Studies on the perfomances of parallel-running UPS systems.

UPS（不间断电源）系统保持计算机、通信或医疗系统连续地供应电能，而不管设施的主电源的干扰和中断。为了提高系统的功率容量，UPS常被并联使用，本课题详细研究了带电容滤波整流器的UPS并联运行系统的性能，并基于状态空间法从理论上阐明了系统各参数对流经UPS的交叉电流、有功功率和无功功率的影响。结果表明，交叉电流的增加与个别UPS的电源电压的幅度和相位的差异，这种增加的交叉电流使整个系统的无功功率增加，降低功率因数。它还表明，有一个相当大的影响电容器的UPS的输出滤波器上的交叉电流。提出了一种带观测器和电压降补偿的数字控制UPS新控制算法，并与带前馈环节的常规PID控制系统进行了比较，结果表明，该控制算法能获得良好的电压波形。最后提出了一种抑制系统交叉电流的新算法。

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.