ST has a strong portfolio for motor control applications. Smooth operation and high efficiency are driving development in the motor control area. The growing demand for higher efficiency is supported by developments in field oriented control (FOC) software for PMSM, PMAC and induction motors running on high performance microcontrollers coupled with power transistors and high voltage gate driver ICs. For lower power applications new highly integrated controller/driver ICs for steppers run the steppers smoother and with higher positioning precision.
Brushed DC
Traditionally used in applications for speed and positioning control these easy to drive motors are used in applications ranging from a few watts to several horse power. When only one direction of rotation is needed, a single transistor PWM can be used for speed control. For positioning applications or when both directions of rotation are needed, a full H-bridge with PWM control is used. At lower power levels the DC motor can be driven from an fully integrated power IC that includes the drivers and power transistors. For higher power, discrete MOS or IGBT are used with high voltage gate drivers to implement the H-Bridge. A low cost microcontroller can be used to implement the speed control algorithm and control the bridge. Accurate position or speed control will require a sensor like a tach or an encoder. Simple speed adjustment may be done open loop without feedback .
Single Phase AC Induction
Single phase induction motors have been the most common motor used for large appliances. The rotor is typically an aluminum squirrel cage and the stator is two coils and a phase-shift capacitor. Typically the starting coil and phase shift capacitor are switches off by a centrifugal switch when the motor reaches speed. The control is often simply on/off control using Triacs or ACS devices.
Three-Phase AC Induction
Three-phase induction motors are brushless motors. The stator is copper wound and the rotor is typically an aluminum squirrel cage. The typical drive configuration is a three phase bridge (3 half bridges) modulated to provide three sine wave voltages to the stator. Typically used in higher power applications, drive is often discrete IGBT with high voltage gate drivers, or by power modules integrating three half bridges and related gate driving stages. Field Oriented Control or Scalar (Volts / Hertz) control algorithms are implemented in microcontroller that control the inverter.
Brushless DC (Three-Phase BLDC)
Brushless DC motors have permanent magnets on the rotor and externally commutated coils on the stator. The electronic commutation replaces the function of the brushes in a DC motor and typically drives the stator coils in steps based on the sensed rotor position. The primary benefit of a brushless DC motor is it's inherent efficiency and reliability. These motors are becoming more common as designers press for improved efficiency in the system. Typical configurations are a three phase motor driven by 3 half bridges. In low power applications the drivers can be integrated into a smart power IC. For higher power, discrete IGBT and high voltage gate driver ICs are used for the half bridges. For many applications, sensorless drives have eliminated the need for the hall effect sensors used in the past. The 6 step commutation and the speed control are typically implemented in a low end microcontroller.
Stepper Motor
Commonly used low power applications, like printers and automation, stepper motors provide excellent positioning and speed control at low cost. The motor has a permanent magnets on the rotor and coils wound on the stator. These motors typically have many pole pairs and provide native resolutions from 7.5 to 1.8 degrees per step. Simple control is done by stepping the polarity of the stator current through 4 steps. Common configurations are Unipolar and 2 phase bipolar wound motors. Less common configurations include 3 and 5 phase motors. Common controls use integrated driver ICs that integrate the control and power stage on a single smart power IC.
Brushless AC (Three-phase PMSM)
Brushless AC motors, also know as Permanent Magnet Synchronous Motors (PMSM) or Permanent Magnet AC motors (PMAC) have permanent magnets on the rotor and externally commutated coils on the stator. They differ from a Brushless DC motor primarily in that the stator coils are driven by a sinusoidal waveform. The primary benefits of a brushless AC motor is it's inherent efficiency smooth operation and reliability. Typical configurations are a three phase motor driven by 3 half bridges. In low power applications the drivers can be integrated into a smart power IC. For higher power, discrete MOS or IGBT and high voltage gate driver ICs are used for the half bridges. For many applications, sensorless Field Oriented Control (FOC) drives have eliminated the need for the encoders used in the past. The sinusoidal drive and FOC algorithm may be easily implemented in a low cost 32 bit microcontroller.
Switched Reluctance
Constructed with a laminated iron stack on the rotor and wound field coils on the stator, the switched reluctance motor is a brushless motor that has no permanent magnets. SR motors have found use in high speed applications such as vacuums and high velocity air blowers. The motors are typically driven with a three phase asymmetrical half bridge with each half bridge driving one of the three phases. High voltage gate drivers and MOS or IGBT transistors are typically used in the asymmetrical bridge. Microcontrollers provide the commutation and speed control for the bridge.
Universal
Universal motors may be used with an AC or DC supply current. The advantages of universal motors are specifically high starting torque, very compact design and high running speeds. Simple controls running off of the AC mains can be implemented with a low end microcontroller and a single Triac or ACS. Improved performance can be achieved using a DC chopper drive that rectifies the AC mains and then uses a Power MOS to provide a PWM drive to the motor. Although most are unidirectional motors, bidirectional motors can be made using two coils on the stator and energizing only one for the correct direction.
