In-depth analysis of UPS and detailed explanation of basic UPS application considerations

UPS, or uninterruptible power supply, is a system device that connects a battery (mostly lead-acid maintenance-free battery ) to a host computer and converts direct current into mains power through module circuits such as the host inverter. It is mainly used to provide a stable and uninterrupted power supply to a single computer, computer network system or other power electronic equipment.

　　Functions and uses of UPS

　　UPS is the abbreviation of the English name of Uninterruptible Power System. It appeared with the birth of computers and is one of the commonly used peripheral devices of computers. In fact, UPS is a constant voltage and constant rating uninterruptible power supply with energy storage device and inverter as the main component. In its early development, UPS was only regarded as a backup power supply. Later, due to power grid quality problems such as voltage surge, voltage spike, voltage transient, voltage drop, continuous overvoltage or undervoltage and even voltage interruption, the electronic systems of computers and other equipment were disturbed, resulting in serious consequences such as damage to sensitive components, loss of information, and flushing of disk programs, causing huge economic losses. Therefore, UPS has received increasing attention and has gradually developed into a power protection system with functions such as voltage stabilization, frequency stabilization, filtering, anti-electromagnetic and radio frequency interference, and anti-voltage surge.

Currently, a wide variety of UPS power supply equipment 　　can be purchased on the market , with output power ranging from 500VA to 3000kVA. When there is AC power supplied to the UPS, the UPS stabilizes the AC power (220V±5%) and then supplies power to the computer. At this time, the UPS is an AC AC voltage stabilizer, and it also charges the battery inside the machine. Due to different UPS designs, the UPS adaptability range is also different. The change of UPS output voltage within ±10-15% is generally considered a normal computer voltage. When the AC power is abnormal or interrupted, the UPS immediately supplies the power of the battery inside the machine to the computer system through inverter conversion to maintain the normal operation of the computer system and protect the computer's software and hardware from loss.

　　Classification and characteristics of UPS

　　UPS power supplies can be divided into two categories according to their working mode: backup type and online type. According to their output waveform, they can be divided into two types: square wave output and sine wave output. When the mains is supplying power normally, the mains directly supplies power to the load through the AC bypass channel and then through the conversion switch, and the inverter inside the machine is in a stopped working state. This UPS power supply is essentially equivalent to a mains voltage stabilizer with extremely poor voltage stabilization performance. In addition to improving the amplitude fluctuation of the mains voltage, it has basically no improvement on the adverse effects of the mains voltage frequency instability, waveform distortion, and interference from the power grid. Only when the mains power supply is interrupted or lower than 170V, the battery will supply power to the UPS inverter and provide a voltage-stabilized and frequency-stabilized AC power supply to the load. The advantages of the backup UPS power supply are high operating efficiency, low noise, and relatively cheap price. It is mainly suitable for occasions where the mains fluctuation is not large and the power supply quality requirements are not high.

　　When the mains is in normal operation, the online UPS first converts the AC power into a DC power source, then performs pulse width modulation and filtering, and then converts the DC power back into an AC power source, that is, it usually provides AC power to the load in the form of an inverter after the AC power is rectified. Once the mains is interrupted, the battery immediately switches to provide AC power to the load in the form of an inverter. Therefore, for the online UPS, under normal circumstances, whether there is mains or not, it always supplies power to the load through the inverter of the UPS, thus avoiding all the effects caused by voltage fluctuations and interference of the mains grid. Obviously, the power supply quality of the online UPS is significantly better than that of the backup UPS, because it can achieve frequency and voltage stabilization for the load, and when the mains power is converted to battery power, the conversion time is zero. The UPS with square wave output has poor load carrying capacity (the load is only 40-60% of the rated load) and cannot carry inductive loads. If the load is too large, the third harmonic component contained in the square wave output voltage will increase the capacitive current flowing into the load, and in severe cases, it will damage the load power filter capacitor. The relationship between the output voltage waveform distortion and the load of the sine wave output UPS power supply is not as obvious as that of the square wave output UPS power supply. The load capacity is relatively strong and can carry a micro-inductive load. Regardless of the type of UPS power supply, when they are in the inverter power supply state, unless it is absolutely necessary, they should not be fully loaded or overloaded, otherwise the failure rate of the UPS power supply will increase significantly.

