Digital Control of Uninterruptible Power Supplies Based on Predictive Voltage and Current Regulators

The features of a digital control technique for uninterruptible power supplies (UPS’s) are described. The control is based on voltage and current predictive regulators, aiming to achieve a dead-beat type of response for the closed loop system. This way, the technique is able to achieve a good quality of dynamic performance, guaranteeing low distorted output voltage waveforms even in the presence of non-linear and highly distorting loads. The knowledge of the output filter parameters with a reasonable level of accuracy is the only data required to properly tune the controller. Besides, the only sensed quantities are the output voltage and the inverter output current. The controller also maintains the conventional multi-loop structure which, allowing the implementation of overcurrent protection for the power converter, is very often encountered in commercial UPS systems. The validity of the proposed strategy is demonstrated by means of simulation and experimental results referring to a single-phase UPS laboratory prototype (1 kVA). The digital controller is implemented by means of the connection of a ADSP21062 floating point DSP and of a ADMC401 motion control DSP, both by Analog Devices.