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Product category: DC/AC Inverters
News Release from: Siemens Automation and Drives | Subject: Cirrus Technologies
Edited by the Electronicstalk Editorial Team on 9 October 2001

Motor drives get rolling roads running

Automotive equipment supplier Cirrus Technologies has teamed up with Siemens Automation and Drives to produce a new generation of rolling roads for use in end of line manufacturing applications

Automotive equipment supplier Cirrus Technologies has teamed up with Siemens Automation and Drives to produce a new generation of rolling roads for use in end of line manufacturing applications and facilities for vehicle development. The Siemens drives used in this application are both efficient and intelligent.

When the driven wheels of the vehicle rotate the rollers, motors act as generators producing electricity which is recovered by the variable speed drive system.

As the drives are arranged in a common DC bus configuration the recovered power contributes to other demands of the rig with any surplus energy being fed back into the mains supply.

This new design of road uses a single large roller, rather than dual rollers, for each vehicle wheel.

This innovative principle whereby each of the four rollers are independently driven, is expected to become widely used in automotive assembly plants as well as research and development facilities.

The Siemens drive system was specifically chosen for this application as it provides the highest achievable dynamic response.

A feature essential for this new generation of road rigs.

The low inertia characteristics of the Siemens 1PH7 Square Frame Motors ensures that low effort is required for acceleration whilst high power density delivers ensures a smaller overall size.

The space saving which has been achieved in the design has proved invaluable at most sites.

Rolling roads have to accommodate an increasingly complex variety of test conditions for the widest possible range of vehicles.

The independent roller concept provides the flexibility needed for individual wheel assessment whilst operating a mixed build of vehicles, each having very different characteristics.

Unhindered by track or wheelbase limitations, the individual roller performance required for a specific test is computed separately by each Masterdrive unit.

The integral intelligence of the Siemens drives is essential to producing the quality performance needed at each roller.

For each test run, operators enter the basic vehicle specification, the control system calculates the test constants and the intelligent drives then assess the motor performance needed.

A vector control algorithm solves the wheel specific problems arising from changes in air resistance, mass, speed, road friction and other variants.

The algorithm is based on a complex road load equation, which includes the rolling road's own characteristics as well as vehicle and ambient condition variants.

A scaled torque output instruction is delivered to each drive where the vector control of each Simovert Masterdrive ensures precise compliance with the algorithm output.

Drives incorporate comprehensive diagnostic aids for monitoring, self-calibration and immediate fault recognition; closed loop vector control is used to deliver the precise performance required of each roller.

There is continuous communication between all drives using a dedicated Siemens Simolink optical fibre bus and, where matched performance is required from two or four rollers, one drive acts as the master control.

The master roller for front wheel drive (FWD) and four wheel drive (4WD) vehicles is the front left with the back right used for rear wheel drive (RWD) units.

A Siemens Simatic S7-300 PLC (Programmable Controller) in conjunction with the Cirrus Stratus4 vehicle test system provides effective management of the total system capabilities.

The control package developed by Siemens and Cirrus enables a variety of test parameters, crucial to car safety, to be measured, including dynamic stability control, traction and cruise control.

The built in human-machine interface (HMI) enables operators to check and verify system control functions without leaving the rig.

The HMI and PLC communicate with the Siemens drives by way of a standard Profibus communication link within the rig whilst an Ethernet connection is used to communicate with the Stratus4 test computer and the remotely located, supervisory control systems.

Compared with more conventional designs this new generation of rolling roads delivers massive operational flexibility, the advantages of which have already been recognised by vehicle manufacturers.

Advantages to users include lower power consumption, a reduced mounting depth, less moving parts and the ability to accurately simulate any road condition at each vehicle wheel.

The new unit has no clutches, brakes or drive-train and consequently maintenance is much reduced.

In addition, the system precision is so high that customers are reporting that separate measurement equipment, such as that needed for brake tests and speedometer calibration, is no longer necessary.

The system flexibility extends to all vehicles, be they of FWD, RWD or 4WD format.

Low operating costs result from the reduced power consumption of the frequency controlled AC drives, a large proportion of which is due to the surplus energy recovered from vehicle driven rollers.

This 'free' electricity is distributed to other points of demand using the common DC bus.

Any surplus power is fed back into the mains supply through the active front end (AFE) which serves all drives.

The return of power to the mains supply, which is an integral part of the equipment package, is only possible because the low level of harmonic currents, and resulting voltage distortion, transmitted into the supply network.

With multiple-sourced, sophisticated control systems in use throughout modern industry, the harmonic characteristics of individual items of plant are a serious issue.

Harmonic pollution of the electricity supply can seriously effect the performance of equipment both on-site and off-site.

For this reason Siemens drives with active front end (clean power technology) already have the lowest harmonic profile, allowing it to meet the most stringent national, European and US standards and regulations.

This new rolling road development by Cirrus and Siemens provides the enhanced capability which operators need to satisfy the increasing demands of legislation and specific dynamic tests.

The objective measurements of quality and performance also add to the services now expected by vehicle purchasers many of whom will soon be able to appreciate first hand, the qualities of this package.

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