What is a Motor Drive?

Defining a drive can be a bit tricky. Some drives are wholly incorporated into the controller, so that the profile generation takes place in the controller as well as the torque command for the motor. On the other hand, a drive can also refer to the specific power electronic circuitry needed to drive the motor. Electric motors that drive industrial machines need some way to control motor speed. And at its most basic level, a motor drive controls the speed of the motor.

Some manufacturers refer to a controller and motor together as a drive system. However, from the electrical side of things, the drive is often specifically the electrical components that make up the variable frequency inverter itself. So drives are the interface between the control signals and the motor and include power electronic devices such as SCRs (silicon controlled rectifiers), transistors, and thyristors.

Matching the correct drive to the type of motor in an application is critical for getting the best fit for torque, speed, and efficiency. There are a wide range of drives available depending on the needs of the specific application and motor type. In general though, drive types typically fall into two categories; dc and ac drives.

DC drives control dc motors. A basic dc drive is similar in operation to an ac drive in that the drive controls the speed of the motor. For dc motor control, a common method is a thyristor-based control circuit. These circuits consist of a thyristor bridge circuit that rectifies ac into dc for the motor armature. And varying the voltage to the armature controls the motor’s speed.

AC drives
AC drives control ac motors, such as induction motors. These drives are sometimes known as variable frequency drives or inverters. AC drives convert ac to dc and then using a range of different switching techniques generate variable voltage and frequency outputs to drive the motor.

An adjustable speed drive is a general term used sometimes interchangeably with variable speed drive or variable frequency drive. Again, from an electrical perspective, all of these ultimately refer to the frequency converter circuitry.

An ac motor’s speed is determined by the number of poles and the frequency. Thus, as frequency is adjusted the motor’s speed can be controlled as well. A common way to control frequency is by the use of pulse width modulation (or PWM). A PWM drive sends pulsed inputs to a motor and by modulating the pulse width, making it either narrower or wider, increases or decreases the average dc voltage seen by the motor.

Another powerful kind of drive function is known as regenerative braking or regen braking. This is a way of stopping a motor’s rotation by using the same solid-state components that control the motor’s voltage. The energy generated from braking can be channeled back into the ac mains or into filter capacitors. Advantages of regen drives include the ability to run a motor in either forward or reverse direction without having to physically switch the polarity of the motor leads and without the need for reversing contactors or switches.

Hitachi Introduces High Performance AC Drive Model

Hitachi America, Ltd., Industrial Components & Equipment Division, announced the new SJ700-2200HFU2 model inverter, with a 440 A output current capability. This new model fills in the gap at 300-350 hp in the SJ700 series, which now completely covers the range from ½ to 600 hp.

The SJ700 significantly expands on the performance, capabilities and functions of its predecessor, the SJ300. Hitachi reasserts its technological leadership with an improved vector control algorithm and auto-tuning function that enables the open-loop SJ700 (SLV) to develop more than 200% starting torque at 0.3 Hz. Using Hitachi’s unique “0 Hz Domain” open-loop control mode, the SJ700 can develop 150% torque near 0 Hz, ideal for vertical lift applications. In closed-loop mode with encoder feedback, the SJ700 performance is unmatched, delivering in excess of 100% torque at 0 Hz.

Another major new element in the SJ700 is Hitachi’s EzSQ (Easy Sequence) built-in programming function. It’s like having a PLC inside the inverter! In many cases, the need for a separate PLC can be eliminated. The user develops EzSQ programs on a PC, and then downloads them to the inverter using the simple-to-use configuration/programming software provided at no charge.

The SJ700 can deliver true servo-like position control when mated with a general-purpose induction motor and encoder, offering a low-cost motion control alternative. The SJ700, given a position command, speed command, and acceleration/deceleration times, can move the motor shaft from position A to position B following the defined profile and then maintain the shaft in “servo lock” status.

Hitachi has added other new features into the SJ700, such as patented micro-surge voltage suppression (to protect the motor winding insulation), advance trip avoidance functions, configurable sink/source logic on I/O, built-in dynamic braking circuit in models up to 30 hp (22 kW), built-in EMC filter up to 75 hp (55 kW).

The SJ700 also includes built-in RS485 Modbus/RTU communication, and options for other communications networks, such as Ethernet Modbus/TCP, DeviceNet, Profibus and LonWorks. Others, such as Ethernet/IP are in the works. The SJ700 can be configured via the front-mounted keypad or using Hitachi’s ProDrive PC-based software.

