Studies on the perfomances of parallel-running UPS systems.

UPS（不间断电源）系统使计算机、通信或医疗系统在设备主电源受到干扰和中断的情况下仍能持续地提供电能。为了增加系统的功率容量，ups经常并联使用。本课题详细研究了负载电容滤波整流器的并联UPS系统的性能，并基于状态空间方法从理论上阐明了系统各参数对流经UPS的交叉电流以及有功、无功功率的影响。结果表明，随着各个ups电源电压的幅值和相位的不同，交叉电流也随之增大，而交叉电流的增大使得整个系统的无功功率增大，从而降低了功率因数。结果还表明，ups输出滤波器中的电容对交叉电流有相当大的影响。提出了一种新的带观测器和压降补偿的数字控制UPS控制算法，与传统的带附加前馈环的PID控制系统相比，该控制方法获得了良好的电压波形。最后提出了一种新的抑制系统交叉电流的算法。

The UPS (uninterruptible power supply) systems keep computers, communication, or medical systems continuously supplied with electric energy in spite of disturbances and interruptions in the primary power supply to the facilities. In order to increase power capacity of the system UPSs are often used in parallel.In this project, the performances of a parallel-running UPS system loaded with a capacitor-filtered rectifier are investigated in detail, and the effects of various parameters of the system on the cross current, which circulates through the UPSs, as well as the active and reactive powers are theoretically clarified based on the state space method. It is shown that the cross current increases with the difference in the magnitudes and phases of the source voltages of the individual UPSs, and this increase in the cross current makes the reactive power of the whole system increase, reducing the power factor. It is also shown that there is a considerable effect of the capacitor in the output filter of the UPSs on the cross current. A new control algorithm with observer and voltage drop compensation for a digitally controlled UPS is then proposed, and it is shown that an excellent voltage waveform is obtained with this new control when compared with the system with conventional PID with additional feed-forward loop. A new algorithm for suppressing the cross current of the system is finally proposed.