Electric Motors ME350 Basic types >DC Motors:speed and rotational direction control via voltage 二 Easy to control torque via current low voltage 二 linear torque-speed relations 三 Quick response >AC Motors:smaller,reliable,and cheaper 二 speed fixed by AC frequency 二 low torque at low speed 二 difficult to start 6
6 ME 350 • Basic types ¾DC Motors: speed and rotational direction control via voltage = Easy to control torque via current = low voltage = linear torque-speed relations = Quick response ¾AC Motors: smaller, reliable, and cheaper = speed fixed by AC frequency = low torque at low speed = difficult to start Electric Motors
Objectives of this Lecture ME350 Describe the factors that must be specified to select a suitable motor Describe the principles of operation of DC motors. Describe the general form of a motor performance curve. Describe the advantages and disadvantages of DC motors compared with AC motors. Describe four basic designs of DC motors,and describe their performance curves. 7
7 ME 350 Objectives of this Lecture • Describe the factors that must be specified to select a suitable motor • Describe the principles of operation of DC motors. • Describe the general form of a motor performance curve. • Describe the advantages and disadvantages of DC motors compared with AC motors. • Describe four basic designs of DC motors, and describe their performance curves
DC Motors:Principles of Operation ME350 A wire carrying current experiences a force in a magnetic field. F-(lx B) Magnetic Flux Density(磁通量) Induced force (Tesla) Current Length of wire in the (amp) direction of i(m) IxB I×B=|IBsin B 8
8 ME 350 DC Motors: Principles of Operation • A wire carrying current experiences a force in a magnetic field. Magnetic Flux Density (磁通量) (Tesla) = i l ×BF )( Induced force Current (amp) Length of wire in the direction of i (m) ×BI I B θ =× BIBI sin θ
Electromagnetic Force ME350 A wire carrying current in a magnetic field. D F=ilB (1 wire length) Note:a dot will represent a current out of the page and a cross(x)will represent a current into the page. 9
9 ME 350 Electromagnetic Force • A wire carrying current in a magnetic field. B i F = ilB ( l = wire length) Note: a dot will represent a current out of the page and a cross( ×) will represent a current into the page
Electromagnetic Force ME350 The force is perpendicular to both the magnetic field and current F B 10
10 ME 350 Electromagnetic Force • The force is perpendicular to both the magnetic field and current