Solomon Technologies

Marine

Motor Controllers

STI motor controllers are three-phase, pulse-width-modulated (PWM) brushless, servo amplifiers. They convert DC from the batteries into a trapezoidal pulse – the commutation signal – that emulates three-phase alternating current in the stator windings. An ignition (on-off) key switch turns on the motor controller, just like the ignition of a car. When the switch is turned on, a capacitor is energized in the control circuit. A solenoid switch is activated, and current flows to the motor.

There are many advantages to this type of controller.

It allows for automatic regeneration of electricity whenever the prop is rotated by the water rushing by it. In a sailboat this normally occurs for long periods of time under sail as the prop turned by the water pressure. In a power boat, it occurs briefly when power is reduced, the boat slows down and water passing by the prop turns it and the motor. As the motor turns the magnetic fields from the rotor permanent magnets pass through the stator windings creating electric fields. The prop and motor become a hydroelectric generator. The controller senses the electricity produced, activates the transistor switches (IGBT or MOSFET) to collect all three phases, passes it through a filtering capacitor and sends it back to the batteries. An externally mounted capacitor helps absorb reverse emf when the motor drive is regenerating.

It can drive a three-phase permanent-magnet motor, which is more efficient than the more common single-phase permanent-magnet units and turns more smoothly at low speeds.

It easily reverses motor direction by running the signals from Hall-effect sensors through inverters before they are decoded to drive the power transistors. This reverses the “firing order” from ABC to CBA, allowing the motor to run with equal power in reverse.

It is a closed unit with no maintenance needed.

The science behind the STI motor/controller system

The STI motor and three-phase pulse-width-modulated brushless, servo amplifier controller work together to produce superior motor performance. The rising and falling commutation signal produces expanding and contracting magnetic fields in the stator windings. These fluctuating fields attract and repel the stationary fields from the permanent magnets around the rotor and cause it to spin.

The commutation is accomplished electronically through a rotor position feedback device (Hall effect sensor) and appropriate logic circuitry. Although the DC power supply voltage from the batteries is constant, the PWM amplifiers can vary it, along with the pulse frequency, to increase or decrease speed. Current is drawn as required to keep the rotor turning at the specified speed. This is referred to as the “current loop” mode of operation. The width of the trapezoidal pulses indicates the amps drawn. A narrow pulse means low amperage, a wider pulse, higher amperage, hence the term “pulse width modulation.”

Hall-effect sensors in the stator windings sense the rotor’s position and send this information back to the amplifiers, indicating which of the three winding phases to power next. As rotor speed increases, Hall-effect feedback occurs at a higher rate, keeping rotor rpm and phase excitation in synch.

The controller produces a digital signal that is easily controlled by computer. This opens up many possibilities for automated and remote military operation, e.g. in unmanned surface vessels for hazardous, mine-hunting missions.