Frequency converter

The frequency converter is a device that converts a commercial power supply (50 Hz or 60 Hz) into an AC power of various frequencies to realize a variable speed operation of the motor, wherein the control circuit completes control of the main circuit, and the rectifier circuit converts the alternating current into direct current, The DC intermediate circuit smoothes the output of the rectifier circuit, and the inverter circuit reverses the DC power to AC power.

First, the frequency converter control method

1. U/f=C sinusoidal pulse width modulation (SPWM) control mode is characterized by simple control structure, low cost, good mechanical properties and hardness, which can meet the requirements of smooth speed regulation of general transmission, and has been in the industry. Various fields are widely used. However, in this mode of control, at low frequencies, the torque is affected by the voltage drop of the stator resistance due to the lower output voltage, which reduces the maximum output torque. In addition, its mechanical characteristics do not have DC motor hard, dynamic torque capability and static speed regulation performance are not satisfactory, and the system performance is not high, the control curve will change with the load change, the torque response is slow, the motor turns The moment utilization rate is not high, and the performance is degraded due to the existence of the stator resistance and the dead zone effect of the inverter at a low speed, and the stability is deteriorated. Therefore, people have also studied vector control frequency control.
2. Voltage space vector (SVPWM) control mode <br> It is based on the premise of the three-phase waveform overall generation effect, aiming at the ideal circular rotating magnetic field trajectory close to the motor air gap, generating a three-phase modulation waveform at a time, with an inscribed polygon Approaching the way the circle is controlled. After practice, it has been improved, that is, the introduction of frequency compensation can eliminate the error of speed control; estimate the magnitude of the flux linkage through feedback to eliminate the influence of stator resistance at low speed; close the output voltage and current to improve the dynamic accuracy and stability. However, there are many control circuit links and no torque adjustment is introduced, so the system performance has not been fundamentally improved.
3. Vector control (VC) mode vector control The principle of variable frequency speed regulation is to make the stator currents Ia, Ib, Ic of the asynchronous motor in the three-phase coordinate system pass the three-phase-two-phase transformation, which is equivalent to the two-phase stationary coordinate system. The lower alternating current Ia1Ib1 is equivalent to the direct current Im1, It1 in the synchronous rotating coordinate system by the rotational transformation of the rotor field, which is equivalent to the exciting current of the direct current motor; It1 is equivalent to the armature proportional to the torque. Current), then imitate the control method of the DC motor, obtain the control quantity of the DC motor, and realize the control of the asynchronous motor through the inverse transformation of the corresponding coordinates. The essence is that the AC motor is equivalent to a DC motor, and the two components of speed and magnetic field are independently controlled. By controlling the rotor flux linkage and then decomposing the stator current to obtain two components of torque and magnetic field, coordinate transformation is used to realize orthogonal or decoupling control. The proposed vector control method has epoch-making significance. However, in practical applications, because the rotor flux linkage is difficult to accurately observe, the system characteristics are greatly affected by the motor parameters, and the vector rotation transformation used in the equivalent DC motor control process is complicated, making the actual control effect difficult to achieve the ideal analysis. result.

Second, the frequency converter manufacturer

Shenyang Sida Inverter Factory is a local manufacturer mainly engaged in the production of frequency converters. Our factory has long been committed to the research and development of AC frequency conversion technology and is a technology-intensive enterprise. "First-class technology, first-class enterprise" is our business goal. "Survive by quality, develop by technology, and market by service" is our business philosophy. The product adopts 16-bit high-speed microprocessor of American Intel Company; Siemens IGBT of Germany, IPM power module of Japan as main switching component, software adopts optimized SPWM modulation technology, which makes the product compact and reliable. After years of accumulation, we are not only in personnel , technical and economic lay a solid foundation, and in many industries have made many sincere cooperation friends.
With the growth of sales performance, our engineering business has gradually expanded to many industries such as food and beverage, water treatment, mechatronics, and automatic welding machines. We believe that Shenyang Sida will be able to make outstanding achievements in various fields. Good and high-quality technical service is our commitment to you. After the equipment is qualified, the hardware will be repaired free of charge within one year, and the quality of the hardware will be guaranteed to be processed free of charge in time to ensure the normal operation of the production. Provide technical support and services for equipment installation, commissioning and operation in a timely manner, and timely upgrade software for customers according to customer requirements to ensure reliable and safe operation of the system. We believe that we can provide you with satisfactory engineering and technical services. Shenyang Sida Inverter Speed ​​Control Factory is an ideal platform to realize the value of life. The company introduces the successful management mode of modern high-tech enterprises, people-oriented, engineering quality and engineering services as the company's survival and development.

Third, the frequency converter classification

According to the main circuit working mode classification, it can be divided into voltage type inverter and current type inverter; according to the switch mode classification, it can be divided into PAM control inverter, PWM control inverter and high carrier frequency PWM control inverter; sorted according to working principle It can be divided into V/f control inverter, slip frequency control inverter and vector control inverter; according to the purpose classification, it can be divided into general inverter, high performance special inverter, high frequency inverter, single phase inverter And three-phase inverters.