An elevator system comprises a motor drive for moving an elevator car. The motor drive usually comprises a hoisting machine of the elevator and also a power supply apparatus, such as a frequency converter, of the hoisting machine. The elevator car is moved in the elevator hoistway e.g. with suspension ropes traveling via the traction sheave of the hoisting machine of the elevator. The elevator car and the counterweight are suspended on different sides of the traction sheave such that their weight difference produces a force difference acting on the traction sheave, which force difference in turn affects the magnitude of the torque needed from the elevator motor when driving the elevator. With a balanced load the torque requirement of the elevator motor is at its minimum, and the torque requirement increases when loading the elevator car to be either heavier than the balanced load or lighter than the balanced load. The torque requirement of the elevator motor incorporated in an elevator system without counterweight, on the other hand, is proportional to the type of elevator system with counterweight in which the elevator car is loaded to be heavier than a balanced load.
When the torque requirement of the elevator motor increases, the current of the elevator motor increases. The increase in current, on the other hand, increases the loading exerted on the elevator motor and also on e.g. the frequency converter supplying power to the elevator motor. When the current increases the copper losses of the elevator motor increase; likewise, the current of the solid-state switches, such as IGBT transistors, of the frequency converter increases when the current of the elevator motor increases.
When dimensioning the frequency converter and the elevator motor, the aim is to select the values for maximum permitted loading to be as close as possible to the value set by the maximum transport capacity required of the elevator. This is because overdimensioning of the frequency converter and of the elevator motor would incur extra costs; additionally, in this case the size of the frequency converter, of the elevator motor and also of any cooling apparatus possibly needed would grow to be unnecessarily large, which would hamper the placement of these devices e.g. in the elevator hoistway.
Experts subordinate to, and under the direction of, the applicant are thus continuously striving to develop control methods and operating methods of an elevator motor for improving the performance of both the elevator motor and of the power supply apparatus of the elevator motor.
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