CHAPTER V Motor Drives Motor drive systems definitions Review of motor principles Mechanical Requirements of Motor Drives Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Electric Motor Drives DEFINITION: Electric drives for motor is used to draw electrical energy from the mains and supply the electrical energy to the motor at whatever voltage, current and frequency necessary to achieve the desired mechanical output. General arrangement for variable speed drive. Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Example of Motor Drive System: Air Conditioning System Three Main Elements of Motor Drives: Electric Motor (DC, AC, SRM, Stepper) Load Type Control Requirements of Drives: Variable speed Controllable Torque Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Motor: Review of general principles Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Flux in C-core Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Air-gap flux densities Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Evolution of motor geometry Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Torque Production Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Mechanical System requirements for drives: Linear motion f e f L x Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Rotating motion f r torque  Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Motor and load interaction TL Tem Jeq m Jeq = combined load–motor moment of inertia m = motor speed (rad/s) TL = load torque Tem = motor torque Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Example(1) Motor Load TL Tem Jeq m Jeq = combined load–motor moment of inertia m = motor speed (rad/s) TL = load torque Tem = motor torque Using the motor-load structure as above, assume the motor has a combined inertia of 0.058kgm2. The load torque is negligible. Calculate the required electromagnetic torque if the speed is to be increased from standstill to 1,800rpm in 5 sec. Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Example(2) The speed profile of the rotating system shown in previous example. (Jeq=0.058kgm2) is shown below. Assume the load torque is 5 N.m. Calculate and plot, as a function of time the electromagnetic torque required from the motor 0.2 0.1 0.3 0.4 0.5 t(s) speed (rad/s) 300 –300 Section B Section A Section C Section D Section E Section F Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Torque and Power T d Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Friction Friction within motor and load appose rotation Examples: Bearings (to support rotating structure) Air (drag/windage) Ditction (friction at zero speed) Moving objects: Coulomb friction (independent of speed) Viscous friction (increases linearly with speed) Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB

Load Types Centrifugal (squared) Torque Load torque is a function of speed Example: Fans Torque Speed Constant Torque Load torque is independent of speed Example: Low speed hoist, elevator Torque Speed Power Electronics and Drives (Version 3: 2003): Dr. Zainal Salam, UTM-JB