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Motor Control Sensor Feedback Circuits

Sensors are a critical component in a motor control system. They are used to sense the current, position, speed and direction of the rotating motor. | Microchip AN894 Motor Control Sensor Feedback Circuits Author Jim Lepkowski Microchip Technology Inc. INTRODUCTION Sensors are a critical component in a motor control system. They are used to sense the current position speed and direction of the rotating motor. Recent advancements in sensor technology have improved the accuracy and reliability of sensors while reducing the cost. Many sensors are now available that integrate the sensor and signal-conditioning circuitry into a single package. In most motor control systems several sensors are used to provide feedback information on the motor. These sensors are used in the control loop and to improve the reliability by detecting fault conditions that may damage the motor. As an example Figure 1 provides a block diagram of a DC motor control system to show the sensor feedback provided for a typical motor control. A list of the sensors that can be used to feedback information to a microcontroller are listed below Current sensors - Shunt resistor - Current-sensing transformer - Hall effect current sensor Speed position sensors - Quadrature encoder - Hall efect tachometer Back EMF Sensorless control method Power Management Torque Speed Direction FIGURE 1 Typical DC Motor Block Diagram. 2003 Microchip Technology Inc. DS00894A-page 1 AN894 CURRENT SENSORS The three most popular current sensors in motor control applications are Shunt resistors Hall effect sensors Current transformers Shunt resistors are popular current sensors because they provide an accurate measurement at a low cost. Hall effect current sensors are widely used because they provide a non-intrusive measurement and are available in a small IC package that combines the sensor and signal-conditioning circuit. Current-sensing transformers are also a popular sensor technology especially in high-current or AC line-monitoring applications. A summary of the advantages and disadvantages of each of the current sensors is provided in Table 1. Figure 2 shows an example .