Carel convegno

CONTROL SYSTEM WITH DC INVERTER TECHNOLOGY

Integrated control system with dc inverter
technology for heat pumps

Biagio Lamanna
Application Competence Centre, Carel Industries srl

Biagio Lamanna - Application Competence Centre, Carel Industries srl


Objective
• Compressor characterization with inverter BLDC

• Develop control algorithm to HP with inverter

• Compressor envelope management

• Comparison between traditional technology and
inverter AC



What does BLDC mean?
BLDC (brushless direct current) motor
BPM (brushless permanent magnet) motor
DC (direct current) inverter
IPM (interior permanent magnet) motor
SPM (surface permanent magnet) motor
EC (electronic controlled) motor

Different NAMES for the
SAME technology



Why BLDC inverter compressors?
Electric motor evolution:

• AC asynchronous induction motor
Both compatible with standard on-off technology and inverter use
Good performances only for motors developed specifically for inverter use
Energy waste due to the need to create the rotor magnetic field

• DC brushless motor (SPM)
The rotor is a permanent magnet, there is no energy waste
The magnets of SPM motors need to be fixed on the rotor surface using adhesive,
high speed is not allowed

• DC brushless motor (IPM)
The magnets of SPM motors are inside the rotor
Highest efficiency and performances
High speed
Requires a top level BLDC inverter



The motor structures of the IM (induction motor), SPM (Surface permanent magnets),
IPM (Interior permanent magnets)

Comparison table of IM, SPM and IPM motor technology




The efficiency improvement of the brushless motor technology versus the
induction motor can be estimated on 4-5%




New unit testing and
rating procedures based
on partial load and
seasonal efficiency



Variable speed compressors can
match the partial load giving an
extremely high unit efficiency due to…

…the improved efficiency of the
compressor at partial load as motor
performance and basic COP…

Increased
Pressure

efficiency

… together with improved efficiency of
both heat exchangers
Enthalpy



BLDC compressor controlled speed

Unit performances with BLDC compressors
ON-OFF AC INVERTER DC BRUSHLESS INVERTER

6.0

5.0

4.0
C.O.P.

3.0

2.0

1.0

0.0
0% 20% 40% 60% 80% 100% 120%

LOAD



Control system description
• Compressor inverter

• Electronic Expansion Valve (EEV)

• One single electronic control board with semi-graphic
user interface display

• Software application for the management of the whole
unit



Heat pump test scheme
Condenser

Liq. Rec. Oil Separator

Filter
Compr. Compr.
On-Off Inverter
Flow Meter

EEV
Evaporator



System Test



Possible System

The created system allows you to simulate:

Geothermal probe ► Constant evaporation temperature

Variation of the load ► Changing ambient temperature

Several real installations ► Different condensing flow



Features & Benefits of an integrated solution
Others CAREL System




Compressor safeguard

Managed function
Compressor start up procedure
Compressor working envelope
Compressor timings
Compressor minimum pressure drop
Suction superheat
Discharge superheat
Discharge gas temperature




Unit safeguard and performance

Managed function
Compressor start failure management
Compressor equalization at start-up
Drive alarm management
Speed regulation according to the application
needs
Drive parameter pre-set for different
compressors
Drive custom parameters load and save
management
Drive complete user interface


CAREL control algorithm details
Compressor working envelope:

• Min/Max compressor ratio
• Min pressure differential
• Max motor current
• Max/min discharge pressure
• Max/min suction pressure
• Max discharge temperature
(different for each zone)
• Min/Max compressor speed
(different for each zone)
• Different management for
each compressor!




Compressor working envelope management:

Unit capacity reduction by EEV control in case of low
compressor ratio, high suction pressure, high motor
current, etc…
Compressor capacity reduction in case of high discharge
pressure and/or temperature, low suction pressure, etc…
Drive acceleration/deceleration ramp control to avoid
going out from the safety working areas



Compressor windings temperature management:

By means of measuring:
• compressor shell temperature
• compressor discharge gas temperature and superheat
• compressor motor current

The control system can:
stop the compressor due to high shell temperatures even if…
… the drive can manage the compressor speed in case of high
motor current without stopping it and…
… both EEV and compressor control modules can regulate the
discharge superheat or temperature for optimal compressor
performance with maximum compressor speed by means of the
safety liquid injection



Unit start-up management:

The synchronization between compressor, drive
and EEV management allows to take care of:
Pressure differential before start
Equalization, if needed or… Speed (rps)

… compressor start-up even with up to 10barg pressure
difference. Speed ref.

Initial Speed ACC ramp = 2rps/s
Pressure differential after start ( greater than the 50 rps

minimum allowed) Min Speed
DEC ramp = 2rps/s

20 rps ACC ramp = 2rps/s
Oil recovery after start
Quickly
Compressor warm up Time (s)
1 min or more (default = 3 min)

Compressor timings (minimum ON time, minimum OFF
time, minimum time between different starts)
Start-up quick retry in case of start failure
Wrong wiring, blocked rotor, damaged motor windings,
or any start-up problem.



Compressor alarm management:
Centralized alarm management for all unit components:
• The unit can work even with broken probes
• Critical alarms manual reset by user interface or remote monitoring system
• Automatic to manual alarm reset after a defined number of attempts
• All alarms in the same UI:
Unit alarms (i.e. low temperature, low water flow, high pressure, etc)
Compressor alarms (i.e. high discharge temperature, out of envelope,
low compressor ratio, etc.)
Drive and motor alarms (i.e. high motor current, low supply voltage,
communication offline, etc.)
Valve alarms (i.e. stepper motor damaged, low suction superheat,
etc.)



Results
• Compressor with AC inverter: max efficiency
75% of range

• Compressor with BLDC with inverter: max
efficiency around 50% of range

• On-Off Compressor: efficiency related to duty
cycle



Conclusion
A BLDC inverter compressor unit:

• Has the top level compressor motor technology
• Meets all present and future efficiency rating specifications
• Grants high performances due to the wide range of cooling
capacity modulation that allows the best application
temperature control

Technology Saving

INV AC vs. On-Off 8,60 %
INV BLDC vs. On-Off 25,30 %
INV BLDC vs. INV AC 15,40 %



Conclusion

A full integrated system for HP application:

• Meets ALL compressor manufacturer specifications (with their
official approval!)
• Allows to use the compressor in the full speed range in all the
working envelope conditions
• Avoids the unit OEM to spend months of R&D development
• Grants a full control on the unit with plenty of extra features
compared with a stand alone inverter drive that allow to reach
the best performance level



Conclusion

A full customizable system for HP application:

• Meets all unit manufacturer needs in terms of performance/cost
compromise
• Allows the unit manufacturers to keep their knowledge about the
application and customize any part of the software and user
interface
• Has many user interface solutions for each different user profile


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