AC Motor Electric Drive System Comparison

Commonly used AC motor electrical transmission systems include rotor series resistance, dynamic braking (also known as energy-consuming braking), cascade speed regulation, rotor pulse speed regulation, eddy current brake speed regulation, stator voltage regulation and frequency conversion speed regulation, etc. Now in the AC electric drive system of cranes, there are mainly three kinds that are widely used and mature: rotor series resistance, stator voltage regulation and frequency conversion speed regulation. The following is a comparison of the performance of these three transmission systems, see the table below for details.

Transmission type	Traditional rotor string resistance system	Stator voltage regulation and speed regulation system	Frequency conversion speed control system
control target	winding motor	winding motor	Inverter motor
Speed ratio	< 1:3	Digital 1:20 Analog 1:10	Generally up to 1:20 closed-loop system can be higher
Speed regulation accuracy	/	higher	high
gear speed adjustment	Can’t	Number: yes	Can
mechanical properties	soft	hard	Open loop: Hard Closed loop: Hard
Speed regulation energy consumption	big	bigger	Energy feedback type: no Energy consumption type: small
Parameter management with fault display	none	Digital: Yes Analog No	have
Communication Interface	none	Digital: Yes Analog: No	have
external device	Many, complex lines	Less, simple lines	Less, simple lines
Environmental adaptability	less demanding on the environment	less demanding on the environment	higher environmental requirements

The series resistance speed control system is completely controlled by the contactor and time relay (or PLC), which has a great impact on the mechanical structure and electrical system, and affects the normal service life of the crane. The contactor has serious arcing, high frequency of damage, and heavy maintenance workload.

The pressure regulation and speed regulation system has a stable starting and braking process, high speed regulation accuracy, hard mechanical characteristics, strong overload capacity, strong adaptability to the environment, strong maintainability, and high overall cost.

The frequency conversion speed regulation system has the highest control performance and speed regulation accuracy, and is more suitable for high-precision workplaces. It has relatively high environmental requirements, the simplest line control, and various control functions are rich and flexible. It will be a mainstream speed regulation method in the future.

Post time: Mar-21-2023