Modeling and analysis of shared/common DC bus operation of AC drives .1.

The Shared/Common bus operation of AC drives is becoming popular in many industrial applications due to it's advantages such as cost reduction, reduced space requirements, and improved reliability. Depending on the application requirements, there are presently two methods to interconnect DC buses of AC drives; Shared-bus and common-bus. Very little or no work has been done in analyzing the use of such system configurations in industrial applications. In a shared-bus configuration, complete drive units are connected through dc bus fuses to form a common bus. These schemes require individual devices for protection and control, and still may cause bus fuse failures due to poor coordination among each drive's DC bus precharge circuits consisting of different converter front ends, such as diode and SCR. During the normal motoring operation of such systems, the proper load sharing of input converters must also be ensured, not to cause any device failures or nuisance tripping by exceeding the front end converter ratings. This may also require additional hardware between positive and negative busses depending upon the precharge configurations. The common bus drive systems used in a coordinated system can also be beneficial to user by using regenerative energy of larger drives to supply the other small drives which are motoring. The reliability of such operations must be ensured by analyzing the system and properly selecting the bus fuse sizes. The other version of common bus configuration is the concept of one large converter supplying many inverters to reduce the number of supporting components. However, as the number of parallel drives increases it is difficult to select the proper device ratings by testing. Therefore, an analytical method to determine the way of connecting the system with right components is an essential to the system integrator. This paper analyzes the different shared/common bus configurations in precharging, motoring and regenerating, and addresses how to select the components, and connect the system together to ensure a trouble free operation, using PSpice simulations.