Power Electronics I ENEE502 Lecture 1 PDF

Power Electronics I ENEE502 Lecture 1 Power Electronic Switches Course Instructor: Dr. Eng. Noha Shouman [email protected] 1 General rules Every week the instructor will assign problems In the tutorial, some of the assigned...

Power Electronics I ENEE502 Lecture 1 Power Electronic Switches Course Instructor: Dr. Eng. Noha Shouman [email protected] 1 General rules Every week the instructor will assign problems In the tutorial, some of the assigned problems will be worked out on the board Three quizzes will be conducted to evaluate your performance and the quiz mark will be based on the best 2 Three In-class assignments will be conducted to evaluate your performance and the assignment mark will be based on the best 2 It is necessary to go through the lab manual before attending each lab session as there will be pre-lab quiz each lab session You are kindly requested to print out the lab report before going to the lab session The lab instructor will evaluate your performance during the lab and a lab report has to be submitted to your lab instructor at the end of each session 2 Marking scheme and textbook Assignments 10% Quizzes 10% Lab 10% Project 5% Mid-term 25% Final 40% Total 100% Textbook: Stephen J. Chapman, Electric Machinery Fundamentals, McGraw Hill, ISBN 0--07- 246523--9, M.H.Rashid,PowerElectronicsHandbook Cyril W.Lander,PowerElectronics 3 Course objectives Describe the characteristics of different power electronic devices Recognize the basic operation, losses and efficiency of the power electronics converters. Develop power electronics’ models for controlling the speed of DC motors Analyze power electronics circuits 4 Course outlines Introduction to power electronics Characteristics of power electronic switches Switching power loss Single phase rectifier Three phase rectifier DC chopper DC electric drives 5 Lecture objectives Introduction to power electronics and electric drives Diodes Thyristors 6 Introduction Power electronics is a technology used to provide fast control on industrial applications aw well as electric power transmission Power electronics is the key feature in electric drive systems There are many applications for electric drive systems Cranes, robots, electric vehicles, hydraulic pumps, household appliances Electric drive systems involve controlling electric motors coupled to mechanical loads in different modes of operations Most modern electric drives use power electronic converters to control the operation of electric motors Electric machines Power electronics converters 7 Power Electronic Converters There are four main types of power electronic converters 1) Rectifiers are electrical devices that convert fixed AC voltage to DC voltage with variable magnitude AC DC 2) Inverters are electrical devices that convert fixed DC voltage to AC voltage with variable magnitude and frequency DC AC 8 Power Electronic Converters There are four main types of power electronic converters 3) DC choppers are electrical devices that convert fixed DC voltage to DC voltage with variable magnitude DC DC 4) AC choppers are electrical devices that convert fixed AC voltage to AC voltage with variable magnitude and frequency AC AC 9 Power Electronic Devices Power electronic devices operate as electronic switches, and they are classified into three main types 1) Uncontrolled electronic switches (diodes) The switches are turned on and off according to the conditions of the circuit. 2) Semi-controlled electronic switches (thyristors) The switches’ turn on is based on both the conditions of the circuit and the presence of an external signal (firing pulse). Regarding the switches’ turn off, it is based on the conditions of the circuit 3) Controlled electronic switches (IGBT, MOSFET,GTO) The switches’ turn on and off are based on the conditions of the circuit and in the presence of an external signal 10 Power Diodes A power diode or high-power diode is semiconductor device has two terminals and p-n junction It conducts if the voltage of the anode is higher than the cathode and is turned off when the current passing from the anode to the cathodes falls to zero and the voltage is reversed. Switching conditions: On state: 𝑽𝑨𝑲 > 𝟎 OFF state: 𝑽𝑨𝑲 < 𝟎, 𝒊𝑨𝑲 = 𝟎 11 Power Diodes I-V Characteristics of power diode Under steady state conditions, the diode has two main states: 1) Forward conducting state (𝑽𝑨𝑲 > 𝟎) The p-n junction is forward biased The diode is in the ON state The current increases exponentially as the voltage increases The forward voltage drop 𝑽𝑫𝒇 Forward voltage drop depends on the diode’s type ranging from (0.2V-1.5V) 12 Power Diodes I-V Characteristics of power diode Under steady state conditions, the diode has two main states: 2) Reverse blocking state (𝑽𝑨𝑲 < 𝟎, 𝒊𝑨𝑲 = 𝟎) The p-n junction is reversed biased. The diode is in the OFF state. A very small leakage current will Reverse leakage current flow. If the voltage is increased till it reaches 𝑽𝑹𝑩𝑫 , reverse breakdown Reverse breakdown (avalanche breakdown) will occur voltage and diode will be damaged 13 Thyristors Thyristor is a high speed switch consisting of alternating P-type and N-type semiconductors (P-N-P-N) and is also called silicon controlled rectifier (SCR) The thyristor has the highest power rating and the lowest frequency of operation among all power electronics devices It is a 4 layers, 3 junctions, 3 terminals, current controlled (𝑖𝐺 ), latching device Switching conditions: On state: 𝑽𝑨𝑲 > 𝟎, 𝒊𝑮 > 𝟎 OFF state: 𝑽𝑨𝑲 < 𝟎, 𝒊𝑨𝑲 = 𝟎 (𝒊𝑨𝑲 < 𝑰𝑯 ) 14 Thyristors I-V Characteristics of thyristor Under steady state conditions, the diode has three main states: 1) Reverse blocking state (𝑽𝑨𝑲 < 𝟎) 𝐽1 & 𝐽3 are reversed biased while 𝐽2 is forward biased The thyristor is in the OFF state A very small leakage current will flow If the voltage is increased till it reaches 𝑽𝑹𝑩𝑫 , reverse breakdown (avalanche breakdown) will occur and thyristor will be damaged 15 Thyristors I-V Characteristics of thyristor Under steady state conditions, the diode has three main states: 2) Forward blocking state (𝑽𝑨𝑲 > 𝟎), 𝒊𝑮 = 𝟎 𝐽1 & 𝐽3 are forward biased while 𝐽2 is reversed biased The thyristor is in the OFF state A very small leakage current will flow If the voltage is increased till it reaches 𝑽𝑭𝑩𝑶 , forward breakdown will occur and thyristor will start to conduct without a gate signal. This will cause the lifetime of the switch to decrease. 16 Thyristors I-V Characteristics of thyristor Under steady state conditions, the diode has three main states: 3) Forward conducting state (𝑽𝑨𝑲 > 𝟎), 𝒊𝑮 > 𝟎) The thyristor is in the ON state 𝐽1 , 𝐽2 & 𝐽3 are forward biased The current increases exponentially as the voltage increases There will be forward drop voltage 𝑽𝑻 ranging between (1.2V-2.2V) 17 Thyristors Latching current The minimum value of current passing through the thyristor to remain in the conduction mode after removing the pulse. (It switches from the forward blocking mode to the forward conducting mode) Holding current The minimum value of current passing through the thyristor to remain in the conduction mode after the switch has already turned on. (It is already in the conduction mode and needs to stay in the conduction mode) 18 Switches’ Model Linearized model The diode and thyristor can be represented by a battery and a resistance during the ON state and by an open circuit in the OFF state V ON state OFF state 19 Switches’ Model Ideal model The diode and thyristor can be represented by a battery and a resistance during the ON state and by an open circuit in the OFF state ON state OFF state 20 Learning outcomes Today’s lecture Power electronic switches I-V characteristic of the switching Latching current of thyristor Holding current of thyristor Next lecture Rectifier 21 Good Luck