AC Motor Control System

Digital Power & Motion's AC Motor Control System is a CAN network of Embedded Variable Frequency Drives connected to a main Sequencer, to orchestrate their motion.  At each VFD, Magnetic Encoders track the position of an alternating pole magnetic strip.  The VFDs act intelligently to position the mechanical device, a door typically, connected to the motor based on feedback from the encoders.  Up to 99 VFDs can be connected to the sequencer over a network up to 5000' in length.  The VFD sequencer can act independently or accept commands from a higher level controller via a separate CAN port.

Variable Frequency Drive

Our Embedded Variable Frequency Drive is actually a custom Programmable Logic Controller with an AC Motor Controller peripheral built in.  It can take digital inputs, encoder feedback, and commands from a CAN or Modbus RTU interface and control the speed and direction of the motor load. It can operate independently of any external controller, or it can be commanded by our VFD Sequencer thousands of feet away using the built in CAN port.

  • Power output:
    • 0-240 VAC 3φ volts/hertz control
    • Up to 2HP intermittent duty, 6.5A 50% duty cycle at 50°C
    • 15A IGBT module
  • Dynamic braking for dissipating regenerative power
  • Warnings and shutdowns for DC Link under/over voltage and motor over current
  • Higher power possible with different IGBT modules
  • Fully isolated CAN & RS-485 ports
  • Six fully isolated 24VDC NPN inputs with LED status indication
  • Power Input: 100-260VAC 50/60Hz single phase
  • Environmental: -40 to 85 °C no load.  Derated to -40 to 50 °C for 6.5A @ 50% DC
  • Safety Agency Approval:  UL
  • Expansion Module Features:
    • Six additional 24VDC inputs with LED status indication
    • Six normally open dry contacts (1FormA) rated 8A @ 250VAC with LED status indication
    • Two analog inputs configurable for multiple voltage/current inputs
    • Absolute encoder interface via Synchronous Serial Interface (SSI).  An RJ-45 jack is provided for this enabling direct connection to Fraba absolute encoders.
    • Incremental encoder interface via quadrature NPN inputs
    • Modbus RTU RS-485 port

VFD Sequencer

Our Sequencer is designed to control a network of Variable Frequency Drives.  Generically speaking though, it is simply a custom Programmable Logic Controller with inputs, outputs, network ports and a user interface.


  • 128 x 64 graphic LCD display
  • Rotary encoder with momentary push switch for user input
  • Hierarchical menu system for intuitive access to process variables and parameters
  • Two fully isolated DeviceNet CAN ports and one USB port
  • Ten fully isolated 120VAC digital inputs with LED status indication
  • Four normally open dry contacts (1FormA) rated 8A @ 250VAC with LED status indication
  • Real time clock
  • UL approved

DC Motor Control

We have extensive experience designing DC motor controllers, especially for stepper motors. Our designs range from basic unipolar steppers to high-power bipolar steppers.

  • PWM control of average voltage for speed control
  • H-bridge control for rotation direction
  • Encoder position feedback for servo control
  • Simple unipolar stepper control
  • High-power, bipolar stepper control
  • High-power, high-speed current-mode control to overcome armature inductance
  • Micro-stepping for smooth operation