Xiao D, who works in market development, and Ms. Can have a good relationship. Not long ago, they talked about something: the customer wanted to replace all the motors in the equipment with variable frequency motors, but he was undecided and worried that he would not be able to get the expected return.
In reality, the crux of customers' hesitation lies in their lack of understanding of why they should use frequency converters and what kind of transformative changes frequency converter power supply will bring to motor applications. Here, Ms. Can will specifically discuss frequency converters for motors, analyzing how frequency converters bring disruptive changes to motor applications.
Overview of frequency converters for motors
Motor frequency converters can be broadly classified into three types.
●Standard function type. Provides basic V/F frequency conversion speed control, suitable for general applications where speed control accuracy and torque control performance requirements are not high.
●High-performance type. V/F frequency conversion speed regulation with torque control function is commonly used in constant torque loads such as hoists.
● Vector control or direct torque control type. Vector control frequency converters must be used in high-performance applications with high dynamic performance requirements, such as steel rolling and papermaking.
Applications of frequency converters
In the era when inverter technology was not yet mature, high-performance applications such as fans and pumps were mostly equipped with pole-changing multi-speed three-phase asynchronous motors. However, due to the stepped speed regulation, they could not achieve smooth speed adjustment over a wide range, let alone performance optimization. Nowadays, inverters are widely used, and inverter motors specifically designed for fan and pump loads are optimized to maintain high levels of electrical performance such as efficiency and power factor throughout the entire speed range.
Three-stage regulation of load or output for fans, pumps, etc.
●Traditional regulation methods. Air and water supply volumes are adjusted by regulating the opening of inlet or outlet baffles or valves. This method requires high power input and consumes a significant amount of energy during the flow throttling process of the baffles and valves.
● The multi-speed three-phase asynchronous motor with pole changing features stepped speed regulation. When operating under full load, the multi-speed three-phase asynchronous motor runs at high speed; when the air volume or water supply needs to be reduced, the motor switches to medium or low speed, significantly reducing the input power and achieving extremely significant energy-saving effects.
● Variable frequency speed control (VFD) for three-phase asynchronous motors. When using VFD, if the flow requirement decreases, the requirement can be met by reducing the speed of the pump or fan. Typically, dedicated VFD motors for this application have optimized performance indicators over a wide speed range, maintaining a consistently high "flow rate/energy consumption" ratio.
Soft start and permanent magnet synchronous frequency conversion applications
Asynchronous motors driven by frequency converters not only achieve stepless speed regulation, but also keep the motor starting current within less than twice the rated current, and the starting torque can reach about twice the rated torque. Therefore, there are no starting problems for three-phase asynchronous motors driven by frequency converters, and high-performance soft start is an inherent characteristic.
High-performance permanent magnet synchronous motors, such as permanent magnet motors for new energy vehicles and permanent magnet motors for ship propulsion, all use frequency converters for driving. In such applications, the frequency converter is usually a highly integrated dedicated drive power module, which is manufactured as an integral part of the motor body to form a permanent magnet synchronous motor system.
Variable frequency drives (VFDs) have expanded the application areas of motors, breaking many design taboos, such as low-speed direct-drive wind turbines with speeds as low as tens or hundreds of RPMs, and high-speed direct-drive spindles and automotive-specific motors with speeds as high as tens of thousands of RPMs. With the upgrading of applications and increasingly refined professional requirements, motor VFDs will inevitably develop in multiple dimensions, including high-performance general-purpose, special-purpose mechatronics, and intelligent manufacturing applications, driving continuous innovation and upgrading of motor design concepts and motor manufacturing.
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