1.
April 26, 2016
How to Select the Right Motor & Drive
for High Speed Applications
Olivier Delor
Product Manager, Motors

2.
Agenda
• Before Starting
• A quick recap of motor technology
• Application Requirements
• How to calculate power
• Motor Selection
• Drive Selection
• Field weakening mode
• Permanent current at low speed
• Frequency
• Maximum BEMF capability
• Protection module selection
• Summary Chart
• Market & Applications
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3.
Before Starting: Recap of Motor
Technology
Synchronous PMAC brushless motors offer many advantages over
asynchronous motors (often used in electro-spindle applications):
• 1.5 time more compact for the
equivalent power (reduced
footprint)
• Higher efficiency => Energy
saving
• Full torque at low speed
• Lower rotor temperature for :
• better accuracy
• lower vibration level
• 3x longer bearings lifecycle
• Inertia 2 times less (to increase
acceleration /
deceleration and decrease
cycle time)
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Parker synchronous motor

4.
Application Requirements
• The maximum speed,
• The maximum continuous torque that will be
used at low speeds for the roughing machining
operation or for big diameter machining
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In the first instance, we have to understand the application requirements in continuous mode:
Torque
Max
continuous
Torque
Max Speed
Speed
Case study
Maximum speed = 20000 tr/mn
Maximum continuous torque = 22 Nm
However, if the power (torque x speed) is
calculated at this stage, the result will often be
so huge that it will exceed what is needed – the
drive will be oversized and far too expensive.
Power (kW) = Torque (Nm) x Speed (tr/mn) / 9549 =
22 x 20000 / 9549 = 46 kW

5.
Application Requirements
How to Calculate the Power
For this reason, the maximum
continuous power required by the
spindle must be defined, running with
a field weakening mode to limit the
drive size.
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Speed
Torque
Max Power
and
constant
Base speed
Field Weakening mode
Max Torque
Max Speed
Oversized
Power
At this stage we should choose at least a drive with power rating of 55 kW (> 46 kW).
But the application requires 12 kW
Case study

6.
Motor Selection: Needs
When these data are clearly defined, the motor choice is easy. It has to be able to:
- Reach the maximum speed, because the centrifugal force generates heavy stress on
the magnets and on the rotor up to a limit in rotation. The rotors of HKW and MGV
motors have embedded magnets in the rotor that assure the best fitting.
- Provide the maximum torque at low speeds
- Have a winding configuration able to provide the power
- Run in field weakening mode, which is not a common capability of synchronous
motors with permanent magnets.
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Case study (HKW Parker range as an example)
Max. speed = 20000 tr/mn
Max. torque = 22 Nm

7.
Motor Selection
A high speed motor is generally operated at constant torque up to its base speed and at
constant power but reduced torque above the base speed.
Indeed, a high torque output is required for starting and for acceleration, but above base
speed, a reduced torque at rated power is enough to overcome friction effects (Figures 1
and 2). So the motor can run in field weakening mode at rated power up to its maximum
speed. The ratio of the maximum speed to the base speed is called the field-weakening
ratio. The higher that field-weakening ratio, the smaller and less expensive the drive
required to run the motor to its maximum speed.
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8.
Drive Selection : Field Weakening
Mode
When it comes to drive, the first step is
to check if it has a field weakening
mode, it means it manages the phase
advance between the current I and the
back electromotive force (BEMF) of the
motor in accordance with the power
need:
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9.
Drive Selection: Permanent Current at
Low Speed
Next, we select the drive size to provide suitable rated current (Io) to the motor
which will generate the maximum torque needed. To calculate this current, we
will use the torque constant (Kt) of the motor expressed in Nm/Arms.
Indeed, when we divide the desired torque by this constant, the result is the
minimum current that the drive will need to provide.
Io(Arms) =
Torque(Nm)
Kt(Nm/Arms)
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Case study
Io(Arms)= Torque(Nm) / Kt(Nm/Arms) = 22 / 0.772 = 28.5
A
Parker AC890 18.5 kW ouput current = 29 A
(instead of 55 kW with the primary rating data)

