Three Ways to Control a Single-Phase Induction Motor : Page 4 of 4

Resources Required
Resource Unidirectional Bidirectional H-bridge Bidirectional with three-phase bridge Notes
Program memory 1.5 Kbytes 2.0 Kbytes 2.5 Kbytes --
Data memory ~20 bytes ~25 Bytes ~25 bytes --
PWM channels 2 channels 2 channels 3 channels Complementary with dead time
Timer 1 1 1 8- or 16-bit
Analog-to-digital converter 3 to 4 channels 3 to 4 channels 3 to 4 channels Motor current, temperature measurements, speed control potentiometer
Digital I/Os 3 to 4 3 to 4 3 to 4 For user interfaces like switches and displays
Fault inputs 1 or 2 1 or 2 1 or 2 For over current/ over voltage/ over temp, etc.
Complexity of control algorithm Low Medium High --
Cost Comparison
Unidirectional Bidirectional with H-bridge Bidirectional with three-phase bridge
Input converter section Low - Single phase diode bridge rectifier High - Due to voltage doubler circuit Low - Single phase diode bridge rectifier
Output inverter section Low - Two half bridges Medium - Two half bridges. The power switches rated higher voltage High - three-phase inverter. Using Integrated Power Modules (IPM) is better choice than discrete components
Motor Medium - Starting capacitor required Low - Starting capacitor is removed from the motor Low - Starting capacitor is removed from the motor
Development time Short Mid-range Long
Overall cost Low Medium Medium - Efficient control for the given cost

Another advantage of using the three-phase control method is that the same drive-hardware topology can be used to control a three-phase induction motor. In this scenario, the microcontroller should be reprogrammed to output sine voltages with 120-degree phase shift to each other, which drives a three-phase induction motor. This reduces the development time.

Single-phase induction motors are very popular in appliances, and industrial and consumer applications. PSCs are the most popular type of single-phase induction motors. Controlling the motor speed has many advantages, such as power efficiency, reduced audible noise and better control over the application. In this article, we discussed different methods of speed control that can be used with a PSC motor in unidirection and bidirection. Controlling a PSC motor using a three-phase inverter topology provides the best results.

Phase voltage when the motor is running in forward and reverse directions.
Web Resources
An overview of motor types, motor classification, and applications using Microchip's PICs and dsPICs:
Datasheet programming specs and application notes for PIC 18FXX31 microcontroller:
Motor control development tools from Microchip:

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