General electrical engineer to summarize the influence of frequency converter for motor

1 the efficiency of the motor and the problem of temperature rise In either in the form of a

frequency converter, both in the operation of the different degree of harmonic voltage and current,

make the motor in non-sinusoidal voltage, power flow operation. At the current widespread use of sine wave type PWM inverter as an example, the basic is zero, the low-order harmonic larger than the rest of the 220v electric motor carrier frequency times the left and right sides of

higher harmonic components as: 2 u + 1 (u for modulation ratio). Can lead to higher harmonic motor stator copper loss, rotor copper loss, iron loss and the increase of the additional loss, the most significant is the rotor copper loss; For asynchronous motor is close to the base wave frequency corresponds to the synchronous speed of rotation, therefore, higher harmonic voltage to a larger slip cutting rotor after conducting bar, will produce very big rotor loss; In addition, also should be considered because of skin effect produced by the additional copper loss. These losses will make motor extra heat, low efficiency, output power decreases, and such as ordinary motor running in the inverter output non-sinusoidal power supply conditions, the general temperature will increase 10% to 20%. 

2 motor insulation strength problem At present middle and small converter, many are using the

PWM control mode. It's about several thousand to more than 10 KHZ carrier frequency, which makes the

motor stator winding to withstand high voltage build-up rate, equivalent to impose great impulse

voltage gradient on motor, the motor of the turn-to-turn insulation withstand more ordeal. In

addition, the rectangular produced by PWM inverter chopper superposition of impulse voltage on the

motor operating voltage, which not only high peak and the high frequency impulse voltage, would pose

a threat to the electric motor 12v 500w insulation of the motor, to ground

insulation under the repeated impact of high pressure can accelerate ageing. 3 harmonic

electromagnetic noise and vibration Ordinary motor using frequency inverter power supply, can make the electromagnetic, mechanical, ventilation and other factors caused by the vibration and noise

becomes more complicated. Frequency conversion power harmonic and motor electromagnetic part contains all of the time the inherent space harmonic interference each other and form all kinds of

electromagnetic vibration force. When the electromagnetic wave frequency and motor of the body's natural vibration frequency is consistent or close to, will produce resonance phenomenon, so as to increase the noise. Due to the motor operating frequency range wide, wide speed change range, all

kinds of the electromagnetic wave frequency is difficult to avoid the components of the motor of the

inherent vibration frequency. 

Four shaft voltage increase Shaft voltage refers ac motor to two axes voltage or voltage between shaft and shaft, for motor frequency conversion power supply, usually on each phase voltage on the motor is balanced, however, because each phase rectifier components and control components differences in features, may be a momentary voltage imbalance, produced in the shaft larger shaft voltage; Combined with the harmonic voltage on the rotor will be bearing oil film as medium to form a earth capacitance, producing a capacitive current; The current flows through the oil film between shaft and bush, if critical lubrication condition, the oil film will be destroyed, there will be a large current flows through the oil film, thus shortening bearing alloy, bearing life or damage to the accident. 5 motor for frequent starting and braking ability to adapt As a result of the inverter power supply, motor can under low frequency and voltage start, in the form of no impact current and frequency converter is available for braking modes of the brake quickly, create conditions for the realization of the frequent starting and braking, and the

mechanical system and electromagnetic system of the motor is in circulation under the action of

alternating force, brings to the mechanical structure and insulation structure fatigue and

accelerated aging problem. 6 low-speed cooling problems First of all, the impedance of the

asynchronous motor is not ideal, when power frequency is low, the power loss caused by high order

harmonic. Second, general motors in speed decreases, current and magnetic flux basic keep

inconvenience, but the cooling air volume and speed of three proportional to reduce, cause the low

speed of a motor cooling conditions deteriorate, a sharp increase in temperature is difficult to

realize the constant torque output. General electrical engineer pointed out that, in view of the

above issues ahead of protective 8500w gasoline generator measures to prolong the

service life of click.