Designed to be a product for the global market, the SJ700 carries CE, UL, cUL and c-Tick marks, and is RoHS compliant.

Hitachi
www.hitachi.com

Emsflower precision control in greenhouses by Riwo Engineering

Emsflower currently has around 26 hectares of greenhouse and grows more than 500 million plants every year. Its problem on how to minimize costs in automation system for plant handling and watering was solved by automation provider Riwo Engineering, along with the Control Techniques Drive Center.

Riwo Engineering’s new automation system had to encompass spraying and pest control, watering, autonomous function of individual sections and central control, precise positioning overruns of 250m, the transport of plants, and the means to transport water and power along 150m. This system is easy to use and all at a limited cost.

The system is composed of trolleys with plastic wheels that run on overhead rails along every 8m-wide greenhouse bay. The two wheels placed on each trolley are powered by asynchronous motors with encoders controlled by Control Techniques’ 1,5kW Unidrive SP AC drives.

The modules and trolleys, powered by Unidrive SP drives from Control Techniques, communicate through CT-Net along with the master drive and thence with the master computer. CT-Net enables several drives to be connected into a master, while the onboard programming allows the required degree of repeatability and accuracy to be reached. Its open structure, which is based on the Modbus protocol, provides the master with a low cost interface. Control Techniques’ Unidrive SP is an advanced “solutions platform” AC drive, which is configurable into five operating modes – closed and open loop, vector, regenerating and servo modes – compatible with standard networks that is configurable for all types of AC motors such as linear motors and accepts 14 position feedback protocols.

Allen-Bradley PowerFlex 753 AC Drive from Rockwell Automation

MILWAUKEE, WI — The new Allen-Bradley PowerFlex 753 AC drive from Rockwell Automation provides machine builders and manufacturers with the versatile motor control they need for general-purpose applications. Designed to meet global user needs, the drive supports multiple languages and complies with global standards and certifications. The second release in the PowerFlex 750 series, the PowerFlex 753 drive is suited for many industries and applications, including fans, pumps and conveyors.

Like the PowerFlex 755 AC drive, the PowerFlex 753 AC drive offers many control hardware options. The DeviceLogix control technology helps meet requirements for stand-alone applications by giving users control flexibility to combine inputs and/or outputs, as well as local logic functions, to determine the drive’s behavior. The drive also helps manufacturers minimize downtime because users can configure the drive to provide advanced notification of operating data on cooling fans, I/O relay cycles, motor run-time hours and potential fault warnings. Additionally, Embedded Safe Torque-Off and Safe-Speed Monitoring options help customers reduce overall system costs while helping to protect personnel and equipment, and improve productivity.

Engineers designed the PowerFlex 750 series with a slot-based mechanical architecture that allows customers to tailor the drive with as few or as many options – such as I/O, feedback, safety and communications– as their application requires. The PowerFlex 753 and PowerFlex 755 drives share these hardware options, which help customers reduce inventory. The PowerFlex 753 drive is available in power ranges from 0.75 to 250 kW or 1 to 350 Hp at 400/480V AC and 540/650V DC input.

Rockwell Automation, Inc.
www.ab.com/drives/powerflex/755

Lenze-AC Tech Announces EtherNet/IP for SMVector

UXBRIDGE, MA – Lenze-AC Tech announces the release of EtherNet/IP as an optional communication protocol for the SMVector Drive. According to Mike Bailey, Product Sales Manager at Lenze-AC Tech, the SMVector AC Drive can seamlessly operate on an EtherNet/IP network with the addition of a simple plug-in communication module. “Other network protocols are also available as option modules including CANopen, DeviceNet, Profibus and Modbus RS-485,” states Bailey.

EtherNet/IP is a member of the DeviceNet and ControlNet family of Common Industrial Protocols (CIP) developed by Allen-Bradley (Rockwell Automation – ROK). As a member of the CIP family, EtherNet/IP can utilize the same set of pre-defined common objects, thus making communication between devices from different manufacturers much easier.

