Variable Speed Drive (VSD)
Frequency Inverter Application - General
BITZER Kühlmaschinenbau GmbH
2013
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with integrated FI
BITZER // Climatechno 2013// Page 2
The Use of Frequency Inverters with
BITZER Compressors – General
Why Frequency Inverter?
 Possibility for infinite speed modulation
with 3-phase asynchronous motors
Pros:
/ Infinite capacity control




Higher part load energy efficiency
Without additional pressure fluctuation
Steady suction pressure and TX valve operation
Smaller temperature differences at HX
(higher suction pressure, lower discharge pressure)
/ Trans-synchronous operation  Smaller compressor
 Enhanced capacity control range
/ Soft start function
 Reduced starting current with full motor torque
 No start unloader required
 Reduced mechanical load
 Minimized danger of liquid slugging during start-up
BITZER // Climatechno 2013// Page 3
The Use of Frequency Inverters with
BITZER Compressors – General
Speed control of compressor
Energy savings: 15%
Page 113 (of 270)
http://www.umweltbundesamt.de/uba-info-medien/mysql_medien.php?anfrage=Kennummer&Suchwort=3743
BITZER // Climatechno 2013// Page 4
The Use of Frequency Inverters with
BITZER Compressors – General
VSD with suction pressure control - vs.- fixed speed // Example
0.1 bar
VSD
average
evap. temp.
with fixed
speed
compressor
Source: FrigoPack (www.frigokimo.com)
BITZER // Climatechno 2013// Page 5
The Use of Frequency Inverters with
BITZER Compressors – General
Why Frequency Inverter?
/ Fixed frequency rack system
Setpoint
- 4°C
to - 12C
-18°C
Δt14 K
BITZER // Climatechno 2013// Page 6
The Use of Frequency Inverters with
BITZER Compressors – General
Why Frequency Inverter?
/ Infinite capacity control
to -12°C
Setpoint
Δt 4K
BITZER // Climatechno 2013// Page 7
The Use of Frequency Inverters with
BITZER Compressors – General
Cons:
/ Power consumption at 50 Hz slightly higher compared to direct operation
(losses in power electronics, compressor motor)
/ Due to wide speed range risk of resonances and vibrations in pipe work
/ Higher efforts in projecting and selection of components
/ Very often higher installation costs (higher investments)
BITZER // Climatechno 2013// Page 8
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
BITZER // Climatechno 2013// Page 9
Frequency Inverter – Basic Principle
Pulse Width Modulation
L1
L2
L3
Rectifier
Transition
Circuit
(Capacitors)
Inverter
(IGBT’s)
Motor
3~
Control Circuit
Control Voltage
Net work throttles
(recommended
due to EMC)
BITZER // Climatechno 2013// Page 10
Sine wave throttles
(depending on FI output quality)
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
BITZER // Climatechno 2013// Page 11
The Use of Frequency Inverters with
BITZER Compressors – General
Function of Frequency Inverter
Frequency Modulation
n Motor =
f x 60
Number of pole pairs
– n Slip
U / f - Operation: Inverter must control voltage and frequency in a
constant ratio
 Motor torque required remains constant with positive
displacement compressors
Consequences if no voltage adaptation
 Increased motor current
 Risk of motor overheating
 Decrease of motor torque
BITZER // Climatechno 2013// Page 12
Requirements on Motor Characteristics
and Layout of Frequency Inverter
With Positive Displacement Compressors (Recips, Scroll, Screws)
 Torque remains “constant" with speed change
 Power absorbed changes approx. proportional to the speed
Mechanical side:
M =
P x 9,55
Electrical side:
[Nm]
n (1/min)
BITZER // Climatechno 2013// Page 13
P=UxI
x
3 x cosj [W]
Requirements on Motor Characteristics
and Layout of Frequency Inverter
Mechanical side and electrical side combined:
M =
UxI
x
3 x cosj x 9,55
[Nm]
n
~ constant
•„Demanded“ torque (M) = remains constant from mechanical side
• U/n ~ U/f = constant (by inverter controller)
 Current “I” remains (almost) constant
(with constant operating conditions, e.g. SST, SCT)
Above max. voltage (without voltage adaption):
 Ratio U/f declines
 Absorbed current rises
 Danger of motor (temperature) overload!
