1, the efficiency of the motor and the problem of temperature rise
Regardless of the form of the inverter
The English translation of the inverter is VFD (Variable-frequencyDrive), which may be one of the few examples of modern technology translated from Chinese to English. (But VFD can also be interpreted as Vacuumfluorescentdisplay, vacuum fluorescent tube, so this translation is not commonly used). The frequency converter is a variable frequency technology and a microelectronic technology, and the electric drive component of the alternating current motor is controlled by changing the frequency and amplitude of the working power of the motor. The inverter has been called VVVF (VariableVoltageVariableFrequencyInverter) in the Asian region such as China and Korea. In operation, different degrees of harmonic voltage and current are generated to operate the motor under non-sinusoidal voltage and current. Rejecting the data introduction, taking the sinusoidal PWM type inverter commonly used at present as an example, the lower harmonics are basically zero, and the remaining higher harmonic components which are about twice as large as the carrier frequency are: 2u+1 (u For the modulation ratio).
PWM, pulse width modulation, is a control technique that uses a digital output of a microprocessor to control an analog circuit. PWM is widely used in many fields from measurement and communication to power control and conversion due to its simple control, flexibility, high efficiency and good dynamic response. PWM is a term in switched-mode regulated power supplies. This is classified according to the control mode of the voltage regulator. In addition to the PWM type, there are PFM type and PWM and PFM hybrid type. Many microcontrollers today have PWM controllers.
Higher harmonics cause an increase in the stator copper loss, rotor copper (aluminum) consumption, iron loss and additional losses, most notably the rotor copper (aluminum) consumption. because
Asynchronous motors are the most widely used and most demanding types of motors. An asynchronous motor is an AC motor that converts electromechanical energy into mechanical energy by an electromagnetic gap rotating magnetic field interacting with an induced current of a rotor winding to generate electromagnetic torque. Asynchronous motor for motor operation. Because the rotor winding current is induced, it is also called induction motor.
It is rotated at a synchronous speed close to the fundamental frequency. Therefore, after the high-order harmonic voltage cuts the rotor bar with a large slip, a large rotor loss is generated. In addition, the additional copper consumption due to the skin effect needs to be considered. These losses will cause the motor to generate extra heat, reduce the efficiency, and reduce the output power. For example, if the ordinary three-phase asynchronous motor is operated under the non-sinusoidal condition of the inverter output, the temperature rise will generally increase by 10%-20%.
A power source is a device that provides power to an electronic device, also known as a power supply, that provides the power required by all components in the computer.
2, motor insulation strength problem
At present, many small and medium-sized inverters use PWM control. His carrier frequency is about several thousand to ten kilohertz, which makes the stator winding of the motor to withstand a high voltage rise rate, which is equivalent to applying a steep shock voltage to the motor, so that the inter-turn insulation of the motor is more resistant. A harsh test. In addition, the rectangular chopper surge voltage generated by the PWM inverter is superimposed on the operating voltage of the motor, which poses a threat to the insulation of the motor to the ground, and the ground insulation will accelerate aging under the repeated impact of high voltage.
3. Harmonic electromagnetic noise and vibration
When the ordinary asynchronous motor is powered by the inverter, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated. Frequency Power
The variable frequency power supply converts the AC power in the mains through AC→DC→AC, and the output is pure sine wave. The output frequency and voltage can be adjusted within a certain range. It is different from the variable frequency speed controller used for motor speed regulation, and also different from ordinary AC power supply. The ideal AC power supply is characterized by stable frequency, stable voltage, internal resistance equal to zero, and a pure sine wave (no distortion). The variable frequency power supply is very close to the ideal AC power supply. Therefore, the advanced developed countries are increasingly using the variable frequency power supply as the standard power supply to provide the best power supply environment for the electrical appliances, and to objectively assess the technical performance of the electrical appliances. There are two main types of variable frequency power supplies: linear amplification and SPWM switching. Each time harmonic contained in the motor interferes with the inherent spatial harmonics of the electromagnetic portion of the motor to form various electromagnetic exciting forces. When the frequency of the electromagnetic force wave is equal to or close to the natural vibration frequency of the motor body, a resonance phenomenon will occur, thereby increasing noise. Since the operating frequency range of the motor is wide and the range of the rotational speed is large, the frequencies of various electromagnetic force waves are difficult to avoid the natural vibration frequency of each component of the motor.
4. The ability of the motor to adapt to frequent starting and braking
Since the inverter is powered, the motor can be started at a low frequency and voltage with no inrush current, and can be quickly braked by various braking methods provided by the inverter, in order to achieve frequent starting and braking. The conditions are created, so that the mechanical system and the electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and the insulating structure.
5, cooling problems at low speed
First, the impedance of an asynchronous motor is not ideal. When the power supply is a device that supplies power to an electronic device, also called a power supply, it provides the power required by all the components in the computer. When the frequency is lower, the loss caused by higher harmonics in the power supply is larger. Secondly, when the normal asynchronous motor is reduced in speed, the cooling air volume is proportional to the cube of the rotational speed, which causes the low-speed cooling condition of the motor to deteriorate, and the temperature rise sharply increases, making it difficult to achieve constant torque output.
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