Now, in many applications using electric motors, the technology requires different speeds. Variable speed drives (VSDs) play an important role in the drive efficiency of electric motors in industrial applications, both at the design stage and on the shop floor.
The rectifier, intermediate circuit, inverter and control unit are the key components of the VSD unit. A rectifier converts alternating current (AC) to direct current (DC). In intermediate circuits, the rectified DC supply is usually regulated by a combination of inductors and capacitors. Inverters convert rectified and regulated DC power back to AC power of variable frequency and voltage. Typically, this is accomplished by generating high-frequency pulse-width modulated signals with varying frequencies and effective voltages. The control unit supervises the entire operation of the VSD; it monitors and controls the rectifier, intermediate circuit.
VSD applications with various loads:
The VSD will be interfaced with a sensor such as a pressure sensor or flow sensor and programmed to maintain a certain value (set point). They can interface with multiple sensors, enable interlocks and other control functions, and interface with current computer networks that provide real-time operational data.
The energy saving potential of a VSD depends on the characteristics of the load being driven. There are three types of loads: variable torque, constant torque and constant power. Variable torque loads are common in centrifugal fans and pumps and offer the greatest potential for energy savings. This is because torque varies with the square of speed (H1/H2=(N1/N2)2), while power varies with the square of speed (P1/P2=(N1/N2)3). And the flow rate changes according to the speed change (Q1/Q2=(N1/N2)).
A constant torque load is a load in which the torque does not change with the speed, and the power absorbed is proportional to the speed, which means that the power consumed is proportional to the useful work done.
Conveyors, agitators, crushers, surface winders, positive displacement pumps and air compressors are typical of constant torque applications. On a constant power load, the power absorbed is constant, while torque is inversely proportional to speed. Variable speed fan controls can be used in a wide range of applications including most types of ventilation systems, extraction systems, industrial cooling and boiler combustion air control systems.
The curves in the figure below show that using a VSD to regulate the flow of the pump instead of traditional throttling control can result in significant power and cost savings. Among them, the dotted line represents the power input to the fixed speed motor, and the solid line represents the power input to the variable speed drive (VSD). The shaded area reflects the energy saved using VSD for a given flow rate.
VSDs come in a wide range of sizes, from 0.18kW to several MW, and can be optimized for specific applications. VSDs typically have an efficiency of 92-95% with a loss of 5-8% due to the additional heat dissipation caused by high frequency electrical switching and the additional power required by the electronic components. Losses can often be made up for by savings in motors.
Now, in many applications using electric motors, the technology requires different speeds. Variable speed drives (VSDs) play an important role in the drive efficiency of electric motors in industrial applications, both at the design stage and on the shop floor.
The rectifier, intermediate circuit, inverter and control unit are the key components of the VSD unit. A rectifier converts alternating current (AC) to direct current (DC). In intermediate circuits, the rectified DC supply is usually regulated by a combination of inductors and capacitors. Inverters convert rectified and regulated DC power back to AC power of variable frequency and voltage. Typically, this is accomplished by generating high-frequency pulse-width modulated signals with varying frequencies and effective voltages. The control unit supervises the entire operation of the VSD; it monitors and controls the rectifier, intermediate circuit.
VSD applications with various loads:
The VSD will be interfaced with a sensor such as a pressure sensor or flow sensor and programmed to maintain a certain value (set point). They can interface with multiple sensors, enable interlocks and other control functions, and interface with current computer networks that provide real-time operational data.
The energy saving potential of a VSD depends on the characteristics of the load being driven. There are three types of loads: variable torque, constant torque and constant power. Variable torque loads are common in centrifugal fans and pumps and offer the greatest potential for energy savings. This is because torque varies with the square of speed (H1/H2=(N1/N2)2), while power varies with the square of speed (P1/P2=(N1/N2)3). And the flow rate changes according to the speed change (Q1/Q2=(N1/N2)).
A constant torque load is a load in which the torque does not change with the speed, and the power absorbed is proportional to the speed, which means that the power consumed is proportional to the useful work done.
Conveyors, agitators, crushers, surface winders, positive displacement pumps and air compressors are typical of constant torque applications. On a constant power load, the power absorbed is constant, while torque is inversely proportional to speed. Variable speed fan controls can be used in a wide range of applications including most types of ventilation systems, extraction systems, industrial cooling and boiler combustion air control systems.
The curves in the figure below show that using a VSD to regulate the flow of the pump instead of traditional throttling control can result in significant power and cost savings. Among them, the dotted line represents the power input to the fixed speed motor, and the solid line represents the power input to the variable speed drive (VSD). The shaded area reflects the energy saved using VSD for a given flow rate.
VSDs come in a wide range of sizes, from 0.18kW to several MW, and can be optimized for specific applications. VSDs typically have an efficiency of 92-95% with a loss of 5-8% due to the additional heat dissipation caused by high frequency electrical switching and the additional power required by the electronic components. Losses can often be made up for by savings in motors.
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