Ihis paper descrites a new control methcd for a high-frequency link inverter using cycloconverter techniques a d discusses its cutput voltage characteristics.In t h i s mthcd, the cyclmverter ccnverts a high frequency voltage to a low frequency voltage by operating in three mcdes: positive rectifying d e , negative rectifying d e and free-&eeling mode. Pulse width dulation (€'"I control is performed at the cycloconverter.Numerical analysis and experiments show that the cutput voltage can be proportionally controlled by a reference voltage and that the cut@ i-mmmics can be decreased to a sufficient low level.A surge reduction circuit is presented for the inverter. This circuit can effectively reduce the switching surge. High ccnversion efficiency of over 90% is obtained under an output pxer of 1 kW. 1.In recent years, m y low prw uninterruptible power supplies (UPSs) of less than 5 kVA have been used to protect quipnent such as p e r m 1 cnnputers, word processors and loa1 area network terminals, fran failures and tenprary disturbances of the cannercia1 AC p e r supply. As these upss are often installed in offices, decreasing in size and weight of UPSs has teccme an iIIprtant goal.The size and weight of a UPS can be reduced by using a high-frequency link inverter, in which the l w frequency transformer is replaced by a high frequency one using high frequency switching techniques. Conventional highfrequency link inverters use three powerconversion stages: a Cc to high-frequency AC cmversion stage, a high-frequency AC to CC conversion stage and a Dc to lar-frequency AC CUIversion stage. Since these omversion stases are cawcted in cascade, the Conversion loss becanes large.The number of conversion stages can be decreased by utilizing cyclaxxlverter techni attain a high-frequency link inverter m' Fs). l h i s papr descrites a new m t r o l methd for a high frequency link inverter using cycloconverter techniques, and discusses its output voltage characteristics. CIRCUIT m G € i R A T I a AND CPERATICN Circuit OxfiqurationThe basic circuit configuration of the high-flink inverter is sham in Fig. 1. ' Ihe main circuit is rrmposed of a prinary inverter circuit, a high-frequency transforner, a cyclooomrerter circuit and an AC filter. S5 -,S are bidirecti-1 ordoff switches thraqh whicfl current can f l w in both directions. 'Ihe block diagram of the m t r o l circuit is Skmn in Fig. 2 . This control circuit is canp e d of an oscillator (OSC), a FiM signal generation circuit and logic circuits for the prinary inverter and for the cycloaxlverter. All these circuits are s y n c h i z e d by the oscillator signal. Primry w cycloconverter AC Filter Imerter Transformer s -s . uidirecti-1 switcher 5 8' Fig. 1 Basic configuration of the high frequency link inverter. PWH signal generation circultFig. 2 Block diagram for the m t r o l circuit.
This paper reports a reliability evaluation method of power supply system with battery backup. When one evaluates the reliability of power supply system, the failure rate of conventional flooded batteries can be neglected because this type of battery is very reliable. There have been, however, some failures with valve-regulated lead-acid (VRLA) batteries losing their capacity within a few years after installation. So, it is necessary to clarify the power supply system reliability evaluation method that consider battery failure. First, by analyzing the distribution curve of operating time before failure using the Weibull plot method, it is shown that VRLA battery have a failure mode similar to that of common electronic components. Then, it is presented a reliability evaluation method that considers battery failure. This reliability can be evaluated by adding both unavailabilities within and outside of the battery reserve time. The former is obtained with the probabilities of the battery failing within the reserve time and of the power conversion block repair time not exceeding the battery reserve time. The latter is obtained with the probability of the power conversion block repair time exceeding the battery reserve time.
The introduction of sealed lead-acid batteries, which do not need refills of water, greatly reduced the amount of maintenance required. However, it is difficult to estimate the battery's deterioration because they are sealed.A useful battery test system for estimating the battery deterioration was developed in NIT and NIT Power and Wlilding Facilities Inc. It can measure the battery's capacity in less than 1 m without affecting telecomnunications equipnent or power equipment, is accurate to within lo%, and is compact, light, and easy to handle.In this system, the battery's internal resistance which is calculated from the transient voltage change at the battery's terminal, and current which flows through the circuit, is used to determine the extent of deterioration in the battery. The pulse width of the transient voltage was set to some hundreds microseconds from the mutual relationship between the voltage drop and the battery's capacity.A regression expression was developed using batteries with artificially accelerated deterioration, and a total of 250 sets of 200-Ah sealed lead acid batteries now in use were applied for field experiments. Then, this system was confirmed to be accurate at estimating the batteries' capacity within an error of lo%, according to the regression expression applied after analyzing the relationship between the internal resistance and the battery's capacity. Errors of less than 10% were achieved for every brand of battery.We also verified that neither telecmications equipment nor power equipment was affected by this measurement.The system has been introduced in our battery's maintenance operation and has shown its usefulness to find out deteriorated batteries with ease.
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