The difference between inverter motors and ordinary motors is mainly manifested in the following two aspects.
First, ordinary motors can only work for a long time in the vicinity of the industrial frequency, while the inverter motor can work for a long time in conditions seriously higher than, or lower than, the industrial frequency; as an example, our country's industrial frequency is 50Hz, ordinary motors, if a long time in the 5Hz, will soon fail, or even damaged; and the emergence of inverter motors, to solve the ordinary motor this shortcoming.
Second, the heat dissipation system of ordinary motors and inverter motors is different. Ordinary motor cooling system and speed is closely related, or, motor speed is fast, the cooling system is effective, motor speed is slow, the cooling effect will be greatly reduced, and inverter motor does not have this problem.
Ordinary motor plus frequency converter, it is possible to realize the frequency operation, but not the real frequency motor, if a long time in the non-frequency state of work may be to the damage of the motor.
1. The influence of frequency converter on the motor is mainly in the efficiency of the motor and temperature rise frequency converter in operation can produce different degrees of harmonic voltage and current, make the motor, in the non-sinusoidal voltage, current operation inside the high harmonic will cause the motor stator copper consumption, rotor copper consumption, iron consumption and additional loss increase, the most significant is the rotor copper consumption, these losses will make the motor extra heat, efficiency reduction, power output These losses will cause additional heating of the motor, lower efficiency and output power, and the temperature rise of the ordinary motor is generally increased by 10%-20%.
2. the insulation strength of the motor
Frequency converter carrier frequency from a few thousand to more than ten kilohertz, so that the motor stator winding to withstand a very high rate of voltage rise, equivalent to the motor to impose a very steep shock voltage, so that the motor turn-to-turn insulation to withstand a more serious test.
3. harmonic electromagnetic noise and vibration
Ordinary motor using inverter power supply, will make the electromagnetic, mechanical, ventilation and other factors caused by the vibration and noise become more complex. Various harmonics contained in the frequency conversion power supply and motor electromagnetic part of the inherent space harmonics interfere with each other, forming a variety of electromagnetic excitation force, thus increasing the noise. Due to the motor's wide range of operating frequency, speed changes in a wide range, a variety of electromagnetic force wave frequency is difficult to avoid the motor's structural parts of the inherent vibration frequency.
4. the cooling problem at low speed
When the power supply frequency is low, the loss caused by the high harmonics in the power supply is large; secondly, when the speed of the variable speed motor is lowered, the cooling air volume decreases proportionally to the third power of the speed, resulting in the heat of the motor is not emitted, and the temperature rises dramatically, making it difficult to realize the constant torque output.
5. for the above situation, frequency conversion motor adopts the following design.
As far as possible to reduce the stator and rotor resistance, reduce the fundamental copper consumption, in order to make up for the high harmonics caused by the increase in copper consumption of the main magnetic field unsaturated design, a consideration of the high harmonics will deepen the saturation of the magnetic circuit, and the second is to consider in order to improve the output torque at low frequency can be appropriate to increase the output voltage of the frequency converter.
Structural design, mainly insulation level increase; motor vibration, noise problems are fully considered; cooling method using forced ventilation cooling, that is, the main motor cooling fan using an independent motor drive, the role of the strong cooling fan is to ensure that the motor is cooled at low speed. Inverter motor coil distribution capacitance is smaller, the resistance of the silicon steel sheet is larger, so that the impact of high-frequency pulses on the motor is smaller, the motor's inductive filtering effect to be better.
Ordinary motors, i.e., industrial frequency motors only need to consider the starting process and the working condition of one point of the industrial frequency (public number: electromechanical human pulse), and then design the motor; while inverter motors need to consider the starting process and the working condition of all the points in the inverter range, and then design the motor. In order to adapt to the frequency converter output PWM broadening wave analog sinusoidal alternating current contains a large number of harmonics, specially made inverter motor, its role can actually be understood as a reactor plus ordinary motor.
How to distinguish between ordinary motors and inverter motors?
I. Ordinary motor and inverter motor structure difference
1. Higher insulation level requirements
General inverter motor insulation grade F or higher, to strengthen the insulation to ground and turn insulation strength, especially considering the ability to withstand shock voltage insulation.
2. Higher vibration and noise requirements for inverter motors
Inverter motor to fully consider the motor components and the overall rigidity, try to improve its intrinsic frequency, in order to avoid the resonance phenomenon with the secondary force wave.
3. Inverter motor cooling method is different
Inverter motors generally use forced ventilation cooling, that is, the main motor cooling fan using an independent motor drive.
4. Different requirements for protection measures
For the capacity of more than 160kW inverter motor should be used bearing insulation measures. Mainly easy to produce the magnetic circuit asymmetry, but also produces shaft current, when other high-frequency components of the current generated by the combination of the role of the shaft current will be greatly increased, resulting in damage to the bearings, so the general need to take insulation measures. For the constant power frequency conversion motor, when the speed exceeds 3000/min, special grease with high temperature resistance should be used to compensate for the temperature rise of the bearings.
5. Different cooling systems
The cooling fan of inverter motor adopts independent power supply to ensure continuous cooling ability.
II. Ordinary motor and frequency conversion motor design differences
1. Electromagnetic design
For ordinary asynchronous motors, the main performance parameters to be considered in redesign are overload capacity, starting performance, efficiency and power factor. As for the inverter motor, since the critical rate is inversely proportional to the power supply frequency, it can be started directly when the critical rate is close to 1. Therefore, the overload capacity and the starting performance do not need to be considered too much, and the key problem to be solved is how to improve the motor's adaptability to the non-sinusoidal power supply.
2. Structure design
In the structural design, the main thing is to consider the non-sinusoidal power supply characteristics of the inverter motor insulation structure, vibration, noise, cooling mode and other aspects of the impact, the main problem is how to improve the motor's ability to adapt to non-sinusoidal power supply.