The approximated sine wave is an AC waveform that conditionally approaches a pure sine wave. It can have a stepped shape of the envelope, be represented by a sequence of pulses of a rectangular or trapezoidal shape of different polarity. An AC signal, in the form of an approximated sinusoid, is present at the output of most used uninterruptible power supplies (UPS).
Designation of Uninterruptible Power Supplies
The main task of the UPS is to save AC voltage supplying consumers during its sudden disappearance in the network. They do not perform the function of stabilizing the mains voltage, but are emergency sources of AC voltage with an approximated sinusoid. Uninterruptible power supplies are not intended for continuous operation of equipment connected to them in the event of an accident on mains voltage lines.
UPSs must provide consumers with sufficient power to complete processes that cannot be interrupted suddenly. During operation of the UPS with an approximated sinusoid, conditions will be created for a regular load disconnection. This will keep it working with future use. Often you can find a link to an UPS-uninterruptible power supply. UPS in it is an abbreviation of the English designation of the UPS.
Classification of sources
Depending on the requirements for the quality of the AC supply voltage, UPS uninterruptible power supplies can be divided into several types:
- off-line sources, which are emergency sources of backup type;
- line-interactive or linear-interactive sources, capable of stabilizing the mains voltage with insignificant deviations from the nominal value, and switching to the emergency power supply mode with an approximated sinusoid when it completely disappears;
- on-line, or a UPS with double conversion of electrical energy, providing the connected load with stabilized mains voltage at significant differences and performing the functions of an emergency source when it is completely turned off.
An uninterruptible source of any kind includes a rechargeable battery, which is a store of electrical energy. Depending on the requirements for the power quality of devices that are the load of a UPS with an approximated sinusoid, one or another circuitry solution is used.
Off-line UPS
A passive UPS of this kind is a source of backup action. Its switching device with normal quality parameters of the mains voltage provides direct connection of the load to the mains. In the event of a short-term voltage failure at the input of the UPS, the switching device switches the power supply to the emergency (standby) mode. The source of electrical energy in this case is the built-in battery.
Its DC voltage is converted by an inverter into a modified sine wave of AC voltage, which is supplied through the contacts of the switch's electromagnetic relay to power the load. To recharge the battery (battery) is a voltage rectifier external power supply. To protect it from high-frequency interference arising from the operation of a pulse inverter, a filter is provided in the UPS. Its elements also protect the load devices from short-term surges of the mains voltage.
Line Interactive Sources
Line-interactiv UPS, in contrast to the backup action source, is able to stabilize the mains voltage when the load is directly connected to it through the contacts of the electromagnetic relay. This is ensured by using an autotransformer in the input circuit. Switching its windings is done automatically depending on the magnitude of the mains voltage. When it increases or decreases, the alternating voltage at its output retains the nominal value of 220 V. An autotransformer of the most common UPSs of this type regulates in the range (150-270) V changes in the voltage of the external supply network.
Switching of the contactor and the transition to emergency power supply of the load with a modified sinusoid occurs when the mains voltage is excessively changed outside the control range. The accuracy of regulation is determined by the number of taps (steps) of the autotransformer. In the emergency power supply mode of the load devices with an alternating voltage of an approximated sinusoid, the operation occurs in the same way as in an off-line UPS.
On-line UPS
Double conversion of electrical energy in uninterruptible power supplies of this type allows you to get an approximated sine wave of the output alternating voltage, approaching in shape to a pure sine. The mains voltage, converted into direct voltage by the rectifier, then undergoes the inverse conversion by the inverter into alternating voltage, which is used to power the load.
The built-in battery is charged with direct current rectifier and is included in emergency operation. The direct current energy accumulated by it is converted by the inverter into the output alternating voltage supplying the load equipment. A source circuit of this kind allows the connection of an additional external battery for the UPS.
When the mains voltage is restored within its normal value, the load is switched from the primary AC mains. The electric capacity of the battery for the UPS determines the time during which consumers can work with a sudden loss of mains voltage.
UPS Specifications
UPS selection is based on its technical specifications. The technical characteristics that determine the quality of meeting the requirements for products for this purpose include:
- power at the output of the source with the connected load, measured in volt-amperes (VA) or watts (W);
- output voltage range with connected load, measured in volts (V);
- switching time, which determines the transition time of the load power supply in standby mode from the battery, measured in milliseconds (ms);
- the range of the input mains voltage, within which the UPS is able to stabilize the output voltage without switching to the backup battery mode;
- the coefficient of nonlinear distortion, which determines the percentage difference between the shape of the output signal from the pure sine wave;
- operating time in stand-by standby mode of power supply from the battery with the connected load, determined by the electric capacity of the internal battery;
- the life of their own batteries, depending on the technology of their manufacture.
When choosing a UPS, the price of the uninterrupted plays a significant role. It directly depends on the circuitry solutions used by the developer when creating the model chosen by the consumer, and ranges from two to tens of thousands of rubles.
Areas of use
UPS uninterruptible power supplies can be used in conjunction with active load - devices that include switching power supplies.
UPSs are not used for powering consumers with a significant reactive inductive component (power line transformers of electronic devices of old models, motor windings, pumps for heating household boilers). Each of the existing uninterruptible power supply circuits is designed for a certain circle of consumers, taking into account its advantages and disadvantages.
Conclusion
The article provides a brief overview of the current uninterruptible power supply with a modified sinusoid. The circuitry solutions used by the developers when creating them are considered. After reading the material, the reader who is interested in acquiring a UPS to solve his problems will be able to study the set of documentation for it without experiencing any difficulties. It should not be forgotten that a high product implies a higher price when buying.