Abstract: For controlling the current in an inductive load, the gate current used to fire thyristors in a rectifier is controlled to reach zero at exactly the same time, within a given half-wave, as the current in the inductive load which receives the voltage from the rectifier, keeping gate voltage on as long as thyristor current is on. A discontinuous thyristor converter current signal is detected and used to generate an enable signal in conjunction with a thyristor gate voltage. The enable signal, in synchronism with a power supply line voltage, provides a pair of channeling signals which then, depending upon whether the field current is positive or negative, activate the gate voltages of the thyristors such that the gate voltages end exactly at that time, within a given half-wave, where the generator field current becomes discontinuous.

Abstract: Automatic and manual adjustment of a new elevator system installation is accomplished by means of a service tool for interacting with software resident in the elevator system whereby various control parameters such as the feed forward gain of the drive system, the start time delay for delaying initiation of a start torque profile for bypassing the velocity loop during starting, the polarity of the feedback signals, e.g., armature current, velocity, motor field current, and other parameters, may be adjusted automatically, while others, such as the impedance of an elevator brake, may be adjusted by a technician responding to automatic prompts.

Abstract: Start jerk and acceleration overshoot on elevator starting are reduced by bypassing and delaying application of an elevator closed loop velocity control system. A bypassing starting torque increases the torque of the motor before the onset of motion, at which time the starting torque is leveled off and held constant and the velocity speed reference profile is started. A small creep velocity dictation injected into the closed velocity loop in addition to the starting torque command causes the difference between the speed profile and the sensed speed to be very small during starting. Moreover, by selecting lift brake current in such a way as to promote a smooth brake opening and by selecting an increasing starting torque profile which overcomes the declining brake torque just after the brake begins to open, the torque needed to compensate for the load can be evenly balanced with the release of brake torque.