BITZER // Climatechno 2013// Page 14
Frequency Inverter − Voltage & Frequency
with Constant Torque (Supply 400V-3-50 Hz)
Speed range limit for
standard recips)
400
Voltage
[V]
A
B
Examples
C
300
200
Nominal Motor Voltage:
100
A:
400 V-3-50 Hz 40P / 40D
B:
380 V-3-60 Hz 35P / 35D
C:
230 V-3-50 Hz 40S
0
0
10
20
30
BITZER // Climatechno 2013// Page 15
40
50
60
70
80 87
Frequency
[Hz]
Frequency Inverter – Power & Torque
with Motor Winding Layout for 230V-3-50Hz
Speed range limit for
standard recips)
[%] 180
160
140
120
Current I
100
Torque M
80
60
40
20
0
0
10
20
30
0
50
100
150
BITZER // Climatechno 2013// Page 16
40
50
200 230
60
70
300
80 87
350
Frequency [Hz]
400 Voltage [V]
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
BITZER // Climatechno 2013// Page 17
The Use of Frequency Inverters with
BITZER Compressors – General
General Selection Criteria
Frequency and Speed Ranges
/ Depending on compressor technology and application
 Reciprocating, scroll, screw compressor
 Open drive, semi-hermetic, hermetic
 Motor layout & power supply
 Operating conditions, refrigerant, thermal load
Inverter selection for max. operating current, see technical data
(e.g. KP-100)
Increased starting torque during starting phase
/ Example for piston compressors
 depending on number of cylinders (2 // 4 // 6) factors (2 // 1,6 // 1,5)
BITZER // Climatechno 2013// Page 18
The Use of Frequency Inverters with
BITZER Hermetics & Semi-hermetics
Special Requirements on Frequency Inverter and Connection Wires
Critical Frequency and Speed Ranges
/ Dependent on operating conditions resonances may occur in certain
frequency (speed) ranges
/ Examination by tests under real conditions
 critical frequency ranges must be skipped by adequate programming
of the inverter
Note of Voltage Magnitude
/ Consider length of wire in manufacturer's documentation!!
/ Possible problems: motor noise / insulation failures
Screened wires (incl. grounding) from inverter to motor
(Electro Magnetic Compatibility)
BITZER // Climatechno 2013// Page 19
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
BITZER // Climatechno 2013// Page 20
The Use of Frequency Inverters with
BITZER Compressors – General Issues
Open Drive Compressors
Selection Criteria for Motor and Inverter
Motor selection according to manufacturer's requirements
Special Criteria:
/ Air flow is not in proportion to the motor speed
 increased power with trans-synchronous operation
 possibly insufficient cooling with sub-synchronous operation
Motor Selection / Application Range
/ dependent on inverter design and quality of sine wave additional spare
capacity for the motor may be required
Inverter selection according to specification of motor and inverter
manufacturers
BITZER // Climatechno 2013// Page 21
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
/ Basic principle & function
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
BITZER // Climatechno 2013// Page 22
NEW ECOLINE VARISPEED
KP-102-4
CE4 Varispeed Series
BITZER // Climatechno 2013// Page 23
NEW ECOLINE VARISPEED
Cooling Capacity (R404A)
[W]
to = -5°C; tc = 40°C
SGT 20 C, without liquid subcooling
70.000
87Hz
60.000
50.000
40.000
30.000
87Hz
20.000
87Hz
25Hz
10.000
0
30Hz
25Hz
2DES3.F1Y
4FES5.F1Y
4EES6.F1Y
BITZER // Climatechno 2013// Page 24
4DES7.F3Y
4CES9.F3Y
4VES10.F4Y
4TES12.F4Y
4PES15.F4Y
4NES20.F4Y
NEW ECOLINE VARISPEED
Special Design Features (1)
Shielded motor cable
// short and preassembled
Solidly flanged FI
// no vibrations
Suction gas cooled FI
// no air filter (service) needed
// no load restrictions at
high ambient temp.
