### Frequency converter speed regulation, ordinary asynchronous motor has such a big impact

Date：2023-10-20 Author：XINDA MOTOR

**1. The harmonic current appearing in the stator winding due to stator copper loss increases I2R.**

**2. When the rotor copper loss is at the harmonic frequency, the resistance of the stator winding can generally be considered to be constant.**

When a synchronous motor is operated from a non-sinusoidal supply, the time-harmonic magnetic potential induces harmonic rotor currents, as in an asynchronous motor operating near its fundamental synchronous speed.

**3. The harmonic current appearing in the stator winding due to stator copper loss increases I2R.**

When the skin effect is ignored, the stator copper loss under non-sinusoidal current is proportional to the square of the total effective value of the current. Through experiments, it was found that due to the existence of harmonic currents and the corresponding emergence of leakage flux, the degree of saturation of the magnetic circuit of leakage flux increases, so the excitation current increases, thereby increasing the fundamental wave component of the current.

**4. When the rotor copper loss is at the harmonic frequency, the resistance of the stator winding can generally be considered to be constant.**

When a synchronous motor is operated from a non-sinusoidal supply, the time-harmonic magnetic potential induces harmonic rotor currents, as in an asynchronous motor operating near its fundamental synchronous speed.

**5. The core loss in the harmonic iron loss motor also increases due to the occurrence of harmonics in the power supply voltage; each harmonic of the stator current establishes a time harmonic magnetomotive force in the air gap.**

The total magnetic potential at any point in the air gap is the combination of the fundamental wave and the time harmonic magnetic potential. For a three-phase 6-step voltage waveform, the peak magnetic density in the air gap is about 10% larger than the fundamental wave value, but the increase in iron loss caused by time harmonic flux is very small. The stray losses caused by the end leakage flux and the chute leakage flux will increase under the action of harmonic frequencies, which must be considered when using non-sinusoidal power supply: the end leakage effect in the stator and rotor windings All exist, mainly due to eddy current loss caused by leakage magnetic flux entering the end plate. Due to the change in the phase difference between the stator magnetic potential and the rotor magnetic potential, the chute leakage flux is generated in the chute structure, and its magnetic potential is largest at the end, causing losses in the stator and rotor cores and teeth.

**6. The size of motor efficiency harmonic loss is obviously determined by the harmonic content of the applied voltage.**

The harmonic component is large, the motor loss increases and the efficiency decreases. But most static inverters do not produce harmonics below the fifth order, and the amplitudes of higher harmonics are smaller. The voltage of this waveform does not seriously reduce the efficiency of the motor. Calculations and comparative tests on medium-capacity asynchronous motors show that their full-load effective current increases by approximately 4% compared to the fundamental wave value. If the skin effect is ignored, the copper loss of the motor is proportional to the square of the total effective current, and the harmonic copper loss is 8% of the fundamental loss. Considering that the rotor resistance can increase by an average of three times due to the skin effect, the harmonic copper loss of the motor should be 24% of the fundamental loss. If copper losses account for 50% of the total motor losses, harmonic copper losses increase the overall motor losses by 12%. The increase in iron loss is difficult to calculate because it is affected by the construction of the motor and the magnetic materials used.

**7. If the high-order harmonic components in the stator voltage waveform are relatively low, like in the 6-step wave, the harmonic iron loss will not increase by more than 10%.**

**8. The core loss in the harmonic iron loss motor also increases due to the occurrence of harmonics in the power supply voltage; each harmonic of the stator current establishes a time harmonic magnetomotive force in the air gap.**

The total magnetic potential at any point in the air gap is the combination of the fundamental wave and the time harmonic magnetic potential. For a three-phase 6-step voltage waveform, the peak magnetic density in the air gap is about 10% larger than the fundamental wave value, but the increase in iron loss caused by time harmonic flux is very small. The stray losses caused by the end leakage flux and the chute leakage flux will increase under the action of harmonic frequencies, which must be considered when using non-sinusoidal power supply: the end leakage effect in the stator and rotor windings All exist, mainly due to eddy current loss caused by leakage magnetic flux entering the end plate. Due to the change in the phase difference between the stator magnetic potential and the rotor magnetic potential, the chute leakage flux is generated in the chute structure, and its magnetic potential is largest at the end, causing losses in the stator and rotor cores and teeth.

**9. The size of motor efficiency harmonic loss is obviously determined by the harmonic content of the applied voltage.**

The harmonic component is large, the motor loss increases and the efficiency decreases. But most static inverters do not produce harmonics below the fifth order, and the amplitudes of higher harmonics are smaller. The voltage of this waveform does not seriously reduce the efficiency of the motor. Calculations and comparative tests on medium-capacity asynchronous motors show that their full-load effective current increases by approximately 4% compared to the fundamental wave value. If the skin effect is ignored, the copper loss of the motor is proportional to the square of the total effective current, and the harmonic copper loss is 8% of the fundamental loss. Considering that the rotor resistance can increase by an average of three times due to the skin effect, the harmonic copper loss of the motor should be 24% of the fundamental loss. If copper losses account for 50% of the total motor losses, harmonic copper losses increase the overall motor losses by 12%. The increase in iron loss is difficult to calculate because it is affected by the construction of the motor and the magnetic materials used.

**10. If the higher harmonic components in the stator voltage waveform are relatively low, like in the 6-step wave, the harmonic core loss will not increase by more than 10%.**