Tech Briefs Magazine - December 2023 - MD-4

Demand-Based Hydraulic
Pump Systems
Fixed displacement vane pumps (pictured above) are coupled to fixed-speed electric motors, providing constant
flow to a hydraulic circuit. (Image: Danfoss)
minimize fuel consumption. However,
industrial applications still use fixedspeed
electric motors, and the motor
sizing criteria are like standard pressure-compensated
pumps.
Recently, hydraulic pump systems
have improved with the addition of
electronic control with variable frequency
drives (VFDs) and utilizing
IIoT, leading to transformative reductions
in power consumption, noise,
and heat loss.
This filter cart features a VFD that controls the gear pump's
flow. (Image: Motion)
4
Variable Frequency
Drives (VFDs)
Varying the electric motor speed
with a VFD controlling pump flow
rates is new, especially with drive costs
dropping in recent years. Many power
utilities have promoted using VFDs
to reduce power consumption and
operational costs. While using a VFD
in simple applications such as air compressors
or fan drives may be adequate,
hydraulic system dynamics are much
different and require faster response
times reacting to machine functions.
Using a VFD with either a fixed or
variable pump allows adjustment of
input speed to the pump to vary the
flow, within the limitations of the pump
speed range. However, hydraulic systems
move at high frequency, so changing
the input speed to adjust flow will
not meet the requirements. Another
consideration is that squirrel-cage induction
motors controlled by VFD only
provide constant torque and not constant
horsepower. As the speed changes,
so does the horsepower to maintain
the constant torque requirement (i.e.,
a 10-hp motor running at half speed is
only a 5-hp motor).
Current trends toward connectivity of
hydraulic systems via IIoT provide a new
opportunity to create energy-efficient
pump systems. Using controllers that vary
an electric or servo motor speed based on
feedback such as pressure and torque allows
pump systems to match machine flow
and load requirements exactly. If there is
no excess flow from the pump system,
there is no wasted energy and heat loss.
There are several benefits of a pump system
that can match a machine operation's
actual flow and pressure requirements.
Energy Savings. As the pump system
monitors pressure, the variable speed induction
or servo motor adjusts speed to
match the pressure demand. As valves
shift and actuators move, pressures in the
system change. The control system determines
the flow required to match the
demand and adjusts the motor speed accordingly.
If the machine function is
holding pressure for an extended period,
the controller will reduce the speed of
the motor only to supply the necessary
flow to maintain pressure. The constantly
changing speed of the motor results in
reduced energy costs - in some cases by
as much as 80 percent - over traditional
fixed-speed pump systems. Additionally,
servo motors have a lower inertia and
smaller diameter, allowing quicker speed
and directional changes.
Reduced CO2 Emissions. Many facilities
are looking at their carbon footprint and
ways
to reduce their
impact on the
planet. Variable speed demand-based
pump systems do just that. When average
energy demand declines with a variable
speed motor system, so do the offsetting
CO2 emissions. As power demand varies
and there are minimal power losses
during a machine cycle, the associated
greenhouse gas emissions can be reduced
by up to 70 percent.
Lower Noise. Many manufacturing and
assembly facilities establish noise limits for
worker safety and comfort. Traditional
hydraulic pump systems are noisy and
often need to be placed in separate rooms
far from the equipment they service. If
this is not possible and the pump systems
are close to machine operators, noise reduction
could be required via costly enclosures.
Variable speed demand-based
systems tend to be quieter, and the noise
quality is more reasonable in close
Motion Design, December 2023

Tech Briefs Magazine - December 2023

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