Download Paralleled DC to AC Inverters for Telecom Applications

Paralleled DC to AC Inverters for Telecom
Applications
Preface
In Telecom sites there are two voltages – AC and DC. The DC voltage
supports Telecom equipment and the AC voltage operates various AC
equipment, like computers, LANs, Modems, Hubs, etc.
The DC voltage is backed up by batteries and is highly reliable. This is
the reason it can also support the AC equipment.
The DC voltage is usually 48V when the positive pole is connected to the
ground.
Since reliability is the most common requirement, as with many other
Telecom applications, DC/AC Inverters with N + 1 configuration are used
more and more.
Specifications needed for Telecom inverters
Input :
48V (40 ÷ 57)
Protection :
against reverse polarity
Low RFI noises:
from inverter to the DC bus
Output:
230V ± 2%
Waveform:
sine wave with max 2% THD
Protection:
over load and short circuit
Efficiency:
85%
Noise Acoustic:
less then 50db
MTBF:
200,000h
Isolation:
between input & output
Weight:
minimum
Load:
any load capacitive or inductive
Communication:
RS 232
Parallel:
to allow increase of load in future and increase in reliability (2001 Parallel
Inverter System)
Mechanical:
19” rack, hot swap plug in
Har Hotzvim Industrial Park,
14 Hartum St., P.O.B. 45029, Jerusalem 97774, Israel
Tel: 02-588-8222 Fax: 02-582-8875
Email: [email protected] web: www.gamatronic.com
Cd\articles\Inverter
Gamatronic Electronic Industries Ltd.
Technologies
Ferro resonance DC to AC Inverter
Figure 1: Ferro Resonance DC to AC Inverter
This DC to AC Inverter uses the Ferro Resonance transformer to regulate the output
sinewave and protect against overload.
Advantages:
Disadvantages:
•
Very reliable
•
Heavy weight
•
Rugged
•
Slow dynamic response
•
Simple control
•
Acoustic noise
•
No feedback
•
Suitable for any kind of load
•
No DC at output voltage
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Paralleled DC to AC Inverters for Telecom Applications
Gamatronic Electronic Industries Ltd.
The PWM DC to AC Inverter
Figure 2: P.W.M. D.C. to A.C. Inverter
This inverter is using High Frequency PWM switching for the switching elements.
Advantages:
Disadvantages:
•
Very reliable
•
•
Low weight
•
Small size
•
Fast dynamic response
•
Suitable for any load
•
No DC. at output voltage
Bulky 50Hz/TRAFFO
Paralleled DC to AC Inverters for Telecom Applications
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Gamatronic Electronic Industries Ltd.
The Double Conversion
Figure 3: Double Conversion DC/ AC Inverter
Using High Frequency (HF) for Isolation and reduction of overall weight.
This technology is used by Benning (Germany).
Advantages:
Disadvantages:
•
Small weight
•
Low efficiency
•
Fast dynamic response
•
Complicated
•
Expensive
•
Not suitable for all the loads
•
D.C. possibility in the output
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Paralleled DC to AC Inverters for Telecom Applications
Gamatronic Electronic Industries Ltd.
DC to Rectified AC
Figure 4: DC to Rectified AC Inverter
Using an HF Transformer for isolation reduces the overall weight. It is limited by low
Power Factor load
This technology is using by CE + T (Belgium),.
Advantages:
Disadvantages:
•
Low weight
•
Complicated design
•
Fast dynamic response
•
Expensive
•
Not suitable for any load
•
Very limited for capacitive load
•
Possibility of output D.C. voltage
Paralleled DC to AC Inverters for Telecom Applications
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Gamatronic Electronic Industries Ltd.
Single Conversion HF Bridge
Figure 5: Single Conversion DC / AC Inverter
Uses an HF Bridge for switching and an isolation transformer at the output.
This is Gamatronic’s own technology.
Advantages:
Disadvantages:
•
Suitable for all loads
•
Medium weight
•
Fast dynamic response
•
No D.C. at output
•
High efficiency
•
Very reliable
•
Medium sized
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Paralleled DC to AC Inverters for Telecom Applications
Gamatronic Electronic Industries Ltd.
Parallel DC to AC Inverter
Parallel redundant inverters operation means an N + 1 configuration. This topology
enables the connection of up to 16 units in parallel. We can achieve two important
advantages with parallel configuration – flexibility to increase the load if needed in
the future, and high reliability of the output load (N +1) in that the N inverter supplies
the load and the extra inverter is also a reserve.
For example, if the load is 5KVA, high reliability is achieved by using 3 units of DC
to AC Inverters of 3KVA each in parallel configuration. In case one of the inverters
fails, the other two are sufficient to continue to support the load.
Suppose the load increases in time to 13KVA - then 6 units of 3KVA Inverters are
actually 5 +1. If one unit fails the other 5 are sufficient to continue to support the
load.
Figure 6: IP2001 - The Front Panel
Figure 7: IP2001 - The Back Panel
Paralleled DC to AC Inverters for Telecom Applications
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Gamatronic Electronic Industries Ltd.
To parallel inverters:
•
Output voltage should be exactly the same
•
No phase shift between outputs
•
Similar dynamic response between the inverters
•
Current share between the inverters should be controlled
•
If the Inverter fails it should be switched off very fast to short the output
•
Control is by a non-democratic “slave” and “master” – each inverter can operate
as either a “master” or a “slave”. If the roll of the Inverter changes it doesn’t
affect the output voltage.
Figure 8: Parallel Inverters
Additional reliability by adding Static Switch
I/3
I/3
I
I/3
Figure 9: S.S. to Increase Output Redundancy
Adding a Static Switch to the output increases reliability even more.
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Paralleled DC to AC Inverters for Telecom Applications
Gamatronic Electronic Industries Ltd.
The table below details the Static Switch’s technical specifications:
PARAMETER
DESCRIPTION
AC input and output
Single phase with a common neutral
Nominal power
STSW1 – 06: 6KVA
STSW1 – 10: 10KVA
STSW1 – 15: 15KVA
Input voltage range
197 – 253V
187 – 242V (selectable)
Other values are available.
Input frequency range
50 ±2Hz
50 ±4Hz
60 ±2Hz
60 ±4Hz (selectable)
Other values are available.
Transition time in the synchronized mode
1
Transition time in the non-synchronized mode
<3msecs
1
<15msecs
Signals and indicators
6 LEDs, 3 keys, audible alarm, dry
contact relay, RS232 interface
Efficiency
99.9%
Size in mm (W × H × D)
480 × 135 × 210
Weight
~5kg
Regulations
Complies with the IEC950 standard
In the Inverter fails the line supplies the load.
The most important parameter is the frequency and phase of the system. Technology
uses the microcontroller to establish a PWM control by the master Inverter, to feed
current to all the inverters so they share the current equally.
The idea is that the first inverter is the master, dominating the PWM - and all the
other inverters are slaves. However, when the leading inverter fails the next inverter
becomes the master and leads the PWM.
Gamatronic offers its IP2000 Inverter!
Paralleled DC to AC Inverters for Telecom Applications
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