10.
Drive Selection: Frequency
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We have to be careful selecting the drive size because when as size increases, the output
frequency has a nasty habit of decreasing. For this reason you should double-check the
drive’s ability to provide sufficient frequency. Here, you should calculate the minimum
frequency requested by the motor to reach maximum speed with the following formula:
Frequency(Hz) ≥
MaxSpeed(tr/min) × Nomber of Pole
60 × 2
Case study
Maximum speed = 20000 tr/mn
HKW155 : 6 poles
Parker AC890 max. frequency : 1000 Hz
Frequency(Hz) ≥
20000 ×6
60×2
= 1000 Hz
The result must be less than or equal to the maximum output frequency of the drive. This is
not to be confused with the PWM frequency of the drive that corresponds to the switching
frequency.

11.
Drive Selection: Maximum BEMF
Capability
The next step is specific to the synchronous motor with magnets, because this device is, as
well as being a motor, and a very powerful generator able to reach high voltages. So, during
the high speed operation, the back electromotive force of the motor has to be below the
maximum DC voltage of the drive’s power bus. The Typical power bus values are 540VDC
for a 400VAC power supply and do not exceed 850VDC in general. Check the value of the
voltage of the back electromotive force of the motor at maximum speed. This limit is given
by another motor constant: Ke expressed in Vrms / 1000rpm:
BEMFPhase to phase(Vpeak) = Ke(Vrms / 1000rpm) ×
MaxSpeed(rpm)
1000
× 2
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Case study
BEMFPhase to phase(Vpeak) = Ke(Vrms / 1000rpm) ×
MaxSpeed(rpm)
1000
× 2
= 46.20 x 20000/1000 x 2 = 1307 Vpeak

12.
The results are best plotted in vector diagrams showing axe mode, field weakening
mode below the maximum voltage of the drive, and field weakening mode beyond the
maximum voltage of the drive.
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Drive Selection: Maximum BEMF
Capability

13.
Drive Selection: Protection Module
As shown in the latter diagram, the voltage of the back electromotive force is over the drive
limit due the high maximum speed.
In this case and only in this case, a protection module has to be added. This is because, in
the event of an incident or motor control loss (resolver fault), the motor can become a
generator (driven by the load inertia). Here, the BEMF is on the terminals of the drive and, at
extreme speeds, the motor and the drive will be damaged by excessive voltage. In general,
the protection modules shall short-circuit the motor or the motor voltage are clipped. In all
cases, the motor, the drive and the protection module have a maximum voltage limit (around
2000Vpeak or 1400Vrms phase to phase).
Finally, the protection module and the drive must withstand the short-circuit of the motor
current (Icc) to ensure the integrity of the components.
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BEMFPhase to phase(Vpeak) = 1307 Vpeak > 850V (for AC890)  A protection module is needed
Case study

14.
Summary chart
This chart will help you find the best solution to meet your technical
and economic application requirements.
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15.
Markets & Applications
Machine tools
Parker HKW motors are high
performance permanent magnet
synchronous servomotors for
spindle applications up to 276 kW
(up to 50000 tr/mn).
• High speed,
• Compactness,
• Low inertia,
• Motion quality
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www.parker.com/eme/hkw
Test rigs
Highly responsive with exceptional
dynamic performance, MGV motors are
ideally suited to the needs of simulation
testing in many automotive or
aeronautical applications up to 230 kW
(up to 45000 tr/mn)
• High acceleration,
• High speed,
• Low inertia

16.
Questions?
Olivier Delor - Product Manager, Motors
Electromechanical & Drives Division Europe
E-Mail: odelor@parker.com
Parker Hannifin Manufacturing France SAS
4 Boulevard Eiffel - CS40090
21604 Longvic Cedex - France
www.parker.com/eme
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