E. Devices: The Diode Basic Structure Symbol Diode packages Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University V/I CHARACTERISTICS Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Diode Approximation: Ideal model Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University Power Diodes 1- General purpose Rating up to 6000V, 4500A Rectifying diodes used for power frequency 2- High speed (or fast recovery) Rating up to 6000V, 1100A Reverse recovery time 0.1 to 5μs Essential for high-frequency switching 3- Schottky Low on-state voltage 0.3V Very small recovery time (typically nanoseconds). Leakage current increases with voltage rating Rating limited to 100V, 300A Introduction Introduction to Power to Power Electronics Electronics Alexandria University Alexandria University RECTIFIERS AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Introduction Rectification is a process that converts AC into DC. This is usually required to drive dc loads from an ac supply. AC-DC converters come in various configurations depending on the requirements of the application. Basically, they can be classified according to the following criteria: 1. Single-phase or Three-phase depending on the ac source characteristics. 2. Half-wave or Full-wave depending on whether rectification is applied only in one half cycle of the ac source or in both cycles. 3. Controlled or Uncontrolled depending on the type of switches used (diodes → uncontrolled, thyristors → controlled). AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University UNCONTROLLED RECTIFIERS AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Half Wave Uncontrolled Rectifier: R Load Positive half cycle Negative half cycle The output wave voltage Diode conduction angle = 180 AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R Load (Cont.) The diode rectifies the ac source and creates an output voltage that has a DC component. The average (DC) value of the output voltage is as follow: AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R Load (Cont.) Peak Reverse Voltage (PRV) =-Vm The RMS value of the output voltage is: The Average output dc power is 2 𝑉𝑑𝑐2 𝑉𝑚 2 𝑝𝑑𝑐 = 𝑉𝑑𝑐𝐼𝑑𝑐 = 𝐼𝑑𝑐 𝑅 = = 2 𝑅 𝜋 𝑅 The RMS output dc power is 2 𝑉 2 𝑉𝑟𝑚𝑠 𝑚 𝑝𝑎𝑐 = 𝑉𝑟𝑚𝑠 𝐼𝑟𝑚𝑠 = 𝐼𝑟𝑚𝑠 2𝑅 = = 𝑅 4𝑅 The power factor is 𝑝 𝑝𝑎𝑐 𝑝𝑓 = = 𝑆 𝑉𝑟𝑚𝑠 𝐼𝑟𝑚𝑠 AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Example (1) For the shown half-wave rectifier, the source is a sinusoid of 120 Vrms at a frequency of 50 Hz. The load resistor is 5 Ω. Determine (a) the average load current, (b) the dc and ac power absorbed by the load and (c) the power factor of the circuit. (a) AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Example (Solution) (b) 𝑉𝑚 2 169.72 𝑝𝑑𝑐 = 2 = 2 = 583.57 𝜋 𝑅 𝜋 ×5 𝑉𝑟𝑚𝑠 2 84.92 𝑝𝑎𝑐 = = = 1441.6 𝑅 5 (c) The RMS current in the resistor is The power factor is 𝑝 𝑝𝑎𝑐 1441.6 𝑝𝑓 = = = = 0.707 𝑆 𝑉𝑟𝑚𝑠 𝐼𝑟𝑚𝑠 120 ∗ 17 AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load β Observations: 1.Load current is maintained beyond π. 2.Load voltage now has a negative portion. AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load (1) The DC component of the output voltage is 𝛽 𝑉𝑚 𝑉𝑚 𝑉𝑑𝑐 = ∫ 𝑠𝑖𝑛𝜔𝑡 𝑑𝜔𝑡 = (1 − 𝑐𝑜𝑠𝛽) 2𝜋 2𝜋 0 The DC component of the output current is 𝑉𝑚 𝐼𝑑𝑐 = (1 − 𝑐𝑜𝑠𝛽) 2𝜋𝑅 The solution of equation (1) can be obtained by expressing the current as the sum of the forced response and the natural response: AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load For this first-order circuit, the natural response has the form Where 𝐿 𝜏= A = constant 𝑅 Adding the forced and natural responses gets the complete solution. (2) The constant A is evaluated by using the initial condition for current: t=0, i(𝜔t)=0. Using the initial condition and equation (2) to evaluate A yields AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load Substituting for A in equation (2) gives The final current equation can be written as (3) The point when the current reaches zero in Eq. (3-12) occurs when the diode turns off. The first positive value of 𝜔t in equation (3) that results in zero current is called the extinction angle 𝛽. To find 𝛽, substitute 𝜔t= 𝛽 in equation (3) Which reduces to There is no closed-form solution for 𝛽, and some numerical method is required. AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load To summarize, the current in the half-wave rectifier circuit with RL load is expressed as The dc component of the output current is Or it can be found as 𝛽 𝑉𝑚 𝑉𝑚 𝑉𝑚 𝑉𝑑𝑐 = ∫ 𝑠𝑖𝑛𝜔𝑡 𝑑𝜔𝑡 = (1 − 𝑐𝑜𝑠𝛽) 𝐼𝑑𝑐 = 𝐼𝑜 = (1 − 𝑐𝑜𝑠𝛽) 2𝜋 2𝜋 2𝜋𝑅 0 AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-L Load The RMS value of Io can be written as Or it can be written as 𝛽 1 𝑉𝑚 2 1 𝑉𝑟𝑚𝑠 = ∫(𝑉𝑚 𝑠𝑖𝑛𝜔𝑡)2 𝑑𝜔𝑡 = (𝛽 − 𝑠𝑖𝑛2𝛽) 2𝜋 4𝜋 2 0 𝑉𝑟𝑚𝑠 𝑉𝑟𝑚𝑠 1 𝑉𝑚 2 1 𝐼𝑟𝑚𝑠 = = = (𝛽 − 𝑠𝑖𝑛2𝛽) 𝑍 𝑅2 + (𝜔𝐿)2 𝑅2 + (𝜔𝐿)2 4𝜋 2 AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Example (2) For the RL half-wave rectifier, R=100Ω, L=0.1 H, 𝜔=377 rad/s, and Vm=100 V. Determine (a) an expression for the current in this circuit, (b) the average current, (c) the rms current, (d) the power absorbed by the RL load, and (e) the power factor. (a) Using a numerical root-finding program, 𝛽 is found to be 3.50 rad, or 201o. AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Example (Solution) (b) Io can be also found from 𝑉𝑚 100 𝐼𝑑𝑐 = 𝐼𝑜 = 1 − 𝑐𝑜𝑠𝛽 = 1 − 𝑐𝑜𝑠201 = 0.308 𝐴 2𝜋𝑅 2𝜋100 (c) 1 𝑉𝑚 2 1 1 1002 1 𝐼𝑟𝑚𝑠 = (𝛽 − 𝑠𝑖𝑛2𝛽) = (3.5 − 𝑠𝑖𝑛7) = 0.489 A 𝑅2 + (𝜔𝐿)2 4𝜋 2 106.9 4𝜋 2 (d) (e) Note that the power factor is not cosθ. AC totoDC Introduction Converters Power Electronics Alexandria University Alexandria University Example(2) For a 120 V, 60 Hz source driving a 20 Ω resistor and 0.05H inductance, calculate: – Zero-crossing angle – RMS load voltage and current – Average power given to the load – Input power factor Full Wave Uncontrolled Rectifier AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University Example (Solution) AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University HW Uncontrolled Rectifier: R-C Load AC toAC totoDC Introduction Converters DC Converters Power Electronics Alexandria University Alexandria University FW Uncontrolled Bridge Rectifier: R-Load Observations: 1. D1 and D2 conduct in the positive half-cycle and D3 and D4 conduct in the negative one. 2. The average (dc) value of the output voltage is as follow: 1  2Vm  0 m Vdc = V sin t d (t ) =  AC AC to DCto IntroductionDC Converters Converters to Power Electronics Alexandria University Alexandria University FW Uncontrolled Bridge Rectifier: R-L Load Observations: 1. D1 and D2 conduct in the positive half-cycle and D3 and D4 conduct in the negative one. 2. The average (dc) value of the output voltage is as follow: 1  2V Vdc =  Vm sin t d (t ) = m  0  3. The average (dc) value of the output current is as follow: I dc = Vdc = m If ωL>>R (load inductive impedance is much larger than 2V R  R its resistive part), then the ripples are extremely small. AC AC to DCto IntroductionDC Converters Converters to Power Electronics Alexandria University Alexandria University Exercice For a 1-φ, full-wave bridge converter with an RMS voltage of 120 V, and R = 20 Ω, determine the average voltage and current and the average power supplied to the load. Ans: [108V, 5.4A, 583.61 W] AC AC to DCto IntroductionDC Converters Converters to Power Electronics Alexandria University Alexandria University THREE-PHASE RECTIFIERS AC AC to DCto DC Converters Converters Alexandria University Alexandria University Advantages of Three-Phase Rectifiers Higher output voltage for given input voltage. Lower amplitude ripples. i.e., output voltage is smoother Higher frequency ripples, simplifying filtering. (lower size of filter circuit parameters because of higher ripple frequency) Higher overall efficiency. AC AC to DCto DC Converters Converters Alexandria University Alexandria University Three-Phase HW Uncontrolled Rectifier We assume the load current to be essentially dc (i.e., the inductance of the load is high). The output voltage at any instant of time is given by: vo(t)=max(van(t),vbn(t),vcn(t)) Each diode conducts only for 1/3 of the period (120°). AC AC to DCto DC Converters Converters Alexandria University Alexandria University Three-Phase HW Uncontrolled Diode D1 conducts for only 1/3 of the whole period, between [ϖ/6,5ϖ/6]. The average (DC) value of the output voltage is as follow: 1 56 3 3 3 2 2  m Vdc = V sin t d (t ) Vm = VLL 2 2 = 3 6 - Where VLL is the rms of the line to line voltage One of the drawbacks of this topology, it shows a dc component in the ac line current. AC AC to DCto DC Converters Converters Alexandria University Alexandria University Three-Phase FW Uncontrolled Rectifier Current flows through one diode from the top group and one from the bottom; The output voltage at any instant of time is given by: AC AC to DCto DC Converters Converters Alexandria University Alexandria University Three-Phase FW Uncontrolled The ripple component on the output voltage, which is much smoother than that of a single-phase converter, has six times the frequency of the line voltage; that's why the converter is also referred to as a six-pulse converter. There is no DC component in the ac line current The average (dc) value of the output voltage is as follow: Vdc = Vo = V pn − Vnn = 3 2 VLL − (− 3 2 VLL ) = 3 2 V = 1.35VLL 2 2  - Where VLL is the rms of the line to line voltage AC AC to DCto DC Converters