(Fig. 1a).
To ease the installation and reduce the wiring errors, a simple serial installation with merely two cores on the basis of the system bus can be used with ACTIVE inverters (Fig. 1b). Not only the reduction of the installation efforts, but also further benefits in application result.
Function
The system bus of the ACTIVE inverters is a CAN-based communication medium. It enables quick exchange of data between ACTIVE inverters as well as access to parameter data of all the ACTIVE inverters on the system bus from a system bus master.
The functionality of the system bus is closely based on the CANopen standard. The system bus has three PDO channels (Process Data Objects) for each ACTIVE inverter for quick exchange of process data. In addition, two SDO channels (Service Data Objects) exist for parameterisation.
Arbitrary data of the ACTIVE inverters can be transmitted via the three PDO channels, each with one transmission and one reception channel. This enables, for example, master/slave configurations and cascading with very little efforts, high precision and at high speed.
Each transmission channel and reception channel comprises 8 Bytes, which can be occupied at will with objects. This results in a very high flexibility for the various applications. The selection of the transmission objects and assignment of the reception objects is done simply with the VPlus visualisation software. No additional configuration tool is necessary.
SDO channel 1 is used for access to the parameters of the ACTIVE inverters on the system bus. This is done with the help of a field bus actuation in the master inverter. A controller can address all the ACTIVE inverters via one field bus actuation.
SDO channel 1 is reserved for a PC-based visualisation tool, enabling access to the parameterisation of all the ACTIVE inverters parallel to the operation of a control.
Fig. 2 shows the logical connections between ACTIVE inverters on the basis of the system bus in two-wire technique
Performance
The number of participants on the system bus is up to 64 ACTIVE inverters. The system bus can be operated with transmission rates of up to 1 MBaud and enables an effective useful data rate of 320 kBaud. In this way, the coupling of functions in ACTIVE inverters with real time behaviour is possible.
Benefits
Thanks to the use of the CAN technology with the reasonably priced construction elements available there, a favourable-cost component for the realisation of the system bus is available.
The VPlus visualisation software is used for commissioning, enabling the configuration of the system bus in the same way as the parameterisation of the functions in an ACTIVE inverter. The user is in an environment which is familiar to him. Thanks to clearly organised structures, the necessary parameters for the settings of the system bus are easy to see.
Only a few parameters need setting to produce a functional system.
With the possibility of transmitting the data existing in one ACTIVE inverter to further ACTIVE inverters, completely new approaches to the realisation of applications result. For example, analogue variables of an ACTIVE inverter can be transmitted to further appliances with all the devices receiving precisely the same data. The faults occurring in parallel connection of analogue inputs due to scanning errors and drift are eliminated. Actual figures of an ACTIVE inverter can be transmitted to other ACTIVE inverters as nominal figures. This enables simple realisation of, for example, gear functions and cascading.
If a field bus actuation is used in an ACTIVE inverter configured as a system bus master, all the inverters on the system bus can be addressed by it. In this way, a distinct reduction in costs is achieved by field bus components becoming superfluous.
Example of application
The example of application (Fig. 3) describes a real application from mechanical engineering. The entire configuration comprises six ACTIVE inverters, which fulfil various functions in the machine. A main drive works with two subsidiary drives in the form of an electronic gear. The nominal speed of the slave inverter is derived from the speed list figure of the master inverter and transmitted to the slave inverter via the system bus (PDO channel). In addition, there are three further subsidiary drives in the drive system. They are actuated by the machine controls via the master inverter and the system bus (SDO channel).
The entire parameterisation of all the ACTIVE inverters is done from the machine controls via the field bus actuation in the master inverter and the system bus.
These benefits result here:
• Use of only one RS485 field bus actuation instead of six.
• Avoidance of wiring for the reference frequency couplings of the electronic gear.
• All the drives can be reached centrally for the controls via the main drive.
