The basic concept of servo is accurate, precise, and fast positioning. Frequency conversion is a necessary internal component of servo control, and it also exists in servo drives (requiring stepless speed regulation).

But the servo controls both the current loop, speed loop, and position loop by closing them, which is a big difference. In addition, the structure of servo motors is different from that of ordinary motors, and they need to meet the requirements of fast response and accurate positioning.

The AC servo motors currently in circulation on the market are mostly permanent magnet synchronous AC servo motors, but due to process limitations, it is difficult to achieve high power. Synchronous servo motors with a power output of more than ten KW are extremely expensive. Therefore, AC asynchronous servo motors are often used when field applications permit. In this case, many drives are high-end frequency converters with encoder feedback closed-loop control.

The so-called servo is to meet the requirements of accurate, precise, and fast positioning, as long as it meets the requirements, there is no dispute over servo frequency conversion.

The technology of AC servo itself draws on and applies the technology of frequency conversion. Based on the servo control of DC motors, it imitates the control mode of DC motors through the PWM method of frequency conversion, which means that AC servo motors must have a frequency conversion link.

Frequency conversion is the process of rectifying AC power at frequencies of 50 and 60Hz into DC power, and then inverting it into a frequency adjustable waveform similar to sine and cosine pulse electricity through various controllable gate transistors (IGBT, IGCT, etc.) through carrier frequency and PWM regulation. Due to the adjustable frequency, the speed of the AC motor can be adjusted (n=60f/p, n speed, f frequency, p pole pairs).

Due to the differences in performance and functionality between frequency converters and servos, their applications are not quite the same

1. In situations where speed control and torque control are not very demanding, frequency converters are generally used, and there are also cases where position feedback signals are added to the upper level to form a closed loop for position control using frequency converters, but the accuracy and response are not high. Some frequency converters now also accept pulse sequence signals to control speed, but it seems that they cannot directly control position.

2. In situations where strict position control is required, only servo can be used to achieve it. Additionally, servo response speed is much faster than frequency conversion, and servo control is also used in situations where speed accuracy and response requirements are high. Almost all motion situations that can be controlled by frequency conversion can be replaced by servo. The key points are twofold: firstly, servo is much more expensive than frequency conversion, and secondly, the reason for power: the maximum power of frequency conversion can reach several hundred KW, or even higher, while servo can only reach tens of KW.