DC/DC-converters in parallel operation with digital load distribution control

The parallel operation of power supply circuits, especially in applications with higher power demand, has several advantages. One of the most important aspects is to improve the power system reliability and the operational redundancy by it. There is also a trend in producing standard power converter modules which can be connected in parallel to cover a wide power range. This significantly reduces the costs of development and existing systems can be extended easily. A main problem of the parallel operating power converters is to attain an accurate equalization of the modules' output currents. There are different solutions of this problem arising in literature. All these approaches try to reach this goal with a minimum of technical complexity in order to keep costs at a low level. In recent years the implementation of digital control concepts in switching power supply systems seems to be of growing interest. Digital control offers several possibilities: functions of communication can be embedded quite easily; control structures and parameters can be changed by modifying only the software; adaptive control systems are realizable; and complex control strategies become possible. In this paper, parallel operating DC/DC power converters are combined with a digital control unit, thus allowing a complex control strategy called load distribution control (LDC) possible. This new method of LDC is described in detail in the paper. Simulation results are presented as well as experimental verifications.