variable speed drive (vsd) frequency inverter application - general bitzer kühlmaschinenbau gmbh...

Variable Speed Drive (VSD)

Frequency Inverter Application - General

BITZER Kühlmaschinenbau GmbH

2013

BITZER // Climatechno 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


The Use of Frequency Inverters withBITZER 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



Speed control of compressorEnergy savings: 15%

Page 113 (of 270)

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average evap. temp. with fixed speed compressor

VSD

VSD with suction pressure control - vs.- fixed speed // Example

0.1 bar

Source: FrigoPack (www.frigokimo.com)


- 4°C

-18°C to - 12C

Δt14 K


Why Frequency Inverter?

/ Fixed frequency rack system

Setpoint



Why Frequency Inverter?

/ Infinite capacity control

to -12°C

Δt 4K

Setpoint



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)



Contents

/ Pros & cons





/ Semi-hermetic compressor with Integrated FI


Frequency Inverter – Basic Principle

RectifierTransition

CircuitInverter(IGBT’s)

Control Circuit

Motor3~

Control Voltage

L1L2L3

Pulse Width Modulation

Sine wave throttles(depending on FI output quality)

Net work throttles(recommended due to EMC)

(Capacitors)



Contents

/ Pros & cons








n Motor =f x 60

Number of pole pairs– n Slip

Function of Frequency InverterFrequency Modulation

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


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

M = [Nm] P = U x I x Ö3 x cosj [W]P x 9,55

n (1/min)

Mechanical side: Electrical side:


Requirements on Motor Characteristics and Layout of Frequency Inverter

Above max. voltage (without voltage adaption): Ratio U/f declines Absorbed current rises Danger of motor (temperature) overload!

~ constant

M = [Nm]U x I x Ö3 x cosj x 9,55

n

Mechanical side and electrical side combined:

• „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)


Frequency Inverter − Voltage & Frequency with Constant Torque (Supply 400V-3-50 Hz)

Voltage

0

100

200

300

400

0 10 20 30 40 50 60 70 80 Frequency [Hz]

87

[V]

Nominal Motor Voltage:

A

A: 400 V-3-50 Hz 40P / 40D

B

B: 380 V-3-60 Hz 35P / 35D

C

C: 230 V-3-50 Hz 40S

ExamplesSpeed range limit for standard recips)


Frequency Inverter – Power & Torque with Motor Winding Layout for 230V-3-50Hz

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50 60 70 80 Frequency [Hz]

Torque M

Power P

[%]

0 50 100 150 200 300 350 400 Voltage [V]230

87

Current I

Speed range limit for standard recips)



Contents

/ Pros & cons







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)


The Use of Frequency Inverters with BITZER Hermetics & Semi-hermetics

Special Requirements on Frequency Inverter and Connection WiresCritical 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)



Contents

/ Pros & cons







The Use of Frequency Inverters with BITZER Compressors – General Issues

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

Open Drive Compressors



Contents

/ Pros & cons







NEW ECOLINE VARISPEED

KP-102-4

CE4 Varispeed Series


0

10.000

20.000

30.000

40.000

50.000

60.000

70.000

2DES-3.F1Y

4FES-5.F1Y

4EES-6.F1Y

4DES-7.F3Y

4CES-9.F3Y

4VES-10.F4Y

4TES-12.F4Y

4PES-15.F4Y

4NES-20.F4Y

[W]Cooling Capacity (R404A)to = -5°C; tc= 40°C SGT 20 C, without liquid subcooling

25Hz30Hz

25Hz

87Hz87Hz

87Hz



NEW ECOLINE VARISPEEDSpecial Design Features (1)

Solidly flanged FI

// no vibrations

Suction gas cooled FI // no air filter (service)

needed// no load restrictions at

high ambient temp.

Shielded motor cable// short and

preassembled


NEW ECOLINE VARISPEEDSpecial Design Features (2)

Easy commissioning// FI completely parameterized

Full torque up to 87Hz// motor delta connected

(230V-50Hz 400V-87Hz)

Up to 70% more capacity// compared to fixed speed version// infinite control range more than

3:1


NEW ECOLINE VARISPEEDCompressor 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


NEW ECOLINE VARISPEEDCompressor 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 mATerminals 2 & 8: 0..10 V


NEW ECOLINE VARISPEEDFailure 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



Payback Period

(following example based on previous compressor models, but results based on NEW ECOLINE expected to be similar)


VARISPEED Compressors // Payback Period (1)

Example: Cooling capacity 37kW + 5kW reservesConditions: 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

Number of comp. 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 %

Control type steps infinite


Type Qo [kWh]

P in [kWh]

Annual

COP

4DC-7.2Y Rack (steps) 324120 84482 3,84

4EC Rack (infinite) 324120 79445 4,08

Results: 6 % higher annual COP (system)!

Payback period below 2 years!

VARISPEED Compressors // Payback Period (3)

Annual energy consumption

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



Contents

/ Pros & cons






Any Questions?

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variable speed drive (vsd) frequency inverter application - general bitzer kühlmaschinenbau gmbh...

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