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  • Electrical /

    Uninterruptible power systems

    The mains supply are not stable for a number of objective and subjective reasons. Deviations size or shape of the applied voltage is called distortion or interference. These distortions have different effects on electrical work and may even damage the unit. Since itself modern electronic equipment is expensive and the most susceptible to the damaging effects of noise on the input voltage, in some cases it is necessary to protect the equipment from such influences. The most demanding of stability parameters of a power equipment used for medical life support systems, computer systems of banks, insurance companies, office LAN and production management systems.

    Existing types of sources

    To address food insecurity are different devices: stabilizers, filters, uninterruptible power supply (UPS). In all their diversity sometimes difficult to understand even the most experienced user. Introduce widely used in the world of manufacturers of uninterruptible power supply classification allows to share all the uninterruptible power supply into three main classes: OFF-LINE, LINE-INTERACTIVE, ON-LINE. Recently, the market appeared uninterruptible power supply, attributable to technology manufacturers Delta conversion (Delta Conversion - No. 1996) of Silcon Power Electronics A/S.

    OFF-LINE (Stand-By)

    In OFF-LINE uninterruptible power supply input voltage is fed through a line filter, which filters high frequency noise, thereby smoothing the shape of the input voltage. If the voltage of the external network goes beyond a certain range (many manufacturers adjustable) - the UPS switches to battery operation, with the output voltage often has a trapezoidal shape (this form is almost no effect on the computers of some manufacturers, in the past due to the use of pulsed power supply).

    Weaknesses of these devices:

    • lack of good filtration and stabilization characteristics Electrosignal in " normal ";
    • even at low voltage dips and surges uninterruptible power supply switches to on internal battery;
    • the presence of the transition time on the battery (~ 5 ms) in case of emergency.

    Advantages of such sources - their simplicity and efficiency.

    LINE-INTERACTIVE
    (Hybrid, FERRORESONANT, TRIPORT etc.)

    These uninterruptible power supply can be described as modified OFF-LINE, since the only difference is the presence of additional voltage regulation circuits (" boosters ", " air-conditioning lines ", etc.). Basically, these circuits are used to increase or decrease the input voltage in order to bring its value to the standard required value. Designating particular implementation, the producers called uninterruptible power supply of this specific class names are often deceptive. Some models of LINE-INTERACTIVE UPS serious shortcomings, as they regulate the voltage nodes capable of generating stable distortion (due to the presence of a complex feedback loop) and unpredictable transients.

    The disadvantage of such devices, as well as uninterruptible power supply Class Off-Line, is the presence of the transition time on the battery (~ 5 ms) in case of emergency. Recommended for protection of low-cost servers, workstations, fax machines and other devices critical to the voltage failure, and non-critical to the shape of the output signal and switch to batteries.

    Delta Technology

    UPS, created by Delta Technology - a system of compensation type, which compensate for possible changes in the voltage of the first harmonic of the mains supply, weakening their appearance at the output due to the voltage boost, adjustable negative feedback from the entrance of the uninterruptible power supply.

    System " Delta-conversion " It consists of two inverters (Delta inverter - a device №1 and main inverter - a device №2), performed by the special 4-quadrant diagram and control and regulation systems. Both inverter connected to a common battery and depending on the voltage in the line take over the functions or the inverter or rectifier.

    For example, if a line voltage drop occurs, the unit 2 operates as an inverter, and the device 1 as a rectifier. And vice versa, when the voltage increases device 1 assumes the function of the inverter and the rectifier device 2. The system works in automatic control mode as the output voltage and input power factor. A feature of this scheme is the fact that the conversion process is subjected to only the portion of the electrical energy which is necessary to convert the load to obtain qualitative parameters.

    Under ideal conditions, when the voltage is comply with the quality of food load (voltage and current correspond to par, missing all sorts of failures, emissions, noise and interference), electric power is fully transferred to the load, and is not converted twice, both in the uninterruptible power supply, double-conversion, in this case, there is no loss on the conversion.

    In a real situation, when the network settings are not perfect, there is the traditional double conversion power. But the system " Delta ", conversion is obtained, " intelligent ", than the classical scheme of double conversion, because not all the energy converts, but only the part that you need. For example, when the input voltage deviation of 15%, a double conversion undergo only 15% of energy. If we take the total losses in the traditional uninterruptible power supply with the scheme of double conversion is 10%, the system " Delta-conversion " energy losses will be: 0,15 × 10% = 1,5%.

    In the event of a power outage, the main inverter is powered by the battery, and the circuit works on the same principle as in the classic double-conversion.

    Thus, the system " Delta ", transformation has almost all the advantages of traditional double conversion scheme, but it is more effective.

    Advantages: high efficiency (up to 97%) over a wide load range, low heat generation due to low power losses, input power factor - almost equal to unity in a wide range of load changes.

    Weaknesses: in contrast to the circuit with a double energy conversion, uninterruptible power supply with Delta Conversion is not able without power consumption from the battery (AB) provide the required stability of the output frequency (+ 0.05 + 0, 1%) under the current instability of the mains frequency, ie, reaction uninterruptible power supply with Delta Conversion to change the frequency of the supply voltage is the same as power failure, which reduces the life of the batteries at frequent them going, and the value of AB is, on average, 40% of the uninterruptible power supply.

