Abstract : Asynchronous motors have become the primary drive equipment in industrial and mining enterprises, but they often operate under light load or no-load conditions. This paper proposes an optimization method for the power factor of asynchronous motors under light load and no-load conditions. Based on practical industrial applications, it utilizes existing AC drive equipment to achieve self-optimizing control of three-phase asynchronous motors under light load and no-load conditions. This method is simple and effective, achieving energy-saving control of asynchronous motors under light load and no-load operating conditions. Keywords: optimization; self-optimization control; energy saving control Application of 6SE70 Series inverters in Control of Saving Energy For Asynchronous Motor [align=center]YANG Bin (The Engineering Technical College of Chengdu University of Technology, Leshan, 614007, China)[/align] Abstract : Asynchronous motors have been the most important driving equipment and widely applied to industrial and mining enterprises. However, they often run at no load and light load state. This paper puts forward a method of optimized power factor to solve the problem of asynchronous motor at no load and light load state, and to use alternating current driving equipment for carrying out a control of self-optimization of asynchronous motor at no load and light load state from industrial practices. The method is simple and efficient, which can achieve optimal energy control effect. Key words: optimization; control of self-optimization; control of saving energy 1 Overview Three-phase asynchronous motors are widely used as the main prime mover for electrical transmission in industrial and mining enterprises due to their simple structure, convenient maintenance, relatively rigid mechanical characteristics, and low price. In many operating conditions, high-power asynchronous motors often operate under light load and no-load conditions. At these times, the motor's power factor and mechanical efficiency are very low, resulting in significant energy waste. This paper analyzes the problem of low power factor in three-phase asynchronous motors under light load or no-load conditions based on the operating theory of motors, and attempts to use the widely used 6SE70 AC drive in industrial settings to achieve self-optimizing control of the asynchronous motor under these conditions, thus achieving energy-saving control effects for three-phase asynchronous motors under light load and no-load conditions. [b]2 Theoretical Analysis of Power Factor Optimization 2.1 Causes of the Problem[/b] On the one hand, when the asynchronous motor operates under light load and no-load conditions, the rotor speed is close to the synchronous speed, and the slip is very small, meaning the rotor winding is essentially open-circuited. At this time, the rotor current is close to zero, and the stator current is almost entirely excitation current, used to generate the main magnetic flux and stator and rotor leakage flux. Maintaining the main magnetic field in the air gap and the leakage magnetic fields of the stator and rotor requires a certain amount of reactive power. This inductive reactive power must be obtained from the power input. Therefore, the larger the excitation current or the larger the leakage reactance of the stator and rotor, the lower the power factor of the motor. 2.2 Theoretical Analysis and Optimization Calculation of Power Factor According to the principles of motor theory, the complex electromagnetic relationship inside a three-phase asynchronous motor can be transformed into a simple relationship between electrical quantities, that is, replaced by a circuit that is equivalent to the actual asynchronous motor in terms of energy relationship. This is the familiar type 1 and type 2 equivalent circuit. According to the definition of the power factor of an asynchronous motor, after simplification, we have the following expression: Where, let,. In the formula: — stator leakage impedance; — excitation impedance; — excitation current; S — slip; — leakage impedance of the rotor winding referred to the stator side. Let then, we can obtain the extreme value of function (1) in the interval (0, 1). We call the slip corresponding to this extreme point the characteristic slip under the power factor, denoted by. This extreme point is the maximum power factor operating point that we want to optimize. Here, a 30kW asynchronous motor was selected as the object of debugging. Its specific parameters are as follows: Ω, Ω, Ω, Ω, Ω, Ω, Ω, Ω. According to the above parameters, the asynchronous motor can be optimized and calculated. Its optimized slip is 0.0456 and the maximum power factor is 0.7918. Under no-load conditions, since the rotor winding is open, the rotor current is close to zero, and the stator current and power factor can be obtained by the following formula. (3) Since the above calculation is the result obtained under the assumption that the rotor current is zero, in reality, the power factor under no-load conditions should be slightly higher than this value, between 0.3 and 0.4. By comparing the data before optimization, it can be clearly found that the optimized power factor has been greatly improved under no-load conditions. [b]3 Structure, control principle and implementation of intelligent energy-saving controller for three-phase asynchronous motor 3.1 Energy-saving working principle of controller[/b] The optimization calculation method has been given above. Because there is a transformation relationship between speed and slip, the problem of controlling slip can be easily transformed into the problem of controlling the running speed of a three-phase asynchronous motor under no-load or light-load conditions. This achieves the goal of energy-saving control of the motor under light-load or no-load conditions. Modern fully digital frequency converters can achieve high control accuracy and good dynamic performance for the speed control of three-phase asynchronous motors. For example, the Siemens 6SE70 series variable frequency speed controller has extremely high speed control accuracy (+0.01%) in its PG vector control mode. The following is a structural principle diagram of the