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what effect freewheeling diod
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Why freewheeling diode is used?
1. Consider a simple half wave rectifier circuit consisting of an ac source a diode and a series R-L load.2. now during the positve half cycle of the source current, the diode conducts but it stops conducting when the negative half cycle starts.3. For an R-L load load current lags the source voltage and tries to flow in the previous direction even when the source voltage has reversed.4. This action due to the inductance, builds a high voltage across the diode which may exceed its forward breakdown limit and permanently damage it.5. Thus freewheeling diodes are used to short the load during negative half cycles and hence prevent the voltage breakdown of the semiconductor switches used in the control circuit.
What is motoring mode of DC motor?
Read this Part I:DC Motor principles pg 1 Part I: Principles of DC Drive Control Learning Objectives: * to learn the basic characteristics of DC motors and their control parameters * to understand the various operating modes DCmotors and their representation: The basic principle of a DCmotor is the production of a torque as a result of the flux interaction between a "field" produced on the STATOR (either produced by a permanent magnet, or a field winding) and the current circulating in the "armature" windings on the ROTOR. In order to produce a torque of constant sign, the armature winding loops are connected to a set of "brushes" which commutate the current appropriately in each loop according to their geometric position. The commutator is a MECHANICAL RECTIFIER. Note that reversal of either the field current or the armature current results in a torque in the opposite direction. However, reversal of both fields does not change the torque direction, hence it can be used as a "universal motor" with DC or AC feed if both windings are in series. Basic Equations of a DC Machine: Steady state conditions (assume all time varying quantities have a constant average value) ( ) ( ) ( ) ( ) ( ) P T developed power T K I I A B T electrical torque V R I E R I K I armature voltage E K I Counter emf or Back EMF V R I fieldwinding d e e t f a load a a a a a v f v f f f f w w w w = = = + + = + = + = = (The back emf assumes that the magnetizing characteristic, E(If) is linear) Speed control: we can extract: v f a a a K I V - R I w = and one can control the speed with 1) Va "Voltage Control" 2) If "Field Control" 3) Ia (with If fixed) "Demand Torque" In practice, for speeds less than the base speed (rated), the armature current and field currents aremaintained at fixed values (hence constant torque operation), and the armature voltage controls the speed. For speeds higher than the base speed, the armature voltage is maintained at rated value, and the field current is varied to control the speed (note the hyperbolic characteristic). However, N +V (free wheeling diode) Armature Current (Rf, Lf) (La, Ra) Eo Rfc Field Control Resistor Fig 1: DC Motor Part I:DC Motor principles pg 2 this way the power developed Pd is maintained constant. This mode is referred to as "field weakening" operation. Case of Series Motor (or Universal Motor) In this case the field winding is series with the armature winding, hence If and Ia are equal. This leads to: v a a a f a K I V - (R + R )I w = One can either control the armature voltage (Voltage Control), or the armature current (Current Control) which is a measure of the torque control. Td , Pd Torque Power constant torque constant power speed Ia If Fig 2: Control Modes Torque Power constant torque constant power speed Td Ia Fig 3: DC Series Motor Control Part I:DC Motor principles pg 3 OperatingModes of DCMotors: Motoring: The back emf E < Va both Ia and If are positive. The motor develops a torque to meet the load torque. Dynamic Breaking: The voltage source is removed, and the armature is shorted. The kinetic energy stored in the rotor of the motor is dissipated in the armature resistance since the machine now works as a generator. Note here that theoretically, since the armature voltage is proportional to the speed, the motor would never stop... but in fact because there is also friction and viscous friction (windage), the motor will stop as soon as the speed is at a certain low value. Regenerative Breaking: The back emf E > Va , the machine acts as a generator, and the armature current flows towards the source, hence energy stored in the machine rotor is fed back to the source. Note however that this will cause the machine to slow down usually until E=Va and then revert to mode 1. Plugging: Plugging iswhen the field current is reversed, hence the back emf changes sign, and the equation of the machine becomes: a a a V = -E - R I hence a a a R I V E + = which means a very high torque generated in the opposite direction of rotation. Avery powerful breaking takes place. However it must be noted that the armature has to be opened as soon as the motor reaches zero speed, otherwise it will start rotating in the opposite direction. N +Va Rfc (La, Ra) E Ia (Rf, Lf) +Vf If Fig 4: Motoring Forward Tem w rated torque V1 V2 V3 V2 Tload FIG 5 torque speed V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 6: Dynamic Breaking + Ia R V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 7: Regenerative Breaking + Ia Part I:DC Motor principles pg 4 Two Transistor control of regenerative operation When the main switch opens, the armature current I(a1) has to be dissipated through the freewheeling diode. Then if one closes switch T1, the machine behaves as a generator with the energy stored in its inertia. Therefore the armature current I(a2)will start flowing and follws I(1). After a certain time one opens the switch T1, and the current I(a2) has to be redirected via diode D2 back to the source with I(2). This is because of the inductance of the machine acts as an emf restoring the flux stored in the magnetic field. Then one closes T1 again and so on. The chopping rate of switch T1 can be set in order to control the average current (Ia2), usually 1.5 times rated value. This is possible only if the speed is fast enough to provide terminal voltage. When the emf E reaches E=Ra.I(rated), the switch T1 remains closed for maximum breaking possible with the given emf. Four Quadrant Operation: Figure 8 summarizes the modes of operation in a four quadrant representation. Torque Speed Forward MOTORING Forward BREAKING Reverse BREAKING Reverse MOTORING Fig 8: 4 quadrant operation V2 N +Va (La, Ra) E Fig 7: Regenerative Control + T1 i2 i1 ia1 ia2 average Ia
What is diod?
what is diod
What does diod iyts welsh but in English?
'Diod' means 'drink'; iyts (?)
What is the market cap for Diodes Incorporated DIOD?
As of July 2014, the market cap for Diodes Incorporated (DIOD) is $1,293,903,427.60.
When did Farrah Diod die?
Farrah Diod died on January 15, 2012, in Paris, le-de-France, France.
What year diod heydrich get married?
1946
What is theory of zenor diode?
theory of zonar diod
What is a freewheeling engine?
In a freewheeling engine, the piston tops and the valve bottoms do not share the same mechanical space, even if the timing belt or chain breaks.
What is the definition of freewheeling?
Freewheeling refers to a person riding a bicycle without peddling such as down a hill. The word has been popularized to include personality traits indicating that a person is carefree.
Operation of half wave rectifier with freewheeling diode?
efreqw
What is the symbol for Diodes Incorporated in NASDAQ?
The symbol for Diodes Incorporated in NASDAQ is: DIOD.
Does the 2002 dodge stratus have a interference or non-interference freewheeling engine?
Non-Interference
What has the author Maria Sara Rodriquez written?
Maria Sara Rodriquez has written: 'Freewheeling 1'
