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KEB G6 VFD and Lenze i550 VFD Comparison

Jeff Kardell | January 18th, 2022

When searching for an open-loop VFD for your application, there are many options in the automation world. This blog post shows an in-depth comparison between the KEB Combivert G6 and the Lenze i550. Learn the commonalities and differences between the two products when it comes to communication options, input and output power options, functional safety, and more.


Comparing a Lenze i550 frequency inverter with the KEB G6 open loop Drive Side-by-side
Side-by-side comparison of Lenze’s i550 VFD line and KEB’s G6 Drives.


Target Applications 

The G6 and i550 are both open-loop VFDs, which means they can run three-phase induction motors without using an encoder or feedback device. They do this by managing the velocity of the motor through V/Hz and Sensorless Vector control. The G6 also supports SCL (synchronous-sensorless control), which controls AC PM (permanent magnet) servo motors without feedback for high-efficiency fan and pump applications. 

Typical open-loop applications include food production, packaging technology, conveyor and storage technology, pumps, and compressors. 


Communication Options 

Another key component is the type of fieldbus protocol that you are using to communicate with the PLC or HMI.   

The G6 VFD communication options include EtherCAT, VARAN, IO Link, and CANopen. While it is not compatible with EtherNET/IP, KEB supports this protocol in our S6 VFD series. 

The Lenze i550 VFD covers a broad range of communication options. It communicates over fieldbus protocols of CANopen, EtherCAT, EtherNET/IP, IO-Link, Modbus RTU, Modbus TCP, Powerlink, Profibus, and Profinet. 


Related Article: Ethernet/IP vs EtherCAT


Input and Output Power Options 

The input power is critical when choosing an open-loop VFD for your application.  Ensuring the end user’s facility has the correct power supply available to operate the VFD prevents issues from occurring during the initial install. 

KEB’s G6 drive has two options for input power, a 230V single-phase and a 400/480V three-phase power. In the 230V single-phase class, the G6 operates motors up to 2 HP. However, with a power supply of 400/480V three-phase, the G6 can control motors up to 40 HP. Any open-loop applications with motors larger than 40 HP and up to 600 HP will need to be run with KEB’s F6 series drive.  

The Lenze i550 has broader options of available input power. It differs from the G6 by having the option of 120V, single-phase power for controlling motors from 1/3rd HP to 1 ½ Hp.  In its offering of 230V power, the i550 accepts a power supply of 230V with one or three phases. With a 230V, single-phase supply, it operates motors ranging from 1/3rd HP to 3 Hp, and the 230V, three-phase power is 1/3rd HP to 7.5 Hp. With a power supply of 400/480V three-phase power, the Lenze i550 can control motors in the range of ½ Hp to 150 Hp. 


Available I/O 

Both the G6 and i550 have a large offering of I/O options. The table below shows the number of programmable digital inputs and outputs, analog inputs and outputs, and relays on each drive. 


Comparison Chart showing two open loop VFDs. Lenze i550 VFD vs KEB G6 Drive
Comparison of available I/O between the KEB G6 drive and the Lenze i550 VFD.


An advantage of the G6 is the additional digital inputs and relay. For example, the two relays could be programmed to control a brake and signal a fault on the VFD, or the additional digital inputs could trigger a jog function or error reset. 


Functional Safety  

In some applications, functional safety is a requirement. When choosing the VFD for your application, it’s important that it meets the required safety standards.   

KEB’s G6 VFDs come standard with an integrated 2-channel safety function Safe Torque Off (STO), according to category 3, EN ISO 13849-1 PL e / IEC EN 62061, SIL 3. These inputs are designed in a way that safety switchgear units with test pulse (OSSD signals) can be connected. The first channel switches off the pulse pattern of the control CPU, and the 2nd switches off the supply of the gate control of the IGBT’s in the driver.   

Related Article: What is Safe Torque Off?


Graph showing Safe Torque Off or STO functional safety feature in VFD applications
This graph shows Safe Torque Off (STO) functional safety available in VFD applications.


Additionally, the function SS1 (Safe Stop 1) can be covered together with an external safety timing relay. The drive is decelerated within a fixed time and is set to STO (stop category 1, EN 60204-1).


Graph showing Safe Stop 1 or SS1 safety feature in VFD applications
This graph shows the Safe Stop 1 (SS1) safety feature in VFD applications.


KEB’s G6 drives also offer SSM (Safe Speed Monitor) on devices with EtherCAT and IO-Link control. SSM with level f=0Hz is a TÜV-certified safety function that is used to quickly stop an inertia load and ensures the motor is stopped before providing an output back to the safety controller. It is commonly referred to as a safety gate or safety latch function where an operator is frequently opening an access door on the machine. It is unique in providing a safetycertified output for when the motor is being stopped, without the use of encoder feedback.

Find more information about SSM at this link: Drive Functional Safety for Machinery Doors, Gates, and Latches.   


Graph showing Safe Speed Monitor or f=0Hz safety feature in VFD applications
This graph shows the Safe Speed Monitor (SSM) feature in VFD applications.


For the Lenze i550 drive, functional safety is also available with the option to add Safe Torque Off (STO) to the configuration of the VFD. It is also in accordance with category 3, EN ISO 13849-1 PL e / IEC EN 62061, SIL 3. 


Dimensional Sizing 

Both the G6 and Lenze i550 drives come in a variety of housing sizes, mounting configurations, and heat sink options. Housing sizes and breakdowns based on motor size can be found at the links below. 


Additional Information 

Internal braking transistor 

  • The G6 and i550 have an internal braking transistor to allow the connection of an external braking resistor to help dissipate additional DC-bus voltage and convert it to heat. 

Internal EMC Filter 

  • KEB’s G6 VFDs have the option to be equipped with an internal EMC filter ready for installation, whose special property is minimum leakage current (<5 mA) against the earth and motor cable lengths up to 100m. 
  • Lenze’s i550 VFDs have an option to add an internal EMC filter to the drive, but it is not standard for all configurations. 

Protection Ratings 

  • Both VFDs have a standard protection rating of IP20. 

Motor Temperature Monitoring 

  • The G6 and i550 both include terminals to connect an external PTC thermistor or thermal contact for analysis of thermal signals of connected motors. Motor thermal protection is an essential component of a smart system that can monitor the internal temperature of a motor’s windings and prevent damage due to overheating. 



KEB’s G6 VFD is a suitable alternative to the Lenze i550 in nearly all open-loop applications.  Contact a KEB engineer today to discuss your application and a KEB solution. 

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