Operating behaviour of speed-variable BLDC motors under load

Due to their high efficiency and the excellent dynamic properties, BLDC machines have replaced direct current machines in many speed and position control systems. Permanently excited synchronous machines which behave like a direct current machine with a commutated drive are BLDC machines.

The high efficiency is achieved thanks to the permanent excitation. The rotors can be produced with a very low moment of inertia, which allows for highly dynamic behaviour.

Objectives

• Energy requirement for starting under load
• Energy requirement for change of direction of rotation
• Behaviour of working machines
• Torque is constant as with lifts; cranes (T_L = const.)
• Torque rises lineally with speed; extruder, flexing work (T_L ~ n)
• Torque rises quadratically with speed; turbo machines, fans, pumps (T_L ~ n²)
• Torque decreases inversely proportional to speed; lathes and milling machines, winding machines.(T_L = 1/n)
• Flywheel mass

The learner will get to know the behaviour of working machines on a drive with BLDC motor. In the first few experiments, the efficiency of a speed-variable drive is investigated. In later experiments, the different behaviours of work machines are presented. Characteristics diagrams and time diagrams are recorded and analysed for evaluation purposes.

Highlights:

• The measurements are carried out with the CASSY Machine Test.
• All measurement channels are potential-free and can therefore be used freely.
• All measurements can be carried out with or without a computer.
• In order to protect against overheating, the stator windings of the BLDC motor are equipped with thermal detectors.
• The BLDC motor has a didactic terminal board

All functions of the Converter Controller CASSY and the Machine Test CASSY 0.3 can be operated quickly and directly via the display, the rotary wheel and the buttons on the unit. All settings and measurement results can be saved on the unit and quickly called up again later or simply downloaded.

In addition, the Converter Controller CASSY and the Machine Test CASSY 0.3 is fully controllable in real time via RJ45 Ethernet, W-LAN and USB-C interfaces.

These interfaces can be used by the following software:

• CASSY Lab 2 for drives and energy systems,
• MATLAB® and LabVIEW ™
• Lab Docs Editor Advanced

Several integrated servers are available in Converter Controller CASSY and the Machine Test CASSY 0.3 for the local media connection of at least four end devices simultaneously.

For more details, see product data 7735290 or 7735291 Converter Controller CASSY and the 7731900 or 7731901 Machine Test CASSY 0.3.

The entire equipment is equally suitable for self-studies in a laboratory with low voltage (230 V AC / DC or 120 V AC / DC) and - with a mobile trainer - for a teaching demonstration in the education of the fundamentals. The experiments can be carried out as an interactive experiment or with a manual and software.

The target group consists of commercial apprentices and students of electrical engineering. The course offers experiments at an intermediate level and also allows for the necessary insight into machine behaviour for scientific interpretation at undergraduate level.

In the following configurations there are further extended experiments performed with the educational frequency converter and a BLDC machine:

• E2.6.1.1 Basics of commutation technology
• E2.6.1.2 Block commutated synchronous machine
• E2.6.1.3 Sinus-commutated permanently excited synchronous machine with surface magnets
• E2.6.2.3 AC servo with industrial permanently excited synchronous machine

Topics

• Energy efficiency of drives
• Work machines with:
• • T_L = const.
  • T_L ~ n
  • T_L ~ n²
  • T_L ~1/n
  • Flywheel mass
• real work machine