American Micronic Instruments

I. Introduction

Computer users and information managers in underdeveloped countries face unusual difficulties in trying to cope with the AC power problems. Among the problems are:

frequent blackouts due to unreliable electrical utility service;

1.	chronic brownouts (low voltage) due to undercapacity;
-	-
2.	generally poor quality of the power, in areas such as distortion, spike/noise, frequency, sags/surges and dropouts, especially when generators are used to supplement utility power.

Of course, these problems also exist in developed countries. However, in underdeveloped countries in Africa, South America and Asia, such power problems can occur so often as to cause unacceptable levels of computer down time and data loss. Uninterruptible power supply systems, which are designed to counter such power problems, also experience greater failure rates because of the severity and the frequency of the power problem. Therefore, providing UPS protection for underdeveloped countries poses a special challenge to UPS manufacturers.

II. Differences in UPS Requirements

A UPS designed for the developed countries (say the United States) will face the following difficulties when installed in an underdeveloped country. AMI designs special models to face the requirements of under developed countries.

1.	Because of frequent blackouts, the batteries in the UPS, whether online or standby, will be discharged and charged very often. Furthermore, because the duration of the blackout is usually longer than in developed countries, the batteries will be discharged deeper. These two factors combine to drastically reduce the expected lifetime of the battery. For example, a typical lead-acid battery will last for about 1,200 discharge/charge cycles when the depth discharge is 30% of battery capacity. However, when the depth of discharge is 50%, this number is reduced to 450. And when the depth of discharge is 100%, the number is reduced to below 200. A UPS in the U.S. may experience a 100% discharge/charge cycle about 5 to 10 times a year. In underdeveloped countries, this may occur almost every day, reducing the expected life of the UPS to less than a year.
-	-
2.	Because of the frequency of power disturbances, the power electronic circuitry in the UPS must work far more often and under greater stress. This is especially true for standby UPS systems, which must make the transfer to battery backup every time there is a power disturbance. But online systems must also work harder to cope with the chronic brownouts and blackouts.
-	-
3.	The batteries cannot be charged fully when the power disturbances occur so frequently. Consequently, the UPS cannot provide the rated backup time during each power disturbance. This can cause severe problems with computers that depend on the UPS to provide a minimum amount of time to shut down the system in an orderly manner.
-	-
4.	Frequency fluctuations in the power adds a whole new dimension of problems for the UPS to deal with, because in developed countries where the UPS systems are designed, the constancy of the AC power frequency is taken for granted. This may not be true in developed countries, especially when generators are used. The problems caused by frequency deviations may range from an increase in inverter/AC transitions to outright malfunctions.

III. Solutions for Reliable and Cost-effective UPS Protection

All the above problems with power quality provide UPS manufacturers with a difficult challenge in trying to design UPS systems for underdeveloped countries. It must be recognized that no UPS system can provide foolproof protection against all types of power problems, especially at a reasonable cost. To provide the best solution to power problems in underdeveloped countries requires an intelligent application of technology, coupled with an intimate familiarity with the nature of the problems. AMI’s UPS systems currently have the following features particularly useful in underdeveloped countries.

The ferroresonant design of these UPS systems make them particularly suitable for installations experiencing chronic brownouts, surges and sags. The automatic voltage regulation feature of these UPS systems can tolerate a wide range of input voltage, from +20% to –35% of nominal levels. For developed countries, it is not necessary to use the full range of the ferroresonant transformer. Besides, such large deviations from nominal levels usually indicate a severe power problem that must be fixed. However, in underdeveloped countries, the full range can be used for maximum benefit. In addition, the common surges, sags and spikes are smoothed out by the ferroresonant transformer.

Furthermore, since the inverter in these UPS systems works only when a power disturbance too severe for the ferroresonant transformer to handle occurs, the batteries and electronics are utilized for their maximum reliability and lifetime.

These UPSs with their sensitive detection circuitry, respond in less than 1 ms to power disturbances. However, in underdeveloped countries, such sensitivity can lead to frequent inverter/AC transfers that will reduce the lifetime of the battery and long-term reliability. However, the calibration of the thresholds, and the sensitivity of the detection circuitry, can be adjusted accordingly to minimize these transfers. Furthermore, these UPSs have an important hysteresis feature that can be very helpful in these situations. A hysteresis in the transfers is illustrated best by an example. Suppose a UPS (230V, 50Hz, 500VA unit) is calibrated to transfer to inverter mode at an input voltage of 200V. However, once the transfer to inverter is made, it will not transfer to AC until the input voltage exceeds about 208V. This margin of 8V is the hysteresis, and it can be reduced or increased, depending on the frequency of brownouts. This ensures increased reliability of the transfer electronics when the input voltage is hovering around 200V since the UPS will not be constantly switching back and forth between inverter and AC.

For underdeveloped countries, these UPSs can be best utilized by setting the brownout and overvoltage thresholds about 10% below and above their normal levels, and doubling the normal amount of hysteresis.

Fast Frequency Detection

Since all AMI UPS products currently manufactures synchronize the inverter output to the input AC, it becomes necessary to detect when the input frequency goes out of range of the phase detector, as can happen when power is provided by a miscalibrated generator or an unreliable utility. A UPS/Generator digital filter currently under development provides such detection in less than 1 cycle, much faster than conventional analog filters. When coupled with either a AMI standby or online UPS system, this filter will protect against both a too high or a too low frequency from damaging the computer or the UPS.

Improved Testing

To simulate the type of power problems encountered in underdeveloped countries requires more extensive testing of each UPS to ensure reliability. To this end, we have already added a number of tests and checks, including tests with an actual generator, to all units that are shipped to countries with known power problems. In addition, more tests are under study, including frequency, surge, dropouts, etc.

Improved Design

AMI is constantly striving to perfect the design of UPS systems. In UPS systems for underdeveloped countries, we are currently pursuing the following areas for improvement:

1.	Intelligent Adaptation to Local Environments. Since the power problems encountered in different countries and different installations are unique in many respects, the UPS is required to adapt its own operating parameters to match the normal power encountered in normal use, and only provide backup power when the power deviates significantly from these norms. For example, if the normal input voltage varies during the day due to air-conditioning usage, etc., the UPS will adapt its brownout and overvoltage thresholds to match the normal levels, as long as the equipment connected to the UPS could handle it. This will provide both maximum protection against power disturbances and unnecessary inverter/AC transfers.
-	-
2.	Advanced Battery Charging Methods. AMI is investigating sophisticated charging methods to both improve the lifetime of the battery under worst-case scenarios, and to reduce the amount of time required for full charge.

In conclusion, the power problems encountered in underdeveloped countries pose a special challenge to all UPS manufacturers. AMI’s current products have already undergone numerous improvements to meet the challenge, and will continue improving to solve even the most difficult problems.