The main function of a variable frequency speed control device on an AC motor is to control the power supply. Its fundamental working principle is essentially to output a certain ratio of voltage and frequency in order to achieve the purpose of controlling the motor’s speed and torque. In terms of functionality, the preset functional parameters will also vary. For different application scenarios, the modulated parameters may differ as well. However, in principle, the core focus remains “controlling the motor and outputting appropriate voltage and frequency,” ensuring a certain current and speed limit, logical correlation, and other key objectives that guide functional parameter design.

1. Control Mode Selection: The commonly used method currently is V/F control, which is suitable for general applications where only speed adjustment is needed. It requires setting the V/F curve to meet constant torque or fan/pump load requirements. Generally, factories preset it to constant torque V/F mode. Vector control is usually applied in applications with high requirements for speed and torque accuracy, such as winding/unwinding equipment, hoists, synchronization, and tension control devices. Within vector control, there are sensorless vector control and encoder closed-loop vector control. There is also DTC (Direct Torque Control), generally used in cranes and other applications requiring precise torque control.
2. Voltage and Frequency Design: There are specific requirements for input voltage. In China, the standard three-phase voltage is usually 380V, so most systems are designed for 400V standards. The rated frequency of motors is typically 50Hz, corresponding to commonly used four-pole motors with a speed of 1500 RPM. Some inverters allow selection of the number of pole pairs, thus changing the motor speed accordingly. Frequency includes maximum frequency, starting frequency, minimum frequency, etc. Some equipment must also consider resonance issues, so skip frequencies and similar functions are preset. Frequency is basically proportional to motor speed. Some textile equipment inverters also have oscillating frequency functions, allowing frequency to change according to a specific pattern.
3. Torque Issues: In some cases, torque control is required, which can only be achieved by vector-type products. Internally, the equipment involves selections between speed loop and current loop, speed loop output limiting parameters, and optimization of PID parameters. General-purpose models at startup often include torque boost parameters, used to compensate the V/F parameters, making motor startup smoother.
4. Start/Stop and Speed Adjustment Function: This includes selection of start source and frequency source parameters. For example, factory presets usually allow operation via the keypad panel for starting and setting the frequency. In actual use, this can be changed to terminal control or communication-based control methods.
5. In some applications, rapid I/O speed adjustments are required; therefore, many variable frequency drives support multi-speed functions. Different I/O terminals can be assigned different frequency values, which can be set specifically in the parameters. Some models also include timing functions for coordinating multi-speed time control.
6. Some protective functions are essential, such as overheat protection, overload protection, overcurrent protection, and even optional phase loss protection. These are all preset at the factory to values close to the motor specifications. However, in actual usage, they need to be adjusted according to the specific conditions of the equipment.
7. Some interlocking functions: Most inverters come with built-in simple PLC functions that can perform basic logic control. For example, when one machine starts, another machine can be controlled to start accordingly, and the given speed can be adjusted proportionally. In some applications, PID functions are available for closed-loop process control, such as constant pressure water supply systems. Changsha Sunye Electric Co., Ltd. (established in 2010) and Shenzhen Sunye Electric Co., Ltd. (established in 2002) are national high-tech enterprises specializing in R&D, manufacturing, and sales of inverters, industry-specific integrated machines, servo drives, and new energy products.
Sunye Electric owns independent intellectual property rights, with products certified by national authorities and multiple software copyrights and IP certificates. Significant investment is made annually in new technologies and product development, with numerous patents and software copyrights approved. The company possesses core platform technologies such as construction hoist drivers, high-performance vector inverters, servos, and permanent magnet synchronous motor controls. Medium- and low-voltage inverters and servo drives are widely used in industries such as lifting, stone processing, HVAC, machine tools, metal products, wire and cable, plastics, printing and packaging, textile and chemical fibers, building materials, metallurgy, coal mining, municipal services, and automotive manufacturing. Guided by the philosophy of “Innovation, Technology, Strength,” driven by the corporate spirit of “Unity, Progress, Pragmatism, Innovation,” and adhering to the business principle of “Sincerity and Excellence, Mutual Benefit and Coexistence,” the company aims to provide industry-leading products through comprehensive quality management, continuous improvement, and pursuit of zero defects.
Address: Sunye Electric Industrial Park, No. 669 Xinsheng Road, High-Tech Zone, Changsha City
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