Suppliers of energy feedback devices for frequency converters remind you that in modern industry, motors are a type of high energy consuming power equipment with a wide range of applications. According to statistics, China's total installed capacity is about 400 million kilowatts, with an annual electricity consumption of about 600 billion kilowatt hours, accounting for 70-80% of industrial electricity consumption. China mainly relies on small and medium-sized motors, accounting for about 80%, while the amount of electricity consumed by small and medium-sized motors accounts for 90% of the total loss. In the practical application of motors in China, there is a significant gap compared to foreign countries, with a unit efficiency of 75%, which is 10% lower than foreign countries; The operating efficiency of the system is 30-40%, which is 20-30% lower than the international advanced level. Therefore, small and medium-sized motors in China have great energy-saving potential, and promoting motor energy conservation is imperative.
Due to its simple structure, easy manufacturing, low price, durability, reliable operation, and suitability for harsh environments, asynchronous motors have been widely used in industrial and agricultural production. Especially for the dragging of pumps and fans in various industries, energy-saving work of motors for dragging pumps and fans is highly valued.
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
Variable frequency speed regulation saves electricity, as the name suggests, only variable frequency speed regulation can save electricity. Below is an analysis of the energy-saving principles for two typical load applications.
(1) Constant torque load applications
Constant torque load means that regardless of changes in speed, the load torque remains constant.
The following formula: P=K * T * N
K=coefficient
P=shaft power
T=load torque
N=rotational speed
From the above formula, it can be seen that the shaft power is directly proportional to the motor speed. When the motor speed is adjusted due to the needs of the process, the corresponding proportion of power saving can naturally be achieved.
(2) Variable torque load applications
Centrifugal fans and pumps belong to typical variable torque loads, and their working characteristics are: most of them operate continuously for a long time. Since the load torque is proportional to the square of the speed, once the speed exceeds the rated speed, it will cause serious overload of the motor. Therefore, fans and pumps generally do not operate beyond the rated frequency.