Drive Descriptions

Motor Generator (MG)
Until the late 1980's, many elevators used MG technology, which consisted of a DC generator and DC hoist motor. An AC induction motor turned the DC generator, which was directly connected to the DC hoist motor. DC power provides high starting torque, smoother elevator ride and good speed control when compared to previous systems. This drive system is the least energy efficient.

Silicon Controlled Rectifiers (SCR Drives)
SCR drives for DC motors convert AC power to DC power. Common SCRs use either 6-pulse or 12-pulse drives.

Pulse Width Modulation (PWM)
PWM Drives control either an AC or DC motor and utilize several types of power transistors. These transistors are switched rapidly on and off, generating variable-width pulses, to regulate the current that is sent to the motor.

Variable Voltage Variable Frequency (VVVF)
Today's elevator systems include VVVF drives, which use an AC hoist motor rather than a DC hoist motor. The VVVF provides smooth acceleration and deceleration, excellent speed control and reduced noise levels.

Regenerative Drives (Regen)
Regenerative energy is produced by an elevator motor operating in what is known as overhaul condition, when the motor acts as a generator. Energy is produced on elevator descent when the car is heavier than the counterweight; and it is produced on elevator ascent when the counterweight is heavier than the car. Traditionally, this generated energy was dissipated through resistors as heat into the machine room. With the use of Regenerative Drives, the energy can be fed back into the building or power grid as clean, safe energy.