Les fournisseurs de systèmes de freinage à économie d'énergie par servocommande rappellent que les servovariateurs servent à piloter les servomoteurs, qu'il s'agisse de moteurs pas à pas ou de moteurs asynchrones à courant alternatif. Ils sont principalement utilisés pour un positionnement rapide et précis, et sont couramment employés dans les situations exigeant une grande précision lors des opérations de démarrage et d'arrêt.
Un convertisseur de fréquence est conçu pour convertir le courant alternatif en un courant adapté à la régulation de la vitesse d'un moteur, afin de l'entraîner. De nos jours, certains convertisseurs de fréquence permettent également la commande de servomoteurs, mais il s'agit de deux choses différentes ! Quelle est la différence entre un servomoteur et un convertisseur de fréquence ? Consultez l'explication fournie par l'éditeur.
Deux définitions
Un convertisseur de fréquence est un dispositif de contrôle de l'énergie électrique qui utilise la fonction marche/arrêt des semi-conducteurs de puissance pour convertir le courant d'alimentation à fréquence industrielle en un autre courant. Il permet notamment le démarrage progressif, la régulation de vitesse à fréquence variable, l'amélioration de la précision de fonctionnement et la modification du facteur de puissance des moteurs asynchrones à courant alternatif.
Le convertisseur de fréquence peut entraîner des moteurs à fréquence variable et des moteurs à courant alternatif ordinaires, servant principalement de régulateur de vitesse du moteur.
Un convertisseur de fréquence se compose généralement de quatre parties : un redresseur, un condensateur haute capacité, un onduleur et un contrôleur.
A servo system is an automatic control system that enables the output controlled variables such as the position, orientation, and state of an object to follow any changes in the input target (or given value). The main task is to amplify, transform, and regulate the power according to the requirements of the control command, making the torque, speed, and position control of the driving device output very flexible and convenient.
A servo system is a feedback control system used to accurately follow or reproduce a process. Also known as a follow-up system. In many cases, a servo system specifically refers to a feedback control system where the controlled variable (system output) is mechanical displacement, displacement velocity, or acceleration. Its function is to ensure that the output mechanical displacement (or rotation angle) accurately tracks the input displacement (or rotation angle). The structural composition of servo systems is not fundamentally different from other forms of feedback control systems.
Servo systems can be divided into electromechanical servo systems, hydraulic servo systems, and pneumatic servo systems according to the type of driving components used. The most basic servo system includes servo actuators (motors, hydraulic cylinders), feedback components, and servo drivers. If you want the servo system to operate smoothly, you also need a higher-level mechanism, PLC、 And specialized motion control cards, industrial control computers+PCI cards, to send instructions to servo drives.
Working principle of both
The speed regulation principle of a frequency converter is mainly limited by four factors: the speed n of the asynchronous motor, the frequency f of the asynchronous motor, the motor slip rate s, and the number of poles p of the motor. The speed n is proportional to the frequency f, and changing the frequency f can change the speed of the motor. When the frequency f varies within the range of 0-50Hz, the range of motor speed adjustment is very wide. Variable frequency speed regulation is achieved by changing the frequency of the motor power supply to adjust the speed. The main method used is AC-DC-AC, which first converts the power frequency AC power supply into DC power supply through a rectifier, and then converts the DC power supply into AC power supply with controllable frequency and voltage to supply the motor. The circuit of a frequency converter generally consists of four parts: rectification, intermediate DC link, inverter, and control. The rectification part is a three-phase bridge uncontrolled rectifier, the inverter part is an IGBT three-phase bridge inverter, and the output is a PWM waveform. The intermediate DC link includes filtering, DC energy storage, and buffering reactive power.
The working principle of a servo system is simply based on open-loop control of an AC/DC motor, where speed and position signals are fed back to the driver through rotary encoders, rotary transformers, etc. for closed-loop negative feedback PID control. In addition, with the current closed-loop inside the driver, the accuracy and time response characteristics of the motor's output following the set value are greatly improved through these three closed-loop adjustments. The servo system is a dynamic follower system, and the steady-state balance achieved is also a dynamic balance.
The difference between the two
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 method of DC motors through the PWM method of frequency conversion. In other words, AC servo motors must have the process of frequency conversion: frequency conversion is to first rectify the AC power of 50 or 60Hz into DC power, and then invert 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 adjustment. Due to the adjustable frequency, the speed of AC motors can be adjusted (n=60f/p, n speed, f frequency, p pole pairs).
1. Different overload capacities
Servo drives generally have a 3-fold overload capacity, which can be used to overcome the inertia moment of inertial loads at the moment of starting, while frequency converters generally allow a 1.5-fold overload.
2. Control accuracy
The control accuracy of servo systems is much higher than that of frequency converters, and the control accuracy of servo motors is usually ensured by the rotary encoder at the back end of the motor shaft. Some servo systems even have a control accuracy of 1:1000.
3. Different application scenarios
Variable frequency control and servo control are two categories of control. The former belongs to the field of transmission control, while the latter belongs to the field of motion control. One is to meet the requirements of general industrial applications with low performance indicators, pursuing low cost. The other is to pursue high precision, high performance, and high response.
4. Different acceleration and deceleration performance
Under no-load conditions, the servo motor can process from a stationary state to 2000r/min in no more than 20ms. The acceleration time of the motor is related to the inertia of the motor shaft and the load. Usually, the larger the inertia, the longer the acceleration time.
Market competition between servo and frequency converter
Due to the differences in performance and functionality between frequency converters and servos, their applications are not very similar, and the main competition is focused on:
1. Competition in technological content
Dans ce même domaine, si l'acheteur a des exigences techniques élevées et complexes concernant les machines, il choisira des servomoteurs. Dans le cas contraire, il optera pour des variateurs de fréquence. Les machines de haute technologie, telles que les machines-outils à commande numérique et les équipements électroniques spécialisés, nécessiteront des servomoteurs.
2. Concurrence par les prix
La plupart des acheteurs privilégient le coût au détriment de la technologie, optant souvent pour des onduleurs moins chers. Or, comme chacun sait, le prix des servomoteurs est plusieurs fois supérieur à celui des convertisseurs de fréquence.
Bien que l'utilisation des servosystèmes ne soit pas encore généralisée, notamment pour les servosystèmes chinois, leur emploi reste rare comparé aux produits étrangers. Cependant, avec l'accélération de l'industrialisation, les avantages des servosystèmes seront progressivement reconnus et les acheteurs les apprécieront. De même, la technologie des servosystèmes en Chine continuera de progresser, que ce soit par appât du gain ou par conviction historique de contribuer à la revitalisation du pays. Nous sommes convaincus que de plus en plus de fabricants investiront dans la recherche et le développement des servosystèmes, marquant ainsi le début de l'âge d'or de l'industrie chinoise des servosystèmes.