In variable frequency speed regulation system, vector control strategy is an important technical path to achieve energy saving and stable operation. The core of vector control is to decompose the stator current of the three-phase asynchronous motor into the excitation current component that generates the magnetic field and the torque current component that generates the torque, and control them independently, which is similar to the control method of DC motor. By accurately controlling these two current components, the motor can adjust the output torque and speed in real time according to the actual needs of the load. Under light load conditions, vector control can reduce the excitation current, reduce the iron loss and copper loss of the motor, and thus reduce energy consumption. For example, in variable load applications such as fans and water pumps, when the required flow or pressure of the system decreases, the motor speed is reduced by vector control, and the torque is accurately adjusted at the same time, so that the motor can still maintain efficient operation at low speed, which has a significant energy saving effect compared with the traditional fixed speed operation mode. In addition, vector control can also improve the dynamic response performance of the motor, so that the motor can quickly reach a stable state when the speed changes, avoiding the impact of excessive speed fluctuations on the stability of equipment operation.
Direct torque control (DTC) strategy also plays an important role in variable frequency speed regulation. Direct torque control abandons the complex coordinate transformation in vector control, directly calculates the motor's flux and torque in the stator coordinate system, and directly controls the flux and torque through bang-bang control. This strategy detects the motor's stator voltage and current, directly calculates the motor's flux and torque values, and then compares them with the given values. According to the comparison results, the appropriate voltage vector is selected to control the inverter output, thereby quickly adjusting the motor's flux and torque. In some application scenarios with high requirements for dynamic response, such as elevators and cranes, direct torque control can quickly respond to load changes, adjust the motor output torque in time, and ensure the stability of equipment operation. At the same time, direct torque control does not require precise motor parameters, and has strong robustness to motor parameter changes. Even if the motor parameters change during operation, it can maintain good control performance, which reduces maintenance costs and control difficulties to a certain extent. Moreover, under partial load conditions, direct torque control can optimize the motor's operating state, reduce unnecessary energy loss, and achieve energy-saving operation.
Another commonly used control strategy is intelligent control methods such as fuzzy control and neural network control. Fuzzy control is based on fuzzy logic, which converts the operator's experience and knowledge into fuzzy rules, and adjusts the control parameters through fuzzy reasoning and decision-making. In a three-phase asynchronous motor with variable frequency speed regulation, fuzzy control can automatically adjust the output frequency and voltage of the inverter according to the input quantities such as the motor's speed deviation and speed deviation change rate through pre-set fuzzy rules, so that the motor can quickly reach a stable operating state. This control method does not require an accurate mathematical model, has good adaptability to motor parameter changes and external interference, and can achieve stable operation under complex working conditions. Neural network control uses the self-learning and adaptive capabilities of neural networks to establish a mapping relationship between the motor's operating state and control parameters through learning a large amount of sample data. During operation, the neural network can automatically adjust the control parameters according to the real-time operating state of the motor and optimize the motor's operating performance. For example, in some occasions where the load changes frequently and irregularly, neural network control can quickly learn the load change pattern, adjust the motor's speed and torque in time, and achieve energy saving and stable operation. Intelligent control methods provide more flexible and intelligent control methods for high efficiency three-phase asynchronous motors in variable frequency speed regulation applications, especially for complex working conditions where traditional control methods are difficult to meet requirements.
In addition to the above control strategies, methods based on model predictive control (MPC) are also gradually applied to variable frequency speed regulation systems of high efficiency three-phase asynchronous motors. The principle of model predictive control is to establish a prediction model of the motor, predict the future behavior of the system under different control strategies based on the current system state and future control objectives, and then select the optimal control strategy through the optimization algorithm to enable the system to achieve optimal performance in the future. In variable frequency speed regulation, model predictive control can comprehensively consider multiple variables such as motor speed, torque, current, and voltage, predict the operating state of the motor under the action of different voltage vectors, and select the voltage vector that can enable the motor to quickly reach the target speed and with the lowest energy consumption as the control output. This control method has forward-looking and optimization capabilities, and can respond to system changes in advance to avoid energy waste and unstable operation caused by control lag. For example, in the drive motor system of electric vehicles, model predictive control can optimize the motor's operating strategy in real time according to the vehicle's driving conditions and battery status, while ensuring the vehicle's dynamic performance, maximizing energy efficiency and extending the driving range.
In addition, in the variable frequency speed regulation system, the use of appropriate speed closed-loop and current closed-loop control is also the basis for achieving energy saving and stable operation. Speed closed-loop control detects the motor's speed in real time through a speed sensor (such as an encoder) installed on the motor shaft, and feeds the speed back to the controller. The controller compares the actual speed with the given speed and adjusts the inverter's output frequency according to the deviation, thereby achieving precise control of the motor's speed. Current closed-loop control monitors and controls the motor's stator current in real time to ensure that the motor's current remains within a reasonable range during operation, avoiding overheating and increased energy consumption of the motor due to excessive current. Through the synergistic effect of speed closed-loop and current closed-loop, the motor can maintain a stable speed and output torque under different load conditions, while optimizing the motor's operating efficiency and reducing energy consumption. In some constant speed operation scenarios, such as winding equipment in textile machinery, speed closed-loop control can ensure the stability of the speed of the equipment during long-term operation, avoiding the impact of speed fluctuations on product quality; while current closed-loop control can prevent the motor from overloading due to load changes, improving the reliability and service life of the equipment.
In practical applications, it is also necessary to consider the matching of the control strategy with the inverter hardware and the compatibility of the system. Different types of inverters differ in performance and function, and their built-in control algorithms and hardware circuits have an important impact on the implementation of the control strategy. For example, some high-performance inverters have more powerful computing power and richer control functions, and can better support complex control strategies, such as vector control and model predictive control; while some economical inverters may be more suitable for simple control strategies, such as V/F control. In addition, the system composed of high-efficiency three-phase asynchronous motor and inverter needs to work in coordination with other devices and systems. For example, in industrial automation production lines, the motor drive system needs to communicate and link control with PLC, sensors and other devices. Therefore, when selecting a control strategy, it is necessary to comprehensively consider the hardware performance of the inverter, the compatibility of the system, and the actual application requirements to ensure that the control strategy can effectively achieve the goal of energy saving and stable operation.
In the variable frequency speed regulation application scenario, the high efficiency three-phase asynchronous motor achieves energy saving and stable operation through a variety of control strategies such as vector control, direct torque control, intelligent control, model predictive control, etc., combined with speed closed-loop and current closed-loop control, and reasonable consideration of the matching of the control strategy and the hardware system. The continuous development and innovation of these control strategies will further improve the performance and efficiency of three-phase asynchronous motors in variable frequency speed regulation systems, and promote energy saving and consumption reduction and sustainable development in the industrial field.
