Active magnetic bearing

About company
Our company profile is design, manufacture, maintenance service and repair of high-speed electric machines.

Contactless supportsmagnetic bearings

Magnetic bearings
(as per GOST R ISO 14839-1 – 2011):

AMB – active magnetic bearing;

PMB  – permanent magnetic bearing;

SMB – super-conducting magnetic bearing;

HMB – hybrid magnetic bearing


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1 - magnetizing coil; 2 – radial position sensor; 3 - 3 sensor target; 4 - radial rotor core; 5 - axial centre; 7- shaft; D – inner diameter of stator core; d – outer diameter of stator core; δᵣ - nominal clearance; δᵣ = (D-d)/2; Lₜ - overall length of bearing (including electric magnet windings); L - effective length of bearing; W – pole width; A - area of one pole; A =  WL


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1 – rotor; 2 – sensor target; 3 – axial position sensor;  4 - stator core; 5 – stator coil; 6 - (clearance) centre of an axial AMB; 7 - axial bearing disc; dₐ - outer diameter of rotor disc; Dₒ - outer diameter of stator outer pole; dₒ - inner diameter of stator outer pole; d - outer diameter of stator inner pole; D - inner diameter of stator inner pole; δₐ - nominal clearance; Aₐ - area of pole pair; Aₐ = Π/4(Dₒ² - dₒ² + d² - D²)

AMB design

AMB consists of electromechanical part or magnetic bearing (MB) itself, and electronic control system. MB comprises of a rotor, a stator with electromagnet windings in slots and rotor position sensors.


Functional scheme of active magnetic bearing 

Using data from position sensors, this system controls the rotor position and influences the magnetic field in the gap by changing the current magnitude in the electromagnet windings. Controlling the current magnitude ensures stable rotor centerline position and the required stiffness and damping values ​​of the suspension.

Rotor displacement from a given equilibrium position is measured by position sensors, the signal from them is compared with the controller settings and used to correct the rotor position along the corresponding axis.

ERGA AMB:
Radial AMB, axial AMB and sensor supports

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Main features:
Load capacity of one radial bearing – 50 kg
Load capacity of an axial bearing – 100 kg


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AMB combined position sensor

AMB control system fragments 

Electromagnet control module (ECM)
 An electromagnet module generates currents of a complementary pair of suspension electromagnets. The signals of the control unit arrive to the drivers of field transistors.

Maximum current of the module - 35A, voltage - 400V.

The relatively high voltage of the module is necessary to ensure high speed of the current loop (rapid increase and decrease in the current of AMB electromagnets with 2.6 mH inductance).

Current sensors measure the currents of electromagnets and transmit analog signal to the control unit via a communication cable.


AMB control system fragments
AMB controller 

AMB controller provides signal processing and generation of electromagnet modules control signals.

Main functions of the control unit:

• forming of supply voltage of of AMB position sensors;

• signal processing of AMB position sensors;

• signal processing of current sensors of AMB electromagnets;

• Forming of ECM control signals;

• processing of signals from electric machine phase current and voltage sensors;

• forming of inverter control signals;

• transmission of diagnostic data and external control signals via RS-485 channel.

The controller is based on FPGA (field-programmable gate array). After comparing various options, FPGA from the Xilinx Spartan-6 family was selected. 24 thousand logic gates are quite enough for the tasks of parallel control of AMB and inverter.

The cycle of control signal generation is 2 μs: 1 μs for processing the signals of ADC sensors and 1 μs for calculation according to preprogrammed algorithms.

FPGA XC6SLX25-2FT256I is used in BGA package and the circuit board is multilayer to provide signal tracing.

AMB ADVANTAGES

Advantages
Results
No mechanical contact
No wear 

Unlimited life
Lower maintenance costs     

No lubrication

No lubrication and oil supply system (pumps, filters, seals, collectors, etc.)
Environmentally friendly

High rotation frequency
Reducing overall dimensions of the machine. High speed technologies.
Low power consumption

Lower operating costs due to energy saving
Low heat dissipation
Low friction factor

Operation in extreme conditions 

Operation  in vacuum
Operation at low and high temperatures (from -150 to + 450°C)
Operation in radiation environment
Operation in harsh environment
Super Clean Technology

Large clearance
Pollution Immunity
Electronic control system
Control of rotor axis position 

Creation of controllable microdisplacements of the rotor in the gap
Rotor rotation around the axis of inertia (rotor self-alignment) and absence of vibration caused by imbalance
Possibility of creating a system for active damping of rotor vibrations

Adjustable stiffness and suspension damping

High positioning accuracy
Favored transition over critical speeds
No noise or vibrations 

Using sensor signals to control operation parameters

Rotation speed control
Bearing load control
Rotor position control
Rotor imbalance and balancing control


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