Making the Right Connections when Communicating to your Motor Drive Applications

Making the Right Connections when Communicating to your Motor Drive Applications

by Danail Baylov

The previous blog in the series unveiled the mastermind behind the motor drive application: the main controller. Today, we’re diving into the critical role that connectivity plays. To send desired control inputs to a motor drive from the main system controller (typically a programmable logic controller (PLC)) requires that the system be network connected. As well as control inputs, a drive has many parameters to be configured and parametrized by the user.

From the motor drive the user/control system may need to gather live values, such as torque, current, speed, position, and set slopes and units and many more parameters. All of these are communicated over the external interface as highlighted in Figure 1. In broad terms, greater drive connectivity, especially Ethernet-based connectivity is seen as a really important factor in the digitalization of the automation industry since it potentially enables visibility and network access to every single end device in an automation system.

Figure 1: Detailed Variable Speed Drive Architecture

Organizations such as ODVA, PI North America and EtherCAT Technology Group help to standardize motor-drive communications by defining protocols such as EtherNet/IP, PROFIBUS/PROFINET and EtherCAT. These represent the most common protocols used in industrial automation today [1]. The most common physical communication layer types are serial links such as RS-485 or RS-422 and Ethernet. The protocols are built on top of these two physical layers. So which protocol should you choose for your connectivity solution? Let’s break down the main facts for PROFIBUS/PROFINET,  EtherNet/IP and EtherCAT and decide from there.

PROFIBUS/PROFINET

PROFIBUS is the most widely used protocol over serial links (RS-485), and PROFINET uses Ethernet.  PROFIDRIVE is the standard “application profile” for drive technology that sits on top of the PROFIBUS and PROFINET communication systems, as illustrated in Figure 2.

 

Figure 2: PROFIDRIVE profile

A profile such as PROFIDRIVE defines application specific parameters and functions to make it easier to communicate over the network between similar devices such as motor drives [2]. PROFIDRIVE allows for the integration of standard drive and “motion control” functionality with PLC sequencing logic, including functions such as :

  • Motor-Current Control
  • Speed Control
  • Position Control
  • Path Interpolation
  • Logic Control

EtherNet/IP

EtherNet/IP is based on the standard Ethernet physical layer and enables a peer-to-peer connection that allows for the distribution of real-time motion control information among multiple controllers and drives using the Common Industrial Protocol (CIP). The drive application profile CIP MotionTm, as a part of CIP, is built on a common, standard Ethernet stack. This means that in addition to the Physical and Data Link layers defined in the IEEE-802.3 specification, CIP uses the standard Network and Transport layers typically deployed in general Ethernet applications. This allows for devices to easily interconnect using standard switches, routers and other infrastructure components. The CIP MotionTm peer-to-peer connection is designed to transmit high-speed motion data from a producing controller or device to multiple consuming controllers or devices over a single multicast connection [3].

EtherCAT

EtherCAT is a real-time Industrial Ethernet technology originally developed by Beckhoff Automation. The focus during the development of EtherCAT was on short cycle times (≤ 100 µs), low jitter for accurate synchronization (≤ 1 µs) and low hardware costs.  EtherCAT embeds its payload in a standard Ethernet frame. Since the EtherCAT protocol is optimized for short cyclic process data, bulky protocol stacks, such as TCP/IP or UDP/IP, can be eliminated. In applications with spatially distributed processes that require simultaneous action, precise synchronization is particularly important. In contrast to completely synchronous communication, where communication errors have an immediate impact on quality, distributed synchronized clocks have a high degree of tolerance for jitter in the communication system. Therefore, the EtherCAT solution for synchronizing nodes is based on these distributed clocks (DC) [4]. CAN over EtherCAT (CoE) and specifically the CiA 402 profile is the most popular EtherCAT application profile used in motor drives. With the CoE protocol, EtherCAT provides the same communication mechanisms as in CANopenR Standard EN 50325-4: object dictionary, mapping of process data objects (PDO) and service data objects (SDO). Even the network management is similar. This makes it possible to implement EtherCAT with minimal effort in devices that were previously outfitted with CANopen, and large portions of the CANopen firmware can even be reused. The device profiles, such as the CiA 402 drive profile, can also be reused for EtherCAT.

Which Protocol Comes Out on Top?

The following table compares the three communication protocols highlighted in this blog. Each have their strengths and application specific features and the table below shows some typical supporting products from ADI which cater for all the protocols [5].

Protocol

Motor Drive Application

Use Cases/Features

ADI Supporting Products

EtherCAT

CiA 402

EtherCAT is optimised for fast cycle times down to <50us where tight synchronization is needed -  most popular in servo drives

ADIN1200

ADIN1300

FIDO5200

ADIN2299

MAX14942

ProfiNET/ProfiBUS

ProfiDrive

ProfiNET has the greatest market share and has connectivity to a very wide range of other automation hardware and infrastructure, especially devices from Siemens.

Ethernet I/P

CIP Motion

Ethernet I/P has the most transparent capability for use with other Ethernet traffic and systems, and is dominant in USA systems. It generally does not allow for sub-ms cycle times like EtherCAT and Profinet IRT.

 The next blog in this series will discuss how cybersecurity protection can be applied to the communication and control blocks.

 

References

[1] “Industrial Communications Report – 2023 Analysis”, Omdia

[2] PROFIdrive - The Leading Drive Control Profile: PROFINET

[3] CIP MotionTm | Common Industrial Protocol | ODVA Technologies

[4] EtherCAT Technology Group | HOME

[5] Industrial Ethernet Solutions from Analog Devices