Standard EN 50598: Energy Efficiency with Electric Drive Systems

The energy efficiency of a drive system is significantly more challenging than simply optimising the efficiencies of the individual components. The new European standard EN 50598 takes this into account and describes in EN 50598 Part 2 how to calculate the energy efficiency of a complete drive module (CDM = variable speed drive) and the power drive system (PDS, CMD + motor). Standardisation is thus consistently progressing from the individual component to the entire drive system.  
 
The standard consists of three parts:

Part 1: General requirements for setting energy efficiency standards for power driven equipment using the extended product approach and semi analytic model

This part describes the responsibilities and tasks of the different interest groups using this standard as well as the necessary data flow.

Part 2: Energy efficiency indicators for power drive systems and motor starters 
In this part, energy-efficiency indicators are specified for power drive systems, motor starters and complete drive modules used for electrically driven work machines in the power range of 0.12 kW to 1000 kW.
  • Definition of efficiency classes for motor systems and CDMs
  • Definition of 8 operating points
  • Methods for determination (measurement and calculation) of losses in the 8 operating points of a complete motor system and its components
  • Measurement methods for CDMs
  • Losses of the reference motor, the reference CDM and the reference PDS in the predefined 8 operating points 


Part 3: Quantitative eco design approach through life cycle assessment including product category rules and the content of environmental declarations

In this part of the standard the ecodesign topic is dealt with and essential environmental aspects for product design of motor systems (motor starters / variable speed drives, motor) are defined.

Efficiency classes

Efficiency classes of motors        

The standard methods for measurement of losses and efficiency of motors are described in IEC 60034-2. The IE-classes at 100 per cent load (100 per cent speed, 100 per cent torque) for line fed motors are defined in IEC 60034-30-1.
 

Efficiency classes of variable speed drives

To avoid overmodulation and for reasons of comparability the efficiency classes of complete drive modules are defined for the 90/100 operating point (100 per cent current, 90 per cent motor frequency). The standard EN 50598-2 defines the relative losses (in relation to the nominal output power) of CDMs for the efficiency classes as IE0 to IE2. Compared to a reference CDM (defined in the standard as IE1) the IE2 CDM has at least 25 per cent less and the IE0 at least 25 per cent more losses.

Efficiency classes of electric drive systems (power drive systems, PDS)

The efficiency classes for electric drive systems are defined for 100 per cent torque and 100 per cent motor speed. The standard EN 50598-2 defines the relative losses of the drive system for efficiency classes IES0 to IES2. Compared to a reference PDS (defined as IES1 in the standard) the IES2 system has at least 20 per cent less and the IES0 at least 20 per cent more losses.
 
The addition of efficiency classes is not possible, an IE1 variable speed drive and IE1 motor doesn‘t automatically result in an IES2 for the complete system. Higher ordinal numbers in IE(S) class in general mean reduced losses.

Determination of losses

In order to simplify the effort of measurements and calculations the losses of the power drive systems and components motor, CDM and softstarter are defined in 8 operation points in the speed-torque-diagram. All common types of power-driven machines are covered (quadratic, constant, linear, hyperbolic torque characteristic).
 
As CDMs do not provide torque and speed, but voltage and current at the output, the losses of CDMs are defined in the torque current over motor stator frequency diagram.
 
The absolute losses of a power drive system are determined by addition of the respective absolute losses of the CDM, the motor and auxiliaries (e.g. input choke, DC link losses) in the 8 operating points. 

Determination of losses of a Power Drive System without available motor:

In this case the losses of a reference motor (3-phase asynchronous motor, 4-pole, efficiency class IE2, 50 Hz for converter feed) which are defined in the standard are used for calculating the losses of the PDS in the 8 operating points.
 

Determination of losses of a Power Drive Systems without available CDM:

In this case the losses of a reference CDM (400 V, efficiency class IE1) which are defined in the standard are used for calculating the losses of the PDS in the 8 operating points.