1. Motor loss analysis

The losses of the motor mainly include stator copper loss, stator core loss, rotor core loss, permanent magnet eddy current loss, mechanical loss (bearing friction loss + wind wear loss) and stray loss.

The size of the resistor affects the economy and operating characteristics of the motor. When designing the motor, if the winding is selected with a lower electrical density, a larger cross-sectional area of the conductor will be required. When the number of turns remains unchanged, the winding resistance will be small and the copper loss will be less. However, the slot area will increase, and copper will not be used. More; if you choose higher electrical density, you can choose thin copper wire, but this will increase the winding resistance and increase the copper loss.

There are two main methods for calculating iron loss that are widely used at present. One is based on the eddy current loss caused by the fundamental magnetic field evenly distributed in the silicon steel sheet, the hysteresis loss caused by alternating magnetization and the stator slotting proposed by Bertotti in 1987. The other is a three-term separated iron loss model based on the additional loss caused by the air gap permeability harmonic magnetic field in the iron core. The other is a two-term separated iron loss model based on eddy current loss and hysteresis loss. The material-related constants in these two methods are provided by the electrical steel sheet manufacturer or obtained by fitting the iron loss curve, so the iron losses obtained by the two methods are basically the same. Comparing the iron loss obtained by these two methods with experimental data usually requires correction coefficients.

When the permanent magnet synchronous motor is running, the fundamental wave magnetomotive force generated by the armature reaction of the winding current rotates synchronously with the fundamental wave magnetomotive force generated by the permanent magnet. The stator part is greatly affected by the fundamental wave magnetomotive force, so the magnetic density fluctuates greatly; while the rotor rotates synchronously with the fundamental wave magnetomotive force, and the magnetic density fluctuation is small. Therefore, the rotor iron loss is generally smaller than that of the stator.

The eddy current loss of the permanent magnet is caused by factors such as the slotting of the stator and the non-sinusoidal distribution of the stator magnetomotive force. The air gap contains a large number of harmonic magnetic fields. These harmonic magnetic fields alternate in the permanent magnet to produce eddy current losses. Generally obtained by simulation.   

The bearing is located between the end cover and the rotating shaft, connecting the dynamic and static components of the motor. During the rotation of the motor, mechanical friction loss will occur; the outer surface of the rotor will skip the air and cause wind friction loss. Generally, it takes 0.5% of the power.

2. Improved motor efficiency 

Generally speaking, the greater the power of the motor, the easier it is to increase the maximum efficiency of the motor. In small-power micromotors, generally only copper loss, basic iron loss and mechanical loss are considered, and the motor efficiency is generally 60-80%; for motors above 10kW, copper loss, iron loss, permanent magnet eddy current loss, mechanical loss and Stray loss can reach more than 90%. The power of automobile drive motors is generally between 50kW and 1MW. Using NdFeB permanent magnet synchronous motors, it can achieve more than 97% or even 98%. The maximum efficiency of wind power generation motors above megawatt level is generally between 98% and 98.5%. .

Measures to improve motor efficiency include reducing motor losses through optimized design and improving manufacturing accuracy through process improvements.

Measures to reduce copper loss mainly include reducing the stator resistance by increasing the slot full rate and reducing the end length, and reducing the phase current by increasing the proportion of reluctance torque;

Measures to reduce iron loss mainly include using low-loss high-quality cold-rolled silicon steel sheets (increased cost) to reduce the eddy current loss of the motor; adjusting the groove shape and selecting a reasonable magnetic flux density (considering copper loss comprehensively) to reduce fundamental iron loss; Increase the length of the core (increased cost) and reduce the magnetic flux density to reduce losses; improve the manufacturing quality of the core and ensure the insulation on the surface of the silicon steel sheet;

The main measures to reduce mechanical losses include selecting high-quality low-friction bearings (grease, oil lubrication), improving shape and position tolerance accuracy, ensuring the assembly quality of the motor, and reducing friction losses, etc.;

Measures to reduce stray losses mainly include using multiple slots in the stator slot and optimizing the stator slot width (the motor slot is reduced and the motor leakage reactance is increased, thereby better filtering the higher-order winding harmonics caused by PWM waves. function, so that the armature reaction caused by high-order harmonic current is weakened, and the sudden change at the edge of the notch is reduced accordingly), non-magnetic conductive materials are used at both ends of the core; "sinusoidal" windings are used to weaken the high-order harmonics in the magnetic field, weakening For additional losses, appropriately increase the air gap, use magnetic slot wedges, accurately control the slope degree, and adopt special slopes and other measures.