UPS for Numpties EN62040-3 UPS Classification


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EN62040-3 UPS Classification

UPS Classification according to EN62040-3

Why the Need?
The simple terms of identifying technology was by Online (double conversion), Line Interactive or Offline (Standby). These define a UPS topology (i.e. its building blocks) but not all the fundamental information required. In addition, manufacturers introduce new terms such as Quasi online, True Online, Single Conversion online, Pseudo Sine Wave, Digital Interactive etc, that only confuse the situation. The classification was brought out in an attempt to address the situation.

The Classification

Stage 1. Degree of dependence of output on the input

The Voltage and/or Frequency Output is either directly related to the input (i.e. what goes in comes out) or DEPENDENT, or they are not direclty related (i.e. what goes in isn't necessarily what comes out) i.e.INDEPENDENT. This gives rise to 3 classifications:

VFI - Both the Voltage and Frequency Output are Independent of the Input
VI - The Voltage is Independent but the frequency is dependent.
VFD - Both the Voltage and Frequency Output are Dependent on the Input

Note that VI implies frequency dependency (FD). Examples are a line interactive UPS that uses a tap changing transformer to buck or boost the input voltage. The output voltage is no longer the same as in the input voltage, hence Voltage Independent, however the output frequency will still be the same, hence this is Frequency Dependent. In addition you cannot have VD/FI due to the laws of physics.

Stage 2: Output Waveform Classification

This consists of two letters: -Wn,Wb, where Wn is the waveform type when in normal operation and Wb is the waveform type when on battery. Wn and Wb are either:

S - A sinewave waveform of total harmonic distortion of less than 8% for both linear and non-linear loads
X - A sinewave waveform of total harmonic distortion of less than 8% for linear loads only
Y - A non-sine wavefore of total harmonic distortion of greater than 8% independent of load

So, for a unit that passes the mains straight through in normal operation, and activates a square wave inverter when on battery will be designated SY. A poor quality online system which provides an output sinusoidal waveform that is subject to distortion may be XX or even YY. A good quality online or line interactive unit with a good sinewave inverter will be SS.

Stage 3: Dynamic Characteristics

This consists of three numbers - n1,n2,n3 defined as follows:

n1 - The level of deviation of the output voltage when the UPS reverts to or from battery
n2 - The level of deviation of the output voltage when the UPS is subject to a 100% change of a linear load on battery
n3 - The level of deviation of the output voltage when the UPS is subject to a 100% change of a non-linear load on battery

The numbers are registered between 1 & 3, with 1 being the best and 3 being the worst. These are deduced from the following diagram:

Comparison against known Topologies

Offline or Standby UPS - Now VFD:

What goes in, comes out. Except when the mains power fails, the battery provides power to the inverter. This is then switched to the output.

Line Interactive - Now VI:

VI units have some voltage regulation usually provided by switching taps on a transformer. Thus, the output voltage may differ from the input. Should the mains power fail, then the battery provides power to the inverter, this is then switched to the output.

Online Double Conversion - Now VFI:

In VI units, the power is converted to DC and this supplies the inverter. The inverter waveform is therefore completely independent from the input. When the mains fails, power is continued to be supplied to the inverter from the battery with no change in the output. The only change in output occurs when the unit reverts to bypass, and even then, this is only in the event of a fault.

Examples

1. A "Standby" UPS has no voltage regulation and outputs a square wave when on battery. There is a delay of around 8ms when the unit transitions from mains to battery.

As the unit output is dependent on the input the unit is classified VFD
As the output is sinewave when in normal mode independent of the load, then the first letter is "S"
As the output has high harmonic content when on battery, the second letter is "Y"
As the voltage disappears momentarily when transition to battery, the first number is 3
The second two numbers depend upon the quality of the inverter, but we will assume standby systems to be 2 & 2

This unit is therefore designated VFD SY 322

2. A "Line Interactive" UPS has output voltage regulation and outputs a pseudo-sine wave when on battery. There is a delay of around 4ms when the unit transitions from mains to battery.

As the outputvoltage is regulated using a transformer, the Voltage is Independent but the Frequency is Dependent. Therefore VI
As the output is sinewave when in normal mode independent of the load, then the first letter is "S"
As the output has high harmonic content when on battery, the second letter is "Y". This is the case even though the waveform is pseudo sine.
As the voltage disappears momentarily when transition to battery, the first number is 3
The second two numbers depend upon the quality of the inverter, but we will assume non sinewave inverters to be 2 & 2

The unit is therefore designated VI SY 322

3. A "Line Interactive" UPS has output voltage regulation and outputs a sine wave when on battery from a good quality inverter. There is a delay of around 4ms when the unit transitions from mains to battery.

As the output voltage is regulated using a transformer, the Voltage is Independent but the Frequency is Dependent. Therefore VI
As the output is sinewave when in normal mode independent of the load, then the first letter is "S"
As the output has a low harmonic content when on battery, the second letter is "S" or "X", depending upon the quality of the inverter. Good quality systems will be "S".
As the voltage disappears momentarily when transition to battery, the first number is 3
The second two numbers depend upon the quality of the inverter, but we will assume sinewave inverters to be 1 & 1

The unit is therefore designated VI SS 311

4. An "Online" UPS outputs a sine wave from a good quality inverter. There is a delay of around 4ms when the unit transitions from inverter to bypass

As the output waveform is derived from the inverter at all times the output voltage and frequency are independent hence the unit is designated VFI
As the output is sinewave when in normal mode independent of the load, then the first letter is "S"
As the output has a low harmonic content when on battery, the second letter is "S" or "X", depending upon the quality of the inverter. Good quality systems will be "S".
As the voltage does not change when transitioning to battery, the first number is 1
The second two numbers depend upon the quality of the inverter, but we will assume 1 & 1

The unit is therefore designated VFI SS 111

Authored: Tony Bell BEng MIET 21 September 2009