1, the problem of motor efficiency and temperature rise
No matter what form of frequency converter
The English translation of the frequency converter is VFD (Variable-frequencyDrive), which may be one of the few examples of modern technology from Chinese reverse translation to English. (But VFD can also be interpreted as Vacuum Fluorescent Display, vacuum fluorescent tubes, so this translation is not commonly used). Inverter is the application of frequency conversion technology and microelectronic technology, by changing the frequency and amplitude of the motor power supply to control the AC motor drive components. Inverter in China, South Korea and other Asian regions affected by the Japanese companies have been called VVVF (VariableVoltageVariableFrequencyInverter). , In operation have different degrees of harmonic voltage and current, the motor in non-sinusoidal voltage and current operation. Refused data, the current commonly used sine wave PWM inverter, for example, the low-order harmonic is essentially zero, the remaining higher than the carrier frequency about twice the higher harmonic components: 2u +1 (u For the modulation ratio).
PWM that pulse width modulation, is a kind of control technology that uses the digital output of the microprocessor to control the analog circuit. PWM is widely used in many fields ranging from measurement and communication to power control and transformation because of its advantages of simple control, flexibility, high efficiency and good dynamic response. PWM is the term switching power supply. This is classified according to the regulation of regulated voltage, besides PWM type, there are PFM type and PWM, PFM mixed type. Many microcontrollers today have PWM controllers in them.
High harmonics cause stator copper losses, rotor copper (aluminum) losses, iron losses, and additional losses, most notably rotor copper (aluminum) losses. because
Induction motor is the most widely used in all types of motors, the largest one. Induction motor is composed of air gap rotating magnetic field and rotor winding induced current to produce electromagnetic torque, so as to realize the conversion of electromechanical energy into mechanical energy. Asynchronous motor for motor operation. Because of the rotor winding current is induced, also known as induction motor.
Is close to the fundamental frequency corresponding to the synchronous speed of rotation, therefore, the higher the harmonic voltage to a larger slip cut rotor bar, it will have a great rotor loss. In addition, the additional copper consumption due to the skin effect needs to be considered. These losses will make the motor extra heat, reduce efficiency, reduce output power, such as the ordinary three-phase asynchronous motor running in the inverter output of non-sinusoidal conditions, the temperature increase is generally increased by 10% – 20%.
A power supply is a device that provides power to an electronic device, also referred to as a power supply, which provides the power needed by all components of a computer.
2, motor insulation strength problem
At present small and medium-sized frequency converter, many adopt PWM control mode. His carrier frequency is about a few thousand to a dozen kilohertz, which makes the motor stator windings to withstand a high rate of voltage rise, equivalent to the imposition of a steep motor surge voltage, the motor turns to withstand more insulation Harsh test. In addition, the PWM chopper generated by the rectangular chopper impulse voltage superimposed on the motor operating voltage, the motor will pose a threat to the insulation, insulation to high voltage repeated impact will accelerate the aging.
3, harmonic electromagnetic noise and vibration
Ordinary asynchronous motor inverter power supply, will make the electromagnetic, mechanical, ventilation and other factors caused by the vibration and noise become more complex. Frequency Power
Inverter is the AC power AC through AC → DC → AC conversion, the output is pure sine wave, the output frequency and voltage within a certain range of adjustable. It is different from the frequency control for motor speed controller, but also different from ordinary AC power supply. Ideal AC power is characterized by frequency stability, voltage stability, internal resistance is equal to zero, the voltage waveform is pure sine wave (no distortion). The frequency conversion power is very close to the ideal AC power supply. Therefore, the advanced developed countries increasingly use the variable frequency power supply as the standard power supply, so as to provide the best power supply environment for electrical appliances and facilitate the objective assessment of the technical performance of the electrical appliances. There are two main types of variable frequency power supply: linear amplification and SPWM switch. Contained in each of the time harmonics and motor electromagnetic part of the inherent space harmonics interfere with each other to form a variety of electromagnetic excitation force. When the frequency of the electromagnetic force wave and the natural frequency of the motor body is the same or close to the resonance phenomenon, thus increasing the noise. Due to the wide range of motor operating frequency, speed range, a variety of electromagnetic force wave frequency is difficult to avoid the inherent vibration frequency of the motor components.
4, the motor on the frequent start, brake adaptability
As a result of inverter power supply, the motor can be started at low frequency and voltage with no rush current, and can be quickly braked by various braking methods provided by the inverter. In order to achieve frequent starting and braking Created the condition that the mechanical system and the electromagnetism system of the motor are under cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and the insulation structure.
5, low-speed cooling problems
First, the impedance of an asynchronous motor is less than ideal. When the power supply is a device that supplies power to an electronic device, also referred to as a power supply, it provides the power needed by all the components in the computer. When the frequency is low, the power loss caused by higher harmonics is larger. Second, the normal asynchronous motor revolving speed decreases, the cooling air flow rate and the third power of the proportional decrease, causing the motor low-speed cooling conditions deteriorate, the temperature rise dramatically increased, it is difficult to achieve constant torque output.
5 major impact on the motor inverter
1, the problem of motor efficiency and temperature rise