Manufacturers and users of uninterruptible power supply have long noticed the cooperation between generator set and UPS, especially the adverse impact of current harmonic generated by rectifier on power supply system, such as voltage regulator of generator set and synchronous circuit of ups. Therefore, UPS system engineers designed the input filter and applied it to UPS, and successfully controlled the current harmonic in the application of ups. These filters play a key role in the compatibility between ups and generator set.

事实上所有的输入滤波器都使用电容器和电感来吸收UPS输入端 具破坏性的电流谐波。输入滤波器的设计考虑了UPS电路固有的和在满载情况下的 大可能的全部谐波畸变的百分比。大多数滤波器的另一个益处是提高带载UPS的输入功率因数。然而输入滤波器的应用带来的另一个后果是使UPS整体效率降低。绝大多数滤波器消耗1%左右的UPS功率。输入滤波器的设计一直在有利和不利因素之间寻求平衡。

In fact, all input filters use capacitors and inductors to absorb destructive current harmonics at the input of ups. The design of the input filter takes into account the percentage of all possible harmonic distortion inherent in the ups circuit and under full load. Another benefit of most filters is to improve the input power factor of on-board ups. However, another consequence of the application of input filter is to reduce the overall efficiency of ups. Most filters consume about 1% of UPS power. The design of input filter always seeks a balance between favorable and unfavorable factors.

为了尽可能提高UPS系统的效率，近期UPS工程师在输入滤波器的功耗方面做了改进。滤波器效率的提高，从很大程度上取决于将IGBT(绝缘门级晶体管)技术应用到UPS设计中。IGBT逆变器的高效率导致了对UPS的重新设计。输入滤波器可以吸收某些电流谐波，同时吸收很小一部分有功功率。总之，滤波器中感性因素对容性因素的比率降低了，UPS的体积变小了，效率提高了。然而新问题是UPS与发电机的兼容性又出现了，替代了老问题。

In order to improve the efficiency of UPS system as much as possible, UPS engineers have recently made improvements in the power consumption of input filter. The improvement of filter efficiency largely depends on the application of IGBT (insulated gate transistor) technology to UPS design. The high efficiency of IGBT inverter leads to the redesign of ups. The input filter can absorb some current harmonics and a small part of active power at the same time. In short, the ratio of inductive factor to capacitive factor in the filter is reduced, the volume of UPS is reduced and the efficiency is improved. However, the new problem is that the compatibility between ups and generator appears again, replacing the old problem.

功率因数的问题

Power factor problem

通常，人们把注意力放在UPS电源满载或接近满载情况下的工作状态。绝大多数工程师都能表述满载情况下的UPS工作特性，特别是输入滤波器的特性，然而很少有人对滤波器在空载或接近空载时的状况感兴趣。毕竟UPS及其电气系统在轻载状态下的电流谐波影响很小。然而，UPS空载时的工作参数，特别是输入功率因数对于UPS与发电机的兼容性相当重要。

Usually, people pay attention to the working state of UPS under full load or near full load. Most engineers can describe the working characteristics of UPS under full load, especially the characteristics of input filter. However, few people are interested in the condition of filter under no-load or near no-load. After all, ups and its electrical system have little influence on current harmonics under light load. However, the working parameters of UPS under no-load, especially the input power factor, are very important for the compatibility between ups and generator.

新设计的输入滤波器，在减少电流谐波及提高满载情况下的功率因数方面有了较好的效果。但是在空载或很小负载情况下却衍生出一个电容性超前的极低的功率因数，特别是那些为了满足5% 大电流失真度的滤波器。一般情况下，当负载低于25%时大多数UPS系统的输入滤波器会导致明显的功率因数降低。尽管如此，输入功率因数却很少会低于30%，有些新的系统甚至已达到空载功率因数低于2%，接近于理想的容性负载。

The newly designed input filter has a good effect in reducing current harmonics and improving power factor under full load. However, in the case of no-load or very small load, a very low power factor with leading capacitance is derived, especially those filters that meet 5% high current distortion. In general, when the load is less than 25%, the input filter of most UPS systems will lead to significant power factor reduction. Nevertheless, the input power factor is rarely lower than 30%, and some new systems have even reached no-load power factor lower than 2%, which is close to the ideal capacitive load.

这种情况不影响UPS电源输出和关键负载，市电变压器和输配电系统也不受影响。

This situation will not affect the output of UPS power supply and key loads, and the municipal power transformer and transmission and distribution system will not be affected.

但发电机就不同了，发电机工程师知道：发电机带大容性负载时工作会不正常，当接入较低功率因数负载，典型的低于15%～20%容性时，由于系统失调，可能导致发电机停机。在市电停电后出现这种停机?应急发电机系统带动UPS系统负载将造成灾难性事故。

However, the generator is different. The generator engineer knows that the generator will not work normally when it is loaded with large capacitive load. When it is connected to a load with low power factor, typically lower than 15% ~ 20%, the generator may be shut down due to system imbalance. Such shutdown after mains power failure? The load of UPS system driven by emergency generator system will cause catastrophic accident.

由于下述两种原因停机给关键负载带来危险： ，发电机需要人工重启，并且必须在UPS电池放电结束前;第二，在停机前发电机可能引起系统的”过压”，它可能损坏电话设备、火警系统、监控网络甚至UPS模块。更糟糕的是，在事故发生后，很难区分责任，找出问题所在并予以纠正。UPS厂商说UPS系统测试完好，并指出其它地方相同的设备没有发生类似问题。发电机厂商说是负载的问题，无法调整发电机来解决问题。同时，用户工程师则说明他的规格要求，希望两个厂商相互兼容。要了解为何会发生事故及如何避免(或如何在关键应用中找出解决方案)，需要了解发电机与负载的工作关系。

Shutdown brings danger to key loads due to the following two reasons: the generator needs to be restarted manually and must be restarted before the discharge of UPS battery; Second, before shutdown, the generator may cause "overvoltage" of the system, which may damage telephone equipment, fire alarm system, monitoring network and even UPS module. Worse, after the accident, it is difficult to distinguish responsibilities, find out the problem and correct it. The ups manufacturer said that the UPS system was tested in good condition and pointed out that there were no similar problems with the same equipment in other places. The generator manufacturer said it was a load problem and it was impossible to adjust the generator to solve the problem. At the same time, the user engineer explained his specification requirements and hoped that the two manufacturers would be compatible with each other. To understand why accidents occur and how to avoid them (or how to find solutions in key applications), we first need to understand the working relationship between generator and load.

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