energy-saving control achieved using this frequency converter, as shown in Figure 1. [align=center] Figure 1[/align] The working process of the intelligent energy-saving controller shown in Figure 1 can be described as follows: (1) The controller samples the stator current I[sub]1[/sub] and speed n of the motor; (2) By judging the magnitude of the sampled stator current I[sub]1[/sub], it indirectly determines whether the three-phase asynchronous motor is operating under no-load or light-load conditions, thereby deciding which given mode to start. Here, λ is called the threshold coefficient (λ≤1), which can be specifically selected according to the actual situation. I₀ is the no-load current of the motor, and λI₀ is the starting threshold of the no-load or light-load state given mode of the three-phase asynchronous motor; (3) When I₁ < λI₀, that is, the three-phase asynchronous motor is working in the no-load or light-load state, the no-load or light-load state given mode is immediately started to make the three-phase asynchronous motor work in the energy-saving control state; (4) When I₁ ≥ λI₀, the load state given mode is started to make the three-phase asynchronous motor run at the pre-given load speed. The above-mentioned intelligent energy-saving controller can identify the working state of the three-phase asynchronous motor, so it can freely switch between the two given modes to achieve self-optimization control in the no-load or light-load state and achieve the energy-saving purpose in this state. 3.2 Basic settings of simple application parameters The predefined and function definition parameter modules of the 6SE70 series frequency converter are stored in the device. These parameter modules can be combined with each other, allowing users to realize their application plans with minimal parameter setting steps. Parameter modules are suitable for the following functional groups: (1) Motors (with rated nameplate data input function for automatic parameter setting of open-loop and closed-loop control); (2) Open-loop and closed-loop control types; (3) Setting and command sources. Parameter setting is activated by selecting a set of parameter modules from each functional group, and then simple application parameter setting begins. Based on the user's selection, the necessary parameters generate the required control function. 3.3 Judgment Function [align=center] Figure 2 Judgment Function [/align] Figure 2 shows one of the free modules in the 6SE70 series frequency converter, used to implement the energy-saving controller's judgment function under light load, no-load, or load conditions. U141.01 and U141.02 store two variables to be compared. The value of U141 determines the required comparison channel to be enabled. For example: when U141=0, channel |A| is enabled. 3.4 Fixed Setpoint Module Figure 3 shows the fixed setpoint module, used to set the system's fixed setpoint parameters. Here, P411F is set to the rated load setpoint speed, i.e., its value is stored in register KK0051; it is set to the no-load or light-load state setpoint speed, i.e., its value is stored in register KK0052. [align=center]Figure 3 Fixed Setpoint Module[/align] 3.5 Setpoint Selection Module [align=center]Figure 4 Setpoint Selection Module[/align] Figure 4 shows the 4µs dual-word analog signal selection switch in the 6SE70 series frequency converter. The value of the switch quantity in U180 automatically selects one of the two variables in U181. Here, it is used as the setpoint selection module for this system, allowing free switching between the two setpoint states. After setting all the fixed parameters, the values ​​of the rated load speed nf and the no-load or light-load speed n0 must be entered into U180.01 and U180.02, that is, the values ​​in KK0051 and KK0052 are connected to U180.01 and U180.02 (here, n0 is calculated according to the formula [img=100,24]http://www.chuandong.com/uploadpic/THESIS/2008/4/2008040717025433514C.jpg[/img]). The selected result is stored in the KK0528 register and connected to the main setpoint P443.B of the 6SE70 series frequency converter. This completes the setpoint setting of this system. By following the above steps, the main parameters and functions of this system can be set. In the above setup process, each parameter is identified by its parameter name and parameter number, indicating its single meaning. I have not provided a detailed explanation of the parameter names and numbers involved, but you can refer to "6SE7087-6QX60 (AC Version) Vector Control Complete Guide". After completing the above steps, the motor can automatically switch between two given speeds, achieving self-optimization control of the three-phase asynchronous motor. This achieves energy saving in no-load and light-load states while ensuring the motor operates normally at the speed required by the site under rated load. 4 Conclusion By optimizing the power factor of the asynchronous motor under no-load and light-load conditions, an optimized slip rate is obtained. Simultaneously, by applying the 6SE70 series frequency converter to reasonably set various parameters for indirect slip rate control, self-optimization control of the three-phase asynchronous motor in light-load and no-load states is achieved, thereby reducing energy consumption and saving energy. This method is simple and easy to implement, and has widespread significance and value. References [1] Lu Jianqiu, Du Qingzhen. Automatic optimization control of power factor of asynchronous motor [J]. Journal of Xi'an University of Science and Technology, 2002 (12). [2] Song Yinbin. Fundamentals of Electric Motor Drive [M]. Metallurgical Industry Press, 1984. [3] Xie Yingpu. Electric Motor. Sichuan University Press, 1994. About the Author Yang Bin (1976-), male, from Xinzhou, Hubei, Master, assistant lecturer of the School of Engineering and Technology, Chengdu University of Technology, mainly engaged in teaching and research work in electrical transmission, intelligent control and other fields. Contact address: Office of Department of Automation, School of Engineering and Technology, Chengdu University of Technology, No. 222 Xiaoba Road, Shizhong District, Leshan, Sichuan. Contact number: 15984396175 [email protected]