BITZER // Climatechno 2013// Page 25
NEW ECOLINE VARISPEED
Special Design Features (2)
Up to 70% more capacity
// compared to fixed speed version
// infinite control range more than 3:1
Full torque up to 87Hz
// motor delta connected
(230V-50Hz  400V-87Hz)
Easy commissioning
// FI completely parameterized
BITZER // Climatechno 2013// Page 26
NEW ECOLINE VARISPEED
Compressor Installation (Example with CE3-F1)
/ Shielded connection cable between inverter and
compressor is pre-assembled
/ Power supply has to be connected to frequency
inverter
/ Check suction and discharge line for resonances
under real operating conditions
BITZER // Climatechno 2013// Page 27
NEW ECOLINE VARISPEED
Compressor Installation
Operation and control // Frequency inverter F1
The compressor/ inverter unit is controlled by an external controller.
It can be operated with factory defaults, no parameterization is required.
There are two characteristic curves preprogrammed within the inverter. Depending on
the control line connection on terminal a voltage (0..10 V) or current (4..20 mA)
dependent characteristic curve can be used.
Terminals 1 & 8: 4..20 mA
Terminals 2 & 8: 0..10 V
BITZER // Climatechno 2013// Page 28
NEW ECOLINE VARISPEED
Failure Analysis
/ Generally no additional adjustment by manual control unit required
 Inverter is pre-programmed to its assigned compressor
/ If required, pre-programmed parameter can be changed –
especially in case of vibrations within the installation
 Multiple frequency ranges can be masked out
BITZER // Climatechno 2013// Page 29
NEW ECOLINE VARISPEED
Payback Period
(following example based on
previous compressor models,
but results based on NEW ECOLINE
expected to be similar)
BITZER // Climatechno 2013// Page 30
VARISPEED Compressors // Payback Period
Example:
(1)
Cooling capacity 37kW + 5kW reserves
Conditions:
R404A; to= -8 °C; tc= 20°C … 45°C; Δtoh= 20K; Dtcu=10K
Installation place: Berlin
Rack
3x 4DC-7.2Y
2x 4EC-6.2Y + 1x 4EC-6.F1Y
3
3
Capacity max.
42,4 kW
43,9 kW
Capacity min.
14,1 kW
5,6 kW
Control range
33 / 66 / 100 %
12,8 … 100 %
steps
infinite
Number of comp.
Control type
BITZER // Climatechno 2013// Page 31
VARISPEED Compressors // Payback Period (3)
Annual energy consumption
Type
Qo
[kWh]
P in
[kWh]
Annual
4DC-7.2Y Rack (steps)
324120
84482
3,84
4EC Rack (infinite)
324120
79445
4,08
Results:
COP
6 % higher annual COP (system)!
 Payback period below 2 years!
To be considered:
/ Comparison based on constant load – variable load requirements
lead to additional COP weakness of fixed speed compressor applications
/ Winter operation leads to additional COP weakness of fixed speed application
BITZER // Climatechno 2013// Page 32
Variable Speed Drive //
Frequency Inverter Application - General
Contents
/ Pros & cons
√
/ Basic principle & function
√
/ Requirements on motor characteristics and layout of frequency inverter
/ Selection criteria (inverter, cables)
√
√
/ Special considerations for open drive compressors
/ Semi-hermetic compressor with Integrated FI
√
√
Any Questions?
BITZER // Climatechno 2013// Page 33