Anbieter von Energierückkopplungsgeräten für Frequenzumrichter weisen darauf hin, dass Motoren in der modernen Industrie zu den energieintensivsten Anlagen mit vielfältigen Anwendungsbereichen zählen. Statistiken zufolge beträgt Chinas installierte Gesamtleistung rund 400 Millionen Kilowatt, bei einem jährlichen Stromverbrauch von etwa 600 Milliarden Kilowattstunden, was 70–80 % des industriellen Stromverbrauchs entspricht. China setzt hauptsächlich auf kleine und mittelgroße Motoren (ca. 80 %), deren Stromverbrauch 90 % der Gesamtverluste ausmacht. Im praktischen Einsatz von Motoren in China besteht im Vergleich zu anderen Ländern eine deutliche Lücke: Der Wirkungsgrad einzelner Motoren liegt bei 75 % und damit 10 % niedriger als im Ausland; der Systemwirkungsgrad beträgt 30–40 % und liegt damit 20–30 % unter dem internationalen Standard. Daher bergen kleine und mittelgroße Motoren in China ein großes Energiesparpotenzial, und die Förderung der Energieeinsparung bei Motoren ist unerlässlich.
Aufgrund ihrer einfachen Bauweise, der unkomplizierten Fertigung, des niedrigen Preises, der Langlebigkeit, des zuverlässigen Betriebs und der Eignung für raue Umgebungen finden Asynchronmotoren breite Anwendung in der Industrie und Landwirtschaft. Insbesondere beim Antrieb von Pumpen und Ventilatoren in verschiedenen Branchen wird der energiesparende Betrieb dieser Motoren sehr geschätzt.
With the rapid development of science and technology, especially the high development and application of power electronics technology, microelectronics technology, and automatic control technology, the energy-saving effect of frequency converters has become more significant. It can not only achieve stepless speed regulation, but also operate efficiently under different loads, with good dynamic characteristics, and can achieve high-performance, high reliability, and high-precision automatic control. Compared to other speed regulation methods such as voltage reduction speed regulation, pole changing speed regulation, slip speed regulation, AC cascade speed regulation, etc., variable frequency speed regulation has stable performance, wide speed regulation range, and high efficiency. With the development of modern control theory and power electronics technology, AC variable frequency speed regulation technology is becoming increasingly perfect and has become the trend of AC motor speed regulation. Variable frequency speed control devices (VFDs) have been widely used in the industrial field.
The use of frequency converters for speed control signal transmission is fast, the control system has a small time delay, the response is sensitive, the control accuracy of the adjustment system is high, the use is convenient, and it is conducive to improving production output, ensuring quality, and reducing production costs. Therefore, the use of frequency converters is a popular product for energy-saving and consumption reduction in factories and mining enterprises.
Variable frequency motor energy-saving device is a revolutionary new generation of motor specific control product. Based on microprocessor digital control technology, it dynamically adjusts the voltage and current in the motor operation engineering through its built-in dedicated energy-saving optimization control software. Without changing the motor speed, it ensures that the output torque of the motor matches the load demand accurately, effectively avoiding the waste of electrical energy caused by excessive output of the motor.
AC motors are currently the most widely used motors, accounting for about 85% of all types of motors. They have the advantages of simple structure, low cost, and no maintenance required. However, their weakness is the difficulty of speed regulation, which limits their use in many applications or requires mechanical means to achieve speed regulation.
There are two typical applications of frequency converters in terms of load types: 1. Constant torque application; 2. Variable torque application. In terms of application purposes, the main objectives are: 1. To improve the process, ensuring the rotational speed during the process, the rotational speed under different loads, and accurate positioning. With its excellent speed regulation performance, it can improve productivity, enhance product quality, improve comfort, rationalize equipment, adapt or improve the environment, etc. 2. The main purpose of energy-saving transformation is to achieve significant results by controlling the speed of fans and pumps that require flow or pressure regulation.
The principle of variable frequency speed regulation
Motor loads such as fans, water pumps, air compressors, hydraulic oil pumps, and circulation pumps account for the vast majority of the power consuming equipment used in enterprises. Due to technical limitations, almost all flow, pressure, or air volume control systems for such loads are valve controlled systems, where the motor is driven at rated speed and the system provides constant flow, pressure, or air volume. When the equipment's operating requirements change, the load flow, pressure, or air volume is adjusted by overflow, relief valves, or proportional regulators located at the outlet end to meet the changing needs of the equipment's operating conditions. After the overflow valve or proportional control valve overflows, a large amount of energy will be released, and this dissipated energy is actually a part of the energy absorbed by the motor from the power grid, causing great waste of electrical energy. From the working characteristics of this type of load, it can be seen that the motor power is proportional to the cube of the speed, and the speed is proportional to the frequency. If we change the working mode of the motor so that it does not always operate at the rated working frequency, but instead uses a variable frequency adjustment control system for start stop control and adjustment operation, its speed can be continuously adjustable within the range of 0~2900r/min, that is, the output flow rate, pressure or air volume can also be continuously adjustable within the range of 0~100%, so as to accurately match the working needs of the load and achieve the goal of energy conservation and consumption reduction.
The AC motor speed is as follows: n=60f (1-s)/p
In the formula: n=motor speed
F=power frequency
P=number of poles of the motor
S=slip rate
As can be seen from the equation, the synchronous speed n of an AC motor is directly proportional to the power frequency f. Therefore, changing the power frequency can change the motor speed and achieve the purpose of speed regulation.
Principle of variable frequency speed regulation for energy saving
Drehzahlregelung mit variabler Frequenz spart Strom. Wie der Name schon sagt, ist dies die einzige Möglichkeit, Strom zu sparen. Im Folgenden werden die Energiesparprinzipien für zwei typische Lastanwendungen analysiert.
(1) Anwendungen mit konstanter Drehmomentbelastung
Konstantes Lastmoment bedeutet, dass das Lastmoment unabhängig von Drehzahländerungen konstant bleibt.
Die folgende Formel: P=K * T * N
K = Koeffizient
P = Wellenleistung
T = Lastdrehmoment
N = Rotationsgeschwindigkeit
Aus der obigen Formel geht hervor, dass die Wellenleistung direkt proportional zur Motordrehzahl ist. Wird die Motordrehzahl prozessbedingt angepasst, lässt sich somit eine entsprechende Energieeinsparung erzielen.
(2) Anwendungen mit variabler Drehmomentbelastung
Kreiselventilatoren und -pumpen zählen zu den typischen Lasten mit variablem Drehmoment und zeichnen sich durch folgenden Betrieb aus: Die meisten laufen über lange Zeiträume im Dauerbetrieb. Da das Lastdrehmoment proportional zum Quadrat der Drehzahl ist, führt eine Überschreitung der Nenndrehzahl zu einer starken Überlastung des Motors. Daher werden Ventilatoren und Pumpen im Allgemeinen nicht mit einer Frequenz über der Nennfrequenz betrieben.