    ON-LINE

    The principle of this class is to double (and sometimes triple) the conversion of electrical energy. Uninterruptible power supply converts 100% supplied to it to the input AC to DC, and then performs the inverse transformation. Thus, in the UPS class ON-LINE, even in normal AC current passes two transformations (forward and reverse) before it goes to the protected load. This leads to three obvious positive effects:

    • firstly, the best filters all kinds of network interference;
    • Second, interference from a load does not fall in the external network;
    • Thirdly, (but not least) there is no phase jump and time switches to the battery, which is common to all other classes of uninterruptible power supply, when the load is fed from the battery.

    Typical switching time on battery from classes OFF-LINE and LINE-INTERACTIVE is 4-5 ms. (according to advertising material). However, it should be borne in mind that the reaction time is really only in the " interruption input line ", and when other distortions of the input parameters, this time can increase by more than 5 times. According to various sources modern computers can retain data when the input voltage for 15 - 20 ms., But with longer intervals reckoned particularly critical switching time becomes when eaten computers in a local area network.

    Uninterruptible Power Supply Class On-Line double conversion of energy does not have the time to go to the battery (as the output inverter feeds the connected load by energy derived from either the rectifier or from the battery permanently connected), so the output sine wave has no discontinuities and distortions. Some manufacturers of uninterruptible power supplies AB conserve resources through the use of so-called " virtual battery " (the WB), to supply the load when using the energy stored is not AB, and large capacitors (Fig. above, the WB is connected between the rectifier and inverter) is connected in parallel to AB. This reduces the number of cases of short-term use of the main battery and increases its service life. The output voltage is always sinusoidal, and its frequency is always defined and stable crystal oscillator inside the uninterruptible power supply, regardless of the form and frequency of the input voltage, which provides greater electromagnetic compatibility compared with sources of other types of uninterruptible power supply.
    Of course, the presence of such large differences in the types of uninterruptible power supply results in a significant difference in value. And recommended criteria for the selection of computer equipment is a uninterruptible power supply in a price range not exceeding 20% ​​of the value of protected consumers. The following are examples of the use of uninterruptible power supply.

    What type of source select

    Type of interference The consequences for computers Protection Devices degree of protection
    Power Surges
    Surge
    Reset memory. The occurrence of errors. The failure of the equipment. Twinkling lights Surge part
    Stabilizers Yes
    UPS OFF-LINE UPS No
    LINE-INTERACTIVE part
    UPS ON-LINE Yes
    High voltage Spikes
    High emissions
    Reset memory. Failure of the equipment items. Surge Yes
    Stabilizers Yes
    UPS OFF-LINE Yes
    UPS LINE-INTERACTIVE Yes
    UPS DELTA CONVERSION Yes
    UPS ON-LINE Yes
    Power Sags
    Sags (short)
    Reset memory. The occurrence of errors. The failure of the equipment. Twinkling lights Surge No
    Stabilizers Yes
    UPS OFF-LINE part
    UPS LINE-INTERACTIVE part
    UPS DELTA CONVERSION Yes
    UPS ON-LINE Yes
    Electrical Line Noice
    High-frequency noise
    errors. Resetting RAM. " hang " computer systems. Failure of the drive. Surge No
    Stabilizers part
    UPS OFF-LINE part
    UPS LINE-INTERACTIVE part
    UPS DELTA CONVERSION Yes
    UPS ON-LINE Yes
    Frequency Variations
    Coast frequency
    " hang " computer systems. Failure of the drive. Loss of data. Surge No
    Stabilizers No
    UPS OFF-LINE No
    UPS LINE-INTERACTIVE part
    UPS DELTA CONVERSION part
    UPS ON-LINE Yes
    Browmout
    Spiking voltage (long)
    Data loss. Exit standing equipment. Surge No
    Stabilizers part
    UPS OFF-LINE part
    UPS LINE-INTERACTIVE part
    UPS DELTA CONVERSION Yes
    UPS ON-LINE Yes
    Power Failure
    Voltage loss
    Data loss. Unpredictable consequences. Surge No
    Stabilizers No
    UPS OFF-LINE Yes
    UPS LINE-INTERACTIVE Yes
    UPS DELTA CONVERSION Yes
    UPS ON-LINE Yes

    The classification of UPS systems
    topology

    By topology to distinguish between the following three categories of basic uninterruptible power supply systems:

    • Distributed;
    • Centralized;
    • Combined.

    Distributed system of guaranteed power supply

    The distributed system is composed of many small uninterruptible power supplies, each of which protects the individual pieces of equipment - usually a computer, at least - domain. It is the simplest and most common UPS system.

    For advantages of this system should include:

    • Each element of a computer system is powered from a separate uninterruptible power supply, specially selected for the power and the degree of protection. This allows you to efficiently spend money on the purchase of uninterruptible power supplies, choosing important and in difficult operating conditions, elements of computer networks more expensive models.
    • Operation of the distribution system in simple computer systems is fairly obvious. Each user is responsible for only its uninterruptible power supply.
    • The system simply increase gradually additional purchasing uninterruptible power supply.
    • The efficiency of the system can be maintained temporarily replace the failed uninterruptible power supply important elements of a computer system units, protecting less important elements.
    • Low-power uninterruptible power supply does not require skilled personnel to install them.

    Weaknesses of this system are obvious:

    • Rather high cost of protecting one place (in comparison with the centralized system) at a low-class protection.
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