　　UPS and load matching

　　Some UPS use watts (W) or kilowatts (kw) to indicate their output power, such as 500W, 1kw, etc.; some UPS use volt-amperes (VA) or kilovolt-amperes (kVA) to indicate their output power, such as 3000VA, 5kVA, etc. The general conversion relationship between VA and W is: watt is 0.8 times volt-amperes, such as 3kVA=2.4kw. UPS is used for line load power supply, and each UPS has a specific output power capacity. For example, the maximum output power of a 3kVA UPS is 3kVA or 2.4kw. At this time, it is required that the total power consumption of the equipment connected to this UPS cannot exceed 2.4 kilowatts. Usually, the equipment is marked with power consumption (or rated power). At this time, the total rated power of all equipment connected to the UPS should not exceed the output power of the UPS. This method is usually called matching the UPS output power with the load power consumption. However, the startup power of some devices is 3-5 times the rated power (for example, if the rated power of a printer is 200W, then when calculating the load matching, it should be converted as 5×200W=1000W). Except for printers, the startup power of other computer peripherals is usually slightly greater than the rated power, so when considering matching, it is best to perform load matching at 80% of the UPS output power.

Before adding external batteries　　to a standard UPS , when its output power is completely matched with the load power consumption (i.e. full load), it can generally supply power for about 6-10 minutes from the time the city power is interrupted (the specific values ​​are recorded in the UPS manual of each model). If the load power consumption is only half of the UPS output power (commonly called half load or 50% load rate, such as a 1000W UPS connected to a 500W load), it can supply power for 12-25 minutes. The UPS power supply time at different loads can be calculated by referring to the method of doubling the time by halving the load. Precautions for use The correct use of UPS power can not only reduce the chance of UPS failure, but also effectively extend its service life.

　　Usually you should pay attention to the following points:

　　(1) When using a UPS power supply , you should strictly abide by the relevant provisions of the manufacturer's product manual to ensure that the sequence of the live wire and neutral wire of the mains power connected to the UPS meets the requirements.

　　(2) The main purpose of equipping a UPS is to prevent the computer from losing information and damaging the hard disk due to sudden power outages, but some equipment is not afraid of sudden power outages when working (such as printers, etc.). In order to save UPS energy, the printer can be directly connected to the mains without going through the UPS. If it is a network system, the UPS can be considered to only supply power to the host (or server) and its related parts. This ensures that the UPS can be used on the most important equipment and saves investment.

　　(3) Do not overload the UPS. The maximum load of the UPS should be 80% of its nominal load (e.g., for a 1000W UPS, match the load at 80% load rate, i.e. 800W; for a 1000VA UPS, convert 80% to 800W and then match the load at 80% load rate, i.e. 640W). If overloaded, the inverter transistor will often break down in the inverter state. In addition, when using the UPS, it is strictly forbidden to connect inductive loads such as fluorescent lamps, but only pure electrical loads or smaller capacitive loads.

　　(4) Pay attention to the order of power on and off: turn on the UPS first, and then turn on the load power switch later (preferably 1-2 minutes later, so that the UPS can fully enter the working state), and turn on the load power switches one by one: the order is exactly the opposite when shutting down, turn off the load power switches one by one, and then turn off the UPS. The UPS should be turned on for a long time, and the loads such as computers should be turned on only when they are used. After use, just turn off the power switches of the loads such as computers.

　　(5) Do not turn off and on the UPS power supply frequently.

　　It is generally required to wait at least 6 seconds after turning off the UPS power supply before turning it on again. Otherwise, the UPS power supply may be in a "failed to start" state, that is, the UPS power supply is in an abnormal state with neither AC power output nor inverter output.

　　(6) The energy in the battery of the UPS may be exhausted or nearly exhausted for some reason. In order to compensate for the battery energy and increase the battery life, the UPS should be charged continuously in a timely and long time (usually not less than 48 hours, with or without load) to avoid malfunctions due to battery exhaustion. A newly purchased or long-stored UPS should be charged for 12 hours before use. A UPS that is not used for a long time should be charged for 12 hours every 3 months. If it is in a high-temperature area, it should be charged every 2 months. Using the UPS without charging will damage the battery .