According to Lenze-AC Tech company officials, Lenze-AC Tech worked together with Allen-Bradley engineers to ensure complete product compatibility. “We first added EtherNet/IP to our PositionServo Drive and since then, our customers have been looking for EtherNet/IP for their AC Drive Solutions,” says Bailey, and he adds, “Allen-Bradley remains the largest implementer of EtherNet/IP, with most applications in the packaging and automotive markets; providing Allen-Bradley compatibility and multiple communication options for all of our products allows our customers to choose the fieldbus that best fits their automation application as well as their physical network.” Bailey explains that EtherNet/IP is a popular industrial network solution because it can support a nearly unlimited amount of nodes, can be used on a single point connection for configuration and control and permits devices to send and receive messages simultaneously.

Lenze-AC Tech
www.lenze-actech.com

VLT® Micro Variable Frequency Drives

LOVES PARK, IL – Danfoss Drives’ VLT® Micro Drive is now available in an M4 frame size covering the three-phase 380 – 480 VAC, 15 – 20 HP range. The M4 is just 250mm tall (292mm with flange) x 125mm wide x 241mm deep. They feature conformal coated PCBs per IEC 60721-3-3, class 3C3, and provide serial communication via RS 485 Modbus RTU and FC protocols. A detachable Local Control Panel (LCP) with or without a potentiometer, an LCP copy function, as well as a panel-front mounting kit for the LCP, all facilitate ease of use. In addition to the new frame size, VLT Micro Drives are also available in single-phase 200 – 240 VAC, 0.25 – 2 HP; three-phase 200 – 240 VAC, ? – 2 HP; and three-phase 380 – 480 VAC, 0.5 – 3 HP power range configurations.

The VLT Micro Drive includes a number of features that provide real, tangible benefits to users in industrial appliance, water and HVAC applications, as well as to OEM machine builders. The drive offers true side-by-side mounting without any derating due to its compact book-style design. An Automatic Energy Optimizer function allows the drive to consume less energy while the Automatic Motor Adaptation feature leverages the motor’s full operating potential. Users will also benefit from up to 150% more torque for up to a full minute, eliminating the need to oversize the drive.

The extremely compact VLT® Micro Drive provides IP20 protection even without the terminal cover. It can be commissioned in minutes to perform even complex operations. Approximately 100 parameters can be set to optimize energy efficiency and operation. A “flying start” feature provides more uptime while an electronic thermal relay eliminates the need for external motor protection. A built-in RFI filter saves on cost and space. The VLT® Micro Drive also features a smart logic controller – a simple yet clever way to seamlessly integrate the drive and motor for optimum application performance. This feature allows users to program the controller to react on virtually any event, often eliminating the need for a PLC.

Additional features include built-in AC and DC brake functions that help the drive transform kinetic energy from the application into braking power, intelligent heat management and coated electronics for maximized drive reliability and life, and the ability to copy settings via a local control panel (LCP) to easily set up multiple drives.

www.danfossdrives.com

Rockwell Launches the New Allen-Bradley PowerFlex 755 AC Drive

MILWAUKEE, WI — Representing the first drive from the new Allen-Bradley PowerFlex 750 series, the PowerFlex 755 AC drive meets global user needs for versatile motor control, integration ease and high performance to help increase productivity. Available in power ranges from 7.5 to 250 kW or 10 to 350 hp at 400/480V AC and 540/650V DC input, the PowerFlex 755 AC drive supports multiple languages, meets global standards and certifications, and is suited for many industries, including converting, automotive, machinery, food and beverage, material handling, metals, mining, and tire and rubber.

The PowerFlex 755 AC drive offers customers more versatility than any other drive in its class in terms of motor control and supporting control hardware options. Examples include:

•To adapt drive control to specific application requirements, engineers embedded Allen-Bradley
DeviceLogix control in the drive. This can give users control flexibility to combine inputs and/or
outputs and local logic functions to determine the drive’s behavior.
•To enable data-driven decisions, embedded Ethernet allows users to easily configure, control and
collect drive data over EtherNet/IP networks.
•To minimize downtime, users can configure the drive to provide advanced notification of operating
data on cooling fans, I/O relay cycles, motor run-time hours and potential fault warnings.
•Embedded Safe Torque-Off and Safe-Speed Monitoring safety options help customers reduce
overall system costs while helping to protect personnel and equipment, and improve productivity.

Engineers designed the PowerFlex 755 AC drive with a slot-based mechanical architecture that allows customers to tailor the drive with as few or as many options – I/O, feedback, safety, communications and auxiliary control power – as their application requires.

www.rockwellautomation.com