24-12-2012, 06:12 PM
Ceiling Fan Speed Control
Ceiling Fan Speed Control.pdf (Size: 335.9 KB / Downloads: 78)
Introduction
This application note introduces a method for controlling
a single-phase AC induction motor. This motor is widely
used in ceiling fans due to various advantages over other
types of motors. It is low cost, low maintenance, and has
direct connection to the AC power source.
Using the MC9RS08KA2 MCU series combined with
the basic TRIAC topology is cost-performance solution.
The traditional mechanical speed control of the ceiling
fan can be replaced with this solution avoiding problems
such as non-linearity on speed.
Single Phase Induction Motor Control Theory
Single-phase induction motors are the most used. These motors have only one stator winding, operate with
a single-phase power supply, and are also squirrel cage. Because of the single phase, the motor is not
self-started when connected to a power supply. The necessary torque is not generated therefore causing the
motor to only vibrate and not rotate.
To provide the starting torque most single-phase motors have a main and auxiliary winding, both in
quadrature to help generate the phase-shifted magnetic field.
Typical Solutions
Motors commonly used in ceiling fans are single-phase induction motors with a PSC starting mechanism.
Most of them have three different speeds that are mechanically selected by pulling a chain. Every time the
chain is pulled, the motor circuit changes to a predefined coil winding that causes the speed to vary. It is
recommended that the fan be set at maximum speed. Considering that the load of the motor is proportional
to the consumed current it is not the same range of speed variation with the load then without it. The range
of speed variation needs to be recalculated.
Proposed Solution and Phase Angle Control
When the TRIAC switch is connected between the AC power supply and the motor, the power flow can
be controlled by varying the RMS of the AC voltage. This is called an AC voltage controller. There are
two types of control normally used:
— On-off control — TRIAC switches connect the load to the AC source for a few cycles and then
disconnect it for another few cycles of the source voltage
— In phase control — TRIAC switches connect the load to the AC source for a moment in each
cycle Figure 3
A reliable speed control of a ceiling fan AC motor can be accomplished by combining the MC9RS08KA2
and the phase angle control using a TRIAC. A benefit of this approach is avoiding non-linearity that is
present if using only the TRIAC. Another benefit is, it can replace the mechanical speed variation
commonly used in ceiling fans.
Instructions
Board Configuration
Steps for configuring the board:
1. Pull out every jumper in j101 except for RESET and LED 0
2. Connect the j101 SW0 pin on the push button side of PTA5 on j102. The push button SW0 connects
to PTA5
3. Make sure the board is in host mode, j202 in the USB, and j203 VDD enabled
4. Set jumpers on j101 to RESET and LED