Converters Alexandria University Alexandria University CONTROLLED RECTIFIERS AC AC to DCto DC Converters Converters Alexandria University Alexandria University P.E. Devices: The Thyristor The thyristor also know as silicon-controlled rectifier (SCR) is a 4-layer pnpn device similar to the 4-layer diode except with three terminals: anode (A), cathode (K), and gate (G). Cathode Gate Anode Basic Structure Thyristor packages Symbol AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Thyristor: Equivalent circuit The SCR operation can best be understood by considering its internal pnpn structure as a two-transistor arrangement. The upper pnp layers act as a transistor, Q1, and the lower (npn) layers act as a transistor, Q2. Notice that the two middle layers are “shared”. AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Thyristor: Turn-ON When IG=0, as shown in Figure (a), the device acts as a 4-layer diode in the off state. In this state, the very high resistance between the anode and cathode can be approximated by an open switch. AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Thyristor: Turn-ON (Cont.) When a positive pulse of current (trigger) is applied to the gate, both transistors turn on. This action is shown in Figure (b), IB2 turns on Q2, providing a path for IB1 out of the Q2 collector, thus turning on Q1. The collector current of Q1 provides additional base current for Q2 so that Q2 stays in conduction after the trigger pulse is removed from the gate. By this regenerative action, Q2 sustains the saturated conduction of by providing a path for IB1; in turn, Q1 sustains the saturated conduction of Q2 by providing IB2. Thus, the device stays on (latches) once it is triggered on, as shown in Figure (c). AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Thyristor: I-V Characteristics Once triggered on, the thyristor will be latched on conducting even when the gate current is no longer applied. Turning off: decreasing current to be near zero (below holding current IH) with the effect of external power circuit. The process of turning off is also referred to as the commutation process. Thyristors provide controlled Turn ON but their Turn OFF cannot be controlled directly. AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Thyristor: I-V Ideal Characteristics AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Methods of Turning ON the thyristor Gate Current: positive pulse with sufficient amplitude and duration to the gate; High voltage across anode and cathode (above the forward break over voltage VFBO). AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University Methods of Turning OFF the thyristor Diverting the anode current to an alternate path. Shorting the SCR from anode to cathode. Applying a reverse voltage (by making the cathode positive with respect to the anode) across the thyristor. Forcing the anode current to zero for a brief period. Momentarily reducing supply voltage to zero. AC to DC Introduction Converters to Power Electronics Alexandria University Alexandria University HW Controlled Rectifier: R Load The thyristor (SCR) has to be forward biased, before it can be turned on. A gate pulse of appropriate amplitude (and duration) has to be applied. The firing angle (α) is measured from the zero-crossing of the source voltage and can take any value between 0 and 180 degrees. AC AC to DCto DC Converters Converters Alexandria University Alexandria University HW Controlled Rectifier: R Load (Cont.) The average (DC) value of the output voltage is as follow: = Vm - At α=0°(diode operation) → dc V  - At α=180 → dc ° V = 0V AC AC to DCto DC Converters Converters Alexandria University Alexandria University HW Controlled Rectifier: R-L Load Observation: As long as the forward Ldi/dt voltage is greater in magnitude than the negative ac voltage, the thyristor will continue to be forward biased and the current flow continues. AC AC to DCto DC Converters Converters Alexandria University Alexandria University FW Controlled Bridge Rectifier: R-Load Observations: [0,π] → T1 and T2 are forward biased, [α,π] → conduction. [π,2π] → T3 and T4 are forward biased, [α+π,2π] → conduction. The average (dc) value of the output voltage is as follow: 1  Vm Vdc =   Vm sin t d (t ) =  (1+ cos  ) AC AC to DCto DC Converters Converters Alexandria University Alexandria University FW Controlled Bridge Rectifier: R-L Load Observation The average (DC) value of the output voltage is as follow: 1  + 2Vm   Vdc = Vm sin t d (t ) = cos   AC AC to DCto DC Converters Converters Alexandria University Alexandria University FW Controlled Bridge Rectifier: R-L The average (dc) value of the output voltage is as follow: Vdc = 2Vm cos   0